Assessment of muscle blood flow by laser-Doppler flowmetry during hemorrhage in SHR

Skeletal muscle blood flow was assessed via laser-Doppler flowmetry (LDF) in the gracilis muscle of anesthetized 12- to 15-wk-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) control rats subjected to graded hemorrhage. Tissue perfusion was assessed at 20 specific sites in the muscle before and 20 min after each of five successive 1-ml withdrawals of blood. Mean LDF signals recorded from the gracilis muscle of SHR and WKY were similar during the prehemorrhage control period. After hemorrhage, mean arterial pressure and calculated vascular resistance of the gracilis muscle were higher in SHR than in WKY, and SHR exhibited a greater reduction of LDF signal in response to hemorrhage than WKY. Although SHR and WKY had a similar number of low flow sites (LDF signal less than 0.17 V) during the control period, successive blood volume withdrawals led to a significantly greater increase in the number of poorly perfused areas in the muscles of the hypertensive animals. The results of this study suggest that LDF is a useful tool to assess tissue perfusion during circulatory stress and that hemorrhage causes a greater decrease in skeletal muscle blood flow in SHR than in WKY. More severe reductions in tissue perfusion may contribute to the reduced ability of hypertensive animals to survive after hypotensive hemorrhage.