Comparison of hemodynamic responses during dynamic exercise in the upright and supine postures after orthotopic cardiac transplantation

Abstract

Abnormal hemodynamic responses during supine exercise have been well documented in orthotopic cardiac transplant recipients. To determine the effect or posture, central hemodynamics were studied in 20 patients during a change from supine to sitting and during graded upright bicycle exercise (group U) and were compared with those of 20 patients matched for age, gender and time from transplantation who were studied after passive leg elevation and during exercise in the supine posture (group S).Passive leg elevation resulted in a 9% increase in stroke index (34 ± 6 to 37 ± 6 ml/m2, p < 0.001) and a 10% increase in cardiac index (3.1 ± 0.4 to 3.4 ± 0.5 liters/mm per m2, p < 0.001) in group S patients compared with a 15% reduction in stroke index (34 ± 7 to 29 ± 6 ml/m2, p < 0.001) and a 9% decrease in cardiac index (3.2 ± 0.6 to 2.9 ± 0.5 liters/min per m2, p < 0.001) in group U patients on assuming the sitting posture. Likewise, both the pulmonary capillary wedge pressure and right atrial pressure increased significantly (13 ± 4 to 17 ± 8 mm Hg, p < 0.001 and 5 ± 3 to 7 ± 3 mm Hg, p < 0.001) with passive leg elevation in group S and decreased on sitting (12 ± 6 to 8 ± 5 mm Hg, p < 0.001 and 5 ± 3 to 3 ± 2, p < 0.001) in group U. Exercise heart rate was slow to rise in both postures and peak heart rate did not differ significantly in the two groups. Stroke index and cardiac index increased to a greater extent in group U during early exercise and, as a result, were not different in the two groups at peak exercise. However, pulmonary capillary wedge pressure was 69% higher (27 ± 7 versus 16 ± 7 mm Hg, p < 0.0001) and right atrial pressure 67% higher (15 ± 5 versus 9 ± 5 mm Hg, p < 0.0001) at peak exercise in the supine posture, although the absolute increase was similar in both groups.The marked increase in ventricular filling pressures during exercise and the differences between supine and upright exercise imply an abnormal left-shifted and steep diastolic pressure-volume relation in the transplanted heart.