Which design innovation was introduced to inhalers in the 1990s that dramatically improved medication delivery and is now standard in most asthma medications?

The medical industry has seen remarkable innovations in product design over the decades, often responding to critical healthcare needs with ingenious solutions. Some designs have become iconic, representing major breakthroughs in patient care and treatment efficacy. This trivia question focuses on a revolutionary design change that transformed a common medical device and saved countless lives.

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Dose counter mechanism
Hydrofluoroalkane (HFA) propellants replacing CFCs
Built-in peak flow meter
Temperature-regulated medication chamber