A clinical method for assessing the ventilatory response to hypoxia.

A method for assessing the ventilatory response to hypoxia suitable for clinical application was developed. We used a rebreathing method to create progressive hypoxia, kept Pco2 constant, and plotted ventilation against oxygen saturation rather than against oxygen tension. Subjects rebreathed from a 6-liter bag initially containing 7 per cent CO2, 24 per cent O2, and the balance N2. End-tidal Pco2 was held at “mixed venous” level by a variable CO2 absorbing bypass. Rebreathing was continued until end-tidal Po2 fell to 30 to 40 mm Hg (saturation 50 to 60 per cent). Oxygen saturation was measured continuously by ear oximetry. The interindividual range in 9 normal subjects for the change in expired ventilation divided by the change in oxygen saturation was 0.26 to 4.12 liters per min per 1 per cent fall in oxygen saturation (So2), and in all studies, linear plots were obtained. In repeated studies, variation in response within subjects was significantly less than between subjects (F = 10.15; p < 0.01). Venti...