Effects of prolonged exercise to exhaustion on left-ventricular function and pulmonary gas exchange.

The purpose of this study was to simultaneously examine left-ventricular (LV) function and pulmonary gas exchange during prolonged constant-rate cycling in an attempt to explain the exercise-induced impairment in gas exchange. Eleven competitive cyclists rode their racing bicycles on a computerized cycle trainer at 25 W below the lactate threshold until exhaustion (exercise time = 2.51 +/- 0.86 h). LV systolic function was evaluated with two-dimensional echocardiography while arterial blood gases were used to assess pulmonary gas exchange. All variables were assessed concurrently before, during, and after exercise. LV function and cardiac output increased at the onset of exercise and were maintained until exhaustion. The alveolar-arterial P(O(2)) difference (A-a D(O(2))) increased within 15 min of the onset of exercise, was unchanged through to exhaustion, and returned to baseline 5 min post-exercise. Gas exchange was not related to cardiovascular function at the onset, or at end exercise. The results indicate that the widening A-aD(O(2)) during exercise is due to a readily reversible change in gas exchange function.