Attempting to lower your cholesterol in 7 days is unlikely to produce dramatic results; however, you can immediately start building habits that will lower your LDL (“bad”) cholesterol and raise your HDL (“good”) cholesterol over time. Significant reduction in cholesterol will usually take several weeks to months, though a trend of improvement may be seen sooner.

Below are key steps to jump-start your journey toward better heart health.

Key Steps to Lower Cholesterol Quickly

Nutrition

Surveying your current eating habits may help you understand opportunities for change. Generally, increasing the amounts of soluble fiber in your diet and decreasing the amounts of saturated fat is beneficial.

• Increase soluble fiber: Soluble fiber binds and prevents the absorption of cholesterol in your digestive system. Prior studies have shown increasing consumption of soluble fiber results in moderate decreases in LDL cholesterol. A meta-analysis of 67 randomized controlled trials found that for every 1 gram of soluble fiber consumed per day, LDL cholesterol was reduced by about 0.78 mg/dL.

• Reduce saturated fat: A meta analysis from 2016 studied the effect of replacing saturated fat with polyunsaturated fat or monounsaturated fats. The results showed that for every decrease in saturated fats of 1% total daily calories and reciprocal increase of alternate fats there was a reduction in LDL cholesterol between 1.3-2.1 mg/dL. These reductions in LDL cholesterol correlate well with reductions in cardiovascular events. A comprehensive review from 2020 analyzed data from 15 randomized controlled trials with over 59,000 participants. The review found that reducing dietary saturated fat led to a 21% reduction in the risk of cardiovascular events (like heart attacks and strokes). Notably, a greater reduction in saturated fats led to a greater protection from cardiovascular events.

Exercise

Your current level of activity will help determine recommended changes to your routine.

• Move more: A 2007 meta-analysis showed that to increase your HDL cholesterol you need to participate in at least 120 minutes of exercise per week. After that, every 10 minute increase in exercise led to a 1.4 mg/dL increase in HDL cholesterol. The effect of exercise on HDL cholesterol was also more noticeable for people with BMI less than 28 and for those with total cholesterol greater than 220. We also know that some activity is better than no activity, regardless of level of intensity or time. Studies on cardiorespiratory fitness, which can be measured by VO2max, have shown the largest benefit on health outcomes at the lowest end of fitness levels. For people who don’t currently exercise, starting with 30 minutes of moderate activity (like brisk walking) most days of the week would be a great way to get started. For people who already exercise, it’s helpful to look at your routine to ensure you are getting the most benefit from your efforts. Generally, a combination of aerobic and resistance training are preferred.

Lifestyle

Beyond nutrition and exercise there are several other lifestyle changes that can have a positive impact on your cholesterol levels. Some of these may include quitting smoking, shedding excess weight, reducing stress, and optimizing for quality sleep.

• Quit smoking: For people who smoke, quitting has significant improvements on heart health, particularly through increases in HDL cholesterol, an effect that is stronger in women.

• Manage stress: A recent study examined the effects of a 12 week program of yoga and meditation on lipid levels. At the end of the program participants noted reductions in total cholesterol, triglycerides, and LDL.

• Prioritize sleep: Sleep deprivation is thought to decrease the expression of genes that encode cholesterol transporters and at the same time increase expression of inflammatory responses, which can contribute to increased cardiovascular risk.

Five Practical Tips for Your First Seven Days

Getting started on these changes can be overwhelming. These tips can help you get started toward better cardiovascular health:

1. Limit your intake of saturated fat to less than 6% of your total daily calories (about 13 grams of sat. fat for a 2000 calorie diet).

2. If you eat red meat, keep portions under 3 ounces, no more than 3 times per week.

3. Increase fiber intake to 25-35 grams daily, focusing on sources rich in soluble fiber.

4. Aim for 150 minutes of moderate-intensity exercise per week (moderate-intensity is 50-70% of your maximum heart rate or at a pace where you can talk comfortably, breathe harder, and start to sweat).

5. Review your sleep habits and make adjustments for better rest.

When to Follow Up

Lowering your cholesterol is a dedicated effort that requires a long-term commitment. Setting goals and realistic expectations can help you keep momentum on your health journey.

We recommend checking your cholesterol 12 weeks after your initial changes to make sure you are making progress. If your cholesterol is very high or you have a high cardiovascular risk, consult with your primary care doctor to discuss a plan that will make sense for you. This may include medications alongside lifestyle changes.

Remember, every small step you take now can lead to big improvements in your heart health over time. For support and personalized guidance, check out Empirical Health.

Heart disease kills more people than all cancers combined—but it’s also the area of health most in your control. 80% of heart attacks can be avoided, and your risk is predictable using statistical models up to 30 years in advance.

Today, we’re launching Empirical’s heart health program across 30+ states, reaching over 200 million people.

We help you measure key heart biomarkers (including ApoB), predict your personal risk, and build a tailored action plan—covering nutrition, medication, and exercise.

Here’s how it works. Or get started now.

Measure: 85+ biomarkers for $190

Empirical heart health starts with a $190 test measuring 85+ biomarkers—available at 2,200+ locations nationwide.

You’ll get insights into key heart markers like:

• ApoB: every 10 mg/dL drop cuts heart disease risk by 9%

• Lp(a): up to 6x more atherogenic than regular LDL

• Cholesterol & Triglycerides: core inputs into heart attack risk predictors.

• 80+ others: inflammation (hs-CRP), cell counts, electrolytes, creatinine, glucose, ketones, and more.

Predict: heart attack risk models

Next, we show how your heart attack risk could change by age 70—

• If you do nothing

• If you follow a tailored plan with medication, diet, and exercise

Many people cut their risk by 50% or more with the right changes.

Prevent: personalized action plans

“Eat less red meat.” “Eat more greens.” You’ve heard it all before.

This is different. We build a biomarker-driven nutrition plan tailored to your bloodwork—targeting the exact nutrients that matter for your heart. These plans have been shown in the medical literature to be about twice as effective as a simple “eat more fruits and vegetables” diet.

And tracking? Just snap a photo of your meal.

Get started now

Help us save one million people from heart disease by 2027. Get started yourself or share with a loved one:

https://www.empirical.health/product/comprehensive-health-panel

The statement is hyperbolic, but shows how the approach to lipid management is changing. In 2019, the European Society of Cardiology concluded that ApoB is a more accurate marker of cardiovascular risk than LDL-C. In 2021, the Canadian Cardiovascular Society recommended ApoB over LDL-C as the primary metric for lipid management. ApoB has become the gold standard of cardiovascular risk.

The U.S., however, still lags behind. Less than 1% of the insured population gets their ApoB tested each year.

The rest of this post will explain why ApoB is widely considered the best lipid marker of cardiovascular risk, and why getting more people tested can help save lives.

Want to skip ahead and get your ApoB test? Empirical Health's advanced cardiovascular panel includes ApoB and other critical heart health biomarkers.

What is the ApoB blood test?

ApoB stands for Apolipoprotein B.

Lipoproteins are molecules in your blood made of fats (e.g. cholesterol, triglycerides) and proteins. They’re critical for many physiological processes, like hormone production, bile acid synthesis, and cell membrane formation.

However, at excess quantities, some lipoproteins are atherogenic—meaning they can enter your arterial walls, form plaques, and cause heart attacks.

Source: Cleveland Clinic

There are four main atherogenic lipoproteins:

LipoproteinFunctionSizevLDL: Very Low-Density LipoproteinTriglyceride transportLargeIDL: Intermediate-Density LipoproteinIntermediate LDL precursorMediumLDL: Low-Density LipoproteinDeliver cholesterol to cellsSmallLipoprotein(a)Deliver cholesterol to cellsSmall

An apolipoprotein is a protein wrapper around a lipoprotein that helps makes it soluble in plasma, maintains its structure, and helps with binding during tissue uptake. Apolipoprotein B (ApoB) is the only one found on all four atherogenic lipoproteins—exactly one per particle.

The unit of measure for an ApoB blood test is mg/dL, the total mass of ApoB molecules in one deciliter of your blood.

