Table 2.

Summary of differences between target end-tidal ($P_{{\text{T},\text{CO}}_2}$), end-tidal ($P_{{\text{ET},\text{CO}}_2}$) and arterial ($P_{\text{a}{\text{CO}}_2}$) $P_{{\text{CO}}_2}$, reported as mean ±s.d. (95% CI) and categorized by breathing frequency and experimental phase

Breaths min−1	6	12	18	24	(12, 18, 24)
Phase I: $P_{{\text{T},\text{CO}}_2}$ constant, $P_{{\text{T},\text{CO}}_2}$ varied
$P_{{\text{ET},\text{CO}}_2}$–$P_{{\text{T},\text{CO}}_2}$	2.38 ± 0.99*	0.98 ± 1.43	1.20 ± 1.55	0.62 ± 1.67	0.93 ± 1.53
	(1.83, 2.93)	(0.19, 1.77)	(0.34, 2.06)	(−0.30, 1.54)	(0.47, 1.39)
$P_{\text{a}{\text{CO}}_2}$–$P_{{\text{T},\text{CO}}_2}$	1.86 ± 2.52	1.61 ± 2.19	2.10 ± 2.10	1.44 ± 2.33	1.72 ± 2.17
	(0.46, 3.25)	(0.40, 2.82)	(0.94, 3.26)	(0.15, 2.73)	(1.06, 2.37)
Phase II: $P_{{\text{T},\text{CO}}_2}$ varied, $P_{{\text{T},\text{CO}}_2}$ constant
$P_{{\text{ET},\text{CO}}_2}$–$P_{{\text{T},\text{CO}}_2}$	2.11 ± 1.93*	0.94 ± 1.71	0.75 ± 1.64	0.83 ± 1.75	0.84 ± 1.66
	(1.04, 3.18)	(−0.01, 1.89)	(−0.16, 1.66)	(−0.14, 1.79)	(0.34, 1.34)
$P_{\text{a}{\text{CO}}_2}$–$P_{{\text{T},\text{CO}}_2}$	1.24 ± 2.49	1.48 ± 2.04	1.14 ± 2.41	1.27 ± 2.64	1.30 ± 2.33
	(−0.14, 2.61)	(0.35, 2.61)	(−0.19, 2.48)	(−0.20, 2.73)	(0.60, 2.00)
Combined Phases
$P_{{\text{ET},\text{CO}}_2}$–$P_{{\text{T},\text{CO}}_2}$	2.24 ± 1.51*	0.96 ± 1.55	0.97 ± 1.59	0.72 ± 1.68	0.89 ± 1.59
	(1.68, 2.81)	(0.39, 1.54)	(0.38, 1.57)	(0.10, 1.35)	(0.55, 1.22)
$P_{\text{a}{\text{CO}}_2}$–$P_{{\text{T},\text{CO}}_2}$	1.55 ± 2.48	1.55 ± 2.08	1.62 ± 2.27	1.36 ± 2.45	1.51 ± 2.25
	(0.62, 2.47)	(0.77, 2.32)	(0.77, 2.47)	(0.44, 2.27)	(1.04, 2.00)

Data show $P_{{\text{CO}}_2}$ differences in mmHg.

^*P < 0.02.