Determination of left ventricular diastolic wall stress and elasticity in situ. A methodological investigation*)

Summary

A methodological study of the requirements for reliable determination of the left ventricular end-diastolic pressure-volume relationship, wall stress and wall elasticity was performed using angiocardiographic measurement of the inner volume and wall thickness, as well as simultaneous measurement of left ventricular pressure on closed-chest dogs. The reliability of the actual roentgenological volume determination was tested by comparing x-ray and direct volume measurement of ventricular casts.

The close correlation of angiocardiographic volume determination with direct volume measurement reveals that the area-length method of Sandier and Dodge permits reliable determination of left ventricular enddiastolic volume. During diastasis, the diastolic portion of the pressure-volume loop of an individual contraction coincides substantially with the static pressure-volume relationship, at low and medium heart rates. Only the pressure and volume changes during this period, corresponding to a short portion of the pressure-volume loop, should be used for an approximate determination of static wall elasticity, particularly in the volumeloaded heart. Under the conditions of the present experiments, ca. 50 % of the shift in the left ventricular diastolic pressure-volume relationship under hypoxia can be attributed to the influence of increased right ventricular filling. In an early phase of hypoxia, a contracture-like effect can be simulated by an increase in right ventricular pressure, although actual contracture does not yet occur. As in contracture, the decrease in ventricular distensibility due to geometric conditions neither changes the slope of the relation between reciprocal compliance @@@_lineEquation@@@ and ventricular pressure (P) nor the relation between tangent elastic modulus (E) and wall stress (σ).

Supported by the Deutsche Forschungsgemeinschaft