Breathing during exercise in dogs - passive or active?.
Ainsworth, Dorothy M., Curtis A. Smith, Kathleen S. Henderson, and
Jerome A. Dempsey.
Dept. Clinical Sciences; CVM-Cornell University; Ithaca, NY 14850
and The John Rankin Laboratory of Pulmonary Medicine, Dept.
Preventive Medicine, University of Wisconsin, Madison, WI 53705
APStracts 3:0130A, 1996.
The activation patterns of the costal and crural diaphragm and
transversus abdominis (TA) muscle, and their relationship to
esophageal pressure (Pes) changes and footplant were examined in five
chronically-instrumented dogs who breathed at high frequencies at
rest and during exercise. In two tracheostomized dogs, measurements
were made of diaphragmatic length via sonomicrometry and of airflow,
and related to diaphragmatic electrical activity and Pes. Dogs
exhibited either a high frequency breathing pattern, characterized by
Pes changes occurring at 2-6 Hz, or a mixed frequency breathing
pattern characterized by low amplitude Pes oscillations (4-6 Hz)
superimposed upon a slower breathing rate of 0.5-1 Hz. Regardless of
the type of breathing pattern elected or of the various
breathing:stride frequency ratios observed during exercise, decreases
in Pes were always associated with phasic EMG activity of the costal
and crural diaphragm and with phasic diaphragmatic muscle shortening.
The TA EMG activity coincided with an increasing Pes from peak
negative values in resting dogs and exhibited both an expiratory and
a locomotory modulation during exercise. Although footplant may have
contributed to some airflow generation when dogs utilized the mixed
frequency pattern, these data demonstrate that the movement of air
into and out of the lungs in stationary or exercising dogs requires
phasic neural activation of the diaphragm and other respiratory
muscles.
Received 7 August 1995; accepted in final form 26 February 1996.
APS Manuscript Number A863-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96