Table 2. The different components of work of breathing at different PetCO₂ levels.

PetCO2 (mmHg)	Wi (J/L)			Wex (J/L)			Wtot (J/L)			Wrs (J/L)			Wel (J/L)			WPEEPi (J/L)
	Normal	COPD		Normal	COPD		Normal	COPD		Normal	COPD		Normal	COPD		Normal	COPD
40	0.42±0.22*	0.84±0.47		0.00±0.00*	0.03±0.04		0.50±0.26	0.88±0.47		0.11±0.07**	0.36±0.20		0.31±0.15	0.50±0.34		0	0.02±0.05
50	0.66±0.33	0.96±0.34		0.00±0.01*	0.11±0.11		0.66±0.34	0.94±0.32		0.14±0.14*	0.33±0.16		0.51±0.21	0.60±0.25		0	0.13±0.15
55	0.77±0.40	1.09±0.55		0.01±0.02*	0.07±0.09		0.78±0.40*	1.15±0.59		0.23±0.21	0.37±0.13		0.54±0.25	0.73±0.51		0	0.18±0.20
60	0.89±0.46*	1.42±0.48		0.09±0.15	0.07±0.11		0.97±0.47	1.49±0.55		0.32±0.24	0.39±0.16		0.57±0.28*	1.02±0.47		0	0.51±0.27
65	1.06±0.36	1.40±0.46		0.06±0.05	0.17±0.15		1.12±0.40	1.51±0.56		0.38±0.24	0.33±0.15		0.69±0.16	1.06±0.32		0	0.54±0.18
70	1.26±0.45*	1.65±0.63		0.24±0.28	0.17±0.21		1.50±0.71	1.83±0.73		0.49±0.45	0.49±0.27		0.77±0.15*	1.16±0.40		0	0.65±0.26

*, the P value of both groups was <0.05. **, the P value of both groups was <0.01. Wi, inspiratory work; Wex, expiratory work; Wtot, total work of breathing; Wrs, work to overcome airway resistance; Wel, work to overcome elestance; W_PEEPi, work done to overcome intrinsic PEEP.