Hypoxia And Altitude Sickness

Introduction

Some health conditions can be induced when an individual reaches high altitudes since the air pressure, as well as oxygen levels at such places, are much lower compared to those at sea level. Such knowledge would be necessary for anyone who has plans of venturing into elevated areas, whether it is to do with leisure activities like hiking or sports like skiing, or even working purposes such as mountain climbing or pilot operations.

Acute mountain sickness or altitude sickness is a disorder which has symptoms that show when one climbs up to elevations more than 2,500 metres (that is around 8,200 feet).^1,2 It occurs due to the low oxygen at higher altitudes and as a result of the body’s adaptation. The degree of altitude sickness may vary from individual to individual; however, typical symptoms would include headache, nausea, fatigue, dizziness, and sleep problems. High-altitude cerebral oedema (HACE) and high-altitude pulmonary oedema are among some of the dangerous conditions of acute mountain sickness that require immediate medical care.

Hypoxia, on the other hand, is when an individual has a low level of oxygen in the body tissues.³ It can happen at any altitude but is usually prevalent at higher altitudes where the air is thinner. Some factors that lead to hypoxia include low atmospheric pressure, inadequate ventilation, or illnesses that affect oxygen delivery. Hypoxia symptoms can be mild, such as dyspnea and confusion, or severe, such as organ failure or loss of consciousness.

One of the things that people need to know when they go up to a high-altitude environment is how hypoxia and altitude sickness are caused, and what impacts they have to reduce the risk as much as possible, thus making their stay safer. Travellers who can recognise symptoms and take preventive measures like gradual acclimatisation and good hydration will be less likely to get high altitude-related diseases and will have a pleasant time enjoying their experiences of high altitude.

Types of altitude sickness

Acute mountain sickness (AMS)

This is the mildest form of altitude sickness caused by rapid exposure to low amounts of oxygen, usually occurring within 8-10 hrs of travelling at high altitude.⁴ Symptoms include: 

• Headache
• Vomiting
• Nausea
• Insomnia
• Dizziness
• Confusion
• Lethargy

High-altitude pulmonary oedema (HAPE)

Acute mountain sickness sometimes gets complicated and progresses to high-altitude pulmonary oedema. This condition causes your lungs to be filled with fluid and develop breathing problems.^2,5,6 Symptoms include:

• Frequent coughing
• Frothy or blood-mixed sputum
• Shortness of breath with or without exertion
• Tachycardia and tachypnea
• Cyanosis
• Heaviness over chest
• Palpitations

High-altitude cerebral oedema (HACE)

This is the most severe form of high-altitude sickness and can become life-threatening.^2,5,6 This condition causes your brain tissue to swell and develop extrapyramidal symptoms such as: 

• Headache and confusion
• Fatigue
• Bladder and bowel dysfunction
• Nausea and vomiting
• Paralysis
• Visual defect
• Lack of coordination
• Seizures
• Coma 
• Death

Factors influencing altitude sickness

Rate of ascent

The rate at which we ascend to higher altitude is directly proportional to the severity of altitude sickness. Most people don’t experience any significant symptoms up to 2400 metres. However, at higher altitudes(above 3000 metres), special precautions should be taken. It is recommended to acclimatise for a few days after reaching 3000 metres and only ascend 300 to 500 metres per day with a gap on every extra day.^2,6 It is also recommended to give our body time to acclimatise after every 1000-metre ascend.

Individual health factors

Altitude sickness can be particularly devastating for people with preexisting underlying health conditions. If you have any health conditions below, you must consult a health professional before going to higher altitudes.²

• Anaemia
• Sickle cell disease
• Chronic obstructive lung disease(COPD)
• Coronary heart disease and other heart conditions
• Obstructive sleep apnea(OSA)
• Lungs malignancies
• Dehydration
• Hypertension
• Diabetes 
• Thyroid disorders
• Previous history of altitude sickness

Genetic predisposition

In the past centuries, the high-altitude regions have been inhabited and worked by people in significant numbers like Sherpas and Tibetans in the Himalayas, or Quechua and Aymara in the Andes. In these areas, adaptation to high altitude varies among populations. For instance, haemoglobin concentration is higher among Andeans than among Himalayans, while ventilation response is higher among Himalayans than among Andeans due to their habitat being oxygen deficient.²

One of the aspects involved in the cellular response to hypoxia is the inhibition of some cellular functions and gene suppression. On the other hand, some genes are induced and certain cells are activated upon exposure to an oxygen deficit. Hypoxia-inducible factor 1 also plays an important role in the physiological response to this problem, which includes increased availability of oxygen and facilitated adjustment to deprivation.^2,7

