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.