Contractile properties of slow and fast muscle following tourniquet ischemia

Tourniquet application is commonly used during sur gery on an extremity to create a bloodless field. Inves tigations have focused on the ultrastructural, histo chemical, and biochemical effects of tourniquet isch emia on muscle. Few studies, however, have examined the influence of tourniquet ischemia on the contractile properties of muscle. The purpose of this study was not only to examine this latter consideration, but also to determine whether slow and fast muscles exhibit a differential response. In adult male guinea pigs, the plantaris and soleus muscles of control (N = 5) and experimental legs (N = 5) were tested for time-peak- tension (TPT), one-half relaxation time (½RT), maximal twitch tension (Pt), and maximal tetanic tension (Po). The experimental leg was subjected to a 2 hour tour niquet which was placed around the thigh. Muscles of this leg were tested following a 2 hour recovery period. In three of the five animals, no response could be elicited from either the plantaris or soleus muscles of the experimental leg. In those instances where the experimental muscles were capable of generating force, the plantaris was clearly more effected. While tension production in the soleus was reduced by ap proximately 55%, the plantaris exhibited approximately a 90% decrease in tension output. Furthermore, both TPT and ½RT demonstrated consistent changes. These results indicate that the contractile properties of both the soleus and plantaris are dramatically effected by a 2 hour tourniquet. They further suggest that there may be a differential response based upon fiber type.