Effect of Altitude on Breathing: With the contemporary transit systems and mountain excursions, access to high mountains are made possible that were formerly only accessible to hardy climbs is now attainable. Symptoms of high altitude illness can be triggered by travel to heights higher than 2500 metres. Thousands of people visit high-altitude areas each year for tourism, adventure, or to train and compete in various sports.

Unfortunately, the effects of acute altitude sickness can make or break these trips, and the symptoms vary from person to person. To understand why people are affected differently, we must first examine how altitude affects the body. Let us know the Effect of Altitude on Breathing, Gas Exchange in Lungs, Acclimatisation and Oxygen-Dissociation Curves.

Gas Exchange in Lungs

This is not the truth, despite popular perception that when one climbs higher in height, there is ‘less air.’ Despite the difference in altitude, the gases that make up the air around us remain the same: 20.93 per cent oxygen (O₂), 0.03 per cent carbon dioxide (CO₂), and 79.04 per cent nitrogen. What does alter, though, is that as the altitude rises, the partial pressure of oxygen decreases.

1. The partial pressure of oxygen refers to the percentage of total gas pressure exerted by oxygen on the volume of gases in the atmosphere. This is partly due to gravitational attraction. At higher elevations, air molecules have less ‘weight’ (which puts pressure on lower air molecules) and less atmosphere pressing down from above. This is where the term “thin air” comes from.

2. This is significant because our lungs rely on a pressure gradient, or the difference in pressures of gases such as O2 and CO2, to transport oxygen from our alveoli, or lungs’ air sacs, to our blood.
3. The pressure of O2 in the air we breathe and the O2 in the blood surrounding our lungs approaches equally when we ascend to greater elevations, and the partial pressure of O2 lowers. When this happens, gas exchange is hampered, and the oxygen we inhale isn’t transported as efficiently from our lungs to our bloodstream. As a result, getting the oxygen, we need to our brain and muscles while running becomes much more difficult.

Learn About Mechanism of Breathing Here

Consequences of High Altitude

The consequences of high altitude are as follows:

1. Lowlanders will not be able to exert as much physical effort at High Altitude as they could at sea level.
2. Fortunately, the human body has a series of physiological reactions to compensate for hypoxia, including increased breathing, hemodynamic and hematologic alterations, and metabolic changes, all of which are referred to as acclimatisation.
3. The time it takes for these adaptations to occur varies depending on the person’s physiology, the height reached, and the rate of ascent.
4. The amount of oxygen in the body decreases when barometric pressure changes; high-altitude (HA) conditions have detrimental effects on the normal functioning body of people who are used to living at low altitudes, leading to hypobaric hypoxia.
5. After extended exposure to hypoxia, body weight, muscular structure and exercise capability, mental performance, and sleep quality all suffer.
6. The consequences of high-altitude travel are influenced by
   a. Rate of ascent to altitude
   b. Final altitude attained
   c. Altitude at which a person sleeps
   d. Individual physiology.

Acclimatisation

The adaptation of the human body to a higher altitude climate is referred to as acclimatisation. Many compensatory processes are triggered to counteract the negative effect when climbing to a moderate altitude (between 3000 and 4250 metres or 10,000 and 14,200 feet). The person eventually becomes used to the rarefied air. Some changes occur immediately, while others take time.

Natural Acclimatisation

Natives born and raised at high altitudes experience natural acclimatisation. Permanent acclimatisation is achievable at a maximum height of roughly 5,500 metres (18,000 feet) (Peruvian Andes). The locals have a short body structure with a broad chest, resulting in a high ventilatory capacity to body mass ratio. The right heart is frequently hypertrophied with relatively high pressure in the pulmonary artery to fill up the increased pulmonary capillary system properly.

The mechanism of O₂ transfer in these natives is also complex, as seen in the adjacent diagram when contrasted to that of an unacclimatised person.

Oxygen-dissociation Curves

The dissociation curve for the person residing at high altitude shows:

1. Low arterial blood Po2 (40 mm Hg) compared to 100 mm Hg for a person at sea level.
2. Because of the high haemoglobin concentration, the O₂ content of arterial blood is higher than that of a person at sea level, despite the low pressure.
3. Despite the low arterial Po₂, the venous Po₂ of high altitude residents is only 10 mm Hg lower than that of sea-level dwellers. Although highlanders’ oxygen consumption is often higher than that of sea-level residents, there is little doubt that the tissues of the naturally acclimatised person can use oxygen more effectively.
4. There is an increased alveolar capacity and an increased RBC synthesis.
5. The rightward shift of the oxyhaemoglobin dissociation curve leads to more oxygenation of Hb (haemoglobin) and more oxygen availability to tissues.

