Breathing Simulators

• Existing methods for in-vitro performance evaluation of spacers and holding chambers used with pressurized metered-dose inhalers are largely based on their function with adult patients. 
• The special requirements of the large population of young children with respiratory difficulties are not well served by tests that measure drug delivery at 30 l/min under continuous flow conditions. 
• Aspects, such as inhalation valve resistance and dead space between the inhalation valve and the patient's lips, which may be unimportant with patients having larger tidal volumes, can be of major significance when the spacer or holding chamber is used with young children, particularly those with restricted airways. 
• Furthermore, the proper functioning of inhalation and exhalation valves associated with holding chambers cannot be adequately tested under constant flow conditions. 
• There is therefore a case to be made for developing test methods for drug delivery devices used by infants or small children that more closely match breathing behavior for these patients.
• Faced with these issues, an attempt has been made at Trudell Medical International to evaluate the performance of spacers and holding chambers for use by infants and small children in a way that is believed to mimic the clinical situation more realistically. 
• To do this, measurements of total mass per actuation of the pMDI from the spacer or holding chamber are determined by filter collection at representative breathing patterns (tidal volume, inspiratory/expiratory ratio, rate per minute) using a simulator. 
• TMI uses various types of breathing simulators, including the Compass system (PARI GmbH – see illustration below), as well as both pediatric and adult ventilator-test lung systems. 
• The simulation of aerosol delivery from a holding chamber with facemask attached is challenging, as it is necessary to simulate both the facial profile and skin surface texture to obtain realistic mask fit and sealing. The ADAM model child face developed at Trudell Medical overcomes these concerns, and aerosol delivery is characterized by collection on filter media (Filtrete^†, 3M Corp., St Paul, MN) located just inside the lips of the model.