Table 1.

Cardiorespiratory and sympathetic variables during eucapnia, isocapnic hypoxia (peripheral chemoreflex activation), hypercapnic hyperoxia (central chemoreflex activation) and hypercapnic hypoxia (combined peripheral and central chemoreflex activation) in women and men

						ANOVA P values
		Eucapnia	Isocapnic hypoxia	Hypercapnic hyperoxia	Hypercapnic hypoxia	Sex	Trial	Interaction
Respiration
SpO2 (%)	Women	97 ± 1	86 ± 2	99 ± 1	89 ± 1	0.109	<0.0001	0.065
	Men	97 ± 1	87 ± 3	99 ± 0	91 ± 2		a , b , c , d , e , f
VT (l)	Women	0.93 ± 0.27	0.92 ± 0.31	1.43 ± 0.41 † , ‡	1.73 ± 0.41 † , ‡ , §	0.132	<0.0001	0.006
	Men	0.85 ± 0.22	1.08 ± 0.30	1.81 ± 0.35 * , † , ‡	2.06 ± 0.39 * , † , ‡ , §
Rf (breaths·min−1)	Women	13 ± 5	16 ± 5	18 ± 5	22 ± 5	0.517	<0.0001	0.519
	Men	15 ± 4	16 ± 5	20 ± 4	24 ± 7		b , c , d , e , f
Perception of breathlessness (a.u.)	Women	0 ± 0	1 ± 1	5 ± 2	7 ± 2	0.699	<0.0001	0.857
	Men	0 ± 0	1 ± 1	5 ± 1	7 ± 2		b , c , d , e , f
Cardiovascular
HR (beats·min−1)	Women	70 ± 10	78 ± 10	73 ± 9	84 ± 12	0.706	<0.0001	0.658
	Men	69 ± 7	75 ± 5	73 ± 6	83 ± 8		a , c , d , e , f
SBP (mmHg)	Women	113 ± 10	122 ± 9	125 ± 15	143 ± 17	0.011	<0.0001	0.844
	Men	126 ± 10	134 ± 8	141 ± 14	153 ± 18		a , b , c , e , f
DBP (mmHg)	Women	71 ± 7	75 ± 5	79 ± 10	89 ± 9	0.861	<0.0001	0.554
	Men	68 ± 12	75 ± 13	82 ± 14	88 ± 12		b , c , d , e , f
MAP (mmHg)	Women	85 ± 7	92 ± 5	96 ± 11	108 ± 11	0.265	<0.0001	0.526
	Men	88 ± 12	98 ± 11	104 ± 15	112 ± 12		a , b , c , e , f
CO (l·min−1)	Women	5.6 ± 1.7	6.2 ± 1.6	5.8 ± 1.6	7.0 ± 2.5	0.543	<0.0001	0.216
	Men	5.9 ± 1.2	6.8 ± 1.5	6.6 ± 1.7	7.2 ± 1.8		a , c , e , f
COi (l·min−1·m−2)	Women	3.3 ± 1.1	3.6 ± 1.0	3.4 ± 1.1	4.1 ± 1.5	0.676	<0.0001	0.158
	Men	3.1 ± 0.7	3.5 ± 0.9	3.4 ± 1.0	3.7 ± 1.1		a , c , e , f
SV (ml)	Women	84 ± 20	82 ± 22	83 ± 21	86 ± 28	0.582	0.939	0.179
	Men	87 ± 18	90 ± 18	91 ± 23	86 ± 20
TPR (mmHg·l−1·min−1)	Women	16.5 ± 5.4	16.2 ± 5.6	18.3 ± 8.0	17.6 ± 8.0	0.742	0.004	0.998
	Men	15.6 ± 4.5	15.4 ± 5.4	17.3 ± 7.1	16.7 ± 5.0		b , d
TPRi (mmHg·l−1·min−1·m−2)	Women	9.5 ± 2.7	9.3 ± 2.7	10.5 ± 3.8	10.1 ± 3.9	0.229	0.004	0.992
	Men	7.9 ± 2.1	7.8 ± 2.5	8.8 ± 3.3	8.5 ± 2.2		b , d
Sympathetic
MSNA BF (bursts·min−1)	Women	11 ± 3	15 ± 4	22 ± 6 † , ‡	30 ± 8 † , ‡ , §	0.468	<0.0001	0.027
	Men	11 ± 5	15 ± 5	19 ± 6 †	24 ± 6 * , † , ‡
MSNA BI (bursts· 100 heartbeats−1)	Women	16 ± 2	19 ± 2	30 ± 3 † , ‡	36 ± 3 † , ‡	0.574	<0.0001	0.015
	Men	17 ± 2	20 ± 2	25 ± 2 † , ‡	30 ± 2 † , ‡
MSNA amplitude (%)	Women	100 ± 0	119 ± 35	195 ± 34 † , ‡	218 ± 63 † , ‡	0.104	<0.0001	0.031
	Men	100 ± 0	131 ± 45	147 ± 56 *	170 ± 64 * , †

All variables are n = 10 women and n = 10 men. The main effects of sex, breathing trial and their interaction were examined using mixed model ANOVA with repeated measures. SpO₂, oxygen saturation; V_T, tidal volume; Rf, breathing frequency; a.u., arbitrary units; HR, heart rate; SBP, systolic blood pressure; DBP, diastolic blood pressure; MAP, mean arterial pressure; CO, cardiac output; CO_i, cardiac output index; SV, stroke volume; TPR, total peripheral resistance; TPR_i, total peripheral resistance index; MSNA, muscle sympathetic nerve activity; BF, burst frequency; BI, burst incidence. Where a significant interaction is observed, differences identified during post hoc analysis (t tests with Bonferroni correction) are identified as

^* P < 0.05 vs. women,

^† P < 0.05 vs. eucapnia,

^‡ P < 0.05 vs. isocapnic hypoxia,

^§ P < 0.05 vs. hypercapnic hyperoxia.

Where a significant main effect of trial, but no interaction, is observed, differences identified during post hoc analysis (t tests with Bonferroni correction) are shown as

^a P < 0.05 eucapnia vs. isocapnic hypoxia,

^b P < 0.05 eucapnia vs. hypercapnic hyperoxia,

^c P < 0.05 eucapnia vs. hypercapnic hypoxia,

^d P < 0.05 isocapnic hypoxia vs. hypercapnic hyperoxia,

^e P < 0.05 isocapnic hypoxia vs. hypercapnic hypoxia,

^f P < 0.05 hypercapnic hyperoxia vs. hypercapnic hypoxia.