P3 - ECGs and Pulse Oximetry

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  • Created by: kat-y
  • Created on: 15-11-16 20:23

ECGs

An action potential is the change in voltage along the membrane of a cardiac muscle cell or a neurone whenever an electrical impulse travels alongs it.

The AP is sent to each muscle cell to tell it when to contract because each muscle cell must contract at exactly the same time to push the blood out of the heart whenever the heart beats.

Electricity can be conducted as the human body contains a high proportion of water with dissolved salt in it. The APs are conducted through the body to the skin. This is where the APs can be detected to produce an ECG (electrocardiogram)

An ECG is an image of the electrical signals by the heart.

It can be used to monitor heart action - the ECG can diagnose heart problems such as damaged muscles or blockades.

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Working out how fast the heart is beating

There is a regular pattern if a heart is beating normally

ECGs are printed on graph paper with a standard scale. How fast the heart is beating can be worked out using this.

The frequency (hertz)  of the heartbeat per second = 1 divided by the time period (in seconds).

Number of beats per minute = the frequency x 60

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Pulse Oximetry

A pulse oximetry allows the pulse rate to be measured as well as the amount of oxygen in the blood to be determined.

Patients may wear a pulse oximetry during intensive care, an operation and in recovery.

It consists of two LEDs and a detector (photodetector). One emits red light and the other emits infrared radiation.

The oxygen of the blood can be determined by the difference in absorbance of the two LEDs (percentage oxygen saturation). This is because oxygenated blood absorbs more infrared compared to deoxygenated blood. Each heart beat causes a surge of oxygenated blood in the arteries.

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Pacemakers

When action potentials do not spread across the heart properly, people can have heart problems. The heart may not be able to beat properly.

A pacemaker is a device that helps the heart to beat properly by detecting APs and applying electrical signals to regulate the heart action. It can be inserted above the patient's heart when the heart beats too slow or there is a block in the heart's conductive tissue.

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