Dry Powder Inhalers Have Internal Resistances
Background: Inhaled bronchodilators are the cornerstone for treatment of those with COPD. However, it is important that the person be able to inhale the medication deep into the lungs in order to open the airways and make it easier to breathe.
Of the four different inhaling devices for bronchodilators, the most common is called the pressured metered-dose inhaler shown in the figure below. Simply pressing the canister down releases a spray (aerosol) from the mouthpiece.
Many bronchodilators are available in dry powder inhalers (see below). All dry powder devices have an internal resistance. As a result, you need to inhale “hard and fast” to literally pull the powder out of the device and inhale it deep into the lungs.
Pressurized metered-dose inhaler.
There is a simple breathing test to determine if you have enough inspiratory force to inhale the powder successfully out of the inhaler. This test is called peak inspiratory flow rate (abbreviated PIFR). Here is a picture of the In-Check DIAL used to measure PIFR.
Dry powder inhalers have an internal resistance.
Study: Dr. Loh and colleagues at the Winston-Salem Baptist Medical Center in North Carolina measured PIFR in patients just before discharge from the hospital for a flare-up (exacerbation) of COPD. The study results are published on-line in the Annals of the American Thoracic Society on April 13 (doi: 10.1513/AnnalsATS.201611-903OC).
Results: 52% of the 123 subjects had a PIFR below 60 liters/min. A value of 60 or higher is considered “optimal” to inhale the powder deep into the lungs. Those with PIFR less than 60 liters/min were more likely to be readmitted to the hospital over 90 days for another COPD flare-up (28%) compared with subjects who had PIFR at least 60 or higher (14%).
Conclusions: The authors concluded that a low PIFR is common in those admitted to the hospital for a COPD flare-up. They recommended that the medical team measure PIFR before discharge, especially if a dry powder is being prescribed.
My Comments: With a PIFR of less than 60, it more likely that some or most of the powder stays in the mouth and throat. IF you are taking a dry powder bronchodilator and IF you find that it does not help you breathe easier, then you should ask your health care provider to measure your PIFR. If an In-Check DIAL is not available to test your PIFR, then you should ask about a different delivery system – possibilities include a pressurized metered-dose inhaler, a soft mist inhaler, or a nebulizer.
In-Check DIAL to measure peak inspiratory flow rate
Woman inhaling aerosol from nebulizer
Soft mist inhaler