Measurement of diaphragmatic blood flow and oxygen consumption in the dog by the Kety-Schmidt technique.

To assess energy expenditure of the diaphragm directly, a method was devised for percutaneous catheterization of the left inferior phrenic vein in dogs. Necropsy studies, including retrograde injection of india ink and measurement of radioactivity in diaphragmatic muscle strips, suggested that the territory drained by the inferior phrenic vein was uniformly perfused, and that there were no major anastomoses between this bed and adjacent ones. Diaphragmatic blood flow ( Q di) was calculated from the integrated diaphragmatic arteriovenous difference of (85)Kr by the Kety-Schmidt technique. Diaphragmatic oxygen consumption ( Vo(2) di) was determined as the product of Q di and the diaphragmatic arteriovenous oxygen content difference [(A-V)O(2) di]. When lightly anesthetized dogs breathed quietly, Q di was 22+/-SD 6 ml/min/100 g, (A-V)O(2) di was 6.1+/-SD 2.5 ml/100 ml, and VO(2) di averaged 1.2+/-SD 0.3 ml/min/100 g. This represented 1.0+/-SD 0.2% of total body oxygen consumption. VO(2) di remained relatively constant during quiet breathing, whereas Q di varied directly with cardiac output and reciprocally with (A-V)O(2) di. The oxygen consumption of the noncontracting diaphragm was 60+/-SD 20% of the level measured during quiet breathing. The energy expended by the diaphragm to support simple hyperventilation was small. A 100% increase in minute ventilation, induced by inhalation of 5% CO(2) in 21% or 14% O(2), increased Q di 13%, (A-V)O(2) di 19%, and VO(2) di 40%. The diaphragm consumed 0.13+/-SD 0.09 ml O(2) for each additional liter of ventilation. In four dogs, pneumonia appeared to increase VO(2) both by increasing minute ventilation and by increasing the energy cost per liter of ventilation.