Chronic mountain sickness (CMS) is a disease in which the proportion of blood volume that is occupied by red blood cells increases (
polycythaemia
Polycythemia (also known as polycythaemia) is a laboratory finding in which the hematocrit (the volume percentage of red blood cells in the blood) and/or hemoglobin concentration are increased in the blood. Polycythemia is sometimes called erythr ...
) and there is an abnormally low level of oxygen in the blood (
hypoxemia
Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the body ...
). CMS typically develops after extended time living at high altitude (over ). It is most common amongst native populations of high altitude nations.
The most frequent symptoms of CMS are headache, dizziness,
tinnitus
Tinnitus is the perception of sound when no corresponding external sound is present. Nearly everyone experiences a faint "normal tinnitus" in a completely quiet room; but it is of concern only if it is bothersome, interferes with normal hearin ...
,
breathlessness
Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing dis ...
,
palpitations
Palpitations are perceived abnormalities of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart.
Symptoms include a rapi ...
, sleep disturbance, fatigue,
loss of appetite
Anorexia is a medical term for a loss of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a loss of appetite, some of which may be harmless, while others i ...
, confusion,
cyanosis
Cyanosis is the change of body tissue color to a bluish-purple hue as a result of having decreased amounts of oxygen bound to the hemoglobin in the red blood cells of the capillary bed. Body tissues that show cyanosis are usually in locations ...
, and dilation of veins.
CMS was first described in 1925 by
Carlos Monge Medrano, a
Peru
, image_flag = Flag of Peru.svg
, image_coat = Escudo nacional del Perú.svg
, other_symbol = Great Seal of the State
, other_symbol_type = Seal (emblem), National seal
, national_motto = "Fi ...
vian doctor who specialised in diseases of high altitude.
While
acute mountain sickness
Altitude sickness, the mildest form being acute mountain sickness (AMS), is the harmful effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation. People can respond to high altitude in different ways. Sympt ...
is experienced shortly after ascent to high altitude, chronic mountain sickness may develop only after many years of living at high altitude. In medicine, high altitude is defined as over , but most cases of CMS occur at over .
It has recently been correlated with increased expression of the genes ''
ANP32D'' and ''
SENP1
Sentrin-specific protease 1 is an enzyme that in humans is encoded by the ''SENP1'' gene.
General
So far there are six SUMO proteases in humans that have been designated SENP1-3 and SENP5-7 (sentrin/SUMO-specific protease).1 The six proteases p ...
''.
Diagnosis
CMS is characterised by
polycythaemia
Polycythemia (also known as polycythaemia) is a laboratory finding in which the hematocrit (the volume percentage of red blood cells in the blood) and/or hemoglobin concentration are increased in the blood. Polycythemia is sometimes called erythr ...
(with subsequent increased
haematocrit
The hematocrit () (Ht or HCT), also known by several other names, is the volume percentage (vol%) of red blood cells (RBCs) in blood, measured as part of a blood test. The measurement depends on the number and size of red blood cells. It is nor ...
) and
hypoxaemia
Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in artery, arterial blood. Hypoxemia has many causes, and often causes Hypoxia (medical), hypoxia as the blood is not supplying enough oxygen ...
; raised blood pressure in the lungs (
pulmonary hypertension) can develop over time and in some cases progress to heart failure (
cor pulmonale
Pulmonary heart disease, also known as cor pulmonale, is the enlargement and failure of the right ventricle of the heart as a response to increased vascular resistance (such as from pulmonic stenosis) or high blood pressure in the lungs.
Chronic ...
).
CMS is believed to arise because of an excessive production of red blood cells (
erythrocytes
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...
) due to the low oxygen levels at altitude, which increases the oxygen carrying capacity of the blood. The increased levels of erythrocytes causes increased blood viscosity and uneven blood flow through the lungs (
V/Q mismatch). However, CMS is also considered an adaptation of pulmonary and heart disease to life under chronic hypoxia at altitude.
