Determination of the amplitude and phase relationships between oscillations in skin temperature and photoplethysmography-measured blood flow in fingertips

Abstract

It is well established that skin temperature oscillations in fingertips coexist with blood flow oscillations and there is a certain correlation between them. At the same time, the reasons for differences in waveform and the delay between the blood flow and temperature oscillations are far from being fully understood. In this study we determine the relationships between spectral components of the blood flow and temperature oscillations in fingertips, and we ascertain the frequency dependences of amplitude attenuation and delay time for the temperature oscillations. The blood flow oscillations were considered as a source of thermal waves propagating from micro-vessels towards the skin surface and manifesting as temperature oscillations. The finger temperature was measured by infrared thermography and blood flow was assessed by photoplethysmography for ten healthy subjects. The time-frequency analysis of oscillations was based on the Morlet wavelet transform. The frequency dependences of delay time and amplitude attenuation in temperature compared with blood flow oscillations have been determined in endothelial (0.005-0.02 Hz) and neurogenic (0.02-0.05 Hz) frequency bands using the wavelet spectra. We approximated the experimental frequency dependences by equations describing thermal wave propagation through the medium and taking into account the thermal properties and thickness of a tissue. Results of analysis show that with the increase of frequency f the delay time of temperature oscillations decreases inversely proportional to f(1/2), and the attenuation of the amplitude increases directly proportional to exp f(1/2). Using these relationships allows us to increase correlation between the processed temperature oscillations and blood flow oscillations from 0.2 to 0.7 within the frequency interval 0.005-0.05 Hz. The established experimental and theoretical relationships clarify an understanding of interrelation between the dynamics of blood flow and skin temperature, and define possibilities and limitations of temperature measurements as a method of blood flow assessment in extremities.

Skin temperature variations as a tracer of microvessel tone

“…Knowing the decay rate of temperature oscillations and the LDF-ST phase shift for each frequency, we can recover the blood flow pulsations using the ST series. A similar problem was considered in [19], where the photoplethysmography-measured blood flow was compared with the temperature field obtained with the infrared camera. However, application of photoplethyzmography to determine the functional state of the microcirculation is under discussion [20], while LDF is the most common technique.…”

Method of Digital Processing of Video Thermogramms at Execution of the Open Heart Operations with Filtration of Visual Fields of Myocardium

“…При цьому технологія візуалізації допускає реєстрацію теплової реакції на зовнішнє нагрівання [6,7] або охолодження [8] тканин. Другий напрям робіт пов'язаний зі спро-бою не тільки візуалізувати анатомічні особли-вості судин, але й установити зв'язок температур-них параметрів із показниками кровотоку [9][10][11].…”

Thermo-Electrical Analogy of Skin Properties and Low-Pass Filter, Correlation between Skin Temperature and Blood Flow Oscillations in Extremities

“…При этом установлено наличие дисперсии, а также затухание температурной волны в биоткани [11][12][13]. Анализ рассматриваемого в данной работе упрощенного уравнения Шитцера (3) демонстрирует уменьшение амплитуды температурного сигнала и наличие САГАЙДАЧНЫЙ и др.…”

“…Проведенные нами ранее исследования взаимосвязи колебаний температуры и кожного кровотока в области пальцев [11][12][13][14][15] продемонстрировали эффективность подхода, в соответствии с которым колебания кровотока можно рассматривать как источник тепловых волн, распространяющихся в коже и регистрируемых как изменение температуры поверхности кожи. При этом связь между двумя сигналами устанавливалась с помощью спектральных преобразований, в которых входным сигналом являлись колебания кровотока, а выходным -колебания температуры.…”