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Body composition and maximum alactic anaerobic performance during a one month stay at high altitude
No full textProlonged 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 út, 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
Muscle oxygenation and pulmonary gas exchange kinetics during cycling exercise on-transitions in humans
No full textNear-infrared spectroscopy (NIRS) was utilized to gain insights into the kinetics of oxidative metabolism during exercise transitions. Ten untrained young men were tested on a cycle ergometer during transitions from unloaded pedaling to 5 min of constant-load exercise below (VT) the ventilatory threshold. Vastus lateralis oxygenation was determined by NIRS, and pulmonary O2 uptake (Vo --> Vo2) was determined breath-by-breath. Changes in deoxygenated hemoglobin + myoglobin concentration Delta[deoxy(Hb + Mb)] were taken as a muscle oxygenation index. At the transition, [Delta[deoxy(Hb + Mb)]] was unmodified [time delay (TD)] for 8.9 +/- 0.5 s at VT (both significantly different from 0) and then increased, following a monoexponential function [time constant (tau) = 8.5 +/- 0.9 s for VT]. For >VT a slow component of Delta[deoxy(Hb + Mb)] on-kinetics was observed in 9 of 10 subjects after 75.0 +/- 14.0 s of exercise. A significant correlation was described between the mean response time (MRT = TD + tau) of the primary component of Delta[deoxy(Hb + Mb)] on-kinetics and the tau of the primary component of the pulmonary Vo2 on-kinetics. The constant muscle oxygenation during the initial phase of the on-transition indicates a tight coupling between increases in O2 delivery and O2 utilization. The lack of a drop in muscle oxygenation at the transition suggests adequacy of O2 availability in relation to needs
HUMAN RED-BLOOD-CELL AGING AT 5,050-M ALTITUDE - A ROLE DURING ADAPTATION TO HYPOXIA
No full textTo test the hypothesis that the human red blood cell aging process participates actively in the adaptation to hypoxia, we studied some physical and biochemical hematologic variables in 10 volunteers at sea level (SL) and after 1 (1WK) or 5 wk (5WK) of exposure to 5,050-m altitude. The 2,3- diphosphoglycerate-to-hemoglobin ratio (2,3-DPG/Hb) was 0.88 ± 0.03 (mol/mol) at SL and increased to 1.08 ± 0.03 (P = 0.002) and 1.28 ± 0.05 (P < 0.0001) at 1WK and 5WK, respectively. The average red blood cell density (D50), which is inversely proportional to the fraction of young red blood cells and is therefore an index of the red blood cell aging process, was 1.1053 ± 0.0007 g/ml at SL and decreased to 1.1046 ± 0.0008 g/ml (NS) and 1.1018 ± 0.0008 g/ml (P < 0.0001) at 1WK and 5WK, respectively. D50 was correlated with 2,3-DPG/Hb at SL (P = 0.004), only weakly at 5WK (P = 0.1), but not at all at 1WK. The arterial O2 saturation was correlated with the change of 2,3-DPG/Hb in 1WK (P = 0.02) and that of D50 in 5WK (P = 0.04). It is concluded that short-term (1WK) increase of 2,3-DPG/Hb is not associated with the erythropoietic response but is presumably due to respiratory alkalosis. By contrast, after prolonged hypoxia (5WK), erythropoiesis may provide an efficient way for increasing blood 2,3-DPG through an augmented proportion of young red blood cells
Muscle oxygenation and pulmonary gas exchange kinetics during cycling exercise on-transitions in humans
No full textNear-infrared spectroscopy (NIRS) was utilized to gain insights into the kinetics of oxidative metabolism during exercise transitions. Ten untrained young men were tested on a cycle ergometer during transitions from unloaded pedaling to 5 min of constant-load exercise below (VT) the ventilatory threshold. Vastus lateralis oxygenation was determined by NIRS, and pulmonary O2 uptake (Vo --> Vo2) was determined breath-by-breath. Changes in deoxygenated hemoglobin + myoglobin concentration Delta[deoxy(Hb + Mb)] were taken as a muscle oxygenation index. At the transition, [Delta[deoxy(Hb + Mb)]] was unmodified [time delay (TD)] for 8.9 +/- 0.5 s at VT (both significantly different from 0) and then increased, following a monoexponential function [time constant (tau) = 8.5 +/- 0.9 s for VT]. For >VT a slow component of Delta[deoxy(Hb + Mb)] on-kinetics was observed in 9 of 10 subjects after 75.0 +/- 14.0 s of exercise. A significant correlation was described between the mean response time (MRT = TD + tau) of the primary component of Delta[deoxy(Hb + Mb)] on-kinetics and the tau of the primary component of the pulmonary Vo2 on-kinetics. The constant muscle oxygenation during the initial phase of the on-transition indicates a tight coupling between increases in O2 delivery and O2 utilization. The lack of a drop in muscle oxygenation at the transition suggests adequacy of O2 availability in relation to needs
