Chronic Mountain Sickness and the Heart

doi:10.1016/j.pcad.2010.02.012

Progress in Cardiovascular Diseases

Volume 52, Issue 6, May–June 2010, Pages 540-549

https://doi.org/10.1016/j.pcad.2010.02.012 Get rights and content

Abstract

Chronic Mountain Sickness (CMS) is an important high-altitude (HA) pathology in most mountainous regions of the world. Although its most characteristic sign is excessive erytrocytosis (EE), in the more severe stages of the disease, high-altitude pulmonary hypertension (HAPH), with remodeling of pulmonary arterioles and right ventricular enlargement is commonly found. The degree of ventricular hypertrophy depends on the vasoconstrictor pulmonary response, the intensity of vascular resistance and the level of altitude, and therefore on the degree of hypoxemia. This chapter briefly summarizes the existing data regarding the clinical and pathophysiological features of the cardiopulmonary system in CMS, with emphasis in findings from research in the Andes. The literature shows variability in cardiac output values in CMS, which might be related to the degree of EE. Recent findings have shown that cardiac output (l/min) is lower in CMS when compared with sea-level (SL) dwellers. Mean pulmonary acceleration time (ms) is significantly lower in CMS subjects than in SL and HA natives, and pulmonary vascular resistance index (Wood units) is higher in CMS and HA natives when compared with SL dwellers. Systemic blood pressure has similar values in CMS patients and healthy HA natives, but some differences arise in its control mechanisms. Although CMS individuals have a less effective vasoconstrictor reflex, their tolerance to orthostatic stress is similar to that of healthy HA natives which might be explained in terms of the larger blood volume present in CMS subjects. At present research is directed to design strategies on pharmacological intervention for CMS treatment. Recently, a clinical trial with acetazolamide, in patients with CMS has proven to be effective in increasing mean pulmonary acceleration time and decreasing pulmonary vascular resistance index, which might be indirectly due the reduction of hematocrit

Section snippets

Respiratory aspects of CMS

The primary finding in patients with CMS is excessive erythrocytosis. This excessive increase in the number of red blood cells is caused by hypoxemia, which develops mainly because differences in the respiratory pattern of CMS individuals. Compared with healthy HA natives at the same altitude, patients with CMS are relatively hypoxic and hypercapnic.20, 21 Alveolar hypoventilation is the main respiratory feature, but also, ventilation-perfusion mismatch, and widened alveolar-arterial Po₂

Excessive erythrocytosis and the heart in CMS: effect of hematocrit on cardiac function

Increased [Hb] has long been considered beneficial at high altitude because the increased oxygen-carrying capacity of blood would compensate for decreased arterial oxygen saturation. The increase in [Hb] should act to maintain oxygen transport to tissues, thereby, reducing the need to increase cardiac output in hypoxemic subjects. This concept however has been challenged because with a low oxygen saturation (low Po₂), increasing [Hb] would be of help up to a certain point, and thus, only a

Systemic blood pressure control and blood flow in CMS

Although systolic blood pressure in CMS patients is often similar to that of healthy highlanders, some small differences arise in the control mechanisms. It has been shown that Andean HA dwellers have a great tolerance to orthostatic stress that might be attributed to the increased hematocrit and blood volume. The CMS individuals show an exceptional tolerance to orthostatic stress but no significantly different from HA controls, yet CMS individuals tend to respond with smaller increases in

Cardiac features of CMS

Thirty years ago, Peñaloza and Arias-Stella⁵⁹ studied extensively the cardiac characteristics and pulmonary circulation of Andean dwellers and patients with severe CMS. Their findings point to the presence of pulmonary hypertension and right ventricular hypertrophy in CMS subjects.9, 10, 60, 61 They also demonstrated a direct relationship between Ppa and right ventricle size. In addition, a prominent main pulmonary artery was found in all patients. Clinical characteristics of pulmonary

Pulmonary hypertension in CMS

The cause of HAPH is the increase in pulmonary vascular resistance (PVR); the underlying mechanism involves sustained and exaggerated pulmonary vasoconstriction and remodeling of the pulmonary vascular wall in response to chronic hypoxia due to proliferation and decreased apoptosis of pulmonary artery smooth muscle cells. The effects of chronic hypoxia on pulmonary artery pressure are reflected in the negative correlation that exists between Ppa and SaO₂ at high altitude.59, 69, 70 Arterial

Treatment

Recently, increasing attention is being drawn to different phenomena that may be involved in the causal chain of CMS and that were previously overlooked. These include CMS risk and environmental factors, such as early prenatal or postnatal exposure to different agents, and/or the different genetic susceptibilities in different populations and individuals. However, until having a complete understanding of which mechanisms are better targets for intervention, at present, treatment is directed to

Statement of Conflict of Interest

All authors declare that there are no conflicts of interest.

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