Impact of Altitude on Cardiovascular Physiology: Literature Review and Update

Introduction: More than 140 million people in the world live at high altitudes, above 2,500 meters (m) above sea level. Oxygen is vital for cellular metabolism; therefore, hypoxic conditions found at high altitude affect all physiological functions. Metods: A search for information was carried out in the SciELO, Scopus, PubMed/MedLine databases, the Google Scholar search engine, as well as in the ClinicalKeys services. Advanced search strategies were used to retrieve the information, by structuring search formulas using the terms "Cardiovascular Physiology", "Cardiovascular Physiology at Altitude", as well as their translations into Spanish " Fisiología Cardiovascular " and " Fisiología Cardiovascular en la altitud ". Results discussion: The heart is composed of three main types of cardiac muscle: atrial muscle, ventricular muscle, and specialized excitatory and conductive muscle fibers. The efficiency and work of the heart as a pump is often measured in terms of cardiac output, or the amount of blood the heart pumps per minute. Cardiac output is the product of stroke volume and heart rate Cardiovascular Changes at Altitude It is possible to think of the goal of acclimatization as maintaining oxygen delivery to the tissues as close to normal as possible. The cardiovascular system is central to this. Acute exposure to high altitude produces an increase in heart rate and cardiac output both at rest and for a given amount of work compared with sea level. In general, the normal heart tolerates even severe hypoxia very well. The heart, as a hemodynamic pump, has two mechanisms at its disposal to enhance its performance: heart rate and stroke volume, which together constitute cardiac output. The altitude electrocardiogram shows a variably increased amplitude of the P wave, deviation of the QRS axis to the right, and signs of right ventricular overload and hypertrophy. Conclusions: Advances in high-altitude research have shown that the cardiovascular system deploys some efficient mechanisms of acclimatization to oxygen deprivation, and the healthy heart adapts to hypoxia, even when severe, with preservation of systolic function and only minor impairment of LV and RV diastolic function. With acclimatization, desensitization of the adrenergic system, together with increased parasympathetic influence, leads to a decrease in maximum heart rate and protection of the myocardium against potentially damaging energy imbalances. Acute exposure to high altitude stimulates the adrenergic system, increasing heart rate and cardiac output; although arterial pressure remains stable, pulmonary artery pressure increases due to hypoxic pulmonary vasoconstriction. Our improved understanding of the effect of altitude hypoxia on the cardiovascular system will allow better-informed, evidence-based advice for patients with pre-existing cardiovascular disease