Peripheral circulatory factors limit rate of increase in muscle O2 uptake at onset of heavy exercise

2001 ◽  
Vol 90 (1) ◽  
pp. 83-89 ◽  
Author(s):  
Maureen J. MacDonald ◽  
Heather L. Naylor ◽  
Michael E. Tschakovsky ◽  
Richard L. Hughson
Keyword(s):  
Blood Flow ◽  
Forearm Blood Flow ◽  
Muscle Blood Flow ◽  
Venous Blood ◽  
Lactate Concentration ◽  
Exercise Bout ◽  
Handgrip Exercise ◽  
Acid Base ◽  
Rate Of Increase ◽  
Forearm Exercise

We used an exercise paradigm with repeated bouts of heavy forearm exercise to test the hypothesis that alterations in local acid-base environment that remain after the first exercise result in greater blood flow and O2 delivery at the onset of the second bout of exercise. Two bouts of handgrip exercise at 75% peak workload were performed for 5 min, separated by 5 min of recovery. We continuously measured blood flow using Doppler ultrasound and sampled venous blood for O2 content, Pco 2, pH, and lactate and potassium concentrations, and we calculated muscle O2uptake (V˙o 2). Forearm blood flow was elevated before the second exercise compared with the first and remained higher during the first 30 s of exercise (234 ± 18 vs. 187 ± 4 ml/min, P < 0.05). Flow was not different at 5 min. Arteriovenous O2 content difference was lower before the second bout (4.6 ± 0.9 vs. 7.2 ± 0.7 ml O2/dl) and higher by 30 s of exercise (11.2 ± 0.7 vs. 10.8 ± 0.7 ml O2/dl, P < 0.05). Muscle V˙o 2was unchanged before the start of exercise but was elevated during the first 30 s of the transition to the second exercise bout (26.0 ± 2.1 vs. 20.0 ± 0.9 ml/min, P < 0.05). Changes in venous blood Pco 2, pH, and lactate concentration were consistent with reduced reliance on anaerobic glycolysis at the onset of the second exercise bout. These data show that limitations of muscle blood flow can restrict the adaptation of oxidative metabolism at the onset of heavy muscular exertion.

Dependence of muscleV˙o 2on blood flow dynamics at onset of forearm exercise

1996 ◽  
Vol 81 (4) ◽  
pp. 1619-1626 ◽  
Author(s):  
R. L. Hughson ◽  
J. K. Shoemaker ◽  
M. E. Tschakovsky ◽  
J. M. Kowalchuk
Keyword(s):  
Blood Flow ◽  
Muscle Blood Flow ◽  
Venous Blood ◽  
Lactate Concentration ◽  
Flow Dynamics ◽  
Cross Sectional ◽  
Mean Response Time ◽  
Rate Of Increase ◽  
Blood Flow Dynamics ◽  
Forearm Exercise

Hughson, R. L., J. K. Shoemaker, M. E. Tschakovsky, and J. M. Kowalchuk. Dependence muscle ofV˙o 2on blood flow dynamics at the onset of forearm exercise. J. Appl. Physiol. 81(4): 1619–1626, 1996.—The hypothesis that the rate of increase in muscle O2 uptake (V˙o 2 mus) at the onset of exercise is influenced by muscle blood flow was tested during forearm exercise with the arm either above or below heart level to modify perfusion pressure. Ten young men exercised at a power of ∼2.2 W, and five of these subjects also worked at 1.4 W. Blood flow to the forearm was calculated from the product of blood velocity and cross-sectional area obtained with Doppler techniques. Venous blood was sampled from a deep forearm vein to determine O2 extraction. The rate of increase inV˙o 2 musand blood flow was assessed from the mean response time (MRT), which is the time to achieve ∼63% increase from baseline to steady state. In the arm below heart position during the 2.2-W exercise, blood flow andV˙o 2 musboth increased, with a MRT of ∼30 s. With the arm above the heart at this power, the MRTs for blood flow [79.8 ± 15.7 (SE) s] and V˙o 2 mus(50.2 ± 4.0 s) were both significantly slower. Consistent with these findings were the greater increases in venous plasma lactate concentration over resting values in the above heart position (2.8 ± 0.4 mmol/l) than in the below heart position (0.9 ± 0.2 mmol/l). At the lower power, both blood flow andV˙o 2 musalso increased more rapidly with the arm below compared with above the heart. These data support the hypothesis that changes in blood flow at the onset of exercise have a direct effect on oxidative metabolism through alterations in O2transport.

