Effect of helium breathing on intercostal and quadriceps muscle blood flow during exercise in COPD patients

2011 ◽  
Vol 300 (6) ◽  
pp. R1549-R1559 ◽  
Author(s):  
Ioannis Vogiatzis ◽  
Helmut Habazettl ◽  
Andrea Aliverti ◽  
Dimitris Athanasopoulos ◽  
Zafeiris Louvaris ◽  
...  
Keyword(s):  
Blood Flow ◽  
Oxygen Delivery ◽  
Muscle Blood Flow ◽  
Arterial Oxygen ◽  
Vastus Lateralis Muscle ◽  
Intercostal Muscle ◽  
Muscle Oxygen ◽  
Copd Patients ◽  
Locomotor Muscles ◽  
Blood Flow Redistribution

Emerging evidence indicates that, besides dyspnea relief, an improvement in locomotor muscle oxygen delivery may also contribute to enhanced exercise tolerance following normoxic heliox (replacement of inspired nitrogen by helium) administration in patients with chronic obstructive pulmonary disease (COPD). Whether blood flow redistribution from intercostal to locomotor muscles contributes to this improvement currently remains unknown. Accordingly, the objective of this study was to investigate whether such redistribution plays a role in improving locomotor muscle oxygen delivery while breathing heliox at near-maximal [75% peak work rate (WRpeak)], maximal (100%WRpeak), and supramaximal (115%WRpeak) exercise in COPD. Intercostal and vastus lateralis muscle perfusion was measured in 10 COPD patients (FEV1 = 50.5 ± 5.5% predicted) by near-infrared spectroscopy using indocyanine green dye. Patients undertook exercise tests at 75 and 100%WRpeak breathing either air or heliox and at 115%WRpeak breathing heliox only. Patients did not exhibit exercise-induced hyperinflation. Normoxic heliox reduced respiratory muscle work and relieved dyspnea across all exercise intensities. During near-maximal exercise, quadriceps and intercostal muscle blood flows were greater, while breathing normoxic heliox compared with air (35.8 ± 7.0 vs. 29.0 ± 6.5 and 6.0 ± 1.3 vs. 4.9 ± 1.2 ml·min−1·100 g−1, respectively; P < 0.05; mean ± SE). In addition, compared with air, normoxic heliox administration increased arterial oxygen content, as well as oxygen delivery to quadriceps and intercostal muscles (from 47 ± 9 to 60 ± 12, and from 8 ± 1 to 13 ± 3 mlO2·min−1·100 g−1, respectively; P < 0.05). In contrast, normoxic heliox had neither an effect on systemic nor an effect on quadriceps or intercostal muscle blood flow and oxygen delivery during maximal or supramaximal exercise. Since intercostal muscle blood flow did not decrease by normoxic heliox administration, blood flow redistribution from intercostal to locomotor muscles does not represent a likely mechanism of improvement in locomotor muscle oxygen delivery. Our findings might not be applicable to patients who hyperinflate during exercise.

Heliox increases quadriceps muscle oxygen delivery during exercise in COPD patients with and without dynamic hyperinflation

2012 ◽  
Vol 113 (7) ◽  
pp. 1012-1023 ◽  
Author(s):  
Zafeiris Louvaris ◽  
Spyros Zakynthinos ◽  
Andrea Aliverti ◽  
Helmut Habazettl ◽  
Maroula Vasilopoulou ◽  
...  
Keyword(s):  
Blood Flow ◽  
Oxygen Content ◽  
Oxygen Delivery ◽  
Quadriceps Muscle ◽  
Arterial Oxygen ◽  
Arterial Oxygen Content ◽  
Muscle Oxygen ◽  
Peripheral Muscle ◽  
Copd Patients ◽  
Gastric Pressure

