The number of individuals exposed to high altitude through air travel and recreational activities has greatly increased in the past few decades. Changes in physiological functions during high altitude exposure vary with an individual’s physical fitness, cultural habits, geographical locations, and genetic variation . While high altitude is well tolerated by most individuals, patients with cardiovascular disease, as well as some healthy individuals, are at risk of complications from tissue hypoxia, sympathetic stimulation, increased myocardial demand, and alterations in hemodynamics that may occur with exposure to high altitude [2,3].
The aforementioned complications are caused by the acute effects of hypobaric hypoxia, where the exposure to high altitude provides a unique physiologic challenge to the cardiovascular system. The cardiovascular response to high altitude in both healthy individuals and in patients with cardiovascular disease will be reviewed here. A general overview of high altitude disease will also be included to provide a comprehensive understanding. (See "High altitude illness: Physiology, risk factors, and general prevention".)
Most importantly, this topic will discuss the impact of high altitude on the heart. Altitude exposure can also lead to a variety of well-described clinical syndromes including some not directly involving the cardiovascular system, such as acute mountain sickness, high altitude pulmonary edema, high altitude cerebral edema, and high altitude retinal hemorrhage. These maladies are discussed in detail within this report. (See "High altitude pulmonary edema" and "Acute mountain sickness and high altitude cerebral edema" and "High altitude illness: Physiology, risk factors, and general prevention", section on 'Other altitude-related illnesses'.)
BAROMETRIC PRESSURE AND PIO2
When moving from sea level to high altitude, there are reductions in atmospheric pressure, oxygen pressure, humidity, and temperature . It is noteworthy to point out that significant changes occur beyond the critical height of 2500 meters (8200 feet) above sea level . Factors such as degree of change in elevation, degree of hypoxia, rate of ascent, level of acclimatization, exercise intensity, previous history of severe high-altitude illness, history of migraines, genetics, and age also significantly affect the degrees of change that the human body will experience through prolonged ascents . One study of young adult Chinese men aged 18 to 35 years noted that older age (those 26 to 35 years old) was an independent risk factor for acute mountain sickness upon rapid ascent to high altitude (from 500 to 3700 m), and that the prevalence of acute mountain sickness increased with increasing age .
Although altitude is the most obvious determinant of barometric pressure and its resulting physiologic stress, other factors can contribute to a reduction in barometric pressure and can increase the physiologic consequences of altitude: