Abstract
According to Heymans 1 and Koch, 2 , 3 changes in pressure within the carotid sinuses set up reflexes which have a powerful influence upon the respiratory center. Their observations are fully confirmed by the results of perfusion of the carotid sinuses of 15 dogs, 5 rabbits, and 4 cats, with Locke's solution or with blood from a donor animal, by means of a pump. Heymans' 1 conclusion, that the respiratory stimulant effect of occlusion of both common carotids is entirely the result of carotid sinus reflexes, is not confirmed; denervation of the carotid sinuses, while usually diminishing and sometimes abolishing the stimulant effect upon breathing, occasionally does not decrease or may actually increase the respiratory effect of the occlusion, in decerebrate cats and narcotized dogs; hypertension as a result of the denervation introduces a new factor in that carotid occlusion does not reduce cerebral blood-flow to as low a level as before; a negative result from the occlusion does not then prove that a previous positive result was entirely due to reflexes from the carotid sinuses. Carotid occlusion lowers endosinusal pressure by 36% (average) in dogs; it reduces cerebral (torcular) venous outflow by about 45% (average) in dogs. Occlusion of the vertebral arteries reduces torcular outflow only by 25% (average) in dogs, and in one animal it had no measurable effect; absence of circulatory and respiratory stimulation from occlusion of the vertebrals does not therefore necessitate the conclusion that the stimulant effects of carotid occlusion are due entirely to reflexes from the carotid sinuses.
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