Post occlusive hyperaemic effect of tissue under static and dynamic loading conditions [using laser perfusion imager]

Post-occlusive hyperaemic response of cutaneous microcirculation at a site on the volar surface of the forearm 4-5 cm distal to the elbow has been evaluated using the laser Doppler perfusion imager. Nine healthy young subjects were studied following three types of externally applied loading conditions: (static) pressure only, combination of pressure and shear, and (dynamic) combination of pressure and cyclic shear; each applied for a duration of 3 minutes. Pressure loading of 172 mmHg was applied, with and without the application shear stresses. For dynamic loading, cyclic shear was applied at a rate of 1 Hz. Multiple scans were conducted over an area of 1400 mm/sup 2/ during the first 400 to 600 seconds of the post-occlusion period. Peak hyperaemic flow was established immediately after occlusion for the static loading conditions, while this peak flow (at 204% resting level) was maintained for a longer period of time after the application of cyclic shear. The half-life of hyperaemic response was observed within 100 seconds post-occlusion after static loading but was about doubled after dynamic loading. It was also found that hyperaemic flow did not decay following a single exponential decay pattern, but can be better represented with two exponential decay time constants. The observed adversity effect of dynamic loading to tissue prompts a reevaluation of the strategy in pressure sore prevention.