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Biomedical subjects

B Kayser

Publications and source records attributed to B Kayser.

At least 55 records · Page 3Linked to original sources
PubMed1993

Treatment of acute mountain sickness by simulated descent: a randomised controlled trial.

OBJECTIVE: To evaluate the therapeutic efficacy of a portable hyperbaric chamber for treatment of acute mountain sickness. DESIGN: Controlled randomised trial over two mountaineering seasons. SETTING: High altitude research laboratory at 4559 m above sea level. SUBJECTS: 64 climbers with acute mountain sickness randomly allocated to different treatments. INTERVENTIONS: One hour of treatment in the hyperbaric chamber at a pressure of 193 mbar or 20 mbar as control or bed rest. MAIN OUTCOME MEASURES: Symptoms of acute mountain sickness before, immediately after, and 12 hours after treatment. Permitted intake of analgesic and antiemetic drugs in the follow up period. RESULTS: Treatment with 193 mbar caused greater relief of symptoms than did control treatment or bed rest. During the 12 hour follow up period intake of analgesics was similar (58-80% of subjects in each group). Symptom scores had improved in all subjects after 12 hours with no significant differences between groups. CONCLUSIONS: One hour of treatment with 193 mbar in a portable hyperbaric chamber, corresponding to a descent of 2250 m, leads to a short term improvement in symptoms of acute mountain sickness but has no beneficial long term effects attributable to pressurisation.

Acute Disease↗
PubMed1993

Alpha-motoneuron excitability at high altitude.

It has been hypothesized that chronic hypobaric hypoxia could lead to inhibition of the alpha-motoneuron pool, thus limiting the maximal activation of working skeletal muscles. To test this hypothesis six subjects [32 (SEM 2) years] were evaluated in resting conditions, at sea level and after acclimatization at 5,050 m. The recruitment curves of the Hofmann-reflex (H-) and the direct muscle-response. (M-) of the right soleus muscle were obtained by stimulating the posterior tibial nerve with different intensities while recording the electromyogram of the soleus muscle. From the recorded data the net alpha-motoneuron excitability (ratio of maximal H-reflex to M-response Hmax:Mmax ratio), the threshold and gain for both responses, obtained from linear regressions through the rising phase of the recruitment curves of both responses, as well as the latency times of both responses were determined. The latency times and the Hmax:Mmax ratio were unchanged at altitude. The thresholds of both responses and the gain of the M-response were unaltered. The gain of the H-response was significantly higher at altitude when compared to sea level.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Limitations to VO2max in humans after blood retransfusion.

Seven young, healthy male subjects performed maximal exercise on a cycloergometer with central venous and arterial catheters, before and after autologous retransfusion of red blood cells. Maximal oxygen consumption (VO2max), blood gas composition and haemodynamic variables were measured, in order to test the hypothesis of monofactorial vs. polyfactorial VO2max limitation. Autologous blood retransfusion led to significant increases in haemoglobin concentration and consequently arterial oxygen concentration during maximal exercise, while maximal cardiac output, heart rate and stroke volume were not significantly changed. The relationship between maximal oxygen delivery (cardiac output.arterial oxygen concentration; (Q.CaO2)max and maximal oxygen consumption in this study was VO2max (L.min-1) = 0.02 + 0.64.(Q.CaO2)max (L.min-1), the slope being significantly less than unity. These results suggest that (Q.CaO2)max plays but a fractional role in limiting VO2max, in agreement with recent models concerning the resistance to oxygen flow in the respiratory system (di Prampero and Ferretti, Respir. Physiol. 80: 113-128, 1990). The relative increase in VO2max after blood retransfusion matched the relative increase in 'aerobic performance', measured as the maximal power output that could be maintained aerobically for 30 min. Furthermore, the increase in maximal power output (15 +/- 3 watts) could account for almost all of the extra oxygen consumption. This match suggests that there is an inability to fully utilize muscle oxidative capacity in the normocythaemic state.

Adult↗
PubMed1993

Body composition and maximum alactic anaerobic performance during a one month stay at high altitude.

