The effect of beta adrenergic blockade on pulmonary hypertension, right ventricular hypertrophy and polycythaemia, induced in rats by intermittent high altitude hypoxia

Adult male rats were used to study the effect of a beta blocking agent on pulmonary hypertension and right ventricular hypertrophy induced by intermittent high altitude (IHA) hypoxia (8 hr daily, 5 days a week, stepwise up to the simulated altitude of 7000 m). Trimepranol was injected subcutaneously in a single dose of 10 mg/kg/b.w. one hour before each IHA exposure. Administration of the beta blocking drug caused significant changes of haematocrit values even in animals kept under normoxic conditions. The initial deep decrease was followed by a slow return to control values; prolongation of treatment led to a further significant decrease of the haematocrit curve. The polycythaemic response of IHA-exposed and Trimepranol-treated animals was, therefore, significantly less pronounced as compared with the hypoxic non-treated group. Administration of Trimepranol to IHA-exposed rats significantly decreased the values of right ventricular systolic and mean pressure, right ventricular hypertrophy as well as the degree of muscularization of pulmonary arteries. It may be assumed that the protective effect of Trimepranol is due to a) changes in pulmonary vascularization, b) reduction of polycythaemia, and c) lower cardiac output, induced by the negative inotropic and chronotropic effect of this drug.

Chronic mountain sickness

Chronic mountain sickness was first described in the Peruvian Andes. It consists of an excesive polycythemia for the altitude of residence. Its main symptoms are of cerebral congestion and occasionally of right heart insufficiency. The authors postulate that it is caused by a decay of the ventilatory rate with age with the corresponding increase in hematocrit.

The incidence, importance, and prophylaxis of acute mountain sickness

Acute mountain sickness (A.M.S.) and its severe complications, high-altitude pulmonary oedema (H.A.P.O.) and cerebral oedema (C.O.), were studied in 278 unacclimatised hikers at 4243 m altitude at Pheriche in the Himalayas of Nepal. The overall incidence of A.M.S. was 53%, the incidence being increased in the young and in those who flew to 2800 m, climbed fast, and spent fewer nights acclimatising en route. It was unrelated to sex, to previous altitude experience, to the load carried, and to recent respiratory infections. The severity of A.M.S. was inversely related to age (independent of rate of ascent) and the highest altitude attained, and was highly ocrrelated with speed of ascent. There were 7 cases of H.A.P.O. and 5 with the more intractable C.O. and, of these 12, 11 had flown in, 9 had spent only one night at Pheriche, and none were on acetazolamide. 11 required evacuation. Acetazolamide, compared in a double-blind study with a placebo and also compared with no tablets at all, reduced both the incidence and the severity of A.M.S. in those who flew to 2800 m but not in those who hiked up to that altitude. Prevention consists in slow ascent, rapid recognition of warning signs, and prompt descent to avoid progression.

Human coagulation abnormalities during acute exposure to hypobaric hypoxia

Multiple coagulation studies were carried out in eight healthy young men at sea level (SL) and after 1, 24, and 48 h at a simulated altitude of 4,400 m. Platelet aggregation, as induced by ADP, epinephrine, and collagen, was not significantly altered by high-altitude (HA) exposure. Mean 2,3-diphosphoglycerate, a physiological inhibitor of platelet aggregation, rose (P less than 0.001) after 24 h at HA and remained elevated while no changes in circulating catecholamines were observed. Platelet count, factor 3 availability, and membrane lipid peroxide formation were likewise unaltered at HA, as were prothrombin and thrombin times and protamine paracoagulation test. However, mean partial thromboplastin time was significantly shortened (P less than 0.01) after 1 and 24 h at HA, recovering to SL control by 48 h. Fibrinogen and factor VIII levels also fell (P less than 0.01 and P less than 0.02) after 1 h at HA but returned to the preexposure values by 24 h. Fibrin degradation products were transiently detectable in three subjects at HA. Thus, although normal platelet function did not appear to be modified by short-term exposure to simulated high altitude, evidence for a coagulopathy was obtained.

Pulmonary gas exchange in acute mountain sickness

The severity of acute mountain sickness (AMS) was investigated in healthy volunteers, airlifted to high altitude (5,360 m). Blood gases were measured at 2,990 m and 5,360 m. Symptoms of AMS were found in all subjects, but ranged from malaise to vomiting with intractable headache. The clinical severity of AMS was directly related to the arterial PCO2 and inversely to pH, but unrelated to the PO2 on arrival at high altitude. However, PO2 fell and was lowest 48 h after arrival at high altitude in those subjects with the most severe AMS. These were the only subjects to show an increase in the alveolar-arterial PO2 difference and in the venous admixture ratio during the first 48 h. These abnormalities in gas exchange, which developed in the subjects with the most marked cerebral symptoms, suggest that the manifestations of cerebral and pulmonary dysfunction at altitude develop simultaneously, a finding that suggests coexisting cerebral and pulmonary edema.

