Abstract
Marked bradycardia with pulse rates from 30 to 50 per minute is produced in normal young adults by therapeutic doses (3 to 10 mg subcutaneously) of neosynephrin—l-a-hydroxy-β-methylamino-3 hydroxy ethylbenzene hydrochloride (Keys and Violante 1 ). The effect persists for 30 to 60 minutes or more and is not attended by any symptoms or sensations of cardiac or respiratory embarrassment. Since repeated trials failed to disclose any significant change in the total oxygen usage during the bradycardia it seemed probable that the total minute output of the heart was not seriously diminished. If this were so there should be a very appreciable increase in the stroke output. We have investigated this question with the roentgenkymographic method of Keys and Friedell. 2
Trained normal young men and women subjects were used. All studies were made in the post-absorptive state in the early morning with the subject seated in a roller chair in a quiet room. When a roentgenkymographic exposure (R.K.G.) was made (66 inches), the chair was rolled into position and the subject cooperated only to the extent of holding the breath during the 1.5 second exposure. After a preliminary rest of 20 minutes or more, one or 2 R.K.G.S were made before injection of the drug. R.K.G.S were made subsequently when the bradycardia was well established—usually 10 or 15 minutes later—and when the bradycardia had begun to diminish. In some cases a final R.K.G. was made when the pulse and blood pressure were nearly normal again.
A striking alteration of the heart size was frequently apparent even from casual inspection of the resulting films. When the areas of the anterior-posterior projections were measured it was found that there is an increase of 5 to 20% or more during the period of bradycardia.
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