| 1. |
- Calbet, Jose A. L., et al.
(författare)
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On the mechanisms that limit oxygen uptake during exercise in acute and chronic hypoxia: role of muscle mass
- 2009
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Ingår i: Journal of Physiology. - : Wiley. - 1469-7793 .- 0022-3751. ; 587:2, s. 477-490
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Tidskriftsartikel (refereegranskat)abstract
- Peak aerobic power in humans ((V) over dot(O2), peak) is markedly affected by inspired O-2 tension (F-IO2). The question to be answered in this study is what factor plays a major role in the limitation of muscle peak. (V) over dot(O2) in hypoxia: arterial O-2 partial pressure (P-a,(O2)) or O-2 content (C-a,C-O2)? Thus, cardiac output (dye dilution with Cardio-green), leg blood flow (thermodilution), intra-arterial blood pressure and femoral arterial-to-venous differences in blood gases were determined in nine lowlanders studied during incremental exercise using a large (two-legged cycle ergometer exercise: Bike) and a small (one-legged knee extension exercise: Knee) muscle mass in normoxia, acute hypoxia (AH) (F-IO2 = 0.105) and after 9 weeks of residence at 5260 m (CH). Reducing the size of the active muscle mass blunted by 62% the effect of hypoxia on. (V) over dot(O2,peak) in AH and abolished completely the effect of hypoxia on. (V) over dot(O2,peak) after altitude acclimatization. Acclimatization improved Bike peak exercise Pa, O-2 from 34 +/- 1 in AH to 45 +/- 1 mmHg in CH(P < 0.05) and Knee Pa, O-2 from 38 +/- 1 to 55 +/- 2 mmHg(P < 0.05). Peak cardiac output and leg blood flow were reduced in hypoxia only during Bike. Acute hypoxia resulted in reduction of systemic O-2 delivery (46 and 21%) and leg O-2 delivery (47 and 26%) during Bike and Knee, respectively, almost matching the corresponding reduction in. (V) over dot(O2,peak). Altitude acclimatization restored fully peak systemic and leg O-2 delivery in CH (2.69 +/- 0.27 and 1.28 +/- 0.11 l min(-1), respectively) to sea level values (2.65 +/- 0.15 and 1.16 +/- 0.11 l min(-1), respectively) during Knee, but not during Bike. During Knee in CH, leg oxygen delivery was similar to normoxia and, therefore, also. (V) over dot(O2,peak) in spite of a P-a,P-O2 of 55 mmHg. Reducing the size of the active muscle mass improves pulmonary gas exchange during hypoxic exercise, attenuates the Bohr effect on oxygen uploading at the lungs and preserves sea level convective O-2 transport to the active muscles. Thus, the altitude-acclimatized human has potentially a similar exercising capacity as at sea level when the exercise model allows for an adequate oxygen delivery (blood flow x C-a,C-O2), with only a minor role of P-a,P-O2 per se, when P-a,P-O2 is more than 55 mmHg.
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| 2. |
- Osada, Takuya, et al.
(författare)
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Alterations in the blood velocity profile influence the blood flow response during muscle contractions and relaxations
- 2006
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Ingår i: Journal of Physiological Sciences. - 1880-6546. ; 56:3, s. 195-203
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Tidskriftsartikel (refereegranskat)abstract
- The present study examined the influences of the muscle contraction (MCP) and relaxation (MRP) phases, as well as systole and diastole, on the blood velocity profile and flow in the conduit artery at different dynamic muscle contraction forces. Eight healthy volunteers performed one-legged dynamic knee-extensor exercise at work rates of 5, 10, 20, 30, and 40 W at 60 contractions per minute. The time- and space-averaged, amplitude-weighted, mean (V-mean) and maximum (V-max) blood flow velocities were continuously measured in the common femoral artery during the cardiosystolic (CSP) and cardiodiastolic (CDP) phases during MCP and MRP, respectively. The V-max/V-mean ratio was used as a flow profile index where a ratio of approximately (similar to) 1 indicates a "flat" velocity profile, and a ratio significantly greater than (>>) 1 indicates a "parabolic" velocity profile. At rest, a "steeper' parabolic velocity profile was found during the CDP (ratio: 1.75 +/- 0.06) than during the CSP (ratio: 1.31 +/- 0.02). During the MRP of exercise, the V-max/V-mean ratio shifted to be less steep (p < 0.05) than at rest during the CDP (ratio: 1.41-1.54) at 5, 10, 20, 30, and 40 W; whereas it was slightly higher (p < 0.05) at 30 and 40 W than at rest during the CSP (ratio: 1,43-1.46). During the MCP, the parabolic blood velocity profile was enhanced (p < 0.05) at higher contraction forces, >= 20W during the CDP (ratio: 2.15-2.52) and >= 30W during the CSP (ratio: 1.49-1.77), potentially because of a greater retrograde flow component. A higher blood flow furthermore appeared during the MRP compared to during the MCP, coinciding with a greater uniformity of the red blood cells moving at higher blood velocities during the MRP. Thus part of the difference in the magnitude of blood flow during the MRP vs. MCP may be due to the alterations of the blood velocity flow profile.
