Cardiac fatigue after prolonged exercise.

To determine the effects of prolonged exercise on systolic and diastolic left ventricular function, we studied 21 athletes before, at the finish (within 11 +/- 5 min), and during recovery (28 +/- 9 hr) after the Hawaii Ironman Triathlon (2.4 mile swim, 112 mile bike, 26.2 mile run). Two-dimensionally guided M mode echocardiograms were digitized for wall thickness, cavity dimension, fractional shortening, and peak rates of cavity enlargement and wall thinning. Pulsed Doppler left ventricular inflow recordings were analyzed for peak early and late velocities and their ratio. Left ventricular diastolic dimension was reduced at race finish (5.4 +/- 0.6 to 5.1 +/- 0.6 cm) and remained reduced after 1 day of recovery (5.2 +/- 0.6 cm, p less than .05). Fractional shortening fell at race finish (39 +/- 5% to 35 +/- 5%), although systolic blood pressure was unchanged, and rose to 40 +/- 4% after recovery (p less than .05). The return to prerace shortening values after recovery occurred despite continued reduction in diastolic size. Peak circumferential shortening did not change significantly. Individual reductions in fractional shortening were correlated with increases in systolic cavity size (r = -.64, p less than .01), but not with decreases in diastolic size. The stress-shortening relationship was displaced downward at race finish, but returned toward baseline after 1 day of recovery, despite a persistent reduction in cavity size. This suggests that the decrease in shortening was due to impaired contractility as well as altered preload.(ABSTRACT TRUNCATED AT 250 WORDS)