Effect of chronic airflow limitation on resting oxygen consumption

The work of breathing in patients with severe chronic airflow limitation is increased even at rest but little is known about the magnitude of this increase. Resting oxygen consumption (VO2), carbon dioxide production (VCO2), and respiratory quotient (RQ) were measured in 13 patients with severe chronic airflow limitation (mean FEV1 0.78 1, vital capacity 2.1 1) and compared with those of 13 age, weight, and height matched control subjects. Whereas mean RQ was the same in the two groups (0.82), mean VO2 and VCO2 were higher in the patients (+ 18 ml min-1 and + 15 ml min-1 respectively). When VO2 was standardised for body surface area it was 10.9% higher in the patients (p less than 0.05). If the increased resting VO2 in these patients were solely due to increased activity of the respiratory muscles, it would represent a fourfold increase in the oxygen cost of breathing.