The number of individuals exposed to high altitude through air travel and recreational activities has increased greatly in recent decades. Changes in physiological functions during high altitude exposure vary with an individual’s physical state, cultural habits, geographical locations, and genetic variation . While high altitude is well tolerated in 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].
These complications are caused by the acute effects of hypobaric hypoxia where the high altitude provides a unique physiologic challenge to the cardiovascular system. The cardiovascular response to high altitude exposure in healthy individuals and in patients with heart disease will be reviewed here. A general discussion of high altitude disease is discussed separately. (See "High altitude illness: Physiology, risk factors, and general prevention".)
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: acute mountain sickness, high altitude pulmonary edema, high altitude cerebral edema, and high altitude retinal hemorrhage. These are discussed separately. (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
An understanding of barometric pressure, the primary determinant of the partial pressure of oxygen in inspired air (PiO2), is essential to understanding the cardiovascular stress of high altitude. When moving from sea level to high altitude, there are reductions in atmospheric pressure, oxygen pressure, humidity, and temperature . Significant changes occur above 2500 meters 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 migraine, genetics, and age also affect the degree of changes experienced by the human body .
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: