The Heart

Cardiac Output & Electrical Activity

Cardiac Output & Electrical Activity

Cardiac output refers to the volume of blood which is being pumped by the blood in the space of one minute. Stroke volume, on the other hand, is the amount of blood being pumped from one ventricle with each heartbeat.

It’s possible to figure out cardiac output using the stroke volume by using the following calculation:

cardiac volume = stroke volume x heart rate

Heart rate can be calculated by using a pressure graph and measuring the time taken for one cardiac cycle. This value is then put into the following equation:

heart rate (beats per minute) = 60 cycle time(s)

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Electrical Activity

One of the most amazing attributes of the heart is its ability to contract of its own accord. This is due to the fact that cardiac cells are myogenic. The regulation of contractions is controlled by nervous and hormonal stimuli.

Located on the right atrium is a bundle of cells called the sinoatrial node (SAN). This is nature’s pacemaker and controls the heart rate. When this node is stimulated it starts off a wave of electrical impulses which spread over the atria and result in atrial systole.

This electrical signal is then registered by another node: the atrioventricular node (AVN). This node allows the signal to pass through the apex of the heart, down to the bottom of the ventricles, through the Bundle of His which is specialised conducting cardiac muscle. From here, the signal is spread through the ventricles via Purkinje fibres. Once they’ve filled with blood this causes the ventricles to contract from the bottom up.