Photoplethysmography (PPG) is a simple and low-cost optical technique that can be used to detect blood volume changes in the microvascular bed of tissue. It is often used non-invasively to make measurements at the skin surface. The PPG waveform comprises a pulsatile ('AC') physiological waveform attributed to cardiac synchronous changes in the blood volume with each heart beat, and is superimposed on a slowly varying ('DC') baseline with various lower frequency components attributed to respiration, sympathetic nervous system activity and thermoregulation. Although the origins of the components of the PPG signal are not fully understood, it is generally accepted that they can provide valuable information about the cardiovascular system. There has been a resurgence of interest in the technique in recent years, driven by the demand for low cost, simple and portable technology for the primary care and community based clinical settings, the wide availability of low cost and small semiconductor components, and the advancement of computer-based pulse wave analysis techniques. The PPG technology has been used in a wide range of commercially available medical devices for measuring oxygen saturation, blood pressure and cardiac output, assessing autonomic function and also detecting peripheral vascular disease. The introductory sections of the topical review describe the basic principle of operation and interaction of light with tissue, early and recent history of PPG, instrumentation, measurement protocol, and pulse wave analysis. The review then focuses on the applications of PPG in clinical physiological measurements, including clinical physiological monitoring, vascular assessment and autonomic function.

https://iopscience.iop.org/article/10.1088/0967-3334/28/3/R01/pdf

Photoplethysmography and its application in clinical physiological measurement.

Photoplethysmography and its application in clinical physiological measurement

Ubiquitous blood pressure (BP) monitoring is needed to improve hypertension detection and control and is becoming feasible due to recent technological advances such as in wearable sensing. Pulse transit time (PTT) represents a well-known potential approach for ubiquitous BP monitoring. The goal of this review is to facilitate the achievement of reliable ubiquitous BP monitoring via PTT. We explain the conventional BP measurement methods and their limitations; present models to summarize the theory of the PTT-BP relationship; outline the approach while pinpointing the key challenges; overview the previous work toward putting the theory to practice; make suggestions for best practice and future research; and discuss realistic expectations for the approach.

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Toward Ubiquitous Blood Pressure Monitoring via Pulse Transit Time: Theory and Practice.

The aging population, prevalence of chronic diseases, and outbreaks of infectious diseases are some of the major challenges of our present-day society. To address these unmet healthcare needs, especially for the early prediction and treatment of major diseases, health informatics, which deals with the acquisition, transmission, processing, storage, retrieval, and use of health information, has emerged as an active area of interdisciplinary research. In particular, acquisition of health-related information by unobtrusive sensing and wearable technologies is considered as a cornerstone in health informatics. Sensors can be weaved or integrated into clothing, accessories, and the living environment, such that health information can be acquired seamlessly and pervasively in daily living. Sensors can even be designed as stick-on electronic tattoos or directly printed onto human skin to enable long-term health monitoring. This paper aims to provide an overview of four emerging unobtrusive and wearable technologies, which are essential to the realization of pervasive health information acquisition, including: 1) unobtrusive sensing methods, 2) smart textile technology, 3) flexible-stretchable-printable electronics, and 4) sensor fusion, and then to identify some future directions of research.

/pdf/unobtrusive-sensing-and-wearable-devices-for-health-wgdblf1mea.pdf

Unobtrusive Sensing and Wearable Devices for Health Informatics

BACKGROUND
Depression, anxiety and somatization are the most common mental disorders in primary care as well as medical specialty populations; each is present in at least 5-10% of patients and frequently comorbid with one another. An efficient means for measuring and monitoring all three conditions would be desirable.


METHODS
Evidence regarding the psychometric and pragmatic characteristics of the Patient Health Questionnaire (PHQ)-9 depression, generalized anxiety disorder (GAD)-7 anxiety and PHQ-15 somatic symptom scales are synthesized from two sources: (1) four multisite cross-sectional studies (three conducted in primary care and one in obstetric-gynecology practices) comprising 9740 patients, and (2) key studies from the literature that have studied these scales.


RESULTS
The PHQ-9 and its abbreviated eight-item (PHQ-8) and two-item (PHQ-2) versions have good sensitivity and specificity for detecting depressive disorders. Likewise, the GAD-7 and its abbreviated two-item (GAD-2) version have good operating characteristics for detecting generalized anxiety, panic, social anxiety and post-traumatic stress disorder. The optimal cutpoint is > or = 10 on the parent scales (PHQ-9 and GAD-7) and > or = 3 on the ultra-brief versions (PHQ-2 and GAD-2). The PHQ-15 is equal or superior to other brief measures for assessing somatic symptoms and screening for somatoform disorders. Cutpoints of 5, 10 and 15 represent mild, moderate and severe symptom levels on all three scales. Sensitivity to change is well-established for the PHQ-9 and emerging albeit not yet definitive for the GAD-7 and PHQ-15.


CONCLUSIONS
The PHQ-9, GAD-7 and PHQ-15 are brief well-validated measures for detecting and monitoring depression, anxiety and somatization.

