Numerical Simulation of Salbutamol Deposition in VHC Devices

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Valved holding chamber (VHC) devices are an essential piece of technology for pressurized Metered-Dose Inhaler (pMDI) users who cannot properly coordinate their inhalation with the actuation of the spray. The unique design characteristics of the VHC devices, particularly the one-way inhalation valve, make this device performance evaluation complex to execute. Another VHC role is to reduce the throat deposition, caused by the pMDI high velocity spray. When it is fired it into the device, the coarser particle fraction of the emitted plume is reduced by directly impacting onto the walls. A computational model was developed for a better understanding of the geometric features that affect the reduction of the spray plume by the VHC. This model predicted the transport, evaporation of propellant and wall deposition of the pMDI spray inside the VHC device. A constant flowrate of 60 L/min, passing through the device, was assumed. This model was applied for six VHCs: Aerochamber, A2A Spacer, Compact SpaceChamber, SpaceChamber, Nebuchamber and Volumatic. The results show that the use of a VHC against a solitary pMDI, reduced the throat deposition by 57.9% (Compact SpaceChamber) to 79.7% (A2A Spacer). It was verified that droplets with diameter ≥ 17 µm (mainly composed by propellant) deposit in the further portion of the VHC body by direct impaction. Particles between 3 µm and 17 µm tend to sediment by gravity force. Drug particle mass deposited in the valve of the Volumatic (8.0 µg – Coin valve design) was highest and lowest for the Nebuchamber (1.8 µg – Duck valve design). The deposition in the VHC body was highest for the AeroChamber (31.9 µg) and lowest for the Nebuchamber (14.5 µg). VHC devices design could be improved by modifying the dimensions of the body to target a specific coarse particle diameter range with the help of numerical tools.