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Keramidas, Michail E.ORCID iD iconorcid.org/0000-0002-7440-2171
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Publications (10 of 86) Show all publications
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
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
Keramidas, M. E., Gadefors, M., Nilsson, L.-O. & Eiken, O. (2018). Physiological and psychological determinants of whole-body endurance exercise following short-term sustained operations with partial sleep deprivation. European Journal of Applied Physiology, 118(7), 1373-1384
Open this publication in new window or tab >>Physiological and psychological determinants of whole-body endurance exercise following short-term sustained operations with partial sleep deprivation
2018 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 118, no 7, p. 1373-1384Article in journal (Refereed) Published
Abstract [en]

The study examined the effects of short-term field-based military training with partial sleep deprivation on whole-body endurance performance in well-trained individuals. Before and after a 2-day sustained operations (SUSOPS), 14 cadets performed a 15-min constant-load cycling at 65% of peak power output (PPO; CLT65), followed by an exhaustive constant-load trial at 85% of PPO (CLT85). Physiological [oxygen uptake (O-2), heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), and regional oxygenation (TOI) in the frontal cerebral cortex and vastus lateralis muscle] and psychological [effort perception (RPE), affective valence (FS), and perceived activation (FAS)] variables were monitored during exercise. SUSOPS reduced time to exhaustion in CLT85 by 29.1% (p = 0.01). During the CLT65 trial, SUSOPS potentiated the exercise-induced elevations in O-2 and HR (p < 0.05), and blunted MAP (p = 0.001). CO did not differ between trials. Yet, towards the end of both CLT85 trials, CO tended to decline (p 0.08); a response that occurred at an earlier stage in the SUSOPS trial. During CLT65, SUSOPS altered neither cerebral nor muscle TOI. The SUSOPS CLT85 trial, however, was terminated at similar leg-muscle deoxygenation (p > 0.05) and lower prefrontal cortex deoxygenation (p < 0.01). SUSOPS increased RPE at submaximal intensities (p = 0.05), and suppressed FAS and FS throughout (p < 0.01). The present findings indicate, therefore, that a brief period of military sustained operations with partial sleep deprivation augment cardiorespiratory and psychological strain, limiting high-intensity endurance capacity.

Place, publisher, year, edition, pages
SPRINGER, 2018
Keywords
Autonomic dysfunction, Cerebral oxygenation, Effort, Fatigue, Motivation, Muscle oxygenation
National Category
Physiology
Identifiers
urn:nbn:se:kth:diva-232243 (URN)10.1007/s00421-018-3869-0 (DOI)000436848500009 ()29687266 (PubMedID)2-s2.0-85045844918 (Scopus ID)
Note

QC 20180720

Available from: 2018-07-20 Created: 2018-07-20 Last updated: 2018-07-20Bibliographically approved
Salvadego, D., Keramidas, M. E., Kölegård, R., Brocca, L., Lazzer, S., Mavelli, I., . . . Grassi, B. (2018). PlanHab(*): hypoxia does not worsen the impairment of skeletal muscle oxidative function induced by bed rest alone. Journal of Physiology, 596(15), 3341-3355
Open this publication in new window or tab >>PlanHab(*): hypoxia does not worsen the impairment of skeletal muscle oxidative function induced by bed rest alone
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2018 (English)In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 596, no 15, p. 3341-3355Article in journal (Refereed) Published
Abstract [en]

