Carbon Dioxide, Hypoxia, Epinephrine Cardiac "Sensitization" Tests

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Carbon Dioxide, Hypoxia, Epinephrine Cardiac "Sensitization" Tests

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Title: Carbon Dioxide, Hypoxia, Epinephrine Cardiac "Sensitization" Tests
Author: Lambertsen, CJ
Abstract: In tests for cardiac arrhythmia production by synthetic inhalants such as Chloroflurocarbons, epinephrine infusion is used to "sensitize" the canine heart in testing new compounds for arrhythmia inducing potential. Conference discussion raised the topic of cardiac sensitization and arrhythmia production by altered atmospheric carbon dioxide and oxygen composition, i.e., hypoxia and hypercapnia. EPA requested appraisal of a cited reference to a relevant study in dogs. This report provides additional information and conclusions.Studies of human exposure to increased atmospheric carbon dioxide, hypoxia or exercise indicate that normal physiologic responses include increased sympathetic nervous system activity, with its elevation of blood epinephrine and norepinephrine levels. With moderate degrees of hypoxia or hypercapnia or exercise, occurrence of ventricular premature contractions is rare and not remarkable. With high and prolonged exposures to carbon dioxide, or prolonged strenuous exercise while breathing carbon dioxide, the frequency of cardiac arrhythmias increases. It is generally considered that these are part of the composite responses to influences of the normal sympathetic nervous system activity, especially including the increased circulating epinephrine. It is further considered that the augmented sympathetic activity is induced by effects within the central nervous system, not by direct influences upon the heart. The resulting effects upon the heart (increased contractility, rate, output, extrasystoles) are therefore largely what would be produced by artificial intravenous infusion of epinephrine at rates producing blood levels equivalent to those in states of exercise or altered atmospheric composition.
Description: The items forming the Rubicon Research Repository Christian J. Lambertsen collection are generously donated by the Lambertsen Family. All items in this collection are released through Creative Commons Attribution + Noncommercial + ShareAlike (BY-NC-SA) licenses in an attempt to encourage the use of these works to further scientific understanding of physiology.
URI: http://archive.rubicon-foundation.org/10579
Date: 1993

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