| 1. |
- Eiken, Ola, et al.
(author)
-
Effects of local arteriosclerosis on carotid baroreflex sensitivity and on heart rate and arterial pressure variability in humans
- 2006
-
In: Clinical Physiology and Functional Imaging. - 1475-0961 .- 1475-097X. ; 26:1, s. 9-14
-
Journal article (peer-reviewed)abstract
- The study examined whether the alterations in heart rate variability (HRV) and baroreflex sensitivity (BRS) observed in patients with coronary artery disease can also be discerned in otherwise healthy subjects with mild-to-moderate arteriosclerosis in the carotid artery bifurcation. Based on the results of carotid duplex ultrasonography, subjects were designated as either having no arteriosclerotic lesions (n = 18), unilateral (n = 19) or bilateral lesions (n = 18) in the bifurcation. Electrocardiograms were recorded and simultaneous and continuous records of arterial pressure were obtained. Resting HRV was determined by calculating the spectral power density in three frequency bands: 0-0.05 Hz [very low frequency (VLF) band], 0.05-0.15 [low frequency (LF) band] and 0.15-2 Hz (high frequency band), whereas the arterial pressure variability (APV) was determined from spectral power density of the VLF and LF bands. Carotid BRS was evaluated by measuring R-R intervals during application of pulse-synchronous graded pressures (40 to -65 mmHg) in a neck-chamber device. Analysis of variance revealed no effect of mild-to-moderate carotid arteriosclerosis on the spectral components of HRV and APV or on BRS. It thus appears that mild-to-moderate asymptomatic carotid arteriosclerosis does not affect carotid BRS, APV or HRV at rest.
|
|
| 2. |
- Tribukait, Arne, et al.
(author)
-
Changes in the perceived head transversal plane and the subjective visual horizontal induced by Coriolis stimulation during gondola centrifugation
- 2006
-
In: Journal of Vestibular Research-Equilibrium & Orientation. - 0957-4271 .- 1878-6464. ; 16:3, s. 105-116
-
Journal article (peer-reviewed)abstract
- For studying the influence of the vertical semicircular canals on spatial orientation in roll, the subjective visual horizontal (SVH) and the subjective transversal plane of the head (STP) were measured in a situation where the vertical canals sense a roll-velocity stimulus while the otolith organs persistently signal that the head is upright in roll. During gondola centrifugation (resultant gravitoinertial force vector 2.5 G, gondola inclination 66 degrees) subjects were exposed to controlled rotational head movements (angular speed 27 degrees/s, magnitude 40 degrees) about the yaw (body z-) axis, produced by means of a motor-driven helmet. This causes a roll-plane Coriolis stimulus to the canals, while the otoliths persistently sense upright head position in roll. The subjects reported intense sensations of rotation and tilt in the roll plane. This was reflected in tilts of both the SVH and STP. The initial tilt of the SVH was 13.0 +/- 9.7 degrees (mean +/- S.D., n=10). The STP was changed in the opposite direction. The initial tilt was 23.8 +/- 12.2 degrees (mean +/- S.D., n=5). The changes in the SVH and STP were not of equal magnitude. A few subjects who had almost no deviations in the SVH showed pronounced tilts of the STP. The time constant for exponential decay of the tilts of the SVH and STP was on average approximately 1 minute. These findings indicate that a difference in activity of the vertical canals in the right versus left ear may cause substantial tilts of the SVH even if there is no asymmetry in the activity of the otolith system. Further, the canal stimulus may induce a tilt of the fundamental egocentric frame of reference.
|
|
| 3. |
|
|
| 4. |
- Arvedsen, SK, et al.
(author)
-
Body height and arterial pressure in seated and supine young males during +2 G centrifugation
- 2015
-
In: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 309:9
-
Journal article (peer-reviewed)abstract
- It is known that arterial pressure correlates positively with body height in males and it has been suggested that this is due to the increasing vertical hydrostatic gradient from the heart to the carotid baroreceptors. Therefore we tested the hypothesis that a higher gravitoinertial stress induced by the use of a human centrifuge would increase mean arterial pressure (MAP) more in tall than in short males in the seated position. In short (162-171cm, n=8) and tall (194-203cm, n=10) healthy males (18-41y), brachial arterial pressure, heart rate (HR) and cardiac output were measured during +2G centrifugation, while they were seated upright with the legs kept horizontal (+2Gz). In a separate experiment, the same measurements were done with the subjects supine (+2Gx). During +2Gz MAP increased in the short (22±2 mmHg, p<0.0001) and tall (23±2 mmHg, p<0.0001) males, with no significant difference between the groups. HR increased more (p<0.05) in the tall than in the short group (14±2 versus 7±2 bpm). Stroke volume (SV) decreased in the short group (26±4 mL, p=0.001) and more so in the tall group (39±5 mL, p<0.0001; short vs tall p=0.047). During +2GX, systolic arterial pressure increased (p<0.001) and SV (p=0.012) decreased in the tall group only. In conclusion, during +2Gz MAP increased in both short and tall males with no difference between the groups. However, in the tall group HR increased more during +2Gz which could be caused by a larger hydrostatic pressure gradient from heart to head leading to greater inhibition of the carotid baroreceptors.
|
|
| 5. |
|
|
| 6. |
- Baer, R, et al.
(author)
-
Effects of continuous positive- and negative-pressure breathing on the pattern of breathing in man during exercise.
- 1989
-
In: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 137:2, s. 301-7
-
Journal article (peer-reviewed)abstract
- Breathing pattern and static lung volumes were studied in 10 subjects at rest and during incremental-load cycle ergometry under three different conditions, viz. with normal pressure in the airways (control) and during continuous positive- and negative-pressure breathing (CPPB, CNPB) of +15 and -15 cmH2O. End-expiratory, end-inspiratory and mid-expiratory volumes were increased by CPPB and decreased by CNPB; these effects were especially pronounced at rest and during mild exercise. Both at rest and during exercise mean inspiratory flow (VT/TI) was exaggerated by CPPB and attenuated by CNPB. At rest these changes were due mainly to concomitant changes in tidal volume (VT) which was increased by CPPB and decreased by CNPB, while inspiratory time duration (TI) was relatively unaffected by pressure breathing. The transition from rest to loadless pedalling induced an increase in VT but no change in TI in the control condition, whereas in the CPPB and CNPB conditions TI decreased and VT remained unaltered. This CPPB- and CNPB-induced change in the volume-time threshold relationship at the onset of pedalling is attributed to increased stretch receptor activity in the extrathoracic portion of the trachea as a result of the increments in transmural pressure. During the course of exercise there was an inverse relationship between the slope of the VT-TI curve and the mid-expiratory volume in that the slope was greater in the control than in the CPPB condition and greatest during CNPB, suggesting that in exercise hyperpnoea the VT-TI relationship is also determined by pulmonary and/or thoracic wall stretch receptors capable of sensing the absolute lung volume.
|
|
| 7. |
- Baer, R, et al.
