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 in-vivo situation more realistically. To do this, measurements of total unit dose from the spacer or holding chamber are determined by filter collection at representative breathing patterns using a simulator.

TMI uses various types of breathing simulators. An example would be a pediatric ventilator and a two-compartment training test lung. The system developed at Trudell Medical for testing masked holding chambers consists of filter media (Filtrete™, 3M Corp., St Paul, MN) located at the approximate distance that the patient's lips would be if the spacer or holding chamber was in normal use.

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