Hypercapnic ventilatory control in patients with chronic airflow obstruction: a follow-up study

A four year follow-up study of ventilatory control has been performed in 50 patients with chronic airflow obstruction. Hypercapnia was induced by rebreathing, and both the ventilation and the mouth pressures produced during transient airway conclusion during inspiration were obtained. Both the chemoreceptor sensitivity to hypercapnia (delta P/delta PCO2) and the ventilatory response (delta V/delta PCO2) measured during the initial study were shown to be unrelated to prognosis when the outcome of these patients was determined four years later. A relationship between initial hypercapnia and survival was found. Twenty of the patients were restudied. No significant change occurred in the chemosensitivity to hypercapnia over the four year period. In the initial study and the follow-up study hypercapnia was also found to be associated with a reduced chemoreceptor sensitivity. Although both chemosensitivity to hypercapnia and survival were found to be separately related to arterial CO2 tension, there was no direct relationship between them. These results suggest that any possible influence of chemosensitivity on survival is likely to be overshadowed by other factors.