Some reports suggest that heliox breathing during exercise may improve peripheral muscle oxygen availability in patients with chronic obstructive pulmonary disease (COPD). Besides COPD patients who dynamically hyperinflate during exercise (hyperinflators), there are patients who do not hyperinflate (non-hyperinflators). As heliox breathing may differently affect cardiac output in hyperinflators (by increasing preload and decreasing afterload of both ventricles) and non-hyperinflators (by increasing venous return) during exercise, it was reasoned that heliox administration would improve peripheral muscle oxygen delivery possibly by different mechanisms in those two COPD categories. Chest wall volume and respiratory muscle activity were determined during constant-load exercise at 75% peak capacity to exhaustion, while breathing room air or normoxic heliox in 17 COPD patients: 9 hyperinflators (forced expiratory volume in 1 s = 39 ± 5% predicted), and 8 non-hyperinflators (forced expiratory volume in 1 s = 48 ± 5% predicted). Quadriceps muscle blood flow was measured by near-infrared spectroscopy using indocyanine green dye. Hyperinflators and non-hyperinflators demonstrated comparable improvements in endurance time during heliox (231 ± 23 and 257 ± 28 s, respectively). At exhaustion in room air, expiratory muscle activity (expressed by peak-expiratory gastric pressure) was lower in hyperinflators than in non-hyperinflators. In hyperinflators, heliox reduced end-expiratory chest wall volume and diaphragmatic activity, and increased arterial oxygen content (by 17.8 ± 2.5 ml/l), whereas, in non-hyperinflators, heliox reduced peak-expiratory gastric pressure and increased systemic vascular conductance (by 11.0 ± 2.8 ml·min−1·mmHg−1). Quadriceps muscle blood flow and oxygen delivery significantly improved during heliox compared with room air by a comparable magnitude (in hyperinflators by 6.1 ± 1.3 ml·min−1·100 g−1 and 1.3 ± 0.3 ml O2·min−1·100 g−1, and in non-hyperinflators by 7.2 ± 1.6 ml·min−1·100 g−1 and 1.6 ± 0.3 ml O2·min−1·100 g−1, respectively). Despite similar increase in locomotor muscle oxygen delivery with heliox in both groups, the mechanisms of such improvements were different: 1) in hyperinflators, heliox increased arterial oxygen content and quadriceps blood flow at similar cardiac output, whereas 2) in non-hyperinflators, heliox improved central hemodynamics and increased systemic vascular conductance and quadriceps blood flow at similar arterial oxygen content.

scholarly journals Blood flow does not redistribute from respiratory to leg muscles during exercise breathing heliox or oxygen in COPD

2014 ◽  
Vol 117 (3) ◽  
pp. 267-276 ◽  
Author(s):  
Zafeiris Louvaris ◽  
Ioannis Vogiatzis ◽  
Andrea Aliverti ◽  
Helmut Habazettl ◽  
Harrieth Wagner ◽  
...  
Keyword(s):  
Blood Flow ◽  
Muscle Blood Flow ◽  
Work Of Breathing ◽  
Abdominal Muscle ◽  
Mechanical Work ◽  
Chronic Obstructive ◽  
Time To Exhaustion ◽  
Vastus Lateralis Muscle ◽  
Oxygen Breathing ◽  
Locomotor Muscles

In patients with chronic obstructive pulmonary disease (COPD), one of the proposed mechanisms for improving exercise tolerance, when work of breathing is experimentally reduced, is redistribution of blood flow from the respiratory to locomotor muscles. Accordingly, we investigated whether exercise capacity is improved on the basis of blood flow redistribution during exercise while subjects are breathing heliox (designed to primarily reduce the mechanical work of breathing) and during exercise with oxygen supplementation (designed to primarily enhance systemic oxygen delivery but also to reduce mechanical work of breathing). Intercostal, abdominal, and vastus lateralis muscle perfusion were simultaneously measured in 10 patients with COPD (forced expiratory volume in 1 s: 46 ± 12% predicted) by near-infrared spectroscopy using indocyanine green dye. Measurements were performed during constant-load exercise at 75% of peak capacity to exhaustion while subjects breathed room air and, then at the same workload, breathed either normoxic heliox (helium 79% and oxygen 21%) or 100% oxygen, the latter two in balanced order. Times to exhaustion while breathing heliox and oxygen did not differ (659 ± 42 s with heliox and 696 ± 48 s with 100% O2), but both exceeded that on room air (406 ± 36 s, P < 0.001). At exhaustion, intercostal and abdominal muscle blood flow during heliox (9.5 ± 0.6 and 8.0 ± 0.7 ml · min−1·100 g−1, respectively) was greater compared with room air (6.8 ± 0.5 and 6.0 ± 0.5 ml·min−1·100 g·, respectively; P < 0.05), whereas neither intercostal nor abdominal muscle blood flow differed between oxygen and air breathing. Quadriceps muscle blood flow was also greater with heliox compared with room air (30.2 ± 4.1 vs. 25.4 ± 2.9 ml·min−1·100 g−1; P < 0.01) but did not differ between air and oxygen breathing. Although our findings confirm that reducing the burden on respiration by heliox or oxygen breathing prolongs time to exhaustion (at 75% of maximal capacity) in patients with COPD, they do not support the hypothesis that redistribution of blood flow from the respiratory to locomotor muscles is the explanation.