Limitations of standard lipid panels

A standard lipid panel in the U.S. includes:

• Total cholesterol

• HDL

• Triglycerides

• LDL-C

• Cholesterol/HDLC Ratio

• LDL/HDL Ratio

• Non HDL Cholesterol

You’ll notice it doesn’t include ApoB. One reason for this is increased cost vs. other countries, but the end result is that treatment for high cholesterol is mostly based on LDL-C in the U.S.

As mentioned in a previous post about predicting your risk of a heart attack, the LDL-C value on your lipid panel is not measured directly, it’s estimated using the Friedewald equation:

LDL-C = Total Cholesterol - HDL Cholesterol - (Triglyceride / 5)

Your LDL-C (LDL-calculated) estimates the mass of cholesterol carried by LDL particles in one deciliter of blood. There are several limitations of this estimate:

1. Inaccurate at high and low triglyceride levels (> 400 mg/dL or <100 mg/dL)

2. Assumes that the ratio of Triglycerides to vLDL cholesterol is 5:1, which isn’t always true

3. Ignores cholesterol carried by other atherogenic particles: vLDL, IDL, and Lipoprotein(a)

ApoB vs LDL: why ApoB is a better measure of atherogenic risk

Physiologically, it’s now believed that the number of atherogenic particles is a better predictor of cardiovascular risk than the cholesterol inside LDL particles. Even cholesterol-poor LDL particles can be harmful if there are a lot of them.

Since each atherogenic lipoprotein has exactly one ApoB, measuring ApoB gives you a direct particle count. More particles = more chances to enter artery walls = higher risk of a blockage.

ApoB, LDL-C, and non-HDL cholesterol are often aligned, but some clinical contexts are more likely to show discordance. For example:

• 51% of patients with metabolic syndrome had high LDL-C but normal ApoB (2021 study)

• Men, Hispanics, older patients, statin use, and high triglycerides, and high BMI showed more discordance (2024 study)

• 20% of women had discordance in this 2017 study

In young adults, the 2016 CARDIA study quantified the value of ApoB over LDL-C when they diverge. It assessed long-term cardiovascular risk by measuring standard lipid panels and ApoB levels in adults aged 18–30, then evaluating coronary artery calcification (CAC)—a marker of plaque buildup—via CT scan 25 years later. It found that young adults with high ApoB and normal LDL-C had 55% higher odds of developing CAC in the future, but those with high LDL-C and normal ApoB did not show a statistically significant increase in CAC risk.

In other words—although LDL-C and ApoB are often aligned, when they are not, ApoB is a superior predictor of heart disease risk.

Source: “Discordance Between Apolipoprotein B and LDL-Cholesterol in Young Adults Predicts Coronary Artery Calcification: The CARDIA Study”, Wilkins et al.

How to lower your ApoB naturally

Each 10 mg/dL decrease in ApoB is associated with a ~9% decrease in heart disease.

The good news is that you can reduce your ApoB through nutrition:

• Increase soluble fiber

• Reduce saturated fat

(Surprisingly, dietary cholesterol does not have a strong effect on the number of atherogenic particles for most people.)

The mechanism for how your diet affects your ApoB is related to cholesterol metabolism. Your liver extracts ApoB-containing lipoproteins from your blood and uses them to create bile acid. During digestion, these bile acids are secreted into your gut to help break down fats. 95% of bile acids are then reabsorbed so they can be reused.

Eating soluble fiber disrupts this cycle. In the gut, soluble fiber absorbs water and thickens into a gel. This gel physically traps bile acid, prevents it from being reabsorbed back to your liver, and it gets excreted. Your liver then senses less bile acid, so it breaks down more ApoB-containing lipoproteins from your blood to replenish.

Eating saturated fat has the opposite effect. Saturated fats are broken down and absorbed in the gut before reaching the liver. This causes the liver to increase production of vLDL (and eventually LDL) and also reduce the clearing of atherogenic lipoproteins from the blood.

How to lower your ApoB with medication

The primary medications to reduce ApoB are statins. Statins decrease your liver’s synthesis of cholesterol and increase your liver’s removal of LDL particles from the blood. The most common is Atorvastatin (Lipitor), with over 100 million prescriptions filled in the U.S. each year. Statins are remarkably effective, with severe patients seeing a 20-40% reduction in ApoB in just a few months, inexpensive (~$5/mo), and safe, with the most common side effect (muscle pain) occurring in <1% of patients.

How can you get your ApoB measured?

Empirical Health’s advanced cardiovascular panel includes ApoB testing, along with a complete lipid panel, and Lipoprotein(a), which is an atherogenic lipoprotein primarily determined by genetics.

ApoB test cost

The entire advanced cardiovascular panel includes 55 biomarkers for $175.

Testing can be completed in a single blood draw at one of 2,000 locations nationwide, and most results come back within a couple days. Within the Empirical Health app for iPhone and Android, you can take several steps to improve your biomarkers:

1. Review your results with and MD

2. Discuss and start any new medications

3. Get a customizable nutrition and exercise plan

While an annual doctor's visit can give you a lot of helpful guidance and reassurance that today you are healthy, a 15 minute visit once per year misses the context of your daily routine and is often not enough to address all of your medical questions. In fact, a recent study demonstrated that it would take a primary doctor 26.7 hours per day to manage all the work required for a standard panel of 2500 patients.

Some people have tried to complement traditional medical care with wearable device data. While these devices do show promise in monitoring chronic disease and in their predictive potential, most people only receive raw data that is hard to relate to their symptoms or specific conditions.

Is there a way to monitor your health on a more consistent basis, perhaps outside of the doctor's office and with tools that are becoming more accessible to the average person? Our most recent feature, Radar, aims to address this problem – to give people more routine insights into their day-to-day health by combining metrics from wearable devices, lab tests, and self-reported data.

Our Considerations as we Designed Radar

As we developed our scoring system, we focused on three key principles:

• Broad applicability: Our tool should be effective and meaningful across various clinical scenarios and diverse patient populations.

• User-friendly accessibility: Using Radar should be easy and convenient.

• Transparency: Users should receive clear and understandable information.

To achieve these objectives, the design considers evidence-based recommendations and research studies. Radar weighs data points from wearable sensors, lab testing, and health questionnaires to calculate a single comprehensive score that is composed of six subcategories: heart health, lung health, kidney and liver health, mental health, sleep health, and activity.

The Science Behind Radar

Radar is currently composed of approximately 40 different measurements. These were chosen by combining recommended guidelines from the United States Preventive Service Task Force, the American College of Cardiology, the American Academy of Family Physicians, amongst others.

Wearable Device Sensor Data

Phones and wearable devices capture hundreds of individual markers per week for the average user. Many of these, like heart rate or oxygen saturation are reflective of the vital signs captured during a doctor’s visit. These can also be helpful in gauging various issues, like cardiovascular health or sleep patterns.

Resting heart rate provides a helpful example. Over time research has shown that a higher resting heart rate can indicate a greater risk for cardiovascular disease. A 2017 meta analysis re-emphasized this positive correlation noting that a higher resting heart rate predicted an increased risk of stroke, heart failure, heart disease, cancer, and all-cause mortality across various populations.

These data points can be quite powerful as several studies have shown promise in predicting various health conditions including Parkinson’s disease, atrial fibrillation, and depression.

Biometrics From Lab Testing

Lab testing is standard practice in medical care. Some lab tests provide direct information about the function of an organ system, while others indirectly signal how your organs are working together to tackle necessary tasks. We chose specific biomarkers that are broadly applicable and that have concrete meaning independent of a person’s specific history.

One example of this is albumin – a commonly measured serum protein. Albumin, which is often overlooked in routine clinical assessments, is a critical biomarker with significant predictive value for morbidity and mortality across various patient populations. This protein has been researched in surgical patients, individuals hospitalized for COVID-19, those with chronic illnesses, and healthy subjects. In a study involving over 54,000 patients undergoing major non-cardiac surgery, a decrease in serum albumin from >46 g/L to <21 g/L was associated with an exponential increase in 30-day mortality rates from <1% to 29% and morbidity rates from 10% to 65%. Even within the normal range of albumin levels, slight decreases are predictive of adverse outcomes, highlighting its sensitivity as an indicator of preclinical disease and overall health.

