Ventilatory Responces to Inspired CO₂ in Patients with Cystic Fibrosis

¹ Departments of Pediatrics, University of Miami, Miami, Florida; Children's Hospital of San Francisco

A rebreathing method with 100 percent oxygen was used to study the ventilatory response to an increase in alveolar Pco₂ in 23 patients with cystic fibrosis. The patients were divided into two groups on the basis of two-minute nitrogen washout and maximal midexpiratory flow rate. Group 1 consisting of patients with markedly impaired functions and group 2 with less impaired functions were compared with the results of study of eight normal subjects. Initial end tidal Pco₂ levels were the same in all groups. With an increase in the Pco₂ during the rebreathing procedure group 1 had a diminished increase in ventilation, and group 2 had responses similar to those of normal subjects. Disturbances in the mechanics of breathing are implicated to contribute significantly to a diminished ventilatory response to CO₂.