Effects of compression and type of bed surface on the microcirculation of the heel

To assess the effects of compression on the skin microcirculation of the heel using laser Doppler fluxmetry. Parallel groups comparing patients with control groups. Department of Surgery, University College London Medical School, London. Ten patients at risk of developing pressure ulceration, 10 age- and sex-matched healthy subjects and 10 young, healthy volunteers. An acrylic indenter with a slot to accommodate a laser Doppler probe was used to apply compression to the heel region. A pressure sensor was used to measure the applied compression. The resting laser Doppler flux was measured with the subject lying supine. Compression forces were then applied in increments from 50g to 1500g and the corresponding interface pressure (IP) and laser Doppler flux (LDF) recorded. The IP and LDF were also measured from the heel while the subject was lying on a low air-loss system and then on an NHS conventional hospital bed. The resting LDF is lower in the patient group compared to the control groups ( p < 0.05). Compression of the heel caused a progressive decrease in LDF in all groups. Compression greater than 50 mmHg as well as lying on an NHS bed reduced the LDF signal to a minimal value (biological zero). On the low air-loss system, the median LDF was 17% of the resting value in the age-matched control group and 32% in the patient group. The results indicate that the heel microcirculation is vulnerable to compression. The low air-loss system maintained the IP sufficiently low to prevent complete cessation of the heel microcirculation.