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

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 and sigma-epsilon relationships were analyzed by fitting the data to the above mentioned curves during this period of time. This analysis was made in two 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 lymph node 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 hearts differed. The results of the present study, however, demonstrated that the size of the heart 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 less than 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.