THE OXYGEN COST OF BREATHING IN PATIENTS WITH CARDIORESPIRATORY DISEASE

Abstract

O2 cost of breathing (.ovrhdot.VO2resp) was measured in 13 patients with cardiorespiratory disease requiring artificial ventilation as the difference between the O2 consumption during spontaneous respiration (.ovrhdot.VO2tot) and that during artificial ventilation (.ovrhdot.VO2nonresp). Average .ovrhdot.VO2tot was 312 .+-. 90 ml/min (mean .+-. 1 SD); .ovrhdot.VO2nonresp was 246 .+-. 38 ml/min (P < 0.01). Average .ovrhdot.VO2resp was 75 .+-. 82 ml/min (range, 8-286), representing 24% of .ovrhdot.VO2tot or 8.7 .+-. 8.9 ml O2/l ventilation. In normal resting adults, .ovrhdot.VO2resp is 5-10 ml/min, .apprx. 1-3% .ovrhdot.VO2tot or 0.25-2.5 ml O2/l ventilation. .ovrhdot.VO2resp had an exponential relationship with FEV1 [1 s forced expiratory volume] (r = 0.97) in 6 patients who had had prior spirometry. Because minute ventilation was normal in these patients (8.8 .+-. 2.2 l/min), the elevated .ovrhdot.VO2resp represented an increase in the work of breathing and a decrease in the efficiency of the respiratory muscles. Where O2 transport is compromised, artificial ventilation may release substantial quantities of O2 for use by other body systems.