Other markers included in Radar are LDL cholesterol (a useful marker in the management of cardiovascular disease), hemoglobin A1c (commonly used for detecting and managing diabetes, which also has implications for all-cause mortality), and creatinine (a marker of kidney function and helpful in predicting outcomes for specific populations).

Health Questionnaires and Screenings

Some aspects of health are not as easily measured by vital signs or lab tests. To capture some of these areas we include assessments on mental health, validated cardiovascular risk assessments, and sleep questionnaires. When using Radar, there is an option to complete these personal health assessments directly in the Empirical Health app.

One of these assessments, the Patient Health Questionnaire-9, is a commonly used tool to screen for and assess the severity of depression. The scores from this tool have a high sensitivity and specificity for major depressive disorder and are often used in studies to explore the connections between mental health and other physical health conditions. A 2023 study provides a helpful example of its application. In this study of over 23,000 individuals, researchers noted a higher risk for all-cause mortality among adults with moderate to severe depressive symptoms, as measured by the PHQ-9, compared to those without depressive symptoms.

The Calculation that Puts it all Together

To create Empirical Health’s composite score we benchmarked individual metrics against medical norms and population data. For sensor data, like HRV, a user receives full credit for a value in the normal range, extra credit if the value is in the top 25% of all Empirical Health users, and no credit if the value falls outside of the normal range. Similarly, for lab tests like Hemoglobin A1c, a user can get partial credit for being in the prediabetes range (under 6.4%), extra credit for being in the normal range (under 5.7%), and no credit for being outside of the normal range (6.5% or higher).

Each value within a subcategory is weighted in consideration against the other variables that make up that subcategory. For lung health, for example, a user’s smoking status makes up almost half of the total subcategory score.

The composite score is similarly weighted, with heart health and mental health accounting for 50% of the total scoring due to the known impact of these variables on individual and population health.

How do we Ensure Safety?

A comprehensive health score can be a useful tool to help people engage in their health more meaningfully. However, the complexities of the human body make the score far from perfect. At this time the score is not meant to be diagnostic or predictive of disease. It is meant to be a starting point for people to understand the information they may already have access to, as well as the information that is missing to better protect their health. Our goal is to empower people with actionable insights for health improvement.

We encourage people to engage with their primary care doctors for routine examinations or to seek care when they are having symptoms that are bothering them. In an effort to close the loop between data and healthcare access, we have an in-house medical team that can answer questions via chat or see patients for full medical visits.

Where Do We Go From Here?

At Empirical Health, Radar is just the beginning. As we continue on our journey to help people be healthier and happier, we see the potential of health data to achieve precision and personalization. Some of our future projects include:

• Expanding insights into other components of health, like reproduction and fertility, musculoskeletal health, skin health, etc.

• Adding lab values and metrics from other commonly used devices, like continuous glucose monitors.

• Using machine learning algorithms to process data better and to detect future conditions.

• In-app programming to support all health components and create personalized care plans that include lifestyle coaching.

• Continuous improvement of the scoring system to better reflect health status and long term outcomes.

• Tailoring scores to specific cases including individual baselines, progress, and health conditions.

Check out Radar and join us on our vision to transform healthcare!

Today, we're launching Radar - the first step in holistically answering, “am I healthy?”. It distills 40+ biomarkers, including your Apple Watch, your lab tests, and other clinical tools into a single overall health score and six category subscores. Radar uses real-world evidence from the USPSTF (US Preventive Services Task Force), American College of Cardiology, and other validated tools to give you a comprehensive look into your health. Heart health, lung health, mental health, kidney/liver health, and sleep health can all be explored.

What is the Empirical Health Radar?

Radar is designed with you in mind - it includes one composite score and six sub-scores to give you a clear view into your health. We take into account your wearable metrics as well as biometric information, like the results of your lab tests. These reflect heart health, lung health, mental health, kidney/liver health, sleep health, and lifestyle factors. This breakdown makes it easy for you to access the information you need to achieve your health goals.

Take heart health, for example. Apple Watch can't predict heart attacks, but a risk calculator from the American College of Cardiology can tell you your 10-year risk (using metrics like cholesterol and blood pressure). We consider this risk calculation and also weigh any irregular rhythm notifications, your resting heart rate, cardio recovery from your Apple Watch, and the results of your other lab tests to show you a fuller view of your heart health.

How does it work?

The composite score and category scores range from 0-100, with higher numbers indicating better overall health. The inputs cover markers relating to heart health, lung health, kidney/liver health, mental health, sleep health, and activity levels. You can learn more about each input by tapping on each individual metric.

Your health score adjusts with your metrics and is refreshed whenever your metrics change. For example, your score will increase if your sleep quality improves, or if you exercise more vigorously, if you lower your A1c, etc.

Adding Lab Test Results

If you don’t have recent lab tests, you can order these directly in the app. If you have recent results, there are two ways to view that data in Empirical Health:

• Connect clinical records (iOS only)
  If your doctor’s electronic records add data to the Health app on your iPhone, you can share that data with Empirical. Tap “Connect clinical records from Apple Health” and follow the steps. If you haven’t already shared that data with Health, you’ll be prompted to log in to your electronic medical records.

• Upload a PDF or image
  You can also upload a PDF or image of your blood test results. Empirical will automatically capture the relevant lab results.

Getting Started

To access your Health Score, download the free Empirical Health app from the App Store or Play Store or update your app to the latest version. Connect your wearable device and your most recent lab tests, then check out your score!

What's Next?

We're committed to continually improving the Empirical Health Radar. In the coming months, we'll be adding more data points and refining our algorithm to provide even more accurate and actionable insights.

Start your journey to better health today with Empirical Health.

Download Empirical Health for Android now.

Why this matters

WearOS watches track tons of health data, but most of it goes unused by the healthcare system. We think that’s a missed opportunity. So, we built an entire medical practice that uses modern technology to streamline diagnostics, improve treatment, and keep the doctor-patient relationship at the center of care.

Here’s what you can do with Empirical Health:

1. Get evaluated for sleep apnea at home

Let’s say your smartwatch detects signs of sleep apnea — like low deep/REM sleep or irregular breathing. You can talk with an Empirical Health doctor to order an FDA-cleared, at-home sleep apnea test, covered by insurance. No need for overnight stays at a sleep lab. If your smart watch doesn’t include sleep apnea detection, or you’re worried it’s missing something, you can take a clinical assessment (the STOP-BANG questionnaire) within the Empirical Health app to help assess your risk.

2. Improve your heart health

Did you know that every 10 beat per minute drop in your resting heart rate can lower your risk of death by 10-20%? Empirical Health helps track your wearable data, blood pressure, and cholesterol levels to create a personalized care plan to improve your heart health.

3. Get medical care in 30+ US states

Medical care through Empirical Health is available in 30+ U.S. states, covering 200 million people and supported by most major insurance providers. Our medical team can help address your medical concerns including ordering lab testing and medications when necessary.

Cool health stats you should know

We love diving into data, and here are a few health insights that might surprise you:

• The average person gets just 49 minutes of deep sleep per night.

• Heart rate variability (HRV) drops from 51ms (ages 18-35) to 28ms (ages 65+).

• Boosting your VO2 max by just 1 mL/kg/min can cut your risk of death by 9%.

How the Empirical Health App Works

Empirical Health integrates with Android Health Connect and Fitbit APIs, so it works seamlessly with Samsung Galaxy Watches, Google Pixel Watches, Fitbits, and other WearOS devices. Here’s what you’ll find inside the app:

• Today Tab: High-resolution heart rate, sleep, symptom, and workout data, on a daily basis.

• Metrics Tab: Deep dive into over 40 biomarkers, including wearable and blood test results.

• Chat Tab: Talk to a real doctor (if you’re in an eligible location).

• Goals Tab: Set up personalized health plan including nutrition, exercise, and next steps.

Ready to Try It?

Download Empirical Health for Android on the Google Play Store. Take it for a spin and let us know what you think!

