Abstract
BackgroundWhile millions of people are living permanently at high altitude (>2,500 m) worldwide, the mechanisms underlying their tolerance to chronic hypoxia and those responsible for the occurrence of chronic mountain sickness (CMS) remain to be elucidated. Excessive erythrocytosis (EE) is thought to be the main mechanism responsible for CMS symptoms and is included in the definition of CMS, but the precise interplay between EE and symptoms of CMS requires further investigations.MethodsThe present study benefits from an exceptional dataset coming from 1,594 dwellers of La Rinconada, the highest city in the world (5,100–5,300 m). Based on individual clinical characteristics, subjects were categorized according to the presence of EE and CMS diagnosis, based on current guidelines.ResultsIn this population of relatively young [32 (23; 39) years] highlanders residing in La Rinconada for only a few years [3 (2; 5) years], the internal prevalence of EE (44%) was high, whereas the internal prevalence of CMS (14%) was similar compared to previous reports in highlander populations living at lower altitude (∼4,000 m) in the Andes. Individuals with EE reported less symptoms compared to individuals with lower hematocrit values. Multivariable analysis revealed that age and sex are the main factors associated with EE, whereas age, hematocrit and number of years living at La Rinconada are factors associated with CMS symptoms.ConclusionIn this specific population of La Rinconada, high hematocrit values were observed but were associated with limited symptoms. These results raise important questions regarding the definition of EE and CMS and their underlying mechanisms in high-altitude populations.
Highlights
140 million individuals reside at high altitude (>2,500 m) worldwide, the largest populations of highlanders being found in South America (Andean), central Asia (Tibetan and Sherpa), and East Africa (Ethiopian) (West, 2017)
Factors Associated With Chronic mountain sickness (CMS) Symptoms (According to the 7 Symptoms From the Qinghai Questionnaire) Multivariable logistic regression revealed that the factors associated with CMS symptoms score were age, number of years residing in La Rinconada, and hematocrit (Figure 3B)
A striking observation was the dissociation between the presence of excessive erythrocytosis (EE) and the presence of CMS symptoms; that is, individuals with EE reported few symptoms, whereas symptomatic individuals had lower hematocrit compared to asymptomatic counterparts
Summary
140 million individuals reside at high altitude (>2,500 m) worldwide, the largest populations of highlanders being found in South America (Andean), central Asia (Tibetan and Sherpa), and East Africa (Ethiopian) (West, 2017). Chronic mountain sickness (CMS) is a clinical syndrome observed in 5 to 33% of individuals residing permanently at high altitude (Leon-Velarde et al, 2005). That many highlanders show high [Hb] but no symptoms, whereas others report symptoms without [Hb] reaching the above thresholds (Gonzales et al, 2013) These observations have led to consider excessive erythrocytosis (EE) as a specific pathophysiological entity or a preclinical form of CMS in individuals residing permanently at high altitude (Vargas and Spielvogel, 2006). Excessive erythrocytosis (EE) is thought to be the main mechanism responsible for CMS symptoms and is included in the definition of CMS, but the precise interplay between EE and symptoms of CMS requires further investigations
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