IMPROVED RECOVERY FROM LARYNGEAL-STIMULATION-INDUCED APNEA BY ALPHA-ADRENERGIC BLOCKADE IN ADULT-RABBITS

The apnea triggered by laryngeal stimulation (LS) is associated with a redistribution of blood flow towards the heart and the brain that dep ends upon peripheral vasoconstriction. The circulatory component of th e response to LS has been shown to be reduced following injection of l arge dose of beta-adrenergic agonist that more intriguingly blunted th e ventilatory response as well. To test whether the reduction of LS-in duced apnea could be related to the decreased magnitude of the periphe ral vasoconstriction, the effects of the a-adrenergic antagonist urapi dil on the ventilatory and blood pressure responses to LS were studied in 6 adult rabbits. alpha-Adrenergic blockade reduced both the rise i n blood pressure and the magnitude of hypopnea induced by LS. These re sults suggest that the circulatory component of the laryngeal chemoref lex, i.e. the peripheral vasoconstriction, contributes to the magnitud e of the ventilatory depression.