Living at high altitude exposes people to hypobaric hypoxia, meaning there is reduced barometric pressure and lower oxygen partial pressure. This leads to lower arterial oxygen saturation. As a result, people living at high altitude have adapted ways to compensate for the relative lack of oxygen compared to sea level. These adaptations lead to changes in lung structure and function. But are these changes beneficial overall for lung health? There are arguments on both sides.
How high altitude affects lungs
When people first move to high altitude, they experience acute mountain sickness as their body struggles to adapt. This includes symptoms like headache, nausea, fatigue, dizziness, and insomnia. With continued exposure over weeks to months, the body starts acclimating through both ventilatory and non-ventilatory adaptations.
Some of the main ways high altitude affects lung structure and function:
- Increased ventilation and deeper breathing
- Increased lung volumes – both total lung capacity and vital capacity are expanded
- Increased diameter of alveolar ducts and alveoli
- Increased pulmonary arterial pressure – this leads to pulmonary hypertension over time
- Development of more capillaries in alveolar walls – this improves gas exchange
- Increased red blood cell production – improves oxygen carrying capacity
These changes allow the body to take in more oxygen with each breath and compensate for the lower oxygen partial pressure. Studies show that native highlanders have 30-50% greater lung volumes compared to people living near sea level.
Potential benefits of high altitude on lungs
The enlarged lung volumes and increased gas exchange surface from more alveolar sacs and capillaries is often considered beneficial adaptation. Here are some of the proposed advantages:
Increased lung capacity
Having larger lung volumes allows more air to be inhaled and exhaled with each breath. This is helpful for taking in more oxygen in the hypoxic high altitude environment. It could also improve performance for aerobic activities like hiking, running, or skiing at high elevation. The expanded lung capacity does not go away if someone moves back to lower altitude.
Improved gas diffusion
The greater surface area of the air-blood barrier from increased alveoli and capillaries permits faster gas exchange by diffusion. This helps compensate for lower partial pressure of oxygen at altitude. It may also aid oxygen loading and increase maximum oxygen consumption (VO2 max) during exercise.
Enhanced pulmonary blood flow
High altitude exposure encourages growth of new pulmonary capillaries. This vascular remodeling increases blood flow across the lungs for more efficient gas exchange. It may also improve cardiopulmonary circulation.
Increased red blood cells
A beneficial effect of altitude is increased red blood cell production. Having more red blood cells and greater hemoglobin concentration improves oxygen carrying capacity in the blood. This adaptation persists even after returning to lower elevation.
Possibly lower risk of lung infections
One hypothesis is that altitude may strengthen the immune system and lead to enhanced pulmonary defenses against infection. The enlarged alveolar ducts and sacs could reduce airflow resistance and lower risk of respiratory infections. But more research is needed to confirm this theory.
Potential harms of high altitude on lungs
Despite the proposed benefits, there are also negative impacts of high altitude on lungs that must be considered:
Pulmonary hypertension
The increased pulmonary pressures caused by hypoxic vasoconstriction places greater workload on the right heart. Over time, this can lead to pulmonary hypertension, right ventricular hypertrophy, and even right heart failure in susceptible individuals. These changes may not be reversible with return to lower elevation.
Increased blood clot risk
Polycythemia from high red blood cell concentration makes the blood more viscous. This raises the risk of blood clots, including potentially fatal pulmonary emboli.
Impaired gas exchange
Though diffusion capacity may be enhanced by increased surface area, studies show the actual gas transfer across the blood-gas barrier is impaired at altitude. This is due to factors like shortened red blood cell transit time through the pulmonary capillaries.
Greater oxidative stress
The relative hypoxemia of high altitude induces reactive oxygen species formation. This increases oxidative stress on the lungs. There is also evidence of inflammation from upregulated cytokines.
Worsened lung function
Despite larger lung volumes, studies show airflow limitation and reduced pulmonary function in long-term high altitude residents. This may result from remodeling that distorts the architecture of alveolar sacs.
Exacerbation of lung diseases
The hypoxic environment can exacerbate underlying respiratory illnesses like chronic obstructive pulmonary disease (COPD), asthma, cystic fibrosis, and interstitial lung disease. Flare ups are more likely at altitude.
Research on altitude training for athletes
Many competitive endurance athletes utilize altitude training with the aim of improving performance. The goals are to boost red blood cell count, enhance oxygen delivery and uptake, and induce beneficial adaptations like increased capillarization and mitochondrial density.
However, there is debate over the benefits of altitude training:
Potential benefits
- Increased red blood cell mass and hemoglobin concentration
- Higher maximum oxygen consumption (VO2 max)
- Elevated lactate threshold
- Enhanced exercise economy and efficiency
These changes could reasonably improve athletic performance at sea level. But it’s unclear if benefits outweigh the risks and challenges of training at altitude.
Limitations and risks
- Inability to reach target training intensity in hypoxia
- Insufficient stimulus for desired cardiovascular and muscular adaptations
- Impaired glycogen repletion and recovery
- Increased oxidative stress and inflammation
- Immune suppression and higher illness risk
- Loss of biomechanical economy from altered stride pattern
These factors may hinder or even reverse fitness gains and negate the purpose of altitude exposure. More research is still needed on ideal protocols.
Conclusion
There are reasonable arguments on both sides of whether high altitude is good for lungs. The enlarged lung volumes and enhanced gas exchange surface provide some benefits, especially in the context of the hypoxic environment. However, the downsides like pulmonary hypertension, impaired gas transfer, and exacerbation of lung diseases may outweigh the potential advantages.
For athletes using altitude training, it’s unclear if the benefits outweigh the risks. Likely the effects of altitude depend on the individual, length of exposure, elevation reached, underlying health status, and presence of lung disease. More research is still needed, especially on the long-term effects. But for now, it appears increased elevation may not be ideal for lung structure and function overall.