Peak Flow Meters

Asthma is a disease of the lungs, it is known as an obstructive airway disease, because the symptoms are caused by an obstruction to the airways inside the lung. Although this obstruction is characteristically reversible, some residual obstruction is present at rest depending on the severity of the condition. So the more obstruction there is at rest, the more severe the condition is, this in turn will help determine how much and what type of treatment is needed.
The obstruction can be assessed by measuring how fast the air can be expelled by the patient from his lungs, this is called the Peak Expiratory Flow Rate (PEFR) .
To measure the PEFR, we use a peak flow meter.

What is a peak flow meter?

It is a hollow device that when breathed into can measure the velocity of the air passing through it. Because the velocity of the air being expelled is variable, the device records the highest velocity and this is used to calculate the PEFR.

What is the clinical significance of the PEFR?

1. The absolute value is compared to corresponding prerecorded charts that produce the average healthy PEFR for sex and height. So when a patient’s PEFR is recorded, we take their sex and height and determine from the available charts what the average PEFR should be, this will reveal how severe the impairment is.
   In modern machines, this is done automatically (the result is given as % of normal).
   
2. Also series of readings over a period of time will show whether the patient is improving or deteriorating, this in turn will dictate decisions regarding treatment regimen, hospitalization, further investigation etc.