Abstract
Recently Harrison and Leonard 1 have studied the effect of injecting digitalis upon the cardiac output in normal dogs, and found that it diminished. From these experiments they drew the inference that digitalis decreased cardiac output also in patients suffering from heart failure and that its beneficial effect in them was due to this action. It seemed to us that this inference was not justified unless the effect of digitalis upon the size of the heart was also studied.
In making our experiments in dogs the cardiac output was estimated according to the Fick 2 principle. Samples of arterial blood were taken from a femoral artery and those of mixed venous blood from the right ventricle by means of a special cannula inserted into that chamber through the right external jugular vein. 3 The oxygen consumption was measured with a Benedict spirometer equipped with a graphic recording drum. All the dogs were trained in order to accustom them to these procedures.
Tincture of digitalis (Upsher Smith) was injected intravenously. We injected 25 to 30% of the calculated lethal dose for cats which has been regarded as equivalent to the therapeutic dose in man. 4 This dose is multiplied by 1.16 to arrive at a comparable quantity for dogs. 5 Roentgenograms were taken whenever the cardiac output was measured.
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