A “Poor Man’s (DIY) Tilt Table Test”, clinically known as orthostatic vital signs, is a quick and easy test to track your heart rate’s response when moving from a lying to a standing position. Your body’s response to positional changes can be a key indicator of postural orthostatic tachycardia syndrome (POTS) or orthostatic hypotension. To complete the test in its entirety, you would also require a blood pressure cuff to check how your blood pressure reacts to the same position changes. But a modified version of the test can be done just by using your Apple Watch.

As mentioned in our previous blog post, most people do not need a tilt table test to obtain or confirm a diagnosis of POTS. Tilt table testing can sometimes be helpful in cases where POTS is suspected, but orthostatic vital signs are normal.

Tilt Table Test vs Poor Man’s Tilt Table Test

For people who are dealing with symptoms of orthostatic intolerance (feeling unwell with standing up or prolonged standing), there are a few different benefits to performing the “Poor Man’s Tilt Table Test” instead of a tilt table test:

• Orthostatic vital signs can be sufficient to obtain a diagnosis

• Tilt table tests can cost up to $2000

• Obtaining a tilt table test typically requires a lot of coordination and an available clinician to administer the test

Here we’ll provide you with some tips for how you can assess your heart rate’s response to positional changes with your Apple Watch from the comfort of your home.

What is POTS?

For those unfamiliar with postural orthostatic tachycardia syndrome (POTS), it is defined in part by a sustained increase in heart rate when a person changes position from lying/sitting to standing, accompanied by symptoms that may include:

• Dizziness or lightheadedness

• Heart palpitations

• Weakness

• Fatigue

POTS itself is not a disease, but rather a syndrome, which means that it is a presentation of different symptoms that tend to cluster together. For some people, these symptoms have an underlying cause that can be identified, such as anemia or thyroid dysfunction. In other cases, these symptoms are most likely provoked by a combination of genetic and environmental factors. Unfortunately, there is a lot that remains unknown about the exact mechanisms that lead to this experience.

Setting Up Your Apple Watch

Before you begin your DIY tilt table test, it’s important to ensure that your Apple Watch is correctly set up to provide accurate heart rate data. Here’s how to prepare:

1. Check Your Watch’s Fit

   • Proper fit: Ensure your Apple Watch is snug but comfortable on your wrist. A secure fit ensures more accurate heart rate readings.

2. Get Familiar with Heart Rate Tracking

   • View Heart Rate Data: Open the Heart Rate app directly on your Apple Watch to access real-time heart rate information during the test.

3. (Optional) Accessing Health Data on iPhone:

   • Health App Overview: While the Apple Watch automatically tracks your heart rate in the background, you can view historical heart rate data on your iPhone by opening the Health app and navigating to the Heart section to review your heart rate trends and other related metrics.

Tutorial to the DIY Tilt Table Test on Apple Watch

Once your apple watch is fit snuggly and you are familiar with its heart rate tracking app, the DIY tilt table test is straightforward and takes just a few minutes to complete. The following tips can help you complete a version of orthostatic vital signs, though it’s important to keep in mind that the formal testing also requires checking blood pressure:

Step 1: Record Your Resting Heart Rate

1. Lie Down for a Few Minutes: Find a quiet, comfortable place where you can lie down undisturbed like a bed or a couch

2. Check Your Resting Heart Rate: After five or so minutes, open the Heart Rate app on your Apple Watch or check your recent resting heart rate through the Health app on your phone.

3. Record the Resting Rate: Make a mental note or jot down the starting heart rate for reference.

Step 2: Stand Up Slowly

1. Move to a Standing Position: Stand up calmly, avoiding any sudden or fast movement that could artificially spike your heart rate.

2. Wait a Moment: Stand still, allowing your body a moment to adjust.

Step 3: Record the Heart Rate After Standing

1. Measure Immediate Response: Open the Heart Rate app again to view your heart rate right after standing. Note this initial reading.

2. Track Your Heart Rate at Intervals: Check and record your heart rate after 1 minute, 2 minutes, 5 minutes, and 10 minutes of standing to observe any sustained changes.

3. Identify Significant Spikes: According to general POTS criteria, a rise of 30 bpm or more from from rest to standing within 10 minutes may suggest POTS, though this DIY test is not a definitive diagnosis.

Step 4: Compare Results

Take a look at your starting and standing heart rates:

• Normal response: A slight increase (usually less than 20 bpm) when standing is normal.

• More investigation is recommended: A sustained increase of 30 bpm or more that is accompanied by symptoms warrants a more formal evaluation with the guidance of a healthcare provider.

A POTS diagnosis requires a sustained heart rate increase of 30bpm or more

After completing your DIY tilt table test, it’s important to consider what your results mean and what to do with the data. As we mentioned previously, this test can help with diagnosis only when it is done in its entirety (checking both heart rate and blood pressure at the appropriate intervals).

For people who complete the heart rate testing only, if you notice sustained or prolonged increases in heart rate of more than 30 beats per minute when moving from rest to a standing position, we recommend that you discuss your results with a healthcare provider. Your doctor can help offer guidance for any next steps that may be important to receive a comprehensive and accurate evaluation.

At Empirical Health, you can take your health monitoring to the next level. Our app not only facilitates detailed heart rate tracking, but also provides access to board-certified doctors who can help answer questions about your data and can help you bridge the gap between self-monitoring and traditional healthcare. If you are experiencing symptoms that are concerning to you or your health metrics are not where you would like them to be, you can easily book an appointment with our dedicated healthcare professionals to discuss a plan for evaluation and treatment that fits your lifestyle.

Clinical testing of VO2Max typically uses a respiratory mask during intense exercise, such as a treadmill or cycling. But wearables like Apple Watch estimate cardio fitness (their version of VO2 max) to within an accuracy of 1.2 ml/kg/min without requiring a mask.

How do they do that? This article explains the science behind VO2 max, how the Apple Watch’s cardio fitness algorithm works (based on published details from 2021 and 2023 papers), and concrete data from the study used to validate its accuracy. Along the way we’ll cover how to combine physiological ODEs (ordinary differential equations) with flexible neural networks, 9-panel plots used in VO2 max testing, and more.

For details on how to actually use VO2Max, its link to longevity, and how to get a cardio fitness measurement, see our guide to Apple Watch’s cardio fitness metric.

Primer: how VO2Max is measured in the lab

Before we get into how Apple Watch algorithm estimates VO2Max, we have to first define how VO2Max is actually measured in the lab.

VO₂ Max is defined as the maximum volume of O₂ (oxygen) the body can utilize during intense exercise. It’s measured during a cardiopulmonary exercise test (CPET). During a CPET, you wear a respiratory mask while exercising (e.g., cycling or treadmill) at a steadily increasing intensity. As the work intensity rises, you consume more O₂ (oxygen), expel more CO₂ (carbon dioxide), and your heart rate rises.

At some point, the intensity of the workout becomes high enough that your muscles need more oxygen than your heart and lungs can supply. Your muscle cells are then forced to switch from aerobic to anaerobic energy production, so that CO₂ continues increasing while O₂ plateaus. At least, this is the “idealized” test situation—in practice, O₂ may not actually reach a plateau and the test may end when the the ratio of CO₂ to O₂ reaches 1.1, when the patient feels breathless, when an ECG shows signs of stress, etc.

This whole process produces a nine-panel plot, which shows various combinations of O₂ consumed, CO₂ expelled, intensity of exercise (in watts), heart rate, breathing rate, blood oxygen saturation, and so on.

In panel 3, you can see how both O₂ (red) and CO₂ (blue) increase as the exercise intensity ramps up (black). There’s a point around 11 minutes where the two lines diverge (this is the anaerobic threshold). Panel 5 shows that heart rate increases roughly in proportion to O₂.

Cardio fitness: Apple Watch’s maskless approximation of VO2Max

If you wanted to estimate VO2Max without actually measuring O₂ and CO₂, how would you do it? You can make use of two facts:

1. Heart rate and O₂ are proportionate: as your heart rate increases, you’re consuming more oxygen.

2. You can estimate work (in watts) if you know the person’s pace and body weight.

Various methods have been proposed in the medical literature, and as we’ll see, Apple’s algorithm appears to be a more sophisticated version of those using neural networks combined with biophysical ordinary differential equations (ODEs).

