Influence of vagal afferents on diphasic ventilatory response to hypoxia in newborn lambs.

Abstract The effect of vagal afferents on the ventilatory response to hypoxia was studied in eleven awake newborn lambs. Tests were repeated before and after vagotomy in the same lambs in two conditions: with intact upper airways and after intubation. During hypoxia, a diphasic pattern of ventilatory response was observed in both vagotomized and intact lambs. However, face mask-breathing vagotomized lambs had a blunted increase in ventilation (V i ) to hypoxia as compared with intact lambs ( P = 0.0001) and they showed an expiratory braking during all hypoxic time. Furthermore, the normal increase in frequency (f) to hypoxia was abolished after vagotomy. After intubation, expiratory braking disappeared and, consequently, magnitude of the V i response to hypoxia was similar in intact and vagotomized lambs. These changes were due to improved tidal volume response in vagotomized intubated lambs ( P