An instrumented valved holding chamber with facemask to measure application forces and flow in young asthmatic children

Background: Pressurized metered dose inhalers (pMDIs), combined with a valved holding chamber (VHC) and facemask, are often used for young asthmatic children. When using a VHC with facemask, a tight seal between the facemask and the patient's face is crucial for efficient pulmonary aerosol delivery. Realistic parameters for in vitro bench testing are not well known. A custom instrumented OptiChamber Diamond VHC, known as the Facemask Datalogger, was developed to measure the real-time application of force and the air flow through the VHC and facemask. Methods: Thirty asthmatic children aged 1-4 years from the Kinderhaven outpatient clinic, who were prescribed a pMDI/VHC with facemask for regular use, were included in the study. Using the Facemask Datalogger, the parent applied the facemask to the face of the child during normal tidal breathing, and force and flow were recorded. This was repeated three times. A video of the procedure was made and scored on cooperation (scale of 1-5). Results: Mean application force was 4 N (±1.5) equal to 411 g (±156) when expressed as a weight equivalent; intrasubject variability in application force was 23% (±23); intersubject variability in application force was 39%; time needed to empty the VHC was 4.5 sec (±2.9); breaths needed to empty the VHC were 2.9 (±1.1); and mean cooperation score was 4.3 (±0.8). Age was correlated with time (r=-0.49; p=0.006) and breaths needed to empty the VHC (r=-0.75; p<0.001), and observer cooperation score (r=0.65; p<0.001). Conclusions: The Facemask Datalogger is useful for measuring application force and air flow in vivo. Mean application force was lower than assumed in other studies. Older children emptied the VHC faster, with fewer breaths and better cooperation. The data from this study can be used in the future development and testing of new facemasks and VHCs.

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