THE RESPIRATORY EFFECT OF PROLONGED ANOXEMIA IN NORMAL DOGS BEFORE AND AFTER DENERVATION OF THE CAROTID SINUSES

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Abstract
The respiratory responses to pure N2, to gas mixtures of 14.5, 9.5 and 5.1% O2 in N2, and to cyanide injections were studied in 4 dogs before and in 2 dogs after carotid sinus denervation. After denervation the respiratory response to breathing pure N2 was abolished; the response to 9.5% and 5.1% O2 was absent during the first min.; during the 2nd and especially the 3rd min. the rate of breathing increased with no corresponding increase in depth; no marked respiratory response was obtained to 14.5% O2. Denervation abolished the respira- tory response to an immediately stimulatory dose of Na CN, but a definite stimulation followed injection of pyruvic acid cyanohydrin or prolonged intraven. infusion of NaCN. These exps. show that other mechanisms respond to respiratory stimulants after carotid sinus de-nervation. The response comes late and is more a change of rate than of depth. Thus the first reaction to acute anoxemia in unoperated dogs is through the carotid sinus mechanism, while the delayed response is probably through both the carotid sinus regions and other respiratory mechanisms.

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