Physiological Changes To High Altitude
The human biological, physiological, cellular and physical make up is affected by our environment and genetics. This is as understated as saying the sky is blue. As a response and a change to environmental conditions, adaptation is vital to the survival of every organism. Adaptation results in the creation of beneficial characteristics and speciation, the creation of an entirely different type of species. When the new adaptive feature is no longer needed, it becomes vestigial.
By Alexas_Fotos CCO creative commons
Change
An environmental change comes in different forms, it can be biological affecting cells, and it can be entirely physical, in this case, increased altitude.
The earth’s atmosphere serves a protective and structural function. It consists of a layer of gases contained within the earth’s gravity and has a mass of 5.15×1018 kg. With increased altitude, the atmospheric pressure decreases.
Respiratory response to high altitude
At sea level, the percentage of inspired oxygen in the atmosphere is 21%. While this value is unaffected by a change in altitude, it is the partial pressure of oxygen that is affected with increasing altitude.
The atmospheric pressure at sea level is 760mmHg and inspired oxygen is 21%.
The partial pressure of oxygen at sea level would be 760mmHg × 0.21. Therefore, with increasing altitude, the decrease in the partial pressure reduces the partial pressure of oxygen delivered to the tissues.
When the partial pressure of oxygen decreases from 100mmHg to 60mmHg, ventilation increases to match this decrease.
At an elevation of 50000 feet, the partial pressure of oxygen is 18mmHg, a considerably low value when compared with the 159mmHg at sea level. This value at 50000 feet is further diluted by water vapour and the exhaled carbon iv oxide whose partial pressure also decreases with the increased altitude.
Immediate Response to low partial pressure of oxygen
The first response to a decreased low partial pressure of oxygen is by the arterial chemoreceptors that induce an increase in ventilation within seconds. This response can increase to five times normal with the first three days of exposure. But this action also causes an opposite cumulative effect because the increased ventilation also causes increased carbon iv oxide expiration that reduces blood pH. A reduction in pH inhibits the respiratory center.
But in the next few days, this opposing action fades away as the body’s need for oxygen overrides it.
Effect of low partial pressure of oxygen in the unacclimatized person
Hypoxia: In the unacclimatized person, this decreased partial pressure of oxygen leads to hypoxia caused by decreased oxygen delivery to tissues. At a height of above 12000feet, this leads to drowsiness, lassitude, headache, nausea, and euphoria.
Acute mountain sickness: The symptoms include headache, anorexia, insomnia, and breathlessness. These are also linked to the hypoxic conditions. For adequate acclimatization and survival for mountain climbers, they are encouraged to ‘climb high and sleep low’ to ensure progressive acclimatization.
The range of physiological responses that leads to mountain sickness and pulmonary edema are as follows. The hypoxic conditions automatically cause blood to be shunted away from lesser priority areas in the pulmonary circulation. There is also pulmonary vasoconstriction that leads to pulmonary edema over time as pulmonary blood pressure is increased.
Tachycardia: One of the immediate response to high altitude is an increased heart rate to compensate for the hypoxic conditions.
Increased cardiac output: The cardiac output increases more than thirty percent in response to the increased red blood cell production and high blood volume.
High altitude cerebral and pulmonary edema
In addition to the pulmonary vasoconstriction, the increased red blood cell production leads to increased blood viscosity. So, the right side of the heart works excessively. The combined effect of these responses in response to the hypoxia might lead to acute pulmonary edema.
Since the cerebral circulation is of high priority, the pulmonary vasoconstriction is countered by local vasodilation of the cerebral blood vessels. This causes an increased blood supply to the cerebral capillaries, elevating the pressure and causing fluid leakage into cerebral tissues. The resulting cerebral dysfunction can be fatal if the person is not returned to sea level.
Chronic response to high altitude
Increased red blood cells and hemoglobin concentration
One of the principal triggers for increased red blood cell concentration is hypoxia. Erythropoietin is secreted which causes increased red blood cell concentration. As the hematocrit rises, the hemoglobin concentration also rises to facilitate improved oxygen transport.
Improved pulmonary capillary function and increased diffusion capacity.
This increased diffusion of oxygen through the pulmonary membrane to the blood occurs both during exercise and at high altitude and this is in response to the ‘oxygen hunger.’
The combined effect of increased ventilation, high pulmonary arterial blood pressure leads to increased pulmonary capillary blood volume that improves oxygen diffusion to the bloodstream.
Cardiac output
Following the increased cardiac output as an immediate response, over the next few days, the cardiac output decreases to normal since the hematocrit is also high.
Tissue capillary angiogenesis
This is particularly obvious in natives of high altitude regions. To improve the efficiency of oxygen delivery to the tissues, there is an increased growth in the number of systemic capillaries.
Subcellular adaptation
This adaptation is again common to natives of high altitude regions. The number of cellular mitochondria and oxidative enzymes are higher to use the lower partial pressure of oxygen efficiently.
