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- Siebenmann, C, et al.
(författare)
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Hemoglobin mass and intravascular volume kinetics during and after exposure to 3,454-m altitude
- 2015
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 119:10, s. 1194-1201
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Tidskriftsartikel (refereegranskat)abstract
- Siebenmann C, Cathomen A, Hug M, Keiser S, Lundby AK, Hilty MP, Goetze JP, Rasmussen P, Lundby C. Hemoglobin mass and intravascular volume kinetics during and after exposure to 3,454 m altitude. J Appl Physiol 119: 1194-1201, 2015. First published March 6, 2015; doi:10.1152/japplphysiol.01121.2014.-High altitude (HA) exposure facilitates a rapid contraction of plasma volume (PV) and a slower occurring expansion of hemoglobin mass (Hbmass). The kinetics of the Hbmass expansion has never been examined by multiple repeated measurements, and this was our primary study aim. The second aim was to investigate the mechanisms mediating the PV contraction. Nine healthy, normally trained sea-level (SL) residents (8 males, 1 female) sojourned for 28 days at 3,454 m. Hbmass was measured and PV was estimated by carbon monoxide rebreathing at SL, on every 4th day at HA, and 1 and 2 wk upon return to SL. Four weeks at HA increased Hbmass by 5.26% (range 2.5-11.1%; P < 0.001). The individual Hbmass increases commenced with up to 12 days of delay and reached a maximal rate of 4.04±1.02 g/day after 14.9±5.2 days. The probability for Hbmass to plateau increased steeply after 20-24 days. Upon return to SL Hbmass decayed by-2.46 ± 2.3 g/day, reaching values similar to baseline after 2 wk. PV, aldosterone concentration, and renin activity were reduced at HA (P < 0.001) while the total circulating protein mass remained unaffected. In summary, the Hbmass response to HA exposure followed a sigmoidal pattern with a delayed onset and a plateau after ∼3 wk. The decay rate of Hbmass upon descent to SL did not indicate major changes in the rate of erythrolysis. Moreover, our data support that PV contraction at HA is regulated by the renin-angiotensin-aldosterone axis and not by changes in oncotic pressure. © 2015 The American Physiological Society.
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- Santarius, T., et al.
(författare)
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Digitalization and Sustainability : A Call for a Digital Green Deal
- 2023
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Ingår i: Environmental Science and Policy. - : Elsevier BV. - 1462-9011 .- 1873-6416. ; 147, s. 11-14
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Tidskriftsartikel (refereegranskat)abstract
- The relation between digitalization and environmental sustainability is ambiguous. There is potential of various digital technologies to slow down the transgression of planetary boundaries. Yet resource and energy demand for digital hardware production and use of data-intensive applications is of substantial size. The world over, there is no comprehensive regulation that addresses opportunities and risks of digital technology for sustainability. In this perspective article, we call for a Digital Green Deal that includes strong, cross-sectoral green digitalization policies on all levels of governance. We argue that a Digital Green Deal should first and foremost aim at greater policy coherence: Current digital policy initiatives should include measures that service environmental goals, and environmental policies must address risks and advance opportunities of digital technologies to spur sustainability transformations.
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- Flück, D., et al.
(författare)
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Age, aerobic fitness, and cerebral perfusion during exercise: Role of carbon dioxide
- 2014
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Ingår i: American Journal of Physiology - Heart and Circulatory Physiology. - : American Physiological Society. - 0363-6135 .- 1522-1539. ; 307:4
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Tidskriftsartikel (refereegranskat)abstract
- Middle cerebral artery mean velocity (MCAvmean) is attenuated with increasing age both at rest and during exercise. The aim of this study was to determine the influence of the age-dependent reduction in arterial PCO2 (PaCO2) and physical fitness herein. We administered supplemental CO2 (CO2 trial) or no additional gas (control trial) to the inspired air in a blinded and randomized manner, and assessed middle cerebral artery mean flow velocity during graded exercise in 1) 21 young [Y; age 24 ± 3 yr (±SD)] volunteers of whom 11 were trained (YT) and 10 considered untrained (YUT), and 2) 17 old (O; 66 ± 4 yr) volunteers of whom 8 and 9 were considered trained (OT) and untrained (OUT), respectively. A resting hypercapnic reactivity test was also performed. MCAvmean and PaCO2 were lower in O [44.9 ± 3.1 cm/s and 30 ± 1 mmHg (±SE)] compared with Y (59.3 ± 2.3 cm/s and 34 ± 1 mmHg, P < 0.01) at rest, independent of aerobic fitness level. The age-related decreases in MCAvmean and PaCO2 persisted during exercise. Supplemental CO2 reduced the age-associated decline in MCAvmean by 50%, suggesting that PaCO2 is a major component in the decline. On the other hand, relative hypercapnic reactivity was neither influenced by age (P = 0.46) nor aerobic fitness (P = 0.36). Although supplemental CO2 attenuated exercise-induced reduction in cerebral oxygenation (near-infrared spectroscopy), this did not influence exercise performance. In conclusion, PaCO2 contributes to the age-associated decline in MCAvmean at rest and during exercise; however exercise capacity did not diminish this age effect. © 2014 the American Physiological Society.
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- Keiser, S., et al.
(författare)
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Heat training increases exercise capacity in hot but not in temperate conditions: a mechanistic counter-balanced cross-over study
- 2015
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Ingår i: American Journal of Physiology-Heart and Circulatory Physiology. - : American Physiological Society. - 0363-6135 .- 1522-1539. ; 309:5
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Tidskriftsartikel (refereegranskat)abstract
- The aim was to determine the mechanisms facilitating exercise performance in hot conditions following heat training. In a counter-balanced order, seven males ((V) over dotO(2max) 61.2 +/- 4.4 ml.min(-1).kg(-1)) were assigned to either 10 days of 90-min exercise training in 18 or 38 degrees C ambient temperature (30% relative humidity) applying a cross-over design. Participants were tested for (V) over dotO(2max) and 30-min time trial performance in 18 (T18) and 38 degrees C (T38) before and after training. Blood volume parameters, sweat output, cardiac output ((Q) over dot), cerebral perfusion (i.e., middle cerebral artery velocity [MCAv(mean)]), and other variables were determined. Before one set of exercise tests in T38, blood volume was acutely expanded by 538 +/- 16 ml with an albumin solution (T38A) to determine the role of acclimatization induced hypervolemia on exercise performance. We furthermore hypothesized that heat training would restore MCAv(mean) and thereby limit centrally mediated fatigue. (V) over dotO(2max) and time trial performance were equally reduced in T38 and T38A (7.2 +/- 1.6 and 9.3 +/- 2.5% for (V) over dotO(2max); 12.8 +/- 2.8 and 12.9 +/- 2.8% for time trial). Following heat training both were increased in T38 (9.6 +/- 2.1 and 10.4 +/- 3.1%, respectively), whereas both (V) over dotO(2max) and time trial performance remained unchanged in T18. As expected, heat training augmented plasma volume (6 +/- 2%) and mean sweat output (26 +/- 6%), whereas sweat [Na+] became reduced by 19 +/- 7%. In T38 (Q) over dot(max) remained unchanged before (21.3 +/- 0.6 l/min) to after (21.7 +/- 0.5 l/min) training, whereas MCAv(mean) was increased by 13 +/- 10%. However, none of the observed adaptations correlated with the concomitant observed changes in exercise performance.
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