Application Of Volumetric Capnography In The Measurement Of Bronchial Hyperresponsiveness

[Objective] To investigate the sensitivity and specificity of volumetric capnography(VCap)parameters in the measurement of bronchial hyperresponsiveness (BHR) and bronchodilator responsiveness , and compare with the routine spirometry method .[Method] Forty normal subjects and Sixty chronic cough suspect cough variation asthmatic outpatients were selected to perform bronchial challenge test with VCap and spirometry respectively , all of the subjects undertook spirometry followed by volumetric capnography ; everyone should perform bronchodilator reversibility test after bronchial challenge test .[Results]1. There were dose-dependent reductions in the spirometric measurements and VCap parameters (VDT,VDF,VDW,VDL). There was dose-dependent increasion in the VCap parameters(dC3/DV).2. In the forty normal subjects ,FEV1,PEF decreased by 4%,8% (p<0.001) from the baseline value of forced expiratory volume at the highest dose of histamine . There was a dose-dependent reduction from the baseline value of VDT,VDF,VDW by 8%,7%,7% respectively(p<0.001) and dC3/DV increased by 34% (p<0.001) compared with the baseline value at the postchallenge value.Linear regression analysis showed no significant orrelation between the reduction in FEV1 and in VCap parameters at maximum dose of histamine .3. Positive rate of BHR was 50%.In the posifive group, FEV1,PEF and1VDT,VDF,VDW,dC3/DV were significantly changed between the postchallenge value and the baseline value(P<0.01).In the negative group, FEV1,PEF were not significantly changed between the postchallenge value and the baseline value , But VDT,VDF,VDW were significantly changed between the postchallenge value and the baseline value (P<0.05).OF all subjects , FEV1 was close linear correlated with PEF and VCap parameters (except for dC2/DV,dC3/DV,SR23) in the baseline value,the postchallenge value and the postbonchodilator value (P<0.05).Changes in dead space preceded changes in PEF and FEV1 during histamine challenge. The diagnostic criteria of BHR was that VDT decreased by 28%,or VDF increased decreased by 20% or compared with the baseline value at the postchallenge value.4. Changes in dead space preceded changes in PEF and FEV1 during histamine challenge.[Conclusions]1. Volumetric capnography was an alternative method for bronchial hyperesponsiveness measurement .2. The diagnostic criteria of BHR was that VDT increased by 28% or VDF increased by 20% compared with the baseline value at the postchallenge value.3. The dead spaces measurement of VCap may have clinical value when diagnosing asthma or evaluating its severity degree.