pituitrin and Altitude-Sickness

The acute acclimatization to high altitude is underpinned by a diuresis (and to a lesser extent a natriuresis) that facilitates a reduction in plasma volume. This allows a haemoconcentration to occur that increases the oxygen carrying capacity of a given volume of blood, a vital effect in the presence of a reduced partial pressure of oxygen. This critical acclimatization process is orchestrated by the endocrine system. This review will present the key evidence regarding the changes in several important hormones that affect this process.

Topics: Acclimatization; Acute Disease; Altitude Sickness; Atrial Natriuretic Factor; Diuresis; Hormones; Humans; Hydrocortisone; Mountaineering; Natriuretic Peptide, Brain; Plasma Volume; Renin-Angiotensin System; Vasopressins; Water-Electrolyte Balance

Alveolar hypoxia and resulting tissue hypoxia initiates the pathophysiological sequence of high altitude pulmonary edema (HAPE). Very rapid ascent to high altitude without prior acclimatization results in HAPE, even in subjects with excellent tolerance to high altitude. Upon acute altitude exposure, HAPE-susceptible individuals react with increased secretion of norepinephrine, epinephrine, renin, angiotensin, aldosterone and atrial natriuretic peptide. In response to exercise at high altitude, subjects developing acute mountain sickness and HAPE secrete more aldosterone and antidiuretic hormone than subjects who remain well. This results in sodium and water retention, reduction of urine output, increase in body weight and development of peripheral edemas. The hypoxic pulmonary vascular response is enhanced in HAPE-susceptible subjects, thus favouring the development of severe pulmonary hypertension on exposure to high altitude. It has been postulated that uneven pulmonary vasoconstriction enhances filtration pressure in non-vasoconstricted lung areas, leading to interstitial and alveolar edema. The high protein content of the edema fluid in HAPE characterizes this edema as a permeability edema. The prophylactic administration of nifedipine prevents the exaggerated pulmonary hypertension of HAPE-susceptible subjects upon rapid ascent to 4559 m and thus prevents HAPE in most cases. This finding illustrates the crucial role of hypoxic pulmonary hypertension in the development of HAPE. The causal treatment of HAPE is descent, evacuation and administration of oxygen. Treatment of HAPE patients with nifedipine results in a reduction of pulmonary artery pressure, clinical improvement, increased oxygenation, decrease of the alveolar arterial oxygen gradient and progressive clearing of pulmonary edema on chest x-ray. Thus nifedipine offers a pharmacological tool for the treatment of HAPE.

Topics: Aldosterone; Altitude Sickness; Cell Membrane Permeability; Epinephrine; Humans; Hypertension, Pulmonary; Nifedipine; Norepinephrine; Pulmonary Edema; Radiography; Renin-Angiotensin System; Vasopressins

This paper summarizes the main findings of 3 publications of our group [2-4] examining fluid balance at high altitude. Of 57 mountaineers ascending from 1170 m to 4559 m within 22 to 77 hours, 24 developed acute mountain sickness (AMS) and 16 developed high altitude pulmonary edema (HAPE). In 14 cases HAPE was preceded by symptoms of AMS. Independently of the amount of fluid intake, which varied from 2 to 4 l/24 h in these studies, subjects developing AMS showed decreased diuresis and natriuresis compared to healthy controls with similar fluid intake. Higher fluid intake resulted in greater urine output but did not prevent AMS. Higher plasma levels of aldosterone at rest and greater exercise-induced rises of plasma aldosterone and vasopressine may explain the increased water and salt retention in subjects with AMS. Whether these hormonal changes are secondary to a more severe hypoxemic stress or present a primary cause of AMS remains to be determined.

Topics: Adult; Aldosterone; Altitude Sickness; Diuresis; Drinking; Humans; Male; Middle Aged; Mountaineering; Natriuresis; Pulmonary Edema; Vasopressins; Water-Electrolyte Balance

A possible contribution of exercise to the fluid retention associated with acute mountain sickness (AMS) was investigated in 17 mountaineers who underwent an exercise test for 30 min on a bicycle ergometer with a constant work load of 148 +/- 9 (SE) W at low altitude (LA) and with 103 +/- 6 W 4-7 h after arrival at 4,559 m or high altitude (HA). Mean heart rates during exercise at both altitudes and during active ascent to HA were similar. Exercise-induced changes at LA did not differ significantly between the eight subjects who stayed well and the nine subjects who developed AMS during a 3-day sojourn at 4,559 m. At HA, O2 saturation before (71 +/- 2 vs. 83 +/- 2%, P less than 0.01) and during exercise (67 +/- 2 vs. 72 +/- 1%, P less than 0.025) was lower and exercise-induced increase of plasma aldosterone (617 +/- 116 vs. 233 +/- 42 pmol/l, P less than 0.025) and plasma antidiuretic hormone (23.8 +/- 14.4 vs. 3.4 +/- 1.8 pmol/l, P less than 0.05) was greater in the AMS group, whereas exercise-induced rise of plasma atrial natriuretic factor and changes of hematocrit, potassium, and osmolality in plasma were similar in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acclimatization; Acetaminophen; Adult; Aging; Aldosterone; Altitude Sickness; Blood Proteins; Exercise; Exercise Test; Heart Rate; Hematocrit; Hormones; Humans; Male; Middle Aged; Mountaineering; Oxygen Consumption; Pulmonary Edema; Urodynamics; Vasopressins; Water-Electrolyte Balance

