Table 2.

Cardiorespiratory and neural responses to hypoxic end-expiratory apnea

	Normoxic Baseline	Hypoxic Baseline	Hypoxic Apnea	P Value
Heart rate, beats/min	60 ± 3	77 ± 3*	81 ± 5*	<0.01
Systolic blood pressure, mmHg	146 ± 5	149 ± 5	164 ± 10*†	<0.01
Diastolic blood pressure, mmHg	80 ± 3	81 ± 2	93 ± 4*†	<0.01
Mean blood pressure, mmHg	103 ± 3	104 ± 2	117 ± 5*†	<0.01
Oxygen saturation, % $\text{S}{\text{p}}_{{\text{O}}_2}$	99 ± 0	82 ± 1*		<0.01
$\text{P}{\text{a}}_{\text{O}}{}_{{}_2}$, mmHg	108 ± 7	50 ± 4*		<0.01
$\text{P}{\text{a}}_{\text{C}\text{O}}{}_{{}_2}$, mmHg	39 ± 1	36 ± 2*		0.03
Respiratory rate, breaths/min	10 ± 1	10 ± 1		0.17
Tidal volume, L/breath	0.56 ± 0.08	0.76 ± 0.10*		0.045
Minute ventilation, mL/min	5.7 ± 1.0	7.5 ± 1.4		0.14
Burst frequency, bursts/min	20 ± 4	23 ± 4	46 ± 7*†	<0.01
Burst incidence, bursts/100 heartbeats	35 ± 7	30 ± 4	59 ± 7*†	<0.01
Mean burst area, AU/min	1.2 ± 0.3	1.5 ± 0.4	6.2 ± 1.6*†	<0.01
AP frequency, APs/min	192 ± 59	241 ± 72	952 ± 266*†	<0.01
AP incidence, APs/burst	9 ± 2	9 ± 2	18 ± 4*†	<0.01
AP incidence, APs/100 heartbeats	326 ± 89	309 ± 87	1,212 ± 327*†	<0.01
Mean cluster incidence, clusters/burst	4.4 ± 0.7	3.9 ± 0.6	6.3 ± 0.9*†	<0.01
Max cluster incidence, clusters/burst	7.7 ± 1.2	8.0 ± 1.4	7.7 ± 1.1	0.79
Max cluster number	12.0 ± 1.9	12.7 ± 2.3	11.9 ± 2.4	0.65
Data duration, s	121 ± 1	102 ± 12	9 ± 2*†	<0.01

Data are reported as means ± SE for n = 7 subjects [n = 6 for arterial partial pressure of O₂ ($\text{P}{\text{a}}_{\text{O}}{}_{{}_2}$), arterial partial pressure of CO₂ ($\text{P}{\text{a}}_{\text{C}\text{O}}{}_{{}_2}$)], respiratory rate, tidal volume, minute ventilation]. AP, action potential; AU, arbitrary units; $\text{S}{\text{p}}_{{\text{O}}_2}$, arterial O₂ saturation from pulse oximetry. Data were analyzed with a 1-way repeated-measures ANOVA. Normality was assessed with the Shapiro–Wilk test. If not normally distributed, a Friedman repeated-measures ANOVA on ranks was conducted. Pairwise comparisons were done with the Holm–Sidak method. Bold type signifies statistical significance.

^*P < 0.05 vs. baseline;

^†P < 0.05 vs. hypoxia.