Abstract
Head immersion under general anesthesia was performed in sixteen newborn lambs, ten adult rabbits and eight ewes in water at different temperatures (6 to 40 °C). Apnea or reduction in respiratory frequency, bradycardia and rise in arterial pressure occurred in all animals although free access to air was maintained through a tracheal cannula. The same phenomena were observed when water was applied to the larynx and glottis. Local anesthesia of the glottis or severing of the superior and external laryngeal nerves abolished the respiratory as well as the cardiovascular response to head immersion. It is concluded that (1) the “diving reflex” is present in adult rabbits and sheep; (2) the adjustments to diving are fully developed at birth in newborn lambs; (3) two of the afferent pathways of the diving reflex in the sheep are the superior and external laryngeal nerves. It is suggested that the inhibition of the respiratory movements in utero may be regarded as the expression of a diving reflex provoked by the contact of the glottis with liquid.
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