Description:

Presenter: Kyle Miller, MD, MBA

Introduction: Blood pressure (BP) is a continuous and dynamic physiologic variable. The sphygmomanometer has forced clinicians to rely on single snapshots of BP to make clinical decisions about BP control. Ambulatory cuff-based BP monitoring has demonstrated superiority over conventional, single-point office-based cuff measurement and has unveiled the important concept of nocturnal BP dipping; however, it is plagued by poor compliance leading to limited use. Thus, there is an unmet need for an unobtrusive continuous ambulatory BP monitor. Current methods for continuous, non-invasive ambulatory BP monitoring include the use of pulse wave velocity and pulse transit time coupled to electrocardiographic timing of the QRS complex. However, both of these techniques have limitations. We therefore propose a novel method—differential pulse arrival time (DPAT)—to continuously estimate BP non-invasively. We hypothesized that continuous DPAT-derived BP correlates well with cuff-based measurement of BP at rest and during a cold-pressor maneuver.

Methods: Normotensive subjects were fitted with a DPAT device and a Finapres Portapres ambulatory BP monitor. Each subject underwent a standardized protocol consisting of 2 minutes at rest, 2 minutes cold pressor at 40oF, and 2 minutes at rest. The raw data from the DPAT device was then time-matched and compared with the Finapres BP trend.

Results: Over 100 million DPAT data points were collected from 12 normotensive subjects (age range 20-50). DPAT correlated with Finapres blood pressures with a correlation coefficient of 0.8 (Figure 1). The root mean square error for the predicted blood pressure was ±4.76 mmHg for systolic BP and ±4.03 mmHg for diastolic BP.

Conclusions: Differential pulse arrival time obtained by an optical-sensor based system is a viable approach to monitoring continuous BP in normotensives. Future studies in elderly, hypertensive individuals is warranted.