Powers S K, Stewart M K, Landry G
Applied Physiology Laboratory, School of HPERD, Louisiana State University, Baton Rouge 70803.
Aviat Space Environ Med. 1988 Mar;59(3):239-45.
The purpose of these experiments was to examine ventilatory and gas exchange responses to acute head-down tilt. Subjects (N = 5) participated in two series of head-down tilt experiments. Both experimental protocols involved movement from a near-vertical position (120 degrees) to a -30 degrees head-down position. One set of experiments employed venous occlusion (VO) in the legs during the first 30 s of tilt, while the second set was performed without occlusion (control experiment). Oxygen uptake (VO2), carbon dioxide output (VCO2) and expired ventilation (VE) increased significantly (p less than 0.05) above vertical values in both experimental conditions during the first 75 s following tilt. Further, VO2, VCO2, and VE were greater (p less than 0.05) during the VO experiment compared to control immediately following removal of venous occlusion. Although end-tidal CO2 tension (PETCO2) tended to increase following tilt, mean PETCO2 averaged over 15-s periods remained unaltered (p greater than 0.05) during tilt in both experimental protocols compared to the vertical position. These data demonstrate that acute head-down tilt results in an increase in VE and the general maintenance of isocapnia.
这些实验的目的是研究急性头低位倾斜时的通气和气体交换反应。受试者（N = 5）参与了两组头低位倾斜实验。两个实验方案均包括从接近垂直的位置（120度）移动到-30度头低位。一组实验在倾斜的前30秒采用腿部静脉闭塞（VO），而第二组实验不进行闭塞（对照实验）。在倾斜后的前75秒内，两种实验条件下的摄氧量（VO2）、二氧化碳排出量（VCO2）和呼出气通气量（VE）均显著高于垂直位时的值（p < 0.05）。此外，在去除静脉闭塞后，VO实验中的VO2、VCO2和VE立即高于对照实验（p < 0.05）。尽管倾斜后头末二氧化碳分压（PETCO2）有升高趋势，但在两种实验方案中，与垂直位相比，倾斜期间15秒时间段内的平均PETCO2保持不变（p > 0.05）。这些数据表明，急性头低位倾斜会导致VE增加，并总体维持等碳酸血症。
