| 1. |
- Arvedsen, SK, et al.
(författare)
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Body height and arterial pressure in seated and supine young males during +2 G centrifugation
- 2015
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Ingår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 309:9
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
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| 3. |
- Eiken, Ola, et al.
(författare)
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Human cardiovascular adaptation to hypergravity.
- 2022
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Ingår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 322:6, s. R597-R608
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Tidskriftsartikel (refereegranskat)abstract
- Despite decades of experience from high-G exposures in aircraft and centrifuges, information is scarce regarding primary cardiovascular adaptations to +Gz loads in relaxed humans. Thus, effects of G-training are typically evaluated after regimens that are confounded by concomitant use of anti-G straining maneuvers, anti-G suits and pressure breathing. Accordingly, the aim was to evaluate cardiovascular adaptations to repeated +Gz exposures in the relaxed state. Eleven men underwent 5 weeks of centrifuge G training, consisting of 15 × 40 min +Gz exposures at G levels close to their individual relaxed G-level tolerance. Before and after the training regimen, relaxed G-level tolerance was investigated during rapid (ROR) and gradual (GOR) onset-rate G exposures, and cardiovascular responses were investigated during orthostatic provocation and vascular pressure-distension tests. The G training resulted in: (i) a 13% increase in relaxed ROR G tolerance (P < 0.001), but no change in GOR G tolerance, (ii) increased pressure resistance in the arteries and arterioles of the legs (P < 0.001), but not the arms, (iii) a reduced initial drop in arterial pressure upon ROR high G, but no change in arterial pressure under basal resting conditions or during GOR G loading, or orthostatic provocation. The results suggest +Gz adaptation via enhanced pressure resistance in dependent arteries/arterioles. Presumably this reflects local adaptations to high transmural pressures, resulting from the +Gz-induced exaggeration of the intravascular hydrostatic pressure gradients.
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| 4. |
- Elia, Antonis, Dr, et al.
(författare)
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Effects of hyperventilation on repeated breath-holding while in a fasting state: do risks outweigh the benefits?
- 2024
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Ingår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : the American Physiological Society. - 0363-6119 .- 1522-1490. ; 326, s. R319-R329
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Tidskriftsartikel (refereegranskat)abstract
- Breath-holding preceded by either an overnight fast or hyperventilation has been shown to potentiate the risk of a hypoxic blackout. However, no study has explored the combined effects of fasting and hyperventilation on apneic performance and associated physiological responses. Nine nondivers (8 males) attended the laboratory on two separate occasions (≥48 h apart), both after a 12-h overnight fast. During each visit, a hyperoxic rebreathing trial was performed followed by three repeated maximal static apneas preceded by either normal breathing (NORM) or a 30-s hyperventilation (HYPER). Splenic volume, hematology, cardiovascular, and respiratory variables were monitored. There were no interprotocol differences at rest or during hyperoxic rebreathing for any variable (P ≥ 0.09). On nine occasions (8 in HYPER), the subjects reached our safety threshold (oxygen saturation 65%) and were asked to abort their apneas, with the preponderance of these incidents (6 of 9) occurring during the third repetition. Across the sequential attempts, longer apneas were recorded in HYPER [median(range), 220(123–324) s vs. 185(78–296) s, P ≤ 0.001], with involuntary breathing movements occurring later [134(65–234) s vs. 97(42–200) s, P ≤ 0.001] and end-apneic partial end-tidal pressures of oxygen (PETO2) being lower (P ≤ 0.02). During the final repetition, partial end-tidal pressure of carbon dioxide [(PETCO2), 6.53 ± 0.46 kPa vs. 6.01 ± 0.45 kPa, P = 0.005] was lower in HYPER. Over the serial attempts, preapneic tidal volume was gradually elevated [from apnea 1 to 3, by 0.26 ± 0.24 L (HYPER) and 0.28 ± 0.30 L (NORM), P ≤ 0.025], with a correlation noted with preapneic PETCO2 (r = −0.57, P < 0.001) and PETO2 (r = 0.76, P < 0.001), respectively. In a fasted state, preapnea hyperventilation compared with normal breathing leads to longer apneas but may increase the susceptibility to a hypoxic blackout.