Prolonged altitude exposure usually leads to considerable weight loss of which a large part is from muscle tissue. This loss reduces maximum alactic anaerobic muscle power. It was hypothesized that most of the weight loss may simply be the result of malnutrition due to lack of palatable food in an uncomfortable environment. To test this hypothesis eight healthy male subjects (age 33.7 +/- 4.6 S.C. yr), well acclimatized to prevent symptoms of acute mountain sickness, were exposed for 4 weeks to an altitude of 5050 m with access to a large choice of palatable food in comfortable conditions. Body weight (with a scale), body composition (from skinfolds), arm muscle plus bone cross-sectional area (Am + b) and muscle plus bone leg volume (Vm+b) (from skinfolds and circumferences), maximum voluntary contraction force of the elbow flexors (MVC, with a load cell) and maximum jumping height (Hmax, on a platform) were measured before departure (SL) and in the first (ALT1), second (ALT2) and fourth week (ALT4) of their altitude sojourn. Three-day dietary records were obtained at SL and at ALT4. Body mass had decreased significantly at ALT2 (-3.8%) and at ALT4 (-4.6%) likely reflecting changes in body water homeostasis. No changes were found in %fat, Am+b, Vm+b, MVC or Hmax. Average dietary intake at SL was 8.96 +/- 1.45 MJ and had increased to 13.59 +/- 3.07 MJ at ALT4. In conclusion, up to an altitude of 5050 m loss of body mass from fat and muscle tissue, and hence impairment of maximum anaerobic muscle power (alactic) appears to be avoidable by food intake matched to energy expenditure. The latter may be achieved simply by proper acclimatization, sufficient comfort and availability of palatable food.

Adipose Tissue↗
PubMed1993

Maximal lactic capacity at altitude: effect of bicarbonate loading.

The aim of the present study was to test the hypothesis that the net maximal blood lactate accumulation ([La]max) during heavy exercise in lowlanders acclimatized to chronic hypoxia may be limited by the reduced bicarbonate stores. Six men [age 32 +/- 4 (SD) yr] performed supramaximal exercise until voluntary exhaustion at sea level (204 +/- 54 W) and after sojourning for 1 mo at 5,050 m (175 +/- 23 W), without (C) and with (B) oral sodium-bicarbonate loading (0.3 g/kg body wt). Exhaustion time, arterial blood lactate concentration, arterial pH (pHa), arterial PCO2, and intramuscular pH were measured at rest and after exercise. At sea level, exhaustion time increased from 6.5 +/- 2.8 min in C to 7.5 +/- 2.7 min in B (P < 0.05). At altitude, exhaustion times were similar to the sea level C values and the same in C and B. At sea level, resting pHa increased from 7.41 +/- 0.02 in C to 7.46 +/- 0.03 in B (P < 0.001); the corresponding values at altitude were 7.46 +/- 0.04 and 7.55 +/- 0.03 (P < 0.001). Postexercise pHa at sea level was 7.22 +/- 0.02 in C and 7.25 +/- 0.08 in B (NS). After exercise at altitude, pHa was 7.32 +/- 0.04 and 7.44 +/- 0.03 in C and B, respectively (P < 0.001). [La]max increased from 12.86 +/- 1.45 mM in C to 16.63 +/- 1.76 mM in B (P < 0.01) at sea level and from 6.85 +/- 1.40 mM in C to 7.95 +/- 1.74 mM in B (NS) at altitude.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗
PubMed1993

Pressurization and acute mountain sickness.

