Importance of Atrial Compliance in Cardiac Performance

Abstract

Effects of changes in atrial compliance on cardiac performance were analyzed using a circulatory analog model. The atrium was assumed to be a noncontracting chamber with a constant compliance. It connected the venous return system, which was represented by mean circulatory filling pressure and a venous return resistance in accordance with Guyton's concept, with the ventricle, which was characterized by a time-varying elasticity. Atrial compliance was increased from near zero to a value at which atrial volume was twice ventricular stroke volume, while the parameters of ventricular contractility were kept unchanged. Cardiac output increased from 2,400 to 3,240 ml/min with increases in atrial compliance from 0.1 to 20 ml/mm Hg (venous return resistance 0.1 mm Hg sec/ml), whereas mean atrial pressure simultaneously decreased from 3.0 to 2.2 mm Hg. This result indicates that cardiac performance in terms of the cardiac output-mean atrial pressure relationship was markedly improved by increases in atrial compliance in spite of constant ventricular contractility. The analysis of the model strongly suggests that natural atrial compliance in situ, by pooling venous return flow during systole and supplying it to the ventricle during diastole, facilitates the transformation of the continuous venous return flow into the intermittent ventricular filling flow. KEY WORDS ventricular filling cardiac outputStarling's law of the heart atrial function circulatory analog model atrial size venous return• The physiological significance of atrial compliance is not well understood, but some indirect evidence does suggest that it is important in hemodynamics. Brighton et al. (1) Society, 1973) have observed that the addition of a flexible atrium to the inlet of an artificial heart substantially improves the heart's output. However, performance of an artificial heart is not equal to that of the natural ventricle, and doubt still exists about the physiological significance of atrial compliance.The purpose of the present analysis was to evaluate quantitatively the importance of atrial compliance in natural cardiac performance. In animal experiments, it is difficult to change atrial compliance alone without affecting venous return resistance, and slight changes in venous return resistance sensitively affect cardiac output (2). Therefore, a reasonable analog model of the cardiovascular system based on physiological findings in the literature was used in the present study. Atrial compliance was varied in the model while the other parameters of the venous return systemventricular contractile state, valve characterisFrom the Department of Physiology, Faculty of Medicine, University of Tokyo, Japan.Received January 2, 1974. Accepted for publication March 19, 1974. tics, and arterial pressure-were kept constant. The results of this analysis suggest that an atrium with an appropriate compliance can increase cardiac output 35-80%. Figure 1 shows the electric analog model of the circulatory system used in the present study; the right h...

Reservoir and conduit function of right atrium: impact on right ventricular filling and cardiac output

“…Nagano et al (28) found in normal subjects that the left atrium was less compliant than the left ventricle, facilitating blood transfer between the chambers during the early conduit phase. It is not surprising, however, that others have suggested that increased atrial compliance, which promotes reservoir function (17,37), would have a greater positive impact on cardiac output than would supplementation of conduit function (2,36). Hoit and Gabel (14) examined left atrial mechanics during left ventricular dysfunction, comparing the compensatory response with a normal atrium versus a failing atrium (induced with rapid atrial pacing).…”

“…In 1628, William Harvey was the first to identify the atrium as a "receptacle and store-house" and reported that the right atrium was "the first to live, and the last to die" (12). In an elegant computer model, Suga (36) found that increased atrial compliance markedly improved cardiac performance and concluded that a "flexible atrium" (increased receptacle capabilities) would substantially improve the heart's output. Others have predicted that early ventricular filling increases directly with atrial compliance (16,33,38); however, data from intact subjects are limited to support these theories.…”

Prognostic Factors for Survival in Pulmonary Hypertension Due to Left Heart Disease

“…9 The RA maintains CO with a minimal rise 9 or a decrease in RAP. 10 In other words, elevated mean RAP can reflect decompensated right ventricular dysfunction. Previous studies in patients with pulmonary arterial hypertension have reported that mean RAP was associated with survival.…”

Relationships between P wave dispersion, atrial electromechanical delay, left atrial remodeling, and NT-proBNP levels, in patients with hypertrophic cardiomyopathy

“…The LA active emptying fraction in the HCM population has been shown to follow the Frank-Starling mechanism [1], so an increase in LA preload up to a certain point contributes to enhanced LA booster pump function, which might explain why this function does not predict development of AF. On the other hand, LA reservoir function parameters are affected mostly by atrial compliance [25], and show advanced remodeling rather than LA enlargement. This may explain the value of this function in predicting AF [26].…”