INFLUENCE OF VAGAL AFFERENTS ON DIPHASIC VENTILATORY RESPONSE TO HYPOXIA IN NEWBORN LAMBS

The effect of vagal afferents on the ventilatory response to hypoxia w as studied in eleven awake newborn lambs. Tests were repealed before a nd after vagotomy in the same lambs in two conditions: with intact upp er airways and after intubation. During hypoxia, a diphasic pattern of ventilatory response was observed in both vagotomized and intact lamb s. However, face mask-breathing vagotomized lambs had a blunted increa se in ventilation (VI) 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 aboli shed after vagotomy. After intubation, expiratory braking disappeared and, consequently, magnitude of the VI response to hypoxia was similar in intact and vagotomized lambs. These changes were due to improved t idal volume response in vagotomized intubated lambs (P < 0.002) with n o significant change in f response. We concluded that, in awake newbor n lambs, vagal afferents are essential for maintaining the pattern and the magnitude of the ventilatory response to hypoxia, the latter by c ontrolling the motor output to the larynx.