Remote Photoplethysmographic Assessment of the Peripheral Circulation in Critical Care Patients Recovering From Cardiac Surgery

Non-Contact Vision-Based Techniques of Vital Sign Monitoring: Systematic Review

The development of non-contact techniques for monitoring human vital signs has significant potential to improve patient care in diverse settings. By facilitating easier and more convenient monitoring, these techniques can prevent serious health issues and improve patient outcomes, especially for those unable or unwilling to travel to traditional healthcare environments. This systematic review examines recent advancements in non-contact vital sign monitoring techniques, evaluating publicly available datasets and signal preprocessing methods. Additionally, we identified potential future research directions in this rapidly evolving field.

Challenges and prospects of visual contactless physiological monitoring in clinical study

The monitoring of physiological parameters is a crucial topic in promoting human health and an indispensable approach for assessing physiological status and diagnosing diseases. Particularly, it holds significant value for patients who require long-term monitoring or with underlying cardiovascular disease. To this end, Visual Contactless Physiological Monitoring (VCPM) is capable of using videos recorded by a consumer camera to monitor blood volume pulse (BVP) signal, heart rate (HR), respiratory rate (RR), oxygen saturation (SpO2) and blood pressure (BP). Recently, deep learning-based pipelines have attracted numerous scholars and achieved unprecedented development. Although VCPM is still an emerging digital medical technology and presents many challenges and opportunities, it has the potential to revolutionize clinical medicine, digital health, telemedicine as well as other areas. The VCPM technology presents a viable solution that can be integrated into these systems for measuring vital parameters during video consultation, owing to its merits of contactless measurement, cost-effectiveness, user-friendly passive monitoring and the sole requirement of an off-the-shelf camera. In fact, the studies of VCPM technologies have been rocketing recently, particularly AI-based approaches, but few are employed in clinical settings. Here we provide a comprehensive overview of the applications, challenges, and prospects of VCPM from the perspective of clinical settings and AI technologies for the first time. The thorough exploration and analysis of clinical scenarios will provide profound guidance for the research and development of VCPM technologies in clinical settings.

Modified Camera Setups for Day-and-Night Pulse-rate Monitoring

Camera systems have been studied as a means for ubiquitous remote photoplethysmography. It was first considered for daytime applications using ambient light. However, main applications for continuous monitoring are in dark or low-light conditions (e.g. sleep monitoring) and, more recently, suitable light sources and simple camera adaptations have been considered for infrared-based solutions. This paper explores suitable camera configurations for pulse-rate monitoring during both day and night (24/7). Various configurations differing in the recorded spectral range are defined, i.e. straight-forward adaptations of a standard RGB camera by choosing proper optical filters. These systems have been studied in a benchmark involving day and night monitoring with various degrees of motion disturbances. The results indicate that, for the 24/7 monitoring, it is best to deploy the full spectral band of an RGB camera, and this can be done without compromising the monitoring performance at night.

Association of remote imaging photoplethysmography and cutaneous perfusion in volunteers

Remote imaging photoplethysmography (iPPG) senses the cardiac pulse in outer skin layers and is responsive to mean arterial pressure and pulse pressure in critically ill patients. Whether iPPG is sufficiently sensitive to monitor cutaneous perfusion is not known. This study aimed at determining the response of iPPG to changes in cutaneous perfusion measured by  Laser speckle imaging (LSI). Thirty-seven volunteers were engaged in a cognitive test known to evoke autonomic nervous activity and a Heat test. Simultaneous measurements of iPPG and LSI were taken at baseline and during cutaneous perfusion challenges. A perfusion index (PI) was calculated to assess iPPG signal strength. The response of iPPG to the challenges and its relation to LSI were determined. PI of iPPG significantly increased in response to autonomic nervous stimuli and to the Heat test by 5.8% (p = 0.005) and 11.1% (p < 0.001), respectively. PI was associated with LSI measures of cutaneous perfusion throughout experiments (p < 0.001). iPPG responses to study task correlated with those of LSI (r = 0.62, p < 0.001) and were comparable among subjects. iPPG is sensitive to autonomic nervous activity in volunteers and is closely associated with cutaneous perfusion.

Impact of makeup on remote-PPG monitoring

Camera-based remote photoplethysmography (remote-PPG) enables contactless measurement of blood volume pulse from the human skin. Skin visibility is essential to remote-PPG as the camera needs to capture the light reflected from the skin that penetrates deep into skin tissues and carries blood pulsation information. The use of facial makeup may jeopardize this measurement by reducing the amount of light penetrating into and reflecting from the skin. In this paper, we conduct an empirical study to thoroughly investigate the impact of makeup on remote-PPG monitoring, in both the visible (RGB) and invisible (Near Infrared, NIR) lighting conditions. The experiment shows that makeup has negative influence on remote-PPG, which reduces the relative PPG strength (AC/DC) at different wavelengths and changes the normalized PPG signature across multiple wavelengths. It makes (i) the pulse-rate extraction more difficult in both the RGB and NIR, although NIR is less affected than RGB, and (ii) the blood oxygen saturation extraction in NIR impossible. To the best of our knowledge, this is the first work that systematically investigate the impact of makeup on camera-based remote-PPG monitoring.

Modified RGB Cameras for Infrared Remote-PPG

Multi-wavelength cameras play an essential role in remote photoplethysmography (PPG). Whereas these are readily available for visible light, this is not the case for near infrared (NIR). We propose to modify existing RGB cameras to make them suited for NIR-PPG. In particular, we exploit the spectral leakage of the RGB channels in infrared in combination with a narrow dual-band optical filter. Such camera modification is simple, cost-effective, easy to implement, and it is shown to attain a pulse-rate extraction performance comparable to that of multiple narrow-band NIR cameras.