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| 5. |
- Elia, Antonis, Dr, et al.
(författare)
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The effect of dietary intake on apneic performance, cardiovascular and splenic responses during repeated breath holds
- 2022
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Ingår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 323:6, s. R839-R848
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Tidskriftsartikel (refereegranskat)abstract
- Static apneas performed after an overnight fast as opposed to postprandially have been evinced to improve apneic performance. However, no study has explored the effect of dietary intake on apneic performance, cardiovascular or splenic responses over a series of repeated apneas. Ten healthy adults attended the laboratory on three separate occasions (>48-h apart): after a 14-h fast (F14), 1 h postconsumption of a high-calorie, high-carbohydrate (HCHC) meal, or 1 h postconsumption of a low-calorie, low-carbohydrate (LCLC)-based meal. During each visit, the subjects performed a hyperoxic rebreathing trial and a series of three repeated maximal static apneas. Heart rate, peripheral oxyhemoglobin saturation (Sp(O2)), and gas exchange were monitored continuously, whereas splenic volume (SV) and hematology were assessed after the rebreathing and apneas. At rest, after HCHC, the respiratory exchange ratio (0.87 +/- 0.17, P < 0.043), expired minute volume of carbon dioxide (CO2; HCHC, 0.35 +/- 0.09 L/min, P < 0.014), and SV (227 +/- 45 mL, P < 0.031) were higher compared with F14 (0.71 +/- 0.08; 0.23 +/- 0.04 L/min; 204 +/- 49 mL) and LCLC (0.72 +/- 0.07; 0.25 +/- 0.03 L/min; 199 +/- 49 mL). A faster CO2 accumulation was recorded during the HCHC (96 +/- 35 s) rebreathing trial (F14, 162 +/- 42 s, P = 0.001; LCLC, 151 +/- 23 s, P = 0.002). Longer apneas were reported in F14 compared with HCHC (apneas 1-3, P < 0.046) and LCLC (apneas 2-3, P < 0.006). After the first apnea, SV was lower in F14 (141 +/- 43 mL, P = 0.015) compared with HCHC (180 +/- 34 mL). Moreover, after the third apnea, end-tidal partial pressure of oxygen and nadir Spo t were lower in F14 (8.6 +/- 2.2 kPa, P = 0.028; 77 +/- 13%, P = 0.009) compared with HCHC (10.1 +/- 1.7 kPa; 84 +/- 9%). No differences were measured in end-apneic end-tidal partial pressure of CO2, heart rate nor hematology across diets. Fasting improved apneic performance with apneas being terminated at lower oxygen levels through altering the rate of CO2 accumulation but without affecting the cardiovascular responses.
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| 6. |
- Keramidas, Michail E., Assistant Professor, et al.
(författare)
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Acral skin vasoreactivity and thermosensitivity to hand cooling following 5 days of intermittent whole body cold exposure
- 2022
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Ingår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 323:1, s. R1-R15
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Tidskriftsartikel (refereegranskat)abstract
- We sought to examine whether short-term, whole body cold acclimation would modulate finger vasoreactivity and thermosensitivity to localized cooling. Fourteen men were equally assigned to either the experimental (CA) or the control (CON) group. The CA group was immersed to the chest in 14°C water for ≥120 min daily over a 5-day period while the skin temperature of the right-hand fingers was clamped at ∼35.5°C. The CON group was instructed to avoid any cold exposure during this period. Before and after the intervention, both groups performed, on two different consecutive days, a local cold provocation trial consisting of a 30-min hand immersion in 8°C water while immersed to the chest once in 21°C (mild-hypothermic trial; 0.5°C fall in rectal temperature from individual preimmersion values) and on the other occasion in 35.5°C (normothermic trial). In the CA group, the cold-induced reduction in finger temperature was less (mild-hypothermic trial: P = 0.05; normothermic trial: P = 0.02), and the incidence of the cold-induced vasodilation episodes was greater (in normothermic trials: P = 0.04) in the post- than in the preacclimation trials. The right-hand thermal discomfort was also attenuated (mild-hypothermic trial: P = 0.04; normothermic trial: P = 0.01). The finger temperature responses of the CON group did not vary between testing periods. Our findings suggest that repetitive whole body exposure to severe cold within a week may attenuate finger vasoreactivity and thermosensitivity to localized cooling. These regional thermo-adaptions were ascribed to central neural habituation produced by the iterative, generalized cold stimulation.
