Plethysmographic assessment of vasomotor response in patients with congestive heart failure before and after heart transplantation.

Sympathetic vasomotor response is the most important part of the autonomic regulation of circulation, which determines the quality of life. It is disrupted in a number of diseases, particularly in patients with congestive heart failure (CHF). However, experimental evaluation of reflex vasoconstriction is still a non-trivial task due to the limited set of available technologies. The aim of this study is to assess the dynamics of vasomotor response of forearm vessels due to both the deactivation of cardiopulmonary baroreceptors and cold stress using a newly designed imaging plethysmograph (IPG) and compare its performance with classical air plethysmograph (APG). In both vasoconstriction tests, vasomotor response was assessed as a change in the blood flow rate due to venous occlusion compared to that at rest. Both tests were carried out in 45 CHF patients both before and after heart transplantation, as well as in 11 age-matched healthy volunteers. Prior to transplantation, both APG and IPG showed a significant decrease in vasomotor response in CHF patients due to both tests as compared to the control group. After heart transplantation, an increase in vasomotor reactivity was revealed in both vasoconstriction tests. We have found that both plethysmographic techniques provide correlated assessment of changes in the vasomotor response. In addition, we have found that IPG is more resistant to artifacts than APG. The new IPG method has the advantage of measuring blood flow in a contactless manner, making it very promising for experimental evaluation of vasomotor response in clinical conditions.

Intra-abdominal laparoscopic assessment of organs perfusion using imaging photoplethysmography.

BACKGROUND: An objective evaluation of the functional state and viability of biological tissues during minimally invasive surgery remains unsolved task. Various non-contact methods for evaluating perfusion during laparoscopic surgery are discussed in the literature, but so far there have been no reports of their use in clinical settings. METHODS AND PATIENTS: Imaging photoplethysmography (iPPG) is a new method for quantitative assessment of perfusion distribution along the tissue. This is the first study in which we demonstrate successful use of iPPG to assess perfusion of organs during laparoscopic surgery in an operation theater. We used a standard rigid laparoscope connected to a standard digital monochrome camera, and abdominal organs were illuminated by green light. A distinctive feature is the synchronous recording of video frames and electrocardiogram with subsequent correlation data processing. During the laparoscopically assisted surgeries in nine cancer patients, the gradient of perfusion of the affected organs was evaluated. In particular, measurements were carried out before preparing a part of the intestine or stomach for resection, after anastomosis, or during physiological tests. RESULTS: The spatial distribution of perfusion and its changes over time were successfully measured in all surgical cases. In particular, perfusion gradient of an intestine before resection was visualized and quantified by our iPPG laparoscope in all respective cases. It was also demonstrated that systemic administration of norepinephrine leads to a sharper gradient between well and poorly perfused areas of the colon. In four surgical cases, we have shown capability of the laparoscopic iPPG system for intra-abdominal assessment of perfusion in the anastomosed organs. Moreover, good repeatability of continuous long-term measurements of tissue perfusion inside the abdominal cavity was experimentally demonstrated. CONCLUSION: Our study carried out in real clinical settings has shown that iPPG laparoscope is feasible for intra-abdominal visualization and quantitative assessment of perfusion distribution.

Duality in response of intracranial vessels to nitroglycerin revealed in rats by imaging photoplethysmography.

Among numerous approaches to the study of migraine, the nitroglycerin (NTG) model occupies a prominent place, but there is relatively insufficient information about how NTG affects intracranial vessels. In this study we aim to assess the effects of NTG on blood-flow parameters in meningeal vessels measured by imaging photoplethysmography (iPPG) in animal experiments. An amplitude of the pulsatile component (APC) of iPPG waveform was assessed before and within 2.5 h after the NTG administration in saline (n = 13) or sumatriptan (n = 12) pretreatment anesthetized rats in conditions of a closed cranial window. In animals of both groups, NTG caused a steady decrease in blood pressure. In 7 rats of the saline group, NTG resulted in progressive increase in APC, whereas decrease in APC was observed in other 6 rats. In all animals in the sumatriptan group, NTG administration was accompanied exclusively by an increase in APC. Diametrically opposite changes in APC due to NTG indicate a dual effect of this drug on meningeal vasomotor activity. Sumatriptan acts as a synergist of the NTG vasodilating action. The results we obtained contribute to understanding the interaction of vasoactive drugs in the study of the headache pathophysiology and methods of its therapy.

Novel Method to Assess Endothelial Function via Monitoring of Perfusion Response to Local Heating by Imaging Photoplethysmography.

