[Human external respiratory function and blood acid-base balance during prolonged antiorthostatic hypokinesia and during the recovery period].

The study of external respiration and acid-base equilibrium of blood of 35 test subjects exposed to 49-day head-down (-4 degrees) tilting and of 6 test subjects exposed to 182-day head-down (-4 degrees) tilting demonstrated a trend for a decrease in the respiration rate, lung ventilation, oxygen consumption, and a relative increase in the exhalation time. With respect to the arterialized blood gases, a significant decrease in PaO2, an increase in PaCO2 and in the O2 alveolar-arterial difference were seen during the 49-day head-down tilting. During the 182-day head-down tilting a further increase in the CO2 arterio-alveolar difference was noted. These changes suggest shifts of the ventilation-perfusion ration in the lungs and, probably, disturbances of central regulation of respiration induced by head-down tilting. During the recovery period the above changes diminished gradually and disappeared by the 14th and 30th day after the 49- and 182-day head-down tilting, respectively.