THE CAROTID-MANDIBULAR REFLEX IN ACUTE RESPIRATORY FAILURE

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Abstract
Gasping of the severed rat head has been used by several workers as an index of activity of medullary respiratory centers. Present expts. establish the reflex character of gasping in several types of anoxia and locate the actions of anoxia and hypercapnia in the reflex arc. After decapitation, cyanide admn., or inhalation of O2-free gas mixtures, gasping occurs when the carotid bodies remain functionally connected with the medulla but is entirely absent when they are disconnected. Gasping is terminated by central failure. Discharge time (from first to last gasps) decreases with age. For 11-day old rats inhaling pure N, it averages 142 secs., as compared with 200 after decapitation. Addition of CO2 to the N2 (but not to O2) increases discharge time, to a maximum of 320 secs. at 35% CO2. That the prolongation depends on anaerobic processes is shown by the ability of iodoacetate to cut discharge time to 25 secs., whatever the CO2 conc. By perfusing the carotid bodies of one rat with the blood of a 2d and varying independently the gas inhaled by each, the medullary centers and the carotid bodies of an animal were exposed to different conditions. Anoxia both of the brain and the carotid body must be present for gasping to occur. The potentiating action of CO2 is exclusively on the carotid body.

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