Capturing Inhalation Efficiency with Acoustic Sensors in Mobile Phones

Increasing popularity of inhaled therapy for the treatment of asthma and chronic obstructive pulmonary disease (COPD) stimulates research on both drug formulations and smart devices to support efficient pulmonary drug delivery. A major concern is the variability of the drug dose delivered to the lungs from the inhalation devices, due to the following three factors: 1) the drug formulation, 2) the device design, and 3) the patient’s inhalation profile [23]. This paper investigates the use of microphones embedded in modern smartphones to accurately monitor the patient’s inhalation manouvre. In our experiments we focus on dry powder inhalers (DPIs) with a breath-activated capsule spinning mechanism, such as Breezhaler®. We design an algorithm to capture inhalation profiles and evaluate it against measurements obtained with a precise gas flow meter. Our algorithm achieves an average error of up to 4.89 slm (standard liters per minute) given typical inspiratory flow rates through a Breezhaler® between 60 and 130 slm. We detect capsule rotation to ensure the inhalation was effective, and observe that the capsule spinning mechanism helps reduce measurement errors by 2 slm. Given a proper calibration, the proposed algorithm can be used with other capsule-based DPIs, such as HandiHaler®.