Commercial Aviation and Hypoxia

Exposure to high altitudes can have adverse effects on human health. Symptoms may range from mild to severe, and typically involve both the central nervous system and the cardiorespiratory system. The use of pressurized cabins during high altitude flight precludes such problems. Occasional pressurization loss during flight, however, still does occur. Thus, commercial flight crews and passengers must be prepared for such a contingency. Both adequate equipment and training which emphasizes emergency procedures should be provided.

As elevation increases, air decreases in density. For example, at 18,000 feet atmospheric pressure is half its value at sea level. The most significant result of this decreased pressure is a reduction in the partial pressure of oxygen (PO2). This decreased oxygen content of the air at high altitude causes hypoxia (Harding & Mills, 1983, p. 1408).

The relationship between the oxygen saturation of blood hemoglobin and oxygen partial pressure can be graphically described according to the oxygen dissociation curve. At higher oxygen pressures (corresponding to altitudes of between sea level and 10,000 feet) the curve is relatively flat. Thus, although an ascent to about 10,000 feet may result in a fall in alveolar PO2 from the normal 103 mm Hg down to 60 mm Hg, this reduction will only result in a slight drop in the percentage saturation of hemoglobin with oxygen (Harding & Mills, 1983, p. 1408).

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rved muscular incoordination, slurred speech, and loss of touch sensation. As a late feature, loss of auditory acuity may occur. Finally, many investigations have also been performed on the effects of chronic hypoxia. These symptoms include not only problems with the senses, intellect, memory, and judgement, but also the tendency for subjects to have uncontrolled emotional outbursts as well. Inevitably, hypoxia results in stimulation of the cardiovascular and respiratory compensatory mechanisms. For example, with the moderate hypoxia experienced at altitudes of 25,000 feet cardiac output and heart rate are increased. A concomitant reduction in overall peripheral resistance, however, prevents any rise in arterial blood pressure. Lastly, increased respiration can also result in the symptoms of hyperventilation. Thus, individuals exposed to altitude extremes additionally tend to experience lightheadedness, feelings of unreality, anxiety, paraesthesia, blurred vision, and palpitations (Harding & Mills:1983, p. 1410). In general, altitudes above 12,000 feet have a negative effect on human health. Moreover, above 14,000 feet, CNS function may to be substantially altered. Furthermore, it is widely believed that below 10,000 f

Category: Medical - C