THE MEDULLARY ORIGIN OF RESPIRATORY PERIODICITY IN THE DOG

Abstract

Dogs decerebrated by transection after occlusion of the carotids and the basilar artery at the lower border of the pons universally exhibit apneustic breathing, after transection encroaching on the pons and vagotomy. Apneustic breathing, consisting of alternate periods of inspiratory spasm and expiration at slow rates (1 or 2/min. or less), is capable of maintaining life in the dog for several hrs. Animals showing apneustic breathing resume "normal" breathing terminally as the prepn. deteriorates. When a further section encroaching on the medulla is made in "apneustic" animals, the phases of inspiratory spasm are converted into periods of phasic "normal" inspiration and expiration akin to Biot''s breathing, often reverting to "normal," or "normal" breathing appears immediately. Intraven. injn. of cyanide produces apneusis or prolongs and intensifies it. When the carotid bodies and sinuses are denervated, apneusis does not appear after pontine decerebration and vagotomy; "normal" or Biot''s breathing alone occurs. It is concluded that (a) the medullary respiratory center can maintain periodic respiration in the absence of the pons and the vagi;(b) apneusis represents an exaggerated inspiratory response to anox-emic stimulation via the carotid bodies "occluding" the normal respiratory action of the medullary center; and (c) such enhance-ment probably represents unchecked activity of the pontine por-tion of the midbrain facilitatory center.