The Rockport cardio fitness test: a simple method from 1987

The Rockport fitness walking test was proposed in 1987 to estimate VO2Max. Subjects performed multiple 1-mile walk tests as fast as possible. The heart rate and completion time were placed into a linear regression, which yielded this formula to calculate VO2Max based on each subject’s weight, age, sex, fastest time, and heart rate:

VO2max = 6.9652 + (0.0091weight) - (0.0257age) + (0.5955sex) - (0.2240time) - (0.0115*heart_rate)

The accuracy was good (r=0.92 in the initial study). As we’ll see in the next section, Apple appears to be using a similar scientific basis but with a more sophisticated algorithm.

Apple Watch estimates cardio fitness using heart rate and GPS as inputs

Apple Watch requires two things to produce a cardio fitness estimate:

• Outdoor walking/running/hiking workout on flat ground (5% grade or less).

• Heart rate needs to increase more than 30% of the way between your resting heart rate and max heart rate. For example, if your resting heart rate is 60bpm and your max heart rate is 180bpm, you’d need to reach a heart rate of 96bpm or above to get a VO2Max estimate.

These suggest they’re estimating both work and heart rate response to exercise—similar in its basic science to the Rockport test.

Estimating VO2Max with physiological ODEs and neural networks

Note: some background in neural networks is helpful to understand the following section. If you don’t want the details, feel free to just skip to the next section.

In 2023, researchers from Apple published a paper on using biophysical ODEs for fitness estimation using wearables, alongside an open source repo with some Torch neural networks. This gives a glimpse into how modern deep learning algorithms can be used to improve upon the basic science of the Rockport test.

The paper starts by defining heart rate and oxygen response to exercise using a set of ordinary differential equations (ODEs):

Here, I(t) is exercise intensity at time t, f(I(t)) is the instantaneous demand for oxygen, D(t) is oxygen demand at time t, and HR(t) is heart rate at time t. A, B, alpha, beta are learned parameters.

The first equation tells us how the oxygen demand changes over time to match the instantaneous demand from the intensity of the workout. The second equation tells us how drive heart rate toward the pace required to meet that oxygen demand. It includes factors that describe how fast the heart can adapt (A), how difficult it is to reach the maximum heart rate (beta), and how much time it takes to rest down to the resting heart rate (alpha).

Each person’s fitness at a given time is characterized by seven physiological parameters: A, B, alpha, beta, f, HRmin, and HRmax.

Rather than estimate these parameters directly, the researchers trained a neural network that predicts a person’s entire heart rate response to exercise given a latent vector z. The paper doesn’t specify z’s dimension, but in the open source code z is a 32-dimensional vector. They then trained additional neural networks to predict each physiological parameter as a function of that latent factor: A(z), B(z), alpha(z), and so on.

These physiological parameters were then fed into a linear regression to predict VO2 Max. The error was about 5% (not bad). What’s interesting is that the model is interpretable as a result of going through the physiological ODE. For example, you can see an obvious correlation between the predicted A, B, alpha, and beta and VO2 Max in the plots below:

Apple Watch’s cardio fitness algorithm was validated in a study with 221 participants

Apple itself ran a study validating the algorithm, with 534 participants for development and 221 for validation. The algorithm was surprisingly accurate, with a mean error of 1.2 to 1.4 ml/kg/min and a reliability coefficient (ICC) around 0.86–0.89.

You can see a plot of actual VO2Max (x axis) vs the Apple Watch’s estimate (y axis). It’s pretty good!

However, the algorithm does have limitations for people with certain health conditions and on certain medications. From Apple’s own report:

Other medical conditions can also decrease the accuracy of VO2 max estimates on Apple Watch. These include medical conditions or devices that decouple heart rate from movement or exercise (for example, pain, arrhythmias, pacemakers, or cardiac-assist devices); medical conditions that severely limit exercise tolerance, preventing patients from reaching heart rates close to their predicted maximum heart rate (for example, peripheral arterial disease); and medical conditions that significantly increase the difficulty of ambulation, such as skeletal or neuromuscular conditions causing gait inefficiency (for example, multiple sclerosis or cerebral palsy).

What to do if you get a low cardio fitness notification

VO2Max is most commonly improved through zone 5 (high intensity) training. If you want to improve your VO2Max, download Empirical Health for Apple Watch or check out our ultimate guide to Apple Watch health metrics.

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We hope that this feature is able to help all of our users with early detection of mental health issues, timely interventions, and improved communications with their medical team.

What are PHQ-9 and GAD-7 scores

The Patient Health Questionnaire-9 (PHQ-9) and the Generalized Anxiety Disorder-7 (GAD-7) are two widely accepted screening and diagnostic tools for depression and anxiety. These questionnaires help doctors and their patients assess symptom severity and track changes over time. The U.S. Preventive Services Task force recommends everybody be screened for anxiety and depression, including during and after pregnancy.

How It Works

Starting with iOS 17, iPhones introduced the ability to track mental health using PHQ-9 and GAD-7. With iOS 18, Empirical Health can now request permissions to securely read and write this data, bringing seamless mental health monitoring to our app. We then integrate these assessments into the app experience as part of a user’s baseline health metrics. It’s important to note, we take your privacy seriously—Empirical Health requests explicit permission to access this information, and all data is stored and transmitted securely, ensuring it remains private and accessible only to you and those you choose to share it with.

When you complete a mental health assessment in the iOS Health app, the data automatically syncs with Empirical Health, displaying your depression or anxiety risk alongside other key health metrics like resting heart rate, sleep, and exercise. You can also take these assessments directly within the Empirical Health app, with all data syncing to your Health app.

After you complete an assessment we provide you with guidance for next steps, including when it’s recommended that you talk to a doctor. If you don't have a primary care doctor, or can't see them soon enough, you can book a video appointment with an Empirical Health doctor within the app.

Join us in revolutionizing mental health tracking—making proactive care accessible to everyone!

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What is sleep apnea?  

Sleep apnea is a common yet serious disorder where breathing repeatedly stops and starts during sleep. It can lead to various symptoms and health complications, including cardiovascular issues, daytime fatigue, and impaired cognitive function. Many individuals with sleep apnea remain undiagnosed, making early detection crucial.

Who will receive alerts?  

The new Breathing Disturbances feature will be available on Apple Watch Series 9, Series 10, and Ultra 2 when running on iOS 11. Apple reports that the built-in algorithms will use the watch’s accelerometer and analyze a user’s data over a 30-day period. If your data shows consistent signs of moderate to severe sleep apnea, you will receive an alert.  

If you receive an alert, you will be able to export a PDF that includes information like what your breathing disturbances have looked like over a three month period. 

What should you do if you receive a “Possible Sleep Apnea” alert?  

If you receive a notification from your Apple Watch or your Health App suggesting you have “Possible Sleep Apnea”, you can take the following steps to protect your health:

• First, don’t panic, but do take the alert seriously. The Breathing Disturbances feature is only a screening tool and not diagnostic. This means that you will need further evaluation to determine whether you have sleep apnea.

• Second, make an appointment with your primary care doctor. It may be helpful to bring a printout of your Breathing Disturbances report with you to your doctor’s visit; however, this is not required. Your doctor will ask you more questions about any symptoms you may have. Together, you and your doctor will decide whether a formal sleep study is needed to confirm a diagnosis and whether any other testing is needed.

• Third, while you wait for your doctor’s appointment or sleep study to be completed, consider starting on lifestyle adjustments that may help improve your overall quality of life and reduce your sleep apnea risk. These may include reducing alcohol use, committing to a regular sleep schedule, and maintaining a healthy weight.  

What if I don’t get an alert, but I think I may have sleep apnea?  

It is possible that you may have sleep apnea even if you don’t get an alert from your Apple Watch. At this time the notifications for this new feature will only alert people who have a moderate to severe risk for sleep apnea. Mild cases may not receive an alert.  

