The Relation Between Cardiac Size and Cardiac Output Per Minute Following the Administration of Digitalis in Normal Dogs

Studies on the Effect of the Action of Digitalis on the Output of Blood From the Heart. Iii. 12

“…It has also another consequence; the vigor of its action increases. If this consequence were not known from former experience (Cohn and Stewart (24,25,26)) it would have become apparent from the present ones in which the output of blood in diseased persons increases. The difference in the effect in the two types of heart, normal and pathological, results, so we think and as we have formerly stated, from the fact that normal hearts when under its influence become smaller but, being smaller pumps, expel smaller volumes, though contraction is more effective.…”

“…The subjects had been made familiar with the procedures and were not disturbed by them. After the first 24 hours they attended to their usual daily routines except on days of observation when they remained in bed to assure their being in a basal metabolic state. The initial cardiac output in all except one was normal (Subject 4) and agreed with previous measurements in each case (Tables 1 and 2, Figures 2, 3 and 4), with this exception, that the effect of the drug was of shorter duration.…”

The Effect of Digitalis on the Venous Pressure of Normal Individuals

“…Obviously, heart work is a function of the output per beat and is not, as Cohn and Steele suggest, measured by the oxygen consumption of the entire organism. Starling and Visscher (29) have demonstrated that diastolic volume varies with heart work, so that the decreased size of the heart observed by Cohn and Stewart (4,7) should occur as a result of the decreased output. In expelling equal quantities of blood, a small heart must make greater excursions than does a larger heart.…”

“…The observations on direction can be explained only by a peripheral mechanism of digitalis action; those on time support such a mechanlsm, for the change in venous pressure and cardiac output (like that in arterial pressure in dogs) is less prolonged than the effect on the T wave and conduction time; the degree of the venous pressure change is sufficient to explain the observed fall of cardiac output. The correlation which Stewart and Cohn (7) (4), the measurements were made during periods when the dogs were in so-called basal states, the work which their hearts performed may be regarded as constant, and the effects on diastolic size, as measures of the effect of digitalis on tone." Obviously, heart work is a function of the output per beat and is not, as Cohn and Steele suggest, measured by the oxygen consumption of the entire organism.…”

Studies on Digitalis. Ii. Extracardiac Effects on Venous Return and on the Capacity of the Peripheral Vascular Bed

“…The decline in cardiac output following the administration of digitalis to experimental animals (1)(2)(3)(4)(5) and to normal human subjects (6)(7)(8)(9)(10) would appear to be inconsistent with the well known positive inotropic action of this drug. The latter has been further confirmed by direct measurement of myocardial contractile force in both man and dog in the absence of heart failure ( 5,11,12).…”