Remotely detected differential pulse transit time as a stress indicator

Abstract

The human cardiovascular system, controlled by the autonomic nervous system (ANS), is one of the first sites where one can see the "fight-or-flight" response due to the presence of external stressors. In this paper, we investigate the possibility of detecting mental stress using a novel measure that can be measured in a contactless manner: Pulse transit time (dPTT), which refers to the time that is required for the blood wave (BW) to cover the distance from the heart to a defined remote location in the body. Loosely related to blood pressure, PTT is a measure of blood velocity, and is also implicated in the "fight-or-flight" response. We define the differential PTT (dPTT) as the difference in PTT between two remote areas of the body, such as the forehead and the palm. Expanding our previous work on remote BW detection from visible spectrum videos, we built a system that remotely measures dPTT. Human subject data were collected under an IRB approved protocol from 15 subjects both under normal and stress states and are used to initially establish the potential use of remote dPPT detection as a stress indicator.

Non-contact measurement of oxygen saturation with an RGB camera

“…The pulsatile, cardiac-synchronous signals which are caused by colour changes due to the inand outflow of blood will have a relative phase shift between them that is uniquely determined by the maximum pulse transit time within the area of skin observed. From values previously reported in the literature [20], this phase shift is expected to be much smaller than π 2 radians, and the signals can therefore be said to be more in phase with each other than in antiphase. The breathing rate signals are instead caused by changes in colour due to movement, and can be either in overall phase or in antiphase.…”

Robustness of remote stress detection from visible spectrum recordings

“…The dPTT values were determined remotely by identifying the peak position in the correlation function between the BW signals from the two body locations. In our previous studies, we have demonstrated the potential use of this metric for remote stress detection [6].…”

“…The phase shift range was determined based on our dPTT studies [6], in which experimental data from 12 subjects under the first normal and stress states measured dPTT between 3ms to 30 ms. To cover the observed dPTT values, we tested for phase between 1 ms and 40 ms. The noise signals at various SNR levels were also constructed following the method in the Simulated Data section.…”

“…However, recent studies have shown that a heartbeat signal can be measured remotely from visible spectrum recordings based on minor intensity fluctuations [1]- [5]. In our own studies, we have shown that the remotely measured heartbeat signals from two distal body locations can also be used to determine differential pulse transit time (dPTT), which is the difference in the time of arrival of the blood wave (BW) between two remote areas of the body [6], an indirect indicator of pulse transit time (PTT). In literature, PTT has been correlated with the arterial blood pressure [7] [8].…”

Hybrid Optical Unobtrusive Blood Pressure Measurements

“…Currently, contact PPG (cPPG) and imaging PPG (iPPG) are two feasible techniques to acquire the PPG signal [ 17 ]. cPPG uses a sensor containing a simple and low-cost optical component that can detect blood volume changes in the micro-vascular bed of tissue, while iPPG employs a monochrome, RGB (red-green-blue), or IR (infrared) camera to acquire PPG signals remotely under an ambient illumination with, for example, a light-emitted-diode (LED) lamp [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ].…”