  Respiratory sinus arrhythmia (RSA) is heart rate variability in synchrony
with respiration although its functional significance not clear. The loss of
sinus arrhythmia may indicate underlying heart failure or disease; therefore,
there would be a great advantage of knowing how it works and affects the
cardio-respiratory system, especially by providing a mathematical model. To
this end, Windkessel model and cardiovascular partial differential equations
are used to obtain cardiac output based on the elasticity of left ventricle,
which is related to RSA. By solving the corresponding equations, it would be
possible to propose a new model to predict the RSA effects on cardiac output.
