Cardiovascular haemodynamics and shock

Cardiovascular haemodynamics is the study of how blood flows through the cardiovascular system. The physical factors that determine blood flow include the blood pressure and the resistance to this flow. The resistance is determined by vessel length and radius, blood viscosity and the arrangement of these vessels. The arterioles account for more than 60% of the resistance in the cardiovascular system and control local blood flow through organs. In shock states, where there is inadequate tissue perfusion, autonomic outflow to the heart and vessels can be modified by various cardiovascular reflexes to control heart rate, cardiac contractility, vascular tone and blood pressure. It is important to have an understanding of the haemodynamics of the cardiovascular system in order to monitor the circulation and administer fluids and vasoactive drugs in a sensible manner when managing the critically ill patient.