Table 2. Comparison of outflow volumes under different IPs and linear regression analysis results.

Outflow pressure (mmHg)	0 mmHg	5 mmHg	10 mmHg	15 mmHg	20 mmHg	Slope (95% CI)	F	p
20	6.1 ± 1.9	4.7 ± 1.4	3.3 ± 1.9	1.7 ± 1.7	1.1 ± 1.3	−0.26 (−0.34 to −0.17)	40.01	<0.0001
30	8.0 ± 1.2	7.2 ± 1.2	5.7 ± 0.5	4.2 ± 0.7	3.2 ± 0.9	−0.25 (−0.30 to −0.20)	116.5	<0.0001
40	8.8 ± 2.1	8.5 ± 3.1	7.2 ± 2.4	6.2 ± 2.2	5.3 ± 1.9	−0.18 (−0.30 to −0.07)	10.21	0.003

Data are presented as mean ± standard deviation unless otherwise noted. IP: intrathoracic pressure; CI: confidence interval