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Human skin may reflect health conditions. Important and possibly diagnostically potent components of microcirculation are slow flow oscillations-flowmotions, however there is a lack of studies in this field. The present pilot study was devoted to evaluation of multispectral imaging photoplethysmography in determination of different components of flowmotions. Eight subjects were enrolled for the study. During resting conditions video was captured from dorsal aspect of hand at seven different wavelength and flowmotion analysis performed. Results indicate that at the resting conditions neurogenic component along with endothelial are dominant regardless of wavelength, while myogenic has the lowest spectral power. Results confirm the potential of multispectral photoplethysmography for cutaneous flowmotion detection.

Gum disease caused by bacterial infection, systemic conditions or neurogenic inflammation remains a prevalent and important concern of public health in both, developing and developed countries, potentially causing tooth loss if left untreated. Therefore, a simple, cost-effective, and contactless diagnostic tool is needed in dentistry. The present study aims to develop and investigate the feasibility of a motion artefact-free, miniature imaging photoplethysmography system which is dedicated for assessment of gingivitis in the dental office. The device comprised of a sub-miniature monochromatic camera equipped with miniature lens, 4-LED ring illuminator, cross polarizers and bandpass optical filter (CW=540nm, FWHM=25nm). The present pilot study comprised six subjects. The transitory neurogenic gingival inflammation has been induced by topical application of capsaicin containing chilli extract. The photoplethysmography signal was acquired from the same site before and after inflammation, and perfusion maps were computed. During the procedure, the developed imaging system demonstrated motion artefact-free data recordings and high signal to noise ratio. As expected, topical application of chilli extract produced noticeable transitory neurogenic inflammation, detected in perfusion maps. The present findings confirm the potential of imaging photoplethysmography for gingival tissue inflammation assessment, and in the future could be utilized in the dental office.

Peripheral neuropathy refers to peripheral nervous system dysfunction which affects up to 2% of the world's population. This condition is caused by damage to the small nerve fibers, hence its assessment is still challenging due to the lack of simple, non-invasive and objective diagnostic techniques. The present study aimed to develop and evaluate a simple, objective and non-invasive technique for assessment of small cutaneous sensory nerve fiber function. Our approach is based on utilization of imaging photoplethysmography and local skin heating. The effectiveness of the method was evaluated on young, healthy volunteers (n = 14) after 10 minutes of 45-degree local skin heating, while recording a photoplethysmographic signal simultaneously from the intact (control) and anesthetized skin (topical application of Emla gel) regions. In the anesthetized skin region, the local heating evoked flare area was 44% lower than that of intact skin. A similar trend was observed for the perfusion curve- perfusion peak in the anesthetized skin was substantially reduced in comparison to intact. The results indicate for the potential of the imaging photoplethysmography in the assessment of the small nerve fiber function. It is believed that this technique could be utilized in the clinics in the future to examine neuropathy patients and diagnose neuropathy.

A practical assessment of the health of the palm muscle, abductor pollicis brevis (APB), is important for diagnosis of different conditions. Here we have developed a protocol and a probe to utilize diffuse correlation spectroscopy (DCS) to characterize microvascular blood flow changes in the APB during and after sustained isometric exercise, during and after thumb abduction at at 55% of maximum voluntary contraction (MVC). Blood flow in the APB decreased during exercise in the subjects (n=13) with high MVC (n=7) and stayed constant in the ones with low MVC (n=6) suggesting that the mechanical occlusion due to increased intramuscular pressure exceeded the vasodilation elicited by the higher demand. Blood flow changes during exercise negatively correlated with the absolute force applied by each subject. Muscular blood flow increased after exercise compared to the values reached during exercise. In conclusion, DCS allows the study of the response of a small muscle to static exercise.

We present the development and validation of a new approach for quantitative functional imaging of human skin based on the machine learning technique for the analysis of the hyperspectral skin images. The considered skin parameters include blood volume fraction, blood oxygenation, melanin content, and the epidermal layer thickness. Additionally, the degree of residual polarization of the reflected light has been analyzed. The validity of the approach has been confirmed by the initial preclinical tests with the tissue-mimicking phantoms, functional in-vivo skin tests, and pilot clinical study of type II diabetic patients. The proposed technique has great potential to be implemented in clinical practice for monitoring and diagnosis of chronic skin ulcers and other relevant diseases.

