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Kounalakis S.N.,Jozef Stefan Institute | Kounalakis S.N.,Evelpidon Hellenic Military University | Eiken O.,KTH Royal Institute of Technology | Mekjavic I.B.,Jozef Stefan Institute
European Journal of Applied Physiology | Year: 2012

The potentiated exercise-sweating rate observed during acute hypoxia is diminished after a sleep-high trainlow (SH-TL) regimen. We tested the hypothesis that this attenuation of the sweating response after SH-TL is compensated for by an increase in heat loss via vasodilatation. Nine male subjects participated in a 28-day SH-TL regimen. Before (pre-), and after (post-) the SH-TL protocol, they performed an VO2peak test under normoxia and hypoxia. Additionally, pre- and post-SH-TL they completed three 30-min constant-work rate trials on a cycle ergometer. In one trial, the subjects inspired room air while exercising at 50 % of normoxic VO2peak (CT). In the remaining trials, subjects exercised in hypoxia (FIO2 12.5 %), either at the same absolute (HAT) or relative (50 % of hypoxic VO2 peak) work rate (HRT) as in CT. Despite similar exercise core temperature responses between pre- and post-SH-TL trials, sweating rate was potentiated in HAT pre-SH-TL [CT: 1.97 (0.42); HRT: 1.86 (0.31); HAT: 2.55 (0.53) mg cm-2 min-1; p<0.05]. Post-SH-TL exercise sweating rate was increased for CT, and remained unchanged in HRT and HAT [CT: 2.42 (0.76); HRT: 2.01 (0.33); HAT: 2.59 (0.30) mg cm -2 min-1 Pre-SH-TL, the forearm-fingertip skin temperature difference (Tskf-f) was higher in HAT than in CT and HRT by 3.5°C (p<0.05). The inter-condition differences in Tskf-f were diminished post-SH-TL. In conclusion, the decrease in sweating rate during hypoxic exercise, following a SH-TL regimen, was countered by an increase in vasodilatation (reduced Tskf-f), whereas SH-TL enhanced the sweating response during normoxic exercise. The mechanisms underlying these SH-TL-induced alterations in thermoregulatory responses remain to be settled. © Springer-Verlag 2012.


Keramidas M.E.,KTH Royal Institute of Technology | Geladas N.D.,National and Kapodistrian University of Athens | Mekjavic I.B.,Jozef Stefan Institute | Kounalakis S.N.,Evelpidon Hellenic Military University
Clinical Physiology and Functional Imaging | Year: 2013

The purpose of this study was to examine whether the forearm-finger skin temperature gradient (Tforearm-finger), an index of vasomotor tone during resting conditions, can also be used during steady-state exercise. Twelve healthy men performed three cycling trials at an intensity of ~60% of their maximal oxygen uptake for 75 min separated by at least 48 h. During exercise, forearm skin blood flow (BFF) was measured with a laser-Doppler flowmeter, and finger skin blood flow (PPG) was recorded from the left index fingertip using a pulse plethysmogram. Tforearm-finger of the left arm was calculated from the values derived by two thermistors placed on the radial side of the forearm and on the tip of the middle finger. During exercise, PPG and BFF increased (P<0·001), and Tforearm-finger decreased (P<0·001) from their resting values, indicating a peripheral vasodilatation. There was a significant correlation between Tforearm-finger and both PPG (r = -0·68; P<0·001) and BFF (r = -0·50; P<0·001). It is concluded that Tforearm-finger is a valid qualitative index of cutaneous vasomotor tone during steady-state exercise. © 2013 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.


Mekjavic I.B.,Jozef Stefan Institute | Dobnikar U.,University of Maribor | Kounalakis S.N.,Jozef Stefan Institute | Kounalakis S.N.,Evelpidon Hellenic Military University
Applied Physiology, Nutrition and Metabolism | Year: 2013

We evaluated the cold-induced vasodilatation (CIVD) response at 4 different water temperatures. Nine healthy young male subjects immersed their right hands in 35 °C water for 5 min, and immediately thereafter for 30 min in a bath maintained at either 5, 8, 10, or 15 °C. The responses of finger skin temperatures, subjective ratings of thermal comfort and temperature sensation scores were compared between the 4 immersion trials. The number of subjects who exhibited a CIVD response was higher during immersion of the hand in 5 and 8 °C (100%) compared with 10 and 15 °C water (87.5% and 37.5%, respectively). The CIVD temperature amplitude was 4.2 ± 2.6, 3.4 ± 2.0, 2.1 ± 1.6, and 2.8 ± 2.0 °C at 5, 8, 10, and 15 °C trials, respectively; higher in 5 and 8 °C compared with 10 and 15 °C water (p = 0.003). No differences in CIVD were found between the 5 and 8 °C immersions. However, during immersion in 5 °C, subjects felt "uncomfortable" while in the other trials felt "slightly uncomfortable" (p = 0.005). The temperature sensation score was "cold" for 5 °C and "cool" for the other trials, but no statistical differences were observed. Immersion of the hand in 8 °C elicits a CIVD response of similar magnitude as immersion in 5 °C, but with less thermal discomfort.


