Predicting systolic and diastolic aortic blood pressure and stroke volume in the intact sheep

We developed a mathematical model describing the interaction between the he art and the arterial system. The model was constructed and tested on basis of invasive hemodynamic data in six sheep. Data from a first group of three animals (49 cardiac cycles) were used to assess a template time-varying el astance curve for the left ventricle, while the baseline steady-state data of a second group of three animals were used to assess reference cardiac an d arterial parameters in sheep. The model is fully characterized by nine pa rameters, which were converted into 6 dimensionless numbers using the Bucki ngham II theorem. The model was then used to generate LV pressure and volum e and aortic pressure and how for 86 conditions obtained by varying paramet ers 50 to 200% of their reference value. Systolic (SBP) and diastolic (DBP) blood pressure and stroke volume (SV) were determined from these model-gen erated curves and multiple linear regression analysis yielded the following expressions: SEP = P-isovolumic[0.638 - 0.0773 E-max C+ 0.0507 RC/T] (r(2) =0.89); DBP=P-isovolumic [0.438 -0.0712 EmaxC+ -0.0655RC/T] (r(2)=0.88) and SV=LVEDV [1.165-1.040 LVEDV/(LVEDV -V-d) + 0.125 E-max C-0.0777RC/T] (r(2) = 0.93) with P-isovolumic = E-max(LVEDV - V-d), E-max and V-d being the sl ope and intercept of the end-systolic pressure-volume relation, R and C the total peripheral resistance and compliance, LVEDV the left ventricular end -diastolic volume, and T the cardiac cycle length. These expressions were v alidated using data from the second group of three animals obtained during vena cava occlusion at baseline and during administration of dobutamine (61 cycles). The correlation between measured and predicted values was 0.98, 0 .97 and 0.92 for SEP, DBP and SV, respectively. Compared to the measured va lues, SEP and DBP were, on average, underestimated by 5 and 6 mmHg, respect ively, and SV overestimated by 1.4 ml. We conclude that the derived express ions for blood pressure and stroke volume remain valid in the intact sheep for various hemodynamic conditions, and, taking into account their dimensio nless form, may hold in other species and in humans. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.