OBJECTIVEReduced oxygen availability at a high altitude is associated with increased pulmonary arterial pressure (PAP). With the altitude goes up the change of PAP in healthy children is still not clear. The difference of PAP in native Tibetan and Han children at a high altitude are also not clear. Many studies have shown that Doppler echocardiographic estimation of PAP correlates closely to the values obtained with the invasive measurement. Therefore the indexes of PAP in health children living at different altitudes were investigated and the indexes of PAP in Han and Tibetan children at the high altitude were compared by Doppler echocardiography.

METHODSA randomized survey was carried out on the indexes of PAP with Doppler echocardiography (HP-8500 and CAL-163 echocardiographic machine) by two doctors of Qinghai Provincial Women and Children Hospital from June 1998 to July 2002. The survey covering Jiuzhi Qinghai (at 3700 m above the sea level), Xining Qinghai (at 2260 m above the sea level) and Shanghai (at 16 m above the sea level) included a population of 1061 children aged 0 - 14 years. The population of 1061 composed of 218 Han children at Shanghai, 567 Han children at Xining Qinghai and 276 children at Jiuzhi, Qinghai including 118 migrated Han and 148 native Tibetan children. The physical, EKG and chest X-ray examination of each child were carried out to ensure all the subjects were healthy. A pulse oximeter was placed on each child's foot to provide measurements of arterial oxygen saturation (SO2) distal to the ductus arteriosus. The indexes of PAP included right ventricular systolic time interval (RSTI) and mean of pulmonary arterial pressure (mPAP) which was assessed by a multiple regression equation (mPAP=27.79 + 35.42 x PEP/AT-50.85 x AT/ETc). The AT/ETc was that AT/ET was divided by R-R. The RSTI included previous ejection period (PEP), ascending time (AT), ejection time (ET), PEP/AT and AT/ET. All subjects were divided into 7 age groups. The data of PAP indexes were compared among three different altitude groups and age groups. The data of PAP indexes were also compared in Han and Tibetan children living over 3700 m sea level in each age group.

RESULTSWith the altitude increase the SO2 of the subjects obviously reduced and the indexes of PAP changed. The SO2 correlated closely with the PEP, AT, PEP/A, AT/ET and mPAP (r = 0.352, 0.144, -0.394, -0.166 and -0.363, respectively; P < 0.01). The AT and AT/ET in the groups of 2260 m and 3700 m were shorter than those in the group of 16 m (P = 0.03-0.000) in each age group. The PEP and PEP/AT in 3700 m group were longer than those in 2260 m and 16 m groups (P=0.006-0.000) in each age group. The mPAP in 3700 m group was higher than that in 2260 m and 16 m groups in each age group (mean [+/-SE] mmHg, 35.23 +/- 8.72 vs 17.99 +/- 8.78 and 15.86 +/- 8.96 aged 0 - 28 d, 32.06 +/- 13.38 vs 20.72 +/- 5.71 and 14.64 +/- 8.19 aged to 6 mo, 31.83 +/- 10.53 vs 20.89 +/- 10.12 and 14.69 +/- 5.89 aged to 1 yr, 27.58 +/- 13.55 vs 19.12 +/- 9.75 and 17.36 +/- 6.71 aged to 3 yr, 24.19 +/- 8.38 vs 19.64 +/- 9.36 and 16.43 +/- 4.68 aged to 6 yr, 23.90 +/- 11.35 vs 16.77 +/- 6.79 and 14.42 +/- 6.50 aged to 10 yr, 23.08 +/- 7.31 vs 18.53 +/- 7.25 and 15.45 +/- 6.12 aged to 14 yr, P=0.000). With the growth of the children the reduction of PAP was remarkable at 3700 m above sea level (F=5.638 P=0.000), the mPAP indexes of the first, second and third age groups were evidently higher than those of the other age groups. The SO2, RSTI and mPAP in the native Tibetan children were not different from those in the migrated Han children (P > 0.05) in each age group.

CONCLUSIONThe PAP of healthy children at the high altitude was different from that of healthy children at the low altitude. The PAP of the healthy children at 3700 m above sea level was remarkably increased. At 3700 m above sea level the PAP of newborns and infants increased much more compared with that of juvenile. The race may not significantly affect the PAP at the high altitude. The high altitude hypoxic environment might play a major role in the increase of PAP.