Endothelial dysfunction is one of the most important markers of the risk of cardiovascular complications. This study is aimed to demonstrate the feasibility of imaging photoplethysmography to assess microcirculation response to local heating in order to develop a novel technology for assessing endothelial function. As a measure of vasodilation, we used the relative dynamics of the pulsatile component of the photoplethysmographic waveform, which was assessed in a large area of the outer surface of the middle third of the subject's forearm. The perfusion response was evaluated in six healthy volunteers during a test with local skin heating up to 40-42 °C and subsequent relaxation. The proposed method is featured by accurate control of the parameters affecting the microcirculation during the prolonged study. It was found that in response to local hyperthermia, a multiple increase in the pulsation component, which has a biphasic character, was observed. The amplitude of the first phase of the perfusion reaction depends on both the initial skin temperature and the difference between the basal and heating temperatures. The proposed method allows the assessment of a reproducible perfusion increase in response to hyperthermia developed due to humoral factors associated with the endothelium, thus allowing detection of its dysfunction.

Intraoperative visualization and quantitative assessment of tissue perfusion by imaging photoplethysmography: comparison with ICG fluorescence angiography.

Intraoperative monitoring of tissue perfusion is of great importance for optimizing surgery and reducing postoperative complications. To date, there is no standard procedure for assessing blood circulation in routine clinical practice. Over the past decade, indocyanine green (ICG) fluorescence angiography is most commonly used for intraoperative perfusion evaluation. Imaging photoplethysmography (iPPG) potentially enables contactless assessment of the blood supply to organs. However, no strong evidence of this potential has been provided so far. Here we report results of a comparative assessment of tissue perfusion obtained using custom-made iPPG and commercial ICG-fluorescence systems during eight different gastrointestinal surgeries. Both systems allow mapping the blood-supply distribution over organs. It was demonstrated for the first time that the quantitative assessment of blood perfusion by iPPG is in good agreement with that obtained by ICG-fluorescence imaging in all surgical cases under study. iPPG can become an objective quantitative monitoring system for tissue perfusion in the operating room due to its simplicity, low cost and no need for any agent injections.

Design of an Artificial Opal/Photonic Crystal Interface for Alcohol Intoxication Assessment: Capillary Condensation in Pores and Photonic Materials Work Together.

Alcohol intoxication has a dangerous effect on human health and is often associated with a risk of catastrophic injuries and alcohol-related crimes. A demand to address this problem adheres to the design of new sensor systems for the real-time monitoring of exhaled breath. We introduce a new sensor system based on a porous hydrophilic layer of submicron silica particles (SiO2 SMPs) placed on a one-dimensional photonic crystal made of Ta2O5/SiO2 dielectric layers whose operation relies on detecting changes in the position of surface wave resonance during capillary condensation in pores. To make the active layer of SiO2 SMPs, we examine the influence of electrostatic interactions of media, particles, and the surface of the crystal influenced by buoyancy, gravity force, and Stokes drag force in the frame of the dip-coating preparation method. We evaluate the sensing performance toward biomarkers such as acetone, ammonia, ethanol, and isopropanol and test sensor system capabilities for alcohol intoxication assessment. We have found this sensor to respond to all tested analytes in a broad range of concentrations. By processing the sensor signals by principal component analysis, we selectively determined the analytes. We demonstrated the excellent performance of our device for alcohol intoxication assessment in real-time.

Label-free silver triangular nanoplates for spectrophotometric determination of catecholamines and their metabolites.

A novel method towards spectrophotometric determination of catecholamines and their metabolites differing in their functional groups has been developed. This method is based on a change in morphology of silver triangular nanoplates upon the action of cateсholamines and their metabolites, which is manifested by the decrease of the nanoparticle local surface plasmon resonance (LSPR) band intensity or its shift to the short-wavelength region of the spectrum. The shift value of the LSPR band or the change of its intensity increases with increasing concentration of catecholamines or their metabolites, which is proposed for their spectrophotometric determination. The limits of detection of catecholamines and their metabolites under selected conditions increase in the series homovanillic acid < vanillylmandelic acid < L-epinephrine < L-norepinephrine < dopamine and are 0.25, 1.2, 3.0, 64, and 130 µmol L-1, respectively. The selectivity of the proposed method was assessed using vanillylmandelic acid as example. It was found that the determination of vanillylmandelic acid does is not interfered in the presence of 4000-fold excess of Na+, K+, CH3COO-, and 1000-fold excess of Mg2+, Ca2+, Al3+, NO3-. The method also allows for the selective determination of vanillylmandelic acid in the presence of a 1000-fold excess of structurally related substances that do not contain either a catechol fragment or an electron donor substituent. The proposed approach was successfully applied to the determination of catecholamines in pharmaceuticals and artificial urine. Graphical abstract.

