Blood gases and acid-base balance in healthy women under 9-day isolation in closed-environment living

Nowadays, chronic exposure to moderately elevated CO2 is considered to be one of the most important factors causing some disorders in astronauts and cosmonauts on long-term space flights. Among these disorders are vision impairment and intracranial pressure (VIIP) syndrome, increased intracranial pressure, and metabolic consequences induced by microgravity. The objective of the study was to analyze blood gases and acid-base balance in women under 9-days isolation in closed-environment living. It was a part of international experiments simulating flights to the Moon. Materials and Methods. Six practically healthy women were examined before, during and after 9-day isolation. At the same time 4 women (a control group) were examined under normal conditions within the same time limits. The main indicators of acid-base balance (pH, PaCO2, PaO2, BE) were measured. Respiratory minute volume at rest (spirometry test) was conducted; maximum breath holding time after both inhalation and exhalation was measured. Results and Discussion. The data obtained demonstrated that the breathing pattern, breath holding time and acid-base balance had no marked changes in both groups. However, the decrease of pH and increase of PaCO2 were observed on the 7th day in closed-environment living. Changes of these parameters were not accompanied by the activation of compensatory metabolic pathways. The revealed changes in pH and Pa-CO2 were probably due to reduced air ventilation in the chamber and accumulation of CO2, although the air in the closed chamber was connected with the air in the ventilated one. During the recovery period, all the investigated parameters got back to initial levels. Conclusion. 9-day stay of healthy women in a relatively isolated environment with ambient air was not accompanied by evident changes in breathing pattern, pulmonary ventilation volume and acid-base balance parameters. Relative increase in PaCO2 (within physiological range) in blood on the 7th day in closed-environment living was probably due to reduced air ventilation in the chamber during the trial. The results obtained confirm the need for further investigation under prolonged isolation in an airtight module.