Towards ubiquitous blood pressure monitoring in an armband using pulse transit time

Unobtrusive, continuous, and convenient blood pressure (BP) measurement technologies are of high importance to control hypertension and allow titration of care. In this paper, we present novel technologies to facilitate development of an armband system to estimate BP using pulse transit time (PTT) obtained from Ballistocardiogram (BCG) and Photo-plethysmogram (PPG) signals. Specifically, a wearable, acceleration based BCG measurement positioned on the upper arm at the tricep (for proximal timing detection) is paired with a reflectance mode PPG measurement on the inner side of the same arm (for distal timing detection) to extract an estimate of PTT. This unconventional PTT estimate, derived from a relatively short segment of the arterial tree (from the aortic arch to the microvascular bed at the upper arm), was compared to a more established PTT measurement (from the aortic arch to the toe) in four subjects in a pilot study to evaluate feasibility. The PTT measurements were reasonably well correlated for all subjects (r2 = 0.83) for the perturbations employed in this work (hand grip challenge and slow breathing). The results suggest that future investigation of an armband-deployed BCG-PPG based system for PTT measurement is warranted.