Diagnostic accuracy of capnovolumetry for the identification of airway obstruction – results of a diagnostic study in ambulatory care

Table 1 Baseline characteristics

Parameter		Presence of airway obstruction
Parameter	All (n = 1287)	no (n = 916)	yes (n = 371)	Comparison between groups (p-value)
Gender (m/f)	589/698	385/531	204/167	< 0.001
BMI (kg/m²)	26.9 (23.7; 31.1)	27.0 (23.9; 31.2)	26.7 (23.4; 35.3)	0.288
Age (y)	59.0 (47.0; 70.0)	56.0 (42.8; 77.0)	62.0 (53.0; 79.0)	< 0.001
FEV₁ z-Score	−0.92 (−1.98; − 0.05)	−0.47 (− 1.09; 0.24)	− 2.47 (− 3.16; − 1.65)	< 0.001
FEV₁/FVC	74.9 (66.2; 81.4)	78.6 (74.1; 83.8)	59.8 (48.9; 70.9)	< 0.001
FEV₁/FVC z-Score	− 0.63 (− 1.72; 0.25)	− 0.12 (− 0.74; 0.54)	−2.44 (− 3.3; − 1.77)	< 0.001
FVC z-Score	−0.58 (− 1.41; 0.20)	−0.37 (− 1.05; 0.38)	− 1.22 (− 2.02; − 0.33)	< 0.001
sRaw (kPa*s)	0.54 (0.27; 1.04)	0.39 (0.20; 0.62)	1.51 (0.85; 2.54)	< 0.001
Raw (kPa*s/l)	0.20 (0.10; 0.35)	0.14 (0.08; 0.23)	0.45 (0.28; 0.71)	< 0.001
FRC_pleth z-Score	−0.40 (− 1.16; 0.57)	− 0.66 (− 1.32; 0.08)	0.30 (− 0.56; 1.32)	< 0.001
Smoking status (current/ex/never)	253/485/536	154/303/447	99/182/89	< 0.001

The table shows absolute numbers in case of frequencies, median values and quartiles in case of continuous parameters. The groups were compared with each other using the Mann-Whitney-U-test, the categorical variables were compared using the Chi-square statistics. FEV₁, forced expiratory volume in one second; FVC, forced vital capacity; sRaw, specific airway resistance (effective); FRC_pleth, functional residual capacity determined by bodyplethysmography. Z-Scores were computed using the respective prediction equations [20]. The groups were statistically significantly different from each other in all parameters except BMI. Among the 371 patients with airway obstruction, 108 (29%) had asthma, 223 (60%) COPD, 24 (7%) the diagnosis of other respiratory diseases (such as restrictive disorders, pneumonia or other infections, pleural diseases, lung tumor, bronchiectasis), while in 16 (4%) of these patients no respiratory disease was found. Among the 916 patients without airway obstruction, 325 (35%) had asthma verified by bronchial provocation, 243 (27%) suffered from other respiratory diseases (such as restrictive disorders, pneumonia or other infections, pleural diseases, lung tumor, bronchiectasis, chronic bronchitis), and 348 (38%) had no respiratory disease

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