Terada N, Takeuchi T
Department of Physiology, Yamanashi Medical College, Japan.
Am J Physiol. 1993 Jan;264(1 Pt 2):H21-5. doi: 10.1152/ajpheart.1993.264.1.H21.
We examined the hypothesis that head-up and head-down tilt produce a symmetrical hydrostatic load on the veins. Venous pressure was measured in anesthetized monkeys with a transducer-tipped catheter. Changes in venous pressure gradients during head-up tilt corresponded to changes in hydrostatic load. However, changes in venous pressure gradients during head-down tilt were not symmetrical to those during head-up tilt. During head-down tilt, venous pressure in the superior vena cava rose, venous pressure around the right atrium did not change, and venous pressure in the inferior vena cava on the caudal side of the diaphragm rose considerably. The venous pressure of the inferior vena cava caudal to the renal vein then gradually decreased. The inferior vena cava passes through the central tendon of the diaphragm. Thus, during head-down tilt, the gravitational shift of venous blood is impeded by this anatomic structure, and venous pressure around the hepatic vein increases significantly. These data disproved our hypothesis that head-up and head-down tilt induced symmetrical but opposite influences on vena caval pressures.
头高位倾斜和头低位倾斜会对静脉产生对称的流体静力负荷。使用带有传感器尖端的导管在麻醉的猴子身上测量静脉压。头高位倾斜期间静脉压梯度的变化与流体静力负荷的变化相对应。然而，头低位倾斜期间静脉压梯度的变化与头高位倾斜期间并不对称。在头低位倾斜期间，上腔静脉的静脉压升高，右心房周围的静脉压未改变，而膈尾侧下腔静脉的静脉压显著升高。肾静脉尾侧的下腔静脉的静脉压随后逐渐降低。下腔静脉穿过膈的中心腱。因此，在头低位倾斜期间，静脉血的重力转移受到这一解剖结构的阻碍，肝静脉周围的静脉压显著升高。这些数据反驳了我们的假设，即头高位倾斜和头低位倾斜会对腔静脉压力产生对称但相反的影响。
