Time-varying Elasticity Research Articles

Importance of atrial compliance in cardiac performance.

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.

Domestic Distortions, Tariffs, and the Theory of Optimum Subsidy: Some Further Results

Bhagwati and Ramaswami (1963) showed that if there is a distortion, the Paretian first-best policy is to intervene with a tax (subsidy) at the point at which the distortion occurs. Hence a domestic tax-cum-subsidy with respect to production would be first-best optimal when there was a domestic distortion (defined as the divergence between domestic prices and the marginal rate of transformation in domestic production) just as a tariff policy would be first-best optimal under monopoly power in trade (which involves a foreign distortion). An important corollary, for the case of a distortionary wage differential, is that while a tax-cum-subsidy policy with respect to factor use would be first-best optimal. the second-best optimal policy would be a domestic production tax-cum-subsidy rather than a tariff policy. While these central results are valid, Kemp and Negishi (1969) have correctly argued that two subsidiary propositions of Bhagwati and Ramaswami (1963) are false. These are (1) that no tariff (export subsidy) may exist which is superior to free trade in the presence of a domestic distortion, and (2) that no production tax-cum-subsidy may yield greater welfare than nonintervention when the nation has monopoly power. We can demonstrate, however, that the Kemp-Negishi results are, in fact, special cases of the first of the following two theorems in the theory of second-best, which we shall prove: Theorem 1.-If under laissez faire two of the variables DRS, DRT, and FRT are equal while the third has a different value, and the policy measure that will secure equal values of the three variables cannot be applied, some