(author)
-
Effects of triglycyl-lysine-vasopressin on cardiovascular responses to orthostatic stress.
- 1987
-
In: Clinical Physiology. - 0144-5979 .- 1365-2281. ; 7:4, s. 329-35
-
Journal article (peer-reviewed)abstract
- The influence of triglycyl-lysine-vasopressin (TGLVP) on cardiovascular responses to orthostatic stress was studied. Arterial pressures, heart rate (HR) and stroke volume (SV) were measured in eight healthy males subjected to 20 min 70 degrees head-up tilt. On different days they received either 0.01 mg/kg b.w. of TGLVP or a corresponding volume of 0.9% saline i.v. after 15 min supine rest. After the drug injection, in supine subjects, HR had decreased from 58 to 50 beats min-1, total peripheral resistance (TPR) was elevated by 29%, systolic (SAP) and diastolic pressure (DAP) had increased by 7 and 8 mmHg, respectively. During tilt, values for HR and SAP were similar with and without TGLVP whereas DAP and MAP were elevated 8 and 7 mmHg, respectively, by the drug. 4-8 min into the tilt, TGLVP caused an 8% sustained curtailment of SV. Both with and without the drug TPR increased by about 30% in response to head-up tilt. Thus, the marked peripheral arteriolar constriction after vasopressin in the supine position was not affected by head-up tilt. Tilting also abolished the drug-induced elevation in SAP, most likely explained by the reduction in SV. Although TPR was markedly increased by TGLVP during head-up tilt, reflected in the behaviour of DAP, the response of SV speaks against any beneficial effect of this drug on orthostatic tolerance in healthy subjects.
|
|
| 8. |
|
|
| 9. |
- Berg, Hans E., et al.
(author)
-
Hip, thigh and calf muscle atrophy and bone loss after 5-week bedrest inactivity
- 2007
-
In: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 99:3, s. 283-289
-
Journal article (peer-reviewed)abstract
- Unloaded inactivity induces atrophy and functional deconditioning of skeletal muscle, especially in the lower extremities. Information is scarce, however, regarding the effect of unloaded inactivity on muscle size and function about the hip. Regional bone loss has been demonstrated in hips and knees of elderly orthopaedic patients, as quantified by computerized tomography (CT). This method remains to be validated in healthy individuals rendered inactive, including real or simulated weightlessness. In this study, ten healthy males were subjected to 5 weeks of experimental bedrest and five matched individuals served as ambulatory controls. Maximum voluntary isometric hip and knee extension force were measured using the strain gauge technique. Cross-sectional area (CSA) of hip, thigh and calf muscles, and radiological density (RD) of the proximal tibial bone were measured using CT. Bedrest decreased (P < 0.05) average (SD) muscle strength by 20 (8)% in knee extension, and by 22 (12)% in hip extension. Bedrest induced atrophy (P < 0.05) of extensor muscles in the gluteal region, thigh and calf, ranging from 2 to 12%. Atrophy was more pronounced in the knee extensors [9 (4)%] and ankle plantar flexors [12 (3)%] than in the gluteal extensor muscles [2 (2)%]. Bone density of the proximal tibia decreased (P < 0.05) by 3 (2)% during bedrest. Control subjects did not show any temporal changes in muscle or bone indices (P > 0.05), when examined at similar time intervals. The present findings of a substantial loss in hip extensor strength and a smaller, yet significant atrophy of these muscles, demonstrate that hip muscle deconditioning accompanies losses in thigh and calf muscle mass after bedrest. This suggests that comprehensive quantitative studies on impaired locomotor function after inactivity should include all joints of the lower extremity. Our results also demonstrate that a decreased RD, indicating bone mineral loss, can be shown already after 5 weeks of unloaded bedrest, using a standard CT technique.
|
|
| 10. |
- Berg, H E, et al.
(author)
-
Involvement of eccentric muscle actions in giant slalom racing.
- 1995
-
In: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 27:12, s. 1666-70
-
Journal article (peer-reviewed)abstract
- Joint angular movements and muscle activation (EMG), were determined in male elite racers while performing the giant slalom. Movement cycles averaged 3.5 +/- 0.6 s (left plus right turn), and knee angle ranged 66-114 degrees (180 degrees = straight leg). Knee extensor muscle use was dominated (rectified EMG; P < 0.05) by the leg controlling the outside (downhill) ski during the turn. Time spent while decreasing knee angle (eccentric muscle action) of outside leg averaged 1.0 +/- 0.2 s. This phase was longer (P < 0.05) than the average push-off (concentric muscle action) phase of 0.5 +/- 0.1 s. Moreover, EMG activity of the outside leg during eccentric muscle actions exceeded (P < 0.05) that of concentric actions and was similar to that attained during maximum isometric knee extension in laboratory tests. Knee and hip angular movement ranged 20-50 degrees. Average joint velocities equalled 20-40 degrees.s(-1) during the turning phase. Thus, competitive giant slalom skiing is dominated by slow eccentric muscle actions performed at near maximum voluntary force. Because of their greater ability to generate force, eccentric muscle actions may be warranted or even required to resist the G-forces induced during the turn phase.
|
|
| 11. |
- Berg, H. E., et al.
(author)
-
Muscle control in elite alpine skiing
- 1999
-
In: Medicine & Science in Sports & Exercise. - : Ovid Technologies (Wolters Kluwer Health). - 0195-9131 .- 1530-0315. ; 31:7, s. 1065-1067
-
Journal article (peer-reviewed)abstract
- PURPOSE: The purpose of this study was to determine whether muscle control may be influenced by accelerative forces brought about by the downhill displacement of body mass in combination with the sharp turns during alpine skiing. METHODS: Sixteen elite skiers performed either super G (SG), giant slalom (GS), slalom (SL), or freestyle mogul (FM) skiing. Knee and hip joint angles and electromyographic (EMG) activity of the knee extensors were recorded. RESULTS: During the course of a turn, the minimum (deepest stance position) knee angle of the outside (main load-bearing) leg ranged from 60 degrees to 100 degrees, where the smallest angle was obtained in the FM event. Among the traditional alpine disciplines, smaller knee angles were obtained in the high-speed events (i.e., knee angle: SG CONCLUSIONS: We believe these results have important implications for the design of specific training models.
|
|
| 12. |
|
|
| 13. |
- Bjurstedt, Hilding, et al.
(author)
-
Graded ischemia in exercising human skeletal muscles : methods and applications
- 1995
-
In: News in Physiological Sciences - NIPS. - 0886-1714 .- 1522-161X. ; 10, s. 193-197
-
Journal article (peer-reviewed)abstract
- A method was developed for inducing graded blood flow restriction in exercising large muscle groups in humans. The method holds promise as a means to study local and systemic effects of ischemic exercise. Recent applications include studies on the effects of long-term leg ischemia in endurance training.
|
|
| 14. |
|
|
| 15. |
- Brink, Andreas, et al.