Studies of the physiological response of human half-body illumination by a specially designed bed comprising large number of LEDs emitting in the red and near infrared spectral range were carried out in a group of 32 volunteers comprising healthy subjects and hypertension patients. Blood pressure, heart rate and arterial blood oxygen saturation, as well as the bed surface temperature were continuously monitored during the measurement sessions with and without aluminum foil cover on the bed surface. None of the volunteers exhibited any notable changes in the heart rate and blood oxygenation during the procedures. The LightStim LED-bed session did not produce changes of arterial pressure in normotensive group, while decreased blood pressure exhibited 2/3 of hypertensive patients. The thermal emission from the bed may serve as a dominant contributor to the observed effects on cardiovascular system.

The present study introduces a recently developed compact hybrid device for real-time monitoring of skin oxygen saturation and temperature distribution. The prototype involves a snapshot hyperspectral camera, multi-wavelength illuminator, thermal camera, and built-in computer with custom-developed software. To validate this device in-vivo we performed upper arm vascular occlusion on eight healthy volunteers. Palm skin oxygen saturation maps were analyzed in real-time using k-means segmentation algorithm and two-layer optical diffuse model. The prototype system demonstrated a satisfying performance of skin hyperspectral measurements in the spectral range of 507&ndash, 625 nm. The results confirmed the reliability of the proposed system for in-vivo assessment of skin hemoglobin saturation with oxygen and microcirculation.

The purpose of this study was to determine potential of remote photoplethysmography for skin perfusion monitoring, using 540 nm narrowband and 530 nm broadband illuminations. The alterations of cutaneous circulation were produced by topical skin heating protocol. The setup comprises of 530 nm LED light source and two identical cameras operated simultaneously: one equipped with narrowband optical filter (CWL=540nm), and another without filter. Results demonstrate the typical heating test response curve- comprising first peak, nadir and plato phase, which were significantly different in narrowband and broadband illumination. It was concluded that selection of optimal light source parameters is crucially important for registering of physiological responses using rPPG, and therefore require more extensive studies.

The present study is devoted to the assessment of oral mucosa perfusion using remote photoplethysmography (rPPG) technique. The alterations of mucosal perfusion were evoked by regional infiltration anesthesia containing adrenaline. Simple rPPG setup comprising white LED light source, video camera and narrowband optical filter (CWL=540nm), are able to detect subtle microcirculation changes in gingiva. Results demonstrate substantial decrease of rPPG waveform amplitude and subsequently perfusion index in affected gingiva region, following administration of anesthetics. The present study emphasizes clinical advantages of remote photoplethysmography and perfusion index mapping as a simple and cost-effective technique for assessment of oral mucosa function.

In present pilot study application of multi-spectral imaging photoplethysmography for assessment of chronic pain patients during topical skin heating test was proposed. Photoplethysmography signal was recorded at 420nm, 530nm and 810nm illumination from the skin and corresponding perfusion indexes and perfusion maps were calculated. The novel parameter-PPGflare index was introduced and compared in neuropathic patients and healthy volunteers. Preliminary results suggest that neuropathic patients exhibited significantly lower PPGflare index, and that local heating substantially change PPG waveform at heat exposed skin region. Present study emphasizes advantages of imaging photoplethysmography as a simple and cost-effective alternative to Laser Doppler with promising clinical potential in assessment of neuropathic patients. In this respect, we believe that our study adds novel information to the field of existing chronic pain diagnostics.

A practical assessment of the general health and microvascular function of the palm muscle, abductor pollicis brevis (APB), is important for the diagnosis of different conditions. In this study, we have developed a protocol and a probe to study microvascular blood flow using near-infrared diffuse correlation spectroscopy (DCS) in APB during and after thumb abduction at 55% of maximum voluntary contraction (MVC). Near-infrared time resolved spectroscopy (TRS) was also used to characterize the baseline optical and hemodynamic properties. Thirteen (n=13) subjects were enrolled and subdivided in low MVC (N=6, MVC

