Peak Inspiratory Flow Rate as a Criterion for Dry Powder Inhaler Use in Chronic Obstructive Pulmonary Disease.

Abstract

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 five micron in diameter that can be inhaled into the loser respiratory tract. This de-aggregation 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 strength of the respiratory muscles, which may be compromised in those with chronic obstructive pulmonary disease due to lung hyperinflation, hypoxemia, and muscle wasting. A hand-held 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 liters/minute. Observational studies demonstrate that 19% to 78% of stable out-patients with chronic obstructive pulmonary disease, and 32% to 47% of in-patients prior to discharge after admission for an exacerbation have a suboptimal peak inspiratory flow rate (less than 60 liters/minute). These data suggest that peak inspiratory flow rate 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 liters/minute, 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.