(author)
-
Factors of significance for the ability of fighter pilots to visually indicate the magnitude of roll tilt during simulated turns in a centrifuge
- 2024
-
In: Perception. - : SAGE Publications. - 0301-0066 .- 1468-4233. ; 53:2, s. 75-92
-
Journal article (peer-reviewed)abstract
- During coordinated flight and centrifugation, pilots show interindividual variability in perceived roll tilt. The study explored how this variability is related to perceptual and cognitive functions. Twelve pilots underwent three 6-min centrifugations on two occasions (G levels: 1.1G, 1.8G, and 2.5G; gondola tilts: 25°, 56°, and 66°). The subjective visual horizontal (SVH) was measured with an adjustable luminous line and the pilots gave estimates of experienced G level. Afterward, they were interrogated regarding the relationship between G level and roll tilt and adjusted the line to numerically mentioned angles. Generally, the roll tilt during centrifugation was underestimated, and there was a large interindividual variability. Both knowledge on the relationship between G level and bank angle, and ability to adjust the line according to given angles contributed to the prediction of SVH in a multiple regression model. However, in most cases, SVH was substantial smaller than predictions based on specific abilities.
|
|
| 16. |
- Chowdhury, Helena H, et al.
(author)
-
Systemic Hypoxia Increases the Expression of DPP4 in Preadipocytes of Healthy Human Participants
- 2017
-
In: Experimental and clinical endocrinology & diabetes. - : Georg Thieme Verlag KG. - 0947-7349 .- 1439-3646.
-
Journal article (peer-reviewed)abstract
- Dipeptidyl peptidase 4 (DPP4) is a transmembrane glycoprotein involved in protein degradation. Due to its action on incretins, which increase insulin secretion, DPP4 is considered a therapeutic target for type 2 diabetes. Here we have studied the role of single and combined effects of hypoxia and inactivity on the expression of DPP4 in human adipose tissue of 12 adult normal-weight males. Fat biopsies were obtained at baseline and after each of three experimental campaigns. The results revealed that in isolated human preadipocytes the expression of DPP4 was significantly increased by exposure of participants to hypoxia. Physical inactivity per se had no apparent effect on the DPP4 expression. It is concluded that DPP4 may be a marker to monitor indirectly tissue hypoxia, as occurs in obese subjects.
|
|
| 17. |
- Ciuha, Ursa, et al.
(author)
-
Effects of normobaric hypoxic bed rest on the thermal comfort zone
- 2015
-
In: Journal of Thermal Biology. - : Elsevier BV. - 0306-4565 .- 1879-0992. ; 49-50, s. 39-46
-
Journal article (peer-reviewed)abstract
- Future Lunar and Mars habitats will maintain a hypobaric hypoxic environment to minimise the risk of decompression sickness during the preparation for extra-vehicular activity. This study was part of a larger study investigating the separate and combined effects of inactivity associated with reduced gravity and hypoxia, on the cardiovascular, musculoskeletal, neurohumoural, and thermoregulatory systems. Eleven healthy normothermic young male subjects participated in three trials conducted on separate occasions: (1) Normobaric hypoxic ambulatory confinement, (2) Normobaric hypoxic bedrest and (3) Normobaric normoxic bedrest Normobaric hypoxia was achieved by reduction of the oxygen fraction in the air (FiO2=0.141 +/- 0.004) within the facility, while the effects of reduced gravity were simulated by confining the subjects to a horizontal position in bed, with all daily routines performed in this position for 21 days. The present study investigated the effect of the interventions on behavioural temperature regulation. The characteristics of the thermal comfort zone (TCZ) were assessed by a water-perfused suit, with the subjects instructed to regulate the sinusoidally varying temperature of the suit within a range considered as thermally comfortable. Measurements were performed 5 days prior to the intervention (D-5), and on days 10 (D10) and 20 (D20) of the intervention. no statistically significant differences were found in any of the characteristics of the TCZ between the interventions (HAMB, HBR and NBR), or between different measurement days (D-5, D10, D20) within each intervention. rectal temperature remained stable, whereas skin temperature (T-sk) increased during all interventions throughout the one hour trial, no difference in T-sk between 0-5, D10 and D20, and between HAMB, HBR and NBR were revealed, subjects perceived the regulated temperature as thermally comfortable, and neutral or warm, we conclude that regulation of thermal comfort is not compromised by hypoxic inactivity. (C) 2015 Elsevier Ltd. All rights reserved.
|
|
| 18. |
- Ciuha, Urša, et al.
(author)
-
Heat acclimation enhances the cold-induced vasodilation response.
- 2021
-
In: European Journal of Applied Physiology. - : Springer Nature. - 1439-6319 .- 1439-6327. ; 121:11, s. 3005-3015
-
Journal article (peer-reviewed)abstract
- PURPOSE: It has been reported that the cold-induced vasodilation (CIVD) response can be trained using either regular local cold stimulation or exercise training. The present study investigated whether repeated exposure to environmental stressors, known to improve aerobic performance (heat and/or hypoxia), could also provide benefit to the CIVD response.METHODS: Forty male participants undertook three 10-day acclimation protocols including daily exercise training: heat acclimation (HeA; daily exercise training at an ambient temperature, Ta = 35 °C), combined heat and hypoxic acclimation (HeA/HypA; daily exercise training at Ta = 35 °C, while confined to a simulated altitude of ~ 4000 m) and exercise training in normoxic thermoneutral conditions (NorEx; no environmental stressors). To observe potential effects of the local acclimation on the CIVD response, participants additionally immersed their hand in warm water (35 °C) daily during the HeA/HypA and NorEx. Before and after the acclimation protocols, participants completed hand immersions in cold water (8 °C) for 30 min, followed by 15-min recovery phases. The temperature was measured in each finger.RESULTS: Following the HeA protocol, the average temperature of all five fingers was higher during immersion (from 13.9 ± 2.4 to 15.5 ± 2.5 °C; p = 0.04) and recovery (from 22.2 ± 4.0 to 25.9 ± 4.9 °C; p = 0.02). The HeA/HypA and NorEx protocols did not enhance the CIVD response.CONCLUSION: Whole-body heat acclimation increased the finger vasodilatory response during cold-water immersion, and enhanced the rewarming rate of the hand, thus potentially contributing to improved local cold tolerance. Daily hand immersion in warm water for 10 days during HeA/Hyp and NorEx, did not contribute to any changes in the CIVD response.
|
|
| 19. |
|
|
| 20. |
|
|
| 21. |
- Ciuha, U, et al.
(author)
-
Strategies for increasing evaporative cooling during simulated desert patrol mission.
- 2016
-
In: Ergonomics. - : Taylor & Francis. - 0014-0139 .- 1366-5847. ; 59:2
-
Journal article (peer-reviewed)abstract
- The study evaluated the efficiency of two heat dissipation strategies under simulated desert patrol missions. Ten men participated in four trials, during which they walked on a treadmill (45°C, 20% relative humidity), carrying a load of 35 kg; two 50-min walks were separated by a 20-min rest. Cooling strategies, provided by an ambient air-ventilated vest (active cooling condition, AC), or water spraying of the skin during the rest (passive cooling condition, PC), in addition to reduced clothing and open zippers, were compared to conditions with full protective (FP) clothing and naked condition (NC). Skin temperature was higher during NC (37.9 ± 0.4°C; p < 0.001), and rectal temperature and heart rate were higher during FP (38.6 ± 0.4°C, p < 0.001 and 145 ± 12, p < 0.001, respectively), compared to other conditions. Four subjects terminated the trial prematurely due to signs of heat exhaustion in FP. Both cooling strategies substantially improved evaporative cooling.
|
|
| 22. |
|
|
| 23. |
|
|
| 24. |
- Croft, Rodney J, et al.
(author)
-
Effects of Acceleration-Induced Reductions in Retinal and Cerebral Oxygenation on Human Performance.
- 2021
-
In: Aerospace Medicine and Human Performance. - : Aerospace Medical Association. - 2375-6314 .- 2375-6322. ; 92:2, s. 75-82
-
Journal article (peer-reviewed)abstract
- BACKGROUND: Ischemic hypoxia induced by suprathreshold G-force loading can adversely affect vision, cognition, and lead to loss of consciousness (LOC). The purpose of this study was to determine whether reductions in cerebral oxygenation, caused by subthreshold G-forces (up to 4 Gz and of limited durations that do not lead to LOC), would affect visual perception and working memory performance.METHODS: Sixteen subjects performed visual perception and working memory tasks both before and during Gz exposures (1, 2.2, 3, 4 with leg pressurization, 4 with leg and abdomen pressurization) within a human-use centrifuge.RESULTS: As measured using near-infrared spectroscopy, blood oxygenation over medial prefrontal cortex was similar in the 1 and 2.2 Gz conditions, but was reduced to a similar extent in the 3 and 4 Gz conditions. In parallel, visual perception accuracy was reduced in the 3 and 4 Gz conditions, with no difference between the 3 and 4 Gz conditions. No change in reaction time was seen. Conversely, neither accuracy nor reaction time changes were observed for the visual working memory task.DISCUSSION: These results indicate that although visual working memory is not affected, the ability to visually discriminate between stimuli is reduced at G-forces as low as 3 and 4 Gz. This may have important ramifications for pilots who are routinely subjected to such forces.
|
|
| 25. |
|
|
| 26. |
|
|
| 27. |
- Debevec, Tadej, et al.
(author)
-
Acute short-term hyperoxia followed by mild hypoxia does not increase EPO production : resolving the "normobaric oxygen paradox''
- 2012
-
In: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 112:3, s. 1059-1065
-
Journal article (peer-reviewed)abstract
- Recent findings suggest that besides renal tissue hypoxia, relative decrements in tissue oxygenation, using a transition of the breathing mixture from hyperoxic to normoxic, can also stimulate erythropoietin (EPO) production. To further clarify the importance of the relative change in tissue oxygenation on plasma EPO concentration [EPO], we investigated the effect of a consecutive hyperoxic and hypoxic breathing intervention. Eighteen healthy male subjects were assigned to either IHH (N = 10) or CON (N = 8) group. The IHH group breathed pure oxygen (F(i)O(2) ~ 1.0) for 1 h, followed by a 1-h period of breathing a hypoxic gas mixture (F(i)O(2) ~ 0.15). The CON group breathed a normoxic gas mixture (F(i)O(2) ~ 0.21) for the same duration (2 h). Blood samples were taken just before, after 60 min, and immediately after the 2-h exposure period. Thereafter, samples were taken at 3, 5, 8, 24, 32, and 48 h after the exposure. During the breathing interventions, subjects remained in supine position. There were significant increases in absolute [EPO] within groups at 8 and 32 h in the CON and at 32 h only in the IHH group. No significant differences in absolute [EPO] were observed between groups following the intervention. Relative (∆[EPO]) levels were significantly lower in the IHH than in the CON group, 5 and 8 h following exposure. The tested protocol of consecutive hyperoxic-hypoxic gas mixture breathing did not induce [EPO] synthesis stimulation. Moreover, the transient attenuation in ∆[EPO] in the IHH group was most likely due to a hyperoxic suppression. Hence, our findings provide further evidence against the "normobaric O(2) paradox" theory.
|
|
| 28. |
|
|
| 29. |
- Debevec, T., et al.
(author)
-
Effects of prolonged hypoxia and bed rest on appetite and appetite-related hormones
- 2016
-
In: Appetite. - : Academic Press. - 0195-6663 .- 1095-8304. ; 107, s. 28-37
-
Journal article (peer-reviewed)abstract
- Environmental hypoxia and inactivity have both been shown to modulate appetite. To elucidate the independent and combined effects of hypoxia and bed rest-induced inactivity on appetite-related hormones and subjective appetite, eleven healthy, non-obese males underwent three experimental interventions in a cross-over and randomized fashion: 1) Hypoxic confinement combined with daily moderate-intensity exercise (HAMB, FiO2 = 0.141 ± 0.004; PiO2 = 90.0 ± 0.4 mmHg) 2) Bed rest in normoxia (NBR, FiO2 = 0.209; PiO2 = 133.1 ± 0.3 mmHg) and 3) Bed rest in hypoxia (HBR, FiO2 = 0.141 ± 0.004; PiO2 = 90.0 ± 0.4 mmHg). A mixed-meal tolerance test (MTT), followed by an ad libitum meal were performed before (Pre) and after 16-days (Post) of each intervention. Composite satiety scores (CSS) during the MTT were calculated from visual analogue scores, while fasting and postprandial concentrations of total ghrelin, peptide YY (PYY), glucagon-like peptide-1 (GLP-1) and leptin were quantified from arterialized-venous samples. Postprandial CSS were significantly lower at Post compared to Pre in NBR only (P < 0.05) with no differences observed in ad libitum meal intakes. Postprandial concentrations and incremental area under the curve (AUC) for total ghrelin and PYY were unchanged following all interventions. Postprandial GLP-1 concentrations were only reduced at Post following HBR (P < 0.05) with resulting AUC changes being significantly lower compared to HAMB (P < 0.01). Fasting leptin was reduced following HAMB (P < 0.05) with no changes observed following NBR and HBR. These findings suggest that independently, 16-day of simulated altitude exposure (∼4000 m) and bed rest-induced inactivity do not significantly alter subjective appetite or ad libitum intakes. The measured appetite-related hormones following both HAMB and HBR point to a situation of hypoxia-induced appetite stimulation, although this did not reflect in higher ad libitum intakes. Clinical Trial Registration Number: NCT02293772.
|
|
| 30. |
- Debevec, Tadej, et al.