Iconography : The Patient Health Questionnaire Somatic, Anxiety, and Depressive Symptom Scales: a systematic review

A new technique for parallel recording of reflection photoplethysmography (PPG) signals in a broad spectral band (violet to near-infrared) has been developed, and its potential for assessment of blood microcirculation at various depths from the skin surface is discussed. PPG signals have been simultaneously detected at cw laser wavelength sets comprising 405, 532, 645, 807, and 1064 nm. Various signal baseline responses to breath holding and different shapes of the PPG pulses originated from the same heartbeat but recorded at different wavelengths have been observed, indicating a depth variety of the skin blood pulsation dynamics.

/pdf/simultaneous-recording-of-skin-blood-pulsations-at-different-1baml3f8vc.pdf

Simultaneous recording of skin blood pulsations at different vascular depths by multiwavelength photoplethysmography

A newly developed portable multi-channel photoplethysmography (PPG) device has been used for comparative studies of 20 healthy control subjects and 45 patients with diagnosed arterial stenosis in a leg. The peripheral blood pulsations were detected simultaneously at four body sites—the same fingers and toes of both arms and legs. The PPG pulses recorded at the periphery of the stenotic leg, if compared with those of the healthy leg, were much weaker, with delayed arrival as a consequence of increased pulse wave transit time (PWTT) due to higher vascular resistance. The specific PWTT delays for the occluded legs were in the range of 20–80 ms, while in the case of healthy subjects the leg PPG signals arrived without delays or with smaller time-shifts not exceeding 14 ms. The reference bilateral PPG signals detected at the fingertips did not show any notable PWTT delays in both groups. Parallel measurements of local blood pressures by means of the oscillometry method with subsequent calculation of the ankle–brachial index were performed. Convincing correlation between the bilateral differences in the local blood pressure (a routine tool for diagnostics of leg stenosis) and in the corresponding PWTT delay (Pearson's coefficient r = 0.93), as well as between the PWTT delay and the ankle–brachial index (r = −0.96) has been established. From the point of view of PWTT delay, the average value of leg stenosis diagnostic threshold was established to be in the range of 23 ± 9 ms, with full reliability above 32 ms. The obtained data may find further applications in alternative methodologies for detection and/or assessment of arterial occlusions in human extremities.

/pdf/bilateral-photoplethysmography-studies-of-the-leg-arterial-48y6b0ba9t.pdf

Bilateral photoplethysmography studies of the leg arterial stenosis

Wearable health monitoring sensors may support early detection of abnormal conditions and prevention of their
consequences. Recent designs of three wireless photoplethysmography monitoring devices embedded in hat, glove
and sock, and connected to PC or mobile phone by means of the Bluetooth technology, are described. First results
of distant monitoring of heart rate and pulse wave transit time using the newly developed devices are presented.

/pdf/wearable-wireless-photoplethysmography-sensors-487twfcfz8.pdf

Wearable wireless photoplethysmography sensors

Blood pressure is an important parameter for health assessment. Noninvasive continuous beat per beat blood pressure measurement is still a complicated and expensive procedure. There is a lack of agreement on the optimal blood pressure measurement technique. Potentially the most useful indirect parameter for blood pressure monitoring could be pulse wave velocity or the inverse – pulse transit time. The objectives of the study was to determine the relationship between blood pressure and pulse wave velocity under conditions when different cardiovascular parameters change independently but simultaneously with blood pressure and to clarify whether there is a difference in relationship between blood pressure and pulse wave velocity measured by two different methods in different vascular beds. We determined the relationship between arterial blood pressure (systolic, mean) and the pulse wave velocity from 20 healthy volunteers during a post-exercise recovery period after a load cycling test. A significant correlation (p < 0.05) and regression (p < 0.001) between arterial pressure and pulse wave velocity was obtained. Pulse wave velocity measurement measured in different vascular beds showed no impact on correlation of arterial blood pressure and pulse wave velocity. The average difference between measured and calculated arterial blood pressure values did not exceed 10 mm Hg.

/pdf/relationship-between-arterial-pressure-and-pulse-wave-4xclu3s8nz.pdf

Relationship between arterial pressure and pulse wave velocity using photoplethysmography during the post-exercise recovery period

A contactless photoplethysmographic (PPG) device and method is disclosed for determining heart rate and other parameters simultaneously for several people being in rest and in motion. The proposed device comprises: a radiation-sensitive sensor (20) having the field of view (140) for obtaining electronic images (80) of one or more people (40); the sensor (20) being adapted to monitoring the dynamics of tissue blood volume changes, a distance meter (130) adapted for measuring the distance from the photoplethysmographical device (10) to one or more people (40), a distance meter guidance system (120), adapted for setting and changing the orientation of the meter (130), an output unit (100), adapted for displaying one or more people's (40) heart rate and its derived parameters, a signal processing unit (70) adapted for image (80) processing, analysis and storage, as well as adapted for controlling the system (120).

Renars Erts

Papers

Simultaneous recording of skin blood pulsations at different vascular depths by multiwavelength photoplethysmography

Bilateral photoplethysmography studies of the leg arterial stenosis

Wearable wireless photoplethysmography sensors

Relationship between arterial pressure and pulse wave velocity using photoplethysmography during the post-exercise recovery period

Device and method for an optical contactless monitoring of cardiac parameters