Skeletal muscle oxidative function was evaluated in 11 healthy males (mean +/- SD age 27 +/- 5years) prior to (baseline data collection, BDC) and following a 21day horizontal bed rest (BR), carried out in normoxia (P-IO2=133 mmHg; N-BR) and hypoxia (P-IO2=90 mmHg; H-BR). H-BR was aimed at simulating reduced gravity habitats. The effects of a 21day hypoxic ambulatory confinement (P-IO2=90 mmHg; H-AMB) were also assessed. Pulmonary O-2 uptake (<(V) over dot>O-2), vastus lateralis fractional O-2 extraction (changes in deoxygenated haemoglobin+myoglobin concentration, Delta[deoxy(Hb+Mb)]; near-infrared spectroscopy) and femoral artery blood flow (ultrasound Doppler) were evaluated during incremental one-leg knee-extension exercise (reduced constraints to cardiovascular O-2 delivery) carried out to voluntary exhaustion in a normoxic environment. Mitochondrial respiration was evaluated ex vivo by high-resolution respirometry in permeabilized vastus lateralis fibres. <(V) over dot>(O2peak) decreased (P<0.05) after N-BR (0.98 +/- 0.13 L min(-1)) and H-BR (0.96 +/- 0.17 L min(-1)) vs. BDC (1.05 +/- 0.14 L min(-1)). In the presence of a decreased (by similar to 6-8%) thigh muscle volume, <(V) over dot>(O2peak) normalized per unit of muscle mass was not affected by both interventions. Delta[deoxy(Hb+Mb)](peak) decreased (P<0.05) after N-BR (65 +/- 13% of limb ischaemia) and H-BR (62 +/- 12%) vs. BDC (73 +/- 13%). H-AMB did not alter <(V) over dot>(O2peak) or Delta[deoxy(Hb+Mb)](peak). An overshoot of Delta[deoxy(Hb+Mb)] was evident during the first minute of unloaded exercise after N-BR and H-BR. Arterial blood flow to the lower limb during both unloaded and peak knee extension was not affected by any intervention. Maximal ADP-stimulated mitochondrial respiration decreased (P<0.05) after all interventions vs. control. In 21day N-BR, a significant impairment of oxidative metabolism occurred downstream of cardiovascular O-2 delivery, affecting both mitochondrial respiration and presumably the intramuscular matching between O-2 supply and utilization. Superposition of H on BR did not worsen the impairment induced by BR alone.

Place, publisher, year, edition, pages
Wiley, 2018
Keywords
planetary habitats, microgravity, hypoxia, mitochondrial respiration, skeletal muscle oxidative metabolism
National Category
Neurology
Identifiers
urn:nbn:se:kth:diva-233287 (URN)10.1113/JP275605 (DOI)000440417400042 ()29665013 (PubMedID)
Funder
EU, FP7, Seventh Framework Programme, 284438
Note

QC 20180821

Available from: 2018-08-21 Created: 2018-08-21 Last updated: 2018-08-21Bibliographically approved
Eiken, O., Keramidas, M. E., Taylor, N. A. & Grönkvist, M. (2017). Intraocular pressure and cerebral oxygenation during prolonged headward acceleration. European Journal of Applied Physiology, 117(1), 61-72
Open this publication in new window or tab >>Intraocular pressure and cerebral oxygenation during prolonged headward acceleration
2017 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 117, no 1, p. 61-72Article in journal (Refereed) Published
Abstract [en]

Supra-tolerance head-to-foot directed gravitoinertial load (+Gz) typically induces a sequence of symptoms/signs, including loss of: peripheral vision-central vision-consciousness. The risk of unconsciousness is greater when anti-G-garment failure occurs after prolonged rather than brief exposures, presumably because, in the former condition, mental signs are not consistently preceded by impaired vision. The aims were to investigate if prolonged exposure to moderately elevated +Gz reduces intraocular pressure (IOP; i.e., improves provisions for retinal perfusion), or the cerebral anoxia reserve. Subjects were exposed to 4-min +Gz plateaux either at 2 and 3 G (n = 10), or at 4 and 5 G (n = 12). Measurements included eye-level mean arterial pressure (MAP), oxygenation of the cerebral frontal cortex, and at 2 and 3 G, IOP. IOP was similar at 1 (14.1 +/- 1.6 mmHg), 2 (14.0 +/- 1.6 mmHg), and 3 G (14.0 +/- 1.6 mmHg). During the G exposures, MAP exhibited an initial prompt drop followed by a partial recovery, end-exposure values being reduced by ae<currency>30 mmHg. Cerebral oxygenation showed a similar initial drop, but without recovery, and was followed by either a plateau or a further slight decrement to a minimum of about -14 mu M. Gz loading did not affect IOP. That cerebral oxygenation remained suppressed throughout these G exposures, despite a concomitant partial recovery of MAP, suggests that the increased risk of unconsciousness upon G-garment failure after prolonged +Gz exposure is due to reduced cerebral anoxia reserve.