Failure of prostaglandins to modulate the time course of blood flow during dynamic forearm exercise in humans

1996 ◽  
Vol 81 (4) ◽  
pp. 1516-1521 ◽  
Author(s):  
J. K. Shoemaker ◽  
H. L. Naylor ◽  
Z. I. Pozeg ◽  
R. L. Hughson
Keyword(s):  
Blood Flow ◽  
Brachial Artery ◽  
Time Course ◽  
Forearm Blood Flow ◽  
Voluntary Contraction ◽  
Double Blind ◽  
Rate Of Increase ◽  
Forearm Exercise ◽  
Blind Manner ◽  
Exercise In Humans

Shoemaker, J. K., H. L. Naylor, Z. I. Pozeg, and R. L. Hughson. Failure of prostaglandins to modulate the time course of blood flow during dynamic forearm exercise in humans. J. Appl. Physiol. 81(4): 1516–1521, 1996.—The time course and magnitude of increases in brachial artery mean blood velocity (MBV; pulsed Doppler), diameter ( D; echo Doppler), mean perfusion pressure (MPP; Finapres), shear rate (γ˙ = 8 ⋅ MBV/ D), and forearm blood flow (FBF = MBV ⋅ π r 2) were assessed to investigate the effect that prostaglandins (PGs) have on the hyperemic response on going from rest to rhythmic exercise in humans. While supine, eight healthy men performed 5 min of dynamic handgrip exercise by alternately raising and lowering a 4.4-kg weight (∼10% maximal voluntary contraction) with a work-to-rest cycle of 1:1 (s/s). When the exercise was performed with the arm positioned below the heart, the rate of increase in MBV and γ˙ was faster compared with the same exercise performed above the heart. Ibuprofen (Ibu; 1,200 mg/day, to reduce PG-induced vasodilation) and placebo were administered orally for 2 days before two separate testing sessions in a double-blind manner. Resting heart rate was reduced in Ibu (52 ± 3 beats/min) compared with placebo (57 ± 3 beats/min) ( P < 0.05) without change to MPP. With placebo, D increased in both arm positions from ∼4.3 mm at rest to ∼4.5 mm at 5 min of exercise ( P < 0.05). This response was not altered with Ibu ( P > 0.05). Ibu did not alter the time course of MBV or forearm blood flow ( P > 0.05) in either arm position. The γ˙ was significantly greater in Ibu vs. placebo at 30 and 40 s of above the heart exercise and for all time points after 25 s of below the heart exercise ( P < 0.05). Because PG inhibition altered the time course ofγ˙ at the brachial artery, but not FBF, it was concluded that PGs are not essential in regulating the blood flow responses to dynamic exercise in humans.

Evaluation of muscle metaboreflex function through graded reduction in forearm blood flow during rhythmic handgrip exercise in humans

2011 ◽  
Vol 301 (2) ◽  
pp. H609-H616 ◽  
Author(s):  
Masashi Ichinose ◽  
Stephane Delliaux ◽  
Kazuhito Watanabe ◽  
Naoto Fujii ◽  
Takeshi Nishiyasu
Keyword(s):  
Blood Flow ◽  
Forearm Blood Flow ◽  
Pressor Response ◽  
Muscle Blood Flow ◽  
Voluntary Contraction ◽  
Open Loop ◽  
Handgrip Exercise ◽  
Hemodynamic Responses ◽  
Muscle Metaboreflex ◽  
Arterial Blood

Hypoperfusion of active skeletal muscle elicits a reflex pressor response termed the muscle metaboreflex. Our aim was to determine the muscle metaboreflex threshold and gain in humans by creating an open-loop relationship between active muscle blood flow and hemodynamic responses during a rhythmic handgrip exercise. Eleven healthy subjects performed the exercise at 5 or 15% of maximal voluntary contraction (MVC) in random order. During the exercise, forearm blood flow (FBF), which was continuously measured using Doppler ultrasound, was reduced in five steps by manipulating the inner pressure of an occlusion cuff on the upper arm. The FBF at each level was maintained for 3 min. The initial reductions in FBF elicited no hemodynamic changes, but once FBF fell below a threshold, mean arterial blood pressure (MAP) and heart rate (HR) increased and total vascular conductance (TVC) decreased in a linear manner. The threshold FBF during the 15% MVC trial was significantly higher than during the 5% MVC trial. The gain was then estimated as the slope of the relationship between the hemodynamic responses and FBFs below the threshold. The gains for the MAP and TVC responses did not differ between workloads, but the gain for the HR response was greater in the 15% MVC trial. Our findings thus indicate that increasing the workload shifts the threshold for the muscle metaboreflex to higher blood flows without changing the gain of the reflex for the MAP and TVC responses, whereas it enhances the gain for the HR response.

