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breathing at high altitude because it acts as a respiratory stimulant. Most sedatives worsen
hypoventilation during sleep at high altitude and should be avoided.
Sleep periodic breathing is so common at altitude that it should not be considered ab-
normal. Periodic breathing may be present on some occasions and not on others. However,
it may be a sign of a serious disorder if it occurs for the first time during an illness or after
an injury, particularly a head injury.
Some persons have intermittent upper airway obstruction during sleep that may cause
snoring and an unpleasant morning headache and lethargy at altitude. This problem is
called obstructive sleep apnea and is not relieved by acetazolamide. Another form of irreg-
ular breathing during sleep is central sleep apnea. Some defect in the respiratory control
centerinthebraincausesalarmingperiodsofabsentbreathing,followedbyincreasingres-
piration that rises to a peak and then decreases. This disorder resembles periodic breathing
but occurs at any altitude and is not relieved by acetazolamide ( Chapter 25: Altitude and
Common Medical Conditions ) .
Hyperventilation Syndrome
Hyperventilation(overbreathing)iscommon.Thepersonbeginstobreathemorerapidly
and deeply than is appropriate and appears to be suffering from serious disease. However,
this syndrome is almost entirely psychosomatic in origin. Individuals who hyperventilate
tend to be nervous, tense, and apprehensive, although the disorder can occur in apparently
stable persons. Among beginners, apprehension about hazards or fear of exposure might
initiate this reaction. Knowledge of the person's emotional status, particularly unusual
anxiety, helps establish the diagnosis.
Figure 18-1. Actual tracings of periodic respirations: A, increasing and decreasing depth of respira-
tions; B, two to three deep inspirations followed by total cessation of respiration for about twelve
seconds
When a person breathes too rapidly and deeply for more than a short time, an abnor-
mally large amount of carbon dioxide is exhaled, altering the acid-base balance and in-
creasing the alkalinity of the blood, which produces the characteristic symptoms of numb-
ness or tingling around the mouth and in the fingers. Other associated signs and symptoms
include a rapid pulse, dizziness, faintness, sweating, and apprehension. The person often
complains that “the air doesn't go down far enough” and breathes in gasps or takes fre-
quent deep sighs. If hyperventilation persists, these symptoms increase to painful cramps
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