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To the Editor:
—Digitalis affects the heart mainly in two ways: 1. It stimulates the pneumogastric center in the medulla, the resultant inhibition lessening the number of beats of the heart by prolonging the pause in diastole. Relaxation of fibers is increased; added rest is secured. Inhibition of some impulses from auricle to ventricle occurs —hence its value in auricular fibrillation. 2. It affects the heart muscle directly, increasing the strength of the ventricular contractions.Atropin, in sufficient dose, paralyzes the inhibitory terminations of the pneumogastric in the heart, and stimulation of this nerve therefore causes no change in the pulse after its administration. Drugs have no effect in stimulating the pneumogastric after atropin has been given in sufficient dose to paralyze the inhibitory terminations. What is the sufficient dose? Cushny says 1 mg. (about 1/65 grain), and that the administration of sufficient atropin to paralyze the pneumogastric involves unpleasant
McCollom WE. ACTION OF DIGITALIS AND ATROPIN, WITH ESPECIAL REFERENCE TO THE HEART. JAMA. 1919;72(3):214–215. doi:10.1001/jama.1919.02610030060031
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