AJP - Regulatory, Integrative and Comparative Physiology, Vol 262, Issue 5 879-R884, Copyright © 1992 by American Physiological Society
Role of lung inflation in control of air breath duration in African lungfish (Protopterus annectens)
A. I. Pack, R. J. Galante and A. P. Fishman
Center for Sleep and Respiratory Neurobiology, University of Pennsylvania, Philadelphia 19104-4283.
Studies were conducted in the African lungfish (Protopterus annectens) to
investigate the role of lung inflation on control of the duration of the
lung breath. The studies were done in decerebrate spinalectomized animals.
Two types of tests were performed: 1) a no-inflation test (airway occluded)
in which the lungs were not inflated during an air breath, and 2) an
inflation test in which the lungs were inflated at the onset of the lung
breath to different levels of intrapulmonary pressure (2.5, 5.0, 7.5, and
10.0 cmH2O). Lung inflation shortened the duration of the lung breath. The
relationship between intrapulmonary pressure and breath duration was
curvilinear and similar to the relationship between tidal volume and
inspiratory duration in mammals. Likewise, the relationship could be
described by a hyperbola with a linear relationship between intrapulmonary
pressure and the inverse of breath duration. This relationship was
essentially not affected by changing the composition of the gas used to
inflate the lungs: air, oxygen, or nitrogen. Vagotomy, however, largely
abolished the effect of lung inflation on breath duration. Because there is
such similarity between these results and effect of lung inflation on
control of inspiratory time in mammals, it is postulated that neural
circuits for control of respiratory timing were already developed and
similar in the lungfish. Because the muscles used in the lungfish to
ventilate the lung are totally different (buccal force pump) from those in
mammals, the neural circuits for timing control and those for shaping the
pattern of motor output appear to be separate.(ABSTRACT TRUNCATED AT 250
WORDS)
