Caffeine effect on breathing pattern and vagal reflexes in newborn rabbits.

Ventilation, breathing pattern and vagal reflexes were studied in anaesthetized (pentobarbital) newborn rabbits aged 2-7 days before and after injection of 10 mg/kg of caffeine. With caffeine, tidal volume decreased and respiratory frequency increased but minute ventilation remained unchanged. Mean inspiratory flow increased only in the older rabbits. The breath-to-breath variability in tidal volume, mean inspiratory flow, inspiratory and expiratory times observed under control conditions was diminished in several animals following caffeine injection. Vagal pulmonary afferentation was not affected by caffeine. A facilitatory effect of caffeine on the central mechanisms controlling the breathing pattern was indicated by: (1) an enhanced Hering-Breuer expiratory-promoting reflex; (2) lack of effect on the Hering-Breuer deflation reflex; and (3) qualitatively similar effects of caffeine postvagotomy as prevagotomy.