Chemoreflexes From the Heart and Lungs

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Abstract
A number of chemical substances, injected intravenously, cause a profound fall of blood pressure and heart rate, and temporary arrest of respiratory movement; these phenomena are abolished or greatly reduced by cutting the vagi and are reflex in origin. In order to explain the observations, at least 3 reflex mechanisms must be postulated: 1) the coronary chemoreflex, a reflex fall of blood pressure and heart rate caused by injection of certain substances into the coronary circulation (the Bezold-Jarisch effect); 2) the pulmonary depressor chemoreflex, a reflex fall of blood pressure and heart rate elicited by an action on sensory receptors in the lungs; and 3) the pulmonary respiratory chemoreflex, a temporary arrest of breathing which is also due to an action on sensory receptors in the lungs. In addition, the activity of the pulmonary stretch receptors of the Hering-Breuer inflation reflex may also be altered by injection of very small doses of chemical substances. The criteria which must be satisfied before concluding that substances injected into the circulation excite any one of these chemoreflexes are described and their possible physiological significance is discussed.