If you are experiencing any symptoms like fatigue, daytime sleepiness, snoring, frequent nighttime awakening, etc. or you are concerned you may have sleep apnea, you should talk to your primary care doctor to ensure you receive an appropriate evaluation.

The integration of sleep apnea notifications on devices like the Apple Watch represents a significant advancement in personal health monitoring. By providing users with early warnings about potential sleep disorders, it empowers individuals to seek timely medical advice and interventions.  

If your Apple Watch notifies you of potential sleep apnea, take it as an opportunity to engage with your health proactively and consult with healthcare professionals for further guidance. If you don’t have a doctor or are having a hard time connecting with your doctor, you can access a board-certified doctor through Empirical Health, covered by most major insurance!

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Baymax—the personal healthcare assistant from Big Hero 6—may be closer to reality than we think. While LLMs have already passed medical licensing exams, one missing piece has been grounding in objective, physical biomarkers. We think the combination of broadly-available consumer devices like Apple Watch (which generates 240,000 data points per year and has multiple FDA clearances) and health information exchanges (which offer objective outcomes, such as hospitalizations or ER visits) make it possible to ground medical AI in objective physical data.

Today we’re launching Empirical 2.0, which is a step in this direction. Empirical Health 2.0 transforms your biometric data and personal goals into a customized health plan. To ensure safety, your care plan must always be reviewed with a real, human doctor, who can order necessary labs, referrals, or prescriptions. Medical care through Empirical is now available to 200 million people across 27 states.

Examples of how Empirical can help you be healthy

Here are a few scenarios that show how Empirical uses your health data to create an actionable, step-by-step care plan:

• Let’s say you have low deep sleep. Empirical will analyze your Apple Watch sleep stages and bedtime patterns to design a protocol to assess sleep hygiene, risk of sleep apnea, and any need for further testing, reviewed by a doctor.

• Want to increase VO2Max? Empirical crafts an exercise protocol with Norwegian 4x4s, Zone 2 training, and strength training to improve VO2Max.

• Suffering from Long Covid, Dysautonomia, or POTS? Empirical creates a plan to evaluate your symptoms. It starts with taking orthostatic vitals using a heart rate monitor and a blood pressure cuff (essentially, an at-home version of the $1,900 tilt table test). We also use your ECG and blood test results to rule out other causes of tachycardia. Based on the results, Empirical designs a personalized care plan that may include medication, progressive exercise (based on the science behind the CHOP protocol), and hydration strategies.

Care plans may involve additional AI-generated diagnostic steps; to ensure safety and prevent unnecessary medical costs, those are locked behind an appointment with a real human doctor.

Here’s whats new in Empirical Health 2.0

In addition to care plans, we’ve completely redesigned the app and added new features. Here’s a complete list of what’s new:

• App redesign. The visual design of the app is completely refreshed.

• AI-generated care plans. As described above, Empirical will distill your data and your health goals into an actionable care plan. While AI generates the plan, a real doctor reviews it with you (ensuring accuracy) and can order necessary labs, referrals, or prescriptions.

• Support for blood pressure cuffs: connect a third party blood pressure cuff in order to manage hypertension. Our hypertension care plan covers exercise, nutrition, and medication (if prescribed by a doctor).

• Benchmarks. All metrics—resting heart rate, HRV, VO2Max, deep sleep %, REM sleep %, oxygen saturation, etc—are benchmarked against medical norms. We’ll also tell you your percentile, so you can see at a glance where you stand.

• Medical care is available in 27 US states covering 200 million people—up from just 4 states at launch.

• New workout templates to improve VO2Max.

Why does this matter?

We’re facing a massive primary care shortage. Simply providing recommended preventive health would require 27 hours per day from the average primary care doctor—clearly an impossible task.

We think a personal healthcare assistant, paired with a doctor, is one compelling way forward. Rather than being a literal life-size robot, our version of Baymax is a friendly app on our phone and watch that integrates with health sensors and helps you proactively manage your day to day health. Try it today by downloading Empirical Health for Apple Watch on the App Store.

This analysis is based on the sleep apnea risk assessment feature of Empirical Sleep. If you want to check your risk — and talk directly with a doctor about follow-up testing — then download Empirical Sleep for Apple Watch on the App Store.

The cardiovascular signals most correlated with sleep apnea

Cardio recovery & sleep apnea

Cardio recovery—also called called heart rate recovery—measures how how fast your heart rate returns to normal after exercise. It's a good measure of your heart's health and how well your autonomic nervous system (the system that controls involuntary actions like heart rate and digestion) is working. People with sleep apnea often have problems with this system because their breathing stops and starts throughout the night, which stresses their heart.

Resting heart rate & sleeping heart rate

Your resting heart rate (RHR) is the number of times your heart beats per minute when you're at rest. It gives a snapshot of your overall heart health. For those with sleep apnea, the constant interruptions in breathing can activate the fight-or-flight response (part of the autonomic nervous system), which keeps the heart working harder even at rest. This leads to a higher RHR.

So, if someone's resting heart rate is consistently high, it could be a red flag for sleep apnea. The same is true of your average heart rate while asleep.

HRV (heart rate variability)

Heart rate variability (HRV) measures the variations in time between each heartbeat. It reflects how well the autonomic nervous system is balancing the sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) responses. High HRV means your body can adapt well to different situations, but sleep apnea can mess this up. Frequent breathing interruptions at night can lower HRV because they increase stress and reduce the body's ability to relax.

How this analysis correlated Apple Watch sensors with a medical survey instrument

This analysis is based on 1,270 risk assessments for sleep apnea that have been completed through Empirical Sleep. Our risk assessment is based on the STOP-BANG survey. The data was first de-identified to preserve privacy. Then, all Apple Watch metrics — oxygen, cardio recovery, temperature, etc — were normaalized to have a mean of 0 and standard deviation of 1.0. Then, those with high risk and low risk were separated into two groups, with the average of their normalized Apple Watch metrics (oxygen, cardio recovery, temperature, etc) taken for each group and ranked based on difference. In the chart above, a strength of 0.5 means those with high risk are 0.5 standard deviations above (or below) those with low risk.

Talk with a doctor about sleep apnea through Empirical Sleep

You can check your risk of sleep apnea through Empirical Sleep for Apple Watch. And if you’re at medium or high risk, you can talk with a doctor directly in the app to figure out next steps, including FDA-cleared sleep apnea tests covered by insurance.

While wearables like Apple Watch give us lots of raw data on our health metrics, what really matters is insights into the underlying factors behind our metrics.

Today we’re launching a feature in Empirical Health that lets you correlate your health metrics with your symptoms and behaviors.

Try it now — download Empirical Health for Apple Watch today.

Correlations

In Empirical Health, correlations are now automatically shown between any health metric and other health metrics. On the Today screen, just tap on a metric to see its correlations, alongside its trend over time.

Tag your symptoms & behaviors

You can extend these correlations through tags, which let you track your own custom symptoms and daily activities. On the today screen, you can now add custom tags:

For example, if you want to see how dizziness correlates with heart rate, add a custom tag called dizziness, track it daily, and then after 6 days, you’ll see correlations.

Want more?

Download Empirical Health for Apple Watch today. And if you have feedback on this new feature, let us know — hello@empirical.health.

There is: a specific, structured exercise program. While “exercise more” may seem like one of the most banal pieces of health advice, this isn’t that—instead, it’s an exercise program that’s been carefully designed around the unique characteristics and needs of POTS patients.

Empirical Health’s POTS exercise program is rooted in the foundational research of the CHOP / Levine protocol, but updated to use the latest technology, including the iOS 17’s new WorkoutKit feature to preload workouts with pre-calculated heart rate zones to your watch.

Download Empirical Health today and try it out, or read on to learn how it works.

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The science behind the CHOP / Levine Protocol

My co-founder Dr Raquel Rodriguez wrote about the science behind the CHOP and Levine protocols below.

While the details of these protocols vary a bit, they all involve some common characteristics:

• They begin with horizontal exercise, such as rowing, recumbent biking, or swimming — these horizontal exercises allow you to build strength.