Effects of feeding on muscle blood flow during prolonged exercise in miniature swine

1991 ◽  
Vol 70 (3) ◽  
pp. 1097-1104 ◽  
Author(s):  
M. D. McKirnan ◽  
C. G. Gray ◽  
F. C. White
Keyword(s):  
Blood Flow ◽  
Prolonged Exercise ◽  
Regional Blood Flow ◽  
Muscle Blood Flow ◽  
Lactate Concentration ◽  
Exercise Bout ◽  
Cardiovascular Reflexes ◽  
Miniature Swine ◽  
External Work ◽  
Mixed Venous

Eight exercise-trained miniature swine were studied during prolonged treadmill runs (100 min) under fasting and preexercise feeding conditions. Each animal ran at identical external work loads that corresponded to 65% of the heart rate reserve (210-220 beats/min) for the two exercise bouts. Cardiac outputs and stroke volumes were higher and heart rates lower for fed than for fasting runs (P less than 0.05). Preexercise feeding did not alter oxygen consumption, core temperature, mean arterial pressure, and arterial-mixed venous oxygen difference during prolonged exercise; however, mixed venous lactate concentration was lower at end exercise than during fasting conditions (1.2 vs. 2.6 mM, P less than 0.05). Microsphere measurements of regional blood flow revealed significantly higher total gastrointestinal flow (23%) for fed than for fasting conditions. Throughout the exercise bout, blood flow to the biceps femoris, semitendinosus, and tibialis anterior muscles was lower in fed than in fasted nimals (P less than 0.05). Combined hindlimb muscle blood flow averaged 15 ml.min-1.100 g-1 (18%, P less than 0.05) lower under feeding than fasting run conditions. These findings provide further evidence that cardiovascular reflexes originate in the gut after feeding to increase cardiac output and redistribute a portion of the blood flow away from active muscle to the gastrointestinal tract during prolonged exercise.

scholarly journals Systemic hypoxia and vasoconstrictor responsiveness in exercising human muscle

2006 ◽  
Vol 101 (5) ◽  
pp. 1343-1350 ◽  
Author(s):  
Brad W. Wilkins ◽  
William G. Schrage ◽  
Zhong Liu ◽  
Kellie C. Hancock ◽  
Michael J. Joyner
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Blood Flow ◽  
Forearm Blood Flow ◽  
Minute Ventilation ◽  
Exercise Bout ◽  
Dependent Manner ◽  
Forearm Exercise ◽  
End Tidal ◽  
Hypoxic Exercise

Exercise blunts sympathetic α-adrenergic vasoconstriction (functional sympatholysis). We hypothesized that sympatholysis would be augmented during hypoxic exercise compared with exercise alone. Fourteen subjects were monitored with ECG and pulse oximetry. Brachial artery and antecubital vein catheters were placed in the nondominant (exercising) arm. Subjects breathed hypoxic gas to titrate arterial O2 saturation to 80% while remaining normocapnic via a rebreath system. Baseline and two 8-min bouts of rhythmic forearm exercise (10 and 20% of maximum) were performed during normoxia and hypoxia. Forearm blood flow, blood pressure, heart rate, minute ventilation, and end-tidal CO2 were measured at rest and during exercise. Vasoconstrictor responsiveness was determined by responses to intra-arterial tyramine during the final 3 min of rest and each exercise bout. Heart rate was higher during hypoxia ( P < 0.01), whereas blood pressure was similar ( P = 0.84). Hypoxic exercise potentiated minute ventilation compared with normoxic exercise ( P < 0.01). Forearm blood flow was higher during hypoxia compared with normoxia at rest (85 ± 9 vs. 66 ± 7 ml/min), at 10% exercise (276 ± 33 vs. 217 ± 27 ml/min), and at 20% exercise (464 ± 32 vs. 386 ± 28 ml/min; P < 0.01). Arterial epinephrine was higher during hypoxia ( P < 0.01); however, venoarterial norepinephrine difference was similar between hypoxia and normoxia before ( P = 0.47) and during tyramine administration ( P = 0.14). Vasoconstriction to tyramine (%decrease from pretyramine values) was blunted in a dose-dependent manner with increasing exercise intensity ( P < 0.01). Interestingly, vasoconstrictor responsiveness tended to be greater ( P = 0.06) at rest (−37 ± 6% vs. −33 ± 6%), at 10% exercise (−27 ± 5 vs. −22 ± 4%), and at 20% exercise (−22 ± 5 vs. −14 ± 4%) between hypoxia and normoxia, respectively. Thus sympatholysis is not augmented by moderate hypoxia nor does it contribute to the increased blood flow during hypoxic exercise.

