Miles Weinberger, MD
Professor of Pediatrics
Allergy, Immunology, and Pulmonary 

The home peak flow meter is a simple portable device for measuring a component of lung function. It is not a substitute for the sophisticated equipment in your physician's office or pulmonary function laboratory that provides more accurate evaluation of lung function. However, the peak flow meter, by providing the ability to monitor lung function at home, provides potentially valuable information for those who do not experience symptoms from airway obstruction until it becomes severe or who mistake anxiety or hyperventilation as acute asthma.

While some recommend routine use of the peak flow meter, most people with asthma gain little additional information since they readily perceive symptoms of chest tightness, shortness of breath, wheeze, or cough when their asthma is active. However, others do not perceive symptoms early in the course of active asthma. This is especially true for patients with severe chronic asthma. Those with longstanding severe chronic asthma frequently are quite tolerant to living with airway obstruction that would be uncomfortable for others with only occasional or less severe asthma. The peak flow meter can provide potentially valuable information for such individuals. This then provides a useful supplement to the physician evaluations and office pulmonary function appropriate for ongoing care of their asthma.

The peak flow meter measures the fastest flow of expired air that can be produced with maximal effort. Since narrowed airways from asthma will decrease the maximal rate of air flow, this is a measure of active asthma. Therefore, the home peak flow meter, when used properly by people with severe chronic asthma who perceive asthma poorly, may tell you and your physician when airways are narrowing from asthma. Progressively falling peak flow measurements also can provide you and your physician with early warning signs of worsening asthma and permit earlier and therefore more effective intervention for acute exacerbations.

The instructions that come with the peak flow measuring device should be read to understand the operation and care of the instrument. Perform the peak flow by:

  • First relax while taking a few slow moderately deep breaths.
  • Then breathe in as far as you can.
  • Hold your breath while placing the mouthpiece in your mouth beyond your teeth.
  • Seal your lips tightly around the mouthpiece; keep your tongue away from the mouthpiece.
  • Blow out as hard and fast as you can.
  • Repeat at least 2 more times.
  • Record the best of 3 trials on your diary form unless that value was so different from the values of the other 2 efforts that you suspect something may have gone wrong. In that case, repeat one more time and record the best effort that is reasonably reproducible

Sometimes it is also useful to measure the peak flow before and after you use your inhaled bronchodilator. In that case, repeat 3 measurements about 3 to 5 minutes after using your inhaler. Record both the best of 3 measurements before and after the inhaled bronchodilator.

Measurement of the peak flow before and after use of the bronchodilator may be particularly useful in determining the completeness of response to that treatment. Early identification of incomplete response to the bronchodilator is important in knowing when other measures are needed to prevent progression of asthma to more severe or prolonged symptoms.

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