• Start with low intensity exercise, guided by heart rate zones, for short durations (about 3 minutes initially). Strength training is incorporated twice a week. For those using beta blockers, an exertion scale is used instead of heart rate zones.

• Over the course of several months, graduate to longer durations, higher intensities, and upright exercise.

How we used iOS 17’s new WorkoutKit feature to build a POTS exercise program

iOS 17 and watchOS 10 introduced WorkoutKit, which lets developers create iPhone apps that preload workouts onto the Apple Watch. These workouts can be structured to include multiple segments, each of which have custom heart rate zones.

When you add today’s workout onto your watch, it will guide you through each segment. Segments generally guide you to reach a certain heart rate zone (or exertion level, for those on beta blockers) for a certain period of time. In the initial levels of the program, you might spend 3 minutes at a time at your base pace, with recovery in between:

As you advance in the program, the active periods adapt to become longer and more intense, with upright exercises typically being introduced after about two months.

Give it a try

Download Empirical Health on the App Store today.

When Empirical Health first launched in July, the app was available worldwide, but medical care was restricted to just four states.

Today, we’re launching medical care in five midwestern states—Wisconsin, Ohio, Michigan, Indiana, and Minnesota—broadening access to 47 million people.

For people with POTS, Dysautonomia, and Long Covid, access is a problem

Six million people in the US are estimated to have POTS — many of these due to a COVID-19 infection, but also due to other underlying causes such as autoimmune diseases.

But access is a major barrier. Within the five states launching today, only seven cities have POTS specialists. The entire state of Michigan has zero specialists listed on Dysautonomia International’s provider directory. For many patients, that may mean a 2-4 hour drive and months of waiting — just for a 10-15 minute appointment.

Affordable, empathetic POTS testing and treatment

We think there’s a better way. Empirical Health offers testing and treatment for POTS, from real doctors, by combining modern technology (such as the health sensors on Apple Watches) with classic biomarkers (such as in-person blood tests).

Here’s how POTS testing works with Empirical Health:

1. First, you meet your doctor over video to discuss your symptoms, medical history, and any prior testing.

2. Using your Apple Watch and a blood pressure cuff, you do a sit-stand test. You can do this at home.

3. Take a blood test at a local lab (or if you have recent test results, just upload them).

4. Perform an ECG using the Apple Watch or a similar at-home ECG device.

5. Get your results.

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If your test confirms a POTS diagnosis, your doctor will work with you to develop a treatment plan (this may include medications, exercise, compression, and so on) and schedule any follow-up testing.

Covered by insurance

We accept many forms of health insurance, and are working on contracting with more health insurers. For those without insurance, we offer transparent, upfront cash pricing. We understand that many patients avoid care because they don’t know how much it will cost, and we’re committed to making care affordable.

Primary care of the future

Healthcare today often feels antiquated and frankly, backwards. We don’t think it has to be that way — it’s absolutely possible to use the best of modern technology (health sensors, AI), grounded in evidence-based science, to deliver great care to you. Today, we offer general primary care, as well as programs for Long Covid, POTS, heart health, and sleep apnea — over time, our mission is to transform healthcare from reactive to preventive.

Give it a try

Do you or somebody you love need medical care? Then try Empirical Health for Apple Watch on the App Store today. We’re looking forward to meeting you.

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Apple has obtained FDA clearance for a handful of features that relate to atrial fibrillation. One of these features—the irregular rhythm notification—allows Apple Watch to check for irregular rhythms that could indicate the presence of afib.

To use it, you need to:

1. Live in a region where the feature is available

2. Be 22 years of age or older

3. Not have a prior diagnosis of afib

Since the feature uses the optical heart rate sensor for detection, it is available on all Apple Watch models. To enable it, go the Health app on your iPhone, click on Browse > Heart > Irregular Rhythm Notifications and follow the prompts for setup.

What does it mean to get an irregular rhythm notification?

Apple Watch will check your heart beat in the background for signs of an irregular rhythm. This will usually happen when you’re at rest, but the number of checks in a day will vary. If multiple readings confirm that your rhythm is irregular, your Apple Watch will notify you of this finding. Since the watch is not checking all of the time, it is possible that the watch will not catch all instances of an irregular rhythm.

Apple Watch reports that in their studies, this feature had a sensitivity of 88.6% and a detection specificity of 99.3%. This suggests that the watch is quite good at catching a substantial amount of all afib cases and when you get a notification it is most likely correct; however, since these numbers are not 100%, it is possible that some cases of afib will not be caught and some people who get the notification will not actually have afib.

What should you do if you get an irregular rhythm notification?

If you get this notification, it is recommended that you talk to your primary care doctor to ensure you receive an appropriate evaluation and the correct diagnosis. Your doctor will help you obtain an electrocardiogram (ECG) to evaluate your heart rhythm. They will also help you investigate whether there may be another underlying issue that is causing your abnormal rhythm. Finally, your doctor will help you create a management plan to reduce your risk of afib-related complications.

People with afib can live normal lives when their condition is well-managed. If you have received an irregular rhythm notification, reach out to your doctor to make sure the right steps are taken to maintain your health.

It's important to note that the Apple Watch is not a medical device. It is not intended to diagnose, treat, cure, or prevent any disease. Additionally, the Apple Watch's health monitoring features are not perfect and may not be accurate for everyone.

Health features with FDA clearance (for people 22 years and older)

You might recall that Apple has obtained FDA clearance for a handful of features. These have a strong emphasis on atrial fibrillation (afib) monitoring and detection.

• For people with a diagnosis of afib, Apple Watch can track how much time they spend in afib each week. This can help these individuals and their doctors better understand triggers or the efficacy of treatments.

• For people with no history of afib, Apple Watch will check for irregular rhythms that could indicate afib. It takes multiple readings to confirm its findings before alerting you. Notably, it is checking your rhythm when you’re at rest and it does not check all of the time, so it will not catch all instances.

• Anyone with the electrical heart sensor can record a single-lead ECG, which the ECG app will interpret. It will provide a few results, including: sinus rhythm, afib, afib with high heart rate, inconclusive, or poor recording. A result of inconclusive could indicate another arrhythmia or the presence of an ICD or pacemaker, but Apple Watch is not able to distinguish between these.

  

Other features

Apple Watch can collect many other data points. All of these vary widely in their utility as single data points.

• Sleep tracking shows you sleep duration, sleep onset time, time in REM and deep sleep. It can also calculate your respiratory rate and show you oxygenation while sleeping. While these can be interesting insights, the watch cannot tell you if something is abnormal or the significance of your sleep metrics. For the purpose of self-tracking, this data can help you notice changes in your sleep and perhaps how external factors such as illness or stress are impacting you. For some people, their sleep data can be an initial clue that they have an underlying issue, like sleep apnea. Apple makes clear that these functions are not intended for medical use, but the findings sometimes prompt people to seek medical care.

• Another function can check your average nighttime wrist temperature. Apple takes this data one step further to use these measurements for cycle (and retrospective ovulation) tracking - it can tell you when you likely ovulated, after the fact. The watch does not allow you to collect a temperature on-demand.

• Your watch can also alert you to high (>120) and low (<40) resting heart rates (it checks this periodically in the background). These alerts could be an indicator that something is abnormal, but the watch will not be able to interpret what that might mean for you.

• The oxygen monitor on the watch is not FDA approved, but it has been shown to be as accurate as FDA-cleared devices. For some people this could come in handy when they are monitoring respiratory diseases or other issues that affect oxygenation, but a low reading on the watch could easily be an incorrect measurement. For this reason it is often most helpful to notice a trend rather than to be concerned about a single value.

• Mobility data is also collected by Apple Watch. This includes metrics like a six-minute walk distance over time (derived over time for many instances and usually presented as a weekly metric), walking speed, step length, double support time, walking asymmetry, step count, and flights climbed. All of these can be useful for monitoring fitness, but for some people they can also point to possible underlying conditions. A few third-party apps have made use of this data to detect Parkinson’s disease and have obtained FDA clearance for this purpose.