Louwies T.,Flemish Institute for Technological Research | Louwies T.,Hasselt University | Mekjavic P.J.,University of Ljubljana | Cox B.,Hasselt University | And 6 more authors.
Investigative Ophthalmology and Visual Science | Year: 2016

PURPOSE. To assess the separate and combined effects of exposure to prolonged and sustained recumbency (bed rest) and hypoxia on retinal microcirculation. METHODS. Eleven healthy male subjects (mean 6 SD age = 27 ± 6 years; body mass index [BMI] = 23.7 ± 3.0 kg m-2) participated in a repeated-measures crossover design study comprising three 21-day interventions: normoxic bed rest (NBR; partial pressure of inspired O2, PiO2 = 133.1 ± 0.3 mm Hg); hypoxic ambulation (HAMB; PiO2 = 90.0 6 0.4 mm Hg), and hypoxic bed rest (HBR; PiO2 = 90.0 ± 0.4 mm Hg). Central retinal arteriolar (CRAE) and venular (CRVE) equivalents were measured at baseline and at regular intervals during each 21- day intervention. RESULTS. Normoxic bed rest caused a progressive reduction in CRAE, with the change in CRAE relative to baseline being highest on day 15 (ΔDCRAE = -7.5 µm; 95% confidence interval [CI]: -10.8 to -4.2; P < 0.0001). Hypoxic ambulation resulted in a persistent 21-day increase in CRAE, reaching a maximum on day 4 (DCRAE = 9.4 µm; 95% CI: 6.0-12.7; P < 0.0001). During HBR, the increase in CRAE was highest on day 3 (ΔDCRAE = 4.5 µm; 95% CI: 1.2-7.8; P = 0.007), but CRAE returned to baseline levels thereafter. Central retinal venular equivalent decreased during NBR and increased during HAMB and HBR. The reduction in CRVE during NBR was highest on day 1 (ΔDCRVE = -7.9 µm; 95 CI: -13.3 to -2.5), and the maximum ΔDCRVE during HAMB (24.6 µm; 95% CI: 18.9-30.3) and HBR (15.2 µm; 95% CI: 9.8-20.5) was observed on days 10 and 3, respectively. CONCLUSIONS. The diameters of retinal blood vessels exhibited a dynamic response to hypoxia and bed rest, such that retinal vasodilation was smaller during combined bed rest and hypoxia than during hypoxic exposure. © 2016, Association for Research in Vision and Ophthalmology Inc. All rights reserved.


PubMed | Flemish Institute for Technological Research, Simon Fraser University, Hasselt University, KTH Royal Institute of Technology and 2 more.
Type: Journal Article | Journal: Investigative ophthalmology & visual science | Year: 2016

To assess the separate and combined effects of exposure to prolonged and sustained recumbency (bed rest) and hypoxia on retinal microcirculation.Eleven healthy male subjects (mean SD age = 27 6 years; body mass index [BMI] = 23.7 3.0 kg m-2) participated in a repeated-measures crossover design study comprising three 21-day interventions: normoxic bed rest (NBR; partial pressure of inspired O2, PiO2 = 133.1 0.3 mm Hg); hypoxic ambulation (HAMB; PiO2 = 90.0 0.4 mm Hg), and hypoxic bed rest (HBR; PiO2 = 90.0 0.4 mm Hg). Central retinal arteriolar (CRAE) and venular (CRVE) equivalents were measured at baseline and at regular intervals during each 21-day intervention.Normoxic bed rest caused a progressive reduction in CRAE, with the change in CRAE relative to baseline being highest on day 15 (CRAE = -7.5 m; 95% confidence interval [CI]: -10.8 to -4.2; P < 0.0001). Hypoxic ambulation resulted in a persistent 21-day increase in CRAE, reaching a maximum on day 4 (CRAE = 9.4 m; 95% CI: 6.0-12.7; P < 0.0001). During HBR, the increase in CRAE was highest on day 3 (CRAE = 4.5 m; 95% CI: 1.2-7.8; P = 0.007), but CRAE returned to baseline levels thereafter. Central retinal venular equivalent decreased during NBR and increased during HAMB and HBR. The reduction in CRVE during NBR was highest on day 1 (CRVE = -7.9 m; 95 CI: -13.3 to -2.5), and the maximum CRVE during HAMB (24.6 m; 95% CI: 18.9-30.3) and HBR (15.2 m; 95% CI: 9.8-20.5) was observed on days 10 and 3, respectively.The diameters of retinal blood vessels exhibited a dynamic response to hypoxia and bed rest, such that retinal vasodilation was smaller during combined bed rest and hypoxia than during hypoxic exposure.


