Validating cuffless continuous blood pressure monitoring devices

Cuff-based home blood pressure (BP) devices, which have been the standard for BP monitoring for decades, are limited by physical discomfort, convenience, and their ability to capture BP variability and patterns between intermittent readings. In recent years, cuffless BP devices, which do not require cuff inflation around a limb, have entered the market, offering the promise of continuous beat-to-beat measurement of BP. These devices take advantage of a variety of principles to determine BP, including (1) pulse arrival time, (2) pulse transit time, (3) pulse wave analysis, (4) volume clamping, and (5) applanation tonometry. Because BP is calculated indirectly, these devices require calibration with cuff-based devices at regular intervals. Unfortunately, the pace of regulation of these devices has failed to match the speed of innovation and direct availability to patient consumers. There is an urgent need to develop a consensus on standards by which cuffless BP devices can be tested for accuracy. In this narrative review, we describe the landscape of cuffless BP devices, summarize the current status of validation protocols, and provide recommendations for an ideal validation process for these devices. Cuff-based home blood pressure (BP) devices, which have been the standard for BP monitoring for decades, are limited by physical discomfort, convenience, and their ability to capture BP variability and patterns between intermittent readings. In recent years, cuffless BP devices, which do not require cuff inflation around a limb, have entered the market, offering the promise of continuous beat-to-beat measurement of BP. These devices take advantage of a variety of principles to determine BP, including (1) pulse arrival time, (2) pulse transit time, (3) pulse wave analysis, (4) volume clamping, and (5) applanation tonometry. Because BP is calculated indirectly, these devices require calibration with cuff-based devices at regular intervals. Unfortunately, the pace of regulation of these devices has failed to match the speed of innovation and direct availability to patient consumers. There is an urgent need to develop a consensus on standards by which cuffless BP devices can be tested for accuracy. In this narrative review, we describe the landscape of cuffless BP devices, summarize the current status of validation protocols, and provide recommendations for an ideal validation process for these devices. Key Findings•Cuffless, calibration-dependent blood pressure (BP) devices offer the promise of beat-to-beat, noninvasive measurement of BP variability during both awake and sleep periods, with minimal inconvenience to patients.•Cuffless BP devices estimate BP indirectly using principles such as pulse wave velocity, pulse transit time, pulse wave analysis, volume clamping, and applanation tonometry. This is in contrast to cuff-based BP devices, which measure BP directly by sphygmomanometry.•The speed of innovation and proliferation of cuffless BP devices has outpaced the speed of development of regulations for cuffless BP devices. As uptake of these devices continues to increase, there is an urgent need to develop uniform standards for proper validation, especially in the ambulatory setting.•There are numerous limitations for applying traditional validation approaches to cuffless BP devices, including the absence of an ideal referent standard, the lack of direct BP measurement, the violation of static-state assumptions with physical activity, the “zero out” bias phenomenon, the heterogeneity of populations, and an over-reliance on heart rate (HR) for BP estimation.•An ideal validation process for cuffless BP devices should focus on validating change in BP (not BP itself); use a validated device as the referent device that is distinct from the calibration device; include both static and dynamic activity states and both awake and sleep states; rule out an over-reliance of BP on HR; include a representative sample of BPs, wrist sizes, and skin tones; and function across a range of heart rates and common medications. •Cuffless, calibration-dependent blood pressure (BP) devices offer the promise of beat-to-beat, noninvasive measurement of BP variability during both awake and sleep periods, with minimal inconvenience to patients.•Cuffless BP devices estimate BP indirectly using principles such as pulse wave velocity, pulse transit time, pulse wave analysis, volume clamping, and applanation tonometry. This is in contrast to cuff-based BP devices, which measure BP directly by sphygmomanometry.•The speed of innovation and proliferation of cuffless BP devices has outpaced the speed of development of regulations for cuffless BP devices. As uptake of these devices continues to increase, there is an urgent need to develop uniform standards for proper validation, especially in the ambulatory setting.•There are numerous limitations for applying traditional validation approaches to cuffless BP devices, including the absence of an ideal referent standard, the lack of direct BP measurement, the violation of static-state assumptions with physical activity, the “zero out” bias phenomenon, the heterogeneity of populations, and an over-reliance on heart rate (HR) for BP estimation.•An ideal validation process for cuffless BP devices should focus on validating change in BP (not BP itself); use a validated device as the referent device that is distinct from the calibration device; include both static and dynamic activity states and both awake and sleep states; rule out an over-reliance of BP on HR; include a representative sample of BPs, wrist sizes, and skin tones; and function across a range of heart rates and common medications.