  The simulation of blood flow and pressure in arteries requires outflow
boundary conditions that incorporate models of downstream domains. We
previously described a coupled multidomain method to couple analytical models
of the downstream domains with 3D numerical models of the upstream vasculature.
This prior work either included pure resistance boundary conditions or
impedance boundary conditions based on assumed periodicity of the solution.
However, flow and pressure in arteries are not necessarily periodic in time due
to heart rate variability, respiration, complex transitional flow or acute
physiological changes. We present herein an approach for prescribing lumped
parameter outflow boundary conditions that accommodate transient phenomena. We
have applied this method to compute haemodynamic quantities in different
physiologically relevant cardiovascular models, including patient-specific
examples, to study non-periodic flow phenomena often observed in normal
subjects and in patients with acquired or congenital cardiovascular disease.
The relevance of using boundary conditions that accommodate transient phenomena
compared with boundary conditions that assume periodicity of the solution is
discussed.
