04.05 Heart rate, stroke volume and cardiac output

We can measure the cardiac output (CO) or the amount of blood that is pumped out of each ventricle in one minute using the following equation:

CO (ml/min) = HR (beats/min) x SV (ml).

It is important that adequate cardiac output is maintained so that the body tissues receive the blood supply they need. Although the heart can beat of its own accord, heart rate can be changed by the autonomic or involuntary nervous system which is made up of the sympathetic and parasympathetic divisions. Sympathetic nerve activity speeds up heart rate. Parasympathetic nerve activity dominates whenthe body is resting and slows down the heart rate (it is therefore slower than the pacemaker rate). Refer also to section 8.3.