Table 3– Respiratory effects of evoked hypercapnia during sleep without continuous positive airway pressure (CPAP)

	Room air		P_ET,CO2 5 mmHg above baseline		P_ET,CO2 10 mmHg above baseline
	Pentobarbital	Placebo	Pentobarbital	Placebo	Pentobarbital	Placebo
Upper airway resistance cmH₂O·L⁻¹·s	6.4±8.5⁺	2.3±2.5	7.0±11.1	2.7±2.1	9.4±16^§,ƒ	3.3±3.2^§
V′_E L·min⁻¹	6.0±2.3	5.3±1	9.6±3.8	7.9±2.5	12.1±6.5^§	12.1±3.5^§
V_T L·min⁻¹	0.41±0.15	0.37±0.07	0.61±0.19	0.53±0.17	0.87±0.33^§	0.79±2.4^§
Duty cycle^#	0.43±0.13	0.41±0.04	0.44±0.23	0.42±0.05	0.50±0.30	0.42±0.03
Flow rate^¶ mL·s⁻¹	0.27±0.08	0.27±0.05	0.38±0.10	0.36±0.08	0.52±0.22^§	0.53±0.15^§
Phasic GG-EMG activity % max	4.6±7.9	2.1±4.9	5.8±9.9	2.1±1.9	14±24^ƒ,##	3.3±7.7
Tonic GG-EMG activity % max	2.4±6.3	0.64±2.2	3.8±10.4	0.8±3.8	5.2±13.8^##	1.0±3.4

Data are presented as mean±sd. P_ET,CO2: end-tidal carbon dioxide tension; V′_E: minute ventilation; V_T: tidal volume; GG-EMG: genionglossus electromyogram. ^#: measured as time taken for inspiration (t_I)/total time of respiratory cycle; ^¶: measured as V_T/t_I. ⁺: p<0.05 for drug effect, i.e., higher GG-EMG during pentobarbital versus placebo (all GG-EMG data during carbon dioxide insufflation, general linear model (mixed model)), ^§: p<0.05 versus placebo treatment (Wilcoxon); ^ƒ: p<0.05 versus baseline, same study day; ^##: p<0.1 versus placebo treatment.