Hanson P, Slane P R, Rueckert P A, Clark S V
Department of Medicine, University of Wisconsin Medical School, Madison, USA.
Br Heart J. 1995 Aug;74(2):154-8. doi: 10.1136/hrt.74.2.154.
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 output and blood pressure has been attributed to augmented venous return from compression of leg veins, while the decreases in heart rate and forearm vascular resistance are probably due to activation of cardiopulmonary and arterial baroreflexes. Haemodynamic patterns in nine normal men and six heart transplant recipients during 2 min of squatting were examined to determine the role of cardiac innervation in the mediation of these responses.
Stroke volume was monitored by ensemble averaged thoracic impedance cardiography and blood pressure was determined with an Ohmeda fingertip plethysmograph. These techniques provided continuous measurements which were capable of detecting transient and non-steady state changes. Forearm blood flow was measured with venous occlusion plethysmography. Measurements were obtained after 3 min of quiet standing, immediately after squatting, and at 20, 60, and 120 s of sustained squatting.
Both groups exhibited similar increases in stroke volume index (normal individuals 10.5 ml/m2; heart transplant recipients 10.3 ml/m2) and mean arterial pressure (normal individuals 8.5 mm Hg; heart transplant recipients 5.0 mm Hg) which were sustained throughout squatting. Each group also showed an initial decrease in peripheral resistance (normal individuals 3.6 units; heart transplant recipients 7.7 units) followed by a return to baseline values after 20 s. Heart rate decreased in normal individuals (10 beats/min) but was unchanged or minimally increased (2 beats/min) in heart transplant recipients. Forearm vascular resistance was conspicuously decreased in normal individuals (47.8 units) but only minimally (20.9 units) and not significantly in heart transplant recipients.
The major 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 return and are not altered by cardiac denervation. Both groups also exhibited a transient decline in peripheral vascular resistance which is most likely mediated by arterial baroreflexes activated by the acute rise in arterial blood pressure. The absence of a significant decrease in forearm vascular resistance in heart transplant recipients suggests that this response is partially mediated by cardiopulmonary or ventricular baroreflexes or that local forearm flow mediated vasodilatation remains impaired after heart transplantation.
下蹲会使心输出量和动脉血压迅速升高，同时心率和前臂血管阻力立即下降。心输出量和血压的升高归因于腿部静脉受压导致静脉回流增加，而心率和前臂血管阻力的下降可能是由于心肺和动脉压力反射的激活。研究了9名正常男性和6名心脏移植受者在2分钟下蹲过程中的血流动力学模式，以确定心脏神经支配在介导这些反应中的作用。
通过总体平均胸阻抗心动图监测每搏输出量，并用欧姆龙指尖体积描记器测定血压。这些技术提供了能够检测瞬态和非稳态变化的连续测量。用静脉阻断体积描记法测量前臂血流量。在安静站立3分钟后、下蹲后立即以及持续下蹲20、60和120秒时进行测量。
两组的每搏输出量指数（正常个体为10.5ml/m²；心脏移植受者为10.3ml/m²）和平均动脉压（正常个体为8.5mmHg；心脏移植受者为5.0mmHg）均有相似的增加，且在整个下蹲过程中持续存在。每组外周阻力也最初下降（正常个体为3.6单位；心脏移植受者为7.7单位），然后在20秒后恢复到基线值。正常个体心率下降（10次/分钟），而心脏移植受者心率不变或略有增加（2次/分钟）。正常个体前臂血管阻力显著下降（47.8单位），而心脏移植受者仅略有下降（20.9单位）且无显著差异。
正常个体和心脏移植受者对下蹲的主要血流动力学反应（心输出量和血压增加）相似。这些反应主要是由于静脉回流增加，且不受心脏去神经支配的影响。两组外周血管阻力也出现短暂下降，这很可能是由动脉血压急性升高激活的动脉压力反射介导的。心脏移植受者前臂血管阻力无显著下降表明，这种反应部分由心肺或心室压力反射介导，或者心脏移植后局部前臂血流介导的血管舒张仍受损。