Interestingly, the genes that were found to depend on oxygen came to light after the identification of the Erythropoietin hormone; this hormone stimulates the production of red blood cells and allows them to transport oxygen more efficiently. In another study, it was found that there is a genetic variation in the angiotensin-converting enzyme gene which is linked to high endurance performance.²

This gene is more common among elite mountain bikers and other athletes known for their exceptional stamina. Different individuals have varying susceptibilities to high-altitude diseases; some may suffer from life-threatening complications such as cerebral or pulmonary oedema even at lower altitudes, while others can ascend to very high altitudes without requiring extra oxygen. The analysis of genetic factors affecting the adaptation to high altitude is in its infancy.

Physiological effects of altitude sickness

Altitude sickness affects every organ system in the human body and can produce effects ranging from mild to severe. The chart below explains the effects of altitude sickness on different human organ systems.^2,5,6

Diagnosis

Altitude sickness is usually diagnosed using physical examinations based on clinical symptoms and can usually be deduced by the rapid reduction in oxygen saturation. However, in some rare cases and depending upon the severity, diagnostic tests such as chest X-ray, Computed tomography(CT) and Magnetic Resonance Imaging (MRI) can be used to detect the fluid buildup in the lungs and brain.

Prevention and management strategies

The best way to prevent altitude sickness is to acclimate properly before going to higher elevations. Other ways to prevent altitude sickness include:^2,5,6

• Avoiding strenuous activities at higher altitudes
• Avoid alcohol, opioids and antidepressants as they can induce hypoxia
• Consult a medical professional and be prepared before travelling to higher elevations
• The Center for Disease Control and Prevention (CDC) suggests medications such as Acetazolamide be taken at 125 mg every 12 hours as a preventive measure⁸
• The CDC also notes that nifedipine can be used to prevent HAPE⁸
• Drink plenty of water and stay hydrated
• Travel with experienced mountain guides
• Ingestion of carbohydrates has been shown to provide better protection against hypoxia at high altitudes⁶

Treatment options

Descent

The best and perhaps the most reliable initial treatment for altitude sickness is to descend to lower elevations. For mild cases, it is advised to stop ascent and rest until the body is acclimatised. In addition to that, you should also maintain proper hydration.²

Oxygen therapy

Oxygen therapy can be provided in two different settings. In mild cases, oxygen can be given from portable cylinders. However, in severe cases, hyperbaric oxygen therapy is required. Hyperbaric oxygen therapy is given at specially designed facilities and can deliver up to 100% oxygen compared to 21% found in the atmosphere. This will rapidly supply the body with oxygen and help mitigate the consequences of altitude sickness.⁶ 

Medications

Additionally, medications are also used to treat and provide relief from altitude sickness.

• Acetaminophen and Ibuprofen are used to provide relief from headaches caused by altitude sickness^2,6 
• Steroids can be used to reduce cerebral and pulmonary oedema^2,6
• The Denali Medical Research Project done on a high altitude research station (4200 m) on Mt. McKinley, Alaska concluded acetazolamide provides relief from symptoms of high altitude sickness, promotes arterial oxygenation and prevents further pulmonary hypoxia⁹
• Diuretics are also rarely used to provide relief from symptoms of pulmonary oedema⁶

Note: People sometimes try to ascend after being given oxygen therapy and medications for altitude sickness, which should be avoided as it can prove fatal.

Summary

Travellers who journey to high altitudes may be at risk of developing altitude sickness and hypoxia. Among the altitude sicknesses are AMS, HAPE, and HACE which occur when the body fails to adapt to low levels of oxygen beyond 2,500 metres above sea level, which can lead to severe health consequences such as headaches or even life-threatening conditions.

People travelling in higher areas suffer from hypoxia because it limits the amount of oxygen getting into the tissues, thus symptoms start from difficulty in breathing to organ failure. Various factors such as ascent rate, existing health conditions, and genetic makeup determine the level of susceptibility to altitude sickness.

Physiological changes affect multiple systems, with indications ranging from mild signs to serious declines. Diagnosis entails clinical presentation along with pulse oximetry findings, and imaging may be required for severe cases.

Several prevention strategies include gradual acclimatisation, avoiding strenuous activities, and consulting medical professionals before travelling. As for altitude sickness, acetazolamide and other medicines are effective in prevention. Oxygen therapy and drugs can provide relief while descending is the most important treatment.

High-altitude adventurers can stay safe by being knowledgeable about the listed causes, symptoms, and prevention methods, which will help minimise the chances of altitude-related diseases.