Comparative study of the ventilatory responsiveness to CO2 in bronchitic and emphysematous patients with chronic...

The comparative ventilatory responsiveness to CO2 was studied in 13 chronic bronchitics and 14 emphysematous patients, all exhibiting respiratory insufficiency and with FEV1 less than 1,500 ml. The gas inhaled was enriched with oxygen (F1O2 =0.6) and contained 6% CO2, and measurements were taken when the patients had reached a stable state. The ratio delta VE/deltaPaCO2, which represents the ventilatory responsiveness to CO2, was higher in the emphysematous patients (1.18+/-0.51 liters-min-1. Torr-1) than in the bronchitics (0.76+/-0.34, p less than 0.025), but the deviation on either side of the mean was large in each group. The ventilatory responsiveness to CO2 was proportional to the initial PaCO2, FEV1, total airways resistance, total pulmonary work and especially to inspiratory mechanical work done on the lung ( r=-0.73, p less than 0.001). The difference in ventilatory responsiveness to CO2 between the bronchitic and emphysematous patients may be explained by the difference in energy expended in breathing. It was not possible to exclude an effect due to a difference in sensitivity within the respiratory centers, since inspiratory mechanical work was not measured during CO2 inhalation. It was thought likely that mechanical factors play a triggering role, in that they cause a fall in ventilatory responsiveness to CO2 and hypercapnia, the latter causing the central hyposensitivity which maintains the retention of CO2.