IMPORTANCE OF COLLATERAL VESSELS IN AORTIC COARCTATION - COMPUTER-SIMULATION AT REST AND EXERCISE USING TRANSMISSION-LINE ELEMENTS

Coarctation of the aorta causes arterial hypertension in the upper bod y and a low blood pressure downstream. Collateral blood vessels compen sate by reducing the downstream pressure drop. To study the effect of various coarctation and collateral properties, we designed a computer model of the arterial circulation. The model contains a flow sources a nd a library of subroutines for the lines and connectors. Distributed friction and wall viscoelasticity effects are included. Computer simul ation was performed, using published values for vessel dimensions, in an arterial model with a coarctation and one lumped collateral. Rest a nd two levels of exercise (by increased heart rate) were studied. With out a collateral, we found the downstream pressure of the model was ex tremely dependent on the size of the coarctation. A collateral vessel reduced the pressure difference between the up- and downstream circula tions. for a severe coarctation, the length and the diameter of the co llateral were the main factors determining the downstream pressure and flow, whereas wall stiffness of the collateral had little influence. The relationship between mean pressure drop and cardiac output in coar ctation was also dependent on the peripheral resistance in different f low beds, especially during exercise.