THE OXYGEN CONSUMPTION AND EFFICIENCY OF THE RESPIRATORY MUSCLES IN HEALTH AND EMPHYSEMA*

Abstract

The oxygen consumption of the respiratory muscles was measured in 16 normal and 22 emphysematous subjects. In the emphysematous subjects the oxygen consumption of the respiratory muscles is considerably higher than in the normals. In addition, small increases in ventilation are associated with marked increases in oxygen consumption in the emphysematous patient. The efficiency of the respiratory muscles was determined in 9 normal and 7 emphysematous subjects. The efficiency was considerably lower than the normal in the patients with emphysema. The total mechanical work at rest, measured indirectly, tended to be less than the normal in the patients with emphysema, whether expressed as work per minute or work per liter of ventilation. Though the total mechanical work done on lungs and thorax tends to be less at low ventilations in patients with emphysema than in normals, the oxygen cost of breathing is 4 to 5 times greater because of the markedly reduced efficiency of the respiratory muscles. With increases in ventilation there is a disproportionate increase in oxygen consumption of the respiratory muscles in emphysema. This may help to explain the disability present in pulmonary emphysema and the inability of the severely emphysematous patient to meet the increased energy demands of exercise and infection.