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Falling Sick in the Mountains - Pathology of Altitude Related Illness.
Dr Sampurna Roy MD August 2015
"It's always further than it looks.
It's always taller than it looks.
And it's always harder than it looks." - The 3 rules of mountaineering.
|As a child we
all enjoyed climbing, whether it is among the furnitures, over the wall or
up the trees in the garden. Therefore it is not surprising this childhood
pastime, which seems almost a form of instinct, should attract us to the
sport of mountaineering, or climbing mountains.
Mountaineering calls for hard work, courage, caution, patience, strength and skill. It is often difficult and sometimes dangerous, but those who are attracted to it will find it a sport that offers many rewards. There is the pleasure which is given by hard physical exercise, the satisfaction that comes from a challenge successully met and the thrill of adventure in beautiful and lonely places. The most valuable reward is the friendship that grows between those who have faced difficulties together. Doctor are you using social media ?
Climbing in the Alps and trekking in the Andes or in the Himalayas has become very popular in the recent years. Every year thousands of ski, trekking or climbing fans travel to the mountains where they stay at the altitude of more than 2500-3000m above sea level or climb mountain peaks, often exceeding 7000-8000m.
High mountain climbers are at a serious risk from the effects of adverse environmental conditions at high altittude. They may experience health problems resulting from hypotension, hypoxia or exposure to low temperatures.
The severity of those conditions is largely dependent on elevation, time of exposure as well as the rate of ascent and descent.
Almost every second trekker or climber develops two to three symptoms of the high altitude illness after a rapid ascent (> 300 m/day) to an altitude above 4000 m.
Adaptive physiological responses, as well as disease, are associated with both living and travel at high altitudes. From a physiological standpoint, altitudes are separated into three categories : Below 2500 meters ; 2500 to 4000 meters ; and above 4000 meters.
High altitude disease is rare, mainly because of the acclimatization of mountain climbers before extreme altitudes are reached. However, there is an altitude limit beyond which human life cannot be sustained for prolonged periods. Even communities accustomed to live in high altitude do not survive at elevations above 5500 to 6000 meters.
Prolonged stays at this altitude result in weight loss, difficulty in sleeping, and lethargy, perhaps because of the redirection of cellular energy simply for survival.
The oxygen obtained per inhalation at 6000 meters, 75% to 90% is utilized for the effort of inspiration alone.
The changes induced by high altitude are related to a decreased atmospheric pressure and ,therefore, to decreased oxygen availability.
It has been suggested that the decreased oxygen tension and the limited ability of the lungs to extract oxygen at lower pressures produce the hypoxia that is probably the most important factor in causing high-altitude illness.
The low reserve is noted by the observation that physical activity at these heights leads to a decrease in the partial pressure of arterial oxygen, where as comparable physical activity at sea level does not change oxygen saturation. At sea level, cardiac output limits exercise, where as at high altitudes the diffusing capacity of lung for oxygen seems to be the determinant.
The more serious nonfatal diseases are acute and chronic mountain sickness and high altitude deterioration.
Fatal disease can develop in the form of high-altitude pulmonary edema and high-altitude encephalopathy.
Pathology of Altitude Related Illness.
1) Pulmonary Edema due to high altitude:
A disease which poses a direct threat to the lives of mountain climbers is high altitude pulmonary edema . It is a non-cardiogenic pulmonary edema which typically occurs in rapidly climbing unacclimatized lowlanders usually within 2-4 days of ascent above 2500-3000m.
Symptoms associated with high altitude pulmonary edema are incapacitating fatigue, chest tightness, dyspnoe at the minimal effort that advances to dyspnoe at rest and a dry non-productive cough that progresses to cough with pink frothy sputum due to hemoptysis.
It is the most common cause of death resulting from the exposure to high altitude. The risk of high altitude pulmonary edema rises with increased altitude and faster ascent.
Climbers with a previous history of high altitude pulmonary edema , who ascent rapidly above 4500m have a higher chance of illness recurrence.
Tachycardia, right ventricular overload, and a marked reduction in arterial oxygen pressure are seen. There is no change in pH or carbon dioxide retention.
Pulmonary hypertension due to increased resistance is common in patients with high-altitude pulmonary edema. Eventually, cardiac output is decreased and systemic blood pressure falls. The arterioles are dilated, increasing capillary bed pressure and leading to pulmonary interstitial and alveolar edema.
Radiological examination reveals a characteristic patchy pulmonary infiltrate.
