Journal of Applied Physiology, Vol 65, Issue 4 1563-1571, Copyright © 1988 by American Physiological Society
Metabolite changes in the loaded hypoperfused and failing diaphragm
D. Lockhat, C. Roussos and C. D. Ianuzzo
Department of Medicine, Royal Victoria Hospital, McGill University, Montreal, Quebec, Canada.
Metabolite changes in the costal diaphragm were determined in anesthetized
dogs subjected to a moderate inspiratory elastic load and to reduced blood
flow. Diaphragmatic blood flow was reduced by occlusion of the descending
aorta and internal mammary arteries. The goal of this study was to
demonstrate that the failing diaphragm under these conditions shows
biochemical changes similar to that of skeletal muscle fatigue. Selected
metabolite concentrations were determined 1) during mechanical ventilation
and normal blood flow, 2) during blood flow reduction and inspiratory
loading when the ratio of airway pressure to diaphragmatic electromyogram
(Paw/Edi) had decreased by 50% (fatigue), and 3) at 1 h after restoration
of blood flow and mechanical ventilation (recovery). During fatigue,
glycogen, ATP, and phosphocreatine were 30, 50, and 50% of control levels,
respectively. Glucose 6-phosphate and lactate were two- and fivefold
higher, respectively, than control concentrations. During recovery, all
metabolites, except ATP and lactate, returned to control concentrations.
These changes were not seen in resting ischemic skeletal muscles or in the
diaphragmatic samples of the mechanically ventilated animals with
diaphragmatic blood flow limitation. We conclude that when the loaded and
hypoperfused diaphragm fails, as indicated by lower than control Paw/Edi,
metabolite changes similar to that observed in fatigued skeletal muscle
occur.
