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- Eiken, Ola, et al.
(author)
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Cardiac responses to lower body negative pressure and dynamic leg exercise
- 1985
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In: European Journal of Applied Physiology and Occupational Physiology. - 0301-5548 .- 1432-1025. ; 54:5, s. 451-455
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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.
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| 3. |
- Eiken, Ola
(author)
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Effects of increased muscle perfusion pressure on responses to dynamic leg exercise in man
- 1988
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In: European Journal of Applied Physiology and Occupational Physiology. - 0301-5548 .- 1432-1025. ; 57:6, s. 772-776
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Journal article (peer-reviewed)abstract
- Ventilatory, cardiovascular and metabolic functions and work performance were studied in men performing incremental-load dynamic leg exercise until exhaustion. Part I: Responses to supine exercise were investigated in 8 subjects during exposure of the lower body to subatmospheric pressure at -6.67 kPa (-50 mm Hg) (Lower Body Negative Pressure, LBNP). Due to curtailment of stroke volume, cardiac output was reduced by LBNP over a wide range of work intensities, including heavy loads: ventilation, oxygen uptake and blood lactate concentrations increased with work load, but at lower rates than in the control condition. Part II: In 9 subjects, work performance was compared in three conditions: supine exercise with and without LBNP, and upright exercise. Performance in supine exercise was enhanced by LBNP, and was further improved in upright exercise. In supine exercise, the LBNP-induced reduction in blood lactate and enhancement of work performance are attributed to a more efficient muscle blood flow resulting from increased local perfusion pressure. This strongly suggests that the primary limitation of work performance was set by the peripheral circulation in working muscles rather than by cardiac performance. A similar mechanism may, in part, explain why work performance in dynamic leg exercise was greater in the upright than in the supine posture. It is also concluded that supine leg exercise during LBNP is a useful model of upright exercise, with regard to the central circulation and the circulation in working muscles.
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| 4. |
- Ericson, Mats O
(author)
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Mechanical muscular power output and work during ergometer cycling at different work loads and speeds.
- 1988
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In: European Journal of Applied Physiology and Occupational Physiology. - 0301-5548 .- 1432-1025. ; 57:4, s. 382-7
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Journal article (peer-reviewed)abstract
- The aim of the study was to calculate the magnitude of the instantaneous muscular power output at the hip, knee and ankle joints during ergometer cycling at different work loads and speeds. Six healthy subjects pedalled a weight-braked cycle ergometer at 0, 120 and 240 W at a constant speed of 60 rpm. The subjects also pedalled at 40, 60, 80 and 100 rpm against the same resistance, giving power outputs of 80, 120, 160 and 200 W respectively. The subjects were filmed with a cine-film camera, and pedal reaction forces were recorded from a force transducer mounted in the pedal. The muscular work for the hip, knee and ankle joint muscles was calculated using a model based upon dynamic mechanics and described elsewhere. The total work during one pedal revolution significantly increased with increased work load but did not increase with increased pedalling rate at the same braking force. The relative proportions of total positive work at the hip, knee and ankle joints were also calculated. Hip and ankle extension work proportionally decreased with increased work load. Pedalling rate did not change the relative proportion of total work at the different joints.
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| 5. |
- Ericson, Mats O, et al.
(author)
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Power output and work in different muscle groups during ergometer cycling.
- 1986
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In: European Journal of Applied Physiology and Occupational Physiology. - 0301-5548 .- 1432-1025. ; 55:3, s. 229-35
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Journal article (peer-reviewed)abstract
- The aim of this study was to calculate the magnitude of the instantaneous muscular power output at the hip, knee and ankle joints during ergometer cycling. Six healthy subjects pedalled a weight-braked bicycle ergometer at 120 watts (W) and 60 revolutions per minute (rpm). The subjects were filmed with a cine camera, and pedal reaction forces were recorded from a force transducer mounted in the pedal. The muscular work at the hip, knee and ankle joint was calculated using a model based upon dynamic mechanics described elsewhere. The mean peak concentric power output was, for the hip extensors, 74.4 W, hip flexors, 18.0 W, knee extensors, 110.1 W, knee flexors, 30.0 W and ankle plantar flexors, 59.4 W. At the ankle joint, energy absorption through eccentric plantar flexor action was observed, with a mean peak power of 11.4 W and negative work of 3.4 J for each limb and complete pedal revolution. The energy production relationships between the different major muscle groups were computed and the contributions to the total positive work were: hip extensors, 27%; hip flexors, 4%; knee extensors, 39%; knee flexors, 10%; and ankle plantar flexors 20%.
