The fundamental haemodynamic interaction between large and small vessels is important and poorly understood. We aimed to investigate the effect of microvascular rarefaction (MR) and reduced small vessel compliance (SVC) using a mathematical and computational model of the systemic arterial circulation.

Systemic arteries are treated as a bifurcating tree of compliant and tapering vessels. Large and small vessels are treated separately. MR is modelled by altering the area ratio between parent and daughter vessels at bifurcations. Reduced SVC is modelled by altering the value for Young’s modulus within structured trees. Aortic flow profiles (from MRI) of 7 healthy subjects (mean age 51.6y) were used as input to the model. Runs were made at baseline (normal parameters), with modelled MR (area ratio 1.08) and reduced SVC (20% reduction). Pressure and flow waveforms were generated at ascending aorta and radial artery.

Results expressed as change from baseline values. Radial artery (i) decreased compliance - SBP[+3.3%], DBP[−2.6%], pulse pressure (PP)[+13.3%] (i) rarefaction SBP[+12.7%], DBP[+21.1%], PP[−1.4%]. Ascending aorta (i) decreased compliance SBP[+3.3%], DBP[−2.6%], PP[+18.5%] (ii) rarefaction SBP[+10%], DBP[+19.3%], PP[−13.4%].

The predominant effect of decreasing SVC was an increase in pulse pressure with a small increase in peak pressure. Increased MR lead to an increase in both systolic and diastolic pressures with reduced central pulse pressure. These results represent modelled changes in small vessel properties only, with no changes made to large artery parameters. These results suggest that such model represents a useful tool in investigating haemodynamic mechanism, with multiple potential physiological and clinical applications.