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AS Mechanics of Breathing & Spirometer Trace

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Aims -To understand the mechanics of breathing and the role of the diaphragm and intercostal muscles. To link the lung volume capacities to each other.

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What is a spirometer, what does it show, definitions of what it shows and how it works

A spirometer is used to measure lung volume.

The trace from this apparatus tells us a lot about the lungs.

A spirometer can also be used to determine a person's rate of oxygen consumption.

Firstly, it shows that the lungs have a total lung capacity: a maximum quantity of air that the lungs can hold during the deepest possible breath. A spirometer can be used to calculate the vital capacity of the lungs. This is the maximum usable volume of the lungs. Therefore:

Vital capacity = total lung capacity - residual volume

Where the residual volume is the volume of air that remains (resides) in the lungs after breathing. Some air remains in the lungs after breathing because we can never totally empty our lungs even when we have exhaled as much as possible, as there is still some air in the alveoli, bronchi and trachea (these are held open permanently by rings of cartilage).

Secondly, the spirometer shows that during normal breathing, the volume of air in and out of the lungs in each breath is called the tidal volume. In a normal adult at rest, this is about 0.5L.

Thirdly, the trace from the spirometer shows that after breathing in at rest, the organism breathing could inhale an extra 1.5L: the inspiratory reserve volume (IRV). He or she could also breathe out another 1L: the expiratory reserve volume (ERV).These volumes represent the extra volumes of air that we could breathe in and out during exercise.

Finally, we can calculate the ventilation rate from the spirometer: volume of air taken into the lungs in 1 minute.

Ventilation rate = breaths taken per minute times tidal volume.

Risk assessment when using the spirometer

Never do investigations like this without close supervision as rebreathing your own air can be dangerous.

The spirometer produces a trace by means of a ink pen and float (in water).

When you breathe in, the pen goes up and the float goes down, producing a trace. And when you breathe out the float goes up so the pen goes down, producing a trace.

Movement of the float in relation to the pen is inversely proportional. Without the proportion symbol on my keyboard though, this relationship can also be portrayed as so:

Where f = the float and p = the pen.

Comments

These notes are aimed at people studying Edexcel Biology A Level, but will be suitable for other exam boards too.

Originally written by Elements on TSR Forums.

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Revision:Edexcel AS Level Politics Unit 2 - The Student Room

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A spirometer is used to measure lung volume. The trace from this apparatus tells us a lot about the lungs. A spirometer can also be used to determine a person's rate of oxygen consumption. Firstly, it shows that the lungs have a total lung capacity: a maximum quantity of air that the lungs can hold during the deepest possible breath.

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Spirometry is a simple test used to help diagnose and monitor certain lung conditions by measuring how much air you can breathe out in one forced breath.
It's carried out using a device called a spirometer, which is a small machine attached by a cable to a mouthpiece.

Spirometry may be performed by a nurse or doctor at your GP surgery, or it may be carried out during a short visit to a hospital or clinic.

Why spirometry is carried out

Spirometry can be used to help diagnose a lung condition if you have symptoms, or if your doctor feels you're at an increased risk of developing a particular lung condition.

For example, spirometry may be recommended if you have a persistent cough or breathlessness, or if you're over 35 and smoke.

Conditions that can be picked up and monitored using spirometry include:

If you've already been diagnosed with 1 of these conditions, spirometry may be carried out to check the severity of the condition or see how you're responding to treatment.

Spirometry is also a standard test for people being considered for surgery, or to check the general health of people who have other conditions, such as rheumatoid arthritis.

Preparing for the test

You'll be told about anything you need to do to prepare for the test.

If you use bronchodilators (medicines, usually inhaled, that help relax and widen your airways), you may need to stop using it beforehand.

You should also avoid smoking for 24 hours before the test, and avoid drinking alcohol, strenuous exercise or eating large meals for a few hours beforehand.

It's best to wear loose, comfortable clothing on the day of the test.

What happens during a spirometry test

You'll be seated during the test and a soft clip will be placed on your nose to stop air escaping from it.

The tester will explain what you need to do, and you may be asked to have a few practise attempts first.

When you're ready for the test, you'll be asked to:

inhale fully, so your lungs are completely filled with air

close your lips tightly around the mouthpiece

exhale as quickly and forcefully as you can, making sure you empty your lungs fully

This will normally need to be repeated at least 3 times to ensure a reliable result.

Sometimes, the test may need to be repeated around 15 minutes after taking some inhaled bronchodilator medicine.

This can show if you have a lung condition that responds to these medicines.

Overall, your appointment should last around 30 to 90 minutes. You'll be able to go home soon after the tests have finished and return to your normal activities.

Your results

The person carrying out the test won't usually be able to give you your results immediately.

The results will need to be looked at by a specialist first and will then be sent to the doctor who referred you for the test, who will discuss them with you a few days later.

A spirometer measures the amount of air you can breathe out in one second and the total volume of air you can exhale in one forced breath.

These measurements will be compared with a normal result for someone of your age, height and sex, which will help show if your lungs aren't working properly.

The measurements will also show whether any problem with your lungs is "obstructive", "restrictive", or a combination of the two:

obstructive airways disease - where your ability to breathe out quickly is affected by narrowing of the airways, but the amount of air you can hold in your lungs is normal (such as in asthma or COPD)

restrictive lung disease - where the amount of air you can breathe in is reduced because your lungs are unable to fully expand (such as in pulmonary fibrosis).

Risks and side effects

Spirometry is a straightforward test and is generally considered very safe. Some people may feel dizzy, faint, shaky, sick or tired for a short period afterwards.

Most people are able to have a spirometry test safely. But the test increases the pressure inside your head, chest, stomach and eyes as you breathe out, so it may need to be delayed or avoided if you have a condition that could be made worse by this.

For example, spirometry may not be safe if you have, or have recently had, unstable angina, a heart attack, uncontrolled high blood pressure, or an operation to your head, chest, stomach or eyes.

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Spirometry is a simple test used to help diagnose and monitor certain lung conditions by measuring how much air you can breathe out in one forced breath. It's carried out using a device called a spirometer, which is a small machine attached by a cable to a mouthpiece.