spacer

A spacer is a device used to increase the ease of administering aerosolized medication from a metered-dose inhaler (MDI). It adds space in the form of a tube or "chamber" between the mouth and canister of medication. Most spacers have a one-way valve that allows the person to inhale the medication while inhaling and exhaling normally; these are often referred to as valved holding chambers (VHC).
AeroChamber, InspirEase and Volumatic are examples of a spacer.
Spacers help those unable to breathe deeply, as well as those unable to synchronize their breathing so that they inhale just as the MDI is actuated; the latter is known as poor "hand-lung coordination".

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