SYMPATHETIC AND VAGAL INTERACTION IN EMOTIONAL RESPONSES OF THE HEART RATE

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Abstract
Changes in heart rate of unanesthetized dogs and cats, startled by a short, unexpected noise, were recorded electrically. The cardiac responses from normal animals were compared with those from the same animals after various nerves had been cut. Intact dogs and cats yielded a complex pattern of a sudden, high rise in heart rate, beginning immediately after the startle. This was successively followed by a sharp fall, more pronounced in dogs, a second rise of variable height, and thereafter, several undulations in rate until termination of the response in 2-3 min. Adrenaline plays a more prominent role in cats than in dogs; but its action in either sp. appears only after 12 sec. Dogs in which the vagi and depressors were cut and adrenaline excluded, showed pure accelerator activity. The response was similar to that of the normal in promptness and magnitude, but was without secondary fall or further undulations. In dogs and cats with the sympathetic cardio-ac-celerators removed and with adrenaline excluded, startle was promptly followed by inhibition of vagal tone. Cats in addition showed an acceleration that was greater than could be accounted for by loss of vagal tonic influence alone. The effect of respiration on cardiac rhythm is complex and may greatly affect the pattern of response. Apnea may cause a speeding of the heart or may be accompanied by a slowing.

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