| 1. |
- Baer, R, et al.
(författare)
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Effects of continuous positive- and negative-pressure breathing on the pattern of breathing in man during exercise.
- 1989
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 137:2, s. 301-7
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
- Eiken, Ola, et al.
(författare)
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Characteristics of the carotid baroreflex in man during normal and flow-restricted exercise
- 1992
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 144:3, s. 325-331
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Tidskriftsartikel (refereegranskat)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.
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| 3. |
- Eiken, Ola, et al.
(författare)
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Comparison of vascular distensibility in the upper and lower extremity
- 2004
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 181:3, s. 281-287
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Eiken, Ola, et al.
(författare)
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Dynamic exercise in man as influenced by experimental restriction of blood flow in the working muscles
- 1987
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 131:3, s. 339-345
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Tidskriftsartikel (refereegranskat)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.
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| 5. |
- Eiken, Ola, et al.
(författare)
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Effects of blood-volume distribution on the characteristics of the carotid baroreflex in humans at rest and during exercise
- 1994
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 150:1, s. 89-94
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Tidskriftsartikel (refereegranskat)abstract
- Seven supine subjects were studied at rest and during mild to moderate dynamic leg exercise with and without unloading of the cardiopulmonary baroreceptors accomplished by exposing the lower portion of the body to a subatmospheric pressure of 20 mmHg (Lower Body Negative Pressure, LBNP). The function of the cardiac branch of the carotid baroreflex was studied over its full operational range by measuring R-R intervals during application of pulse synchronous graded pressures (40 to -65 mmHg) in a neck-chamber device. Raising the carotid transmural pressure (systolic arterial pressure minus neck-chamber pressure) induced increasing R-R intervals in all conditions. In conformity with previous results from our laboratories it was found that the maximal rate of change in relative R-R intervals and the corresponding transmural pressure were higher during exercise than at rest, indicating that exercise increased the carotid baroreflex sensitivity and shifted its optimal buffering range to higher arterial pressures. LBNP did not affect the characteristics of the reflex at rest nor during exercise. It is concluded that reduced central venous pressure with consequent selective cardiopulmonary receptor disengagement exerts no influence on the carotid baroreflex control of heart rate (HR), as tested over the entire arterial pressure-effector response relation, either at rest or during mild-moderate exercise.
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| 6. |
- Eiken, Ola, et al.
(författare)
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Effects of blood volume distribution on ventilatory variables at rest and during exercise
- 1986
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 127:4, s. 507-512
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Tidskriftsartikel (refereegranskat)abstract
- Ventilatory variables and heart rate (HR) were investigated in eight supine subjects during dynamic leg exercise at 0 and 100 W with and without the lower portion of the body exposed to a pressure of -50 mmHg (lower body negative pressure, LBNP). Resting values of inspired minute volume (V1), and respiratory drive in terms of mouth occlusion pressure (P0.1) were unchanged, whereas HR was higher during LBNP than in the control condition. Exercise values for HR in steady state were not affected by LBNP, whereas V1 was 15 and 11% lower and P0.1 was 20 and 11% lower in this condition at the 0 and 100 W workload levels, respectively. Time courses for V1 at the onset of 100 W exercise were similar with and without exposure to LBNP, indicating that the sudden increase in venous return occurring upon onset of pedalling during LBNP affords no significant stimulus in the initial development of exercise hyperpnoea. That exercise ventilation and P0.1 in steady state were reduced by LBNP suggests diminished humoral and/or locally induced chemical drive due to improved blood flow in exercising muscles resulting in reduced production of muscle metabolites or facilitation of their removal.
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| 7. |
- Eiken, Ola, et al.
(författare)
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Effects of hyperoxia and hypoxia on dynamic and sustained static performance of the human quadriceps muscle
- 1984
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 122:4, s. 629-633
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Tidskriftsartikel (refereegranskat)abstract
- The influence of variations in inspired PO2 on dynamic and static muscle performance of the left quadriceps muscle was studied. Eight subjects performed (1) 60 maximal consecutive dynamic contractions and (2) one sustained exhaustive static contraction at 27% of maximal voluntary contraction (MVC). Breathing mixtures containing 11%, 21% or 99% O2, were administered. Peak torque as an average of the 60 knee extensions was higher (p less than 0.01) during hyperoxia (mean +/- SE = 104 +/- 4 Nm) than during normoxia (98 +/- 4 Nm), but did not differ significantly between hypoxia (95 +/- 5 Nm) and normoxia. Peak torque of individual extensions declined more rapidly during hypoxia than during normoxia, differing in the final 12 extensions by 11% from normoxic values. Static endurance time was reduced (p less than 0.02) during hypoxia (152 +/- 12 s) as compared to normoxia (189 +/- 13 s) and hyperoxia (169 +/- 11 s). No significant difference in endurance time was demonstrated between hyperoxia and normoxia. Thus, hypoxia impaired muscle performance in both dynamic and sustained static exercise, whereas acute hyperoxia improved dynamic but not static muscle performance. The results are interpreted in terms of differences in rate of intramuscular H+ accumulation.
