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 (PPG) is a noninvasive optical technique for detecting microvascular blood volume changes in tissues. Its ease of use, low cost and convenience make it an attractive area of research in the biomedical and clinical communities. Nevertheless, its single spot monitoring and the need to apply a PPG sensor directly to the skin limit its practicality in situations such as perfusion mapping and healing assessments or when free movement is required. The introduction of fast digital cameras into clinical imaging monitoring and diagnosis systems, the desire to reduce the physical restrictions, and the possible new insights that might come from perfusion imaging and mapping inspired the evolution of the conventional PPG technology to imaging PPG (IPPG). IPPG is a noncontact method that can detect heart-generated pulse waves by means of peripheral blood perfusion measurements. Since its inception, IPPG has attracted significant public interest and provided opportunities to improve personal healthcare. This study presents an overview of the wide range of IPPG systems currently being introduced along with examples of their application in various physiological assessments. We believe that the widespread acceptance of IPPG is happening, and it will dramatically accelerate the promotion of this healthcare model in the near future.

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Photoplethysmography Revisited: From Contact to Noncontact, From Point to Imaging

Blood pressure estimation from appropriate and inappropriate PPG signals using A whole-based method

A prospective comparison of bilateral photoplethysmography versus the ankle-brachial pressure index for detecting and quantifying lower limb peripheral arterial disease

This paper proposes a noninvasive dual optical photoplethysmography (PPG) sensor to classify the degree of arteriovenous fistula (AVF) stenosis in hemodialysis (HD) patients. Dual PPG measurement node (DPMN) becomes the primary tool in this work for detecting abnormal narrowing vessel simultaneously in multi-beds monitoring patients. The mean and variance of Rising Slope (RS) and Falling Slope (FS) values between before and after HD treatment was used as the major features to classify AVF stenosis. Multilayer perceptron neural networks (MLPN) training algorithms are implemented for this analysis, which are the Levenberg-Marquardt, Scaled Conjugate Gradient, and Resilient Back-propagation, to identify the degree of HD patient stenosis. Eleven patients were recruited with mean age of 77 ± 10.8 years for analysis. The experimental results indicated that the variance of RS in the HD hand between before and after treatment was significant difference statistically to stenosis (p < 0.05). Levenberg-Marquardt algorithm (LMA) was significantly outperforms the other training algorithm. The classification accuracy and precision reached 94.82% and 92.22% respectively, thus this technique has a potential contribution to the early identification of stenosis for a medical diagnostic support system.

https://www.mdpi.com/1424-8220/18/7/2322/pdf

Levenberg-Marquardt Neural Network Algorithm for Degree of Arteriovenous Fistula Stenosis Classification Using a Dual Optical Photoplethysmography Sensor.

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

Advanced sensor device for shape analysis of the tissue- reflected mean single period photoplethysmography (SPPPG) signals has been designed and clinically tested. The SPPPG signal shape reveals individual features of the patient's cardio-vascular state. Clinical studies of several patient groups (e.g. diabetes mellitus, atherosclerosis obliterans, Raynaud's syndrome) made possible to specify components of the SPPPG signal that are sensitive to the corresponding organic or functional pathologies. Comparison of the right and left arm finger SPPPG signal shapes, for instance, appears to be efficient tool for early screening of unilateral atherosclerosis obliterans.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Potential of advanced photoplethysmography sensing for noninvasive vascular diagnostics and early screening

Time resolved detection and analysis of the skin back-scattered optical signals (reflection photoplethysmography or PPG) provide information on skin blood volume pulsations and can serve for cardiovascular assessment. The multi-channel PPG concept has been developed and clinically verified in this study. Portable two- and four-channel PPG monitoring devices have been designed for real-time data acquisition and processing. The multi-channel devices were successfully applied for cardiovascular fitness tests and for early detection of arterial occlusions in extremities. The optically measured heartbeat pulse wave propagation made possible to estimate relative arterial resistances for numerous patients and healthy volunteers.

