Table 3.

Cardiorespiratory values at volitional exhaustion

	Normoxia (FiO2 = 0.21)		Hypoxia (FiO2 = 0.12)
	Control (n = 14)	Preterm (n = 14)	Control (n = 15)	Preterm (n = 13)
HR, beats/min	183 ± 4	182 ± 4	176 ± 3	175 ± 4
SpO2, %	96.3 ± 1.1	95.8 ± 1.1	77.1 ± 1.1	73.1 ± 1.1*
SaO2, %	97.4 ± 1.2	96.5 ± 1.2	76.7 ± 1.1	72.0 ± 1.2*
$\stackrel{.}{\text{V}}$e, L/min	75.47 ± 4.02	75.41 ± 4.04	72.98 ± 3.93	69.47 ± 4.18
f, breaths/min	42 ± 2	46 ± 2	42 ± 2	45 ± 2
Vt, L	1.77 ± 0.17	1.32 ± 0.17	1.81 ± 0.17	1.50 ± 0.18
$\stackrel{.}{\text{V}}$o2, L/min	2.66 ± 0.12	2.47 ± 0.12	2.13 ± 0.11	1.80 ± 0.12
$\stackrel{.}{\text{V}}$co2, L/min	2.70 ± 0.11	2.54 ± 0.11	2.21 ± 0.11	2.04 ± 0.11

Definition of abbreviations: f = respiratory frequency; Fi_O2 = fraction of inspired oxygen; HR = heart rate; Sa_O2 = arterial blood oxygen saturation; Sp_O2 = oxygen saturation as measured by pulse oximetry; $\stackrel{.}{\text{V}}$co₂ = rate of CO₂ production; $\stackrel{.}{\text{V}}$e = expired minute ventilation; $\stackrel{.}{\text{V}}$o₂ = rate of oxygen consumption; Vt = tidal volume.

Values are reported as least-square means ± SE, adjusted for sex.

^*P = 0.01.