Table 2– Effects of hyperoxia (HOx) and helium-hyperoxia (HeHOx) on physiological and subjective responses to incremental exercise

	Iso-work rate (30 W)			Peak work rate
	HOx	HeHOx		HOx	HeHOx
Subjects n	19		19	24	24
Work rate W				48±23	54±26*
Operating lung volumes
IC L	2.05±0.39	2.14±0.44		1.46±0.34	1.53±0.28*
EELV L	5.29±1.20	5.20±1.16		5.65±1.13	5.57±1.12*
IRV L	1.10±0.39	1.11±0.45		0.47±0.20	0.49±0.30
V_T/IC	0.50±0.10	0.52±0.11		0.69±0.10	0.68±0.16
Metabolic
V′_CO₂ mL·min⁻¹	697±121	619±94*		915±304	870±304*
Cardiovascular
Cardiac output L·min⁻¹	8.7±1.9	9.6±1.3*		11.4±1.9	12.2±2.5
Heart rate beats·min⁻¹	101±14	104±11		120±17	123±18
Stroke volume mL	84±12	92±9*		95±11	99±15
Ventilatory
V′_E L·min⁻¹	25.7±3.2	27.8±3.1*		29.6±8.7	33.2±10.2*
V_T mL	993±137	1085±123*		994±231	1040±290*
Breathing frequency breaths·min⁻¹	26±4	26±3		30±6	31±6
V′_E/MVV	0.70±0.18	0.68±0.14*		0.89±0.18	0.88±0.15
V′_E/V′_CO₂	27.2±4.6	45.6±7.1*		33.0±7.2	39.0±8.5*
t_I/t_TOT	0.34±0.06	0.32±0.07*		0.34±0.07	0.33±0.07*
V_T/t_I L·s⁻¹	1.30±0.28	1.53±0.42*		1.49±0.50	1.76±0.67*
V_T/t_E L·s⁻¹	0.65±0.10	0.66±0.09		0.75±0.23	0.83±0.26*
Gas exchange
P_ETCO₂ mmHg	41±8	35±7*		49±10	45±11*
S_pO₂ %	98±1	98±1		100±16	97±2
Subjective
Dyspnoea scores	3.7 (1.0–5.0)	3.0 (1.0–6.0)		7.0 (5.0–8.5)	7.0 (5.0–9.0)
Leg effort scores	4.0 (3.0–7.0)	4.0 (2.0–7.0)		7.0 (5.0–8.5)	7.0 (5.5–10.0)

Data are presented as mean±sd or median (range), unless otherwise stated. IC: inspiratory capacity; EELV: end-expiratory lung volume; IRV: inspiratory reserve volume; V_T: tidal volume; V′_CO₂: carbon dioxide output; V′_E: minute ventilation; MVV: maximal voluntary ventilation; t_I: inspiratory time; t_TOT: total respiratory time; t_E: expiratory time; P_ETCO₂: end-tidal carbon dioxide tension; S_pO₂: arterial oxygen saturation measured by pulse oximetry. *: p<0.05 for between-intervention differences at a given time point.