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Respiratory nitric oxide and pulmonary artery pressure in Aymara and Caucasian children at high altitude

¹Swiss Cardiovascular Center Bern, University Hospital, 3010 Bern ²Departement of Internal Medicine and Botnar Center for Extreme Medicine, University Hospital, 1011 Lausanne, both in Switzerland, and ³Instituto Boliviano de Biologia de Altura, La Paz, Bolivia

yves.allemann{at}insel.ch

Abstract

Invasive studies suggest that healthy children living at high altitude display pulmonary hypertension, but the data to support this assumption are sparse. Nitric oxide synthesized by the respiratory epithelium regulates pulmonary-artery pressure and its synthesis was reported to be increased in Aymara high-altitude dwellers. We hypothesized that pulmonary-artery pressure will be lower in Aymara than in Caucasian children at high altitude, and that this will be related to increased respiratory nitric oxide.

We, therefore, compared pulmonary-artery pressure and exhaled nitric oxide (a marker of respiratory epithelial nitric oxide synthesis) between large groups of healthy Aymara (n=200, mean±SD age, 9.5±3.6 years) and Caucasian children (n=77) living at high altitude (3'600-4'000 m). We also studied a group of Caucasian children (n=29) living at low altitude.

The systolic right ventricular to right atrial pressure gradient in the Aymara children was normal, even though significantly higher than the one measured in Caucasian children at low altitude (22.5±6.1 vs. 17.7±3.1 mm Hg, P<0.001). In Caucasian children studied at high altitude, the pressure gradient was 33 percent higher than in the Aymara children (30.0±5.3 vs. 22.5±6.1 mm Hg, P<0.0001). In contrast to what was expected, exhaled nitric oxide tended to be lower in Aymara than in Caucasian children living at the same altitude (12.4±8.8 ppb vs. 16.1±11.1, P=0.06), and was not related to pulmonary-artery pressure in either group.

Aymara children are protected from hypoxic pulmonary hypertension at high altitude. This protection does not appear to be related to increased respiratory nitric oxide synthesis.

Key Words: Pulmonary hypertension • hypoxia • children • high-altitude dwellers • nitric oxide