THE DYNAMICS OF THE ISOLATED HEART AND HEART-LUNG PREPARATIONS OF THE DOG

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Abstract
Two preparations, an isolated heart and a closed circuit heart-lung, are described in which the dynamics of the circulation could be analyzed under controlled conditions. The main difference between the 2 preparations are 1, that in the isolated heart preparation the circuit is interrupted between the pulmonary artery and left auricle by an artificial "lung" and a pump for returning blood to a reservoir, while in the heart-lung prepn. the lungs are felt in situ (the artificial "lung," pump, artificial pulmonary peripheral resistance and reservoir being omitted), and 2, that artificial control is obtained in the isolated heart preparation by varying the artificial peripheral resistance placed in both the pulmonary and systemic circuits and/or the reservoir height, while in the heart-lung preparation artificial control is obtained by varying the artificial peripheral resistance placed only in the systemic circuit and/or the amount of blood in circulation. A total of 79 expts. was analyzed, 44 isolated heart and 35 heart-lung prepns. Graphs of various measurements were made of all these expts. using the initial control levels. These were subjected to statistical analysis in order to gain information about the circulatory dynamics in these prepns. and to further knowledge of the cardiodynamics in the intact circulation. In general the expts. were of longer duration, progressive heart failure was longer delayed and less brusque in its development in the heart-lung than the isolated heart prepns. Among the heart-lung prepns. those in which heparinized blood was used survived longer than those with defibrinated blood. The presence of progressive heart failure in some of these prepns. when the initial readings were made did not affect the graphs here analyzed in any significant manner. The significance of the various findings on the interrelation of the variables analyzed is discussed briefly. The outstanding fact observed was the greater degree of interdependence of the various pressures and flows in the heart-lung prepn. compared to the isolated heart. This is attributed to the fact that in the heart-lung prepn. the main change made is in the amt. of circulating blood which tends to affect all the pressures and cardiac output at the same time and in the same direction. The greater freedom of exptl. adjustment in the isolated heart nullified this to a large extent. In the intact circulation, it would appear that the changes would be interrelated somewhat as in the heart-lung prepn. insofar as the adjustments are due to alterations in circulating blood vol. Change in circulating blood vol. is one of the most important, but not the only means, of adjusting the dynamics of circulation in the intact animal. However, the operation of compensatory mechanisms in the intact animal, chiefly of neurogenic origin, would modify the interdependence found in the isolated heart-lung prepn.

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