A peak flow test is a useful way of measuring how fast a patient can expel all the air from their lungs. It is commonly used in diagnosing and monitoring a patient’s asthma. The purpose of this article is to discuss what a peak flow test is, why it can be useful and how it is used.

What is Asthma?

Asthma is a common obstructive respiratory condition that affects both younger and older patients. It can begin in childhood but can also be of later onset and tends to run in families and has a significant link with other atopic conditions such as eczema, hayfever and food and drug allergies.¹

Common symptoms of asthma include:

• Wheezing: A whistling sound after exhalation and inhalation 
• Shortness of breath
• Coughing: A persistent cough, especially at night
• Chest tightness, affecting a patient's ability to breathe²

Asthma is caused by inflammation of the bronchi and bronchioles that transfer air in the lungs. This causes the bronchi and bronchioles to become sensitive and narrow.

Asthma can be well controlled by avoiding triggers such as smoke, exercise, cold air, viral and bacterial infections such as the common cold or allergens such as dust or animal dander or via the use of treatments usually in the inhaled form such as long and short acting bronchodilators and steroids which help to open the lungs airways and reduce inflammation. The asthma treatment varies from person to person, and some patients require more aggressive treatments than others, depending on patient response.³

Asthma is a lifelong condition and needs to be managed appropriately. A good way to monitor asthma and adjust therapy or even diagnose it, is via the use of peak flow.

Complications of asthma

Asthma can be managed well; in some individuals, asthma causes no issues. However, there are cases where it can become worse and result in complications like any illness. Hence, those on asthma treatment must be managed via regular medication and attend regular reviews with a healthcare professional. However, several complications can occur from asthma, such as respiratory infections.⁴

What is a Peak Flow test?

A peak flow test involves using an instrument called a peak flow meter. This is a small handheld instrument in which the patient has to try to blow all the air from their lungs as fast as they can at full force. This is done three times, after which an average is calculated. This can be done in the initial stages to diagnose asthma or can be used to compare a patient’s readings over a period or to previous readings. Peak flow meters can be obtained from a local pharmacy on prescription.⁵

Why is Peak Flow measured?

Measuring how fast someone can expire can enable a peak flow score to be calculated, which can help to decipher if a patient’s airways are compromised or narrowed. This could help to indicate asthma however, other tests such as spirometry are usually required.

If someone is already asthmatic, then measuring asthma regularly can be useful to monitor a patient's condition. The score from the peak flow can indicate if asthma is becoming worse or improving or whether the medication a patient is on needs to be altered based on peak flow readings. It can also help to indicate whether a patient is having an asthma attack.

It can also help in cases of allergic reactions. Measuring peak flow before and after exposure to a possible allergen helps to identify a possible allergy as well as triggers for asthma, such as dust or pollen.⁶

How to use a Peak Flow meter? 

To measure a peak flow reading, it can be done either while sitting or standing, but it should be done each time to ensure consistency. 

• The pointer on the peak flow should be pushed to the first line of the peak meter scale
• Ensure that the peak flow meter is horizontal and that the scale is not obstructed by fingers or hands
• The patient should breathe in as deeply as possible and ensure that their lips are forming a tight seal around the mouthpiece
• Breathe as fast and hard as possible
• Once this has been done, a reading should be taken and noted down

This should be repeated three times, and the highest of the three measurements should be noted as a peak flow score. A common mistake made by patients is to not blow as hard as they can and not seal the lips around the mouthpiece, as some air can blow out and ensure all the expired air goes through the device.⁶

What is a Peak Flow score?

The peak flow score is known as peak expiratory flow (PEF), which is the volume of the air expired in 1 minute L/min. 

What is a normal Peak Flow reading?

The normal reading varies depending on a patient's age, gender and height. In the cases of asthma diagnosis, the current result can be compared with what is supposed to be normal for a patient of a particular age, gender or height. If there is a vast difference between a normal reading and a patient's reading or a difference between readings compared to daytime and evening reading, it can help to indicate asthma. 

The range of normal peak flow readings can be found on a peak flow chart; this can be used by health professionals such as doctors and nurses to check the peak flow readings and if they are in range.

Usually, in healthy individuals, peak flow readings can differ from different periods; usually, peak flow readings are lower in the morning compared to the evenings.

Can Peak Flow help exacerbate acute asthma?

If a patient has untreated asthma, then peak flow readings will generally be low, regardless of a patient's health. If a patient’s bronchi and bronchioles are narrowed, then the peak flow will be lower than expected for their age, gender and size. The peak flow readings will also differ and usually be lower in the morning than the evening. This difference is greater in patients with untreated asthma.

A peak flow chart is usually issued to keep a record of readings, usually, a best of three readings is taken every morning and evening over 2-3 weeks. These readings can be used to alter a patient's asthma management and sometimes can be taken after administering asthma medication to observe the response in their condition.

However, asthma can be particularly useful as it can help to monitor acute asthma exacerbations. Measuring peak flow readings can assess if treatment is working and if peak flow readings improve once treatment is initiated; then, this monitoring can help.

A very big difference in current and previous readings could indicate that asthma control could have worsened, or an asthma attack or exacerbation may be occurring. This may mean that the asthma treatment that a patient is on may need to be stepped up, and a new management plan may be needed. This is done via an asthma action plan, which is reviewed and updated at least annually with an asthma nurse or GP. This action should be taken to any A&E and respiratory consultant meetings if needed. The peak flow readings that should be taken should be the best or highest readings. 

Below is an example of a peak flow chart.⁷

^{Figure 1: Peak flow chart}

Summary

A peak flow test is a simple but effective test which helps healthcare professionals monitor and diagnose asthma but also helps in situations where asthma may have worsened. This can then help to further manage the patient's management and lead to treatment alterations.