The equipment you work with.

You work with several different devices, and although they look different, they have something in common: they pick up a signal from the body, amplify it and display it so it can be interpreted. The better you understand what the device actually measures, the better you can perform the examination and detect when something is wrong.

§ECG — the heart's electrical activity

An electrocardiogram (ECG) records the small electrical impulses that make the heart beat. You place electrodes on the skin — typically on the arms, legs and chest — and the device captures the heart's rhythm and signal pattern as curves. A good recording requires clean skin, correct placement and a patient lying relaxed. Muscle tension, poor skin contact or loose electrodes introduce noise on the curve.

§EEG – brain waves

An electroencephalogram (EEG) measures the brain's electrical activity via many electrodes placed on the scalp in a fixed pattern. The signals are very small, so the examination is sensitive to interference, and it requires care to place the electrodes correctly and ensure good contact. EEG is used, among other things, in the investigation of epilepsy and other conditions affecting the brain.

§Audiometry – hearing

An audiometer plays tones in different frequencies and volumes and the patient marks when the tone can just barely be heard. This is how the hearing threshold is found for each ear. The examination often takes place in a soundproofed room so ambient noise does not interfere. It is important that you give the patient clear instructions so the result reflects hearing and not a misunderstanding of the task.

• 01ECG: electrodes on the skin measure the heart's rhythm — requires clean skin and rest.
• 02EEG: many electrodes on the scalp measure brain waves – very sensitive to noise.
• 03Audiometry: tones find hearing threshold – requires a quiet room and clear instruction.
• 04Spirometry: measures lung volume and exhalation rate — requires the patient's participation.

§Spirometry — lung function

Spirometry measures how much air the patient can breathe in and out, and how quickly. The patient breathes into a mouthpiece according to your instructions, often several times, to get a reliable result. This examination depends entirely on the patient's participation, so your ability to instruct, motivate, and demonstrate the technique is critical to whether the measurement can be used.

§Beware of signal noise

Common to all equipment is that it picks up very small signals – and therefore also easily picks up interference. Poor skin contact, movement, electrical noise from other devices or an anxious patient can ruin a measurement. Much of your craft is to recognize when a measurement is clean enough to use, and when you should correct and take it again. An incorrect measurement is worse than no measurement.

§Maintenance and inspection

The devices must be maintained and checked so you can rely on them. This means cleaning according to guidelines, replacement of consumables, and having the equipment checked and calibrated according to the manufacturer's and department's instructions. You need to know when a device should be checked and what to do if it appears to be malfunctioning. A device that cannot be relied upon does not belong in a patient examination.

“The device measures only what you give it the chance to measure. Good preparation and clean signals are half of a good examination.”