UP UP AND AWAY
Altitudes can be dangerous and hostile to humans. As all hostile environments are characterized by our inability as humans to survive without external means, and the tendency to lack water and food cardinal to staying alive. We distinct between positive vertical altitudes (heights) and negative vertical altitudes (depths). A classic example of a positive vertical altitude would be climbing a mountain, while a classic example of a negative vertical altitude would be diving into the ocean.
This post will focus on positive vertical altitude hostile environments, and how they influence the human body, and can be deadly. The use of positive vs negative vertical altitudes as terms are relative to a relative zero known as mean sea level or MSL. Being at mean sea level is not being at an absolute zero. At the same time, MSL is also a reference for the barometric pressure (atmospheric pressure).
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We convert barometric pressure to atmospheric pressure using the following conversion equation: One bar = 750.062 torr = 0.9869 atm = 100,000 Pa. At sea level, standard air pressure is 29.92 inches of mercury, which is the same of 760 millimeters of mercury (mmHg). Thus, we say that at sea level, barometric pressure is the equivalent of one atmosphere and is 760 mmHg. We want to use mmHg as out unit since breathing related phenomena are measured in mmHg, such as partial pressure gradients.
Increasing positive vertical altitudes are accompanied with three natural challenges to human function:
Barometric pressure changes
Temperature changes
Slopes, if climbing uphill
Reminder: barometric pressure is a force that is exploited in the body to create movement of gases. Positive vertical altitude is the vertical distance measured compared to mean sea level or sea level is localized. Thus, as you climb upwards, the positive vertical altitude (distance) increases, and as you climb downwards, the positive vertical altitude (distance) decreases. The greater the positive vertical altitude gets, the more hostile the environment becomes. Further more, the greater the positive vertical altitude gets, the more it becomes a cold hostile environment in addition.
The higher you climb, the more oxygen's partial pressure decreases, though there is no change to oxygen's percentage of every litter of air (it stays about 20.93% of every litter of air). This creates a change to the oxygen's partial pressure gradient within the body, opposing normal breathing, and normal diffusion of gases according to passive gradients (see separate post about gradients). In other words, the more oxygen partial pressure falls, breathing becomes more and more challenging physically and mechanically.
Compared to mean sea level, a person experiences hypoxia, which is insufficient oxygen supply compared to functional needs. Oxygen partial pressure decreases exponentially with the increase in positive vertical altitude. Accordingly, at about 5,000 meters (16,000 feet), oxygen partial pressure is half (50%) compared to that at mean sea level. This means that breathing is twice as challenging physiologically.
At about 8,850 meters (29,000 feet), oxygen partial pressure is 33% compared to sea level, which means that breathing is three times more challenging physiologically. The “death zone” pertains to positive vertical altitudes greater than 8,000 meters (26,000 feet), where life is unsustainable via natural means (external means are necessary). At 7,500 meters (24,500 feet), sleeping is very difficult, and food digestion is impossible without external means.
Graph: changes in oxygen's partial pressure (mmHg) according to the increase in positive vertical altitude.
Symptoms of acute and rapid exposure may to positive vertical altitude include (yet not limited to):
Acute Mountain Sickness (AMS)
Fatal High Altitude Pulmonary Edema (HAPE)
High Altitude Cerebral Edema (HACE)
Permanent brain damage
Acute Mountain Sickness is the result of the difficulty to adjust to lower oxygen partial pressure. Most occurrences are mild in their severity; symptoms commonly include headaches, vomiting, nausea, loss of appetite, fatigue/malaise (particularly at rest), difficulty sleeping, and dizziness/lightheadedness. Acute Mountain Sickness is self-diagnosable and self-treatable, and resolves within days to weeks at most. It may pass as soon as a day or two in truly mild cases. Acute Mountain Sickness could get worse and result in High Altitude Cerebral Edema.
Fatal High Altitude Pulmonary Edema is the severe form of high positive vertical altitude illness/sickness, leading to death in about half of the cases untreated at all, or untreated on time. Fatal High Altitude Pulmonary Edema is the direct result of untreated hypoxia or severe hypoxia. It is regarded as a form of noncardiogenic pulmonary edema, meaning that it is not related to the heart as the cause.
High Altitude Cerebral Edema (HACE); While it rarely occurs, it's a life threatening mountain sickness, that result from untreated or worsened acute mountain sickness. As part of High Altitude Cerebral Edema (HACE), capillaries in the brain begin leaking blood into the brain, causing it to swell. Initial symptoms include confusion, loss of consciousness, fever, ataxia (loss of muscle control in the arms and legs; lack of coordination), photophobia (abnormal eye sensitivity to light), tachycardia (rapid heart beat), lassitude (physical or mental weariness; lack of energy), and an altered mental state.
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High Altitude Cerebral Edema (HACE) commonly develops within 3-5 days after developing acute mountain sickness, is extremely deadly percentage wise, and fast to kill. With the onset of High Altitude Cerebral Edema (HACE), death tends to follow in high rates within hours, two day at most. People enter a state of coma first, then die. In all three cases, permanent brain damage is a real possibility.
Acute (short term) physiological responses include hyperventilation, tachycardia, and fatigue. Main adaptations include:
Adjusting the homeostasis for CO2
Increased red blood cell production
Increased number and size of cell mitochondria
Increased concentration of hemoglobin and myoglobin
The next post related to positive vertical altitude will include the explanation of how these environments become deadly. Stayed tuned.
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