Relationship between phrenic nerve activitv and ventilation

ELDRIDGE, FREDERIC L. Relationshz) between phrenic nerve activity and ventdation. Am. J. Physiol. 221(Z) : 535-543. 197 1 .-Phrenic nerve discharges were recorded in anesthetized cats simultaneously with a range of tidal volumes. Nerve impulses were processed in a variety of ways. Total impulses per breath and peak impulse frequency correlated poorly with tidal volume. Integrated electrical activity per breath showed an improved, often linear, correlation with tidal volume, but was too dependent upon inspiratory duration to be a satisfactory correlate of volume. Only integrated phrenic activity measured during the 0.1 set coincident with the peak of inspiration showed a consistently linear relationship with tidal volume under a variety of circumstances, including increasing barbiturate dosage, vagal section, and spinal cord transection below the phrenic roots. Analysis of the relationships between phrenic impulse rate and integrated electrical activity shows that with increased tidal volume there is a progressive increase in size of phrenic action potentials which correlate in turn with the size of the diaphragmatic motor unit.