Basal metabolic rate and body composition at high altitudes

Basal metabolic rate (BMR) and body composition were determined in 17 healthy adult males living at an altitude of 14,900 ft above sea level. Using body surface area as a standard of reference and following the criterion of Boothby et al. ( Am. J. Physiol. 116: 468, 1936), the BMR of the high-altitude resident fell within the limits considered normal for healthy adults at sea level. A comparison with the data obtained by investigators in the United States and in India shows that, when either fat-free body mass (FFM), cell mass (C), or cell solids (S) are the standard of reference, the BMR is higher in the high-altitude resident. The higher O2 consumption per kilogram of FFM, C, or S in the high-altitude resident seems to be one of the many mechanisms developed by the body in its process of adaptation to the low O2 tension.

Note:

(With the Technical Assistance of Melquiades Huayna-Vera)

Submitted on October 24, 1960

Myoglobin content and enzymatic activity of muscle and altitude adaptation

Quantitative determinations of myoglobin were made in the sartorius muscle of healthy human subjects native to sea level and high altitude. The specific activities of the reduced form of diphosphopyridine nucleotide oxidase (DPNH-oxidase), DPNH- and the reduced form of triphosphopyridine nucleotide (TPNH)-cytochrome c reductases, transhydrogenase, and isocitric and lactic dehydrogenases were also examined. There was found a significantly higher myoglobin concentration in the muscle of the high-altitude native as compared with the sea-level resident. The enzyme systems DPNH-oxidase, TPNH-cytochrome c reductase, and transhydrogenase similarly showed a significantly higher activity in the altitude resident. It was concluded that the respiratory capacity of the muscle was apparently higher in the altitude native than in the sea-level one. The enhanced enzymatic activity was probably related to the higher pigment content of the skeletal muscle. Results on myoglobin determinations in several other muscles from certain sea-level patients are discussed.

Submitted on July 24, 1961

Body composition at sea level and high altitudes

Simultaneous determinations of total body water and extracellular fluid, using the antipyrine and sucrose infusion methods, have been carried out in 28 adult male residents at sea level and in 28 residents at an altitude of 14,900 ft. Body composition was calculated from these data. The various body spaces, expressed in percentage of body weight, were similar in the two groups, with the exception of the extracellular fluid which was greater in those in the high altitude group ( P < 0.01). Neither racial characteristics nor altitude appear to be factors generally affecting body composition. In individuals having adequate caloric intake body composition seems to be influenced principally by physical activity. In fact, physical inactivity appeared to produce a loss of active tissue and its replacement by fat.

Submitted on November 2, 1960

Pyridine nucleotide oxidases and transhydrogenase in acclimatization to high altitude

Activities of pyridine nucleotide oxidases and transhydrogenase have been examined in heart, liver and rectus femoris muscle of guinea pigs native to sea level and high altitude. There was found an enhanced reduced form of diphosphopyridine nucleotide oxidase (DPNH-oxidase) and transhydrogenase activity in heart and muscle from animals adapted to high altitude. In muscle the higher activity at altitude was due solely to increase in ratio of red to white portions. Both groups showed the pigmented portion twice as active as the white one. In liver, neither the DPNH-oxidase system nor the transhydrogenase were significantly changed in their activities on a fresh weight basis. Nevertheless, the DPNH-oxidase is higher at altitude when the activity is expressed per gram of nitrogen. The reduced form of triphosphopyridine nucleotide oxidase activity was not appreciably changed in any of the studied tissues. It was concluded that adaptation to high altitude is associated with apparent changes in the magnitude of the electron transport pathway. Increased activity in skeletal muscle is probably related to the tissue pigment content.

High altitude-induced pulmonary hypertension in normal cattle

Six months residence at an altitude of 10,000 feet produced significant pulmonary hypertension and arterial oxygen desaturation (86 per cent) in 10 normal steers born at 3,600 feet. Six of these animals, during the course of the experiment, showed a rise in mean pulmonary arterial pressure from 27 to 45 mm. Hg. The remaining four animals developed more severe pulmonary hypertension, and two with mean pressures greater than 100 mm. Hg had right heart failure. All 10 showed right ventricular hypertrophy proportional to the degree of pulmonary hypertension. Ten steers of similar age and origin, maintained as controls at 5,000 feet, showed a mean pulmonary arterial pressure of 27 mm. Hg throughout the experiment. The pulmonary hypertension observed at high altitude is considered to be due to an increased pulmonary vascular resistance resulting from a reduction in the total cross-sectional area of the pulmonary vascular bed. Chronic hypoxia appeared to be the most important etilogical factor responsible for initiating the hypertension. The observed beneficial effects of 100 per cent oxygen inhalation and the prompt recovery of an affected animal when moved to lower altitude supported the concept of pulmonary hypertension induced by hypoxia.

