RESPIRATORY MUSCLE RESERVE IN RATS DURING HEAVY EXERCISE

The extent to which the respiratory pump muscles limit maximal aerobic capacity in quadrupeds is not entirely clear. To examine the effect o f reduced respiratory muscle reserve on aerobic capacity, whole body p eak oxygen consumption ((V) over dotO(2peak)) was measured in healthy Sprague-Dawley rats before and after Sham, unilateral, or bilateral he midiaphragm denervation (Dnv) surgery. (V) over dotO(2peak) was determ ined by using a graded treadmill running test. Hemidiaphragm paralysis was verified after testing by recording the absence of electromyograp hic activity during inspiration. Before surgery, (V) over dotO(2peak) averaged 86, 87, and 92 ml.kg(-1).min(-1) for the Sham, unilateral, an d bilateral Dnv groups, respectively. Two weeks after surgery, there w as no significant change in (V) over dotO(2peak) for either the Sham o r unilateral Dnv group. However, (V) over dotO(2peak) decreased simila r to 19% in the bilateral Dnv group 2 wk after surgery. These findings strongly suggest that the pulmonary system in rats is designed such t hat during heavy exercise, the remaining respiratory pump muscles are able to compensate for the loss of one hemidiaphragm, but not of both.