Abstract

The diapharagm is a skeletal muscle of mixed fiber type that is unique in its requirement to maintain contracile function and fatigue resistance across a wide range of temperatures to sustain alveolar ventilation under conditions of hypo- or hyperthermia. The direct effect of temperature (15-41 deg C) on rat diaphragm isometric contractility and fatigue was determined in vitro. As temperature decreased from 37 to 15 deg C, contraction and relaxation times increased, and there was a left shift of the diaphragms froce-frequency curve, with decreased contractility at 41 and 15 deg C. Fatigue was induced by 10 min of stimulation with 30 trains/min of 5 Hz at a train duration of 900 ms. Compared with 37 deg C, fatigue resistance was enhanced at 25 deg C, but no difference in fatigue indexes was evident at extreme hypothermia (15 deg C) or hyperthermia (41 deg C). Only when the fatigue program was adjusted to account for hypothermia-induced increases in tension-time indexes was fatigue resistance evident at 15 deg C. These findings indicate that despite the diaphragms unique location as a core structure, necessitating exposure to in vivo temperatures higher than found in limb muscle, the temperature dependence of rat diaphragm muscle contractility and fatigue is similar to that reported for limb muscle of mixed fiber type. Verf.-Referat