• Other cardiovascular metrics like resting heart rate, heart rate variability, heart rate recovery, VO2 max, etc. are also captured by Apple Watch. These data as single points in time don’t necessarily mean too much about your health; however, when collected over time, the trends could be a clue about your underlying physiology.

Limits of the Apple Watch for health monitoring

People often wonder if their watch can tell them if they have a medical problem/illness or if it will alert them if something is wrong with their heart. The answer is no. Think of the data from your Apple Watch like a collection of small clues that could point to something unusual. But, none of these clues are specific to any one condition, nor will a single clue be able to uncover an undiagnosed issue. To further complicate things, some of these clues may be aberrant due to normal variation/error in the data capture.

Overall, the Apple Watch is a powerful tool that can help you monitor and get insights about your health and fitness. However, it is by no means comprehensive or a replacement from routine medical care. It is important to be aware of the limits of the device and to see a doctor if you have any concerns about your health.

In part 3 of this series, we will get into possible future uses for this wearable device. In the meantime, if you have questions about your Apple Watch data or you have a health concern, give Empirical Health a try!

First, let’s review the Apple Watch sensors

Beginning with Apple Watch Series 4 all of the devices include an optical heart sensor (which uses photoplethysmography1), an electrical heart sensor (for electrocardiogram2 capture), an accelerometer, and a gyroscope. Apple Watch SE includes all of these, except for the electrical heart sensor. Apple Watch Series 6 added a blood oxygen sensor and Apple Watch Series 8 added sensors to check wrist temperature. Apple Watch Ultra also includes an altimeter, water temperature sensor, and depth gauge - these are not currently relevant for health monitoring, but can be useful for people focused on fitness.

The sensors alone can provide raw data, which Apple interprets into different metrics using algorithms. This results in various readings you can view on your watch or iPhone — from simple numbers such as resting heart rate to more complex predictions such as cycle tracking, irregular rhythm notifications, and sleep stages.

Here is a general breakdown of which sensors populate which metrics:

• Heart-related metrics
  Apple Watch will use the optical heart sensor to show you heart rate, resting heart rate, heart rate variability, heart rate recovery, as well as atrial fibrillation (afib) history and irregular rhythm notifications. The electrical heart sensor powers the ECG app.

• Sleep-related metrics
  Apple Watch can track your sleep patterns, including how long you sleep, how often you wake up, and how much time you spend in each sleep stage. It uses a combination of sensors to arrive at these metrics, mainly the optical heart sensor and accelerometer.

• Cycle tracking

  You can track your period on your Apple Watch, using mostly information you log. Starting with Apple Watch Series 8, the watch can use the temperature sensor to estimate retrospectively when you ovulated.

• Blood oxygen
  Apple Watch tracks your blood oxygen using the blood oxygen sensor. We wrote more here regarding this sensor and its accuracy.

• Wrist temperature

  Apple Watch cannot give you a core body temperature reading, but it can track your wrist temperature overnight, provide you with a baseline measurement, and show you changes from your baseline using the temperature sensors starting on Apple Watch Series 8.

• Fitness tracking
  Apple Watch captures your distance traveled, activity, calories burned, etc. Many of these can be captured by your iPhone alone as it is also equipped with a gyroscope and accelerometer. Some of the data is calculated with information you provided to setup your health and fitness apps, such as height and weight.

Of these features, Apple has obtained FDA clearance for only the ECG application, the irregular rhythm notifications, and (for people with a history of afib) a feature to help track how often someone shows signs of atrial fibrillation. Notably, these are only FDA approved for people 22 years and older.

Beyond FDA clearance, all of the components of the watch depend on using the watch as it was intended. There are various factors that may impact the accuracy of your data, including wearing the watch too tight or loose, using it on an area that has a tattoo, having skin that is damp from sweat or water, etc.

In part 2 of this series, we will get into how the metrics provided by this wearable device can help you monitor your health and the limits of this data. In the meantime, if you have questions about your Apple Watch data, give Empirical Health a try!

Where did the CHOP protocol come from?

The Children’s Hospital of Philadelphia (CHOP) protocol is an exercise routine that was adapted from Dr. Benjamin Levine’s research on how exercise affects patients with postural orthostatic tachycardia syndrome (POTS). Dr. Levine, a sports cardiologist and the founding director of the Institute for Exercise and Environmental Medicine at Texas Health Presbyterian Hospital Dallas, has focused his career on exploring how circulation adapts in response to various factors, including exercise, aging, and environmental stimuli. Over the course of his career Dr. Levine and his team have conducted research on the impact of exercise on human physiology - this has helped build the foundation for helping us understand the role of exercise in POTS.

You may have heard this protocol referred to by different names: Levine protocol, modified CHOP protocol, Dallas protocol, etc. While these may have slight variations from the initial protocol defined by Levine, they are all rooted on the same principle.

How does the CHOP protocol work?

Dr. Levine’s research suggests that people with POTS are no different than people without POTS – everyone’s exercise performance improves with exercise conditioning. More specifically, research in this area has shown that a dedicated exercise protocol could lead to significant improvement in symptoms for a lot of POTS patients. 

In one of Levine’s studies, the researchers coached people with POTS through a 3-month exercise program. The program was designed to accommodate for orthostatic intolerance. As such, people began with 3 weekly sessions of sitting exercises (rowing, swimming, or recumbent bike) for 20-30 minutes targeting specific heart rate zones. Over time the participants increased their activity with longer sessions and eventually more weekly sessions. By the third month of training upright exercise was also incorporated. In addition, people participated in weekly strength training consisting of light weightlifting for 15-20 minutes. The research team found that 53% of participants did not meet the criteria for POTS after the 3-month exercise program and they showed gains in their peak oxygen uptake, cardiac mass, and blood volume. The ability of the heart to pump blood at each beat improved with the training program.

Interestingly, Dr. Levine’s research team has also completed smaller studies that suggest exercise may be superior to beta blockers in regard to improving standing heart rate and quality of life.

How do I incorporate this into my own treatment program?

You don’t need to have formal coaching to benefit from similar positive effects outside of a research environment. 

Generally there are a few guidelines to follow:

• Start slow and pace yourself: recumbent exercise at a lower pace will be a more accessible entry point for a lot of POTS patients. Over time, you will be able to tolerate more frequency and intensity of activity.

• Be consistent: your body requires activity to remain strong; pausing your exercise program will lead to some loss of the gains you have made even after just a few days. Spreading your exercise sessions throughout the week can help avoid this.

• Mix aerobic exercise with strength training: both of these types of exercise work in synergy to improve your cardiac conditioning and your overall muscle strength.

• Be patient and kind to yourself: it will take time to see a noticeable difference with any exercise program. This can be frustrating when you’re not feeling well. If you need to take a break, that’s ok! The training program can always be restarted when you are ready - just make sure to restart slowly.

If you’re looking to buy an Apple Watch for health monitoring, you have four major options as of late 2023.

Apple Watch Series 9 - the latest model

The newest Apple Watch is the Series 9, launched September 2023. It starts at $399 if bought new. This includes all of the health sensors above.

Apple Watch Ultra 2 - the premium option

The Apple Watch Ultra 2 starts at $799, was also launched September 2023, and includes all health features of the Series 9, plus GPS. This is a premium option targeted at serious hikers or athletes.

Apple Watch SE - affordable, but fewer health sensors

Although the Apple Watch SE is more affordable at $249, it’s lighter on health sensors. It includes a heart rate sensor and sleep tracking, but not an FDA-cleared ECG or blood oxygen. If you’re looking for something in this price range, also consider a used Apple Watch Series 6, 7, or 8, which have additional health sensors.

Used Apple Watch Series 6, 7, or 8

If you want all of the health sensors at an affordable price point, a used Apple Watch Series 8 is a good option. It includes all of the health sensors as the Apple Watch Series 9, including the ECG, oxygen, and temperature sensors.

The Apple Watch Series 6 and 7 include ECG and oxygen, but not the temperature sensor.

Buying these models used is a good option is you want more health sensors, but at an affordable price. As of this writing, used Series 8 are selling for about $300, whereas a used Series 6 costs around $180.