Objective: To investigate the diagnostic value of volumetric capnography in the assessment of asthmatic exacerbation.
Methods: Sixty-four patients with asthma exacerbation and 20 normal controls performed spirometry and volumetric capnography recording. The patients with asthma were divided into three sub-groups according to FEV1% pred (A: > 80%, B:40% - 80%, C: < 40%).
Results: FEV1% pred, FEV1/FVC, PEF% pred and MMEF% pred were (98 +/- 9)%, (80 +/- 6)%, (91 +/-15)% and (73 +/- 7)% respectively in the control group, but were (52 +/- 20)%, (50 +/- 10)%, (49 +/-16)% and (28 +/- 16)% respectively in the asthma group, the difference being significant (t = 6.93 - 13.29, all P < 0.01). Compared with the control group, dC2/DV [(19 +/- 6)%/L vs (31 +/- 8)%/L, t = 5. 09, P < 0.01] showed a decrease in the asthma group, dC3/DV [(2.9 +/- 1.2)%/L vs (1.0 +/- 0.4)%/L, t = -6. 14, P < 0.01] and SR23 [(16.8 +/- 10.6)% vs (3.3 +/-1.5)%, t = -6.54, P < 0.01] showed an increase in the asthma group compared to the control group, the difference being significant. Compared with that of the control group, dC2/DV [B:(17 +/-5)%/L, C: (13 +/-4)%/L] showed a decrease (t = -11.82, -16.75, all P < 0.01) and dC3/DV [B:(3.2 +/- 0.8)%/L, C:(4.1 +/-1.2)%/L] and SR23 [B:(17.2 +/- 3.5)%, C:(28.3 +/- 6.9)%] showed an increase (t = 2. 16-26.08, all P < 0.01) in asthma sub-groups B and C. For dC3/DV and SR23, the difference was significant between asthma sub-groups (t = 0.91 -22.18, all P < 0.05). In Pearson correlation analysis, dC2/DV (r = 0.69, 0.54, 0.59, 0.54, all P < 0.01) and dC3/DV (r = -0.62, -0.45, -0.69, -0.58, all P < 0.01) and SR23 (r = -0.75, -0.52, -0.74, -0.62, all P < 0.01) correlated with FEV1% pred, FEV1/FVC, PEF% pred and MMEF% pred.
Conclusion: Volumetric capnography is a quantitative method for evaluating the severity of airflow obstruction and it can be performed easily during tidal breathing.