About 2% of the world’s population suffers from small nerve fiber dysfunction, neuropathy, which can result in severe pain. This condition is caused by damage to the small nerve fibers and its assessment is challenging, due to the lack of simple and objective diagnostic techniques. The present study aimed to develop a contactless photoplethysmography system using simple instrumentation, for objective and non-invasive assessment of small cutaneous sensory nerve fiber function. The approach is based on the use of contactless photoplethysmography for the characterization of skin flowmotions and topical heating evoked vasomotor responses. The feasibility of the technique was evaluated on volunteers (n = 14) using skin topical anesthesia, which is able to produce temporary alterations of cutaneous nerve fibers function. In the treated skin region in comparison to intact skin: neurogenic and endothelial component of flowmotions decreased by ~61% and 41%, the local heating evoked flare area decreased by ~44%, vasomotor response trend peak and nadir were substantially reduced. The results indicate for the potential of the remote photoplethysmography in the assessment of the cutaneous nerve fiber function. It is believed that in the future this technique could be used in the clinics as an affordable alternative to laser Doppler imaging technique.

Skin capillary blood oxygen saturation is a clinically important diagnostic parameter, which provides valuable information for timely treatment of pathological conditions e.g. sepsis, hypoxemia or decompression illness. Hyperspectral imaging is non-invasive optical techniques with high clinical potential, however its use for skin blood oxygen saturation detection is still challenging, therefore in the present study, a method for in-vivo manipulation of skin oxygen saturation was developed, and reliability of the method evaluated by means of hyperspectral imaging in detection of oxygen saturation. In order to produce alterations of skin capillary blood parameters and oxygen saturation, the proximal phalanx of the right middle finger was occluded with a pneumatic cuff for 25 minutes. During the last minute of occlusion, the hyperspectral cubes (HIS) of both occluded and intact finger were captured, and capillary blood sample was collected for analysis with portable whole blood analyzer (REF). The group mean values for SaO2 in intact finger skin was HIS: 89.46%±8.79% versus REF: 95.13±1.46 % and in occluded finger HSI: 25.85% ±14.00%, versus REF: 22.73±9.09 % displaying a small difference between two independent techniques, which indicate the reliability of finger occlusion model.

Assessment of skin microcirculation provides diagnostically valuable information during the early stages of pathologies. The simple, cost-effective and intrusive alternative to existing circulation assessment methods is remote photoplethysmography (rPPG). The objective of the present pilot study was to reveal an effect on sublingual administration of 1 mg nitroglycerin on systemic hemodynamic parameters and rPPG waveforms, at 810 nm and 530nm illumination. The protocol comprised 3 minutes of baseline recording, 15 minutes recording of NTG effect, 2 minutes of arterial occlusion and the following 3 min reactive hyperemia. Two PPG signals were acquired from glabrous skin of the middle finger distal phalange, consecutively at 530 nm and 810nm, 125 fps per channel, and systemic cardiovascular parameters were continuously registered in a beat-to-beat manner with a Finameter-midi system. The NTG effect was observed 0.7- 1.2 minutes post administration, reaching its maximum after 3 minutes. Systemic cardiovascular parameters significantly changed: mean arterial pressure decreased by 7.7±3.6%, total peripheral resistance by 10.5±9.0%, whereas the heart rate increased by 27.2±11.8%. Substantial alterations were observed for rPPG waveforms during NTG effect, decreasing reflection and stiffness indices. It has been concluded that rPPG waveform may provide information related to arterial stiffness, and could be potentially utilized in the clinics.

Sepsis is a potentially fatal disease with mortality rate as high as 50% in patients with septic shock; mortality rate can increase by 7.6% per hour if appropriate treatment is not started. Internationally accepted guidelines for diagnosis of sepsis rely on vital sign monitoring and laboratory tests in order to recognize organ failure. This pilot study aims to explore the potential of hyperspectral and thermal imaging techniques to identify and quantify early alterations in skin oxygenation and perfusion induced by sepsis. The study comprises both physiological model experiments on healthy volunteers in a laboratory environment, as well as screening case series of patients with septic shock in the intensive care department. Hyperspectral imaging is used to determine one of the main characteristic visual signs of skin oxygenation abnormalities - skin mottling, whereas changes in peripheral perfusion have been visualized by thermal imaging as heterogeneous skin temperature areas. In order to mimic septic skin mottling in a reproducible way in laboratory environment, arterial occlusion provocation test was utilized on healthy volunteers. Visualization of oxygen saturation by hyperspectral imaging allows diagnosing microcirculatory alterations induced by sepsis earlier than visual assessment of mottling. Thermal images of sepsis patients in the clinic clearly reveal hotspots produced by perforating arteries, as well as cold regions of low blood supply. The results of this pilot study show that thermal imaging in combination with hyperspectral imaging allows the determination of oxygen supply and utilization in critically ill septic patients.