Early alterations in fluid, electrolytes, and their regulating hormones were investigated in men exposed to 6,000 m simulated altitude (2 h-ascent, 2 h-sojourn, 2 h-return). Hematocrit and serum protein rose with elevated serum osmolality and reduced urine flow upon arrival at 6,000 m, suggesting decreased plasma volume probably due to hypotonic fluid shift to intracellular spaces. Serum K declined reflecting respiratory alkalosis. The exposure raised plasma antidiuretic hormone (ADH), plasma renin activity (PRA), serum cortisol and aldosterone. Increases both in ADH and aldosterone showed close correlations with that in cortisol, suggesting that ADH may be elevated by hypoxic stress in addition to elevated serum osmolality and decreased plasma volume, and that increased secretion of adrenocorticotropin may be the main cause of increased aldosterone, though PRA involvement cannot be excluded. These rises in ADH and aldosterone may act to retain body water, and the latter may exaggerate alkalosis; thus, these hormonal changes may be related to acute mountain sickness.

Topics: Adult; Aldosterone; Altitude; Altitude Sickness; Atmosphere Exposure Chambers; Blood Proteins; Female; Hematocrit; Hormones; Humans; Hydrocortisone; Male; Middle Aged; Osmolar Concentration; Potassium; Renin; Urine; Vasopressins; Water-Electrolyte Imbalance

A general preliminary study is made of possible "fall-out" applications from military technology--especially in certain electronics sectors--enabling such technology to be used for non-military purposes that would greatly benefit society, for example in the biomedical field. The continued and profitable exchange that is rapidly developing, not only between technology and science but also between science and technology in the specific sector of aviation medicine, in discussed in detail. The direct and indirect theoretical and practical applications of aviation medicine in medical science, practical medicine and health services are briefly outlined (apparatus for inhaling oxygen; safety and "delethalisation" methods for accidents caused by violent impact; the application of minor technologies in the fields of immunology and hygiene-prophylaxis to air transport and rescue services; the selection and medico-legal check-ups of all military and civilian flight personnel; the emergency transport of transplant organs and seriously ill patients requiring emergency transplants, etc.). Current and possible future practical applications of the vast experience acquired by space medicine had to solve complex problems relating to space flight and man's survival in space, such as: the absence of gravity (and its functional effects on the body's main system and organs), exposure to cosmic and solar radiation, conditioning and prolonged isolation in the space capsule, modifications in circadian rhythms, "space sickness", etc. Finally, the study recalls that the evolution and refinement of aerospace technology has made it possible to make use of exceptional space conditions, such as "microgravity", to conduct in-depth studies--in extreme conditions--of certain biological phenomena and to gain further knowledge of the genesis and to gain of various vital processes. Another area under study is the production--in extremely favourable conditions--of new, vaccines, enzymes and hormones, new drugs for therapy and prophylaxis and for biopharmacology, and new food sources which are of prime importance for man's future requirements.

Topics: Accidents, Aviation; Aerospace Medicine; Aldosterone; Altitude Sickness; Biomedical Engineering; Epinephrine; First Aid; Humans; Renin; Research; Stress, Physiological; Transportation of Patients; Vasodilation; Vasopressins; Weightlessness

Urinary excretion of electrolytes, creatinine, urea, and antidiuretic hormone--measured as arginine vasopressin (AVP) by radioimmunoassay--was investigated in eight Himalayan mountaineers during ascent on foot from 1900- 5400 m. Specimens were collected from each individual whenever urine was voided, preserved with 1% boric acid, and subsequently pooled to give samples representative of 24-h collections. AVP was found to be reasonably stable under simulated conditions of storage. In all subjects, the observed AVP excretion rates were mostly in the lower region of the normal range and there was generally no correlation with altitude, urine osmolality, electrolyte excretion, or occurrence of AMS symptoms--even in a fatal case of cerebral oedema. It is concluded that AVP does not play a primary role in the changes in fluid balance which accompany either acclimatization to high altitude or the onset of AMS.

Topics: Adult; Altitude; Altitude Sickness; Arginine Vasopressin; Female; Humans; Male; Time Factors; Vasopressins; Water-Electrolyte Balance

Topics: Altitude; Altitude Sickness; Female; Humans; Hypoxia; Male; Vasopressins