Mouth breathing in chickens under rebreathing conditions, cervical vagotomy of heat load.

By recording the lower beak movement, open-mouth breathing was monitored in adult hens restrained in a supine position with the cannulated trachea under rebreathing conditions, bilateral cervical vagotomy or heat load. Tidal volume and respiratory carbon-dioxide and oxygen contents were recorded simultaneously. The beak movement can be a significant indication of hypercapnia and/or increase in respiratory CO2 content, but not of hypoxia or decrease in respiratory O2 content. Vagotomy causes big oscillatory movements of the beak, which do not mainly depend on hypercapnic hypoxia induced by the vagotomy. If the dysfunction of the vagus is aggravated progressively, it will be unable for the pattern and amplitude of beak movement to be any differential indication of this dysfunction from hypercapnia and/or increase in respiratory CO2 content seen at respiratory failure. Two patterns of beak movement are noticed. One appears at an early stage of beak movement and at a certain direct level superimposed with or without small beak-oscillation. The other indicates a bigger oscillatory beak movement than the former. This oscillatory movement is synchronous with the inspiration after vagotomy and hypercapnia. This is the case with hyperthermia at a remarkably high breathing frequency. The amplitude of beak movement is not always proportional to the tidal volume. The onset and end of inspiration cannot precisely be indicated by those of a beak movement.