[Role of external respiration in the formation of the autonomic component in motion sickness]

Time course variations in the ventilation and gas exchange functions of the lungs, gas composition and acid-base equilibrium of blood were investigated in 22 male test subjects, aged 27-49 years, who were kept in the head-down position (-8 degrees) and rocked in parallel swings. The subjects susceptible to motion sickness developed lung hyperventilation and concomitant alveolar-arterial hypocapnia and respiratory alkalosis which may potentiate a symptom-complex of vestibular disorders. To control hypocapnia, the subjects used a hypercapnic breathing mixture (4% CO2, 96% air). This eliminated the above changes in the gas composition and acid-base equilibrium of blood, and in 7 out of 10 subjects alleviated vestibular symptoms and elongated the time of motion tolerance. In addition, the prophylactic effect of hypercapnic exposure showed individual variations which seem to be associated with individual sensitivity of the respiratory center to hypercapnic stimulation.