Travel Reference
In-Depth Information
Theeffectofacuteexposuretoaltitudeonbloodpressureisnotentirelyclear,inpartdue
to differences in study methodologies. Many studies indicate that blood pressure increases
during the first week or two at high altitude, more so with greater altitude. However, a few
investigations have reported no significant change in blood pressure, or even a slight de-
crease.
Whether individuals who have high blood pressure at sea level have an exaggerated
hypertensive response on initial ascent to altitude has not been systematically evaluated.
Anecdotally, some individuals have developed severe hypertension. Such occurrences,
whatevertheirfrequency,arenottrivialproblemsinviewofthelargenumberofhypertens-
ive persons visiting ski resorts and trekking at high altitude.
The magnitude of the blood pressure change in hypertensive individuals may depend
upon the hypoxic stress. At low altitudes, the average increase appears to be minimal, al-
though individual variability is great. Heart rates also increase. The authors of one study
concluded that the blood pressure increase in individuals with normal and elevated pres-
sures was not important at 4000 feet (1200 m) but could become so at 10,000 feet (3000
m).
With acute exposure to higher altitudes, hypertensive individuals do have a greater
blood pressure response than normotensives (individuals with normal blood pressure). Im-
portantly,individualvariationisconsiderable,andafewhypertensiveshaveanexaggerated
pressure increase. Unfortunately, the studies that have been done have not been continued
after the first hours at altitude, so whether blood pressure continues to increase over a peri-
od of days, as it does in normotensive persons, is an important unanswered question. Also
unknown is whether more prolonged stay at altitude might reliably reduce arterial pressure
to below sea-level values, as has been reported in normotensives after five to ten years.
Clearly the scientific basis for advising individuals with hypertension about ascent to
altitude is limited. Because some individuals may become markedly hypertensive, and be-
cause there is no way at present to predict an individual's response, careful blood pressure
monitoring appears prudent.
Which medication is best for altitude-aggravated or induced hypertension and whether
antihypertensivemedicationregimenseffectiveatlowaltitudemaybeinsufficientuponas-
cent to high altitude are two more significant questions not yet answered.
Individuals with hypertension may experience other untoward effects of altitude in ad-
dition to increased blood pressure. They have a greater increase in pulmonary blood pres-
sure in response to hypoxia, which could predispose to high-altitude pulmonary edema, a
relationship yet to be explored. In addition, the central nervous systems of hypertensives
respond in an exaggerated manner to hypoxia. The prevalence of periodic breathing at alti-
tude could cause hypertensives to experience very high levels of sympathetic stimulation
duringsleep,increasing theirriskofexaggerated systemic hypertension, pulmonaryhyper-
tension, and abnormal cardiac rhythms. Normotensives were recently found to have elev-
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