Optical incoherent technique for noninvasive assessment of blood flow in tissues: Theoretical model and experimental study

Incoherent optical fluctuation flowmetry for detecting limbs with hemodynamically significant stenoses in patients with type 2 diabetes

INTRODUCTION

The development of new highly accurate, inexpensive and accessible methods for the detection of lower-extremity peripheral artery disease (LE-PAD) in diabetic patients is required. The aim of this study was to evaluate the accuracy of a new incoherent optical fluctuation flowmetry (IOFF) method in detecting legs with hemodynamically significant stenoses compared to ankle brachial index (ABI) and transcutaneous oximetry (TcPO2) in patients with diabetes mellitus (DM).

MATERIALS AND METHODS

Patients were recruited into 2 groups. Group 1 included patients with DM without LE-PAD and/or diabetic foot syndrome; Group 2 included patients with DM and LE-PAD. All patients underwent the following measurements: ultrasound (reference method), ABI, TcPO2, and the new IOFF method.

RESULTS

The new IOFF method showed a sensitivity of 79.5% and a specificity of 89.8% in detecting limbs with hemodynamically significant stenosis (AUC 0.890, CI 0.822-0.957). TcpO2 allows the diagnosis of LE-PAD with 69.2% sensitivity and 86.2% specificity (AUC 0.817, CI 0.723-0.911). Using a standard ABI cut-off of less than 0.9, the sensitivity and specificity for this parameter were 34.5% and 89.7%, respectively. Increasing the diagnostic cut-off of the ABI on the study group to 0.99 improved sensitivity to 84.6% and specificity to 78% (AUC,0.824 CI 0.732-0.915).

CONCLUSIONS

The new IOFF technique has demonstrated high sensitivity and specificity in the detection of LE-PAD in patients with DM. The high accuracy, rapid measurement, and potential availability suggest that the new IOFF method has a high potential for clinical application in the detection of PAD.

Skin microcirculation reactivity to local thermal hyperaemia in patients with COVID-19 - A pilot observational study

BACKGROUND

Endothelial dysfunction and microvascular disturbances are suggested to play a key role in higher morbidity and worse prognosis in patients with COVID-19 and cardiometabolic diseases.

OBJECTIVE

Study was aimed to establish relationships between the skin microcirculation parameters and various clinical and laboratory indicators.

METHODS

The study included 18 patients with moderate disease according to WHO criteria. Skin microcirculation measurements were performed by laser Doppler flowmetry using a heating test on the hairy skin of the right forearm.

RESULTS

Baseline perfusion only correlated with C-reactive protein (Rs = 0.5, p = 0.034). Microcirculation indices characterising the development of hyperaemia during the first minute of heating (LTH1 and AUC60) showed significant correlations (Rs from 0.48 to 0.67, p < 0.05) with indices of general blood analysis and blood coagulation (fibrinogen, D-dimer, haemoglobin, erythrocyte count and haematocrit). Indexes characterising the dynamics of hyperaemia development over longer time intervals showed correlation with the glomerular filtration rate (Rs = 0.6, p = 0.009).

CONCLUSION

Known COVID-19 risk factors (haemorheological parameters, age) are correlated with the microvascular reactivity to heating in patients with COVID 19. We suggest that, prospectively, the method of laser Doppler flowmetry could be used for non-invasive instrumental assessment of microcirculatory disorders in patients with COVID-19.

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.

Combined Non-Invasive Optical Oximeter and Flowmeter with Basic Metrological Equipment

Optical non-invasive diagnostic methods and equipment are used today in many medical disciplines. However, there is still no generally accepted and unifying engineering theory of such systems. Today, they are developed most empirically and do not always have the desired effectiveness in clinics. Among reasons for their insufficient clinical efficiency, we can claim the limited set of measured parameters, the poorly substantiated technical design parameters, and the lack of metrological certification, which all together lead to large uncertainties and inaccuracies in diagnostic data. The purpose of this study is to develop a new instrument for non-invasive optical oximetry by means of substantiating and creating amore informative tissue oximeter with an enhanced number of measured parameters and equipped with the basic metrological tools—imitational measures. The combination of two related optical diagnostic techniques—a tissue oximetry, including a cerebral one, and a fluctuation flowmetry on a single hardware platform—was used. Theoretical modeling of light transport in tissues was applied to substantiate the main technical design parameters of the device. For each measuring channel, relevant imitation measures for metrological verification and adjustment have been proposed. Some common principles for the operation of such equipment are described in the article, as well.