Background Reduced oxygen availability at high altitude is associatedwith increased neonatal and infant mortality. We hypothesizedthat native Tibetan infants, whose ancestors have inhabitedthe Himalayan Plateau for approximately 25,000 years, are betterable to maintain adequate oxygenation at high altitude thanHan infants, whose ancestors moved to Tibet from lowland areasof China after the Chinese military entered Tibet in 1951.
Methods We compared arterial oxygen saturation, signs of hypoxemia,and other indexes of neonatal well-being at birth and duringthe first four months of life in 15 Tibetan infants and 15 Haninfants at 3658 m above sea level in Lhasa, Tibet. The Han mothershad migrated from lowland China about two years previously.A pulse oximeter was placed on each infant's foot to providemeasurements of arterial oxygen saturation distal to the ductusarteriosus.
Results The two groups had similar gestational ages (about 38.9weeks) and Apgar scores. The Han infants had lower birth weights(mean [±SE], 2773±92 g) than the Tibetan infants(3067±107 g), higher concentrations of cord-blood hemoglobin(18.6±0.8 g per deciliter, vs. 16.7±0.4 in theTibetans), and higher hematocrit values (58.5±2.4 percent,vs. 51.4±1.2 percent in the Tibetans). In both groups,arterial oxygen saturation was highest in the first two daysafter birth and was lower when the infants were asleep thanwhen they were awake. Oxygen saturation values were lower inthe Han than in the Tibetan infants at all times and under allconditions during all activities. The values declined in theHan infants from 92±3 percent while they were awake and90±5 percent during quiet sleep at birth to 85±4percent while awake and 76±5 percent during quiet sleepat four months of age. In the Tibetan infants, oxygen saturationvalues averaged 94±2 percent while they were awake and94±3 percent during quiet sleep at birth and 88±2percent while awake and 86±5 percent during quiet sleepat four months. Han infants had clinical signs of hypoxemia— such as cyanosis during sleep and while feeding —more frequently than Tibetans.
Conclusions In Lhasa, Tibet, we found that Tibetan newbornshad higher arterial oxygen saturation at birth and during thefirst four months of life than Han newborns. Genetic adaptationsmay permit adequate oxygenation and confer resistance to thesyndrome of pulmonary hypertension and right-heart failure (subacuteinfantile mountain sickness).
Source Information
From the Section of Neonatology, Department of Pediatrics, University of Colorado School of Medicine, Denver (S.N.); the Tibet Institute of Medical Science, People's Hospital of the Tibet Autonomous Region, Lhasa, Tibet Autonomous Region, People's Republic of China (P.Y., S., D., J.Z.); and the Cardiovascular Pulmonary Research Laboratory, University of Colorado Health Sciences Center, and the Department of Anthropology, University of Colorado at Denver — both in Denver (L.G.M.).
Address reprint requests to Dr. Niermeyer at the Division of Neonatology, B-070, Children's Hospital, 1056 E. 19th Ave., Denver, CO 80218-1088.
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