Travel Reference
In-Depth Information
(Normal air contains 20 percent oxygen.) As a result, exercise testing has become the pre-
ferredwaytoscreen.Ofseveral thousandindividuals withsuspected coronarydisease who
were tested for twenty minutes with 10 percent oxygen, none developed serious cardiac
events or died. When hypoxia and exercise were combined, however, the results were dif-
ferent. When seventy asymptomatic soldiers (ages thirty to fifty) who already had nonspe-
cificECGchangeswereevaluated, hypoxiaatrestresulted infurtherECGchangesinfour.
However, ten individuals developed changes with exercise at sea level, and twenty deve-
loped changes with the combination of hypoxia and exercise. Although these studies are
interesting, they assessed only ECG changes and only in persons with pretesting ECG ab-
normalities. Nonetheless, hypoxic exercise appears better able to unmask coronary artery
disease (by ECG) than hypoxia at rest or exercise while breathing air containing a normal
amount of oxygen. If acute hypoxic exercise can unmask ECG evidence of coronary artery
disease, altitude exposure may do so as well.
A stay at high altitude may stress the coronary circulation as much or more than acute
hypoxic exercise because the blood concentrations of catecholamines such as adrenaline
are increased during the first few days at altitude, exertion varies, sleep may exaggerate
hypoxemia, temperatures are lower, and other stresses are present.
Does Altitude Exacerbate Stable Cardiac Ischemia?
Small increases in heart rate and blood pressure on initial ascent to altitude may cause
anginaorinduceanginainthosewithcoronaryarterydisease(
Chapter17:HeartandBlood
Vessel Disorders
)
. Altitude alone may aggravate angina, at least immediately after ascent.
Several investigators have concluded that individuals with coronary artery disease who are
well compensated at sea level do well at a moderate altitude after a few days of acclimat-
ization, but during that period their threshold for angina may be lower and activity should
be limited. However, two individuals had untoward events (a relatively high incidence of
complications): one an increase in angina and a second a myocardial infarct. Further study
to better define those who are at risk is needed.
A reunion of the U.S. Army 10th Mountain Division in Vail, Colorado (8250 feet, or
2500 m), provided an opportunity to observe a number of elderly individuals (mean age
69.8 ± 4.4 years) over a period of four days after ascent from near sea level. Of seventy-
seven men and twenty women, twenty were known to have significant coronary artery dis-
ease.Thirty-eighthadabnormalECGsonarrivalathighaltitude.Overthefourdaysathigh
altitude, no clinically significant ECG changes or clinical events suggestive of ischemia
occurred. These elderly individuals with both symptomatic and presumed asymptomatic
coronary artery disease (and frequently hypertension) tolerated moderate altitude well and
had no exacerbation of their stable ischemia.
Does Altitude Increase the Risk of Myocardial Infarction or Sudden Death?
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