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

Table 2 Parameters of capnographic measurements

Parameter		Presence of airway obstruction
Parameter	All (n = 1287)	No (n = 916)	yes (n = 371)	Comparison between groups (p-value)
Slope phase 2, s2 (g/mol*l)	2.89 (2.12; 3.81)	3.04 (2.23; 3.92)	2.59 (1.85; 3.43)	< 0.001
Slope phase 3, s3 (g/mol*l)	0.17 (0.10; 0.30)	0.16 (0.09; 0.27))	0.21 (0.12; 0.34)	0.001
log(s3)	−0.72 (−0.92; − 0.49)	−0.74 (− 0.96; − 0.54)	−0.64 (− 0.85; − 0.44)	< 0.001
Ratio s3/s2	0.06 (0.04; 0.10)	0.05 (0.03; 0.09)	0.09 (0.05; 0.14)	< 0.001
log(s3/s2)	−0.96 (−1.05; − 0.82)	− 1.00 (− 1.10; − 0.85)	− 0.85 (− 1.00; − 0.72)	< 0.001
alpha between s2 and s3 (°)	122.0 (116.0; 130.0)	120.5 (115.0; 127.0)	128.0 (119.0; 135.0)	< 0.001
Volume phase 2 (ml)	108.0 (91.0; 128.0)	109.0 (91.0; 129.0)	106.0 (89.0; 127.0)	0.134
Volume phase 3 (ml)	537.0 (392.0; 783.0)	522.5 (373.0; 751.8)	599.0 (432.0; 858.0)	0.002
Area/volume phase 2 (g/mol)	0.28 (0.24; 0.32)	0.27 (0.23; 0.31)	0.29 (0.25; 0.34)	< 0.001
Area/volume phase 3 (g/mol)	0.06 (0.05; 0.08)	0.05 (0.04; 0.07)	0.08 (0.06; 0.10)	< 0.001

The table shows median values and quartiles. The groups were compared with each other using the Mann-Whitney-U-test. For the explanation of parameters see Fig. 1. log(s3) is the logarithm (base 10) of the parameter s3, log(s3/s2) the logarithm (base 10) of the ratio s3/s2. Before taking the logarithm, the values of 0.03 and 0.05, respectively, were added to the parameter values in order to account for zero values and achieve a distribution being as close to normal as possible. The groups were statistically significantly different from each other in all parameters except volume phase 2

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