Place, publisher, year, edition, pages
Springer, 2017
Keywords
Cerebral anoxia reserve; Cerebral blood flow; G tolerance; G-induced loss of consciousness; Oxyhaemoglobin saturation; Retinal anoxia reserve
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-195347 (URN)10.1007/s00421-016-3499-3 (DOI)000394313300007 ()2-s2.0-84994761979 (Scopus ID)
Note

QC 20161117

Available from: 2016-11-02 Created: 2016-11-02 Last updated: 2017-10-24Bibliographically approved
Keramidas, M. E., Mekjavic, I. B. & Eiken, O. (2017). LunHab: interactive effects of a 10 day sustained exposure to hypoxia and bedrest on aerobic exercise capacity in male lowlanders. Experimental Physiology, 102(6), 694-710
Open this publication in new window or tab >>LunHab: interactive effects of a 10 day sustained exposure to hypoxia and bedrest on aerobic exercise capacity in male lowlanders
2017 (English)In: Experimental Physiology, ISSN 0958-0670, E-ISSN 1469-445X, Vol. 102, no 6, p. 694-710Article in journal (Refereed) Published
Abstract [en]

NEW FINDINGS: What is the central question of this study? What are the distinct and interactive effects of a 10 day exposure to hypoxia and horizontal bedrest on the whole-body peak oxygen uptake and on the regional cerebral and skeletal muscle tissue oxygenation during upright cycle ergometry in male lowlanders? What is the main finding and its importance? A 10 day sustained exposure to hypoxia aggravates the bedrest-induced reduction in peak oxygen uptake during dynamic exercise engaging large muscle groups, but mitigates the skeletal muscle oxidative capacity impairment elicited by bedrest. The study examined the interactive effects of a 10 day exposure to hypoxia and bedrest on the whole-body peak oxygen uptake (V̇O2 peak ) during maximal exercise and on skeletal muscle and cerebral oxygenation during submaximal exercise. Nine males underwent three 10 day confinements, in a Latin-square order, as follows: (i) a normoxic bedrest [NBR; partial pressure of inspired O2 (PI,O2) = 134.2 ± 0.7 mmHg]; (ii) a hypoxic bedrest (HBR; PI,O2 = 102.9 ± 0.1 mmHg at day 1, 91.5 ± 1.2 mmHg at days 3-10); and (iii) a hypoxic ambulation (HAMB; PI,O2 as in HBR). Before, 1 (R+1) and 3 days (R+3) after each confinement, subjects performed exhaustive, incremental-load and moderate-intensity constant-load (CLTs) cycle-ergometry trials, while breathing either room air or a hypoxic gas mixture. During the CLTs, changes in the regional oxygenation of the cerebral frontal cortex and the vastus lateralis and intercostal muscles were monitored with near-infrared spectroscopy. At R+1, the confinement-related impairment in V̇O2 peak was greater after HBR than after NBR or HAMB, regardless of whether the trial was performed in room air or hypoxia (HBR, -16.2%; NBR, -8.3%; HAMB, -4.1%; P = 0.001). During the CLTs, bedrest aggravated the exercise-induced reduction in locomotor and respiratory muscle oxygenation (P ≤ 0.05); an effect that was less after HBR than after NBR (P ≤ 0.05). The hypoxic exercise-induced cerebral vasodilatory response was blunted by HBR, probably because of the marked hyperventilation-dependent hypocapnia, attendant to the sustained hypoxic stimulus. Hence, short-term exposure to hypoxia potentiates the reduction in V̇O2 peak , but it mitigates the impairment in skeletal muscle oxidative capacity induced by bedrest.

Place, publisher, year, edition, pages
John Wiley & Sons, 2017
Keywords
NIRS, VO2peak, acclimation, cerebral oxygenation, high altitude, inactivity, microgravity, muscle oxygenation
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-208671 (URN)10.1113/EP086167 (DOI)000402604500012 ()28393459 (PubMedID)2-s2.0-85020176878 (Scopus ID)
Note

QC 20170613

Available from: 2017-06-11 Created: 2017-06-11 Last updated: 2017-06-30Bibliographically approved
Norrbrand, L., Kölegård, R., Keramidas, M. E., Eiken, O. & Mekjavic, I. B. (2017). No association between hand and foot temperature responses during local cold stress and rewarming.. European Journal of Applied Physiology, 117(6), 1141-1153
Open this publication in new window or tab >>No association between hand and foot temperature responses during local cold stress and rewarming.
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2017 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 117, no 6, p. 1141-1153Article in journal (Refereed) Published
Abstract [en]

PURPOSE: The purpose was to examine whether associations exist between temperature responses in the fingers vs. toes and hand vs. foot during local cold-water immersion and rewarming phases.

