[Six minute walk test in young native high altitude residents]. / Prueba de caminata de 6 minutos en residentes nativos de gran altitud.

Background: The 6-minute walk test is widely used and evaluates the functional capacity to perform sub-maximal exercise, its behavior in healthy young native hight-altitude resident is unknown. Objective: To describe the behavior of the 6-minute walk test in healthy young native hight-altitude resident. Material and methods: Analytical cross-sectional design. Consecutive subjects born and residents of the cities of La Paz and El Alto (Bolivia), both genders, without cardiopulmonary disease or physical limitation were studied. Their altitude, hematological, demographic and simple spirometry variables were informed. The differences were calculated with the t-test for independent or dependent groups according to the type of comparison. A p < 0.05 was considered significant. Results: 110 subjects were studied, at an altitude of 3673 ± 250 meters above sea level, age 24 ± 5 years old, 67 (60.90%) were women. The hemoglobin was 15.20 ± 2.46 g/dL. Prior to the test in 37 (33.63%) subjects the partial oxygen saturation was < 92% (90.92 ± 0.92%), its correlation whit meters walked, r = - 0.244, p < 0.010. Total meters walked: 581 ± 35 (627.3 ± 52.88 sea level); with the reference equations from Enright PL: 542 ± 75 and Osses AR: 459 ± 104, both obtained at < 1000 meters above sea level. Vital signs were whitin normal limits. Conclusion: Sub-maximal exercise capacity estimated with the six-minute walk test at high altitude is lower than that reported at sea level.Reference equations underestimated the meters walked at high altitude.

Introducción: la prueba de caminata de 6 minutos es de amplio uso y evalúa la capacidad funcional para realizar ejercicio submáximo, se desconoce su comportamiento en residentes jovenes sanos nativos de gran altitud. Objetivo: describir el comportamiento de la prueba de caminata de 6 minutos en residentes jovenes sanos nativos de gran altitud. Material y métodos: estudio de diseño transversal análitico. Se estudiaron sujetos consecutivos nacidos y residentes de las ciudades de La Paz y El Alto (Bolivia), de ambos géneros, sin enfermedad cardiopulmonar o limitación fisica. Se acotaron variables de altitud, hematológicas, demográficas y espirometria simple. Las diferencias fueron calculadas con la prueba t para grupos independientes o dependientes según la comparación. Una p < 0.05 fue considerada significativa. Resultados: se estudiaron 110 sujetos, altitud de 3673 ± 250 metros sobre el nivel del mar, edad 24 ± 5 años, 67 (60.90%) fueron mujeres. La hemoglobina 15.20 ± 2.46 g/dL, previo a la prueba, en 37 (33.63%) sujetos, la saturación parcial de oxigeno estuvo < 92% (90.92 ± 0.92%), su correlación con metros caminados r = - 0.244, p < 0.010. Metros caminados totales: 581 ± 35 (627.3 ± 52.88 nivel del mar); con las fórmulas de referencia de Enright PL: 542 ± 75, y de Osses AR: 459 ± 104, ambas obtenidas a < 1000 msnm. Los signos vitales estuvieron dentro de limites normales. Conclusión: la capacidad de realizar ejercicio submáximo estimada con la prueba de caminata de 6 minutos en la gran altitud es menor que la referida a nivel del mar. Las formulas de referencia infraestimaron los metros caminados en la gran altitud.

Possible strategies to reduce altitude-related excessive polycythemia.

We sought to determine the effects of three treatments on hemoglobin (Hb) levels in patients with chronic mountain sickness (CMS): 1) descent to lower altitude, 2) nocturnal O2 supply, 3) administration of acetazolamide. Nineteen patients with CMS living at an altitude of 3,940 ± 130 m participated in the study, which consisted of a 3-wk intervention phase and a 4-wk postintervention phase. Six patients spent 3 wk at an altitude of 1,050 m (low altitude group, LAG), six received supplemental oxygen for 12 h overnight (oxygen group, OXG), and seven received 250 mg of acetazolamide daily (acetazolamide group, ACZG). Hemoglobin mass (Hbmass) was determined using an adapted carbon monoxide (CO) rebreathing method before, weekly during, and 4 wk postintervention. Hbmass decreased by 245 ± 116 g (P < 0.01) in the LAG and by 100 ± 38 g in OXG, and 99 ± 64 g in ACZG (P < 0.05, each), respectively. In LAG, hemoglobin concentration ([Hb]) decreased by 2.1 ± 0.8 g/dL and hematocrit by 7.4 ± 2.9% (both P < 0.01), whereas OXG and ACZG only trended toward lower values. Erythropoietin concentration ([EPO]) decreased between 81 ± 12% and 73 ± 21% in LAG at low altitude (P < 0.01) and increased by 161 ± 118% 5 days after return (P < 0.01). In OXG and ACZG, the [EPO] decrease was ∼75% and ∼50%, respectively, during the intervention (P < 0.01). Descent to low altitude (from 3,940 m to 1,050 m) is a fast-acting measure for the treatment of excessive erythrocytosis in patients with CMS, reducing Hbmass by 16% within 3 wk. Nighttime oxygen supplementation and daily acetazolamide administration are also effective, but reduce Hbmass by only 6%.NEW & NOTEWORTHY To our knowledge, this is the first study examining the effect of three different treatments [descending to lower altitude (from 3,900 m to 1,050 m), nocturnal oxygen supply, and administration of acetazolamide] on changes in hemoglobin mass in patients experiencing chronic mountain sickness (CMS). We report that descent to low altitude is a fast-acting measure for the treatment of excessive erythrocytosis in patients with CMS, reducing Hbmass by 16% within 3 wk. Nighttime oxygen supplementation and daily acetazolamide administration are also effective, but reduce Hbmass by only 6%. In all three treatments, the underlying mechanism is a reduction in plasma erythropoietin concentration due to higher oxygen availability.