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.

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Acute mountain sickness, AMS. See Figure 1. It is the most frequent disease with around 10 to 25% of those who ascend to 2.500m a.s.l., characterized by headache, gastrointestinal discomfort, dizziness, fatigue and sleeping disorders, it is considered a benign and self limited symptom which usually gets resolved in 1 o 2 days, if appropriate measures are taken. The presence and severity of this disease are evaluated by the Lake Louise Score System (Roach, 1993), and other international validated inquiries.

High altitude brain Edema, HABE. See figure 1. This disease is infrequent with 0.5 – 1% of those who rapidly ascend above 4000m, is associated to neurogical symptoms and usually evolves from non treated MAM, that after 2 o more days of permanence at high altitude can get worse and evolve to ECA, which can be lethal.

High altitude Pulmonary Edema, HAPE. Disease characterized by pulmonary signs and symptoms that are developed after 2 o more days of exposure to higher altitudes above 3000m. Its incidence is 0,2% when ascending to 4500m a.s.l. in 4 days and increases to 6% if ascending at the same altitude but in a shorter period of time (2 days) and to 15% if the ascent altitude is 5.500m a.s.l. This disease has a mortality around 50% when not treated and this number shows the dependency between high altitude diseases and ascend velocity (Barstch & Swenson, 2013). In summary, for healthy persons, non acclimatized, it is considered a 2.500m a.s.l. threshold to exhibit high altitude disease and it will be more frequent and severe at higher altitudes. On the other hand, it is infrequent for it to happen below this level and if it occurs, it will be mild (Bartsch & Swenson, 2013).

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).

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Ascent rate: ascent velocity is one of the most important risks (Bartsch, Bailey, Berger, Knauth, & Baumgartner, 2004). Recommendations are to make a slow, staggered ascent, with an ascent rate that should not exceed 300-500m/day from 3.000m a.s.l. (Bartsch & Swenson, 2013). In a recent prospective study, it was found that one of the independent risk factors to suffer acute severe disease, is the ascent rate higher to 400m/day after 3.000m altitude (Richalet et al., 2012).

Sleep at high altitude: on the other hand, guidelines for the prevention and treatment of acute mountain sickness (2010) recommend to emphasize that one of the most important risk factors is the altitude at which you sleep, which is defined as the altitude gained at what you sleep for two nights in a row (regardless of the maximum altitude reached during a determined working day) (Luks et al., 2010). Recommended measures are: a) do not increase sleep altitude more than 500m/day above 3.000m. b) for each 3-4 days of slow ascent, it has to be a rest day on the altitude reached in the last working day (Luks et al., 2010).

History of acute altitude sickness: prior appearance of any forms of acute altitude sickness is a strong predictor of recurrence. Whoever has suffered from high altitude pulmonary edema has a 60% probability of recurrence when ascending to 4,500m a.s.l.  (Bartsch & Swenson, 2013).

Pre-acclimatization: it is considered that previous exposure to high altitude establishes a protection factor for a new ascent. It is also considered as a pre-acclimatization criterion to have been at least 4 days at an altitude superior to 3.000m a.s.l. in the 2 months prior to a new ascent (Bartsch et al., 2004). A recent study proposes that a continuous residence for 2 days at 2.200m a.s.l. or a 1.5 – 4 hours daily exposure in a hypobaric chamber with a simulated altitude superior to 4.000m a.s.l., induces acclimatization, reduces symptomatolology of MAM and improves working capacities after a quickly ascent to 4.300m a.s.l. (Muza et al., 2010).

Individual susceptibility: In most cases, the concept of individual susceptibility was not based on factual physiological measures. It has been considered non susceptible to mountaineers which MAM symptomatolology score has been <3 in previous ascents (Bartsch et al., 2004). On the other hand, it has been classified as susceptible those who have been suffering two or more severe episodes of MAM; ECA o EPA in previous ascents at a minimum altitude of 3.500m a.s.l. (sleeping altitude) o 4.000m a.s.l. (Richalet et al., 2012). From a physiolocial perspective multiple factors have been considered such as the ventilatory response to hipoxia, the SaO2, the pulmonary vascular reactivity, the response to exercice in hipoxia, the intracranial pressure and genetic bases to explain the individual susceptibility of intolerance to hipoxia without having a definitive response.

