A CINEMATOGRAPHIC STUDY OF SYSTOLIC AND DIASTOLIC HEART SIZE WITH SPECIAL REFERENCE TO THE EFFECTS OF ANOXEMIA

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Abstract
The questions, whether the systolic discharge and minute volume are increased by anoxemia of limited degree and if so whether this is due to a primary effect on the ventricle or to secondary changes in venous pressure, arterial heart rate, were reinvestigated. All studies were made on anesthetized dogs with "controlled circulations," i.e., the heart rate, arterial diastolic pressure and venous pressure were kept constant. A cinematographic method for recording changes in heart size during successive moments of the heart cycles was developed and its reliability was determined by physical tests. By enlarging the individual forms of pictures so obtained, redrawing and measuring their surface areas, changes in size during consecutive intervals of about 0.03 sec. could be plotted. In this way the effect of anoxemia on systolic and diastolic size could be studied. The effect on systolic discharge could also be estimated by their difference and the changes noted, compared with alterations in arterial pulse pressure recorded by optical manometers. The results showed that anoxemia produced by gas mixtures containing less than 10% O produces the following sequential changes by direct action on the heart. (a) An increased diastolic volume, independent of changes in venous pressure (increased initial length). (b) An increased systolic discharge. (c) Increased systolic pressure and pulse pressure, when diastolic pressure was kept constant. That any considerable lowering of O tension of blood is compensated for by an increased minute volume can no longer be questioned, for in addition to the secondary effects of anoxemia (such as increase in heart rate), the systolic discharge is also increased by a direct cardiac action. It may incidentally be added that the stimulating effect of asphyxia on the heart appears to be exclusively due to the associated anoxemia, for Wiggers (1929) recently demonstrated that no direct effect of hypercapnia can be demonstrated in similar experiments.

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