Numerous cases of acute mountain sickness (AMS) during trekking were reported to have been successfully treated with portable pressure chambers. The effect of early pressurization during acute altitude exposure in the Alps had not been previously studied. In order to test the hypothesis that an early pressurization of unacclimatized subjects for 3 h could prevent or delay the appearance of symptoms of AMS, 51 previously healthy subjects climbed from 1,030 to 4,360 m within 12 h. Upon arrival at 4,360 m, AMS scores (Lake Louise Consensus Questionnaire '91), oxygen saturation (SaO2), and heart rate (HR) were determined at rest. The subjects were then randomly divided in two groups; one group was pressurized to 200 mBar for 3 h while the other rested. AMS score, HR, and SaO2 were similar in both groups before treatment. AMS score had decreased (from 2.44 +/- 0.41 (S.E.) to 0.89 +/- 0.26, p < 0.05) and SaO2 had increased (from 75.22 +/- 1.32% to 79.07 +/- 1.27%, p < 0.05) in the treatment group 15 min after leaving the pressure chamber whereas the control group had unchanged AMS score (2.50 +/- 0.40 vs. 2.40 +/- 0.40, N.S.) and SaO2 (77.83 +/- 1.41 vs. 76.67 +/- 1.24, N.S.). The next morning, however, AMS score, HR, and SaO2 were similar for both groups. It is concluded that during acute ascent in the Alps, an early 3-h pressurization of unacclimatized subjects does slightly delay the onset of AMS but does not prevent the illness nor does it attenuate its severity upon appearance.

Acute Disease↗
PubMed1992

Branched-chain amino acid supplementation during trekking at high altitude. The effects on loss of body mass, body composition, and muscle power.

To investigate the influence of a branched-chain amino acid (BCAA) supplementation on chronic hypoxia-related loss of body mass and muscle loss, 16 subjects [age 35.8 (SD 5.6) years] participating in a 21-day trek at a mean altitude of 3,255 (SD 458) m, were divided in two age-, sex- and fitness-matched groups and took either a dietary supplementation of BCAA (5.76, 2.88 and 2.88 g per day of leucine, isoleucine and valine, respectively) or a placebo (PLAC) in a controlled double-blind manner. Daily energy intake at altitude decreased by 4% in both groups compared with sea level. After altitude exposure both groups showed a significant loss of body mass, 1.7% and 2.8% for BCAA and PLAC, respectively. Fat mass had decreased significantly by 11.7% for BCAA and 10.3% for PLAC, whereas BCAA showed a significantly increased lean mass of 1.5%, as opposed to no change in PLAC. Arm muscle cross-sectional area tended to increase in BCAA, whereas there was a significant decrease of 6.8% in PLAC (P < 0.05 between groups). The same tendency, although not significant, was observed for the thigh muscle cross-sectional area. On the whole it seemed that PLAC had been catabolizing whereas BCAA had been synthesizing muscle tissue. Single jump height from a squatted position showed a similar tendency to increase in both groups. Lower limb maximal power decreased less in BCAA than in PLAC (2.4% vs 7.8%, P < 0.05). We concluded that BCAA supplementation may prevent muscle loss during chronic hypobaric hypoxia.

Adult↗
PubMed1992

Nutrition and high altitude exposure.

Altitude exposure leads to considerable weight loss. The different hypotheses that have been put forward to explain this phenomenon are discussed reviewing the literature: 1) a primary decrease of food intake due to loss of appetite caused, directly or indirectly, by hypoxia, changes of menus, comfort and habits, 2) a discrepancy between energy intake and energy expenditure due to an increased basal metabolic rate and/or high levels of activity which are not matched by an increased food intake, 3) a loss of body water due to increased insensible loss through increased ventilation in the mountain environment, decreased liquid intake, and/or changes in water metabolism, 4) an impaired absorption of nutrients from the gastrointestinal tract, and 5) a loss of muscle mass due to lack of physical exercise and/or direct effects of hypoxia on protein synthesis. It is concluded that altitude weight loss is due to an initial loss of water and subsequently to loss of fat mass and muscle wasting. Up to altitudes around 5000 m the weight loss from fat and muscle seems to be largely avoidable by maintaining adequate intake in a comfortable setting. Primary anorexia, lack of comfort and palatable food, detraining, and possible direct effects of hypoxia on protein metabolism seem to inevitably lead to weight loss during longer exposures at higher altitudes. In order to minimize losses it is advisable to acclimatize properly, to reduce the length of stay at extreme altitude as much as possible and to maintain a high and varied nutrient intake.

Acclimatization↗
PubMed1992

Regulation of perfusive O2 transport during exercise in humans: effects of changes in haemoglobin concentration.

