Tolerance Curves of Carbon Dioxide during Rebreathing in Normal Subjects, Pulmonary Emphysema and Obesity

The tolerance curves for CO2 were investigated in 11 normal subjects, eight patients with pulmonary emphysema and seven with obesity using the rebreathing method for CO2. The tolerance curves were shifted to the right in emphysema and obesity in contrast to normal subjects for the beginning of hyperventilation by higher partial pressures of alveolar O2. The correlation of these values with PaCO2, was significant only in obesity. The character of the curves and the degree of hyperventilation were not significantly different from that in normal subjects. This confirms the postulate that the decreased response of the respiratory center to CO2 is the primary actor in the decreased respiratory response to CO2 in emphysema and obesity. The values of partial pressures of O2 and CO2 at the termination of the investigation confirmed the elimination of hypoxic stimulus.