Low blood flow at onset of moderate-intensity exercise does not limit muscle oxygen uptake

2010 ◽  
Vol 298 (3) ◽  
pp. R843-R848 ◽  
Author(s):  
Michael Nyberg ◽  
Stefan P. Mortensen ◽  
Bengt Saltin ◽  
Ylva Hellsten ◽  
Jens Bangsbo
Keyword(s):  
Nitric Oxide ◽  
Blood Flow ◽  
Oxygen Uptake ◽  
Oxygen Delivery ◽  
Initial Phase ◽  
Muscle Blood Flow ◽  
Moderate Intensity ◽  
Moderate Intensity Exercise ◽  
Muscle Oxygen ◽  
Muscle Oxygen Uptake

The effect of low blood flow at onset of moderate-intensity exercise on the rate of rise in muscle oxygen uptake was examined. Seven male subjects performed a 3.5-min one-legged knee-extensor exercise bout (24 ± 1 W, mean ± SD) without (Con) and with (double blockade; DB) arterial infusion of inhibitors of nitric oxide synthase ( NG-monomethyl-l-arginine) and cyclooxygenase (indomethacin) to inhibit the synthesis of nitric oxide and prostanoids, respectively. Leg blood flow and leg oxygen delivery throughout exercise was 25–50% lower ( P < 0.05) in DB compared with Con. Leg oxygen extraction (arteriovenous O2 difference) was higher ( P < 0.05) in DB than in Con (5 s: 127 ± 3 vs. 56 ± 4 ml/l), and leg oxygen uptake was not different between Con and DB during exercise. The difference between leg oxygen delivery and leg oxygen uptake was smaller ( P < 0.05) during exercise in DB than in Con (5 s: 59 ± 12 vs. 262 ± 39 ml/min). The present data demonstrate that muscle blood flow and oxygen delivery can be markedly reduced without affecting muscle oxygen uptake in the initial phase of moderate-intensity exercise, suggesting that blood flow does not limit muscle oxygen uptake at the onset of exercise. Additionally, prostanoids and/or nitric oxide appear to play important roles in elevating skeletal muscle blood flow in the initial phase of exercise.

Effect of mild carboxy-hemoglobin on exercising skeletal muscle: intravascular and intracellular evidence

2002 ◽  
Vol 283 (5) ◽  
pp. R1131-R1139 ◽  
Author(s):  
R. S. Richardson ◽  
E. A. Noyszewski ◽  
B. Saltin ◽  
J. González-Alonso
Keyword(s):  
Blood Flow ◽  
Oxygen Uptake ◽  
Muscle Blood Flow ◽  
Knee Extensor ◽  
Arterial Oxygen ◽  
Arterial Oxygen Content ◽  
Muscle Oxygen ◽  
Progressive Exercise ◽  
Maximum Work ◽  
Young Subjects

We studied muscle blood flow, muscle oxygen uptake (V˙o 2), net muscle CO uptake, Mb saturation, and intracellular bioenergetics during incremental single leg knee-extensor exercise in five healthy young subjects in conditions of normoxia, hypoxia (H; 11% O2), normoxia + CO (COnorm), and 100% O2+ CO (COhyper). Maximum work rates and maximal oxygen uptake (V˙o 2 max) were equally reduced by ≈14% in H, COnorm, and COhyper. The reduction in arterial oxygen content (CaO2 ) (≈20%) resulted in an elevated blood flow (Q) in the CO and H trials. Net muscle CO uptake was attenuated in the CO trials. Suprasystolic cuff measurements of the deoxy-Mb signal were not different in terms of the rate of signal rise or maximum signal attained with and without CO. At maximal exercise, calculated mean capillary Po 2 was most reduced in H and resulted in the lowest Mb-associated Po 2. Reductions in ATP, PCr, and pH during H, COnorm, and COhyper occurred earlier during progressive exercise than in normoxia. Thus the effects of reduced CaO2 due to mild CO poisoning are similar to H.

scholarly journals Muscle blood flow, hypoxia, and hypoperfusion

2014 ◽  
Vol 116 (7) ◽  
pp. 852-857 ◽  
Author(s):  
Michael J. Joyner ◽  
Darren P. Casey
Keyword(s):  
Blood Flow ◽  
Oxygen Delivery ◽  
Muscle Blood Flow ◽  
Oxygen Demand ◽  
Arterial Oxygen ◽  
Arterial Oxygen Content ◽  
Sympathetic Vasoconstriction ◽  
Response To Exercise ◽  
Metabolic Vasodilation ◽  
Hypoxic Exercise

Blood flow increases to exercising skeletal muscle, and this increase is driven primarily by vasodilation in the contracting muscles. When oxygen delivery to the contracting muscles is altered by changes in arterial oxygen content, the magnitude of the vasodilator response to exercise changes. It is augmented during hypoxia and blunted during hyperoxia. Because the magnitude of the increased vasodilation during hypoxic exercise tends to keep oxygen delivery to the contracting muscles constant, we have termed this phenomenon “compensatory vasodilation.” In a series of studies, we have explored metabolic, endothelial, and neural mechanisms that might contribute to compensatory vasodilation. These include the contribution of vasodilating substances like nitric oxide (NO) and adenosine, along with altered interactions between sympathetic vasoconstriction and metabolic vasodilation. We have also compared the compensatory vasodilator responses to hypoxic exercise with those seen when oxygen delivery to contracting muscles is altered by acute reductions in perfusion pressure. A synthesis of our findings indicate that NO contributes to the compensatory dilator responses during both hypoxia and hypoperfusion, while adenosine appears to contribute only during hypoperfusion. During hypoxia, the NO-mediated component is linked to a β-adrenergic receptor mechanism during lower intensity exercise, while another source of NO is engaged at higher exercise intensities. There are also subtle interactions between α-adrenergic vasoconstriction and metabolic vasodilation that influence the responses to hypoxia, hyperoxia, and hypoperfusion. Together our findings emphasize both the tight linkage of oxygen demand and supply during exercise and the redundant nature of the vasomotor responses to contraction.

Relation of blood flow to VO2, PO2, and PCO2 in dog gastrocnemius muscle

1988 ◽  
Vol 255 (5) ◽  
pp. H1004-H1010 ◽  
Author(s):  
D. E. Mohrman ◽  
R. R. Regal
Keyword(s):  
Blood Flow ◽  
Steady State ◽  
Gastrocnemius Muscle ◽  
Muscle Blood Flow ◽  
Carbon Dioxide Tension ◽  
Experimental Conditions ◽  
Muscle Oxygen ◽  
Muscle Oxygen Consumption ◽  
Relationship Of ◽  
The Relationship

We pump-perfused gastrocnemius-plantaris muscle preparations at constant pressure to study the relationship of muscle blood flow (Q) to muscle oxygen consumption (VO2), venous oxygen tension (PVO2), and venous carbon dioxide tension (PVCO2) during steady-state exercise at different rates. Tests were performed under four experimental conditions produced by altering the perfusate blood-gas status with a membrane lung. The consistency of the relationship of Q to other variables was evaluated by statistical analysis of fitted curves. Not one of the above listed variables had the same relationship with Q in all four of the experimental conditions we tested. However, we did find that a consistent relationship existed among Q, PVO2, and PVCO2 in our data. That relationship is well described by the equation (Q-23).[PVO2 - (0.5.PVCO2) - 3] = 105 (when Q is expressed in ml.100 g-1.min-1 and PVO2 and PVCO2 in mmHg). One interpretation of this result is that both PO2 and PCO2 are important variables in the control of blood flow in skeletal muscle the combined influence of which could account for nearly all of the hyperemia response to steady-state muscle exercise.