1. Recently it was suggested that submaximal cardiac output (Q) could vary in response to changes in arterial O2 concentration (Ca,O2), so that arterial O2 delivery (Qa,O2 = Q x Ca,O2, in ml min-1) is kept constant. 2. This hypothesis was tested on eight healthy male subjects, at rest and during exercise (50, 100 and 150 W) in three conditions: normaemia (N), after 6 weeks of endurance training (T), and 2 days after subsequent autologous blood reinfusion (P). 3. Measured variables were oxygen consumption (VO2), by open circuit method, Q, by a CO2 rebreathing method, and haemoglobin concentration ([Hb]), by a photometric method. Ca,O2 was calculated as the product of [Hb], arterial O2 saturation (0.97), and the O2 binding coefficient. 4. [Hb] and thus Ca,O2 increased by 2.6% (T vs. N) and subsequently by further 5.8% (P vs. T). VO2 and Qa,O2 were linear functions of power (w), both relationships being unaffected by changes in Ca,O2. As a consequence, the linear Q vs. VO2 relationships were shifted downward as Ca,O2 increased. 5. The VO2 vs. w and the Qa,O2 vs. w relationships had the same slope. Therefore, the difference between Qa,O2 (w) and VO2 (w), equal to O2 flow in mixed venous blood (Qv,O2), was constant. 6. In conclusion, the tested hypothesis was supported by the present results. The observed constancy of Qv,O2 suggested that Qv,O2 may play a key role in regulating the cardiovascular response to exercise.

Adult↗
PubMed1992

Energy expenditure climbing Mt. Everest.

Weight loss is a well-known phenomenon at high altitude. It is not clear whether the negative energy balance is due to anorexia only or an increased energy expenditure as well. The objective of this study was to gain insight into this matter by measuring simultaneously energy intake, energy expenditure, and body composition during an expedition to Mt. Everest. Subjects were two women and three men between 31 and 42 yr of age. Two subjects were observed during preparation at high altitude, including a 4-day stay in the Alps (4,260 m), and subsequently during four daytime stays in a hypobaric chamber (5,600-7,000 m). Observations at high altitude on Mt. Everest covered a 7- to 10-day interval just before the summit was reached in three subjects and included the summit (8,872 m) in a fourth. Energy intake (EI) was measured with a dietary record, average daily metabolic rate (ADMR) with doubly labeled water, and resting metabolic rate (RMR) with respiratory gas analysis. Body composition was measured before and after the interval from body mass, skinfold thickness, and total body water. Subjects were in negative energy balance (-5.7 +/- 1.9 MJ/day) in both situations, during the preparation in the Alps and on Mt. Everest. The loss of fat mass over the observation intervals was 1.4 +/- 0.7 kg, on average two-thirds of the weight loss (2.2 +/- 1.5 kg), and was significantly correlated with the energy deficit (r = 0.84, P < 0.05). EI on Mt. Everest was 9-13% lower than during the preparation in the Alps.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Protein absorption and energy digestibility at high altitude.

To test the hypothesis that malabsorption of dietary protein is partly responsible for the weight loss observed during prolonged altitude exposure, six healthy male subjects [31.8 +/- 4.5 (SD) yr] received 15N-labeled soya protein by mouth and [15N]glycine intravenously at 122 and 5,000 m. From the subsequent 4-day total urine and fecal pools, the different fractions of the administered 15N were determined by mass spectrometry. Weight and skinfold thickness were measured at the beginning and end of the altitude exposure. In addition, the overall digestible energy of the diet at altitude was assessed by a 3-day diet control and adiabatic bomb calorimetric assessment of the energy content of the corresponding fecal pool. The average decrease of the subjects' weight during altitude exposure was 3%. Loss of fat mass at altitude estimated from the skinfold measurements was 9%. Protein absorption, calculated as 100--[fecal excretion of 15N after ingestion of 15N soya protein (% of dose given)--fecal excretion of 15N after injection of 15N glycine (% of dose given)], was not significantly impaired at altitude compared with sea level (96 vs. 97%, respectively), and overall digestible energy at altitude, calculated as 100--percent undigested gross energy in the feces, amounted to 96%. It is concluded that, at least up to an altitude of 5,000 m, malabsorption does not play a role in altitude-related weight loss.