Kounalakis S.N.,Evelpidon Hellenic Military University | Geladas N.D.,National and Kapodistrian University of Athens
Applied Physiology, Nutrition and Metabolism | Year: 2012

We hypothesized that a faster cycling cadence could exaggerate cardiovascular drift and affect muscle and cerebral blood volume and oxygenation. Twelve healthy males (mean age, 23.4 ± 3.8 years) performed cycle ergometry for 90 min on 2 separate occasions, with pedalling frequencies of 40 and 80 r·min -1, at individual workloads corresponding to 60% of their peak oxygen consumption. The main measured variables were heart rate, ventilation, cardiac output, electromyographic activity of the vastus lateralis, and regional muscle and cerebral blood volume and oxygenation. Cardiovascular drift developed at both cadences, but it was more pronounced at the faster than at the slower cadence, as indicated by the drop in cardiac output by 1.0 ± 0.2 L·min -1, the decline in stroke volume by 9 ± 3 mL·beat -1, and the increase in heart rate by 9 ± 1 beats·min -1 at 80 r·min -1. At the faster cadence, minute ventilation was higher by 5.0 ± 0.5 L·min -1, and end-tidal CO 2 pressure was lower by 2.0 ± 0.1 torr. Although higher electromyographic activity in the vastus lateralis was recorded at 80 r·min -1, muscle blood volume did not increase at this cadence, as it did at 40 r·min -1. In addition, muscle oxygenation was no different between cadences. In contrast, cerebral regional blood volume and oxygenation at 80 r·min -1 were not as high as at 40 r·min -1 (p < 0.05). Faster cycling cadence exaggerates cardiovascular drift and seems to influence muscle and cerebral blood volume and cerebral oxygenation, without muscle oxygenation being radically affected.


Zacharakis E.D.,National and Kapodistrian University of Athens | Kounalakis S.N.,Evelpidon Hellenic Military University | Nassis G.P.,National and Kapodistrian University of Athens | Geladas N.D.,National and Kapodistrian University of Athens
Applied Physiology, Nutrition and Metabolism | Year: 2013

The progressive heart rate (HR) increase and stroke volume (SV) decline during prolonged constant-load leg exercise signifies cardiovascular drift (CVdrift); fluid replacement is known to minimize this phenomenon. Like their able-bodied counterparts (AB), paraplegic athletes undergo prolonged exercise during training and competition, which could result in CVdrift. The aim of this study is to address the role of rehydration on preventing CVdrift in spinal cord injured (SCI) paraplegic athletes. Eight SCI athletes with an injury level between C7 and T6 and 9 AB subjects performed 60-min constant-load exercise on a wheelchair ergometer in a thermo-neutral environment. No fluid was taken in 1 trial, whereas 85% of sweat losses were replaced by drinking water in another trial. Cardic output (CO), SV, HR, and oral temperature (Tor) were determined during exercise. Prolonged exercise resulted in similar HR (18 beats·min-1 for AB and 12 beats·min-1 for SCI) and Tor (0.63 °C for AB and 0.71 °C for SCI) elevation and SV decline (-8.5 mL·beat-1 for AB and -5.5 mL·beat-1 for SCI), whereas CO remained unchanged. Water intake restrained the exercise-induced hyperthermia and resulted in smaller SV decline (-4.0 mL for AB and -3.0 mL for SCI, p < 0.01). In conclusion, CVdrift was similar in SCI and AB subjects during prolonged wheelchair exercise. Likewise, the beneficial effects of hydration in both groups were analogous.


PubMed | Evelpidon Hellenic Military University
Type: Journal Article | Journal: Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme | Year: 2012

We hypothesized that a faster cycling cadence could exaggerate cardiovascular drift and affect muscle and cerebral blood volume and oxygenation. Twelve healthy males (mean age, 23.4 3.8 years) performed cycle ergometry for 90 min on 2 separate occasions, with pedalling frequencies of 40 and 80 rmin(-1), at individual workloads corresponding to 60% of their peak oxygen consumption. The main measured variables were heart rate, ventilation, cardiac output, electromyographic activity of the vastus lateralis, and regional muscle and cerebral blood volume and oxygenation. Cardiovascular drift developed at both cadences, but it was more pronounced at the faster than at the slower cadence, as indicated by the drop in cardiac output by 1.0 0.2 Lmin(-1), the decline in stroke volume by 9 3 mLbeat(-1), and the increase in heart rate by 9 1 beatsmin(-1) at 80 rmin(-1). At the faster cadence, minute ventilation was higher by 5.0 0.5 Lmin(-1), and end-tidal CO(2) pressure was lower by 2.0 0.1 torr. Although higher electromyographic activity in the vastus lateralis was recorded at 80 rmin(-1), muscle blood volume did not increase at this cadence, as it did at 40 rmin(-1). In addition, muscle oxygenation was no different between cadences. In contrast, cerebral regional blood volume and oxygenation at 80 rmin(-1) were not as high as at 40 rmin(-1) (p < 0.05). Faster cycling cadence exaggerates cardiovascular drift and seems to influence muscle and cerebral blood volume and cerebral oxygenation, without muscle oxygenation being radically affected.

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