Thermal rhythmography-topograms of the spectral analysis of fluctuations in skin temperature

It has been reported that skin blood flow and, consequently, skin temperature exhibit several periodic fluctuations. Although the mechanisms and physiological basis underlying these fluctuations are not yet well understood, it is thought that the fluctuations originate in the periodic rhythms of the autonomic nervous system. In this study, a program for a far-infrared thermal imaging system was developed which is capable of displaying topograms of the power spectra of an arbitrary frequency range with respect to changes in skin temperature (i.e. thermal rhythm). Thermographic images were taken using a high-speed far-infrared thermal camera. The change in the skin temperature with respect to time at every pixel was obtained from the time series of the thermograms, and the power spectrum was calculated by the FFT method using the personal computer. The amplitude of the power spectrum at an arbitrary frequency range was changed into pseudo-colors at each pixel, and a 2-dimensional or 3-dimensional color image of the amplitude mapping of the power spectrum at each frequency range was obtained. We are now analyzing differences between healthy subjects and patients with Raynaud's syndrome in the distribution of the rhythms of skin temperature using this system.