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The influence of breathhold on peak expiratory flow in normal and asthmatic children.

We have previously demonstrated a 10% reduction in peak expiratory flow (PEF) in healthy adults following a breathhold at total lung capacity (TLC). This fall was attributed to dissipation of airway wall viscoelasticity, increasing airway wall compliance (Caw). To investigate this phenomenon in children and to determine whether the effect of breathhold would be greater in asthmatics than in normal children, 15 asthmatics and 14 normal children (aged 10-15 yrs) performed maximal post expirations (MFE) with and without a 5 s breathhold at TLC. The entire study was repeated following the inhalation of salbutamol (800 micrograms) to relax the airway smooth muscle (and to increase Caw). Breathhold at TLC resulted in a significant decrease in PEF both in the asthmatics (group mean fall 5.8%; p < 0.01) and normal children (group mean fall 10.3%; p < 0.05). Salbutamol diminished this fall, becoming nonsignificant in the normal children. Similar patterns were also seen in forced expiratory volume in one second (FEV1) and in maximal expiratory flow at 50% vital capacity (V'50). These data are consistent with the proposal that breathhold at total lung capacity dissipated viscoelastic energy (increasing airway compliance) and decreased maximal expiratory flows both in normal and asthmatic children. They also demonstrate the need to standardize the forced vital capacity manoeuvre to decrease the variability in the flows recorded during the subsequent forced expiration.