ALTITUDE AND COMMON MEDICAL CONDITIONS - Medicine for Mountaineering and Other Wilderness Activities - page 367

ated nocturnal blood pressure at altitude. Although these concerns about hypertensive in-
dividuals are hypothetical, the issues of untoward events during sleep and susceptibility to
high-altitude pulmonary edema certainly warrant further attention.
Coronary Artery Disease
High-Altitude Residents
Various studies suggest that the incidence of coronary artery disease and consequent
deathratesislowerinpersonslivinglifelongathighaltitude.Firmconclusionsaredifficult
because such variables as age, genetics, smoking, exercise, diet, and migration to lower
altitudeduetoillnesshavenotbeencontrolled,buttheevidenceisnottobediscounted.No
study has ever suggested an increased incidence of ischemic heart disease in high-altitude
residents.
Lowlanders Going to High Altitude
With acclimatization, a normal heart can tolerate even extreme hypoxemia without
ischemic changes or impaired function. A theoretical basis for exacerbation of coronary
artery disease at altitude exists, however. Cardiac work is slightly increased, and the usual
compensatory increase in coronary blood flow may not be attained in those with arterio-
scleroticcoronaryarterydisease.Infact,arterioscleroticcoronaryvesselsthatcannotdilate
may actually constrict, resulting in ischemia (inadequate blood supply).
To assess whether these concerns are significant, four questions need to be examined
( Chapter 17: Heart and Blood Vessel Disorders ) :
1. Does altitude unmask previously unknown coronary artery disease?
2. Does altitude exacerbate stable cardiac ischemia?
3. Does altitude increase the risk for myocardial infarction or sudden death?
4. Does altitude provoke abnormal cardiac rhythms?
Anecdotal reports make it clear that these events may all occur at high altitude as they
do at sea level, but whether altitude is a contributor is unclear. Additional considerations
are the possible influence of cold and the risk of ischemia in those who have no signs or
symptoms of coronary artery disease, particularly the elderly. Finally, what recommenda-
tions make ascent to altitude safer for those with known or unknown coronary artery dis-
ease?
Does Altitude Unmask Previously Unknown Coronary Artery Disease?
Investigation decades ago found that severe hypoxia is stressful for a heart with coron-
ary artery disease but is less stressful than exercise. In a direct comparison, sea-level ex-
ercise produced more ischemia-related electrocardiographic (ECG) changes in individuals
with known coronary artery disease than did inhalation of 10 percent oxygen while at rest.