Modification of the Atrial Sound by the Cold Pressor Test, Carotid Sinus Massage, and the Valsalva Maneuver

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Abstract
Three procedures were investigated for their effect on the atrial sound. The cold pressor test caused the atrial sound to appear in one subject and to become louder in 15 of 28 subjects; it increased the atriosystolic murmur in two subjects with mitral stenosis. These effects were at least partly independent of changes in arterial diastolic pressure and heart rate. Carotid sinus massage decreased the atrial sound in five of 10 subjects and produced an unexplained increase in one. Following release of the strain of the Valsalva maneuver the atrial sound became louder than before the strain; in seven subjects its amplitude increased progressively and the sound also migrated from the first heart sound. Increase of the atrial sound by the cold pressor test is attributed to sympathetic action upon peripheral veins, arteries, and the left atrium; its decrease by carotid sinus massage, to parasympathetic action upon these structures and the cardiac pacemaker; and its increase following release of the strain of the Valsalva maneuver, to combined increases of venous return and cardiovascular sympathetic activity. The proposed explanations require investigation by more direct methods. Sympathetic activity may contribute to the increased amplitude of atrial sounds during states of exercise and heightened emotion and, in part, for their frequent occurrence in thyrotoxicosis.