(author)
-
Exercise Training during Normobaric Hypoxic Confinement Does Not Alter Hormonal Appetite Regulation
- 2014
-
In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:6, s. e98874-
-
Journal article (peer-reviewed)abstract
- Background: Both exposure to hypoxia and exercise training have the potential to modulate appetite and induce beneficial metabolic adaptations. The purpose of this study was to determine whether daily moderate exercise training performed during a 10-day exposure to normobaric hypoxia alters hormonal appetite regulation and augments metabolic health. Methods: Fourteen healthy, male participants underwent a 10-day hypoxic confinement at,4000 m simulated altitude (FIO2 = 0.139 +/- 0.003%) either combined with daily moderate intensity exercise (Exercise group; N = 8, Age = 25.8 +/- 2.4 yrs, BMI = 22.9 +/- 1.2 kg.m(-2)) or without any exercise (Sedentary group; N = 6 Age = 24.8 +/- 3.1 yrs, BMI = 22.3 +/- 2.5 kg.m(-2)). A meal tolerance test was performed before (Pre) and after the confinement (Post) to quantify fasting and postprandial concentrations of selected appetite-related hormones and metabolic risk markers. C-13-Glucose was dissolved in the test meal and (CO2)-C-13 determined in breath samples. Perceived appetite ratings were obtained throughout the meal tolerance tests. Results: While body mass decreased in both groups (-1.4 kg; p = 0.01) following the confinement, whole body fat mass was only reduced in the Exercise group (-1.5 kg; p = 0.01). At Post, postprandial serum insulin was reduced in the Sedentary group (-49%; p = 0.01) and postprandial plasma glucose in the Exercise group (-19%; p = 0.03). Fasting serum total cholesterol levels were reduced (-12%; p = 0.01) at Post in the Exercise group only, secondary to low-density lipoprotein cholesterol reduction (-16%; p = 0.01). No differences between groups or testing periods were noted in fasting and/or postprandial concentrations of total ghrelin, peptide YY, and glucagon-like peptide-1, leptin, adiponectin, expired (CO2)-C-13 as well as perceived appetite ratings (p>0.05). Conclusion: These findings suggest that performing daily moderate intensity exercise training during continuous hypoxic exposure does not alter hormonal appetite regulation but can improve the lipid profile in healthy young males.
|
|
| 31. |
- Debevec, Tadej, et al.
(author)
-
FemHab : The effects of bed rest and hypoxia on oxidative stress in healthy women
- 2016
-
In: Journal of applied physiology. - : American Chemical Society (ACS). - 8750-7587 .- 1522-1601. ; 120:8, s. 930-938
-
Journal article (peer-reviewed)abstract
- Independently, both inactivity and hypoxia augment oxidative stress. This study, part of the FemHab project, investigated the combined effects of bed rest-induced unloading and hypoxic exposure on oxidative stress and antioxidant status. Healthy, eumenorrheic women were randomly assigned to the following three 10-day experimental interventions: normoxic bed rest (NBR; n = 11; PIO2 = 133 mmHg), normobaric hypoxic bed rest (HBR; n = 12; PIO2 = 90 mmHg), and ambulatory hypoxic confinement (HAMB; n = 8: PIO2 = 90 mmHg). Plasma samples, obtained before (Pre), during (D2, D6), immediately after (Post) and 24 h after (Post + 1) each intervention, were analyzed for oxidative stress markers [advanced oxidation protein products (AOPP), malondialdehyde (MDA), and nitrotyrosine], antioxidant status [ superoxide dismutase (SOD), catalase, ferric-reducing antioxidant power (FRAP), glutathione peroxidase (GPX), and uric acid (UA)], NO metabolism end-products (NOx), and nitrites. Compared with baseline, AOPP increased in NBR and HBR on D2 (+ 14%; + 12%; P < 0.05), D6 (+ 19%; + 15%; P < 0.05), and Post (+ 22%; + 21%; P < 0.05), respectively. MDA increased at Post + 1 in NBR (+ 116%; P < 0.01) and D2 in HBR (+114%; P < 0.01) and HAMB (+ 95%; P < 0.05). Nitrotyrosine decreased (-45%; P < 0.05) and nitrites increased (+46%; P < 0.05) at Post + 1 in HAMB only. Whereas SOD was higher at D6 (+ 82%) and Post + 1 (+ 67%) in HAMB only, the catalase activity increased on D6 (128%) and Post (146%) in HBR and HAMB, respectively (P < 0.05). GPX was only reduced on D6 (- 20%; P < 0.01) and Post (- 18%; P < 0.05) in HBR. No differences were observed in FRAP and NOx. UA was higher at Post in HBR compared with HAMB (P < 0.05). These data indicate that exposure to combined inactivity and hypoxia impairs prooxidant/antioxidant balance in healthy women. Moreover, habitual activity levels, as opposed to inactivity, seem to blunt hypoxia-related oxidative stress via antioxidant system upregulation.
|
|
| 32. |
- Debevec, T, et al.
(author)
-
FemHab: Prooxidant/antioxidant balance during and following a 10-day hypoxic bed rest
- 2015
-
Conference paper (peer-reviewed)abstract
- Introduction:Inhabitants of the envisaged planetary habitats will be continuously exposed to reduced gravity and hypoxia. The combined effects of unloading and hypoxia on prooxidant/antioxidant balance are currently unknown.Methods:Healthy female participants underwent the following three, 10-day interventions: i) Normobaric normoxic bed-rest (NBR; n=11; FiO2=0.209) ii) Normobaric hypoxic ambulatory confinement (HAMB; n=9: FiO2~0.141), and iii) Normobaric hypoxic bed-rest (HBR; n=12; FiO2~0.141). Plasma oxidative stress [advanced oxidation protein products (AOPP) and nitrotyrosine], antioxidant markers [superoxide dismutase (SOD) and glutathione peroxidase (GPX)] and nitrites were determined before (Pre), during (Day 2, Day 6), immediately after (Post) and 24-hrs after (Post+1) each campaign.Results:Compared to Pre, the AOPP was only higher on Day 2, Day 6 and Post during the HBR and at Post during the NBR (P<0.05) while the nitrotyrosine was significantly reduced at Post+1 only during the HAMB (P<0.05). Higher levels of SOD were observed during the HAMB at Day 6 and Post+1whereas GPX was reduced at Day 6 and Post during the HBR. Nitrites were significantly higher at Post+1 in the HAMB both, compared to Pre and compared to HBR and NBR (P<0.05).Conclusion:These data suggest that the unloading-induced oxidative stress is exacerbated by exposure to simulated altitude of ~4000m. In addition, even habitual (low) physical activity, performed during hypoxic exposure, seems to blunt hypoxia-related oxidative stress via antioxidant system upregulation.
|
|
| 33. |
- Debevec, T., et al.
(author)
-
Hypoxia aggravates inactivity-Related muscle wasting
- 2018
-
In: Frontiers in Physiology. - : Frontiers Media S.A.. - 1664-042X. ; 9:May
-
Journal article (peer-reviewed)abstract
- 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 < 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 < 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 < 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.
|
|
| 34. |
- Debevec, T., et al.