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| 3. |
- Osada, T, et al.
(författare)
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Alterations in the rheological artery during rhythmic thigh flow profile in conduit femoral muscle contractions in humans
- 2005
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Ingår i: Japanese Journal of Physiology. - 0021-521X. ; 55:1, s. 19-28
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Tidskriftsartikel (refereegranskat)abstract
- The present study examined the rheological blood velocity profile in the conduit femoral artery during rhythmic muscle contractions at different muscle forces. Eight healthy volunteers performed one-legged, dynamic knee-extensor exercise at work rates of 5, 10, 20, 30, and 40 W at 60 contractions per minute. The time and space-averaged, amplitude-weighted mean ( V-mean) and maximum (V-max) blood flow velocities in the common femoral artery were measured during the cardiosystolic phase (CSP) and cardiodiastolic phase (CDP) by the Doppler ultrasound technique. The V-max /V-mean ratio was used as a flow profile index, in which a ratio of similar to 1 indicates a m m "flat velocity flow profile" and a ratio significantly > 1 indicates a "parabolic velocity flow profile ' " At rest, the V-max / V-mean ratio was similar to 1.3 and similar to 1.8 during the CSP and CDP, respectively. The V-max/V-mean ratio was higher (p < 0.01) during the CDP than during the CSP, both at rest and at all work rates. The V-max/V-mean ratio during the CSP was higher Max (p < 0.01) at 30 and 40 W compared to at rest. The V-max/V-mean ratio during the CDP was lower (p < 0.05) at 5 and 10 W compared to at rest. There was a positive linear correlation between blood flow and incremental work rates during both the CSP and CDP, respectively. Thus under resting conditions, the findings indicate a "steeper" parabolic velocity profile during the CDP than during the CSR The velocity profile during the CDP furthermore shifts to being less "steep" during rhythmic muscle contractions at lower intensities, but to being reelevated and normalized as at rest during higher intensities. The "steepness" of the parabolic velocity profile observed during the CSP at rest increased during muscle contraction at higher intensities. In conclusion, the blood velocity in the common femoral artery is parabolic both at rest and during exercise for both the CSP and CDP, indicating the persistence of laminar flow. The occurrence of any temporary slight disturbance or turbulence in the flow at the sight of measurement in the common femoral artery does consequently not induce a persisting "disturbed" and fully flat "plug-like" velocity profile. Instead, the "steepness" of the parabolic velocity profile is only slightly modified, whereby blood flow is not impaired. Thus the blood velocity profile, besides being influenced by the muscle contraction-relaxation induced mechanical "impedance," seems also to be modulated by the cardiac- and blood pressure-phases, consequently influencing the exercise blood flow response.
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| 4. |
- Osada, T., et al.
(författare)
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Differences in exercising limb blood flow variability between cardiac and muscle contraction cycle related analysis during dynamic knee extensor
- 2006
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Ingår i: Journal of Sports Medicine and Physical Fitness. - 0022-4707. ; 46:4, s. 590-597
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Tidskriftsartikel (refereegranskat)abstract
- Aim. Blood flow in peripheral conduit arteries during steady-state, dynamic exercise, can be estimated noninvasively with Doppler ultrasound, by measuring the conduit arterial diameter and the mean blood velocity averaged over consecutive cardiac beat-by-beat cycles (BBcycle) or muscle contraction-relaxation cycles (CRcycle). The precise impact fluctuations in the 1-BBcycle- or 1-CRcycle-rate may impose on the average blood flow measurements has previously not been clearly defined. The hypothesis investigated in the present study was that the blood flow measurements obtained, and its variability, during exercise, may differ between the 1-BBcycle and 1-CRcycle at incremental exercise intensities; as the BBcycle-measurements may be influenced by transient alterations in heart rate; whereas the CRcycle-measurements are dependent on the muscle contraction-relaxation frequencies independent of the exercise intensities per se. The main purpose was therefore to determine if fluctuations in blood flow for 1-BBcycle and 1-CRcycle varies at incremental exercise intensities (work rates) using the one-legged dynamic knee-extensor exercise (DKE) model. Methods. Limb femoral artery blood flow (LBF) was determined, for 1-BBcycle and 1-CRcycle, in 8 healthy male subjects during 4-min of steady-state DKE at 60 contractions per minute at 10, 20,30 and 40 W. The variability of LBF was determined from the coefficients of variation (CVLBF). Results. The CVLBF for the CRcycle-measurements at each work rate were similar (P=NS). The CVLBF for the BBcycle-measurements were higher (P<0.05) at 40 W compared to at 10 W. Furthermore, the CVLBF for the 1-BBcycle was higher (P<0.05) than for the 1-CRcycle at 30 and 40 W, despite almost identical mean LBF values for the BBcycle- and the CRcycle-measurements at each exercise intensity. Conclusions. The present data suggests that estimates of LBF at slightly higher exercise intensities such as above 30 W, for a few number of consecutive BBcycle renders a higher variability than for CRcycle-measurements. This may consequently result in slight over- and under-estimations of LBF compared to the CRcycle-measurement.
