EFFECTS OF COMPRESSION AND TYPE OF BED SURFACE ON THE MICROCIRCULATION OF THE HEEL

Objective: To assess the effects of compression on the skin microcircu lation of the heel using laser Doppler fluxmetry. Design: Parallel gro ups comparing patients with control groups. Setting: Department of Sur gery University College London Medical School, London. Subjects and Ma terials: Ten patients at risk of developing pressure ulceration, 10 ag e- and sex-matched healthy subjects and 10 young, healthy volunteers. An acrylic indenter with a slot to accommodate a laser Doppler probe w as used to apply compression to the heel region. A pressure sensor was used to measure the applied compression. Outcome measures: The vestin g laser Doppler flux was measured with the subject lying supine. Compr ession forces were then applied in increments from 50g to 1500g and th e corresponding interface pressure (IP) and laser Doppler flux (LDF) r ecorded. The IP and LDF were also measured from the heel while the sub ject was lying on a low air-loss system and then on an NHS conventiona l hospital bed. Results: The resting LDF is lower in the patient group compared to the control groups (p < 0.05). Compression of the heel ca used 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 med ian LDF was 17% of the resting value in the age-matched control group and 32% in the patient group. Conclusions: The results indicate that t he heel microcirculation is vulnerable to compression. The low air-los s system maintained the IP sufficiently low to prevent complete cessat ion of the heel microcirculation.