Correspondence between Capnovolumetric and Conventional Lung Function Parameters in the Diagnosis of Obstructive Airway Diseases.
BACKGROUND
Capnovolumetry is of interest as a method for the diagnosis of obstructive airway diseases, requiring little cooperation from the patient.


OBJECTIVE
To help in the interpretation of capnovolumetric parameters, we aimed to identify their correspondence to conventional lung function indices.


METHODS
We studied 978 patients from a diagnostic study with complete functional data and the clinical diagnosis of asthma, chronic obstructive pulmonary disease (COPD), or no respiratory disease. Using path analysis, four capnovolumetric parameters (slope of expiratory phase 3, ratio of slopes of phases 3 and 2, volume of phase 2, and the ratio area/volume of phase 3) previously identified as predictors of airway obstruction in terms of spirometry and body ple-thysmography, were analyzed regarding their relationship to each other and the diagnostic categories of asthma or COPD versus control, or obstruction versus no obstruction. We then identified four lung function parameters showing relationships as much as possible isomorphic to those between capnovolumetric parameters.


RESULTS
The four capnovolumetric parameters were related to COPD and obstruction via both direct and indirect influences, but only two of them to asthma. Regarding the correspondence to lung function parameters, the slope of expiratory phase 3 corresponded best to the ratio of residual volume to total lung capacity, the ratio of slopes of phases 3 and 2 to forced expiratory volume in 1 s, the volume of phase 2 to forced expired flow at 50% of vital capacity, and the ratio area/volume of phase 3 to forced vital capacity.


CONCLUSIONS
Our results indicated an intricate relationship of capnovolumetric parameters to each other and to airway obstruction, asthma, or COPD. The correspondence to conventional lung function measures seemed to reflect the entities lung hyperinflation, overall ventilatory impairment, bronchoconstriction, and ventilated lung volume, in that order. These findings might be helpful for clinicians in the interpretation of capnovolumetry.
['Kellerer|Christina|C|', 'Schneider|Antonius|A|', 'Klütsch|Klaus|K|', 'Husemann|Kim|K|', 'Sorichter|Stephan|S|', 'Jörres|Rudolf A|RA|']
D000328:Adult D000368:Aged D001249:Asthma D019296:Capnography D002245:Carbon Dioxide D016022:Case-Control Studies D005260:Female D006801:Humans D008297:Male D008875:Middle Aged D010993:Plethysmography, Whole Body D029424:Pulmonary Disease, Chronic Obstructive D012129:Respiratory Function Tests
Capnovolumetry Asthma Chronic obstructive pulmonary disease Path analysis Airway obstruction Spirometry Body plethysmography