Dynamic Change of the Upper Airway during Inhalation via Aerosol Delivery Devices

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Abstract
Although it is likely that the upper airway is a major factor in the large inter- and intra-subject variation in deposition of inhaled drug aerosols in the lung, data on the configuration of the upper airway during inhalation is sparse. We have developed a unique method, using magnetic resonance imaging, to reconstruct the upper airway in three dimensions during inhalation from aerosol devices used to deliver medication to patients with asthma, chronic obstructive pulmonary disease, and cystic fibrosis. Ten healthy adults were imaged while inhaling from a pressurized metered dose inhaler (pMDI), a spacer used with pMDI (spacer), and a high-resistance dry powder inhaler, the Turbuhaler (DPI). The mean cross-sectional area of the oropharyngeal region was significantly larger (Wilcoxon's signed-rank test with Bonferroni correction, p < 0.0167) when the DPI (281 [143] mm2, mean [SD]) was used compared to the spacer (205 [32] mm2, p = 0.016) or pMDI (152 [48] mm2, p = 0.013). Considerable variations in the cross-sectional areas of the oral cavity, oropharynx, and larynx were seen when compared to the upper trachea. The main cause for this was the varying position of the tongue during inhalation via the devices. Although differences were observed when comparing the total volume of the upper airway during inhalation via the DPI (70 [17] cm3) to the pMDI (56 [20] cm3, p = 0.037) or spacer (59 [12] cm3, p = 0.022), these did not reach significance. This study shows that there are very significant variations in the configuration of the upper airway when different devices are used for inhalation. These changes are likely to be produced by a number of factors, including tongue position, device airflow resistance, and patient effort.

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