The Heart and Pulmonary Circulation at High Altitudes

Abstract

Abstract-More than 140 million people worldwide live Ͼ2500 m above sea level. Of them, 80 million live in Asia, and 35 million live in the Andean mountains. This latter region has its major population density living above 3500 m. The primary objective of the present study is to review the physiology, pathology, pathogenesis, and clinical features of the heart and pulmonary circulation in healthy highlanders and patients with chronic mountain sickness. A systematic review of worldwide literature was undertaken, beginning with the pioneering work done in the Andes several decades ago. Original articles were analyzed in most cases and English abstracts or translations of articles written in Chinese were reviewed. Pulmonary hypertension in healthy highlanders is related to a delayed postnatal remodeling of the distal pulmonary arterial branches. The magnitude of pulmonary hypertension increases with the altitude level and the degree of exercise. There is reversal of pulmonary hypertension after prolonged residence at sea level. Chronic mountain sickness develops when the capacity for altitude adaptation is lost. These patients have moderate to severe pulmonary hypertension with accentuated hypoxemia and exaggerated polycythemia. The clinical picture of chronic mountain sickness differs from subacute mountain sickness and resembles other chronic altitude diseases described in China and Kyrgyzstan. The heart and pulmonary circulation in healthy highlanders have distinct features in comparison with residents at sea level. Chronic mountain sickness is a public health problem in the Andean mountains and other mountainous regions around the world. Therefore, dissemination of preventive and therapeutic measures is essential. Key Words: altitude Ⅲ altitude sickness Ⅲ hypertension, pulmonary P eople native to high altitude (HA) environments live in an environment of hypobaric hypoxia with low ambient partial pressure of oxygen. As a consequence, they develop alveolar hypoxia, hypoxemia, and polycythemia. Despite this, healthy highlanders are able to perform physical activities similar to and often even more strenuous than those of people living at sea level (SL). This phenomenon has been ascribed to adaptive mechanisms that occur at sequential steps of the oxygen transport system with the main purpose of decreasing the total pO 2 gradient from ambient hypoxic air to mixed venous blood at the tissue level.The heart and pulmonary circulation in healthy people living at HA exhibit important physiological and anatomic characteristics, which resemble those that occur in chronic clinical conditions associated with alveolar hypoxia, hypoxemia, and polycythemia. Healthy HA natives have pulmonary hypertension (PH), right ventricular hypertrophy (RVH) and increased amount of smooth muscle cells (SMCs) in the distal pulmonary arterial branches. All these findings become exaggerated when healthy highlanders lose their capacity for adaptation and develop chronic mountain sickness (CMS). The physiological, pathological, pathogenic, and cl...

Graduated effects of high-altitude hypoxia and highland ancestry on birth size

“…Data on the prevalence of cardiometabolic morbidity and mortality in highland populations are lacking, particularly in studies controlling for high-altitude native ancestry. However, it is known that the human heart undergoes ventricular hypertrophy at altitude (35), that diabetes is a significant public health problem in Bolivia (36), and that patients with chronic mountain sickness in La Paz have marked systemic vascular dysfunction with evidence of impaired peripheral vasodilatation, increased arterial stiffness, and carotid arterial wall thickening (37). It is also known that individuals of Andean ancestry show protection against diabetes and chronic mountain sickness at high altitude (36,38).…”

Serum testosterone levels and excessive erythrocytosis during the process of adaptation to high altitudes

“…81 Similarly, CMS or lack of adaptation to HA, which occurs in natives or long-term residents at altitudes above 3000 m, also increases in a similar fashion. 82,83 These high Hb levels in populations at HA seem to be due to reduced levels of serum hepcidin. During exposure to hypoxia at HA, the levels of hepcidin are reduced, and this reduction is not driven by a reduction in iron storage.…”

“…All of these may contribute to the cause of CMS. 82 It is known that subjects with EE at HA show an increased incidence of CMS compared to subjects with lower Hb levels. 94 Similarly, spontaneous baroreflex sensitivity is significantly lower in subjects with EE.…”

Reoxygenation Reverses Hypoxic Pulmonary Arterial Remodeling by Inducing Smooth Muscle Cell Apoptosis via Reactive Oxygen Species–Mediated Mitochondrial Dysfunction

“…Hypoxic pulmonary hypertension (HPH), resulting from chronic lung diseases or occurring as an idiopathic case at high altitude, is a complicated disorder with high morbidity and mortality in adults and neonates 1, 2, 3, 4. Hypoxia generally gives rise to pulmonary vasoconstriction and vascular remodeling 5.…”