In the treatment of asthma and chronic obstructive pulmonary disease, using a lever aid to improve drug delivery from an inhaler is recommended for patients with poor muscle strength. However, no studies have investigated the effect on hand strength of using a lever aid. Here, we measured hand strength before and after operating a lever aid and tried to predict the required strength. We compared the pinch force required to activate a pressurized metered dose inhaler (pMDI) and a dry powder inhaler as well as the rotational torque required to activate a soft mist inhaler (SMI) before and after attaching a lever aid. We then assessed the correlation between the theoretical and measured pinch force after fitting the lever aid. Use of the lever aid significantly reduced the pinch force required for pMDI operation from 26.13–48.74 N to 4.90–16.87 N. In contrast, using a lever aid significantly reduced the force needed to rotate SMI, although the rotational torque required to operate did not change. There was a significant positive correlation between the theoretical and measured pinch forces required to activate a pMDI fitted with a lever aid. Using a lever aid will increase the number of patients who can use this device.
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