THE RELATIONSHIP OF OXYGEN COST OF BREATHING TO RESPIRATORY MECHANICAL WORK AND RESPIRATORY FORCE

Abstract

In six normal subjects estimates were made of the oxygen cost both of voluntary hyperventilation and of breathing against increased airway resistance. The oxygen cost per unit respiratory mechanical work was greater for resistance breathing than for hyperventilation. By contrast the oxygen cost per unit respiratory force was greater for hyperventilation. When allowance was made for the force exerted against the chest wall (in one subject) the oxygen cost per unit force was described by a single slope for both forms of activity. Respiratory force seemed a more logical parameter to relate to oxygen cost than respiratory mechanical work. The oxygen cost of voluntary hyperventilation was also measured in 4 subjects with heart disease and 5 subjects with obstructive respiratory disease, all with disturbances of respiratory mechanics. The oxygen cost of hyperventilation was normal in the cardiac subjects. In the subjects with chest disease it was high due partly to increased respiratory work per unit volume ventilated and partly to increased oxygen cost per unit respiratory mechanical work. This reduced efficiency was likely the result of mechanical disadvantage of chest muscles resultant on hyperinflation as the oxygen cost per unit respiratory force was also high in these subjects.