Contactless Assessment of Cerebral Autoregulation by Photoplethysmographic Imaging at Green Illumination.

Accurate and practical assessment of the brain circulation is needed to adequately estimate the viability of cerebral blood flow regulatory mechanisms in various physiological conditions. The objective of our study was to examine feasibility of the contactless green-light imaging photoplethysmography (PPG) for assessing cerebral autoregulation by revealing the dynamic relationships between cortical microcirculation assessed by PPG and changes in systemic blood pressure caused by visceral and somatic peripheral stimuli. In anesthetized male Wistar rats, the PPG video images of the open parietal cortex (either with unimpaired or dissected dura mater), electrocardiogram, and systemic arterial blood pressure (ABP) in the femoral artery were continuously recorded before, during and after visceral (colorectal distension) or somatic (tail squeezing) stimulation. In the vast majority of experiments with intact and removed dura mater, both spontaneous and peripheral stimulation-evoked changes in ABP negatively correlated with the accompanying alterations in the amplitude of pulsatile PPG component (APC), i.e., an increase of ABP resulted in a decrease of APC and vice versa. The most pronounced ABP and APC alterations were induced by noxious stimuli. Visceral painful stimulation in all cases caused short-term hypotension with simultaneous increase in cortical APC, whereas somatic noxious stimuli in 8 of 21 trials produced hypertensive effect with decreased APC. Animals with pressure 50-70 mmHg possessed higher negative cerebrovascular response rate of ABP-APC gradients than rats with either lower or higher pressure. Severe hypotension reversed the negative ratio to positive one, which was especially evident under visceral pain stimulation. Amplitude of the pulsatile PPG component probably reflects the regulation of vascular tone of cerebral cortex in response to systemic blood pressure fluctuations. When combined with different kinds of peripheral stimuli, the technique is capable for evaluation of normal and elucidation of impaired cerebrovascular system reactivity to particular physiological events, for example pain. The reported contactless PPG monitoring of cortical circulatory dynamics during neurosurgical interventions in combination with recordings of changes in other physiological parameters, such as systemic blood pressure and ECG, has the appealing potential to monitor viability of the cortex vessels and determine the state of patient's cerebrovascular autoregulation.

Contactless monitoring of the blood-flow changes in upper limbs.

Vasomotor reactivity, which is important to estimate neurogenic regulation of blood vessels in patients with different pathologies, is still assessed by occlusion plethysmography using sensors contacting the limbs. Recently we proposed a contactless approach for measuring blood flow changes during venous occlusion using imaging photoplethysmography [Kamshilin et al., Sci. Rep.7, 4642017]. In this work, the response of the vascular system on the occlusion was studied simultaneously by contact air-plethysmography system and remote optical system under illumination by incoherent polarized green light. A high correlation (r > 0.93) between the waveforms measured by both system was observed. Moreover, we found that the response of the optical system on the venous occlusion is uniform at the whole area of the forearm. The new optical technique is more convenient for assessment of the blood flow dynamics because it can be used for measurements in any part of the body. Method of imaging photoplethysmography is very promising for use in equipment intended for evaluation of neurogenic mechanisms of regulation of vascular blood flow.

Novel contactless approach for assessment of venous occlusion plethysmography by video recordings at the green illumination.

Occlusion plethysmography is an important method for assessment of the status of the cardiovascular system, which provides valuable information concerning arterial and venous blood flow, including mechanisms of their regulation. All up-to-date systems estimate change of the limb's volume during occlusion by contact-type sensors. The objective of the research is demonstration of feasibility of the novel approach to measuring the blood flow during venous occlusion by using imaging photoplethysmography (PPG). Twenty healthy individuals participated in the experiment. We used four synchronized video cameras to record all-around view of the forearm illuminated by the green light. After the recording, the PPG waveform was calculated in more than 4000 non-overlapping Regions of Interest (ROI). In the most of the ROIs, the waveform shape was typical for classical plethysmography with the distinctive linear growth of the signal. Speed of the signal change was the same along the forearm but it varied along the forearm's circumference. These findings allows us to hypothesize that the PPG waveform is the direct consequence of the forearm blood flow. Therefore, the novel technique could be applied to the same medical examinations as the classical plethysmography, but it is more advantageous because of non-contact nature and easiness in implementation.