Optical multichannel sensing of skin blood pulsations

The invention relates to angiology, in particular - to determination of magistral arterial occlusions in arms and legs by means of non-invasive, e.g. photoplethysmographic (PPG) multi-channel registration of blood pulsation signals from anatomically symmetrical sites of arms and/or legs with subsequent signal processing and assessment of difference(s) of the pulse wave transit time accordingly to the measured time shift(s) between the corresponding pulsating signals. The proposed device for detection of the arterial occlusions in arms and/or legs comprises optical PPG contact probes (1, 2, 3, 4) in amount that corresponds to the number of used channels, electronic amplifiers (5, 6, 7, 8) that are amplifying the output signals of all contact probes, microprocessor (9) that provides transfer of the above mentioned signals to the processing units (10 - for arms, 11 - for legs), and the output unit (12) - panel, monitor or similar device that provides indication or signalling about occlusion at the respective arm or leg, e.g. by switching on the corresponding light-emitting diode (12.1, 12.2, 12.3, 12.4).

Method and device for detection of arterial occlusions in arms and legs

BACKGROUND
Peripheral artery disease is widespread in Western societies affecting around 13% of the population above 50 years of age. Despite recent improvements of endovascular treatment, open surgical bypass is still recommended as the treatment of choice for long segment TASC D lesions. The DETOUR procedure was introduced as an endovascular alternative in cases of long-segment superficial femoral artery occlusion. This unconventional technique raises several questions regarding the effect of the bypass graft on femoral venous physiology.


METHODS
We conducted a 3-year follow up study of subjects enrolled and treated in the prospective, multi-center DETOUR study at the Pauls Stradins clinical university hospital, Riga, Latvia. In total, 52 consecutive patients (54 procedures) were enrolled in this study from 2015 until 2019. We performed Venous Clinical Severity Score (VCSS) and Villalta (VS) score assessments, duplex ultrasound measuring femoral and popliteal vein diameters, venous occlusion plethysmography and digital photoplethysmography to assess and compare venous physiology at baseline and at follow-up visits every 6 months.


RESULTS
At baseline mean femoral vein diameter was 11.1mm (SD=1.5). At 36-months following intraluminal stent graft placement, mean femoral vein diameter was 11.1 mm (SD=1.7) with no evidence of enlargement of the femoral vein (p=0.2). Popliteal vein diameter was not significantly changed during 24-months of follow up (p=0.12) but showed a small (0.02mm) statistically significant decrease in diameter at 36-months compared to baseline. During the study period, only one patient (1.9%) developed clinically significant ipsilateral DVT 1-month after surgery. Clinically silent femoral venous thrombosis was documented in 8 legs during 36 month follow up. In one case the thrombus was occlusive and in 7 cases the thrombus was non-occlusive. At baseline, 48 of 52 patients (92%) had no or minor venous symptoms ((VCSS 0-2) with clinically significant venous symptoms in only 4 patients ((VCSS ≥3). At one-month follow-up, the venous clinical severity score increased in all patients compared to baseline. At 6-month follow up, the VCSS had returned to baseline in the majority of patients with no significant changes during the 3-year follow up period. At baseline, all patients had a Villalta score of 0-2 indicating minor or no venous symptoms (mean 0.4 (SD 0.7)). At the 1-month follow-up visit 3 patients (5.8%) had a VS ≥ 3 (two patients had a score of 3 and one patient a score of 4), indicating significant venous symptoms. At the 6-month visit and thereafter, all the VS in all patients had returned to baseline. Transvenous endovascular procedure did not significantly alter venous physiology in treated leg.


CONCLUSIONS
Percutaneous transvenous femoropopliteal bypass provided safe and effective lower-extremity revascularization with minimal effect on long-term venous function. The femoral and popliteal vein remained patent with no compensatory enlargement in response to the presence of the bypass graft within the femoral vein. During 3-year follow up there were no significant changes in venous symptom scores or physiologic function.

Indulis Kukulis

Papers

Bilateral photoplethysmography studies of the leg arterial stenosis

Potential of advanced photoplethysmography sensing for noninvasive vascular diagnostics and early screening

Optical multichannel sensing of skin blood pulsations

Method and device for detection of arterial occlusions in arms and legs

Long term clinical and functional venous outcomes after endovascular transvenous femoro-popliteal bypass.