Estimation of Respiratory Drive with Carbon Dioxide and Helium

Abstract

Fourteen patients with obstructive emphysema showed less rise in ventilation while breathing 3, 5, and 7% carbon dioxide than did 19 normal subjects. This may have been caused either by airway obstruction or by respiratory center depression. When helium replaced nitrogen as the balance gas, oxygen remaining at 21%, the patients increased their ventilation as much as the normal subjects. Helium has been shown to reduce airway resistance, and these results suggest that in this group of patients airway obstruction was the important cause of decreased ventilation. Measurement of the ventilatory response to carbon dioxide and helium offers a promising means of differentiating between respiratory-center depression and airway obstruction.