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PEAK EXPIRATORY FLOW RATE
Pooja Mehta
Family Physician, Vidyanagari, Mumbai, 400 098.
PEFR - peak expiratory flow rate - The maximal airflow rate achieved while forcefully expelling air from the lungs, following maximal inspiration; expressed in litres/ minThus, peak expiratory flow is a measurement, which tells us whether bronchioles are in spasm and if yes, their severity.
Significance of measuring PEFR
- It is helpful in distinguishing between constrictive (TB, silicosis) and obstructive (asthma) lung disease.
- In asymptomatic cases, it may be the only means of diagnosis.
- Can point out specific trigger factors for asthma.
- Can help judge the response to medication.Normal values
These depend on height, age and sex of an individual. Thus values are greater in tall people, adults and in men
Using PEFR in day-to-day practice
1. Every patient’s baseline PEFR must be noted.
2. Judge how low is it as compared to expected value (even on days when the patient is asymptomatic).
3. Look for improvement after nebulisation/ treatment.
4. A reduction in more than 20% of a patient’s baseline value signifies severity.
5. A PEFR of d signifies a critical stage. This patient must be hospitalized, otherwise he may go in respiratory failure.
6. Chronic cases may be asked to purchase there own Peak flow meters and asked to check it 3 times a day. (a Peak flow meter costs only Rs 600/-)The PEFR of an individual should fall within a range of 20% on either side of his predicted normal value.
Can PEFR be increased if expiratory force is greatly increased?
No, this is not possible. You may ask why?
Suppose external pressure is applied to the airways; say due to compression of chest cage- this gets distributed equally to alveoli and the bronchioles, thus compressing them. Alveolar air is forced out into the bronchioles, which being partially collapsed inhibit airflow. If this pressure is increased the bronchioles collapse completely and hence any further increase in expiratory flow is not possible.
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