Spectral analysis of the microcirculatory laser Doppler signal at the Hoku acupuncture point

Abstract

We aimed to characterize the frequency spectra of skin blood flow signals recorded at Hoku, an important acupuncture point (acupoint) in oriental medicine. Electrocardiogram (ECG) and laser Doppler flowmetry signals were measured simultaneously in 31 trials on seven volunteers aged 21-27 years. A four-level Haar wavelet transform was applied to the measured 20 min laser Doppler flowmetry (LDF) signals, and periodic oscillations with five characteristic frequency peaks were obtained within the following frequency bands: 0.0095-0.021 Hz, 0.021-0.052 Hz, 0.052-0.145 Hz, 0.145-0.6 Hz, and 0.6-1.6 Hz (defined as FR1-FR5), respectively. The relative energy contribution in FR3 was significantly larger at Hoku than at the two non-acupoints. Linear regression analysis revealed that the relative energy contribution in FR3 at Hoku significantly increased with the pulse pressure (R(2) = 0.48; P < 0.01 by F-test). Spectral analysis of the flux signal revealed that one of the major microcirculatory differences between acupoints and non-acupoints was in the different myogenic responses of their vascular beds. This information may aid the development of a method for the non-invasive study of the microcirculatory characteristics of the acupoint.

Microcirculatory Changes by Laser Doppler after Infrared Heating over Acupuncture Points – Relevance to Moxibustion

“…23 The increase in ACflux following LH was largest at Hoku, and so changes in the pulsation of flow rate and in the shear stress applied to the vessel walls would also be greatest there. As with our previous conjecture, 9 this might lead to the largest myogenic response, resulting in the changes in the REC of FR3 being greatest at Hoku.…”

“…In order to ensure that subjects were physiologically stable, the chosen baseline data sequences had to satisfy the following criteria: (1) CV of the HR less than 10%, (2) DBP greater than 60 mmHg, (3) SBP less than 130 mmHg, (4) changes in SBP and DBP less than 10 mmHg before and after the LDF recording, and (5) variations in LDF flux signals less than 25%. 9,17 For the LDF signal, several parameters were calculated to elucidate the microcirculatory effects induced by LH. DCflux and ACflux (DC and AC components of the flux, respectively) were defined as the average values of the LDF flux signals, MBC (mean blood concentration) was defined as the average value of the concentration signals, and MBV (mean blood velocity) was defined as the average value of the flux=concentration during each measurement period.…”

“…The greater number of capillaries, rather than arteriovenous shunt vessels, at these measurement sites allows the effects of the latter to be minimized. 8,9 For each experiment, we recorded a 20-minute baseline data sequence (M0), then applied LH and recorded another 20 minutes of data as the heating-effect sequence (segmented every 5 minutes into M1-M4). Before and after the entire procedure, we measured fundamental physiological parameters of the subject, including heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressure (DBP) using a sphygmomanometer (MediGuard 150i, Rossmax).…”

“…17 The experimental setup is detailed in our previous reports. 8,9,17 ECG and LDF signals were measured simultaneously and noninvasively. ECG signals were measured by surface electrodes, and acquired by a preamplifier (lead II, RA-LL; 6600-series, Gould).…”

“…1,5 Each acupuncture point (acupoint) appears to have an abundant distribution of neural or vascular elements, 6,7 and its microcirculatory perfusion differs from those at nearby nonacupoints. 8,9 Many methods in traditional Chinese medicine (TCM), such as acupuncture and acupressure, have been applied to specific acupoints in order to improve their therapeutic effects. For moxibustion therapy, thermal sensitivity of polymodal receptors is suggested to be essential, 7 and thermal, sympathetic vibration, or pharmacological actions, may account for the therapeutic effects of moxibustion.…”