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Eiken, Ola
Publications (10 of 28) Show all publications
Sotiridis, A., Debevec, T., Ciuha, U., Eiken, O. & Mekjavic, I. B. (2019). Heat acclimation does not affect maximal aerobic power in thermoneutral normoxic or hypoxic conditions. Experimental Physiology, 104, 1250-1261
Open this publication in new window or tab >>Heat acclimation does not affect maximal aerobic power in thermoneutral normoxic or hypoxic conditions
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2019 (English)In: Experimental Physiology, ISSN 0958-0670, E-ISSN 1469-445X, Vol. 104, p. 1250-1261Article in journal (Refereed) Published
Abstract [en]

What is the central question of this study? Controlled-hyperthermia heat acclimation protocols induce an array of thermoregulatory and cardiovascular adaptations that facilitate exercise in hot conditions. We investigated whether this ergogenic potential can be transferred to thermoneutral normoxic or hypoxic exercising conditions. What is the main finding and its importance? We show that heat acclimation did not affect maximal cardiac output or maximal aerobic power in thermoneutral normoxic/hypoxic conditions. Heat acclimation augmented the sweating response in thermoneutral normoxic conditions. The cross-adaptation theory according to which heat acclimation could facilitate hypoxic exercise capacity is not supported by our data. ABSTRACT: Heat acclimation (HA) mitigates heat-induced decrements in maximal aerobic power (V̇O2peak ) and augments exercise thermoregulatory responses in the heat. Whether this beneficial effect of HA is observed in hypoxic or thermoneutral conditions remains unresolved. We explored the effects of HA on exercise cardiorespiratory and thermoregulatory responses in normoxic, hypoxic, and hot conditions. Twelve males (V̇O2peak 54.7(5.7) mL·kg-1 ·min-1 ) participated in a HA protocol comprising 10 daily 90-min controlled-hyperthermia (target rectal temperature, Tre  = 38.5 °C) exercise sessions. Before and after HA, we determined V̇O2peak in thermoneutral normoxic (NOR), thermoneutral hypoxic (13.5% Fi O2 ; HYP) and hot (35 °C, 50% RH; HE) conditions in a randomized and counterbalanced order. Preceding each maximal cycling test, a 30-min steady-state exercise at 40% of the NOR peak power output (Wpeak ) was employed to evaluate thermoregulatory responses. HA induced the expected adaptations in HE: reduced Tre and submaximal heart rate (HR), enhanced sweating response and expanded plasma volume. However, HA did not affect V̇O2peak or maximal cardiac output (COmax ) (P = 0.61). Wpeak was increased post-HA in NOR (P < 0.001) and HE (P < 0.001) by 41 ± 21 and 26 ± 22 W, respectively but not in HYP (P = 0.14). Gross mechanical efficiency was higher (P = 0.004) whereas resting Tre and sweating thresholds were lower (P < 0.01) post-HA across environments. Nevertheless, the gain of the sweating response decreased (P = 0.05) in HYP. In conclusion, our data do not support a beneficial cross-over effect of HA on V̇O2peak in normoxic or hypoxic conditions. This article is protected by copyright.

Keywords
Heat training, cardiac output, cross-adaptation
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-240337 (URN)10.1113/EP087268 (DOI)000459938200007 ()30536521 (PubMedID)2-s2.0-85060572881 (Scopus ID)
Note

QC 20190128

Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-08-20Bibliographically approved
Keramidas, M., Kölegård, R., Mekjavic, I. B. & Eiken, O. (2019). Interactions of mild hypothermia and hypoxia on finger vasoreactivity to local cold stress. American Journal of Physiology. Regulatory Integrative and Comparative Physiology
Open this publication in new window or tab >>Interactions of mild hypothermia and hypoxia on finger vasoreactivity to local cold stress
2019 (English)In: American Journal of Physiology. Regulatory Integrative and Comparative Physiology, ISSN 0363-6119, E-ISSN 1522-1490Article in journal (Refereed) Accepted
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-253895 (URN)
Note

