Glycogen content in neonatal diaphragmatic fibers in response to inspiratory flow resistive loads

To study intramuscular glycogen use with increased work loads in the neonatal diaphragm, unanesthetized lambs were subjected to severe inspiratory flow resistive loads. With these loads, transdiaphragmatic pressure and arterial CO2 tension increased several fold above baseline and then remained stable for a period of 10-30 min. This was followed by a decrease in transdiaphragmatic pressure and a marked increase in arterial CO2 tension with severe acidosis. Intramuscular glycogen content was determined histochemically by the periodic acid-Schiff reaction and was quantified microphotometrically by the fiber types (type I, IIa, or IIc) present in the lamb costal diaphragm. Glycogen content in the control diaphragm was greatest in type IIa fibers and lowest in type I fibers. With severe inspiratory flow resistive loads, the greatest decrease in glycogen content was in type IIa fibers, followed by type IIc and type I fibers. Therefore, our data suggest that in the neonatal lamb subjected to inspiratory flow resistive loads the diaphragm uses intramuscular glycogen during increased work loads. These data do not indicate that the marked depletion of glycogen in the diaphragm is the cause of the decrease in diaphragmatic force.