Myocardial relaxation and passive diastolic properties in man.

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Abstract
We have developed a model for assessing the influence of the decaying contractile systolic tension on diastolic wall dynamics and the passive properties of left ventricular muscle. Total measured left ventricular diastolic pressure and stress (sigma T) are determined by two overlapping processes: the decay of actively developed pressure and stress (sigma A) and the buildup of passive filling pressure and stress (sigma*). The decaying contractile stress sigma A is formulated in terms of a relaxation pressure with a time constant (T) assessed during the isovolumic relaxation interval. By subtracting the contribution of sigma A from sigma T we obtain sigma*. With micromanometry, echocardiography, and cineangiography, total and passive stress-strain relations and strain rates were evaluated over the entire filling period in six normal control subjects and in seven patients with aortic stenosis. Elastic stiffness constants (k), the slopes of the linear passive stiffness vs sigma* relations, did not differ in the two groups over a common lower stress range (6/6 normal, k = 9.37 +/- 1.23; 7/7 aortic stenosis, k = 9.34 +/- 1.08). Over a higher sigma* range, transition into a much steeper linear region occurred, and k values were much larger (4/7 aortic stenosis, k = 28.76 +/- 2.02). When diastolic stress levels are elevated, passive stiffness-stress relations can be better described as bilinear, with a much greater wall stiffness constant in the higher than in the lower stress range. Dynamic effects of decaying systolic contractile wall stress components are important in the rapid filling phase in normal hearts as well as in those with aortic stenosis.