SUMMARY Swimming is frequently recommended for cardiac rehabilitation, but little is known of its physiologic consequences in ischemic heart disease. Eight males who had had a myocardial infarction 8-17 months before the study were exercised to exhaustion or angina with 10 W/min-1 ramp on a cycle ergometer in sitting and supine positions. Oxygen uptake (V02) was continuously measured to monitor the physiologic power requirement. All eight patients were taking fl blockers and four were taking digoxin. During sitting cycling, angina occurred in four and ST depression in five; during supine cycling, angina occurred in five and ST depression in six. VO2 was then measured while they swam at their own comfortable speed (mean 0.43 m/sec-') in a swimming flume at water temperatures of 25.5°C and 18°C. In six, the water speed was gradually increased until they were limited by symptoms. Comfortable swimming at 25.5°C was 87% (1.28 1/min-m) and at 18°C 89% (1.30 1/min-m) of sitting peak V02, while heart rates were 92% and 91% respectively. The mean peak VO2 and heart rate did not differ significantly between bicycle and swim tests (peak VO2 sitting 1.49 ± 0.23, supine 1.42 ± 0.24, 25.5°C 1.60 ± 0.17, 18°C 1.52 ± 0.19 1/min-'). Only two patients reported angina while swimming in warm water and one in cold water, although ST depression occurred in six in both swims. The subjective comfort and large muscle groups involved make swimming a good exercise, but the high relative energy cost and failure to identify ischemic symptoms indicate caution in cardiac patients, especially if their swimming skills are poor.THE PHYSIOLOGY of swimming in fit normal subjects and trained swimmers, both young and old, has been described,1-3 but the pathophysiology of swimming in patients with ischemic heart disease has been studied little.4' 5 Our understanding of this condition raises theoretical concerns. Immersion in water6 and a horizontal body position both increase the central blood volume,7 which could stress the limited reserves of patients with ischemic heart disease.8 The large contribution of work from the arms, which results in a higher peripheral vascular resistance than leg work at the same work load,9 the compressive effect of the water on the extremities" 6 and the decreased skin blood flow" 6 all increase the left ventricular afterload and thus might decrease the subjects' peak work level.10 The swimming flume, a kind of "swimming treadmill," offered a controlled and safe environment for evaluating such patients."" Oxygen uptake (VO2) was used as an objective measure of the amount of work performed, and the ECG as an indicator of ischemic changes. The swimming results were related to the subjects' performance in the sitting and supine positions on a bicycle ergometer. Further, swimming tests were performed with water temperatures of 18°C and 25°C to assess the effect of different water temperatures.
Patients and MethodsWe selected eight males, ages [49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66] Prefere...