The photoplethysmogram is a noninvasive circulatory signal related to the pulsatile volume of blood in tissue and is displayed by many pulse oximeters and bedside monitors, along with the computed arterial oxygen saturation. The photoplethysmogram is similar in appearance to an arterial blood pressure waveform. Because the former is noninvasive and nearly ubiquitous in hospitals whereas the latter requires invasive measurement, the extraction of circulatory information from the photoplethysmogram has been a popular subject of contemporary research. The photoplethysmogram is a function of the underlying circulation, but the relation is complicated by optical, biomechanical, and physiologic covariates that affect the appearance of the photoplethysmogram. Overall, the photoplethysmogram provides a wealth of circulatory information, but its complex etiology may be a limitation in some novel applications.

(MIT). He specializes in robotics, biomedical engineering, and system dynamics and control. His current research areas include wearable health monitoring, robotic aids for bedridden patients, vast DOF actuator systems, and multiphysics simulation. He received the B.

It is well known that the photoplethysmogram (PPG) is related to the underlying arterial blood pressure (ABP). However, there is ambiguity regarding the precise relationship of these two circulatory signals: some investigators have described a static relationship, while others have used more complex dynamic characterizations. This paper attempts to reconcile these models, employing results obtained from controlled human subject tests. Our data indicate that there is no simple relationship between the continuous PPG and ABP. However, when several serial beats are aggregated, a static, reproducible relationship is observed. This suggests that, in a stable experimental environment, most of the factors that decouple the ABP and PPG operate over short time scales. When these factors are eliminated through beat averaging, calibrated plethysmography offers a near-continuous estimation of ABP. Our data suggest that this PPG/ABP relationship is not stationary, since it is less consistent over time scales greater than 20 minutes. Variable local ABP was generated by raising and lowering the subjects' hands; this method also offered the means for oscillometric BP measurement without any additional actuator such as a conventional pneumatic cuff.

This paper presents a new principle for noninvasive blood pressure measurements through a modified volume-oscillometric technique that eliminates an inflatable pressure cuff, and instead takes advantage of natural hydrostatic pressure changes caused by raising and lowering the subject's arm. This new methodology provides the distinct advantage of using an absolute gauge pressure reference for measurements, and does not necessarily require additional actuation.