QCR 20190624

Available from: 2019-06-19 Created: 2019-06-19 Last updated: 2019-06-24Bibliographically approved
Ånell, R., Grönkvist, M., Eiken, O. & Gennser, M. (2019). Nitrogen Washout and Venous Gas Emboli During Sustained vs. Discontinuous High-Altitude Exposures. Aerospace Medicine and Human Performance, 90(6), 524-530
Open this publication in new window or tab >>Nitrogen Washout and Venous Gas Emboli During Sustained vs. Discontinuous High-Altitude Exposures
2019 (English)In: Aerospace Medicine and Human Performance, ISSN 2375-6314, E-ISSN 2375-6322, Vol. 90, no 6, p. 524-530Article in journal (Refereed) Published
Abstract [en]

INTRODUCTION: The frequency of long-duration, high-altitude missions with fighter aircraft is increasing, which may increase the incidence of decompression sickness (DCS).The aim of the present study was to compare decompression stress during simulated sustained high-altitude flying vs. high-altitude flying interrupted by periods of moderate or marked cabin pressure increase. METHODS: The level of venous gas emboli (VGE) was assessed from cardiac ultrasound images using the 5-degree Eftedal-Brubakk scale. Nitrogen washout/uptake was measured using a closed circuit rebreather. Eight men were investigated in three conditions: one 80-min continuous exposure to a simulated cabin altitude of A) 24,000 ft, or four 20-min exposures to 24,000 ft interspersed by three 20-min intervals at 8) 20,000 ft or C) 900 ft. RESULTS: A and B induced marked and persistent VGE, With peak bubble scores of [median (range)]: A 2.5 (1-3); B: 3.5 (2-4). Peak VGE score was less in C [1.0(1-2),P < 0.01]. Condition A exhibitedan initially high and exponentially decaying rate of nitrogen washout. In C the washout rate was similar in each period at 24,000 ft, and the nitrogen uptake rate was similar during each 900-ft exposure. B exhibited nitrogen washout during each period at 24,000 ft and the initial period at 20,000 ft, but on average no washout or uptake during the last period at 20,000 ft. DISCUSSION: Intermittent reductions of cabin altitude from 24,000 to 20,000 ft do not appear to alleviate the DCS risk, presumably because the pressure increase is not sufficient to eliminate VGE. The nitrogen washout/uptake rate did not reflect DCS risk in the present exposures.

Place, publisher, year, edition, pages
Aerospace Medical Association, 2019
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-255667 (URN)10.3357/AMHP.5207.2019 (DOI)000468206900003 ()31101137 (PubMedID)2-s2.0-85066253774 (Scopus ID)
Note

QC 20190819

Available from: 2019-08-06 Created: 2019-08-06 Last updated: 2019-08-19Bibliographically approved
McDonnell, A. C., Eiken, O., Frings-Meuthen, P., Rittweger, J. & Mekjavic, I. B. (2019). The LunHab project: Muscle and bone alterations in male participants following a 10 day lunar habitat simulation.. Experimental Physiology, 104(8), 1250-1261
Open this publication in new window or tab >>The LunHab project: Muscle and bone alterations in male participants following a 10 day lunar habitat simulation.
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2019 (English)In: Experimental Physiology, ISSN 0958-0670, E-ISSN 1469-445X, Vol. 104, no 8, p. 1250-1261Article in journal (Refereed) Published
Abstract [en]

NEW FINDINGS: What is the central question of this study? It is well established that muscle and bone atrophy in conditions of inactivity or unloading, but there is little information regarding the effect of a hypoxic environment on the time course of these deconditioning physiological systems. What is the main finding and its importance? The main finding is that a horizontal 10 day bed rest in normoxia results in typical muscle atrophy, which is not aggravated by hypoxia. Changes in bone mineral content or in metabolism were not detected after either normoxic or hypoxic bed rest.

ABSTRACT: Musculoskeletal atrophy constitutes a typical adaptation to inactivity and unloading of weightbearing bones. The reduced-gravity environment in future Moon and Mars habitats is likely to be hypobaric hypoxic, and there is an urgent need to understand the effect of hypoxia on the process of inactivity-induced musculoskeletal atrophy. This was the principal aim of the present study. Eleven males participated in three 10 day interventions: (i) hypoxic ambulatory confinement; (ii) hypoxic bed rest; and (iii) normoxic bed rest. Before and after the interventions, the muscle strength (isometric maximal voluntary contraction), mass (lean mass, by dual-energy X-ray absorptiometry), cross-sectional area and total bone mineral content (determined with peripheral quantitative computed tomography) of the participants were measured. Blood and urine samples were collected before and on the 1st, 4th and 10th day of the intervention and analysed for biomarkers of bone resorption and formation. There was a significant reduction in thigh and lower leg muscle mass and volume after both normoxic and hypoxic bed rests. Muscle strength loss was proportionately greater than the loss in muscle mass for both thigh and lower leg. There was no indication of bone loss. Furthermore, the biomarkers of resorption and formation were not affected by any of the interventions. There was no significant effect of hypoxia on the musculoskeletal variables. Short-term normoxic (10 day) bed rest resulted in muscular deconditioning, but not in the loss of bone mineral content or changes in bone metabolism. Hypoxia did not modify these results.

