The Ventilatory Response to CO₂ of Patients with Diffuse Pulmonary Infiltrations or Fibrosis

1. We have used the rebreathing method to examine the respiratory response to CO₂ in five normal subjects and twelve patients with diffuse pulmonary infiltration or fibrosis. The response to CO₂ was measured in terms of both ventilation and mechanical work rate.

2. The response to CO₂ was, on average, reduced in the patients compared with the normals but the patients had to perform more mechanical work to achieve a given level of ventilation.

3. Six patients had an abnormally low resting mixed venous Pco₂ and four of these also had an abnormally low response to CO₂.

4. The pattern of breathing was identical in patients and normals.

5. The results indicate that the reduced ventilatory response represents a true loss of CO₂ sensitivity and is not simply due to mechanical limitation; but the paradox in some patients of resting hyperventilation and a low level of CO₂ responsiveness is unexplained.