Abstract
Despite evidence that flow-volume curves (FVC) obtained in a body plethysmograph (FVCb) may differ from those obtained by the integration of flow at the mouth (FVCm), it is still common practice to compare FVCm before and after bronchodilator therapy (pre and post BD) in asthmatics. In order to evaluate both the magnitude and source of errors in the flow rate at 50% of vital capacity (Vmax50) that result from using FVCm instead of FVCb, we measured FEVl, static elastic recoil (Pst) and maximum expiratory pressures at FRC (PeFRC). FVCb and FVCm were measured simultaneously with an esophageal balloon in place. Measurements were obtained pre and post BD in 10 asthmatic children aged 8 to 18 years. The mean error in Vmax50m ((Vmax50b-Vmax50m)/Vmax50bX100) pre BD was 25% with a range of 6 to 60%. Post BD it was 13% with a range of -2 to 22%. Pre BD error correlated with both FEVl (%pred) (r=-0.82) and the driving pressure (Pdr=Pes+Pst) at 50% VC (r=-0.74;p<0.05 for both). The PeFRC correlated with Pdr at 50% VC (r=0.74) but not the error in Vmax50. The errors post BD are related to the % increase, in FEVl with BD (r=0.65;p<0.05). Similar results pertained to Vmax25. In conclusion, the use of FVCm instead of FVCb in asthma results in errors that are related to both degree of airflow limitation and the force of the expiration. They also differ pre BD compared to post BD. We therefore suggest that FVCm not be used to assess the response to bronchodilators in patients with asthma.
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Desmond, K., Demizio, P., Allen, P. et al. 1752 POTENTIAL ERRORS IN FLOW-VOLUME CURVES IN ASTHMA. Pediatr Res 19, 402 (1985). https://doi.org/10.1203/00006450-198504000-01770
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DOI: https://doi.org/10.1203/00006450-198504000-01770
