Relation between work output of respiratory muscles and end-tidal CO2 tension

Abstract

End-tidal CO₂ tension, pulmonary ventilation, and work output of respiratory muscles were determined in six normal subjects breathing various mixtures of carbon dioxide in air, with three graded resistances added to both inspiration and expiration. In two individuals, the resistances were also added separately to inspiration or expiration. A linear relationship was found between work output of inspiratory muscles and end-tidal CO₂ tension; this relationship was uninfluenced by added resistance. No consistent relationship was observed between either ventilation or work output of expiratory muscles and end-tidal CO₂ tension. These results suggest that carbon dioxide controls directly the activity of inspiratory muscles alone and that the activity of expiratory muscles is only coincidentally involved. The possible role of intrinsic properties of respiratory muscles and of nervous mediation in the control of breathing is discussed. Submitted on October 22, 1962