Wavelet-based Correlations of Skin Temperature and Blood Flow Oscillations

Abstract

The wavelet transform-based correlation analysis has been used to study skin temperature fluctuations caused by periodic changes in blood flow resulting from oscillations in vasomotor smooth muscle tone. We considered two cases, one in which temperature measurements and blood flow recordings by laser Doppler flowmetry are made simultaneously and another in which two temperature signals are measured concurrently. Twelve healthy subjects participated in our study. The gapped wavelet technique was used to suppress artifacts caused by boundary effects. Simultaneous recordings of skin temperature fluctuations and the signal of the laser Doppler flowmeter provided correlation coefficients essentially exceeding the values obtained for noise signals within three spectral ranges corresponding to myogenic (0.05-0.14 Hz), neurogenic (0.02-0.05 Hz), and endothelial (0.0095-0.02 Hz) regulation mechanisms. Within the frequency range from 0.14 to 2 Hz the values of the correlation function are compatible with the values of noise correlations. The same results were obtained for two concurrently measured temperature signals. Reduction in the amplitude of temperature fluctuations and in the level of correlations with the frequency arises because the skin has the properties of a low-frequency filter. As temperature fluctuations propagate their amplitude decays as an exponential function of frequency. Hence small oscillations in the spectral range reflecting the influence of heartbeat and respiration cannot be distinguished from external thermal noise.

Spectral filtering approach to the skin blood flow imaging in limbs via infrared thermography: its scope and limits

“…Considering sensitivity equal to 0.02 °C the curve shows that the upper limit of permissible frequency for my thermal imaging camera is equal to 0.1 Hz. Similar results have been reported previously in [6,7] for the contact skin temperature measurements.…”

Skin temperature variations as a tracer of microvessel tone

“…The relationship between the blood flow and ST during vasoconstriction and vasodilation provoked by skin local cooling or heating has been studied in [15] and analyzed in terms of the wavelet-based time-localized phase coherence [16]. Measurements carried out on the volar side of the arm [13,15] or on the palm surface of the distal phalanx of the finger [14,17] and, irrespective of certain anatomical features (high arteriolovenular anastomosis content in the distal parts of limbs), gave similar results. Despite the terminological differences (wavelet cross-correlation [14] or wavelet phase coherence [13,16]), these studies employed the same mathematical technique, which is based on wavelet decomposition providing a complex characteristic for two signals relationship.…”

“…At high frequencies the correlation decreases, though appreciable decay occurs at different frequencies: subject 1 has the most extended range of correlation (up to about 0.3 Hz), while subject 5 shows no correlation above 0.05 Hz and has a rather weak correlation at lower frequencies. One of the reasons for the general decrease of correlation at high frequencies is related to the properties of the skin, which acts as a low-frequency filter [14] (see also below Section 5). This results in fast decay of the ST spectrum: oscillations at frequencies above 0.5 Hz are so weak that even the heart rate is not seen.…”

“…Wavelets were used in [13,14] to show the compatibility of both methods at low frequencies (below the respiratory frequency). The relationship between the blood flow and ST during vasoconstriction and vasodilation provoked by skin local cooling or heating has been studied in [15] and analyzed in terms of the wavelet-based time-localized phase coherence [16].…”

Restoration of finger blood flow oscillations by means of thermal imaging

“…Considered method of blood flow restoration by means of temperature measurements can be useful in phase coherence investigations [7][8][9][10] and for development of non-contact methods of blood flow observations. The latter is the most important taking into consideration that a temperature response to trials (cooling of extremities, for example) can be more evident than blood flow response [7].…”