Pressure flow characteristics of the valve in spacer devices 1307 During expiration the flows

During expiration the flows required to close the Volumatic valve were slightly higher than those required to open the valve, but lie still in a range easily achievable by infants. The flows required to close the Nebuhaler valve were significantly higher than those required to close the Volumatic valve. In the vertical position the expiratory flows averaged 73.9 ml/second (range 69-8-81*5 ml/second) for the Nebuhaler and 24-3 ml/second (range 11-7-31-2 ml/second) for the Volumatic. These flows required for valve closure in Nebuhaler may not be achievable by infants. The reported values for peak tidal expiratory flow in normal infants (5 to 11 months of age) are 70 ml/second.5 During most of expiration the flow is likely to be considerably less, especially in infants with obstructive airway diseases. Infants with expiratory flow limitation during tidal breathing can not increase expiratory flows without increasing lung volume. Failure to close the spacer valve exposes the infant to the risk of rebreathing. The intradevice and interdevice coefficients of variation for both types of spacer devices are acceptable. The higher coefficients of variation found during expiration in the Volumatic spacer device than found for Nebuhaler are interesting but of no clinical importance. Thus the intradevice or interdevice variability is not an additional factor to be considered when using airspacers in infancy. Although up to 100 activations of a metered dose inhaler did not result in an increase in the pressure or flow required to open the spacer valve, prolonged use without adequate cleaning could result in the valve becoming 'sticky', thus requiring greater pressures and flows to operate the valve. Furthermore, the simulated inspiration and expiration in the present study were performed using room air. It is possible that humid expired air could cause the valve to become 'sticky'. In conclusion, our results show that the flows required to open the valves in the Volumatic and Nebuhaler spacer devices are within the range of reported values that can be achieved even by flow obstructed infants. Flows required to close the valve, however, may not lie within reported physiological limits for normal tidal breathing of even healthy infants. Further studies, with particular reference to the flows generated during tidal breathing, and the orientation of the device, are needed to evaluate the possible role of aerosol holding chambers in the treatment of wheezy infants.