ten Harkel A D, Beck L, Karemaker J M
Department of Medicine, University of Amsterdam, Academic Medical Centre, The Netherlands.
Acta Physiol Scand Suppl. 1992;604:77-87.
We investigated the influence of ten days 6 degrees head-down tilt (HDT) on short-term cardiovascular control. To help differentiate between the effects of HDT-induced fluid redistribution and changed autonomic cardiovascular modulation under prolonged HDT, the effect of acute posture changes was investigated as well. Six healthy male volunteers were studied. Continuous finger blood pressure was measured non-invasively by means of Finapres. Heart rate (HR) was derived from the electrocardiogram. Responses to forced breathing (FRSA), Valsalva's manoeuvre (VM), Mental Stress (MS) and Sustained Handgrip (SHG) were measured. Changing posture from HDT to standing enhanced the BP and HR responses to VM, both during straining and after release. During prolonged HDT, responses to VM changed toward the pattern seen in the upright posture before HDT, suggesting a strong influence of fluid redistribution. Neither posture nor prolonged HDT influenced HR variation during FRSA and responses to MS and SHG. BP variation during FRSA was influenced by posture but not by prolonged HDT. Thus, cardiovascular reflex tests which reflect the parasympathetic (FRSA) or the sympathetic (MS and SHG) efferents to the heart were not influenced by posture or prolonged HDT. Only the responses to VM were affected by both posture and prolonged HDT. These results are probably due to a decrease in blood volume and stroke volume under prolonged HDT, an increase in venous distensibility and, to a lesser extent, to inadequate cardiovascular regulatory responses.
我们研究了为期十天的6度头低位倾斜（HDT）对短期心血管控制的影响。为了有助于区分HDT诱导的液体重新分布的影响与长期HDT下自主心血管调节的变化，还研究了急性姿势变化的影响。对六名健康男性志愿者进行了研究。通过Finapres无创测量连续手指血压。心率（HR）由心电图得出。测量了对强迫呼吸（FRSA）、瓦尔萨尔瓦动作（VM）、精神应激（MS）和持续握力（SHG）的反应。从HDT姿势变为站立姿势增强了在用力期间和放松后对VM的血压和心率反应。在长期HDT期间，对VM的反应朝着HDT前直立姿势时的模式变化，表明液体重新分布有很大影响。姿势和长期HDT均未影响FRSA期间的心率变化以及对MS和SHG的反应。FRSA期间的血压变化受姿势影响，但不受长期HDT影响。因此，反映对心脏的副交感神经（FRSA）或交感神经（MS和SHG）传出的心血管反射测试不受姿势或长期HDT影响。只有对VM的反应受姿势和长期HDT两者影响。这些结果可能是由于长期HDT下血容量和每搏输出量减少、静脉扩张性增加，以及在较小程度上由于心血管调节反应不足所致。
