Ventricular performance modified by elastic properties of outlow system.

• In 1834, Ernst Heinrich Weber, Carl Ludwig's pi-edeeessor in Leipzig, proposed that during the systolic phase of cardiac cycles, the heart accelerated only the ejected blood volume, which was temporarily stored in the large arteries and forwarded to the tissues during diastole. He postulated that the distensibility of the arterial tree enabled it to receive the ejected stroke volume and that the stretched arterial walls provided the force which caused blood to flow not only in systole but also during diastole. He compared the elastic storage capacity of the arterial tree with devices used in 1834 to transform pulsatile into nonpulsatile flow, such as the "Windkessel" of manually operated fire engines or the compressed-air chambers of pipe organs that were kept charged from bellows operated by the organist with his feet. Weber believed that ejection into an elastic outflow system would save work because pulsatile flow in a rigid conduit would require acceleration of a large mass at the beginning of systole. Although the idea that a distensible chamber would offer less resistance to ventricular ejection has been a part of the thinking of all major schools of cardiovascular physiology, the literature contains few reports which describe how one or more directly measured parameters of cardiac performance were influenced by the elastic properties of the outflow system (i.e., the arterial tree in vivo). Otto Frank published tracings of atrial and ventricular pulse contours in frog hearts