Table 3. Influence of lung injury and PEEP on VRI V_T measurement: ANCOVA.

		ANCOVA		Differences between VRI and EIT
Time point	PEEP [mbar]	Slopes [95% CI]	Intercepts [95% CI]	Mean±SD [ml]	Range [ml]	N
BLH	5	0.95 [0.90/1.00]	12.94 [−0.77/26.65]	−0.95±24.39	−77.34/58.41	63
ALI-0	0	0.99 [0.96/1.04]	0.89 [−13.40/15.19]	−0.74±20.95	−59.38/59.30	63
ALI-5	5	0.96 [0.90/1.02]	12.77 [−6.74/32.28]	−1.37±30.91	−72.46/77.10	63
ALI-10	10	0.90 [0.85/0.95]	26.74 [13.46/40.02]	−1.21±24.64	−59.93/44.21	63
ALI-15	15	0.93 [0.87/0.99]	16.31 [1.85/30.78]	−1.04±22.28	−58.59/47.81	63
Total	0 to 15	0.96 [0.94/0.98]	12.26 [5.95/18.57]	−1.07±24.71	−77.34/77.10	315
F-Test (two-tailed)		P  = 0.07	P  = 0.85

Slopes and intercepts for the different measurement points (BLH: baseline healthy; ALI-0: impaired lungs (ALI) at zero PEEP; ALI-5: ALI at PEEP 5 mbar; ALI-10: ALI at PEEP 10 mbar; ALI-15: ALI at PEEP 15 mbar) are presented on the left. Descriptive measures of the differences in V_T measured by VRI and EIT, displayed as mean±SD (standard deviation) and range [ml] are presented on the right. To investigate the influence of lung damage and PEEP on EIT and VRI V_T measures, an ANCOVA was used to test the equality of slopes and intercepts (using an F test to compare a global model where slope is shared among the data sets, with a model where each dataset gets its own slope). The first P-value tested the null hypothesis that the slopes are all identical (the lines are parallel). The second P-value represents the results of testing the null hypothesis that the intercepts are identical.