[Effect of head-down-tilt hypokinesia on pulmonary blood flow and gas exchange]

The purpose of the study was to investigate gas exchange and lung perfusion during 14-day head-down tilt and immediately thereafter. During head-down tilting pulmonary circulation increased, as suggested by zonal rheography of the lungs and by ECG (increase in the PII-III amplitude and width by 1-2 mm and 0.01-0.02 s, respectively). A significant decrease in O2 tension and a slight increase in CO2 tension of the arterial blood were detected. Immediately post-test pulmonary circulation declined and metabolic acidosis developed simultaneously. Our findings suggest that drugs reducing pulmonary hypertension can be recommended for emergency medical aid in space flight.