Impact of Flow Restrictors on Aerosol Delivery of the Respimat® Soft Mist Inhaler

The modification of an inhaler's air flow resistance influences a patient's inhalation flow profile, thereby affecting the exit velocity of an aerosol leaving the Respimat® mouthpiece. A slower inhalation maneuver results in reduced plume velocity and thus a decreased oropharyngeal deposition due to reduced impaction. This could not only lead to fewer unwanted side effects associated with inhaled therapies, but also enhance lung deposition.

Device prototypes with different air flow resistances were designed using custom-made inserts that can be clipped into the Respimat mouthpiece. The consequences on aerosol characteristics, as well as on in vitro deposition, were analyzed. Computational fluid dynamics simulations contributed to a better understanding of the modified aerodynamic conditions.

Different insert geometries resulted in modified device resistances. However, an increased flow resistance does not necessarily result in an improved in vitro performance. The flow restrictors critically determine aerosol characteristics such as plume velocity and spray pattern, thereby altering in vitro deposition patterns. Quantitative data on mouth-throat deposition and aerosol characteristics are reported.

Integrating flow restrictors into the Respimat mouthpiece offers a promising approach to enhance patient centricity by promoting slower inhalation, thereby reducing the likelihood of suboptimal use. The use of a porous insert acting as a diffuser demonstrated minimal impact on internal airflow dynamics and in vitro deposition, suggesting that such designs can support correct inhalation technique without compromising aerosol performance. By minimizing the influence of patient-dependent factors, this strategy may help standardize the inhalation process and improve therapeutic outcomes. Video Abstract available for this article. Video Abstract (MP4 85313 KB).