Temporal relationships of ventilatory failure, pump failure and
diaphragm fatigue.
Sassoon, Catherine S. H., Steve E. Gruer, and Gary C. Sieck.
Department of Medicine, Veterans Affairs Medical Center, Long
Beach, California 90822, the University of California, Irvine,
California 92717, and the Departments of Anesthesiology and
Physiology, Mayo Clinic, Rochester, Minnesota 55905
APStracts 3:0106A, 1996.
The time course of ventilatory failure, pump failure and diaphragm
peripheral fatigue, was determined during the application of external
inspiratory resistive loads (IRL) in anesthetized rabbits. Pump
failure is defined as the inability of the diaphragm to sustain the
expected force under IRL. To assess contractile fatigue,
transdiaphragmatic pressures (PDI) generated by bilateral phrenic
nerve stimulation at 75 Hz (PDI-75) and 20 Hz (PDI-20) were measured.
The amplitude of evoked diaphragm electromyographic (EMG) signals
(EMGcap) was measured to assess neurotransmission failure. The rate
of rise of spontaneous diaphragm EMG (EMGd/TI) was used as an index
of respiratory drive. Ventilation was evaluated together with
arterial blood gases. During IRL, EMG/TI increased, and there was a
progressive hypercapnic acidosis and hypoxemia indicating ventilatory
failure. In contrast, PDI-75 and PDI-20 were stable until the time of
respiratory arrest (apnea) when they decreased by 34% and 45%,
respectively. EMGcap remained unchanged throughout the IRL and
decreased only slightly at the time of apnea. We conclude that IRL
induces progressive ventilatory failure long before any contractile
fatigue of the diaphragm or pump failure occurs. This suggests that
ventilatory failure is due to central fatigue while pump failure
(apnea) is attributable to multiple factors.
Received 27 January 1995; accepted in final form 31 January 1996.
APS Manuscript Number A107-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96