30 MASL 520 MASL 1080 MASL p Young group (n=25) - - - - Gender (M/F) 14-Nov - - - Age (yr) 26.0 (24.0-28.0) - - - Height (cm) 165 (160-174) - - - Weight (kg) 63 (54-72) - - - BMI (kg/m2) 23.3(19.6-25.1) - - - SBP (mmHg) 115 (108-126) 113 (104-122) 110 (101-120) 0.165 DBP (mmHg) 73 (68-78) 71 (69-79) 70 (66-76) 0.756 MABP (mmHg) 88 (82-92) 85 (81-94) 83 (76-92) 0.326 PP (mmHg) 42 (35-51) 38 (33-50) 36 (32-48) 0.272 HR (bpm) 73 (67-80) 67 (63-78)* 71 (63-77)* 0.003 Mean RRI (ms) 827 (754-889) 896 (768-951)* 850 (778-948)* 0.003 SDRR (ms) 40 (29-60) 48 (38-57)* 48 (39-64)* 0.021 CVRR (%) 4.8 (3.9-6.9) 5.4 (4.8-6.4) 5.8 (4.5-7.1) 0.08 TP (ms2) 698 (351-1201) 778 (567-1349)* 899 (528-1612)* 0.013 VLFP (ms2) 196 (113-297) 237 (139-334) 217 (143-383) 0.21 LFP (ms2) 145 (94-369) 227 (147-581)* 242 (131-524)* 0.024 HFP (ms2) 240 (112-443) 323 (187-588) 308 (166-530) 0.228 nVLFP (nu) 31.3 (20.1-39.6) 26.0 (20.3-36.6) 27.8 (22.9-35.3) 0.887 nLFP (nu) 31.0 (20.4-38.5) 33.4 (24.5-43.4) 32.8 (22.3-43.6) 0.289 nHFP (nu) 42.1 (23.6-52.5) 38.3 (29.4-47.5) 33.9 (27.3-53.6) 0.756 LHR 0.77 (0.43-1.46) 0.81 (0.54-1.47) 0.93 (0.39-1.44) 0.326 Old group (n=24) - - - - Gender (M/F) 14-Oct - - - Age (yr) 51.5 (36.8-54.8)§ - - - Height (cm) 161 (156-168)§ - - - Weight (kg) 61 (50-65) - - - BMI (kg/m2) 22.5 (20.6-24.6) - - - SBP (mmHg) 113 (107-123) 110 (101-117) 106 (100-114)*† 0.003 DBP (mmHg) 73 (68-79) 71 (66-75) 71 (65-74) 0.115 MABP (mmHg) 86 (80-95) 84 (80-87)* 83 (77-87)* 0.05 PP (mmHg) 40 (35-46) 39 (32-45) 37 (33-42)* 0.036 HR (bpm) 75 (68-81) 70 (65-78)* 69 (64-76)* <0.001 Mean RRI (ms) 796 (744-883) 858 (765-924)* 873 (793-941)* <0.001 SDRR (ms) 31 (21-39)§ 36 (29-44)*§ 34 (30-46)*§ 0.008 CVRR (%) 3.7 (2.6-4.7)§ 4.1 (3.4-5.1)*§ 4.0 (3.5-5.2)*§ 0.009 TP (ms2) 272 (154-555)§ 491 (308-685)*§ 488 (252-687)*§ 0.011 VLFP (ms2) 87 (50-200)§ 166 (112-304)* 163 (122-330)* 0.002 LFP (ms2) 89 (34-152)§ 118 (73-250)§ 137 (64-212)§ 0.453 HFP (ms2) 79 (36-178)§ 136 (50-223)*§ 114 (44-211)§ 0.034 nVLFP (nu) 32.9 (27.6-52.3) 40.8 (32.3-52.1)§ 47.5 (30.1-52.6)§ 0.223 nLFP (nu) 29.5 (21.0-40.7) 27.9 (21.2-37.2) 27.5 (23.9-37.2) 0.959 nHFP (nu) 27.8 (21.6-37.6) 30.7 (17.4-35.3)§ 22.3 (15.0-39.4) 0.079 LHR 1.12 (0.68-1.65) 0.96 (0.70-1.88) 1.25 (0.62-2.65) 0.275

Table 5: General characteristics, blood pressures, and HRV measures of young and old subjects at 3 altitudes. Values are median and interquartile range (25th to 75th percentile). *p<0.05 vs. 30 MASL; † p<0.05 vs. 520 MASL (Friedman repeated-measures analysis of variance on ranks with Student-Newman-Keuls test for post hoc pairwise comparisons). §p<0.05 vs. young group (Mann-Whitney rank sum test). BMI: Body mass index; SBP: Systolic blood pressure; DBP: Diastolic blood pressure; MABP: Mean arterial blood pressure; PP: Pulse pressure; HR: Heart rate; RRI: RR intervals; mRRI: mean RRI:SDRR: Standard deviation of RRI; CVRR: Coefficient of variation of RRI; TP: Total power; VLFP: Very-low-frequency power; LFP: Lowfrequency power; HFP: High-frequency power; nVLFP: Normalized VLFP; nLFP: Normalized LFP; nHFP: Normalized HFP; LHR: Low-/ high-frequency power ratio; ms: Millisecond; nu: Normalized unit.