Thesis: Aviation Risks: Pilot Hypoxia the High Altitude

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Aviation Risks: Pilot Hypoxia

The high altitude environment is hostile to human life and to most other life forms that have not evolved in high altitude environments. At altitudes above 5,000 feet, atmospheric pressure begins to drop below the levels required for optimal cognitive and physical functions. The reduction of function caused by insufficient blood oxygen levels

is known as Hypoxia and exists in several different forms. At low altitudes, the effects on pilots is already demonstrable although they may only interfere minimally with the ability to fly; as altitude increases, so do the effects of hypoxia, which dramatically reduce the ability of pilots to perform. Above 10,000 feet, hypoxia is a very serious risk to aviators.

The Physiological Mechanism of Altitude-Induced Hypoxia:

In some respects, the mechanism responsible for altitude-induced hypoxia are widely misunderstood, because they are often attributed to the so-called "thinness" of the air at high altitudes. The assumption is simply that reduced atmospheric pressure by virtue of the reduction in the number of air molecules in the column of air above the aircraft corresponds to reduced oxygen content of the air (Reinhart, 2008). In fact, the proportion of oxygen in air remains constant, at approximately 21%, regardless of atmospheric pressure (Jepperson, 2007).

Certainly, the number of air molecules does decrease as a function of altitude, corresponding to proportionally fewer molecules of oxygen per unit of air volume.

However, the rate at which this reduction in air molecules increases with altitude is only a secondary cause of altitude-induced hypoxia. Rather, the primary cause of hypoxia at altitude is the much greater effect that increases in altitude have on the physiological ability of the pilot to absorb oxygen from the air (Jepperson, 2007; Reinhart, 2008).

Within the blood, hardly any oxygen is actually dissolved directly into blood plasma; it is the hemoglobin that absorb oxygen from the air sacks or alveoli in the lungs and then transport the oxygen throughout the body tissues (Reinhart, 2008). In the presence of reduced oxygen content in air at normal atmospheric pressure, the body can compensate to a certain extent by increasing respiration rates and deeper inhalation because the physiological ability of the hemoglobin to absorb and transport oxygen remains essentially unaffected (Jepperson, 2007).

However, decreasing atmospheric pressure directly affects the ability of the hemoglobin to absorb oxygen, regardless of how much oxygen is actually available

(Jepperson, 2007; Reinhart, 2008). It is precisely this reduced oxygen absorption

capacity of human hemoglobin, and not decreased proportional molecular composition of air or even (necessarily) the absolute amount of oxygen available that causes hypoxia at altitude.

Types of Hypoxia:

Hypoxic Hypoxia is known as "altitude-induced hypoxia" because it is caused strictly by exposure to high altitude atmospheric conditions. In principle, hypoxic hypoxia begins as low as several hundred feet above the ground (and is known to effect hikers, mountain climbers, and athletes who play in high-altitude locations such as Mile

High Stadium in Colorado (Jepperson, 2007; Reinhart, 2008).

In terms of significant effects capable of reducing flight safety, however, altitudes below 5,000 feet are considered "safe" for un-pressurized flight (USDOT, 2003). On the other hand, pilots who typically operate at approximately 5,000 feet or lower, such as in rotary aircraft, are nevertheless susceptible to mild hypoxia, particularly from prolonged atmospheric exposure. Moreover, given the consequences of reduced pilot capacity in the unforgiving environment of air-flight, in many respects, there may really be no such thing as "mild" hypoxia.

Hypemic Hypoxia is known as "anemia-induced hypoxia" because it is caused strictly by biological abnormalities in the blood that interfere with the ability of hemoglobin to absorb oxygen even in the presence of sufficient quantities and at normal atmospheric pressure (Jepperson, 2007; USDOT, 2003). The main factors that cause or contribute to anemic hypoxia are typically low iron levels (i.e. clinical anemia) in the blood, and smoking. Cigarette smoke is rich in carbon monoxide, a molecule that bonds to human hemoglobin several hundred times more readily than oxygen (Jepperson, 2007;

USDOT, 2003).

As a result, smokers generally experience hypoxia sooner (in terms of duration of exposure to high altitude atmospheric conditions) and at comparatively lower altitudes than nonsmokers. In that regard, the effects of carbon monoxide exposure is so dramatic that even nonsmokers exposed to smoke-filled environments will experience reduced resistance to the onset of hypoxia at altitude… [END OF PREVIEW]

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APA Format

Aviation Risks: Pilot Hypoxia the High Altitude.  (2009, April 3).  Retrieved May 20, 2019, from

MLA Format

"Aviation Risks: Pilot Hypoxia the High Altitude."  3 April 2009.  Web.  20 May 2019. <>.

Chicago Format

"Aviation Risks: Pilot Hypoxia the High Altitude."  April 3, 2009.  Accessed May 20, 2019.