Table 2.

Electrocardiogram measurements made in Lowlanders and Sherpa at low and high altitudes during rest and apnea

	Lowlanders			Sherpa
	344 m (n = 14)	5,050 m (n = 14)	5,050 m + Oxygen (n = 7)	5,050 m (n = 8)
Rest
P-wave duration, ms	96 ± 10	77 ± 20b	87 ± 12	97 ± 16c
P-wave amplitude, mV	0.16 ± 0.05	0.14 ± 0.04	0.14 ± 0.06	0.11 ± 0.02b,d
PR interval, ms	169 ± 19	124 ± 27b	146 ± 51	158 ± 38c
QRS duration, ms	71 ± 14	121 ± 3b	119 ± 6b	120 ± 1b
QTc, msa	398 ± 26	456 ± 28b	449 ± 23b	408 ± 15c,d
R-wave amplitude, mV	1.76 ± 0.70	1.24 ± 0.60	1.49 ± 0.45b	1.19 ± 0.22b
T-wave amplitude, mV	0.49 ± 0.19	0.28 ± 0.14b	0.39 ± 0.19b	0.36 ± 0.15b
Apnea
P-wave duration, ms	96 ± 20	74 ± 27	68 ± 22	68 ± 34c,d
P-wave amplitude, mV	0.15 ± 0.05	0.10 ± 0.06b	0.10 ± 0.06b	0.09 ± 0.06b
PR interval, ms	163 ± 31	128 ± 26b	151 ± 55	157 ± 37
QRS duration, ms	74 ± 13	119 ± 4b	117 ± 5b	113 ± 10b
QTc, msa	398 ± 34	410 ± 33e	417 ± 31b	465 ± 51d
R-wave amplitude, mV	1.67 ± 0.79	1.45 ± 0.74	1.65 ± 0.60b	1.25 ± 0.34
T-wave amplitude, mV	0.48 ± 0.19	0.32 ± 0.18b	0.40 ± 0.28	0.37 ± 0.13

All measurements were taken using a standard lead II configuration. Measurements during apnea were taken from the 10 cardiac cycles before volitional breakpoint.

^aFramingham correction (QT + 0.154 × (1 − RR)].

^bSignificantly different from Lowlanders tested at low altitude (344 m), P < 0.05.

^cSignificantly different from Lowlanders tested at high altitude (5,050 m), P < 0.05.

^dSignificantly different from Lowlanders during hyperoxia (5,050 m + oxygen), P < 0.05.

^eSignificantly different from rest within the same condition/group, P < 0.05.