Place, publisher, year, edition, pages
Wiley, 2019
Keywords
bed rest, bone, hypoxia, muscle
National Category
Physiology
Identifiers
urn:nbn:se:kth:diva-255666 (URN)10.1113/EP087482 (DOI)000477977400011 ()31273869 (PubMedID)
Note

QC 20190828

Available from: 2019-08-06 Created: 2019-08-06 Last updated: 2019-08-28Bibliographically approved
Keramidas, M. E., Siebenmann, C., Norrbrand, L., Gadefors, M. & Eiken, O. (2018). A brief pre-exercise nap may alleviate physical performance impairments induced by short-term sustained operations with partial sleep deprivation - A field-based study. Chronobiology International, 35(10), 1464-1470
Open this publication in new window or tab >>A brief pre-exercise nap may alleviate physical performance impairments induced by short-term sustained operations with partial sleep deprivation - A field-based study
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2018 (English)In: Chronobiology International, ISSN 0742-0528, E-ISSN 1525-6073, Vol. 35, no 10, p. 1464-1470Article in journal (Refereed) Published
Abstract [en]

The purpose of the study was to evaluate the recuperative efficacy of pre-exercise napping on physical capacity after military sustained operations (SUSOPS) with partial sleep deprivation. Before and after a 2-day SUSOPS, 61 cadets completed a battery of questionnaires, and performed a 2-min lunges trial and a 3,000-m running time-trial. After the completion of SUSOPS, subjects were randomized to either a control [without pre-exercise nap (CON); n = 32] or a nap [with a 30-min pre-exercise nap (NAP); n = 29] group. SUSOPS enhanced perceived sleepiness and degraded mood in both groups. Following SUSOPS, the repetitions of lunges, in the CON group, were reduced by similar to 2.3%, albeit the difference was not statistically significant (p = 0.62). In the NAP group, however, the repetitions of lunges were increased by similar to 7.1% (p = 0.01). SUSOPS impaired the 3,000-m running performance in the CON group (similar to 2.3%; p = 0.02), but not in the NAP group (0.3%; p = 0.71). Present results indicate, therefore, that a relatively brief pre-exercise nap may mitigate physical performance impairments ensued by short-term SUSOPS.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS INC, 2018
Keywords
Endurance, fatigue, military performance, operational stress, psychological strain, sleep inertia
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-239833 (URN)10.1080/07420528.2018.1490316 (DOI)000450441500014 ()29985669 (PubMedID)2-s2.0-85049646321 (Scopus ID)
Note

QC 20181217

Available from: 2018-12-18 Created: 2018-12-18 Last updated: 2018-12-18Bibliographically approved
Kölegård, R., Da Silva, C., Siebenmann, C., Keramidas, M. E. & Eiken, O. (2018). Cardiac performance is influenced by rotational changes of position in the transversal plane, both in the horizontal and 60° head-up postures. Clinical Physiology and Functional Imaging, 38(6), 1021-1028
Open this publication in new window or tab >>Cardiac performance is influenced by rotational changes of position in the transversal plane, both in the horizontal and 60° head-up postures
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2018 (English)In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 38, no 6, p. 1021-1028Article in journal (Refereed) Epub ahead of print
Abstract [en]