Autopsy findings include severe confluent pulmonary edema, proteinaceous alveolar exudates, and hyaline membrane formation. Capillary obstruction by thrombi has been noted. A dilated heart and enlarged pulmonary arteries are commonly found.
2) Cerebral Edema due to high altitude: (High-altitude encephalopathy)
Symptoms and signs of high altitude cerebral edema are severe headache, which is not relieved by acetaminophen, loss of movement coordination, confusion, stupor, ataxia and mental deterioration ending in coma.
Autopsies have revealed cerebral edema and vascular congestion.
The degree of change in cerebral blood flow at high altitude is influenced by many variables, including arterial oxygen and carbon dioxide tensions, oxygen content, cerebral spinal fluid pH, and hematocrit, but can be collectively summarized in terms of the relative strengths of 4 key integrated reflexes:
(i) hypoxic cerebral vasodilatation;
(ii) hypocapnic cerebral vasoconstriction;
(iii) hypoxic ventilatory response; and
(iv) hypercapnic ventilatory response.
3) Acute Mountain Sickness:
Acute mountain sickness is rare below 2500 meters, but is present to some degree in nearly everyone at 3000 to 3600 meters.
The initial presentation includes headache, lassitude, anorexia, weakness and difficulty in sleeping.
Barometric pressure falls with increasing altitude and consequently there is a reduction in the partial pressure of oxygen resulting in a hypoxic challenge to any individual ascending to altitude. A spectrum of high altitude illnesses can occur when the hypoxic stress exceeds the subject's ability to acclimatize.
The pathophysiological mechanism that underlies this disease is in part related to hypoxia and a shift in plasma fluid to the interstitial space.
Adaptation through a modification of pulmonary function (increased respiratory rate) may lead to some improvement.
Prevention of altitude-related illness by slow ascent is the best approach, but this is not always practical. The immediate management of serious illness requires oxygen (if available) and descent of more than 300 m as soon as possible.
Chronic or subacute exacerbation of this disease also occurs, frequently at lower altitudes, and the symptoms may be severe. The basis of the disease is not known.
4) Systemic Edema due to high altitude:
Systemic edema results from an asymptomic modification of vascular permeability. The changes are noted particularly in the hands, face, and feet. There is evidence of weight gain. These changes usually occur at an altitude over 3000 meters. This disorder is twice as common in women than in men.
When the person returns to lower altitude there is diuresis and the edema disappears. The cause of this condition is not known. It is probably related to endothelial response to hypoxia.
5) Patients with diabetes at high altitude:
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A growing number of subjects with diabetes take part in physical activities at altitude such as skiing, climbing, and trekking.
Exercise under conditions of hypobaric hypoxia poses some unique challenges on subjects with diabetes, and the presence of diabetes can complicate safe and successful participation in mountain activities.
Among others, altitude can alter glucoregulation. Furthermore, cold temperatures and altitude can complicate accurate reading of glucose monitoring equipment and storage of insulin.
These factors potentially lead to dangerous hyperglycemia or hypoglycemia.
6) Gastrointestinal disorder in patients at high altitude:
At altitudes greater than 4000 m about 50-80% of people are affected.
After only short exposure, gastrointestinal mucosal lesions can occur, potentially leading to gastrointestinal bleeding and lessened hunger.
Patients with inflammatory bowel disorders may develop an acute exacerbation.
Changes in external pressure and the production of intestinal gas provide for expansion of the luminal contents of the intestine and increased flatus at altitudes above 3500 meters.
7) Acute splenic syndrome:
Spleen and sickle cells
Acute splenic syndrome is a rare but well-documented complication of sickle cell trait that can present in the setting of low oxygen tension that occurs with major changes in altitude. Acute massive splenic infarction with splenic vein thrombosis following exposure to high altitude in patients with sickle cell trait have been reported.
8) Ocular changes in high altitude Retinal Hemorrhage:
A critical analysis by funduscopic examination revealed that 30% to 60% of those sleeping above 5000 meters had retinal hemorrhage.
The initial effect includes retinal vascular engorgement and tortuousness.
Optic disc hyperemia is also noted, and multiple flame-shaped hemorrhages subsequently occur. These changes are reversible.
9) Decrease in physical and mental performance at high-altitude:
There is general deterioration of health at higher elevations (5500 meters or more). The patient presents with decrease in physical and mental performance. The combination of chronic hypoxia, inadequate fluid intake, and inadequate nutrition, together with decreased plasma volume and hemoconcentration, are aggravating factors.
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