VENTRICULAR PERFORMANCE Effects of supine and lateral positions on cardiac output and intracardiac pressures : an experimental study

Hemodynamic measurements in human subjects and in experimental animals are generally made in the supine position; not much attention is paid to potential beneficial or harmful effects of right or left lateral positions on cardiac output or other hemodynamic variables. To evaluate the potential influence of such positional changes on cardiac performance, we measured cardiac output and left and right ventricular pressures (with micromanometer catheters) in anesthetized experimental animals (eight dogs and nine pigs) in the supine, right lateral, and left lateral positions. Cardiac output increased from supine to left lateral (mean SD, 2.6 +0.9 to 3.1 ± 1.0 liters/min; p < .001) and from supine to right lateral positions (2.6 ± 0.9 to 3.1 ± 1.1 liters/min; p < .001). There was an associated decrease in arteriovenous oxygen saturation difference from supine to left lateral position (31 + 8% to 24 ± 4%; p < .001) and from supine to right lateral position (32 ± 9% to 25 ± 6%; p < .001). Left ventricular systolic and end-diastolic pressures increased from supine to left lateral (128 17/9 ± 2 to 147 19/16 ± 4 mm Hg; both p < .001) and from supine to right lateral positions (128 + 19/9 ± 2 to 141 16/16 ± 7 mm Hg; p < .01 and p < .001, respectively). Similarly, right ventricular systolic and end-diastolic pressures also increased from supine to left lateral (30 ± 7/3 + 2 to 38 + 7/8 ± 2 mm Hg; both p < .001) and from supine to right lateral positions (31 ± 8/3 + 2 to 43 + 8/11 + 4 mm Hg; both p < .001). Systolic and end-diastolic right ventricular pressures were significantly higher in the right lateral position than in the left (both p < .001). Heart rate did not change with positional maneuvers. Neither the sequence of positional changes nor the species of animal (dog vs pig) had any apparent influence on the results. Roentgenographic analysis of the differences in height of the right ventricle relative to the inferior vena cava suggests that changes in hydrostatic pressure may be entirely responsible for the increases in right ventricular end-diastolic pressure when animals are changed from the supine to the left or right lateral positions. We conclude that a change from supine to lateral position significantly increases intracardiac pressures and cardiac output in experimental animals. If confirmed in humans, these findings may have significant implications for the assessment of hemodynamic status of patients in intensive care unit and catheterization laboratory settings and for the treatment of patients in low-cardiac output states. Circulation 73, No. 3, 579-585, 1986. IN INTENSIVE CARE UNITS, catheterization laboratories, and animal research facilities, cardiac output is usually measured with the patient or animal in the supine position; not much attention is paid to potential From the Charles A. Dana Research Institute and the Harvard-Thorndike Laboratory of the Beth Israel Hospital, Department of Medicine, Beth Israel Hospital and Harvard Medical School, Boston. Supported in part by grant RR-01032 from the General Clinical Research Centers Program of the Division of Research Resources, National Institutes of Health. Data analysis was performed on the Clinical Center Core Lab Facilities. Address for correspondence: Patricia C. Come, M.D., Department of Medicine, Cardiology Division, Beth Israel Hospital, 330 Brookline Ave., Boston, MA 02215. Received June 12, 1985; revision accepted Nov. 29, 1985. *Present address: First Department of Internal Medicine, Faculty of Medicine, Kagoshima University, Kagoshima City 890, Japan. Vol. 73, No. 3, March 1986 beneficial or harmful effects of right or left lateral positions on cardiac output or other hemodynamic variables. Indeed, there are few data concerning the influence of supine and lateral positions on cardiac output in experimental animals or human beings. In pregnant women in the third trimester, cardiac output increases by a mean of up to 27% with a change from supine to lateral positions.' In nonpregnant human subjects, contradictory results have been reported.1' 4 Some investigators have described a higher cardiac output in the supine position as compared with right and left lateral positions.4' 6 However, Whitman et al.' found cardiac output to be higher in the left lateral position than in supine and right lateral positions, 579 by gest on A ril 9, 2017 http://ciajournals.org/ D ow nladed from