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| 6. |
- Gudmundson, Peter
(author)
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On The Accuracy Of The Harmonic-Balance Method Concerning Vibrations Of Beams With Nonlinear Supports.
- 1989
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In: Archive of applied mechanics (1991). - 0939-1533 .- 1432-0681. ; 59:5, s. 333-344
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Journal article (peer-reviewed)abstract
- A homogeneous beam supported by a nonlinear cubic rotational spring and excited by a prescribed harmonic translational motion was analysed by the harmonic balance method. Harmonic and subharmonicsolutions were determined as functions of frequency, excitation amplitude and material damping.The results were verified against numerical time integrations of the governing nonlinear differential equations.The numerical method was based on a component mode synthesis technique, using free normal modes and inertia relief attachment modes. It was found that the predictions by the harmonic balance method werein excellent agreement with the numerical solution in a frequency interval covering the three first cantileveredeigen frequencies of the beam. The only exceptions were two narrow frequency intervals in which the numerical solution showed quasi periodic oscillations.
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| 7. |
- Ivanova, L N, et al.
(author)
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Decrease in the response to ADH of the rat kidney as a result of early postnatal treatment with cortisol.
- 1987
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In: Pflügers Archiv. - 0031-6768 .- 1432-2013. ; 408:4, s. 328-32
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Journal article (peer-reviewed)abstract
- Wistar rats were injected just once, intraperitoneally with cortisol (1 microgram/g) or saline at the age of 5 days. The cortisol-treated rats did not differ significantly in the (U/P)osm ratio from the saline-treated controls before 15 days of life. Their response to ADH was distinct but weaker than in the saline controls aged 30 days. This reduced response persisted to 60 days of life. In the collecting tubule fragments, (3H)AVP specific binding was lower in the cortisol-treated rats than in the controls at the age of 20 and 60 days. There was no (3H)AVP specific binding in the proximal convoluted tubules in the cortisol- and saline-injected rats of both ages. The ontogenetic patterns of cAMP specific binding in the papillary cytosolic fraction were different: the early increase in cAMP binding was protracted in the cortisol-treated rats, and no peak appeared at the age of 25 days. Cytosolic protein kinase activity was lower, no peak appeared at 30 days, no activation of protein kinase occurred to the end of weaning in the cortisol-treated rats. The difference between the cortisol and saline groups was abolished by day 30. The interference of cortisol with the ontogenetic changes in AVP binding capacity and cAMP-dependent protein kinase appears to be a plausible cause of the altered development of the response to ADH.
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| 9. |
- Mekjavic, I. B., et al.
(author)
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The pattern of breathing during hypoxic exercise
- 1987
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In: European Journal of Applied Physiology and Occupational Physiology. - 0301-5548 .- 1432-1025. ; 56:6, s. 619-622
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Journal article (peer-reviewed)abstract
- Breathing pattern was studied in six subjects in normoxia (FIO2 = 0.21) and hypoxia (FIO2 = 0.12) at rest and during incremental work-rate exercise. Ventilation (V) as well as mean inspiratory flow (VT/TI) increased with exercise intensity and were augmented in the hypoxic environment, whereas the ratio between inspiratory (TI) and total (Ttot) breath durations increased with exercise intensity but was unaffected by hypoxia. The relationship of tidal volume (VT) and inspiratory time duration (TI) showed linear, coinciding ranges for the normoxic and hypoxic conditions up to VT/TI values of about 2.5 1.s-1. At higher VT/TI values TI continued to decrease, whereas VT tended to level off, an effect which was more evident in the hypoxic condition. The results suggest that the hypoxic augmentation of exercise hyperpnea is primarily brought about by an enhancement of central inspiratory drive, the timing component being largely unaffected by the hypoxic environment, and that at low to moderate levels of exercise hyperpnea inspiratory off-switch mechanisms are essentially unaffected by moderate hypoxia.
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| 10. |
- Szepessy, Anders, 1960-
(author)
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Measure valued solutions of scalar conservation laws with boundary conditions
- 1989
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In: Archive for Rational Mechanics and Analysis. - NEW YORK : Springer-Verlag New York. - 0003-9527 .- 1432-0673. ; 107:2, s. 181-193
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Journal article (peer-reviewed)abstract
- We define a solution concept for measure-valued solutions to scalar conservation laws with initial conditions and boundary conditions and prove a uniqueness theorem for such solutions. This result may be used to prove convergence, towards the unique solution, for approximate solutions which are uniformly bounded in L∞, weakly consistent with certain entropy inequalities and strongly consistent with the initial condition, i.e. without using derivative estimates. As an example convergence of a finite element method is demonstrated.
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