Inspiratory capacity through the Turbuhaler in various patient groups.

The effect of the Turbuhaler depends upon the inspiratory flow rate generated by the patient during the inhalation. In children both the peak inspiratory flow rate and the volume of air inhaled at that inspiratory flow rate are important. An inspiratory flow rate greater than 30L/min is usually considered sufficient to achieve an optimal effect. The exact volume which should be inhaled at flow rates above that level is not known. It is probably low (around 0.1-0.2L). In our clinic, virtually all children older than 5 years can inhale a sufficient volume at an inspiratory flow rate greater than 30L/min after careful tuition. With decreasing age an increasing proportion of children will be unable to inhale a sufficient volume at a flow rate greater than 30L/min, and generally children younger than 5 years should not be prescribed Turbuhaler treatment unless they have shown they are able to use it optimally. Both inspiratory flow rate and inhaled volume are decreased during episodes of acute wheeze. In clinical practice this is only important in the young age groups. The vast majority of school children will still be able to benefit optimally from Turbuhaler treatment during episodes of acute wheeze. Although there is a correlation between expiratory pulmonary function and peak inspiratory flow rate, measurement of expiratory pulmonary function cannot be used to predict whether an individual child can use the Turbuhaler optimally.