Effect of Posture on Cardiac Output

Abstract

Most of the evidence obtained by various investigators employing different methods shows that cardiac output is decreased progressively in the sitting and standing as contrasted to the recumbent position. Recent investigations 1 , 2 , 3 4 , 5 in which the generally accepted more accurate acetylene method was used have given results in the same direction. Grollman, 6 however, using a nitrous oxide method which in his hands gave values agreeing with the acetylene method, found no change with posture. Beilschowsky, 7 using the acetylene method, also found no change. This discrepancy in the findings, augmented by Gladstone's criticism and modification of the acetylene method 8 prompted this reinvestigation of the problem.

Five experienced healthy adult males, ranging in age from 21 to 36 years, served as subjects for determinations made at intervals over periods of 4 to 6 months each. All determinations were made in the morning after the fasting subject arrived at the laboratory and had rested on a comfortable cot for at least 30 minutes. The recumbent determinations were made with the subject supine on the cot, the sitting in a straight-backed chair and the standing with the subject leaning lightly against the wall to prevent swaying. Changes in position were made with as little expenditure of energy as possible. Cardiac outputs were determined about 20 minutes after the assumption of the desired position.

All subjects show a smaller cardiac output in the standing as contrasted to the recumbent position (Table). This difference is further accentuated when only paired determinations (recumbent and standing done on the same day) are compared, the mean difference of 28 such determinations being 21%. The change is apparent regardless of whether the original Grollman 9 or the modified Gladstone method 8 is used.