Sensitivity of Video-Based Pulse Arrival Time to Dynamic Blood Pressure Changes

Smartphones and Video Cameras: Future Methods for Blood Pressure Measurement

Regular blood pressure (BP) monitoring enables earlier detection of hypertension and reduces cardiovascular disease. Cuff-based BP measurements require equipment that is inconvenient for some individuals and deters regular home-based monitoring. Since smartphones contain sensors such as video cameras that detect arterial pulsations, they could also be used to assess cardiovascular health. Researchers have developed a variety of image processing and machine learning techniques for predicting BP via smartphone or video camera. This review highlights research behind smartphone and video camera methods for measuring BP. These methods may in future be used at home or in clinics, but must be tested over a larger range of BP and lighting conditions. The review concludes with a discussion of the advantages of the various techniques, their potential clinical applications, and future directions and challenges. Video cameras may potentially measure multiple cardiovascular metrics including and beyond BP, reducing the risk of cardiovascular disease.

Recent Advances in Atherosclerotic Disease Screening Using Pervasive Healthcare

Atherosclerosis screening helps the medical model transform from therapeutic medicine to preventive medicine by assessing degree of atherosclerosis prior to the occurrence of fatal vascular events. Pervasive screening emphasizes atherosclerotic monitoring with easy access, quick process, and advanced computing. In this work, we introduced five cutting-edge pervasive technologies including imaging photoplethysmography (iPPG), laser Doppler, radio frequency (RF), thermal imaging (TI), optical fiber sensing and piezoelectric sensor. IPPG measures physiological parameters by using video images that record the subtle skin color changes consistent with cardiac-synchronous blood volume changes in subcutaneous arteries and capillaries. Laser Doppler obtained the information on blood flow by analyzing the spectral components of backscattered light from the illuminated tissues surface. RF is based on Doppler shift caused by the periodic movement of the chest wall induced by respiration and heartbeat. TI measures vital signs by detecting electromagnetic radiation emitted by blood flow. The working principle of optical fiber sensor is to detect the change of light properties caused by the interaction between the measured physiological parameter and the entering light. Piezoelectric sensors are based on the piezoelectric effect of dielectrics. All these pervasive technologies are noninvasive, mobile, and can detect physiological parameters related to atherosclerosis screening.

Effect of Ambient Lighting and Skin Tone on Estimation of Heart Rate and Pulse Transit Time from Video Plethysmography

Video-based photoplethysmography (vPPG) enables remote and contactless detection of the peripheral pulse of blood flow. This provides a potential mean to extract heart rate (HR) and pulse transit time (PTT) for the purpose of remote health monitoring. The accuracy of average HR and PTT extracted from a two-minute vPPG recording has been investigated at six different lighting conditions among participants with a range of Fitzpatrick skin scores. 12 healthy volunteers (6 females, 27 ± 6 years) were recruited. The video, electrocardiogram and finger PPG were acquired from immobile resting subjects. The vPPG signals from red, green and blue channels, and a combination of those were investigated. The vPPG signals were extracted from two regions of interest (ROIs): one on the forehead and one on the palm of the left hand. The estimated HR error (HR-error) was significantly lower for vPPG from green channels in both ROIs (ROI1 [p<0.001], ROI2 [p<0.05]). The signal from ROI1 demonstrated lower HR-error than ROI2 (p<0.001). HR-error from the darkest lighting conditions (Lumen 1 and 2) were significantly higher than the others (p<0.05). Furthermore, HR-error showed a positive correlation with skin tone scores in every lighting condition. However, at brighter lighting intensity, HR-error was independent of the skin tone score. PTT calculated from vPPG (vPTT) were compared between the 6 levels of lightings and the result was significantly different (p<0.05). In darker lighting conditions, the vPTT increased. Pulse arrival time measured from PPG (PAT-PPG) was calculated, and a positive correlation was found between the ratio of vPTT/PAT-PPG and skin tone score at six different lightings. However, this dependency decreases in brighter lighting intensity. These results suggest that HR-error and the ratio of vPTT/PAT increase with darker skins and at darker backgrounds. However, at brighter lighting conditions, the skin tone score is not a confounder of vPPG accuracy.