Are You Getting the Most From Your Inhaler?
Peak Inspiratory Flow and Why It Is Important
May 6, 2009
You may already know that Peak Expiratory Flow (PEF) is the amount of air you can blow out of your lungs and that it is measured by a peak flow meter. Your PEF measurement helps you and your doctor determine the openness of your airways. But did you know there is another important measure for people with asthma and chronic obstructive pulmonary disease (COPD) called Peak Inspiratory Flow Rate (PIF)? Your PIF is the speed and volume at which you are able to inhale (or breathe in).
Your PIF and How It Affects What Type of Inhaler You Should Use
Many physicians are now switching their patients from metered-dose inhalers (MDIs) to dry powder inhalers (DPIs) because of the required phase-out of chlorofluorocarbons (CFCs). But, unlike MDIs where the medicine is propelled from the canister by an aerosol, the medicine in a DPI is a dry powder and the device is activated by your own effort to forcefully, and rapidly inhale. To do this properly requires that you have a minimum PIF. Your doctor may measure your PIF rate to determine if you can use certain inhaler medicines.
The PIF required for effective use of a DPI varies considerably between different types of inhalers. For an inhaled medicine to be effective, it must reach the smallest branches of your airways. The higher your PIF, the greater the possibility that the particles of medicine will reach these areas of your lungs. The average PIF for a healthy adult is approximately 30 liters per minute. Unfortunately, many patients (and even some doctors ) do not realize that some DPIs require a patient to have a minimum PIF of 67 liters per minute in order to use them. This could present a problem for people with asthma or COPD who cannot breathe in at this PIF rate.
Many children and adults with severe bronchospasm (tightening of the airways), cannot inspire at this rate, so they will not get the most benefit from their DPI medicine. A study published in the European Respiratory Journal* revealed that out of 57 children below the age of six, a total of 15 were not able to reach a PIF of even 28 liters per minute. And only one of 208 children, six years of age and older, were able to use a commonly-prescribed DPI that requires 67 liters per minute.
The lower the required PIF of a device, the easier it is to use, and the larger the number of patients who will be able to use it. For this reason, many pharmaceutical companies have developed new DPI designed inhalers for people with reduced PIF. So, be sure to ask your doctor about your PIF and if your inhaler is right for you.
*Engel, T, Heinig, J.H., Madsen, F., Nikander, K., “Peak Inspiratory Flow and Inspiratory Vital Capacity of Patients with Asthma Measured With and Without A New Dry-Powder Inhaler Device (Turbuhaler•)”, Eur. Respir. J, 1990. 3. 1037-1041.
Online Resources
The American College of Allergy and Immunology
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