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| 2. |
- 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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| 5. |
- Eiken, Ola, et al.
(författare)
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A new hydrostatic anti-G suit vs. a pneumatic anti-G system : Preliminary comparison
- 2002
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Ingår i: Aviation, Space and Environmental Medicine. - 0095-6562 .- 1943-4448. ; 73:7, s. 703-708
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Tidskriftsartikel (refereegranskat)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.
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| 6. |
- Eiken, Ola, et al.
(författare)
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Adaptation to 5 weeks of intermittent local vascular pressure increments; Mechanisms to be considered in the development of primary hypertension?
- 2021
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Ingår i: American Journal of Physiology. Heart and Circulatory Physiology. - : American Physiological Society. - 0363-6135 .- 1522-1539. ; 320:4, s. H1303-H1312
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Tidskriftsartikel (refereegranskat)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.
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| 7. |
- Eiken, Ola, et al.
(författare)
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Blood pressure regulation V : in vivo mechanical properties of precapillary vessels as affected by long-term pressure loading and unloading
- 2014
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Ingår i: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 114:3, s. 499-509
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Forskningsöversikt (refereegranskat)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.
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| 8. |
- Eiken, Ola, et al.
(författare)
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G tolerance vis-à-vis pressure-distension and pressure-flow relationships of leg arteries
- 2012
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Ingår i: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 112:10, s. 3619-3627
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Tidskriftsartikel (refereegranskat)abstract
- During increased gravitoinertial (G) load in the head-to-foot direction, pressures in dependent vascular beds are commonly raised to levels capable of distending precapillary vessels, which, in turn, may reduce arterial pressure, and hence compromise the capacity to withstand G load (G tolerance). We hypothesized that distensibility in precapillary leg vessels would be lower in a group of subjects possessing high G tolerance (H; n = 7; relaxed G tolerance = 6.6 ± 0.8 G) than in a group with low G tolerance (L; n = 8; G tolerance = 3.9 ± 0.3 G). The groups were matched with regard to gender, age, weight, height, and resting arterial pressure. Arterial pressure-distension and pressure-flow experiments were performed with the subject supine in a pressure chamber with a lower leg protruding to the outside. Increased intravascular pressure in the blood vessels of the outside leg was accomplished by stepwise increasing chamber pressure to 240 mmHg. Diameter and flow in the posterior tibial artery were measured by ultrasonographic/Doppler techniques. Pressure-induced increments in arterial diameter and flow were more pronounced (p < 0.03) in the L (14.1 ± 4.2% and 32 ± 21 ml/min respectively) than in the H (1.7 ± 5.0% and 1.6 ± 25 ml/min) group, and the pressure thresholds at which these increments commenced were lower (by 52 and 48 mmHg, respectively) in the L than in the H group (p < 0.04). Negative correlations were observed between G tolerance and the increments in diameter and flow (p < 0.02). Thus, the wall stiffness of precapillary leg vessels is greater in individuals with high relaxed G tolerance; whether a causal relationship exists remains to be established.
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| 9. |
- 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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