Effect of raised lung volume technique on subsequent measures of V'maxFRC in infants

Partial and "full" forced expiratory maneuvers are both used to assess airway function in infants. Despite the increasing use of the raised volume technique, there is little information regarding the influence of lung inflations as are necessary for the raised volume technique on other measurements of lung function in infants. The aim of this study was to assess whether application of the raised volume technique influences subsequent tidal measurements of maximal expired flow at functional residual capacity (V'maxFRC). Paired measurements of V'maxFRC were obtained in 29 healthy infants (aged 6-65 weeks) before and after raised volume maneuvers, wherein a lung inflation pressure of 3 kPa was used. When compared with measurements prior to raising lung volume, there was a highly significant (P < 0.001) decrease in V'maxFRC by 40 ml.sec(-1) when measurements were repeated (95% CI, -59, -20 ml.sec(-1)), equivalent to a reduction of 20% or -0.6 SD scores in flows. There was no significant change in selected tidal breathing parameters, 95% CI of differences between the two sets of measurements being -1.5, 1.2 bpm for respiratory rate; -0.5, 0.2 ml.kg(-1) for weight corrected tidal volume, and -0.04, 0.01 for tidal breathing ratio (tPTEF:tE). In conclusion, although the mechanism remains unclear, raised volume maneuvers may influence subsequent measures of lung function in infants. Further research is needed to clarify the potential mechanisms. In the meantime, the potential impact of the order of lung function tests within any given study protocol should be considered carefully.