Abstract
Relative to healthy subjects, patients with pulmonary arterial hypertension often present with decreased respiratory muscle strength, resulting in decreased maximum inspiratory pressure. Little is known about the impact of reduced respiratory muscle strength on the ability to achieve the peak inspiratory pressures needed for effective drug delivery when using portable dry powder inhalers (≥1.0 kPa). The objective of this study was to assess the impact of inhaler resistance and patient instruction on the inspiratory flow profiles of pulmonary arterial hypertension patients when using breath-actuated dry powder inhalers. The inspiratory flow profiles of 35 patients with pulmonary arterial hypertension were measured with variants of the RS01 dry powder inhaler. Profiles were determined with a custom inspiratory flow profile recorder. Results showed that going from the low resistance RS01 dry powder inhaler to the high resistance AOS® dry powder inhaler led to increases in mean peak inspiratory pressures for pulmonary arterial hypertension subjects from 3.7 kPa to 6.5 kPa. Instructions that ask pulmonary arterial hypertension subjects to inhale with maximal effort until their lungs are full led to a mean peak inspiratory pressures of 6.0 kPa versus 2.1 kPa when the same subjects are asked to inhale comfortably. Significant decreases in mean peak inspiratory pressures are also observed with decreases in lung function, with a mean peak inspiratory pressures of 7.2 kPa for subjects with FEV1 > 60% predicted, versus 3.3 kPa for those subjects with FEV1 < 50% predicted. In conclusion, despite having reduced respiratory muscle strength, subjects with pulmonary arterial hypertension can effectively use a breath-actuated dry powder inhaler. The probability of achieving effective dose delivery may be increased by using dry powder inhalers with increased device resistance, particularly when subjects do not follow the prescribed instructions and inhale comfortably.