Arterial oxygen saturation during exercise at high altitude

Arterial oxygen saturations were measured on six members of the Himalayan Scientific and Mountaineering Expedition, 1960–61, during a wintering period at 19,000 ft (5,800 m; Pb 380 mm Hg). The determinations were made by ear oximetry and by the analysis of venous blood from the heated hand during rest and exercise at work levels up to 1,200 kg-m/min. Expired gas volumes and gas concentrations were also measured. The average arterial oxygen saturation at rest was 67%, and at work levels of 300 and 900 kg-m/min it was 63 and 56%, respectively. Several readings of less than 50% saturation were recorded during severe exercise. The progressive fall in arterial oxygen saturation as the work level was raised occurred in spite of an increasing alveolar oxygen tension, and the resulting large alveolar-arterial oxygen differences can be explained by the diffusion limitations of the lung.

Submitted on January 12, 1962

BLOCKAGE OF EPINEPHRINE-INDUCED HYPERGLYCEMIA DURING EXPOSURE TO SIMULATED ALTITUDES

Hyperglycemia elicited by subcutaneous injection of epinephrine (10 µg/rat) was completely abolished during the exposure of the rat to a simulated high altitude (220–250 mm Hg). Addition of 5–7% CO2 to the inspired gas during the altitude stress restored the hyperglycemic activity of epinephrine, suggesting that the alkalosis or hypocapnia provoked by hyperventilation, but not hypoxia itself, would be involved in the prevention of the hyperglycemic action of epinephrine. Glucose tolerance tests and in vitro experiments using isolated rat diaphragm showed that the inhibitory action of epinephrine on peripheral glucose utilization was abolished by shifting the pH of body fluids or incubation media toward higher levels. It was concluded that alkalosis, either directly or indirectly, abolished the hyperglycemic action of epinephrine as a consequence of the release of the inhibitory action of epinephrine on muscle glucose utilization.

ALVEOLAR-ARTERIAL OXYGEN GRADIENT IN ANDEAN NATIVES AT HIGH ALTITUDE

The A-a Do2 (alveolar-arterial oxygen tension difference) was determined at three levels of oxygenation in three groups of subjects: 1) normal persons at sea level, 2) normal Andean natives at high altitude, 3) Andean natives with chronic mountain sickness. The values of A-a Do2 in the Andean natives were uniformly higher than in normal sea-level residents at all levels of oxygenation. These findings were accentuated in patients with chronic mountain sickness. It is concluded that there is no decrease in diffusion barrier for oxygen, and there may be increased veno-arterial shunting in the lung and wider distribution of ventilation-perfusion ratios in the high-altitude residents than in normal subjects at sea level; and that part, at least, of the condition of chronic mountain sickness is an accentuation of these changes.

tissue hypoxia; acclimatization; chronic mountain sickness; secondary polycythemia; pulmonary O2 diffusion barrier; pulmonary veno-arterial shunt; pulmonary ventilation perfusion ratio

Submitted on April 3, 1963

PHYSIOLOGIC STUDIES OF PULMONARY EDEMA AT HIGH ALTITUDE

Cardiac catheterization studies have been performed in four patients during acute pulmonary edema at an elevation of 12,300 feet in the central Peruvian Andes.

Pulmonary hypertension, low cardiac output, arterial unsaturation, and low normal pulmonary artery wedge pressures were observed. Oxygen breathing was accompanied by a prompt, marked fall in pulmonary artery pressure and a slight rise in wedge pressure, indicating the presence of anoxic pulmonary arteriolar constriction.

In one patient, pulmonary artery wedge pressures were not elevated during added hypoxia nor during exercise. The blood pressure response to the Valsalva maneuver was normal.

Similar studies were carried out in four subjects after recovery from pulmonary edema. One 9-year-old boy had persisting pulmonary hypertension. None had evidence of underlying cardiac disease. An abnormal rise in pulmonary artery pressure during induced hypoxia was observed in three of four patients.

