Standardization of skeletal muscle ischemic injury

Observations on skeletal muscle function after a timed ischemic interval suggests significant interanimal variability. The purpose of this study is to compare the use of function versus time as a method for standardizing the degree of ischemic injury. Muscle function was measured by recording the isometric contraction to direct supramaximal tetanic stimulation of the anterior tibialis muscle (AT). Muscle cell viability was determined by the reduction of triphenyltetrazolium chloride (TTC)/g tissue measured by a spectrophotometric assay. Twenty-four New Zealand White rabbits underwent an interval of ischemia to one anterior tibialis muscle produced by collateral ligation and unilateral inflow control, using the contralateral AT as a control. The duration of ischemia was determined by one of three methods: Group I, n = 8, underwent ischemia for 3 hr (3 hr); Group II, n = 8, underwent ischemia until AT muscle function decreased to 20% of control (20%); and Group III, n = 8, underwent ischemia until AT muscle function decreased to less than 5% of control (less than 5%). Following the ischemic injury, both physiologic function and cellular viability were measured and expressed as a percentage of control. After 3 hr of ischemia, the mean function was 15.5 with a standard deviation of 20.2, and the TTC reduced/g tissue was 24.7 with a standard deviation of 24.8. When the ischemic interval was determined by a decline of muscle function to 20% of control, the mean TTC reduced was 33.4 +/- 7.6. The mean TTC reduced, when the ischemic interval was terminated when muscle function reached less than 5% of control, was 13.5 +/- 7.2.(ABSTRACT TRUNCATED AT 250 WORDS)