Progression of venoconstriction in patients after heart transplantation during exercise

Changes of both central hemodynamics and peripheral circulation in non-exercising muscle were investigated in 17 patients after successful orthotopic heart transplantation during moderate supine isotonic leg-exercise. Changes of peripheral circulation were measured in 14 healthy controls. The cardiac output rose from 5.71 to 9.45 l/min, the right atrial pressure from 3.5 to 12 mmHg, mean pulmonary arterial pressure from 17.4 to 36.9 mmHg, and pulmonary capillary wedger pressure from 9.5 to 23.5 mmHg. Venoconstriction, already present in the rest in patients after heart transplantation, further increased during the exercise (venous compliance lowered from 0.0454 to 0.0309 ml/mmHg). In controls no changes were observed (venous compliance being 0.0833 at rest and 0.0839 ml/mmHg during exercise). Negative correlation was found between an increase in pulmonary arterial pressure and a decrease in venous compliance. The authors hypothesise that venoconstriction could serve to increase of cardiac output via Frank-Starling mechanisms in patients after heart transplantation. Forearm blood flow during the exercise decreased (from 3.4 to 2.0 ml/100 ml/min), while local peripheral resistance rose (from 35.9 to 78.8 units) in patients after heart transplantation. These changes were not observed in controls.