Acid-base balance and O-2 transport at high altitude
No full textEar lobe blood pH(a), P(a)CO2, P(a)O2, and O2 saturation (S(a)O2) were measured in healthy Caucasians and Sherpas at 3400 m (Namche Bazaar, Nepal, n = 4/5), 5050 m (Pyramid Laboratory, Lobuche, Nepal, n = 20/5) and 6450 m (Camp II of Mt Everest, n = 11/7). In the investigated altitude range, pH(a) increased progressively with altitude from 7.463 ± 0.005 (mean ± SE) to 7.496 ± 0.006 in Caucasians whereas it remained essentially constant (7.45-7.46) in Sherpas. At all altitudes, P(a)CO2 was higher in Sherpas than in Caucasians (P < 0.02). By contrast, P(a)O2 and S(a)O2 were the same in Caucasians and Sherpas at all investigated altitudes. Moreover, in Caucasians sojourning for 3 weeks at 5050 m, P(a)CO2 kept decreasing whereas pH(a), P(a)O2 and S(a)O2 remained constant. These data suggest that: (1) respiratory alkalosis was a common finding both in Caucasians and Sherpas; (2) at 6450 m, Sherpas were less alkalotic due to higher P(a)CO2 than Caucasians, possibly a consequence of a blunted ventilatory response; (3) at 6450 m, S(a)O2 and P(a)O2 were the same in Caucasians and Sherpas despite different P(a)CO2 values. The latter finding could be the consequence of one or more of the following adjustments in Sherpas: (1), an increased efficiency of alveolar O2 transfer. i.e. smaller alveolar-arterial O2 gradient; (2) a decreased (arterial - mixed venous) O2 difference, possibly due to increased cardiac output; (3) a reduced increase of the [2,3-DPG]/[Hb] ratio; but not (4) an elevated gas exchange ratio (R). It is concluded that both physiological and biochemical variables contribute to optimize the O2 transport at altitude. Apparently a more efficient adaptation to hypoxia allows Sherpas to limit alkalosis through a lower ventilatory drive and to maintain S(a)O2 at the same P(a)O2 by decreasing the [2,3-DPG]/[Hb] ratio
EFFECTS OF ACUTE OR CHRONIC HYPOXIA ON REACTIVE OXYGEN SPECIES PRODUCTION ASSESSED BY ELECTRON PARAMAGNETIC RESONANCE
No full textThere is indirect evidence from cells and tissue experiments that acute hypoxia induces
accumulation of reactive oxygen species (ROS). This is also the case for the whole body of animals
and man as appears from muscle proteomic analysis. Electronic Paramagnetic Resonance (EPR) is
the only non-invasive technique available to detect and quantitate ROS accumulation. By means of
a recently developed EPR Scanner (Bruker e-scan) suitable for 50 ìl sample analysis and sensitive
to very low (nM) concentration levels, the time course of ROS in capillary blood could be
monitored: a) in sedentary subjects (n=6) at the onset (square wave), during and after 2-4 h of acute
hypoxic exposure (equivalent to 4500 meters a. s.l.); b) in athletes (n=18) before and after 2wk
exposure to moderate altitude (1860m). The data were compared with complementary enzymatic
assays of Protein Carbonyls, PC and ThioBarbituric Acid Reactive Substances, TBARS. Results: In
(a), a fast, initial elevation of ROS was observed, whose size appears to be related to the subjects’
capillary PO2, followed within 2 h by a return to pre-hypoxia levels. Parenthetically, plasmatic
concentrations of TBARS and PC were significantly increased after 4 h of hypoxia exposure and up
to 1 h into recovery, then resuming pre-hypoxia levels within 8 h; (b) two weeks exposure to
moderate hypoxia induced significant increases in both ROS and oxidative markers concentration.
The experimental conditions under investigation, even though very different for degree of hypoxia
and duration, were both characterized by comparable accumulation of ROS and oxidative damage
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
Effect of aging on human adductor pollicis muscle function
No full textThe effect of aging on the voluntary and electrically evoked contractile properties of the human adductor pollicis muscle was investigated in 70 healthy male subjects aged 20-91 yr, 10 subjects for each decade. Maximum isometric voluntary force declined significantly (range of P values 80 yr) compared with the youngest group (20-29 yr). Maximum relaxation rate dropped by 48.7% from the second to the eighth decade. The decrease became significant (P range <0.05-0.001) with the sixth decade. Isometric endurance, evaluated during 30 s of stimulation at 30 Hz, showed a linear (P < 0.001) increase with age. Aged muscle is thus weaker, slower, and tetanized at lower fusion frequencies but, paradoxically, more resistant to static fatigue
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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