Costal vs. crural diaphragmatic blood flow during submaximal and near-maximal exercise in ponies

1988 ◽  
Vol 65 (4) ◽  
pp. 1514-1519 ◽  
Author(s):  
M. Manohar
Keyword(s):  
Blood Flow ◽  
Cardiac Output ◽  
Left Atrium ◽  
Maximal Exercise ◽  
Muscle Blood Flow ◽  
Intercostal Muscle ◽  
Quiet Breathing ◽  
Blood Flows ◽  
Graded Exercise ◽  
Crural Diaphragm

The present study was carried out 1) to compare blood flow in the costal and crural regions of the equine diaphragm during quiet breathing at rest and during graded exercise and 2) to determine the fraction of cardiac output needed to perfuse the diaphragm during near-maximal exercise. By the use of radionuclide-labeled 15-micron-diam microspheres injected into the left atrium, diaphragmatic and intercostal muscle blood flow was studied in 10 healthy ponies at rest and during three levels of exercise (moderate: 12 mph, heavy: 15 mph, and near-maximal: 19-20 mph) performed on a treadmill. At rest, in eucapnic ponies, costal (13 +/- 3 ml.min-1.100 g-1) and crural (13 +/- 2 ml.min-1.100 g-1) phrenic blood flows were similar, but the costal diaphragm received a much larger percentage of cardiac output (0.51 +/- 0.12% vs. 0.15 +/- 0.03% for crural diaphragm). Intercostal muscle perfusion at rest was significantly less than in either phrenic region. Graded exercise resulted in significant progressive increments in perfusion to these tissues. Although during exercise, crural diaphragmatic blood flow was not different from intercostal muscle blood flow, these values remained significantly less (P less than 0.01) than in the costal diaphragm. At moderate, heavy, and near-maximal exercise, costal diaphragmatic blood flow (123 +/- 12, 190 +/- 12, and 245 +/- 18 ml.min-1.100 g-1) was 143%, 162%, and 162%, respectively, of that for the crural diaphragm (86 +/- 10, 117 +/- 8, and 151 +/- 14 ml.min-1.100 g-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Muscle blood flow during exercise in sedentary and trained hypothyroid rats

1995 ◽  
Vol 269 (6) ◽  
pp. H1949-H1954 ◽  
Author(s):  
R. M. McAllister ◽  
M. D. Delp ◽  
K. A. Thayer ◽  
M. H. Laughlin
Keyword(s):  
Skeletal Muscle ◽  
Blood Flow ◽  
Citrate Synthase ◽  
Vastus Lateralis ◽  
Muscle Blood Flow ◽  
Treadmill Running ◽  
Exercise Intolerance ◽  
Vastus Lateralis Muscle ◽  
Blood Flows ◽  
Vastus Intermedius

Hypothyroidism is characterized by exercise intolerance. We hypothesized that active muscle blood flow during in vivo exercise is inadequate in the hypothyroid state. Additionally, we hypothesized that endurance exercise training would restore normal blood flow during acute exercise. To test these hypotheses, rats were made hypothyroid (Hypo) over 3-4 mo with propylthiouracil. A subset of Hypo rats was trained (THypo) on a treadmill at 30 m/min (15% grade) for 60 min/day 5 days/wk over 10-15 wk. Hypothyroidism was evidenced by approximately 80% reductions in plasma triiodothyronine levels in Hypo and THypo and by 40-50% reductions in citrate synthase activities in high oxidative muscles in Hypo compared with euthyroid (Eut) rats. Training efficacy was indicated by increased (25-100%) citrate synthase activities in muscles of THypo vs. Hypo. Regional blood flows were determined by the radiolabeled microsphere method before exercise and at 1-2 min of treadmill running at 15 m/min (0% grade). Preexercise muscle blood flows were generally similar among groups. During exercise, however, flows were lower in Hypo than in Eut for high oxidative muscles such as the red section of vastus lateralis [277 +/- 24 and 153 +/- 13 (SE) ml.min-1.100 g-1 for Eut and Hypo, respectively; P < 0.01] and vastus intermedius (317 +/- 32 and 187 +/- 20 ml.min-1.100 g-1 for Eut and Hypo, respectively; P < 0.01) muscles. Training (THypo) did not normalize these flows (168 +/- 24 and 181 +/- 24 ml.min-1.100 g-1 for red section of vastus lateralis and vastus intermedius muscles, respectively). Blood flows to low oxidative muscle, such as the white section of vastus lateralis muscle, were similar among groups (21 +/- 5, 25 +/- 4, and 34 +/- 7 ml.min-1.100 g-1 for Eut, Hypo, and THypo, respectively; P = NS). These findings indicate that hypothyroidism is associated with reduced blood flow to skeletal muscle during exercise, suggesting that impaired delivery of nutrients to and/or removal of metabolites from skeletal muscle contributes to the poor exercise tolerance characteristic of hypothyroidism.