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| 8. |
- Eiken, Ola, et al.
(författare)
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Ischaemia in working muscles potentiates the exercise-induced sweating response in man
- 2004
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 181:3, s. 305-311
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Tidskriftsartikel (refereegranskat)abstract
- AIM: The purpose was to examine whether graded ischaemia in the working muscles affects the rate of sweating and the control of exercise core temperature. METHODS: Eight subjects performed cycle ergometry exercise in the supine position with (ischaemic exercise) and without (control exercise) restriction of blood flow in the contracting muscles, accomplished by exposure of the legs to a supra-atmospheric pressure of 6.6 kPa. Each subject performed one exhaustive incremental work rate trial and one steady-state exercise trial (at 33% of control peak work rate), in both the control and ischaemia conditions. RESULTS: Ischaemia decreased work performance by 45% so that in this condition the steady-state work rate level corresponded to 63% of ischaemic peak work rate. Ischaemia did not affect the oesophageal temperature equilibrium in the steady-state trials, but potentiated the exercise sweating response. Exercise responses of mean arterial pressure, heart rate and pulmonary ventilation were potentiated by ischaemia. CONCLUSION: During ischaemic exercise sweat secretion was potentiated by non-thermal and/or local thermal stimuli.
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| 9. |
- Esbjörnsson, M, et al.
(författare)
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Muscle fibre types and enzyme activities after training with local leg ischaemia in man.
- 1993
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 148:3, s. 233-41
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Tidskriftsartikel (refereegranskat)abstract
- Eight healthy men performed supine one-legged training on a bicycle ergometer 45 min per leg four times per week for 4 week. The ergometer and lower body were inside a pressure chamber, the opening of which was sealed at the level of the crotch. One leg trained with impeded leg blood flow (I-leg), induced by an increased (50 mmHg) chamber pressure, at the highest tolerable intensity. The contralateral leg trained at the same power under normal pressure (N-leg). Before and after training biopsies were taken from the vastus lateralis of both legs and maximal one-legged exercise tests were executed with both legs. Biopsies were repeated when the subjects had been back to their habitual physical activity for 3 months. Training increased exercise time to exhaustion, but more in the I-leg than in the N-leg. After training, the I-leg had higher activity of citrate synthase (CS), a marker of oxidative capacity, and lower activity of the M-subunit of lactate dehydrogenase isoenzymes. It also had a higher percentage of type-I fibres and a lower percentage of IIB fibres, larger areas of all fibre types and a greater number of capillaries per fibre. It is concluded that ischaemic training changes the muscle metabolic profile in a direction facilitating aerobic metabolism. An altered fibre-type composition may contribute, but is not enough prerequisite for the change.
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| 10. |
- Mekjavic, I. B., et al.
(författare)
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Inhibition of shivering in man by thermal stimulation of the facial area
- 1985
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Ingår i: Acta Physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 125:4, s. 633-637
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Tidskriftsartikel (refereegranskat)abstract
- The contribution of the facial thermoreceptors to thermoregulatory shivering was studied. Seven subjects were exposed to -3 degrees C ambient air for 1 h. Radiant heat was applied to the facial area during 30 s periods at 10 min intervals and the effects on the integrated electromyographic activity (IEMG) in the brachial biceps, trapezius and femoral rectus muscles, and on the heart rate (HR) were studied. During cold-air exposure mean skin temperature as measured at four sites decreased by 15.5 +/- 0.6 degrees C (mean +/- SE) while rectal temperature remained virtually unchanged. During the radiant heat exposures IEMG activity decreased by 18.9 +/- 2.3%; HR decreased by 11 +/- 1 beats min-1. The changes in IEMG occurred within or slightly below the range of maximum cold receptor sensitivity (20-30 degrees C) and coincided with the maximum rate of change in chin temperature. The observed inhibition of shivering IEMG during locally applied facial heat stimulation suggest that the trigeminal region contributes an important input to the overall thermoregulatory responses.
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