No abstract

Left and right ventricular end diastolic pressure, stroke work, stroke volume, and cardiac output were measured in open and closed chest dogs infused with blood and/or saline. The methods employed permitted repeated determinations of these factors during short time intervals. For nonfatigued hearts in the open chest preparation point to point correlation of end diastolic pressure with the other three variables was very good, but in closed chest animals a number of noncorrelations occurred. Sufficient variation was seen to indicate that factors other than those measured in this study will have to be known before cardiac performance in the intact animal can be fully assessed.T HE RELATIONSHIP between diastolic pressure in the atrioventricular cavity and the response of the ventricle during the following systole is not clear. Measurements by Patterson, Piper and Starling 1 in the heart-lung preparation with constant heart rate and peripheral resistance revealed that with increasing venous return in nonfatigued hearts no constant correlation existed between diastolic pressure and the succeeding ventricular stroke volume; but in contrast Wiggers and Katz 2 found in the open chest dog with saline infusion that changes in stroke volume were never dissociated from alterations in initial intraventricular pressure. In the intact dog and human, observations during infusion indicate both a correlation between cardiac output and mean right atrial pressure 3 ' 4 and a lack of correspondence of these parameters.6 ' ° The latter confusion could arise from the use of methods which give information only on mean atrial pressure and cardiac output measured over many minutes. Such measurements could A portion of this work was presented at the meeting of the American Physiological Society in April, 1952.Received for publication Oct. 1, 1952. well obscure the phasic response of the individual heart beat. The development of a photoelectric method for cardiac output by dye injection 7 and the availability of a technic for measuring phasic pressure from a cardiac cavity 8 make it possible to quantitate the response of the myocardium during a few cardiac cycles. Accordingly, investigations were made to determine the relationship of ventricular end diastolic pressure to stroke work, stroke volume, and cardiac output during intravenous infusion. METHODSExperiments were set up in which infusions of whole blood and/or saline at varying rates and for varying periods of time were made intravenously into anesthetized closed or open chest dogs while cardiac outputs, phasic systemic and ventricular end diastolic pressures were recorded.In the group of closed chest clogs several weeks before the experimental day, a left carotid loop was constructed to facilitate registration of arterial pressure and withdrawal of blood for the determination of cardiac output. At the same time, to aid in the measurement of left ventricular pressure through the intact chest wall, a segment of costal cartilage was removed and the apex of the heart sutured in the de...

Maximum left ventricular work response (and other hemodynamic changes) to infusion of saline and whole blood was compared in normal dogs and in dogs with aorta-caval and multiple peripheral fistulas. In the dogs with fistulas the augmented preinfusion levels of cardiac work and left ventricular end-diastolic pressure approximated those in normal dogs after maximum response to infusion. Following infusion in the dogs with fistulas, end-diastolic pressure characteristically increased but cardiac work did not. Thus maximum cardiac work was of the same order of magnitude in the normal dogs and in the dogs with fistulas. In all groups maximum left ventricular work was effected mainly through an increased cardiac output.

Quantitation of cardiac output by the Stewart-Hamilton method will have extended usefulness if the accuracy of measuring the concentration of Evans blue dye in whole blood is established. Cardiac outputs by this method have been compared in dogs with outputs by the rotameter and the Fick method. The constant-flow photometer (Friedlich) was used initially, but certain difficulties in its use led to the development of a new cuvette densitometer. Comparisons using both these instruments gave average variations of plus 7.0 per cent and minus 5.4 per cent from the reference methods. With proper caution cardiac outputs in dogs can be accurately obtained from dye dilution curves in whole blood.

Infusion of 1-arterenol into anesthetized dogs increased the volume of blood in the heart and lungs, as indicated by an increase in "central blood volume," estimated lung volume and pressure changes in the heart and lungs. An analysis of pressure and flow data in the systemic venous bed during infusion of the drug suggests that important sources of the shifted blood are the peripheral veins and venules.F OWLER AND COWORKERS have demonstrated that both pulmonary artery and "pulmonary capillary pressures" increase during the continuous infusion of 1-arterenol, in the human.1 These workers concluded that the pulmonary hypertension was secondary to an increased pulmonary venous pressure; however, the mechanism of this pressure rise was not investigated. With a constant cardiac output, changes in pulmonary vascular pressures occurring during 1-arterenol infusion could be due to either vasomotor activity in the pulmonary vascular bed, or a volume increase in the pulmonary circuit due to the shift of blood from the systemic circuit. Since the resistance across the pulmonary vascular bed did not change in any consistent manner during 1-arterenol infusion, Fowler concluded that the rise in pulmonary artery pressure was not due to constriction of the pulmonary arteries. These data, together with the general lack of evidence for active pulmonary vasomotor changes, make the second possibility the more likely explanation for the increased pulmonary artery pressure.2 '' Work from various laboratories indicates that systemic vasomotor activity can change the volume of blood contained in the heart and lungs. Johnson observed a decrease in this