scholarly journals Effects of Hematocrit Variations on Cerebral Blood Flow and Oxygen Transport in Ischemic Cerebrovascular Disease

1981 ◽  
Vol 1 (4) ◽  
pp. 413-417 ◽  
Author(s):  
Masahito Kusunoki ◽  
Kazufumi Kimura ◽  
Masaichi Nakamura ◽  
Yoshinari Isaka ◽  
Shotaro Yoneda ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Cerebrovascular Disease ◽  
Oxygen Transport ◽  
Oxygen Delivery ◽  
Inverse Correlation ◽  
Arterial Oxygen ◽  
Brain Oxygenation ◽  
Arterial Oxygen Content ◽  
Ischemic Cerebrovascular Disease

The contribution of hematocrit (Ht) changes on cerebral blood flow (CBF) and brain oxygenation in ischemic cerebrovascular disease is still controversial. In the present study, effects of Ht variations on CBF and oxygen delivery were investigated in patients with ischemic cerebrovascular disease. CBF was measured by the Xe-133 intracarotid injection method in 27 patients, whose diagnoses included completed stroke, reversible ischemic neurological deficit, and transient ischemic attack. Ht values in the patients ranged from 31 to 53%. There was a significant inverse correlation between CBF and Ht in these Ht ranges. Oxygen delivery, i.e., the product of arterial oxygen content and CBF, increased with Ht elevation and reached the maximum level in the Ht range of 40–45% and then declined. The CBF-Ht and oxygen transport-Ht relations observed in our study were similar to those in the glass-tube model studies by other workers rather than to those in intact animal experiments. From these results, it is conceivable that in ischemic cerebrovascular disease, the vasomotor adjustment was impaired in such a manner that the relations among Ht, CBF, and oxygen delivery were different from those in healthy subjects. Further, an “optimal hematocrit” for brain oxygenation was also discussed.

Insights for Blood Flow Restriction and Hypoxia in Leg Versus Arm Submaximal Exercise

2020 ◽  
Vol 15 (5) ◽  
pp. 714-719
Author(s):  
Sarah J. Willis ◽  
Grégoire P. Millet ◽  
Fabio Borrani
Keyword(s):  
Blood Flow ◽  
Oxygen Delivery ◽  
Vascular Reactivity ◽  
Near Infrared ◽  
Biceps Brachii ◽  
Submaximal Exercise ◽  
Blood Flow Restriction ◽  
Arterial Oxygen ◽  
Flow Restriction ◽  
Arm Cycling

Purpose: To assess tissue oxygenation, along with metabolic and physiological responses during blood flow restriction (BFR, bilateral vascular occlusion) and systemic hypoxia conditions during submaximal leg- versus arm-cycling exercise. Methods: In both legs and arms, 4 randomized sessions were performed (normoxia 400 m, fraction of inspired oxygen [FIO2] 20.9% and normobaric hypoxia 3800 m, FIO2 13.1% [0.1%]; combined with BFR at 0% and 45% of resting pulse elimination pressure). During each session, a single 6-minute steady-state submaximal exercise was performed to measure physiological changes and oxygenation (near-infrared spectroscopy) of the muscle tissue in both the vastus lateralis (legs) and biceps brachii (arms). Results: Total hemoglobin concentration ([tHb]) was 65% higher (P < .001) in arms versus legs, suggesting that arms had a greater blood perfusion capacity than legs. Furthermore, there were greater changes in tissue blood volume [tHb] during BFR compared with control conditions (P = .017, F = 5.45). The arms elicited 7% lower tissue saturation (P < .001) and were thus more sensitive to the hypoxia-induced reduction in oxygen supply than legs, no matter the condition. This indicates that legs and arms may elicit different regulatory hemodynamic mechanisms (ie, greater blood flow in arms) for limiting the decreased oxygen delivery during exercise with altered arterial oxygen content. Conclusions: The combination of BFR and/or hypoxia led to increased [tHb] in both limbs likely due to greater vascular resistance; further, arms were more responsive than legs. This possibly influences the maintenance of oxygen delivery and enhances perfusion pressure, suggesting greater vascular reactivity in arms than in legs.

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