Zbignevs Marcinkevics

Imaging photoplethysmography for clinical assessment of cutaneous microcirculation at two different depths.

Abstract. 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.

Effect of probe contact pressure on the photoplethysmographic assessment of conduit artery stiffness

Abstract. Currently, photoplethysmography (PPG) is a frequently studied optical blood pulsation detection technique among biophotonic and biomedical researchers due to the fact that it shows high potential for estimating the arterial stiffness (AS). The extraction of diagnostically useful information requires standardized measurement procedure with good repeatability. However, the effects of a crucially important factor—the optimal contact pressure (CP) of the probe—are often ignored. Also, CP values are not reported to evaluate those effects. It is hypothesized that AS estimated from PPG pulse wave 2nd derivative parameter b/a is strongly inconsistent when recorded at nonoptimal probe CP. Our pilot study confirmed this during in vivo PPG recordings from conduit artery sites on five healthy subjects at variable probe CP (0 to 15 kPa) by using 880 nm reflectance type sensor, force transducer, and PPG alternating current (AC) signal pulse area derived optimal CP criterion. The b/a values, calculated from PPG with variable CP, showed variation >300  percent. In contrast, at the optimal CP, the b/a showed high repeatability (coefficient of variability <5  percent). The effect has been explained with exponential pulse pressure-volume relationship model which indicates the optimal CP range.

Usability of photoplethysmography method in estimation of conduit artery stiffness

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.

Photoplethysmography system for blood pulsation detection in unloaded artery conditions

Photoplethysmography (PPG) is an optical method of blood pulsation recording and has been extensively studied for decades. Recently PPG is widely used in the medical equipment for patient monitoring and in laboratories for research and physiological studies. In spite of the technological progress in the field of medical equipment, there are no generally accepted standards for clinical PPG measurements up to date. One of the most important factors affecting PPG waveform is the contact pressure between tissue and PPG probe. The aim of the current study was to develop and evaluate a system for software-assisted PPG signal acquisition from the unloaded artery. Novel PPG waveform derived Optimal Pressure Parameter (OPP) has been proposed as the reliable indicator of unloaded artery condition. We affirm that PPG measurements provided in balanced transmural arterial pressure conditions might serve as a reference for the unification of contact manner optical plethysmography methods. It is a step forward towards the standardization of the PPG methodology, and showed that the maximal value of the OPP, obtained in the particular experimental trial, indicates the optimal PPG probe contact pressure at that moment. Our developed system has been validated in the experimental series and showed the possibility of determining the correct PPG contact pressure value with high repeatability. It is concluded that this system can provide the necessary feedback to perform reliable PPG signal acquisition from the unloaded conduit artery.

Reliability of Hemodynamic Parameters Measured by a Novel Photoplethysmography Device

Three channel photoplethysmography (PPG) signal pulse wave studies of the leg’s conduit arteries during rest conditions were performed. The obtained data of each channel showed similar values, proving arterial PPG as a reliable and repeatable method to assess arterial waveform parameters. A validation experiment was carried out by acquiring signals from three identical IR PPG sensors, which were placed on different sites over the leg’s conduit arteries during rest conditions. Coefficients of variation (CV) were calculated at a 95% confidence interval by comparing results of each subject during multiple attempts. This data processing leads us to certain criteria of improvements in our methodology. Results show that the arterial PPG technique can give trusted and accurate information about the changes in hemodynamics, and therefore, makes it promising for early diagnostics of vascular disease.

Snapshot hyperspectral system for noninvasive skin blood oxygen saturation monitoring

The present study introduces recently developed compact hyperspectral snapshot system (device and software) for skin oxygen saturation monitoring. This prototype device involves compact snapshot hyperspectral camera, multi-wavelength illuminator, optical filter and crossed polarizers. The device was validated using reference color samples and and in-vivo during finger arterial occlusion tests. The prototype system demonstrated good performance of skin hyperspectral measurements in spectral range of 500-630nm. The results confirmed reliability of developed system for in-vivo assessment of skin blood oxygen saturation.

Hyperspectral evaluation of skin blood oxygen saturation at baseline and during arterial occlusion

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.

Remote photoplethysmography system for unsupervised monitoring regional anesthesia effectiveness

Determining the level of regional anesthesia (RA) is vitally important to both an anesthesiologist and surgeon, also knowing the RA level can protect the patient and reduce the time of surgery. Normally to detect the level of RA, usually a simple subjective (sensitivity test) and complicated quantitative methods (thermography, neuromyography, etc.) are used, but there is not yet a standardized method for objective RA detection and evaluation. In this study, the advanced remote photoplethysmography imaging (rPPG) system for unsupervised monitoring of human palm RA is demonstrated. The rPPG system comprises compact video camera with green optical filter, surgical lamp as a light source and a computer with custom-developed software. The algorithm implemented in Matlab software recognizes the palm and two dermatomes (Medial and Ulnar innervation), calculates the perfusion map and perfusion changes in real-time to detect effect of RA. Seven patients (aged 18-80 years) undergoing hand surgery received peripheral nerve brachial plexus blocks during the measurements. Clinical experiments showed that our rPPG system is able to perform unsupervised monitoring of RA.

Evaluation of nitroglycerin effect on remote photoplethysmogram waveform acquired at green and near infra-red illumination

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.

Novel hybrid technology for early diagnostics of sepsis

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.