Coronary heart disease at altitude.

In the past, it has been assumed that some basic physiologic responses to altitude, exposure in coronary patients are comparable to those in normal young subjects. In fact there are similar changes in sympathetic activation, heart rate, and blood pressure early after ascent, with decrements in plasma volume, cardiac output, and stroke volume as acclimatization proceeds. These responses are described, and experience with coronary patients is reviewed. During the 1st 2 to 3 days at altitude, coronary patients are at greatest risk of untoward events. Gradual rather than abrupt ascent, a moderate degree of physical conditioning, early limitation of activity to a level tolerated at low altitude for somewhat less), and attention to blood pressure control all appear to have protective effects. Ascent to moderate altitude appears to entail little risk in coronary patients who are asymptomatic or have moderate exercise tolerance, provided that the above precautions are observed and that activity does not exceed levels at lower altitude. If activity is to be increased, pre-ascent treadmill exercise testing or Holter monitor data secured under conditions comparable to those anticipated at altitude may provide reasonable guidelines. For coronary patients previously evaluated and known to be in a high-risk category, indications for ascent should be examined more critically, and precautionary measures should be more rigorous. Advice for patients with known coronary disease who may desire to trek at very high altitude must involve individual evaluation, and guidelines remain elusive.