Adult↗
PubMed1991

Muscle structure and performance capacity of Himalayan Sherpas.

The ultrastructure of the vastus lateralis muscle of Sherpas from Nepal [5 males; age 28 +/- 2.8 (SD) yr, indirect maximal O2 consumption 48.5 +/- 5.4 ml.kg(-1).min(-1)] was assessed and compared with those of sedentary lowlanders and of Caucasian climbers before and after high-altitude exposure. The mean cross-sectional area of the fibers was 3,186 +/- 521 microns2, i.e., similar to those of Caucasian elite high-altitude climbers (3,108 +/- 303 microns2) and a group of climbers after a 6- to 8-wk sojourn at 5,000-8,600 m (3,360 +/- 580 microns2) but significantly (P less than 0.05) smaller than that of unacclimatized climbers (4,170 +/- 710 microns2) and slightly, although not significantly, lower than that of sedentary lowlanders (3,640 +/- 260 microns2). The number of capillaries per square millimeter of muscle cross section was 467 +/- 22, not significantly smaller than those of climbers on return from a Himalayan expedition (538 +/- 89) and elite high-altitude climbers (542 +/- 127) but significantly (P less than 0.05) greater than that of sedentary lowlanders (387 +/- 25). The volume density of mitochondria was 3.96 +/- 0.54%, significantly (P less than 0.05) less than the values found for any other investigated group, including sedentary subjects at sea level (4.74 +/- 0.30%). It is concluded that Sherpas, like acclimatized Caucasian climbers, are characterized by 1) facilitated convective and diffusive muscle O2 flow conditions and 2) a higher maximal O2 consumption-to-mitochondrial volume ratio than lowlanders despite a reduced mitochondrial volume density.

Acclimatization↗
PubMed1991

Blood rheology in acute mountain sickness and high-altitude pulmonary edema.

The role of blood rheology in the pathogenesis of acute mountain sickness and high-altitude pulmonary edema was investigated. Twenty-three volunteers, 12 with a history of high-altitude pulmonary edema, were studied at low altitude (490 m) and at 2 h and 18 h after arrival at 4,559 m. Eight subjects remained healthy, seven developed acute mountain sickness, and eight developed high-altitude pulmonary edema. Hematocrit, whole blood viscosity, plasma viscosity, erythrocyte aggregation, and erythrocyte deformability (filtration) were measured. Plasma viscosity and erythrocyte deformability remained unaffected. The hematocrit level was lower 2 h after the arrival at high altitude and higher after 18 h compared with low altitude. The whole blood viscosity changed accordingly. The erythrocyte aggregation was about doubled 18 h after the arrival compared with low-altitude values, which reflects the acute phase reaction. There were, however, no significant differences in any rheological parameters between healthy individuals and subjects with acute mountain sickness or high-altitude pulmonary edema, either before or during the illness. We conclude that rheological abnormalities can be excluded as an initiating event in the development of acute mountain sickness and high-altitude pulmonary edema.

Acute Disease↗
PubMed1989

cDNA clones of the auxin-binding protein from corn coleoptiles (Zea mays L.): isolation and characterization by immunological methods.

An auxin-binding protein (ABP) cDNA clone was selected from a lambda gt11 cDNA library from corn coleoptiles with highly purified IgGanti ABP. The sequence of 794 bp contains an open reading frame (ORF) of 603 bp, coding for a 22 kd protein. There are indications of a signal peptide of 38 amino acids (von Heijne, G. 1983, Eur. J. Biochem., 133, 17-21). A N-glycosylation site can be deduced and a C-terminal KDEL amino acid sequence is detected. An EcoRI fragment containing the beginning portion of the cDNA with about three quarters of the ORF was used to select cDNA clones from an independently produced lambda gt11 cDNA library of corn coleoptiles. Northern blot analysis with in vitro transcribed biotinylated RNA showed a single band of not more than 850 bases. The full-length in vitro transcript directed the in vitro synthesis of a protein which is precipitated by IgGanti ABP. Rabbit antibodies raised against a fusion protein detect the ABP as a double band on Western blots. Only the smaller of the two ABP bands is labeled by two different KDEL-specific IgG preparations.

Base Sequence↗