Consensus for clinical diagnosis of CMS use laboratory values:
haemoglobin
Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...
in Males ≥ 21 g/dL; Females ≥ 19 g/dL,
haematocrit
The hematocrit () (Ht or HCT), also known by several other names, is the volume percentage (vol%) of red blood cells (RBCs) in blood, measured as part of a blood test. The measurement depends on the number and size of red blood cells. It is nor ...
> 65%, and arterial oxygen saturation (SaO2) < 85% in both genders.
Treatment
Migration to low altitude is curative, though not immediate, as the body adapts to the normal oxygen level near sea-level and the haematocrit normalises. Alternatively, bloodletting (
phlebotomy
Phlebotomy is the process of making a puncture in a vein, usually in the arm, with a cannula for the purpose of drawing blood. The procedure itself is known as a venipuncture, which is also used for intravenous therapy. A person who performs a ph ...
) can be performed to lower the haematocrit temporarily; when combined with volume replacement with fluids this can have a longer effect.
Medication with
acetazolamide
Acetazolamide, sold under the trade name Diamox among others, is a medication used to treat glaucoma, epilepsy, altitude sickness, periodic paralysis, idiopathic intracranial hypertension (raised brain pressure of unclear cause), urine alkalin ...
, a
carbonic anhydrase inhibitor
Carbonic anhydrase inhibitors are a class of pharmaceuticals that suppress the activity of carbonic anhydrase. Their clinical use has been established as anti-glaucoma agents, diuretics, antiepileptics, in the management of mountain sickness, ...
, has been shown to improve chronic mountain sickness by reducing
erythropoietin
Erythropoietin (; EPO), also known as erythropoetin, haematopoietin, or haemopoietin, is a glycoprotein cytokine secreted mainly by the kidneys in response to cellular hypoxia; it stimulates red blood cell production (erythropoiesis) in the bo ...
and the resulting polycythaemia, which results in better arterial oxygenation and a lower heart rate.
Oxygen therapy and training in slow breathing techniques has been shown to reduce symptoms through increasing blood oxygenation.
Epidemiology
Although CMS generally affects people native to altitudes higher than , it does not affect populations around the world equally. A 2013 study
reviewed CMS
prevalence rates around the world and found the highest rates were found in Andean countries of South America and the lowest rates in people native to the
East African Mountains The East African mountains are a mountain region in the African Great Lakes, within Kenya, Uganda, Tanzania, Democratic Republic of the Congo, Rwanda and Burundi.
Location and description
The mountains are related to the East African Rift, and are ...
of Ethiopia. CMS prevalence rates reported from the study are summarised below:
* Ethiopia
600–4100 m 0%
*
Tibetan Plateau
The Tibetan Plateau (, also known as the Qinghai–Tibet Plateau or the Qing–Zang Plateau () or as the Himalayan Plateau in India, is a vast elevated plateau located at the intersection of Central, South and East Asia covering most of the Ti ...
(Tibetans): 0.91–1.2%
* Indian Himalayas
000–4200 m 4–7%
* Kyrgyzstan
000–4200 m 4.6%
* Tibetan Plateau (
Han Chinese
The Han Chinese () or Han people (), are an East Asian ethnic group native to China. They constitute the world's largest ethnic group, making up about 18% of the global population and consisting of various subgroups speaking distinctive va ...
): 5.6%
*
La Paz
La Paz (), officially known as Nuestra Señora de La Paz (Spanish pronunciation: ), is the seat of government of the Bolivia, Plurinational State of Bolivia. With an estimated 816,044 residents as of 2020, La Paz is the List of Bolivian cities ...
, Bolivia
600 m 6% to 8%
* Bolivia: 8–10%
*
Cerro de Pasco
Cerro de Pasco is a city in central Peru, located at the top of the Andean mountains. It is the capital of the Pasco region, and an important mining center. At elevation, it is one of the highest cities in the world, and the highest or the sec ...
, Peru
300 m 14.8–18.2%
References
External links
Online calculator illustrating blood oxygen carrying capacity at altitude
{{Consequences of external causes
Effects of external causes
Mountaineering and health