Left ventricular diastolic pressure-volume and stress-strain relationship in children.

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Abstract
Diastolic pressure and volume (P-V) curves were approximately exponential and fitted the equation, dP/dV = aP + b, where a was left ventricular volume elastic constant. Stress and strain (.sigma..epsilon.) curves were expressed by the equation, d.sigma./d.epsilon. = k.sigma. + c, where k was wall stiffness constant. These exponential curves have been fitted over the whole diastole, but theoretically, the mid-diastole should reflect diastolic elastic properties best. In the present study, therefore, special attention was paid to the mid-diastole in each patient, and both P-V ad .sigma..epsilon. relationships were analyzed by fitting the data to the above mentioned curves duing this period of time. This analysis was made in 2 separate groups of patients. One was the control group consisting of 2 patients with normal hearts, 2 patients with mild pulmonary stenosis and 25 patients with post mucocutaneous lymphnode syndrome. The other group consisted of patients with postoperative congenital heart disease, that is, 8 patients, with atrial septal defect and 5 patients with tetralogy of Fallot. The elastic constant (a) could not be compared if the size of the heart differed. The size of the heart apparently was closely related to the constant, a. In the control group, the constant (a) was exponentially related to the size of the heart, and expressed as follows: a = 0.30e-0.037EDV + 0.045 (r = 0.94, P < 0.01). In contrast, the wall stiffness constant (k) was not related to the size of the heart. After surgical repair of congenital heart disease, the stiffness constant in the left ventricle was normal in patients with postoperative atrial septal defect, while it was significantly increased in patients with postoperative tetralogy of Fallot.