Fisiología y Medicina en Altura

Fisiología y Medicina en Altura

High Altitude Physiology and Medicine

Chronic Intermittent Hipoxia in Chile

Chronic Intermittent Hipoxia in Chile

Chronic Intermittent Hipoxia in Chile

Author: Research team HIGHALTMED CHILE University of Antofagasta

Over the past few decades, Chile has experimented an explosive rise of work-related activities at high altitude, especially in the mining industry, as well as an important increase in the number of workers exposed to this condition. Chronic Intermittent Hypoxia is a unique working modality worldwide because it has a component of severe exposure in each ascent and also a chronic exposure component generated by months and years working in these kinds of tasks, for this reason, workers display different risks of accidents and professional diseases in comparison to those who work at sea level.

Modifications to the D.S Nº 594 1999 regulation of basic health and environment conditions in the line of work (Chilean Health Ministry, 2012) have increased the interest on this subject since it brings important challenges to companies and workers from a biomedical and social perspective, and recognizes Chronic Intermittent Hipoxia at high altitude as a cause of short term professional reversible diseases, mainly cardiopulmonary and neurological, changes such as acute mountain disease in all its variaties, and long term sleeping disorders and pulmonary hypertension Polycythemia. At the same time, it establishes contradictions for high altitude work and proposes measures to mitigate the effects of Chronic Intermettent Hipoxia (CIH).

CIH is a type of daily work in the form of an intermittent high-altitude exposure, which initially was named Chronic Intermittent Exposure to later be named Hypobaric Hipoxia (Jimenez, 1995). This model is different from the acute mountain exposure and chronic exposure of native workers with residence and deposits exploitation at high altitude, such as Cerro Pasco, Perú (4.300m a.s.l.); Rinconada, Perú (5.400m a.s.l.), Potosí, Bolivia (4000m a.s.l.), (Leon-Velarde et al., 2000), (Vasquez & Villena, 2001). Working shift modalities in Chile have a severe exposure component in each ascent and a chronic intermittent component generated by months and years of working in these kinds of tasks.

Working in the mining industry requires highly qualified and trained personnel in new technologies management, the majority of these workers come from larges cities across Chile which are mostly at sea level according to the great mining system map.

Mineral exploitation is the first economic activity in Chile and at least 50% of these mining sites are located at high altitude through Los Andes mountain range, as can be seen in the great mining system map. The chronic intermittent hypoxia working modality carries more than 3 decades of stable development (Jiménez, 2003) and has placed Chile as the first producer of copper, natural nitrates, iodine and lithium worldwide.

Acute Factor of Chronic Intermittent Hypoxia

When non adapted healthy people ascend rapidly to high altitude, they are at high risk of suffering any of the debilitating and potentially lethal diseases that take place in the first days after arrival (Hackett & Roach, 2001) (Bartsch & Swenson, 2013). There is consensus about the fact that travelling to elevations 2.500m above sea level, which is a moderate altitude according to specific literature, is associated with risks of exhibiting one or more forms of high-altitude acute mountain disease.

Risk Factors for Suffering Acute Altitude Sickness

In a working context, a risk is a probability that an event occurs which can harm people’s health (Chilean Law 16.744). All risks are likely to be foreseen and minimized in their occurrence, in the case of high-altitude sickness, the question is: what are the known conditions associated with the appearance or not of the risk?

Reached altitude: the symptoms between acute mountain sickness and frequency of appearance are related directly to the reached altitude. These symptoms have been found in recreational mountaineers on 9% at 2.850m; 13% at 3.050m; 34% at 3650m (Maggiorini, Buhler, Walter, & Oelz, 1990). Globally, high altitude acute disease symptomatolology occurs around 10 – 25% of healthy persons, non acclimatized when ascending to 2.500m a.s.l. and 50 to 85% of those who ascend between 4.500 – 5.500m a.s.l. this last range can be usually a disabling and severe disease, if not fatal (Bartsch & Swenson, 2013).

Effects of chronic intermittent hipoxia on the working man

The mining industry utilizes, as working modality, a system of rotative shifts where subjects work at high altitude and rest at low altitude (LA, 500 – 2.000m a.s.l.) or sea level (SL, <500m) for a proportional worked time. The most commons shift modalities exposed to CIH are 4×3 and 7×7, being the latter the most utilized and compatible with the workers socio-family lives.

Studies indicate that long term exposure adjustments to chronic intermittent hipoxia (CIH) tend to resemble chronic hipoxia from the physiological, ventilatory, cardiovascular and erythropoietic response. However, considering the same altitude, there are differences in the neccesary time to complete acclimatization in some parameters. Chronic hipoxia requires a few months to acclimate, meanwhile CIH seems to require several years to stabilize some of the acclimatization parameters, while others do not end up stabilizing at all (Farias et al., 2013).