METHODS: Seventy healthy subjects (58 males, 12 females) immersed their right hand or right foot, respectively, in 8 °C water for 30 min (CWI phase), followed by a 15-min spontaneous rewarming (RW) in 25 °C air temperature.

RESULTS: Temperature was lower in the toes than the fingers during the baseline phase (27.8 ± 3.0 vs. 33.9 ± 2.5 °C, p < 0.001), parts of the CWI phase (min 20-30: 8.8 ± 0.7 vs. 9.7 ± 1.4 °C, p < 0.001), and during the RW phase (peak temperature: 22.5 ± 5.1 vs. 32.7 ± 3.6 °C, p < 0.001). Cold-induced vasodilatation (CIVD) was more common in the fingers than in the toes (p < 0.001). Within the first 10 min of CWI, 61% of the subjects exhibited a CIVD response in the fingers, while only 6% of the subjects had a CIVD response in the toes. There was a large variability of temperature responses both within and between extremities, and there was a weak correlation between finger- and toe temperature both during the CWI (r = 0.21, p = 0.08) and the RW phases (r = 0.26, p = 0.03).

CONCLUSIONS: Results suggest that there is generally a lower temperature in the toes than the fingers after a short time of local cold exposure and that the thermal responses of the fingers/hands are not readily transferable to the toes/foot.

Place, publisher, year, edition, pages
Springer, 2017
Keywords
CIVD, Cold tolerance, Finger, Local cold injury, Rewarming, Toe, Water immersion
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-208670 (URN)10.1007/s00421-017-3601-5 (DOI)000401025200008 ()28421275 (PubMedID)2-s2.0-85017604399 (Scopus ID)
Note

QC 20170612

Available from: 2017-06-11 Created: 2017-06-11 Last updated: 2017-06-12Bibliographically approved
Siebenmann, C., Keramidas, M. E., Rundqvist, H., Mijwel, S., Cowburn, A., Johnson, R. & Eiken, O. (2017). No local or systemic effects of cutaneous exposure to hypobaric hypoxia in humans. Acta Physiologica, 219, 43-43
Open this publication in new window or tab >>No local or systemic effects of cutaneous exposure to hypobaric hypoxia in humans
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2017 (English)In: Acta Physiologica, ISSN 1748-1708, E-ISSN 1748-1716, Vol. 219, p. 43-43Article in journal, Meeting abstract (Other academic) Published
Place, publisher, year, edition, pages
Wiley-Blackwell, 2017
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-242327 (URN)000393916600092 ()
Note

QC 20190207

Available from: 2019-02-07 Created: 2019-02-07 Last updated: 2019-02-07Bibliographically approved
Keramidas, M. E. (2016). Effects of acute and long-term hypoxia on local cold tolerance. In: : . Paper presented at 6th International Conference on the Physiology and Pharmacology of Temperature Regulation. December 5-9, Ljubljana, Slovenia..
Open this publication in new window or tab >>Effects of acute and long-term hypoxia on local cold tolerance
2016 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Exposure to high altitude is commonly considered a predisposing factor for local cold injury. A number of field studies have indeed confirmed that local cold tolerance is impaired in low-oxygen environments, presumably due to hypoxia-induced cutaneous vasoconstriction. However, during acute and long-term high-altitude exposure, the hypoxic stressor typically co-exists with other environmental and behavioral components, viz. hypothermia, malnutrition and physical fatigue, which independently or interactively may affect peripheral blood-flow responses. Laboratory-based, control studies have demonstrated that acute exposure to hypoxia, isolated from other confounding factors, does not potentiate vasoconstriction during local cold stress, but delays spontaneous rewarming following such cold stress. Conversely, it appears that long-term exposure to hypoxia elicits adaptive processes, in particular when the high-altitude acclimatization regimen is combined with physical exercise, that reverse the hypoxia-induced vasoconstriction after local limb cooling. Such adaptive responses do, however, not seem to be transferable to sea-level conditions, i.e. they do not reduce vasoconstriction during normoxic conditions, nor to be homogeneous across the limbs.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-199245 (URN)
Conference
6th International Conference on the Physiology and Pharmacology of Temperature Regulation. December 5-9, Ljubljana, Slovenia.
Note

QC 20170112

Available from: 2017-01-02 Created: 2017-01-02 Last updated: 2017-01-12Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-7440-2171

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