RESUMO
<p><b>BACKGROUND</b>Airway hyperresponsiveness (AHR) is one of the most important characteristics of asthma. This study investigated the parameters, by which assess the airway responsiveness under tidal ventilation.</p><p><b>METHODS</b>Female BALB/c mice were sensitized and challenged with ovalbumin (OVA) (group A), and part of them were treated with budesonide aerosol (group B). All the mice were anaesthetized and mechanically ventilated. The values of tidal volume (Vt), airway pressure (PA), airway flow (F), expiratory lung resistance (RL) and dynamic compliance of the thorax and lung (CT-L) were recorded by the AniRes2003 animal lung function system. In addition, the expiratory volume in the first 0.1 second after the start of expiration (EV0.1) was obtained according to the flow-volume (F-V) curve. The maximal or minimal values of EV0.1, RL and CT-L were documented after each dose of methacholine (MCH) and compared with values from negative control group (group C).</p><p><b>RESULTS</b>(1) When the dose of MCH reached 100 ng/g or 200 ng/g, the decrease of Vt in group A was much more significant than group C (P = 0.001, < 0.001 respectively), but not so between groups B and group C (P = 0.974, 0.362 respectively). (2) With the dose of 25, 50, 100 or 200 ng/g MCH, the decrease in percentage of EV0.1 in group A was much higher than group C (P = 0.012, 0.025, 0.001, 0.003 respectively), while that in group B showed no significant difference as compared with group C (P = 0.507, 0.896, 0.972, 0.785). (3) RL and CT-L: with the dose of 200 ng/g MCH, there was a statistically significant increase of RL in group A compared to group B or group C (P < 0.001, < 0.001 respectively), but no significant difference between groups B and C (P = 0.266). With doses of 100 ng/g and 200 ng/g MCH, there was a statistically significant decrease of CT-L in group A compared to group B (P = 0.001, = 0.001) and group C (P < 0.001, < 0.001 respectively), but no significant difference between groups B and C (P = 0.775, 0.310). (4) Histopathology: there were eosinophilic predominant peribronchial and perivascular inflammatory influx in murine lungs after OVA sensitizing and challenging, which could be counteracted by inhalation of budesonide in group B.</p><p><b>CONCLUSIONS</b>The decline in EV0.1 in response to MCH challenge correlated with simultaneous changes in Vt, RL and CT-L, but more sensitively than all the other parameters. The decline in EV0.1 and inflammation in murine lung could be significantly alleviated by inhalation of nebulized budesonide solution, which indicated that EV0.1 to MCH is a valid measure of AHR in mice.</p>