TABLE 2.

Physiological variables during hypercapnia.

Variable	Young adults N = 20	Older adults N = 19	p-value
Heart rate (beats per minute)
Normocapnia	53 ± 1	54 ± 2	0.62
4% CO2	56 ± 2∗	55 ± 1	0.89
6% CO2	58 ± 1∗	57 ± 1∗	0.65
End-tidal CO2 (mmHg)
Normocapnia	40 ± 1	40 ± 1	0.74
4% CO2	47 ± 1∗	46 ± 1∗	0.38
6% CO2	49 ± 1∗	48 ± 1∗	0.25
Oxygen saturation (%)
Normocapnia	98 ± 1	97 ± 1	0.06
4% CO2	98 ± 1	98 ± 1	0.46
6% CO2	98 ± 1	98 ± 1	0.95
Mean arterial pressure (mmHg)
Normocapnia	94 ± 1	101 ± 2	0.01
4% CO2	93 ± 1	104 ± 3∗	< 0.001
6% CO2	96 ± 1	108 ± 3∗	< 0.001

Data are mean ± standard error. The reported p-value denotes group differences at each protocol stage. ^∗p < 0.05 vs. normocapnia within each group.