Effect of Chronic Pressure and Volume Overload

I NCREASE in chamber volume (and therefore increase in wall surface area) is an appropriate adaptation to an increased volume load.' Conversely, a small thick-walled chamber is better suited to deal with a pressure load.2-4 That the human heart so adapts itself to chronic volume and chronic pressure loads is evident from clinical experience and postmortem studies. However, actual measurements of chamber volume under these conditions are lacking. Detailed study of the adaptation to increased stress requires knowledge of chamber volumes during the different phases of the cardiac cycle and such measurements cannot be obtained post mortem. Technics that measure change in a single ventricular dimension have yielded valuable information.5' 6 However, although applicable to unanesthetized subjects under varying conditions of rest and exercise, they are necessarily indirect measures of absolute volume. The recent development, by Arvidsson,7 of a method for estimating left heart volumes from biplane angiocardiograms and its validation by Dodge and co-workers,8 has made possible measurement of absolute volume and change in volume of individual cardiac chambers. The present study concerns the volume responses of the human heart to chronic pressure or volume overload imposed by congenital cardiac malformations. The method of Arvidsson 7 was thought to measure absolute volumes and volume changes of the