SQUATTING REVISITED - COMPARISON OF HEMODYNAMIC-RESPONSES IN NORMAL INDIVIDUALS AND HEART-TRANSPLANTATION RECIPIENTS

Background-Squatting produces a prompt increase in cardiac output and arterial blood pressure which is accompanied by an immediate decrease in heart rate and forearm vascular resistance. The rise in cardiac out put and blood pressure has been attributed to augmented venous return from compression of leg veins, while the decreases in heart rate and f orearm vascular resistance are probably due to activation of cardiopul monary and arterial baroreflexes. Haemodynamic patterns in nine normal men and six heart transplant recipients during 2 min of squatting wer e examined to determine the role of cardiac innervation in the mediati on of these responses. Methods-Stroke volume was monitored by ensemble averaged thoracic impedance cardiography and blood pressure was deter mined with an Ohmeda fingertip plethysmograph. These techniques provid ed continuous measurements which were capable of detecting transient a nd non-steady state changes. Forearm blood flow was measured with veno us occlusion plethysmography. Measurements were obtained after 3 min o f quiet standing, immediately after squatting, and at 20, 60, and 120 s of sustained squatting. Results-Both groups exhibited similar increa ses in stroke volume index normal individuals 10.5 ml/m(2); heart tran splant recipients 10.3 ml/m(2) and mean arterial pressure (normal indi viduals 8.5mm Hg; heart transplant recipients 5.0 mm Hg) which were su stained throughout squatting. Each group also showed an initial decrea se in peripheral resistance (normal individuals 3.6 units; heart trans plant recipients 7.7 units) followed by a return to baseline values af ter 20 s. Heart rate decreased in normal individuals (10 beats/min) bu t was unchanged or minimally increased (2 beats/min) in heart transpla nt recipients. Forearm vascular resistance was conspicuously decreased in normal individuals (47.8 units) but only minimally (20.9 units) an d not significantly in heart transplant recipients. Conclusions-The ma jor haemodynamic responses to squatting (increased cardiac output and blood pressure) are similar in normal individuals and heart transplant recipients. These responses are primarily due to augmented venous ret urn and are not altered by cardiac denervation. Both groups also exhib ited a transient decline in peripheral vascular resistance which is mo st likely mediated by arterial baroreflexes activated by the acute ris e in arterial blood pressure. The absence of a significant decrease in forearm vascular resistance in heart transplant recipients suggests t hat this response is partially mediated by cardiopulmonary or ventricu lar baroreflexes or that local forearm flow mediated vasodilatation re mains impaired after heart transplantation.