November 12, 2024
How Accurate are Finger Blood Pressure Apps?
As of November 2024, not a single “finger blood pressure app” has received FDA approval. Since blood pressure is the force of blood pushing against vessel walls, the most precise way to measure it is by inserting a catheter into an artery. FDA-cleared and clinically validated tools and monitors can also yield reliable results when used correctly. However, cuffless blood pressure monitoring apps — designed to work with just a smartphone and a finger — do not use any additional hardware to measure blood pressure. Instead, they estimate it using algorithms and indirect data sets collected in an uncontrolled environment. As a result, their readings are not accurate enough for medical use.
List of Blood Pressure Measuring Methods from Most to Least Reliable:
- Intra-arterial blood pressure monitoring (direct measurement): this is the most accurate method, typically used in intensive care or surgery settings. A catheter is inserted into an artery, providing real-time and highly accurate blood pressure readings.
- Auscultatory method, using a manual sphygmomanometer with a stethoscope: this is the traditional method of healthcare professionals listening to the Korotkoff sounds while manually inflating and deflating a cuff. It is highly reliable when performed correctly.
- Automatic oscillometric blood pressure monitors (cuff-based): common in clinics and home-use devices, these measure the oscillations in the arterial wall as the cuff inflates and deflates. They are generally accurate but can vary slightly with positioning and cuff size.
- Wrist blood pressure monitors: these may be more convenient but less reliable than upper-arm monitors, as measurements are more affected by wrist positioning relative to the heart.
- Blood pressure estimation via wearables: these are highly convenient, but their accuracy can vary significantly based on conditions and calibration.
- Blood pressure estimation apps: such apps, using camera sensors or external data, provide the least reliable results. They do not measure blood pressure directly but estimate it with the help of algorithms.
Other invasive methods, such as implantable blood pressure sensors, are used to monitor high-risk patients. For example, implantable pressure monitoring devices for patients with heart failure can detect changes in pulmonary-artery pressure, allowing for early intervention and proactive management.
Which Technologies May Blood Pressure Estimation Apps Use?
- Photoplethysmography (PPG): detects subtle changes in skin color using the camera, primarily for estimating blood flow, which indirectly helps estimate blood pressure levels. PPG is common in wearables like smartwatches.
- Transdermal Optical Imaging (TOI): captures blood volume information by analyzing facial color changes across multiple points. With a wider data range from the face, TOI can provide a broader context for estimating blood pressure.
- Pulse Transit Time (PTT): measures the time a pulse wave takes to travel between two points on the body (e.g., from the heart to the wrist), using this interval to estimate blood pressure.
- Oscillometric Estimation: often found in phone attachments, this method applies pressure sensors that mimic traditional oscillometric techniques in blood pressure cuffs, detecting pulse changes in response to pressure.
- Machine Learning Algorithms and Data-Processing Platforms: use multiple health data points (such as heart rate and demographic data) to estimate blood pressure patterns, though the accuracy may vary widely based on the data and algorithms.
- Electrocardiogram (ECG) Integration: combines signals from ECG and PPG sensors, primarily in wearable devices, to improve blood pressure estimation by capturing more physiological details.
Each technology offers unique advantages but still faces challenges compared to validated cuff-based methods.
Why is Measuring Blood Pressure with a Smartphone and Finger So Challenging?
Blood pressure is sufficiently harder to measure than a person’s heart rate. Nor is it a parameter that can be mathematically derived from a clear-cut formula like BMI. Making accurate medical-grade measurements requires precise physiological data and control over the measurement environment, which smartphone sensors cannot provide. Here are some of the challenges:
- Sensor Limitations: accurate blood pressure readings rely on precise sensing of pressure changes in blood vessels, usually with a cuff and stethoscope or electronic oscillometry. Current smartphone sensors are unable to capture this level of detail because they lack direct access to arterial blood flow and pressure.
- Calibration Requirements: reliable measurements would require regular personal calibration against a validated, cuff-based monitor. Calibration aligns app readings with an individual's actual blood pressure, accounting for personal baselines and nuances, which is necessary because factors such as skin tone, blood vessel characteristics, and ambient light can affect sensor accuracy.
- Environmental Factors: factors like ambient temperature, light exposure and movement can interfere with app measurements, especially when using PPG sensors on a phone. This lack of control introduces significant variability, leading to inaccurate readings.
- Lack of Diversity or access to large population-level databases in the training data leads to biases. Algorithms need to be trained on global datasets that account for diverse skin tones, ages, genders, and physical conditions to ensure general accuracy across populations.
- For Force Sensors the finger contact area can only be estimated, potentially introducing significant errors in blood pressure measurements. Additionally, users may find it physically challenging to maintain consistent pressure on the sensor for the time required to obtain a measurement, which can further compromise accuracy.
- Cold or Damaged Fingertips - may skew the results due to the technology’s reliance of adequate optical pulse wave signals at the fingertip.
- Regulatory Compliance: developing a clinically validated, FDA-approved app requires rigorous testing, calibration, and clinical trials, which is costly and time-consuming.
Why Do Users Seek Finger Blood Pressure Apps?
- Convenience and Accessibility - the idea of measuring blood pressure without a cuff or other special equipment - with just a smartphone and an app - is incredibly appealing.
- Desire for Self-Monitoring and Trust in Technology - people are becoming more health-conscious and want to monitor their vital signs regularly. The allure of a simple app that promises to track blood pressure is strong for those who want to stay informed about their health. With the increasing capabilities of smartphones and apps in general, people tend to trust that there could be a technological solution for almost anything, including measuring blood pressure.
- Misleading Advertising - “finger blood pressure apps” may appear to be more affordable when compared to buying a validated blood pressure monitor. Some apps use marketing tactics that exaggerate their capabilities, claiming to be more accurate or effective than is technologically possible.
- Curiosity and Hope - users may download blood pressure measuring apps out of curiosity, hoping they might actually work or provide some insight, even if they know the accuracy is questionable.
Despite the widespread interest, it is crucial to emphasize that such “finger apps” are not reliable for accurate blood pressure measurement and should not replace traditional methods or medical advice.
Why Are Reliable Blood Pressure Monitoring Methods So Important?
According to a publication in Clinical Hypertension, high blood pressure remains “the leading cause of morbidity and mortality worldwide” with millions of deaths attributed to it each year. Often, hypertension develops without symptoms, meaning regular blood pressure monitoring is essential for early detection and treatment. While finger blood pressure apps showcase clever smartphone innovations, the American Heart Association emphasizes that proper self-monitoring of blood pressure requires a clinically validated device.
Our earlier blog post covered the benefits of keeping a blood pressure diary, and here we encourage you to try using the MedM Health Diary App with your validated device. Health diaries save lives, and keeping one for effective hypertension care is recommended by the World Health Organization (WHO). Ultimately, as accurate and proactive health monitoring becomes more accessible, tracking blood pressure patterns is expected to help reduce complications from hypertension.
