Wavelet Analysis of Skin Blood Oscillations in Persons With Spinal Cord Injury and Able-Bodied Subjects
Abstract
Li Z, Leung JY, Tam EW, Mak AF. Wavelet analysis of skin blood oscillations in persons with spinal cord injury and able-bodied subjects.
Objective
To assess the blood oscillations in the skin over the ischial tuberosity (high-risk area for pressure ulcer) using spectral analysis of laser Doppler flowmetry signals based on wavelet transform.
Design
Wavelet analysis of skin blood oscillations in persons with spinal cord injury (SCI) and able-bodied subjects.
Setting
Seating and body support interface laboratory.
Participants
Ten men were recruited for this study, of whom 5 were able-bodied subjects (age, 31.2±3.3y) and 5 were persons with SCI (age, 37.2±7.3y).
Interventions
External pressure of 16.0kPa (120mmHg) was applied to the ischial tuberosity via 1 specifically designed pneumatic indentor. The loading duration was 30 minutes.
Main Outcome Measures
Skin blood flow was monitored for 10 minutes prior to loading and 20 minutes after the prescribed loading period. With spectral analysis based on wavelet transform, 5 frequency intervals were identified (.01–.02, .02–.06, .06–.15, .15–.40, .40–2.0Hz) corresponding to endothelial related metabolic, neurogenic, myogenic, respiratory, and cardiac activities, respectively.
Results
The relative amplitude of the metabolic component for persons with SCI was significantly lower (F=5.26, P=.032) during the resting conditions as compared with able-bodied subjects. During the postloading period, the response of oscillatory activities was evidently lower in the skin over the ischial tuberosity for persons with SCI when compared with able-bodied subjects. In addition, the relative amplitude of the neurogenic component (.02–.06Hz) during postloading was significantly lower for persons with SCI (F=5.44, P=.029).
Conclusions
These findings suggest that the contributions of endothelial related metabolic and neurogenic activities to the blood perfusion regulation become relatively less for persons with SCI during the resting and postloading periods, respectively.
Department of Health Technology and Informatics, Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China
Reprint requests to Eric W. Tam, PhD, Dept of Health Technology and Informatics, Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China
Supported by the Central Research Grants of the Hong Kong Polytechnic University (grant nos. G-YD72, G-YX35).
No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated.
ABSTRACT