Investigation Into The Effects Of Valve Pressure On Total Delivered Dose (TDD) From Vhcs

Scott Courtney, Benjamin Pratt

Total delivered dose and valve pressure differential tests have been conducted and compared for several valved holding chambers (VHCs). The results of total delivered dose were compared to the corresponding valve pressure results to identify whether or not there is a correlation between valve pressure and the total delivered dose (TDD).
Both total delivered dose and valve pressure differential (VPD) measurements of several valve holding chambers have been conducted to test the hypothesis that the pressures generated by valves have an impact on the VHCs delivered dose. Results show that there is variance in the pressure differentials created by different valve designs, with the cross-valve producing the lowest pressure differentials on inhalation at tidal breathing simulations for both adult and paediatric rates (0.447 and 0.167 cm/H2O) followed by the disc valve (0.661 and 0.291 cm/H2O) then the single slit valves (0.702 – 0.727 and 0.284 – 0.413 cm/H2O). VHCs exhibiting a lower tidal pressure differential deliver a higher dose (82.41 – 74.69 ug, adult; 71.75 – 69.60 ug, paediatric) when compared to VHCs with higher pressure generation (61.28 – 65.90 ug, adult; 60.10 – 66.45 ug, paediatric). In most cases the cross valve and disc valve generated less pressure than the 2 single slit valves; which correlates with the TDD results where the cross valve and disc valve gave a higher dose than the single slit valves in both adult and paediatric breathing rates.

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