(author)
-
Moderate exercise blunts oxidative stress induced by normobaric hypoxic confinement
- 2014
-
In: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 46:1, s. 33-41
-
Journal article (peer-reviewed)abstract
- PURPOSE: Both acute hypoxia and physical exercise are known to increase oxidative stress. This randomized prospective trial investigated whether the addition of moderate exercise can alter oxidative stress induced by continuous hypoxic exposure. METHODS: Fourteen male participants were confined to 10-d continuous normobaric hypoxia (FIO2 = 0.139 ± 0.003, PIO2 = 88.2 ± 0.6 mm Hg, ∼4000-m simulated altitude) either with (HCE, n = 8, two training sessions per day at 50% of hypoxic maximal aerobic power) or without exercise (HCS, n = 6). Plasma levels of oxidative stress markers (advanced oxidation protein products [AOPP], nitrotyrosine, and malondialdehyde), antioxidant markers (ferric-reducing antioxidant power, superoxide dismutase, glutathione peroxidase, and catalase), nitric oxide end-products, and erythropoietin were measured before the exposure (Pre), after the first 24 h of exposure (D1), after the exposure (Post) and after the 24-h reoxygenation (Post + 1). In addition, graded exercise test in hypoxia was performed before and after the protocol. RESULTS: Maximal aerobic power increased after the protocol in HCE only (+6.8%, P < 0.05). Compared with baseline, AOPP was higher at Post + 1 (+28%, P < 0.05) and nitrotyrosine at Post (+81%, P < 0.05) in HCS only. Superoxide dismutase (+30%, P < 0.05) and catalase (+53%, P < 0.05) increased at Post in HCE only. Higher levels of ferric-reducing antioxidant power (+41%, P < 0.05) at Post and lower levels of AOPP (-47%, P < 0.01) at Post + 1 were measured in HCE versus HCS. Glutathione peroxidase (+31%, P < 0.01) increased in both groups at Post + 1. Similar erythropoietin kinetics was noted in both groups with an increase at D1 (+143%, P < 0.01), a return to baseline at Post, and a decrease at Post + 1 (-56%, P < 0.05). CONCLUSIONS: These data provide evidence that 2 h of moderate daily exercise training can attenuate the oxidative stress induced by continuous hypoxic exposure.
|
|
| 35. |
|
|
| 36. |
|
|
| 37. |
|
|
| 38. |
|
|
| 39. |
- Debevec, Tadej, et al.
(author)
-
Separate and combined effects of 21-day bed rest and hypoxic confinement on body composition
- 2014
-
In: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 114:11, s. 2411-2425
-
Journal article (peer-reviewed)abstract
- This study tested the hypothesis that hypoxia exacerbates reductions in body mass observed during unloading. To discern the separate and combined effects of simulated microgravity and hypoxia, 11 healthy males underwent three 21-day campaigns in a counterbalanced fashion: (1) normoxic bed rest (NBR; FiO2 = 0.209; PiO2 = 133.1 +/- A 0.3); (2) hypoxic ambulatory confinement (HAMB; FiO2 = 0.141 +/- A 0.004; PiO2 = 90.0 +/- A 0.4; similar to 4,000 m); and (3) hypoxic bed rest (HBR; FiO2 = 0.141 +/- A 0.004; PiO2 = 90.0 +/- A 0.4). The same dietary menu was applied in all campaigns. Targeted energy intakes were estimated individually using the Harris-Benedict equation taking into account whether the subjects were bedridden or ambulatory. Body mass and water balance were assessed throughout the campaigns. Whole body and regional body composition was determined before and after the campaigns using dual-energy X-ray absorptiometry. Before and during the campaigns, indirect calorimetry and visual analogue scores were employed to assess the resting energy expenditure (REE) and perceived appetite sensations, respectively. Energy intakes were lower than targeted in all campaigns (NBR: -5 %; HAMB: -14 %; HBR: -6 %; P < 0.01). Body mass significantly decreased following all campaigns (NBR: -3 %; HAMB: -4 %; HBR: -5 %; P < 0.01). While fat mass was not significantly altered, the whole body fat free mass was reduced (NBR: -4 %; HAMB: -5 %; HBR: -5 %; P < 0.01), secondary to lower limb fat-free mass reduction. Water balance was comparable between the campaigns. No changes were observed in REE and perceived appetite. Exposure to simulated altitude of similar to 4,000 m does not seem to worsen the whole body mass and fat-free mass reductions or alter resting energy expenditure and appetite during a 21-day simulated microgravity.
|
|
| 40. |
- Debevec, Tadej, et al.
(author)
-
Whole body and regional body composition changes following 10-day hypoxic confinement and unloading-inactivity
- 2014
-
In: Applied Physiology, Nutrition and Metabolism. - : Canadian Science Publishing. - 1715-5312 .- 1715-5320. ; 39:3, s. 386-395
-
Journal article (peer-reviewed)abstract
- Future planetary habitats will expose inhabitants to both reduced gravity and hypoxia. This study investigated the effects of short-term unloading and normobaric hypoxia on whole body and regional body composition (BC). Eleven healthy, recreationally active, male participants with a mean (SD) age of 24 (2) years and body mass index of 22.4 (3.2) kg.m(-2) completed the following 3 10-day campaigns in a randomised, cross-over designed protocol: (i) hypoxic ambulatory confinement (HAMB; FIO2 = 0.147 (0.008); PIO2 = 93.8 (0.9) mm Hg), (ii) hypoxic bed rest (HBR; FIO2 = 0.147 (0.008); PIO2 = 93.8 (0.9) mm Hg), and (iii) normoxic bed rest (NBR; FIO2 = 0.209; PIO2 = 133.5 (0.7) mmHg). Nutritional requirements were individually precalculated and the actual intake was monitored throughout the study protocol. Body mass, whole body, and regional BC were assessed before and after the campaigns using dual-energy X-ray absorptiometry. The calculated daily targeted energy intake values were 2071 (170) kcal for HBR and NBR and 2417 (200) kcal for HAMB. In both HBR and NBR campaigns the actual energy intake was within the targeted level, whereas in the HAMB the intake was lower than targeted (-8%, p < 0.05). Body mass significantly decreased in all 3 campaigns (-2.1%, -2.8%, and -2.0% for HAMB, HBR, and NBR, respectively; p < 0.05), secondary to a significant decrease in lean mass (-3.8%, -3.8%, -4.3% for HAMB, HBR, and NBR, respectively; p < 0.05) along with a slight, albeit not significant, increase in fat mass. The same trend was observed in the regional BC regardless of the region and the campaign. These results demonstrate that, hypoxia per se, does not seem to alter whole body and regional BC during short-term bed rest.
|
|
| 41. |
|
|
| 42. |
- Eiken, Ola, et al.
