Correlation analysis of the temporal dynamics of subcutaneous blood perfusion and skin temperature in post-occlusion reactive hyperaemia test

Abstract

The digital thermal monitoring approach examines dynamic finger temperature in response to post-occlusive reactive hyperaemia (PORH) test and is a cost-effective way to study microvessels’ regulatory functions. The degree of dependency between skin temperature and subcutaneous blood perfusion in the PORH test, however, remains an unsettled subject. The purpose of this study is to evaluate their correlations and explore the prospects of restoring subcutaneous blood perfusion using skin temperature readings. 10 volunteers participated the experimental study of PORH test, and subcutaneous blood perfusion and skin temperature images of hand were captured by laser speckle contrast imaging (LSCI) and infrared (IR) camera respectively. Wavelet cross-correlation (WCC) analysis of extracted LSCI and IR signals in the resting phase of PORH test revealed that as frequency increased within 0.005 ∼ 0.1 Hz, the modules of WCC reduced and phase shift increased. Based on phase shift characteristics, the distances of thermal wave propagation were estimated 0.9 mm ∼ 2.3 mm, which were basically consistent with the measurement depth of LSCI. We further demonstrated that when the frequency-dependent delay and attenuation were taken into account, the correlation of oscillations between LSCI and IR signals improved significantly. Finally, an algorithm was proposed to reconstruct IR signals, which could be used to improve the possibilities of restoring subcutaneous blood perfusion from skin temperature recordings in PORH tests. The prospective applications of this study include indirect measurement of subcutaneous blood perfusion and the assessment of microvessels’ regulatory functions through skin temperature oscillations.