Cardiac Output

In my last blog I described the electical activity which results in a heart beat normally around 70 beats per minute. So how do we get this figure of 70 beats per minute and why is it important. Let us explore more!

Basically cardiac output is the measure of the volume of blood in milliliters per min (mL blood/min) ejected by the heart in one minute to establish the efficiency (or not) of the heart.

• Cardiac Output in mL/min = heart rate (beats/min) X stroke volume (mL/beat)

So if we look at an average persons heart rate at rest of 70 beats per minute, with a resting stroke volume of 70 mL/beat. Then the cardiac output would show:

• 70 (beats/min) X 70 (mL/beat) = 4900 mL/minute.

So why is this important? The heart rate and cardiac output have a direct relationship. As the heart rates increases therefore the cardiac output increases also. Monitoring of cardiac output gives doctors and clinicians the tools to be able to recognize, respond and understand many cardiac emergencies. A general rule of thumb is if a patient has a heart rate that is to fast or to slow then this requires urgent assessment as it could be a result of a blockage of the coronary arteriers which may cause a heart attack (myocardial infarction) or a fatal rhythm disturbance resulting in cardiac arrest.

Also people with heart disease usually have a weak blood supply, thus making their hearts beat slower due to poor electric conductivity. In all cases a electrocardiogram (EKG) is a noninvasive test that measures the electrical activity of the heart. This will detect many heart conditions as a result of high or slow cardiac output being detected in the first instance.