RESEARCH

Project FONDECYT Nº 11180503

Investigation on the prevalence and blood pressure response in miners exposed to chronic intermittent hypoxia in Chile.

In the north of Chile, a vast number of workers from different productive areas operate at High Altitude. As a result of this, a growing number of sea level residents, including subjects with pre-existing cardiovascular conditions such as arterial hypertension, are acutely exposed to high altitude (HA) without previous experience or preparation, unaware of the potential risks carried by high altitude hypobaric hypoxia exposure. Miners are exposed to continuous environmental changes using a rotating shift system modality, where the subjects work at HA and rest at low altitude or sea level for a time proportional to the time worked, defined as chronic intermittent hypoxia (CIH). The most used shift modalities in CIH exposure are 4 on 3 off and 7 on 7 off days; the latter being the most widely used and compatible with the socio-family life of workers. The impact of such a job schedule on the health of workers exposed to these peculiar working conditions has raised global attention, because this type of altitude exposure has until recently been reported only in Chile, and will bring value information of BP response monitored 24 hours in normotensive and hypertensive worker groups. In fact, this last group presents a high risk of coronary and cardiovascular decease with 54% and 47% respectively and it is unknown the effectiveness of antihypertensive treatment on geographical high altitude conditions.

Limited information is available on the BP response to chronic intermittent hypoxia, and even less in hypertensive subjects, and on the effectiveness of antihypertensive drugs in such conditions. The aims of this study will be to explore the effects of altitude exposition time to CIH on 24-hour ambulatory blood pressure, and as secondary objective to explore the BP response in hypertensive exposed to CIH by 24h blood pressure monitoring and to submaximal exercise, and to assess indirectly the efficacy of their currently antihypertensive drugs in this setting.

This study, in particular, will contribute significantly to understanding the physiological and pathophysiological features associated to CIH through application of non-invasive measurements based on state of the art technology combined with validated scientific protocols for data collection. The results expected should clarify the CIH effects on blood pressure response and its involve in human wellbeing and work performance.

In this context, the following research question are presented: What is the blood pressure response in workers exposed to chronic intermittent hypoxia in northern Chile?

Principal Investigator

Dr. Morin Lang Tapia, morin.lang@uantof.cl

Associated professor, Sciences Department of Human Movement and Rehabilitation, University of Antofagasta.

Locations

Geographical

High altitude: Tarapacá region.

Sea level: from Arica y Parinacota to Coquimbo regions, including cities such as Arica, Iquique, Antofagasta, Copiapó, La serena and Coquimbo.

Physical

University of Antofagasta dependencies.

Mountain range chores: Coposa area (3.879 m. asl.), Ujina area (4.203 m. asl.), Rosario area (4.798 m. asl.).

Doña Inés de Collahuasi mining company.

Workers homes.

Research time frame

December 2018 – December 2020

Financial source

Goverment organism FONDECYT

METHODOLOGY

Research problem

In this context, the following research question is presented:

What is the blood pressure response in workers exposed to chronic intermittent hypoxia in northern Chile?

Hypothesis

H1. Workers exposed to CIH showed differences on 24-hour ambulatory blood pressure at HA from SL and these differences are related to exposition time to CIH.

H0. Workers exposed to CIH not showed differences on 24-hour ambulatory blood pressure at HA from SL.

Objectives

Main Objetive

To explore the blood pressure response by 24 hours Blood Pressure Monitoring and submaximal exercise in workers exposed to chronic intermittent hypoxia.

Specific Objetives

To explore the blood pressure response in workers exposed to chronic intermittent hypoxia by conventional BP measurements and by 24 hours Blood Pressure Monitoring.

To explore the predictive factors in the differences on the 24 h blood pressure response between in high altitude respect to sea level in workers exposed to chronic intermittent hypoxia.

To explore the autonomic cardiac regulation response in workers exposed to chronic intermittent hypoxia by heart rate variability (HRV) assessment, performed with monitoring of 24-hour one-lead electrocardiogram (ECG). Besides, the 24-h ECG monitoring enables arrhythmic events determination and classification.

To explore the blood pressure response to exercise in workers exposed to chronic intermittent hypobaria through the measurement of blood pressure before and after the 6-minute walk test.

To compare the blood pressure response of hypertensive workers sea level residents with those exposed to chronic intermittent hypobaria.

Participants

G1. 20 normotensive workers exposed to CIH more than two years (> 3000 m a.s.l.).

G2. 20 hypertensive workers with more than one year of exposure to CIH.

Sample Type

Non-probabilistic for convenience

Participants

Male adults between 19 and 60 years old from mining company located at 3.870 m asl with 7 x7 rotative shifts and sea level residence.

Eligibility Criteria

Inclusion criteria

- Male and female subjects aged 19-60 years that are currently working in 7 x 7 shifts.
- Permanent residence at low (<500 m) altitude.
- Hypertensive controlled workers on antihypertensive treatment.
- Written informed consent to participate in the study.

Exclusion Criteria

- Hypertensive subjects no pharmacologic controlled.
- History of serious mountain sickness.
- Cardiovascular diseases other than hypertension (atrial fibrillation).
- Suspected or confirmed secondary hypertension.
- Diabetes mellitus.
- Other conditions deemed relevant by the investigator.
- BMI ≥35 kg/m^2.
- Pregnancy.
- Elevated probability of noncompliance with the study procedures.

Study Design

Cross-sectional study.

Variables

Dependent

- Conventional BP measurement.
- 24 h. ambulatory BP.
- Heart Rate Variability (HRV).
- Cardiorespiratory capacity.
- Vital signs.
- Severe mountain sickness.