Spectral analysis on the microcirculatory laser Doppler signal at the acupuncture point

We aimed to characterize the frequency spectra of skin blood flow signals simultaneously recorded at Hoku, an important acupoint in oriental medicine, and two nearby nonacupoints to understand the underlying physiological mechanism of acupuncture points. ECG and laser Doppler flowmetry signals were measured simultaneously. A four-level Haar wavelet transform was applied to the measured 20-minute LDF signals, and periodic oscillations with five characteristic frequency peaks were obtained within the following frequency bands: 0.0095-0.021, 0.021-0.052, 0.052-0.145, 0.145-0.6, and 0.6-1.6 Hz (defined as FR1-FR5), respectively. The power in FR3 was significantly larger at Hoku than at the two nonacupoints. Spectral analysis of the flux signal revealed that one of the major microcirculatory differences between acupoints and nonacupoints was in the different myogenic responses of their vascular beds. This information may aid the development of a method to noninvasively study the microcirculatory characteristics of the acupoint.