THE CIRCULATORY RESPONSES OF CHRONIC SPINAL DOGS TO ETHER ANESTHESIA

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Abstract
The adm. of ether to dogs with the spinal cord sectioned below the 10th thoracic segment produces the same changes in blood pressure and heart rate that are shown by normal animals. The inhalation of ether by dogs with the spinal cord cut above the 7th thoracic segment results in an immediate fall in blood pressure. This is associated with a marked bradycardia. During surgical anesthesia the mean blood pressure ranges between 40 and 65 mm. Hg. In this stage the degree of cardiac acceleration is related to the amt. of the residual cardioaccelerator outflow which remains connected with the suprasegmental centers. The adm. of ether to vagotomized high spinal dogs (cord section C-6 to T-l) causes no change in heart rate and produces the same blood pressure responses that are shown by high spinal dogs with intact vagi. Etherization of dogs with bilateral splanchnic nerve section produces in general the circulatory responses observed in normal dogs. For the maintenance of normal blood pressure during ether anesthesia, the suprasegmental control of the sympathetic nervous system must extend below the 6th thoracic segment.

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