It is concluded that pulmonary edema at high altitude is a unique form of pulmonary edema produced by hypoxia under certain conditions of exposure at high altitude. Severe pulmonary hypertension due to anoxic pulmonary arteriolar constriction is present. There is no evidence that pulmonary venous constriction and cardiac failure are causative mechanisms.

CHILDREN AT HIGH ALTITUDE: PULMONARY AND RENAL ABNORMALITIES

Changes in pulmonary arteries and renal glomeruli were assessed in children born and resident at high altitude (Leadville, Colorado). The hypoxia appears to arrest normal neonatal decrease of pulmonary arterial smooth muscle in some of these children. No abnormalities were found in pulmonary veins or capillaries. A quantitative study also demonstrated enlargement of renal glomeruli in the hypoxic children after the first month of life, apparently due to a proliferation of normal glomerular elements.

BASAL OXYGEN UPTAKE OF MAN AT HIGH ALTITUDE

When man native to low altitude is exposed to altitudes in excess of 10,000 ft, is there a change in his basal oxygen uptake? This question was prompted by the unexpected observation of a 20% decrease in resting oxygen uptake of cattle and lambs at high altitude. To elucidate this problem in man, multiple determinations of basal oxygen uptake were made on six individuals, at both 5,200 and 14,150 ft. A small but significant increase in oxygen uptake was observed, probably reflecting the energy required to increase ventilation.

Note:

With the Technical Assistance of Estelle B. Grover and Janet K. Hagerma

Submitted on March 11, 1963

CHANGES IN ALVEOLAR AND ARTERIAL GAS TENSIONS AS RELATED TO ALTITUDE AND AGE

In the summer of 1962 at the White Mountain Research Station the early phases of altitude acclimatization were studied in six of the surviving eight members of the 1935 expedition to the Chilean Andes; they were from 58 to 71 years of age. Alveolar and arterial Po2 and Pco2 were determined for each man a few hours after arrival at 3,093 m and at 3,800 and 4,343 m over the next few days. The effects of age were superimposed on the classical responses to high altitude. The arterial and alveolar Pco2 values showed no significant gradient; the alveolar Pco2 was found to be lower for a given altitude than 27 years before. For example, their average alveolar Pco2 at 4,700 m in 1935 was 27.7 mm Hg as opposed to 25.1 mm Hg at 4,343 m in 1962. The case of Hall was exceptional: his alveolar Pco2 ranged from 21 to 24 mm Hg regardless of altitude for his sojourn of 22 days. In 1935 these six men had a mean A-a Po2 gradient of +3.0 mm Hg at 4,700 m, while in 1962 the gradient over the three altitudes was +12.4 mm Hg. These findings would likely be explained partially by age changes in the pulmonary ventilation-perfusion ratio.

acclimatization; pulmonary ventilation-perfusion ratio; alveolar-arterial Po2 and Pco2 gradients; alveolar hyperventilation; aging and altitude

Submitted on February 19, 1963

MUSCULAR EXERCISE AT GREAT ALTITUDES

Oxygen intake, ventilation and heart rate were measured in six subjects performing ergometer exercise at various altitudes from sea level to 7,440 m (24,400 ft) (Bar. 300 mm Hg) during a Himalayan expedition lasting 8 months. Oxygen intake for a given work rate was constant and independent of altitude, up to the maximum work rate that could be maintained for 5 min. Maximum oxygen intake declined with increase of altitude, reaching 1.46 liters/min at 7,440 m (24,400 ft) in the best subject. Ventilation (STPD) for a given work rate was independent of altitude in light and moderate exercise but increased at each altitude as maximum oxygen intake was approached. Ventilation values of 140–200 liters (BTPS)/min were observed at altitudes above 4,650 m (15,300 ft). Heart rates at altitude were higher at low and moderate work intensities, but the same as or lower than the corresponding sea-level value for the same work load, as maximum oxygen intake was approached. Breathing oxygen at sea-level pressure at 5,800 m (19,000 ft) reduced ventilation and heart rate for a given work rate, restored work capacity almost to sea-level values and increased maximum heart rate. With the aid of data on blood, lung diffusion, and cardiac output from companion studies, the oxygen transport system was analyzed in three subjects, including a high-altitude Sherpa; and evidence is put forward that lung diffusion, cardiac output, and the high oxygen cost of extreme ventilation all contributed to the limitation of exercise at 5,800 m (19,000 ft).

respiration, work and altitude; ventilation, work and altitude; heart rate, work and altitude; O2 transport system at high altitudes; altitude acclimatization

Submitted on July 29, 1963