Peak Inspiratory Flow Rate as a Criterion for Dry Powder Inhaler Use in Chronic Obstructive Pulmonary Disease
Dry powder bronchodilator devices have an internal resistance. Effective use depends on the patient generating an adequate inspiratory flow to break up the powder packets into particles less than 5-μm in diameter that can be inhaled into the lower respiratory tract. This disaggregation takes place inside the device before the dose leaves the inhaler; this process is increased if the acceleration is fast at the start of inhalation. Peak inspiratory flow depends on an individual's effort along with the strength of the respiratory muscles, which may be compromised in those with chronic obstructive pulmonary disease as a result of lung hyperinflation, hypoxemia, and muscle wasting. A handheld inspiratory flow meter can be used with an adjustable dial to simulate internal resistances of dry powder devices to assess whether a patient can achieve an optimal peak inspiratory flow rate of at least 60 L/min. Observational studies demonstrate that 19 to 78% of stable outpatients with chronic obstructive pulmonary disease and 32 to 47% of inpatients prior to discharge after admission for an exacerbation have a suboptimal peak inspiratory flow rate (<60 L/min). These data suggest that peak inspiratory flow rate should be measured against the simulated resistance of the specific dry powder bronchodilator device prior to prescription. If the peak inspiratory flow rate is less than 60 L/min, the patient may not achieve optimal clinical benefit, and a different delivery system, such as a metered-dose or soft mist inhaler or nebulized therapy, should be considered.