Background: Echocardiography is usually performed with the subject/patient lying in the left lateral position (LLP), because the acoustic window is better in this than in the supine position (SP). The aim was to investigate cardiac responses to rotational changes of position in the transversal plane, from SP to LLP while horizontal, and from leaning on the back (HUT-LB) to leaning on the left side (HUT-LL) while tilted 60° head-up from the horizontal. Methods: Healthy men (n = 12) underwent 10-min HUT provocations. Cardiac variables were measured using two-dimensional echocardiography, Doppler, tissue Doppler imaging and arterial pressures using a volume-clamp method. Results: In horizontal posture, cardiac volumes were smaller in SP than in LLP: end-diastolic volume (EDV) by 14%, end-systolic volume (ESV) by 13%, stroke volume (SV) by 14%, and cardiac output (CO) by 16% (P<0·03). In addition, the mitral annular plane systolic excursion (MAPSE) was 11% smaller (P = 0·001) and the left ventricle isovolumic relaxation time (IVRT) 27% longer in SP than in LLP. The ejection fraction, heart rate, arterial pressure and pulmonary ventilation were similar in SP and LLP. During HUT, EDV, SV, CO and MAPSE were smaller, and IVRT was longer, in HUT-LB than in HUT-LL, by −19%, −20%, −17%, −18% and +35%, respectively (P<0·04). Conclusions: Cardiac performance is enhanced in LLP versus SP and in HUT-LL versus HUT-LB, which can be attributed to improved venous return, conceivably, wholly or in part, due to increased hydrostatic pressure gradients between the caval veins and the heart in the LLP and HUT-LL positions.

Place, publisher, year, edition, pages
John Wiley & Sons, 2018
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-238939 (URN)10.1111/cpf.12520 (DOI)000446073500015 ()2-s2.0-85046159223 (Scopus ID)
Note

QC 20181114

Available from: 2018-11-14 Created: 2018-11-14 Last updated: 2018-11-14Bibliographically approved
Grönkvist, M., Levin, B. & Eiken, O. (2018). G Tolerance During Open- vs. Closed-Loop G-Time Control.. Aerospace Medicine and Human Performance, 89(9), 798-804
Open this publication in new window or tab >>G Tolerance During Open- vs. Closed-Loop G-Time Control.
2018 (English)In: Aerospace Medicine and Human Performance, ISSN 2375-6314, E-ISSN 2375-6322, Vol. 89, no 9, p. 798-804Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: +Gz tolerance is traditionally determined in centrifuges with open-loop G control, i.e., the centrifuge is under operator control (open loop), and thus the test subject is unable to influence the Gz load. In modern centrifuges, however, the subject is commonly able to continuously control the Gz load (closed loop). It is a widespread opinion among fighter pilots that +Gz tolerance is higher under closed- than open-loop G control. The aims were to investigate whether +Gz tolerance is higher in closed- than open-loop G control, and whether it is possible to use closed-loop G control during precise determination of +Gz tolerance.

METHODS: Relaxed +Gz tolerance was determined in eight men during rapid Gz-onset rate (ROR) under three conditions: 1) OL-VFB, open loop with visual feedback; 2) OL-NFB, open loop with no visual feedback; and 3) CL, closed loop. Straining +Gz tolerance was determined in 10 men during ROR in OL and CL conditions.

RESULTS: Relaxed +Gz tolerance did not differ between CL (3.66 Gz), OL-VFB (3.70 Gz) and OL-NFB (3.64 Gz). Straining +Gz tolerance was similar in the CL (8.5 Gz) and OL (8.6 Gz) conditions. In the CL condition, the Gz load varied substantially and was on average lower than in the OL conditions, at any stipulated G-time profile.

DISCUSSION: There is no systematic difference in relaxed or straining +Gz tolerance as determined in closed- vs. open-loop G-controlled systems. During closed-loop control, precision and reproducibility are too low to recommend it for accurate determination of relaxed G tolerance.Grönkvist M, Levin B, Eiken O. G tolerance during open- vs. closed-loop G-time control. Aerosp Med Hum Perform. 2018; 89(9):798-804.