Recently, in a large group of subjects, the association between physiological parameters and susceptibility to suffer a severe high altitude disease was evaluated in search for a predictive pattern; the conclusions demostrated that a severe drop in exercise saturation in hipoxia >22% and a ventilatory low response to exercise in hipoxia <0,78 L/min/kg were independent predictors of high altitude acute sickness. This study also mentions age (<45years), feminine gender, history of migraine, physical activity level (the most capable desaturate more) as positive predictive factors to suffer from severe high-altitude acute sickness (Richalet et al., 2012).

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).

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Regarding the cardiorespiratory response, limited evidence shows that some parameters are still changing after two and a half years of monitoring, like increased pressure of the pulmonary artery; persistence symptomatolology of the acute mountain sickness in each ascent and sleep disorders (Richalet et al., 2002), similar findings for pulmonary high blood pressure and right growth ventricle are described on the study of exposed military subjects to chronic intermittent hipoxia for more than 12 years at 3.550m a.s.l. (Brito et al., 2007). Recent data (Parati G. et al., 2014) also indicate that this condition could be related to an increase of the systemic blood pressure, which can be accompanied by a lower treshold for the heart disease symptoms (Caravita S. et al., 2014). Currently, Lang and cols. (FONDECYT PROJECT Nº 11180503) are developing a study that analyzes the 24-hour BP response to both  HA and sea level in normotensive and hypertensive sea level mining workers exposed to CIH for more than 2 years; preliminary results (not published) indicate that BP tends to be higher in hypertensive subjects despite being pharmacological controlled, and that HTA, ergo Bp 24 h > 130/80 – mmHg, surpassed it from 39% s.l. to 89% HA in all participants.

Generally, scientific research has not been conclusive in Chile, given the methodological limitations that associated with sample size and lack of valid clinical instrumentation, consequently adaptative research studies are needed to the regional reality. Lots of questions have arisen on this topic, suggesting the priority to effectively find an innovative line of risk assessment, prevention and mitigation measures that do not interfere with the worker performance.

Technical guide on occupational exposure to Chronic Intermittent Hipoxia at high altitude

The technical guide has been development by the Ministry of Health with the purpose of caring for the health protection of all workers exposed to chronic intermittent hipoxia, whose tasks are carried out over 3.000m a.s.l., independent of the working activity or productive area on which they perform. This guide seeks, on one side, to establish homogeneus standars of caretaking on one hand, and to optimize the use of resourses on the other hand, by avoiding exams duplicity. Within these measures and actions established by the technical norm, there are some procedures that have not had scientific validation through medical instrumentation practice in Chile, also, some of these protocols consider subjective evaluations that can generate bias in the diagnosis of diseases derived from exposure to chronic intermittent hipoxia. Additionally, a large part of the professional health staff does not have specialized training in the operation of these tools.

On the other hand, the guide establishes that every single worker must recieve an annual theoretical-practical training on the risks and health consequences from both, acute exposure and chronic intermittent hipoxia, which should be imparted in person by qualified healthcare personnel. The health personnel who will carry out these courses must have mountain medicine courses, a certificate of 80 chronological hours in occupational health, and a minimun experience of 3 years in a center that performs health evaluations of geographical high-altitude or high-altitude labor.

Training in chronic intermittent hypoxia

Advanced human capital training in this area is fundamental, especially if we talk about professionals in the healthcare area. In all regional mining operations, we can find polyclinics with professionals in charge of providing health care, training, monitoring or evaluating our workers. This is why the professionals must have specialized knowledge in the changes of the functioning of the human being, and the responses it has on high altitude geographical exposure. The acquired knowledge of physiological parameters changes and the organism response can be essential when determining a possible discharge from the polyclinic, when investigating the signs of possible disease or giving appropriate recomendations before any determined symptomatolology. These assertions are based on existing scientific knowledge and, in the legal obligations established by the DS 549.

On the other hand, training should be approached from a multidisciplinary and contextualized perspective to the needs of workers. Training in multidisciplinary environments is based on prevention and health promotion strategies, which have the challenges of accomplishing interdisciplinary work, developing mechanisms that can be sustained over time by training the communities involved (professionals linked to a particular context).