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Decreasing the interval between actuations from 60 to 30 and 15 s does not seem to affect the aerosol characteristics of ProAir and Ventolin. Although some changes were noticed for Proventil, the pMDI outperformed Ventolin that had the lowest fine-particle mass. The use of a valved holding chamber increased fine-particle mass, but introducing a 10-s delay between actuation and inhalation significantly reduced fine-particle mass.
Berlinski et al. (2017) studied this question.