Home assessment of peak inspiratory flow through the Turbohaler in asthmatic patients

Abstract

Background - The efficacy of dry powder inhalers depends on the patient's inspiratory flow. Drug delivery from the Turbohaler (Turbuhaler in some countries), a multidose powder inhaler, is optimal at flows of >40 l/min. The aim of this study was to investigate the peak inspiratory flow that can be generated by asthmatic patients through the budesonide Turbohaler (PIF(TBH)) during maintenance treatment at home. Methods - Thirty asthmatic patients, consecutively recruited from the outpatient clinic, inhaled their maintenance dose of 800 (n = 16) or 1600 μg/day (n = 14) for two months or one month, respectively. The Turbohaler was connected to a modified Vitalograph Compact installed at home to obtain printed PIF(TBH) values for all inhalations. Peak expiratory flow (PEF) was measured twice daily. Results - Flows were remarkably constant with individual mean PIF(TBH) values ranging from 55 l/min to 95 l/min. Only 13 of the 5248 PIF(TBH) recordings taken at home (three patients) were >40 l/min and all were >30 l/min. Weekly mean morning PEF values ranged from 114 l/min to 733 l/min. PIF(TBH) values could not be accurately predicted from lung function parameters in individual patients. Conclusions - In a group of stable asthmatic patients inspiratory flow rates rarely fell below the 40 l/min needed to operate a Turbohaler.