Microcirculation in skeletal muscle during hypoperfusion : An experimental study regarding some psysiological and pharmacological factors influencing blood flow and oxygen pressure distributions

Abstract: The vascular bed in skeletal muscle plays an important role in the regulation of the systemic circulation. The present study was undertaken to investigate how capillary blood flow and oxygenation in skeletal muscle are affected by: a) a reduction in the levels of respiratory gases in blood, hypocapnia or hypoxia, and b) the interaction of anesthetics (pentobarbital, propofol, ketamine) during hemorrhage, and c) hypotension induced pharmacologically by adenosine, sodium nitroprusside or acetylcholine.The experiments were performed on the vastus medialis muscle in mechanically ventilated anesthetized rabbits. Skeletal muscle microvascular perfusion was investigated with a local hydrogen clearance technique (LHC) (using a multi wire microelectrode) and laser-Doppler flowmetry (LDF). Skeletal muscle oxygen pressures (Pt02) and pH wereassessed using a multiwire Clark-type oxygen or an antimony (pH) microelectrode.Hypocapnia (arterial PC02 2.3 kPa) decreased LDF flow and Pt02, whereasmuscle tissue pH remained unchanged. This was interpreted as being due to a reduction in microvascular perfllsion induced by vasoconstriction. This led to a decline in both tissue oxygenation and in the removal of acid metabolites, which counteracted a developing tissue alkalosis. Apart form the vasoregulatory role of carbon dioxide, it appears that muscle tissue pH is an important factor in the control of skeletal muscle perfusion. Hypoxia (arterial P02 4.0 kPa) reduced LHC flow and Pt02. This was reversed by the administration of ritanserin (serotonin antagonist), despite a further reduction in blood pressure. This supports the concept that the decline in capillary perfusion during systemic hypoxia is at least partly mediated by serotonin.Hemorrhage was induced by withdrawal of blood to a mean arterial blood pressure of 40 mmHg, and measurements (LHC, LDF) were carried out during the spontaneous recovery period. When ketarnine wa<> used as anesthetic a higher capillary perfusion was found as compared to pentobarbital or propofol. These differences may be mediated, as suggested by the results from other studies, by the cardiovascular stimulating properties of ketamine, the effects on the renin-angiotensin system by pentobarbital and venomotor tone by propofol.Hypotension, 20-25% reduction in mean arterial blood pressure, induced by adenosine, was associated with a decrease in skeletal muscle capillary blood flow and an increase in PtOz. This may be explained by a redistribution of capillary flow and/or a reduction in local oxygen demand. Hypotension induced by sodiuin nitroprusside to a similar level, on the other hand, increased capillary blood flow, mostly in the high flow range, whereas the oxygen pressure distributions were reduced. This may be caused by an increased local oxygen demand. Acetylcholine-induced hypotension decreased capillary blood flow which was most pronounced in the high flow range, while oxygen pressure distributions decreased homogeneously in a manner similar to that seen during hemorrhage.The findings presented rnay be of importance in clinical situations with compromised skeletal muscle circulation.