(author)
-
A new hydrostatic anti-G suit vs. a pneumatic anti-G system : Preliminary comparison
- 2002
-
In: Aviation, Space and Environmental Medicine. - 0095-6562 .- 1943-4448. ; 73:7, s. 703-708
-
Journal article (peer-reviewed)abstract
- Hypothesis: A newly developed hydrostatic anti-G suit is now commercially available. The suit is said to offer a high level of protection against +Gz acceleration. However, past experience shows that it is difficult to produce a hydrostatic suit with effective high-G protection. Careful testing is, therefore, needed to verify its efficacy. Methods: The G-protective properties of the hydrostatic anti-G suit (Libelle, L) were compared with those of a pneumatic anti-G ensemble (AGE-39) used in the Swedish JAS 39 Gripen aircraft. Three pilots were studied during vertical (+Gz) acceleration in a centrifuge using the following: 1) the L-suit with varied straining maneuvers, 2) the AGE-39 in combination with full anti-G straining maneuvers (AGSM) throughout each high-G exposure (full maneuver, FM), and 3) the ACE-39 in combination with AGSM during the initial part of each high-G exposure (reduced maneuver, RM). G-intensity tolerance was established during exposures to rapid onset rate (ROR) profiles with C-plateau levels ranging from +6.0 to +9.0 Gz. G-endurance was studied during simulated aerial combat maneuvers (SACM) consisting of 10 cycles of 5.5 to 7.5 G. Results: All three pilots tolerated 9.0 C with the pneumatic system both in the RM and FM conditions, their tolerances averaged 6.3 G (range 6.0 to 7.0 G) for the L suit. Thus, during the ROR exposures only the 6.0 G profile was completed by all subjects in all three conditions. At this G-load both muscle straining (as indicated by electromyographic activity in thigh and abdomen) and heart rate were higher in the L than in the RM condition. Mean arterial pressure at eye level was higher in the FM than in the L and RM conditions. Only one subject was able to complete the SACM profile in the L condition. In the RM condition all subjects completed the SACM profile and in the FM condition two subject completed the SACM. Conclusions: Whether the AGE-39 was used in combination with maximal AGSM throughout the duration of each high-G exposure or with AGSM only during the initial part of the high-G exposure, G-intensity tolerance was 9.0 G. While wearing the L-suit, G-tolerance was 6.3 G. Thus, under the conditions tested, the C-protection afforded by the L-suit is not adequate for use in a 9-G aircraft.
|
|
| 43. |
- Eiken, Ola, et al.
(author)
-
Adaptation to 5 weeks of intermittent local vascular pressure increments; Mechanisms to be considered in the development of primary hypertension?
- 2021
-
In: American Journal of Physiology. Heart and Circulatory Physiology. - : American Physiological Society. - 0363-6135 .- 1522-1539. ; 320:4, s. H1303-H1312
-
Journal article (peer-reviewed)abstract
- The aims were to study effects of iterative exposures to moderate elevations of local intravascular pressure on arterial/arteriolar stiffness and plasma levels of vasoactive substances. Pressures in the vasculature of an arm were increased by 150mmHg in healthy men (n = 11) before and after a 5-wk regimen, during which the vasculature in one arm was exposed to fifteen 40-min sessions of moderately increased transmural pressure (+65 to +105 mmHg). This vascular pressure training and the pressuredistension determinations were conducted by exposing the subjects' arm versus remaining part of the body to differential ambient pressure. During the pressure-distension determinations, venous samples were simultaneously obtained from pressurized and unpressurized vessels. Pressure training reduced arterial pressure distension by 40 ± 23% and pressure-induced flow by 33 ± 30% (P < 0.01), but only in the pressure-trained arm, suggesting local adaptive mechanisms. The distending pressure-diameter and distending pressure-flow curves, with training-induced increments in pressure thresholds and reductions in response gains, suggest that the increased precapillary stiffness was attributable to increased contractility and structural remodeling of the walls. Acute vascular pressure provocation induced local release of angiotensin-II (ANG II) and endothelin-1 (ET-1) (P < 0.05), suggesting that these vasoconstrictors limited the pressure distension. Pressure training increased basal levels of ET-1 and induced local pressure release of matrix metalloproteinase 7 (P < 0.05), suggesting involvement of these substances in vascular remodeling. The findings are compatible with the notion that local intravascular pressure load acts as a prime mover in the development of primary hypertension.
|
|
| 44. |
- Eiken, Ola, et al.
(author)
-
Blood pressure regulation V : in vivo mechanical properties of precapillary vessels as affected by long-term pressure loading and unloading
- 2014
-
In: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 114:3, s. 499-509
-
Research review (peer-reviewed)abstract
- Recent studies are reviewed, concerning the in vivo wall stiffness of arteries and arterioles in healthy humans, and how these properties adapt to iterative increments or sustained reductions in local intravascular pressure. A novel technique was used, by which arterial and arteriolar stiffness were determined as changes in arterial diameter and flow, respectively, during graded increments in distending pressure in the blood vessels of an arm or a leg. Pressure-induced increases in diameter and flow were smaller in the lower leg than in the arm, indicating greater stiffness in the arteries/arterioles of the leg. A 5-wk period of intermittent intravascular pressure elevations in one arm reduced pressure distension and pressure-induced flow in the brachial artery by about 50%. Conversely, prolonged reduction of arterial/arteriolar pressure in the lower body by 5 wks of sustained horizontal bedrest, induced three-fold increases of the pressure-distension and pressure-flow responses in a tibial artery. Thus, the wall stiffness of arteries and arterioles are plastic properties that readily adapt to changes in the prevailing local intravascular pressure. The discussion concerns mechanisms underlying changes in local arterial/arteriolar stiffness as well as whether stiffness is altered by changes in myogenic tone and/or wall structure. As regards implications, regulation of local arterial/arteriolar stiffness may facilitate control of arterial pressure in erect posture and conditions of exaggerated intravascular pressure gradients. That increased intravascular pressure leads to increased arteriolar wall stiffness also supports the notion that local pressure loading may constitute a prime mover in the development of vascular changes in hypertension.
|
|
| 45. |
- Eiken, Ola, et al.
(author)
-
Cardiac responses to lower body negative pressure and dynamic leg exercise
- 1985
-
In: European Journal of Applied Physiology and Occupational Physiology. - 0301-5548 .- 1432-1025. ; 54:5, s. 451-455
-
Journal article (peer-reviewed)abstract
- Cardiac responses to dynamic leg exercise at 0, 50, and 100 W in the supine position were investigated with and without the lower portion of the body exposed to a pressure of -6.6 kPa (Lower Body Negative Pressure, LBNP). Resting values for heart rate (HR) and stroke volume (SV) were considerably higher and lower, respectively, during LBNP than in the control condition. At the transition from rest to the mildest exercise during LBNP SV showed a prompt increase by about 40%, but no significant change in the control condition. HR, which increased by 17 beats X min-1 in the control condition, showed during LBNP no change initially and subsequently a small but significant drop below its resting value. Steady-state values for HR at the various levels of exercise were not significantly affected by LBNP, whereas corresponding values for SV were considerably lowered, so that exercise values for cardiac output were about 3 l X min-1 less during LBNP than in the control condition. The reductions in SV and cardiac output indicate residual pooling of blood in intra- and extramuscular capacitance vessels of the legs. With a change from rest to exercise at 100 W during LBNP mean systolic ejection rate (MSER) increased by 67%, the relations between SV and MSER suggesting that ventricular performance was maintained by a combination of the Frank-Starling mechanism and enhanced contractile strength.
|
|
| 46. |
|
|
| 47. |
- Eiken, Ola, et al.
