Change in capnogram waveform is associated with bronchodilator response and asthma control in children
Résumé
BackgroundAirway hyper-reactivity, inflammation and remodeling contribute to inhomogeneity of ventilation-perfusion ratio VAQ in asthma. Short-term variations in V.AQ can cause changes in expired capnographic indices. ObjectivesTo measure acute changes in the phase 3 slope of the volumetric capnogram after beta 2-agonist inhalation (Delta SIII), for comparison with airway response based on FEV1 (Delta FEV1), and asthma control. Subjects and MethodsAfter ethical approval and informed consent, 72 children aged 6-18y, followed up for asthma underwent spirometry and capnography before and after beta-agonist inhalation through a spacer, using a side-stream rapid infrared analyzer. Asthma control was assessed using the GINA questionnaire. ResultsChildren with positive reversibility tests (defined as Delta FEV1>12%) had a significantly higher Delta SIII (mSE: 87.4 +/- 41.4) versus those with negative tests (31.3 +/- 14.0%, P=0.001). Uncontrolled asthma was associated with a significantly larger Delta SIII (103.4 +/- 64.0%, n=7) compared to partly controlled (52.0 +/- 26.1, n=24; P=0.009) and controlled asthma (30.8 +/- 16.3, n=41; P=0.003). Neither Bohr dead space nor Delta FEV1 were different between asthma control groups. Conclusions Delta SIII was significantly larger in children with positive response to beta 2-agonist, and in uncontrolled asthmatics. To our knowledge these are the first data on exhaled CO2 phase III volumetric slope change and asthma control. The observed Delta SIII could be due to an increased ventilation of inhomogeneous peripheral lung units, and merits further evaluation as a potential phenotypic biomarker in asthma.