Cuffless Blood Pressure as a Digital Biomarker

Cuffless blood pressure means estimating arterial pressure without inflating a cuff, typically from features of the pulse waveform recorded optically at the wrist or finger. It is the measure in this library where the distance between what is sold and what is validated is largest, so this page is written primarily to mark that distance.

The physical problem is that no wearable sensor measures pressure. Cuffless devices measure a correlate, usually a timing or morphology feature of the pulse wave, and convert it to a pressure estimate using a model. That model is fitted to the individual during a calibration against a real cuff, and it drifts as vascular properties change with posture, temperature, medication, arousal and time since calibration.

Professional societies have been explicit about the consequences. Both European and American statements have set out that current validation protocols were designed for cuff devices and do not establish whether a cuffless device tracks real pressure change in an individual.

Most implementations derive pulse arrival or pulse transit time, the interval between a cardiac electrical event and the arrival of the pressure wave at a peripheral site, or extract morphological features from the photoplethysmogram alone. A regression or machine learning model maps those features to systolic and diastolic estimates.

Nearly all require initial calibration against a validated cuff, and recalibration at intervals. This is the crux of the accuracy debate: a device calibrated to a person's current pressure will appear accurate while their pressure stays near the calibration point, and the meaningful test is whether it tracks change away from it. Evaluations designed to test exactly that in a commercially available wearable have reported that tracking of induced blood pressure change was poor.

The European Society of Hypertension has published dedicated validation requirements for cuffless devices, which existing consumer implementations largely predate.

The clinical prize is real, which is why the field persists. Blood pressure is the leading modifiable cardiovascular risk factor, cuff measurement is intermittent and disliked, and nocturnal pressure and its variability carry prognostic information that clinic readings miss entirely.

In research today the defensible uses are narrow. Cuffless output can be collected as an exploratory signal alongside validated cuff measurement, and it can be studied as the object of research rather than used as a measurement instrument. It should not be used to titrate antihypertensive treatment, to diagnose hypertension, or as a trial endpoint.

The measure has no questionnaire counterpart, and unlike most entries in this library that is not a gap to be filled: blood pressure's reference standard is a validated cuff, which is why this page is about device to cuff agreement rather than about a patient reported construct.

Calibration dependence is the central limitation. Accuracy decays with time since calibration and is worst exactly where clinical interest is highest, at pressures far from the calibration point.

Regulatory status varies by market and by feature, and a function available in one country may be unavailable or differently labelled in another. Any claim that a given device is cleared should be checked against that market's regulator rather than against marketing copy, and this library does not assert clearance for any cuffless product.

Population level accuracy also masks individual error, and the groups most affected by hypertension are underrepresented in validation datasets. An estimate that is accurate on average across a cohort can be substantially wrong for the person in front of you, which is the only level at which blood pressure is acted on.

• Stergiou GS, et al. European Society of Hypertension recommendations for the validation of cuffless blood pressure measuring devices. J Hypertens. 2023. pubmed.ncbi.nlm.nih.gov
• Mukkamala R, et al. Cuffless blood pressure measurement: where do we actually stand? Hypertension. 2025. pubmed.ncbi.nlm.nih.gov
• Cohen JB, et al. Cuffless devices for the measurement of blood pressure: a scientific statement from the American Heart Association. Hypertension. 2026. pubmed.ncbi.nlm.nih.gov
• Tan I, et al. Evaluation of the ability of a commercially available cuffless wearable device to track blood pressure changes. J Hypertens. 2023. pubmed.ncbi.nlm.nih.gov