A method to assess adherence in inhaler use through analysis of acoustic recordings of inhaler events

Rationale: Poor adherence to inhaler use can be due to poor temporal and/or technique adherence. Up until now there has been no way of reliably tracking both these factors in everyday inhaler use. Objectives: This paper introduces a device developed to create time stamped acoustic recordings of an individual's inhaler use, in which empirical evidence of temporal and technique adherence in inhaler use can be monitored over time. The correlation between clinical outcomes and adherence, as determined by this device, was compared for temporal adherence alone and combined temporal and technique adherence. Findings: The technology was validated by showing that the doses taken matched the number of audio recordings (r² = 0.94, p<0.01). To demonstrate that audio analysis of inhaler use gives objective information, in vitro studies were performed. These showed that acoustic profiles of inhalations correlated with the peak inspiratory flow rate (r² = 0.97, p<0.01), and that the acoustic energy of exhalations into the inhaler was related to the amount of drug removed. Despite training, 16% of participants exhaled into the mouthpiece after priming, in >20% of their inhaler events. Repeated training reduced this to 7% of participants (p = 0.03). When time of use was considered, there was no evidence of a relationship between adherence and changes in AQLQ (r ² = 0.2) or PEFR (r² = 0.2). Combining time and technique the rate of adherence was related to changes in AQLQ (r² = 0.53, p = 0.01) and PEFR (r² = 0.29, p = 0.01). Conclusions: This study presents a novel method to objectively assess how errors in both time and technique of inhaler use impact on clinical outcomes. Trial Registration: EudraCT 2011-004149-42