Bird Respiration: Flow Patterns in the Duck Lung

Abstract

ABSTRACT A heated thermistor probe was designed to determine the direction of air flow in the respiratory system of birds. The probes did not significantly affect the respiratory rates, tidal volumes, or body temperatures of birds implanted with the probes as compared to unimplanted birds. Air-flow directions were determined in the primary bronchus, the craniomedial secondary bronchi, and the caudodorsal secondary bronchi in the lungs of ducks which were either unanaesthetized and at rest, anaesthetized, or panting due to heat load. The recorded air-flow directions suggested the following patterns of air flow in the duck lung for resting respiration. During inspiration air flows to the posterior air sacs directly from the primary bronchus (the most direct route), without passing through the tertiary bronchi, while air flows towards the anterior air sacs via the caudodorsal secondary bronchi and the tertiary bronchi (thus by-passing the most direct route, the craniomedial secondary bronchi connecting these sacs to the primary bronchus). During expiration air flows from the anterior sacs to the primary bronchus via the craniomedial secondary bronchi (the most direct route), but from the posterior sacs through the tertiary bronchi and through branches of the craniomedial secondary bronchi to the primary bronchus (by-passing the most direct route, the portion of the mesobronchus posterior to the craniomedial bronchi). The patterns established for panting and anaesthetized respiration were very similar to those described for resting respiration. There was no indication of an effective shunt operating during panting to avoid excessive ventilation of the exchange surfaces of the lung. Flow in the tertiary bronchi appeared to be in the same direction during both inspiration and expiration (from the caudodorsal secondary bronchi towards the craniomedial secondary bronchi). Such unidirectional flow would permit the operation of a counter-current exchange system, provided that the blood vessels are arranged appropriately around the parabronchi.