Influence of Posture on Cardiac Output and Minute Ventilation During Exercise

IN RESTING MAN, the cardiac output ishigher in the horizontal position than in the upright position. I t is, however, unknown whether this difference persists during the performance of exercise. This study was con-ducted to determine the influence of posture on the cardiac output in normal man during the performance of steady exercise with the legs. Concurrently, observations were also made of minute ventilation and oxygen up-take. Methods The subjects were four healthy medical students, three male and one female, whose ages ranged from 21 to 24 years. Exercise was performed at fixed loads of either 300 or 500 Kg.-M./min., using a bicycle ergometer * in which the work load could be preset, and was independent of the speed of pedaling. Cycle rate was maintained between 70 and 75 per minute. Observations were made in the supine and sitting postures, alternately. A strict time sequence was observed as follows: five minutes ' rest; eight minutes ' exercise with measurement of cardiac output between the fifth and sixth minutes, and expired air collection between the sixth and eighth minutes; posture changed; five minutes ' rest. Observations were then repeated in the new posture in an identical fashion. In addition to 20 comparisons made during exer