Increased chest size
This chronic adaptation again applies to natives and those who have resided in high altitude regions for too long. Due to the increased cardiac output, the heart size might slightly increase. This effect combined with the increased ventilation might lead to an increase in chest size, especially in relation to overall body mass over time.
Altitude and sports Performance
“Live-High, Train-Low"
This maxim has often been used as athletes as a ‘performance enhancer.’ The positive effects of dwelling at high at high altitudes produce beneficial advantages for athletes.
The increased red blood cell production, increased cardiac output, improved pulmonary efficiency and myoglobin and mitochondria concentrations help improve athletic performance. But when athletes return to sea level, the body systems ‘de-training’ or returning to normal might nullify these advantageous features. For this reason, some athletes ‘live at high altitude and train at low altitudes.’
Since 1975 the Denver Broncos own the best home record in the NFL. That is some record. But the city is located 5,280 feet above sea level. Visiting teams will have to puff and huff their way through an environment that would be considerably harsh to their body systems while the Denvers enjoy their home advantage. The Toronto Raptors could have used some of this help. Probably.
High altitude controversy
In May 2007, FIFA banned football matches at more than 2500 feet above sea level. This meant that countries like Bolivia, Ecuador and Colombia would be unable to host home games during FIFA world cup qualifiers. The reason for this ban was not far-fetched especially in light of this ‘advantage’ it gave these countries. In contrast, visiting teams from sea level had to exercise through the harsh conditions caused by the decreased partial pressure of oxygen.
By Klausdie CCO creative commons
The ban was revoked in May 2008.
Players have been known to vomit during world cup qualifiers played at high altitude Bolivia. Recall one of the effects of hypoxic conditions at high altitude is nausea.
Human physiology is beautiful and powerful, especially in its attempt to maintain homeostasis regardless of the change in external conditions. Adaptation can also be behavioral. We change, shift and wiggle our way through societal expectation daily. Imagine if the adaptive process didn’t exist, survival would be impossible.
References
High Altitude football controversy
Denver's Edge: How Altitude Provides Their Teams With The Greatest Home-Field Advantage in Sports
Effect of high altitude on humans
Pressure with height
Atmosphere of the earth
Gas Exchange: Diffusion & Partial Pressure Gradients
Guyton, Arthur C, and John Hall, Textbook of Medical Physiology. Elsevier, 2000.
Oxygen at high altitude
This sort of advantage happens in the NBA too, Colorado which is home to the Denver nuggets is one of the hardest places to win a game in the NBA especially on a back to back. High attitudes certainly provides an unseen advantage.
True. Its not exactly unseen. Every team sports physiologist knows this. They cant just do anything about it.
I've heard many coaches complain about their players having to play at high altitudes, I never really caught the drift, well now I do, thanks to you. As you've mentioned, the home teams still have to work hard to take the advantage.
Let me confess, I was drawn by the picture, but I'm glad I made the decision to read this, I've been greatly enlightened.
One more thing, the answer seems obvious, but permit me to ask : Are you an athlete?
Lol, I wish. I'm just a sports fanatic. I played football a bit in my younger years.
I was also drawn to the picture too. Thanks.
Great post, technically and artistically.
It's a well known condition in my part of the world. Several Universities are known to have a huge home advantage. Colorado, Colorado State, New Mexico, UNReno and Northern Arizona among others. All are over 4000 feet.
Professional sports are affected too. The baseball flies better in Denver than anyplace. Football teams hate to go there. Hockey and Basketball also.
Interestingly (maybe only to me :) ) is that Phoenix is the second highest baseball football and hockey venues. My elevation is under 400 feet, and Phoenix is less than 200 miles of seemingly flat ground from here. Obviously it isn't flat.
Thanks for a great post.
Thank you. I don't think anyone can do anything about it though. It is not as if they can change homes. Nature has given them that advantage.
Since people living in high altitudes are well adapted to hypoxic conditions, I was hoping it will confer some advantage on them in sporting activities, especially in athletic sports such as relay races and marathons. But it seems not to be so. Perhaps you know why?
Good article! keep it up Vanessa
Some studies say it does, but the result is inconclusive because it depends on the region. For example, people living in mountainous regions will fare better if events are hosted in their areas but if the event is hosted at sea level, the body might 'de-train.'
On the other hand, geography gives Kenyans a structural advantage that sees them excel in long distance events. But to maintain this advantage, they have to reside there, and return to sporting locations in time to acclimatize.
The result of this advantage is a sum of all the factors and not just one. That is why is should be so but not always so.
Good work @vanessahampton :) I have heard of people getting sick from altitude as low as 7000 ft (2000m) but to be honest never noticed it myself at much higher altitudes. Obviously, there is a large amount of variation between different people's sensitivity at different altitudes, and to how much they are exerting themselves.
Thank you. True, the sensitivity differs but especially the rate of exertion. The slower they go, the lesser the effect.
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