Pulmonary function tests Flashcards by Tolu Daramola

What are lung function tests used for?

To help establish a diagnosis in lung disease

Helpful in obstructive and restrictive lung disease which are recognisable findings on the tests

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What is the average tidal volume of the lung?

500ml

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What is the average dead space volume of the lung?

150ml

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How much volume of air goes to the alveoli?

350ml

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What is the tidal volume (TV)?

The volume of air taken in during normal quiet breathing

Divided into:
TVi - volume of air inspired

TVe - volume of air expired

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What is the inspiratory reserve volume (IRV)?

Volume of air inspired past the TVi

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What is the expiratory reserve volume (ERV)?

Volume of air expired past the TVe

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What is the residual volume (RV)?

The volume of air that has to remain in the lung to prevent it from collapsing

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What is the functional residual capacity (FRC)?

The total amount of air remaining in the lungs during normal quiet breathing

ERV + RV

Remember you don’t usually breathe out ERV unless you force air out of your lungs, so in normal breathing ERV remains in your lungs

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What is the inspiratory capacity (IC)?

The total amount that your lung is capable of inspiring

TVi + IRV

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What is the total lung capacity (TLC)?

The total amount of air your lungs are capable of holding

VC + RV

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What is the vital capacity (VC)?

The “functional” capacity of your lung

ERV + IRV + TV(i+e)

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What are the 3 main types of pulmonary function tests?

Spirometry

Lung volume testing

Diffusion capacity

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What is spirometry?

A simple test that helps diagnose and monitor pulmonary diseases (e.g., COPD, asthma)

It measures how much air an individual can breathe out in one forced breath

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What are the components of spirometry?

FEV1 = forced expiratory volume in 1 second

FVC = forced vital capacity - total/highest amount of air an individual can force out irrespective of time

Spirogram

Flow loop volume

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What FEV1/FVC ratio suggests obstruction?

< 0.7

What happens to FEV1 and FVC in obstruction?

FEV1 reduced

FVC slightly lower or normal

This is due to reduced elasticity and increased compliance

So the lungs can take air in easily but lack the elasticity to recoil sufficiently to push enough air forcefully hence FEV1 decreases

What happens to FEV1 and FVC in restriction?

Reduced FVC

Normal/slightly low FEV1

Increased recoil and reduced compliance

The lungs become too stretchy/recoils easily and is not able to expand to take enough air in

So the amount of air available to forcefully expire reduces (i.e., FVC reduces)

What are the characteristics of a spirometry?

Function of GENDER + AGE + HEIGHT + RACE

No defined absolute normal or absolute abnormal values

Compare actual values to predicted values

Abnormal result often defined as % predicted < 80

Exception is for FEV1/FVC ratio, which expressed and evaluated as an absolute ratio

What is a positive response in a bronchodilator responsiveness?

Increase FEV1 (and/or FVC) by 12% AND 200ml

This indicates reversible obstruction

NOTE: the lack of a bronchodilator response in the lab does not preclude a clinical response to bronchodilator therapy in real life

What are the different flow loop volume charts and what do they indicate?

What is the methacoline challenge test (MCT)?

A test of airway responsiveness

Looks at how “twitchy” the airways are, by seeing whether they narrow after inhaling (breathing in) methacholine

Used in asthma testing

What is methacoline?

Methacoline is a non-selective muscarinic receptor agonist that acts on airway smooth muscle to induce bronchoconstriction

How is the MCT carried out?

Patient does a spirometry test to check what the baseline lung function is. If this is not too low, they move to the next step
Patient may be asked to breathe in a saline solution via nebuliser before repeating the spirometry test
If there is no change in lung function, the patient will be asked to breathe in a low dose of methacholine via a nebuliser
Spirometry test is repeated immediately after inhalation of methacholine, and again after a few minutes
If lung function does not change after the lowest dose of methacholine, the patient inhales another stronger dose of methacholine. They then do the spirometry test again
As long as they remain unreactive to methacholine, the patient continues the test; inhaling stronger dose of methacholine (usually 5-10 doses in total), followed by spirometry testing
As soon as the lungs show a significant drop in FEV1 of 20% or more, the test is considered complete. The [methacholine] is the test result
Patient will then be given a bronchodilator treatment (usually salbutamol or ipratropium) to inhale
Spirometry test is repeated to ensure lung function has returned to normal

How should you advise patients to prepare for their MCT?

On day of test, don't eat or drink products containing caffeine e.g., coffee, tea, cola drinks, energy drinks, chocolate. Caffeine can act as a weak bronchodilator and cause inaccurate test results Wear loose fitting clothing to your appointment, to allow your chest to expand freely as you will be asked to take deep breaths in and blow out hard during the tests Don't do any vigorous exercise for 30 minutes before the appointment. This may tire you out before the tests Do not eat a large meal within 2 hours before the test. This may make you feel uncomfortable whilst taking the tests

What is the gas transfer test (TLco)?

Measures how well the lungs take up O2 from the inspired air The test result is called the transfer factor (or the diffusing capacity - DLco) TLco refers to the transfer capacity of the lung, for the uptake of CO

What is the TLco used for?

To help diagnose and monitor lung conditions including COPD and pulmonary fibrosis Can also be used to assess the lungs before surgery or to see how a person's lungs react when they receive chemotherapy

Which pulmonary conditions will reduce TLco?

Emphysema Lung infiltration Lobectomy

Which cardiovascular/haematological diseases will reduce TLco?

Pulmonary HTN Low cardiac output Pulmonary oedema Anaemia

Which conditions will increase the TLco?

High cardiac output Pulmonary haemorrhage Polycythaemia

What should patients expect during a TLco test?

Breathe in air containing tiny amounts of helium and CO Asked to take a big breath through a mouthpiece while wearing a nose clip Hold breath for a minimum of 8 seconds, then breathe our steadily into the machine Need to do this a few times, with a pause of a few minutes in between It could take several attempts to get a reliable reading

What should patients not do before the TLco test?

Not smoke Results can be affected by smoking Lung diffusion capacity relies on capillary blood volume and membrane diffusivity. In smokers there is a significant decrease in capillary blood volume

Which results does a gas transfer test give?

TLco - shows how efficiently the lungs work to take O2 from the inspired air. Calculated from Kco and VA Kco - measures how well the airways are performing VA (alveolar volume) - estimates the lung surface area available for gas exchange Low lung efficiency = < 80% of normal predicted values

What is the PEFR?

The peak expiratory flow rate Measured during spirometry but also with hand-held devices at home Do same time each day (there are morning dips) Useful for patients with asthma - picks up exacerbations - assesses response to Tx

How would you tell a patient to do a PEFR?

1. Move the dial all the way to the bottom 2. Take a deep breath and inhale as much air as you can and then hold your breath 3. Place you mouth over the mouthpiece and form a tight seal 4. Blow out as hard and as fast as you can 5. Record the PEFR reading 6. Repeat steps 1-5 three more times 7. Take the highest reading as your PEFR value

How does restriction affect the RV, FRC, & TLC?

Causes a reduction

What conditions can cause decreased lung volumes?

Lung parenchymal process : expansion of the interstitial space (water, scar or inflammation) or "airspace filling process" Pleural disease Chest wall disease Weakness - focal or global - nerve or muscle based

Sources

https://www.ouh.nhs.uk/patient-guide/leaflets/files/59679Pmethacholine.pdf https://www.blf.org.uk/support-for-you/breathing-tests/gas-transfer-tlco Measuring Lung function Module 103 05.01.2018 lecture