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| 5. |
- Osada, Takuya, et al.
(författare)
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Femoral artery blood flow and its relationship to spontaneous fluctuations in rhythmic thigh muscle workload
- 2009
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Ingår i: Clinical Physiology and Functional Imaging. - 1475-0961. ; 29:4, s. 277-292
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Tidskriftsartikel (refereegranskat)abstract
- P>Background and aim: Limb femoral arterial blood flow (LBF) is known to increase linearly with increasing workload under steady-state conditions, suggesting a close link between LBF and metabolic activity. We, however, hypothesized that sudden physiological and spontaneous changes in exercise rhythm, and consequently workload temporarily alter blood flow to the working muscle. LBF and its relation to fluctuations in the contraction rhythm and workload were therefore investigated. Methods: LBF, measured by Doppler ultrasound, and the achieved workload, were continuously measured in nine subjects, aiming to perform steady-state, one-legged, dynamic knee-extensor exercise at 30 and 60 contractions per minute (cpm), at incremental target workloads of 10, 20, 30 and 40 W. Results: In agreement with previous findings, LBF increased positively and linearly (P < 0 center dot 05) with increasing target workload. However, LBF was inversely and linearly related (P < 0 center dot 05) to the actually achieved workload, when measured over 60 consecutive contraction-relaxation cycle bouts, for each target intensity at 30 and 60 cpm respectively. Thus any sudden spontaneous increase or decrease in the achieved workload transiently altered the relationship between LBF and the achieved workload. The influence upon the magnitude of LBF, due to fluctuations in the achieved workload from the target workload, was furthermore similar between target workload sessions at 30 and 60 cpm respectively. LBF was, however, not associated with variations in the contraction frequencies. Conclusions: These findings indicate that a transient sudden increase in the workload more rapidly impedes LBF and that vasodilatation may be elicited to restore the intensity related steady-state LBF response in relation to the average metabolic activity.
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| 6. |
- Rådegran, Göran
(författare)
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Exercise limb blood flow response to acute and chronic hypoxia in Danish lowlanders and Aymara natives
- 2008
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Ingår i: Acta Physiologica. - : Wiley. - 1748-1708 .- 1748-1716. ; 192:4, s. 531-539
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Tidskriftsartikel (refereegranskat)abstract
- Aim: The femoral artery blood flow response to submaximal, one-legged, dynamic, knee-extensor exercise was determined in acute and chronic hypoxia to investigate the hypotheses that with adaptation to chronic hypoxia blood haemoglobin increases, allowing preservation of blood flow as in normoxia. Methods: Sixteen Danish lowlanders participated, in groups of six to eight, in the experiments at sea level normoxia (FiO(2) congruent to 0.21) and acute hypoxia (FiO(2) congruent to 0.11), and chronic hypoxia after similar to 7 and 9-10 weeks at similar to 5260 m altitude breathing ambient air (FiO(2) congruent to 0.21) or a hyperoxic gas (FiO(2) congruent to 0.55). The response was compared with that in six Aymara natives. Results: The haemoglobin and haematocrit increased (P < 0.003) in the lowlanders at altitude vs. at sea level by similar to 39 and 27% respectively; i.e. to a similar (P = ns) level as in the natives. At rest, blood flow was the same (P = ns) in the lowlanders at sea level and altitude, as in the natives at altitude. During the onset of and incremental exercise, blood flow was the same (P = ns) in the lowlanders at sea level and altitude, as in the natives at altitude. Acute hypoxia increased (P < 0.05) blood flow by similar to 55% during exercise in the lowlanders at sea level. Acute hyperoxia decreased (P < 0.05) blood flow by similar to 22-29% during exercise in the lowlanders and natives at altitude. Conclusion: In chronic hypoxia, blood haemoglobin increases, allowing normalization of the elevated exercise blood flow response in acute hypoxia, and preservation of the kinetics and steady-state exercise blood flow as in normoxia, being similar as in the natives at altitude.
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