Respiratory mechanics during methacholine bolus and continuous infusion protocols in asthma model.

Balb/c mice respiratory mechanics was studied in two intravenous methacholine (MCh) protocols: bolus and continuous infusion. The Constant Phase Model (CPM) was used in this study. The harmonic distortion index ( kd ) was used to assess the respiratory system nonlinearity. The analysis of variance showed difference between groups (OVA vs control) and among doses for both protocols. Bolus protocol posttest: there was a difference between OVA and control at 0.3 and 1 mg/kg doses (p<0.0001 and p<0.001) for Rn . Infusion: there was a difference between OVA and control at 192 µg.kg-1 .min-1 dose for Rn , G and H, (p<0.01; p<0.001; p<0.001). An increment was found in kd values near to the observed peak values in bolus protocol. The bolus protocol could better differentiate inflamed and non-inflamed airway resistance, whereas the differences between OVA and control in continuous infusion protocol were associated to airway- and, mainly, parenchyma-related parameters. Moreover, the bolus protocol presented a higher nonlinear degree compared to the infusion protocol.