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| 7. |
- Keramidas, Michail E., Assistant Professor, et al.
(författare)
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Differential responsiveness of glabrous and non-glabrous skin to local transmural pressure elevations; the impact of 5 weeks of iterative local pressure loading
- 2021
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Ingår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 321:5, s. R742-R750
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Tidskriftsartikel (refereegranskat)abstract
- We examined the in vivo pressure-flow relationship in human cutaneous vessels during acute and repeated elevations of local transmural pressure. In 10 healthy men, red blood cell flux was monitored simultaneously on the nonglabrous skin of the forearm and the glabrous skin of a finger during a vascular pressure provocation, wherein the blood vessels of an arm were exposed to a wide range of stepwise increasing distending pressures. Forearm skin blood flux was relatively stable at slight and moderate elevations of distending pressure, whereas it increased approximately three- to fourfold at the highest levels ( P = 0.004). Finger blood flux, on the contrary, dropped promptly and consistently throughout the provocation ( P < 0.001). Eight of the subjects repeated the provocation trial after a 5-wk pressure-training regimen, during which the vasculature in one arm was exposed intermittently (40 min, 3 times/wk) to increased transmural pressure (from +65 mmHg week 1 to +105 mmHg week 5). The training regimen diminished the pressure-induced increase in forearm blood flux by ∼34% ( P = 0.02), whereas it inhibited the reduction in finger blood flux ( P < 0.001) in response to slight and moderate distending pressure elevations. The present findings demonstrate that during local pressure perturbations, the cutaneous autoregulatory function is accentuated in glabrous compared with in the nonglabrous skin regions. Prolonged intermittent regional exposures to augmented intravascular pressure blunt the responsiveness of the glabrous skin but enhance arteriolar pressure resistance in the nonglabrous skin.
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| 8. |
- Keramidas, Michail E., Assistant Professor, et al.
(författare)
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In vivo pressure-flow relation of human cutaneous vessels following prolonged iterative exposures to hypergravity
- 2023
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Ingår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 325:1, s. R21-R30
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Tidskriftsartikel (refereegranskat)abstract
- The study examined intra- and interlimb variations in cutaneous vessel responsiveness to acute and repeated transmural pressure elevations. In 11 healthy men, red blood cell flux was assessed via laser-Doppler flowmetry on both glabrous and nonglabrous skin regions of an arm (finger and forearm) and leg (toe and lower leg), across a wide range of stepwise increasingdistending pressures imposed in the vessels of each limb separately. The pressure-flux cutaneous responses were evaluatedbefore and after 5 wk of intermittent (40 min, 3 sessions per week) exposures to hypergravity (2.6–3.3 G; G training). Beforeand after G training, forearm and lower leg blood flux were relatively stable up to 210 and 240 mmHg distending pressures,respectively; and then they increased two- to threefold (P < 0.001). Finger blood flux dropped promptly (P < 0.001), regardlessof the G training (P = 0.64). At 120-mmHg distending pressures, toe blood flux enhanced by 40% (P 0.05); the increasewas augmented after the G training (P = 0.01). At high distending pressures, toe blood flux dropped by 70% in both trials (P <0.001). The present results demonstrate that circulatory autoregulation is more pronounced in glabrous skin than in nonglabrousskin, and in nonglabrous sites of the leg than in those of the arm. Repetitive high-sustained gravitoinertial stress does not modifythe pressure-flow relationship in the dependent skin vessels of the arm nor in the nonglabrous sites of the lower leg. Yet it maypartly inhibit the myogenic responsiveness of the toe’s glabrous skin.