(author)
-
Characteristics of the carotid baroreflex in man during normal and flow-restricted exercise
- 1992
-
In: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 144:3, s. 325-331
-
Journal article (peer-reviewed)abstract
- Eight subjects were studied in the supine position at rest, during normal dynamic leg exercise (control exercise) and with blood-flow restriction in the working legs (flow-restricted exercise). Graded muscle blood-flow restriction was accomplished by applying a supra-atmospheric pressure of 50 mmHg to the working legs. During incremental-load exercise, flow restriction reduced exercise performance and peak heart rate by 36% and 13%, respectively. The function of the cardiac branch of the carotid baroreflex was studied over its full operational range, at rest and during constant-load control and flow-restricted exercise, by measuring R-R intervals during application of pulse-synchronous graded pressures (40 to -65 mmHg) in a neck-chamber device. Heart rate and arterial pressure were higher during flow-restricted than control exercise, indicating that the flow restriction activated the muscle chemoreflex. Raising the carotid transmural pressure (systolic arterial pressure minus neck-chamber pressure) was accompanied by increasing R-R intervals in all conditions. The set point (point of baseline carotid transmural pressure and R-R interval) coincided with the midportion of the pressure-response curve at rest and with the threshold point of the curve during exercise. The maximal rate of change in relative R-R intervals and the corresponding carotid transmural pressure range were higher during control exercise than at rest and highest during flow-restricted exercise, indicating that exercise and especially flow-restricted exercise increased carotid baroflex sensitivity, and shifted the carotid baroreflex optimal buffering range to higher pressures. The results suggest that the carotid baroflex attenuates exercise heart rate increases mediated by the muscle chemoreflex and/or by central command.
|
|
| 48. |
- Eiken, Ola, et al.
(author)
-
Comparison of vascular distensibility in the upper and lower extremity
- 2004
-
In: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 181:3, s. 281-287
-
Journal article (peer-reviewed)abstract
- Aim: Because of the great differences in hydrostatic pressure acting along the blood vessels in the erect posture, leg vessels are exposed to greater transmural pressures than arm vessels. The in vivo pressure-distension relationship of arteries, arterioles and veins in the arm were compared with those of the leg. Methods: Experiments were performed with the subject (n = 11) positioned in a pressure chamber with an arm or lower leg (test limb) extended at heart level through a hole in the chamber door. Intravascular pressure in the arm/lower leg was increased by stepwise increasing chamber pressure to +180 and +210 mmHg, respectively. Diameters of blood vessels and arterial flow were measured using ultrasonographic/Doppler techniques. Changes in forearm and lower leg volumes were assessed using an impedance technique. The subject rated perceived pain in the test limb. Results: The brachial and radial arteries were found to be more distensible than the posterior tibial artery (P < 0.001). Likewise, the distension was more pronounced in the cephalic than in the great saphenous vein (P < 0.001). In the brachial artery, but not in the posterior tibial artery, flow increased markedly at the highest levels of distending pressure (P < 0.001). At the highest intravascular pressures, the rate of change in tissue impedance was greater in the forearm than the lower leg (P < 0.01). At any given level of markedly increased pressure, pain was rated higher in the arm than in the leg (P < 0.001). Conclusion: It seems that the wall stiffness of arteries, pre-capillary resistance vessels and veins adapts to meet the long-term demands imposed by the hydrostatic pressure acting locally on the vessel walls.
|
|
| 49. |
- Eiken, Ola, et al.
(author)
-
Decompression strain in parachute jumpmasters during simulated high-altitude missions : a special reference to preoxygenation strategies.
- 2023
-
In: European Journal of Applied Physiology. - : Springer Nature. - 1439-6319 .- 1439-6327.
-
Journal article (peer-reviewed)abstract
- PURPOSE: Military parachute operations are often executed at high altitude, from an unpressurized aircraft compartment. Parachute jumpmasters (JM) are thus regularly exposed to 29,500 ft for 60 min. The aim was to investigate the decompression strain during a simulated JM mission at high altitude and to compare two strategies of preoxygenation, conducted either at sea-level or below 10,000 ft, during ascent to mission altitude.METHODS: Ten JM completed, on separate occasions, a 45-min preoxygenation either at sea-level (normobaric: N) or 8200ft (hypobaric: H), followed by exposure to 28,000 ft for 60 min, whilst laying supine and breathing 100% oxygen. At min 45 of the exposure to 28,000 ft, the JM performed 10 weighted squats. Decompression strain was determined from ultrasound assessment of venous gas emboli (VGE) during supine rest (5-min intervals), after three unloaded knee-bends (15-min intervals) and immediately following the weighted squats. The VGE were scored using a six-graded scale (0-5).RESULTS: In condition H, two JM experienced decompression sickness (DCS), whereas no DCS incidents were reported in condition N. The prevalence of VGE was higher in the H than the N condition, at rest [median(range), 3(0-4) vs 0(0-3); p = 0.017], after unloaded knee-bends [3(0-4) vs 0(0-3); p = 0.014] and after the 10 weighted squats [3(0-4) vs 0(0-3); p = 0.014]. VGE were detected earlier in the H (28 ± 20 min, p = 0.018) than the N condition (50 ± 19 min).CONCLUSIONS: A preoxygenation/altitude procedure commonly used by JM, with a 60-min exposure to 28,000 ft after pre-oxygenation for 45 min at 8200 ft is associated with high risk of DCS. The decompression strain can be reduced by preoxygenating at sea level.
|
|
| 50. |
- Eiken, Ola, et al.
(author)
-
Dynamic exercise in man as influenced by experimental restriction of blood flow in the working muscles
- 1987
-
In: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 131:3, s. 339-345
-
Journal article (peer-reviewed)abstract
- The effects of reduced muscle perfusion pressure on dynamic exercise performance and cardiovascular and respiratory functions were investigated. Eight subjects were studied during supine cycle ergometry at stepwise increasing workloads until exhaustion with and without the legs exposed to a supra-atmospheric pressure of 50 mmHg (Leg Positive Pressure, LPP), a novel and convenient means of reducing the perfusion pressure in the working muscles. In the LPP condition exercise performance was reduced by 40% which, judging from assessments of perceived exertion, was due to premature muscle fatigue, indicating local or overall underperfusion of the working muscles. At any given work load, the arterial pressure response was considerably stronger during LPP than in the control condition. LPP also caused greater increases in blood lactate concentration and pulmonary ventilation, the differences from control increasing with the work load. Furthermore, the ventilatory equivalent for O2 at a given work load was markedly higher in the LPP than in the control condition, while exercise-induced decreases in end-tidal PCO2 were considerably exaggerated by LPP. The augmented pressor response during flow-restricted exercise, together with the strong ventilatory response which was out of proportion to overall O2 uptake, suggests increased activation of muscle chemoreflexes by accumulation of metabolic end products, the increased pressor response tending to reduce the local flow error in the working muscles.
|
|
