Abstract
A mathematical model has been constructed which demonstrates the effects of gestational age and postnatal age on mean blood pressure in preterm infants. The model also demonstrates the effect of loss of renal mass on blood pressure (as might occur from catheter-induced emboli). Construction of the model is based on Chm's law: Pressure = Flow X Resistance. Mean arterial pressure is calculated from cardiac output X systemic resistance. The gradually rising mean arterial pressure with increasing gestational age and postnatal age are shown as a function of flow/resistance changes. Analysis of the arterial pressure-urinary output relationship describes the kidney's ability to excrete fluid. If the output of fluid is subtracted from the intake, the rate of change of extracellular fluid volume (EFV) with respect to time (dEFV/dt) is obtained. Integration of dEFV/dt yields a value for EFV which can be used to calculate blood volume. The relationship of blood volume to mean systemic pressure can be used to calculate mean systemic pressure. Subtracting the right atrial pressure from the mean systemic pressure yields the pressure gradient for venous return. The pressure gradient for venous return divided by the resistance to venous return yields the venous return. The cardiac output equals the venous return in the steady state. The data used to construct the blocks are from published reports and new observations. The model is programed in Fossel on a PDP-11 Computer.
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Rawson, J., Freidman, C., Parks, B. et al. 1401 A THEORETICAL MODEL OF THE CARDIOVASCULAR SYSTEM IN PRE-TERM INFANTS. Pediatr Res 15 (Suppl 4), 676 (1981). https://doi.org/10.1203/00006450-198104001-01430
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DOI: https://doi.org/10.1203/00006450-198104001-01430