ALTITUDE AND COMMON MEDICAL CONDITIONS - Medicine for Mountaineering and Other Wilderness Activities - page 376

Brain tumors can be unmasked upon ascent to high altitude, presumably because the in-
tracranial blood flow changes and the brain volume increases. Four such individuals have
now been recognized. In none of the persons had the tumors been previously diagnosed.
Seizures
Acute,severehypoxiamaycauseseizures,afactmorerelevantandbetterknowntoavi-
ation medicine and of questionable relevance for sojourners who take time to acclimatize
and go to more moderate altitudes. In fact, seizures appearing for the first time in sojourn-
ers at altitude without an underlying seizure focus—with or without HACE—appear to be
rare.
In persons with seizure disorders, exacerbation due to altitude has been anecdotally ob-
served when they were not taking their medication. The mechanism of exacerbation might
be related to either the respiratory alkalosis of altitude, similar to the hyperventilation used
inEEGlabstotriggerseizureevents,ortothehypoxia.Personswithseizuredisordershave
had no increase in frequency or severity of seizures when medications were continued at
high altitude.
In contrast to these apparently unusual events, syncope (fainting) is common at altitude.
Since syncope of any cause may be associated with seizure activity (convulsive syncope),
confusion of convulsive syncope with a true seizure is inevitable. Systematic studies of in-
dividuals with seizure disorders are sorely needed to determine whether high altitude is a
risk for these individuals.
Whether an individual with a grand mal seizure at very high altitude might be at greater
risk for residual brain injury is another unanswered question.
THE EFFECT OF ALTITUDE ON DIABETES MELLITUS
Dodiabeticshavemoreproblemsathighaltitude?Theonsetofseverediabeticketoacidosis
in five trekkers at high altitude, three of whom died, raises suspicion of a problem, but
whether incidence or severity is increased at high altitude is unknown. Some reports have
questioned the reliability of selfmonitoring blood glucose devices at high altitude, but a re-
cent study demonstrated reliability of one system at 8800 and 12,100 feet (2668 and 3665
m) in Colorado.
THE EFFECT OF ALTITUDE ON PREGNANCY
A normal mother breathing room air at sea level has an arterial oxygen pressure (PO 2 ) of
85 to 100 mm Hg. The PO 2 in the uterine veins is approximately 40 mm Hg. The PO 2 in
the umbilical vein going to the fetus (analogous to a systemic artery in the adult) is 30 to
35 mm Hg. The PO 2 in the umbilical artery coming from the fetus (similar to the pulmon-