We present simultaneous diffuse correlation spectroscopy (DCS) and time resolved spectroscopy (TR NIRS) measurements on exercising and non-exercising vastus lateralis muscle. We discuss the results at two different exercise levels.

The aim of the study was to develop a prototype system of the smart garment for real time telemetric monitoring of human cardiovascular activity. Two types of photoplethysmography (PPG) sensors for low noise and artefact free signal recording from various sites of the human body that were suitable for integration into smart textile were investigated. The reflectance sensors with single and multiple photodiodes based on "pulse-duration-based signal conversion" signal acquisition principle were designed and evaluated. The technical parameters of the system were measured both on bench and in vivo. Overall, both types of PPG sensors showed acceptable signal quality SNR 86.56±3.00 dB, dynamic range 89.84 dB. However, in-vivo condition tests revealed lower noise and higher accuracy achieved by applying the multiple photodiodes sensor. We concluded that the proposed PPG device prototype is simple and reliable, and therefore, can be utilized in low-cost smart garments.

The feasibility of bispectral imaging photoplethysmography (iPPG) system for clinical assessment of cutaneous microcirculation at two different depths is proposed. The iPPG system has been developed and evaluated for in vivo conditions during various tests: (1) topical application of vasodilatory liniment on the skin, (2) skin local heating, (3) arterial occlusion, and (4) regional anesthesia. The device has been validated by the measurements of a laser Doppler imager (LDI) as a reference. The hardware comprises four bispectral light sources (530 and 810 nm) for uniform illumination of skin, video camera, and the control unit for triggering of the system. The PPG signals were calculated and the changes of perfusion index (PI) were obtained during the tests. The results showed convincing correlations for PI obtained by iPPG530 nm and LDI at (1) topical liniment (r = 0.98) and (2) heating (r = 0.98) tests. The topical liniment and local heating tests revealed good selectivity of the system for superficial microcirculation monitoring. It is confirmed that the iPPG system could be used for assessment of cutaneous perfusion at two different depths, morphologically and functionally different vascular networks, and thus utilized in clinics as a cost-effective alternative to the LDI.

The custom designed video processing software for analysis of B-mode and Doppler-mode ultrasound video has been proposed in this work. The software allows adjusting user-defined thresholds and tolerance levels to enhance contour detection in noisy and artifacted ultrasound images. The developed software is able to evaluate 16 hemodynamic parameters (artery diameter, pulse rate and flow velocity related parameters) in each cardiac cycle. The measurements were performed intermittently recording artery diameter (B-mode) and flow velocity (Doppler-mode). Software has validated in femoral artery measurements. The hemodynamic parameters computed by software were consistent with those obtained by experienced sonographer.

Three channel photoplethysmography (PPG) signal waveform studies of leg conduit arteries during a provocative occlusion test were performed. PPG waveform second derivative amplitude ratio and arterial pulse wave velocity values showed significant correlations with ultrasound (US) reference method of local and regional arterial stiffness (AS), showing the ability to use PPG for AS change quantitative assessment.

Clinically revealed, non-uniform distribution of peripheral vascular diseases throughout the arterial tree suggests that haemodynamic forces can modulate the endothelial dysfunction. In the present study the bilateral differences of deep (DFA) and superficial (SFA) femoral artery blood velocity waveform parameters were examined in relation to artery ramification patterns and subject anthropometry. Young, sedentary women ( n = 25; age 21.2 ± 3.6 years) were enrolled. Anthropometric data as well as systemic cardiovascular parameters (arterial pressure, heart rate and cardiac output) and Doppler velocity spectrum of SFA and DFA were instantly registered in rest conditions. The study revealed a slight and mutually independent anatomical and morphometric asymmetries of femoral arteries in paired legs which were fluctuation type (do not display any directional tendency). Also bilateral asymmetry of artery haemodynamic parameters was related neither to subjects' anthropometric nor artery anatomical parameters. The magnitude of haemodynamic asymmetry is larger for retrograde linear velocity, retrograde shear rate and oscillatory index – parameters which reflect peripheral resistance of microcirculatory bed and thus has a rather functional origin. Possibly, the observed unilateral changes of femoral artery haemodynamic parameters of young healthy and sedentary women could be considered as a sign of potential genesis of artery structure pathological changes in older age.