In the following ways, natives born and raised here outperform the best-acclimatized lowlanders:

(i) The chest is broader, but the body is smaller, resulting in a high ratio of ventilatory capacity to body mass.
(ii) The right heart of these persons is considerably hypertrophied to provide a high head of pressure in the pulmonary arteries so that blood can circulate through a greatly expanded pulmonary capillary system.
(iii) The RBC count and so the haemoglobin content and oxygen capacity of the blood is high. Even though the arterial Po₂ is low, the O₂ content of the arterial blood is higher than those living at lower altitudes.
(iv)The O₂ level of mixed venous blood is likewise higher, however, it has a somewhat lower percentage saturation than individuals living at lower altitudes.

How is Acclimatisation Different from Adaptation?

1. The individual’s genetics limits acclimatization from a biological perspective.
2. The same restriction does not apply since the process occurs over several generations, allowing for acquiring or recombining genetic characteristics that promote survival or performance in a new environment.
3. For example, Tomatoes withstandzing temperatures if the dip occurs over several days rather than all at once. The tomato acclimates to the harsh temperature through this short-term “adjustment.”
4. On the other hand, some desert plants only blossom at night, which ensures that the plant does not dehydrate in the scorching heat of the desert. Desert plants also have a waxy covering on their leaves that aids in dehydration.

Acute Mountain Sickness

Sometimes a well-acclimated mountaineer may develop an acute illness due to failure of compensatory adjustments to high altitudes.

The following effects are noticed:

1. The red cell mass and PCV are both significantly increased.
2. Right heart failure progresses as pulmonary arterial pressure rises to dangerously high levels. The peripheral arterial pressure continues to drop, and mortality occurs as a result of severe pulmonary oedema, which exacerbates the anoxic condition. Most patients recover if they are quickly moved to a lower altitude and given oxygen.
3. Hypoxia is a medical condition in which the body’s or any tissue’s oxygen supply is cut off. It’s not to be confused with hypoxemia, a medical condition in which the blood is deprived of oxygen.
4. Anoxia is a severe kind of hypoxia in which oxygen is virtually completely absent from the tissues. Lack of oxygen to the brain tissues can be lethal, and symptoms can appear minutes after the oxygen supply is cut off. Hypoxia is usually irreversible and has an impact on key organs, including the brain and heart.
5. Asphyxiation, also called asphyxia or suffocation, is when the body doesn’t get enough oxygen. Without immediate intervention, it can lead to loss of consciousness, brain injury, or death.
6. The term “asphyxia” is different from “asphyxiated.” Asphyxia refers to the condition of oxygen deprivation, while asphyxiated means a person has died due to oxygen deprivation.

Summary

Acclimatisation most likely occurs at the cellular level as well, however, the exact nature of this process is unknown. It is known, however, that people of high altitude have a greater ability to utilise oxygen and that their muscle work efficiency is not inferior to that of those living at sea level. People’s bodies begin to acclimatise to the low-oxygen atmosphere after several days or weeks of exposure to altitude (known as “acclimatisation”). The increase in breathing that occurred in the first few seconds of altitude exposure continues, and haemoglobin levels (the oxygen-carrying protein in our blood) rise, as does the ratio of blood vessels to muscle mass.

Despite these physiological adaptations to compensate for hypoxic circumstances, physical performance at altitude will always be lower than at sea level. The only exception is in a relatively quick and intense activity like throwing or hitting a ball, where the lack of air resistance may assist performance. Acute altitude sickness affects a large number of persons who travel to moderate or high altitudes. Headache, nausea, lethargy, dizziness, and disturbed sleep are common symptoms of this sickness, which appear 6 to 48 hours after the altitude exposure begins. The limit of human tolerance and the height at which permanent acclimatisation is achievable is around 5,500 metres (18,000 feet) altitude.

FAQs on Effect of Altitude on Breathing

Q.1. How does high altitude affect oxygenation?
Ans: Because there is less pressure to “push” oxygen molecules together at high altitudes, they are wider apart. This effectively means that there are fewer oxygen molecules in the same volume of air we breathe.

Q.2. What is the oxygen dissociation curve?
Ans: At different oxygen pressures, the oxyhemoglobin dissociation curve shows the proportion of O₂ saturation of haemoglobin.

Q.3. What happens with altitude sickness?
Ans: When one can’t acquire enough oxygen from the air at high altitudes, they experience altitude sickness. Symptoms include a headache, loss of appetite, and difficulty sleeping. It usually happens when persons who aren’t used to high altitudes go from lower elevations to 8000 feet (2500 metres) or higher in a short period of time.

Q.4. Does altitude affect lung capacity?
Ans: Indigenous people living at high altitudes had a bigger lung capacity and a 21–28 per cent lower residual capacity than those living at low altitudes in order to minimise excessive lung ventilation.

Q.5. How does high altitude cause respiratory alkalosis?
Ans: Hyperventilation occurs as the oxygen tension of inspired air reduces with increasing altitude in normal persons. The increased renal excretion of bicarbonate caused by acute respiratory alkalosis returns the pH to normal, resulting in compensated respiratory alkalosis or chronic hypocapnia.

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