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| 9. |
- Keramidas, Michail E., et al.
(författare)
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Interactions of mild hypothermia and hypoxia on finger vasoreactivity to local cold stress
- 2019
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Ingår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : AMER PHYSIOLOGICAL SOC. - 0363-6119 .- 1522-1490. ; 317:3, s. R418-R431
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Tidskriftsartikel (refereegranskat)abstract
- We examined the interactive effects of mild hypothermia and hypoxia on finger vasoreactivity to local cold stress. Eight male lowlanders performed, in a counterbalanced order, a normoxic and a hypoxic (partial pressure of oxygen: similar to 12 kPa) hand cold provocation (consisting of a 30-min immersion in 8 degrees C water), while immersed to the chest either in 21 degrees C [cold trials; 0.5 degrees C fall in rectal temperature (T-rec) from individual preimmersion values], or in 35.5 degrees C water, or while exposed to 27 degrees C air. The duration of the trials was kept constant in each breathing condition. Physiological (T-rec, skin temperature, cutaneous vascular conductance, oxygen uptake) and perceptual (thermal sensation and comfort, local pain, affective valence) reactions were monitored continually. Hypoxia accelerated the drop in T-rec by similar to 14 min (P = 0.06, d = 0.67). In the air-exposure trials, hypoxia did not alter finger perfusion during the local cooling. whereas it impaired the finger rewarming response following the cooling (P < 0.01). During the 35.5 degrees C immersion, the finger vasomotor tone was enhanced, especially in hypoxia (P = 0.01). Mild hypothermia aggravated finger vasoconstriction instigated by local cooling (P < 0.01), but the response did not differ between the two breathing conditions (P > 0.05). Hypoxia tended to attenuate the sensation of coldness (P = 0.10, r = 0.40) and thermal discomfort (P = 0.09, r = 0.46) in the immersed hand. Both in normoxia and hypoxia, the whole body thermal state dictates the cutaneous vasomotor reactivity to localized cold stimulus.
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| 10. |
- Moes, Maaike I., et al.
(författare)
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Combined effects of mild hypothermia and nitrous-oxide-induced narcosis on manual and cognitive performance
- 2024
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Ingår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 326:3, s. R197-R209
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Tidskriftsartikel (refereegranskat)abstract
- Divers are at enhanced risk of suffering from acute cognitive deteriorations, due to the low ambient temperatures, and the narcotic action of inert gases inspired at high pressures. Yet, the behavioral effects of cold and inert-gas narcosis have commonly been assessed in isolation, and during short-term provocations. We, therefore, evaluated the interactive influence of mild hypothermia and narcosis engendered by a subanaesthetic dose of nitrous oxide (N2O; a normobaric intervention analogue of hyperbaric nitrogen) on cognitive function during prolonged iterative exposure. Fourteen men partook in two ~12-h sessions (separated by ≥4 days), wherein they performed sequentially three 120-min cold (20°C) water immersions (CWIs), while inhaling, in a single-blinded manner, either normal air, or a normoxic gas mixture containing 30% N2O. CWIs were separated by 120-min rewarming in room-air breathing conditions. Prior to the first CWI and during each CWI, subjects performed a finger dexterity test, and the Spaceflight Cognitive Assessment Tool for Windows (WinSCAT) test assessing aspects of attention, memory, learning and visuo-spatial ability. Rectal and skin temperatures were, on average, reduced by ~1.2°C and ~8°C, respectively (P<0.001). Cooling per se impaired (P≤0.01) only short-term memory (~37%) and learning (~18%); the impairments were limited to the first CWI. N2O also attenuated (P≤0.02) short-term memory (~37%) and learning (~35%), but the reductions occurred in all CWIs. Further, N2O invariably compromised finger dexterity, attention, concentration, working memory and spatial processing (P<0.05). Present results demonstrate that inert-gas narcosis aggravates, in a persistent manner, basic and higher-order cognitive abilities during protracted cold exposure.
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