Mountain sickness, retinal haemorrhages, and acclimatisation on Mount Everest in 1975

During the 1975 British Everest Expedition, which made the first ascent of the south-west face, observations were made in relation to mountain sickness and the appearance of retinal changes. Two Sherpas with cerebral oedema and one Briton with pulmonary oedema were treated. Retinal haemorrhages occurred in four out of six Britons who were newcomers to altitudes over 6000 m (19 685 ft) but in only two out of 14 Britons who had previously visited these altitudes. Intraocular pressures during ascent to 6000 m were within normal limits. The relevance of the ocular findings to acclimatisation in previous years was examined, the results supporting the hypothesis of a "carry-over" effect from previous visits to high altitude.

Nutritional aspects of high-altitude exposure in women

The nutrient intake and urinary excretion characteristics of eight young university women were studied over a 4-day period at low altitude (140 m) and subsequently over a 7-day sojourn on Pikes Peak (4,300 m). High-altitude exposure was associated with a transient decrease in the consumption of protein, carbohydrate, fat, sodium, calcium, phosphorus, vitamin A, riboflavin, thiamin, and niacin and a more sustained decrease in the consumption of potassium and ascorbic acid. In most instances minimal values were observed during the first 3 days of exposure. The carbohydrate fraction of energy intake was increased at the expense of fat during this time period. Individual hypophagic responses appeared to be related to severity of acute mountain sickness. Altitude had no effect on water consumption but did lead to an average body weight loss of 1 kg. Urinary measurements revealed a marked oliguria during the entire sojourn. These measurements also showed the first 3 days to be associated with a net loss of body nitrogen and sodium. During this time period body potassium and phosphorus were conserved, and probably increased. The urea fraction of body potassium and phosphorus were conserved, and probably increased. The urea fraction of total urinary nitrogen was not affected by altitude exposure, nor was the daily excretion of uric acid and creatinine. Ammonia excretion, however, was reduced to 50% of the low-altitude value and remained at this level throughout the sojourn. With a few exceptions, the qualitative characteristics of altitude hypophagia in women were similar to those reported for men. Quantitatively, however, the responses were much more transient in women.

High altitude pulmonary edema. A rare disease?

Since its original description in the English literature 15 years ago, high altitude pulmonary edema (HAPE) has been the subject of many reports. The clinical and hemodynamic features of HAPE are now well recognized, but its underlying pathophysiology remains unclear. In this article, a case of HAPE is described and the clinical features, proposed pathogenesis, and treatment are discussed. (JAMA 234:491-495, 1975).

Cerebral form of high-altitude illness

Twelve cases of severe altitude illness are reported in which the neurological signs and symptoms dominated the clinical picture. Pulmonary oedema, retinal haemorrhage, thrombophlebitis and pulmonary embolism, bronchopneumonia, and coronary-artery disease were also present in several of the patients but the primary problem seems to have been cerebral oedema. Other published cases support this impression. Patients who were returned to low altitude early in the disease fared well; two patients died, and in both cases evacuation had been delayed. The most effective prevention lies in slow ascent, though in one case reported here the rate of climb was well within the recommended limit. Recommended management is rapid descent to low altitude at earliest indication of cerebral or pulmonary oedema, intravenous dexamethasone or betamethasone in large doses, hydration, diuresis (frusemide has been most used), and perhaps other intravenous therapy with hyperosmolar materials such as mannitol, urea, 50% saline, or 50% sucrose. Prognosis is good if descent and treatment are started early, but permanent damage may be anticipated if the patient is unconscious for any prolonged period before descent.

Acute mountain sickness: increased severity in eucapnic hypoxia

This study examined the hypothesis that prevention of hypocapnia and alkalosis would ameliorate the symptoms of acute mountain sickness (AMS). Five subjects were exposed to simulated high altitude for 4 d with 3.8% CO2 added to the chamber to maintain normocapnia. Four other subjects were exposed for 4 d to hypobaric hypoxia without CO2 supplementation, and became hypocapnic. Barometric pressure was lower in the group with added CO2 so that alveolar oxygen tensions (55-60 mm Hg) would not be different. The severity of symptoms was clearly greater in normocapnic than in hypocapnic subjects. Thus, prevention of hypocapnia did not alleviate AMS symptoms. The efficacy of CO2 addition in reducing symptoms, as reported by earlier workers, was probably the result of induced hyperventilation and partial relief of hypoxia. Indeed, in the present study with two comparably hypoxic groups, CO2 addition augmented the sysptoms, possibly by causing increased cerebral vasodiladation and spinal fluid pressure.