Place, publisher, year, edition, pages
Ingenta, 2018
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-233529 (URN)10.3357/AMHP.5096.2018 (DOI)000442351100004 ()30126512 (PubMedID)
Note

QC 20180903

Available from: 2018-08-22 Created: 2018-08-22 Last updated: 2018-09-07Bibliographically approved
Sotiridis, A., Debevec, T., Ciuha, U., Eiken, O. & Mekjavic, I. B. (2018). Heat acclimation augments peak power output and thermoregulatory responses in thermoneutral but not hypoxic conditions. In: Proceedings from 23rd annual congress of the European College of Sport Science, in Dublin, 2018: . Paper presented at 23rd annual congress of the European College of Sport Science, in Dublin, 2018.
Open this publication in new window or tab >>Heat acclimation augments peak power output and thermoregulatory responses in thermoneutral but not hypoxic conditions
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2018 (English)In: Proceedings from 23rd annual congress of the European College of Sport Science, in Dublin, 2018, 2018Conference paper, Oral presentation with published abstract (Refereed)
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-240351 (URN)
Conference
23rd annual congress of the European College of Sport Science, in Dublin, 2018
Note

QC 20181217

Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2018-12-17Bibliographically approved
Kölegård, R., Da Silva, C., Siebenmann, C., Keramidas, M. E. & Eiken, O. (2018). Hjärtats minutvolym vid olika kroppspositioner. In: : . Paper presented at SANMA Scientia et Valebat V.
Open this publication in new window or tab >>Hjärtats minutvolym vid olika kroppspositioner
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2018 (Swedish)Conference paper, Oral presentation only (Refereed)
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-239612 (URN)
Conference
SANMA Scientia et Valebat V
Note

QC 20181212

Available from: 2018-11-28 Created: 2018-11-28 Last updated: 2018-12-12Bibliographically approved
Debevec, T., Ganse, B., Mittag, U., Eiken, O., Mekjavic, I. B. & Rittweger, J. (2018). Hypoxia aggravates inactivity-Related muscle wasting. Frontiers in Physiology, 9(May), Article ID 494.
Open this publication in new window or tab >>Hypoxia aggravates inactivity-Related muscle wasting
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2018 (English)In: Frontiers in Physiology, ISSN 1664-042X, E-ISSN 1664-042X, Vol. 9, no May, article id 494Article in journal (Refereed) Published
Abstract [en]

Poor musculoskeletal state is commonly observed in numerous clinical populations such as chronic obstructive pulmonary disease (COPD) and heart failure patients. It, however, remains unresolved whether systemic hypoxemia, typically associated with such clinical conditions, directly contributes to muscle deterioration. We aimed to experimentally elucidate the effects of systemic environmental hypoxia upon inactivity-related muscle wasting. For this purpose, fourteen healthy, male participants underwent three 21-day long interventions in a randomized, cross-over designed manner: (i) bed rest in normoxia (NBR; PiO2 = 133.1 ± 0.3 mmHg), (ii) bed rest in normobaric hypoxia (HBR; PiO2 = 90.0 ± 0.4 mmHg) and ambulatory confinement in normobaric hypoxia (HAmb; PiO2 = 90.0 ± 0.4 mmHg). Peripheral quantitative computed tomography and vastus lateralis muscle biopsies were performed before and after the interventions to obtain thigh and calf muscle cross-sectional areas and muscle fiber phenotype changes, respectively. A significant reduction of thigh muscle size following NBR (-6.9%, SE 0.8%; P &lt; 0.001) was further aggravated following HBR (-9.7%, SE 1.2%; P = 0.027). Bed rest-induced muscle wasting in the calf was, by contrast, not exacerbated by hypoxic conditions (P = 0.47). Reductions in both thigh (-2.7%, SE 1.1%, P = 0.017) and calf (-3.3%, SE 0.7%, P &lt; 0.001) muscle size were noted following HAmb. A significant and comparable increase in type 2× fiber percentage of the vastus lateralis muscle was noted following both bed rest interventions (NBR = +3.1%, SE 2.6%, HBR = +3.9%, SE 2.7%, P &lt; 0.05). Collectively, these data indicate that hypoxia can exacerbate inactivity-related muscle wasting in healthy active participants and moreover suggest that the combination of both, hypoxemia and lack of activity, as seen in COPD patients, might be particularly harmful for muscle tissue.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2018
Keywords
Bed rest, Fiber type, Hypoxemia, Muscle loss, Vastus lateralis
National Category
Physiology
Identifiers
urn:nbn:se:kth:diva-229207 (URN)10.3389/fphys.2018.00494 (DOI)000432406900001 ()2-s2.0-85046994713 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, 284438
Note

QC 20180601

Available from: 2018-06-01 Created: 2018-06-01 Last updated: 2018-06-01Bibliographically approved
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