Muscle chemoreflex elevates muscle blood flow and O2 uptake at exercise onset in nonischemic human forearm

2001 ◽  
Vol 91 (5) ◽  
pp. 2010-2016 ◽  
Author(s):  
Stéphane Perrey ◽  
Michael E. Tschakovsky ◽  
Richard L. Hughson
Keyword(s):  
Blood Flow ◽  
Forearm Blood Flow ◽  
Muscle Blood Flow ◽  
O2 Uptake ◽  
Exercise Onset ◽  
Human Forearm ◽  
Forearm Exercise ◽  
Type Of Exercise ◽  
Adaptation Phase ◽  
Muscle Chemoreflex

We tested the hypothesis that increases in forearm blood flow (FBF) during the adaptive phase at the onset of moderate exercise would allow a more rapid increase in muscle O2 uptake (V˙o 2  mus). Fifteen subjects completed forearm exercise in control (Con) and leg occlusion (Occ) conditions. In Occ, exercise of ischemic calf muscles was performed before the onset of forearm exercise to activate the muscle chemoreflex evoking a 25-mmHg increase in mean arterial pressure that was sustained during forearm exercise. Eight subjects who increased FBF during Occ compared with Con in the adaptation phase by >30 ml/min were considered “responders.” For the responders, a higherV˙o 2  mus accompanied the higher FBF only during the adaptive phase of the Occ tests, whereas there was no difference in the baseline or steady-state FBF orV˙o 2  mus between Occ and Con. Supplying more blood flow at the onset of exercise allowed a more rapid increase in V˙o 2  mussupporting our hypothesis that, at least for this type of exercise, O2 supply might be limiting.

scholarly journals Hyperbaric hyperoxia reduces exercising forearm blood flow in humans

2011 ◽  
Vol 300 (5) ◽  
pp. H1892-H1897 ◽  
Author(s):  
Darren P. Casey ◽  
Michael J. Joyner ◽  
Paul L. Claus ◽  
Timothy B. Curry
Keyword(s):  
Skeletal Muscle ◽  
Blood Flow ◽  
Forearm Blood Flow ◽  
Muscle Blood Flow ◽  
Hyperbaric Hyperoxia ◽  
Exercise Hyperemia ◽  
Forearm Vascular Conductance ◽  
Forearm Exercise ◽  
The Impact ◽  
Hyperemic Response

Hypoxia during exercise augments blood flow in active muscles to maintain the delivery of O2 at normoxic levels. However, the impact of hyperoxia on skeletal muscle blood flow during exercise is not completely understood. Therefore, we tested the hypothesis that the hyperemic response to forearm exercise during hyperbaric hyperoxia would be blunted compared with exercise during normoxia. Seven subjects (6 men/1 woman; 25 ± 1 yr) performed forearm exercise (20% of maximum) under normoxic and hyperoxic conditions. Forearm blood flow (FBF; in ml/min) was measured using Doppler ultrasound. Forearm vascular conductance (FVC; in ml·min−1·100 mmHg−1) was calculated from FBF and blood pressure (in mmHg; brachial arterial catheter). Studies were performed in a hyperbaric chamber with the subjects supine at 1 atmospheres absolute (ATA) (sea level) while breathing normoxic gas [21% O2, 1 ATA; inspired Po2 (PiO2) ≈ 150 mmHg] and at 2.82 ATA while breathing hyperbaric normoxic (7.4% O2, 2.82 ATA, PiO2 ≈ 150 mmHg) and hyperoxic (100% O2, 2.82 ATA, PiO2 ≈ 2,100 mmHg) gas. Resting FBF and FVC were less during hyperbaric hyperoxia compared with hyperbaric normoxia ( P < 0.05). The change in FBF and FVC (Δ from rest) during exercise under normoxia (204 ± 29 ml/min and 229 ± 37 ml·min−1·100 mmHg−1, respectively) and hyperbaric normoxia (203 ± 28 ml/min and 217 ± 35 ml·min−1·100 mmHg−1, respectively) did not differ ( P = 0.66–0.99). However, the ΔFBF (166 ± 21 ml/min) and ΔFVC (163 ± 23 ml·min−1·100 mmHg−1) during hyperbaric hyperoxia were substantially attenuated compared with other conditions ( P < 0.01). Our data suggest that exercise hyperemia in skeletal muscle is highly dependent on oxygen availability during hyperoxia.

Vasodilation contributes to the rapid hyperemia with rhythmic contractions in humans

1998 ◽  
Vol 76 (4) ◽  
pp. 418-427 ◽  
Author(s):  
J K Shoemaker ◽  
M E Tschakovsky ◽  
R L Hughson
Keyword(s):  
Blood Flow ◽  
Forearm Blood Flow ◽  
Perfusion Pressure ◽  
Blood Velocity ◽  
Pulsed Doppler ◽  
Contraction Rate ◽  
Handgrip Exercise ◽  
Arterial Diameter ◽  
Exercise Tests ◽  
Rhythmic Contractions

The hypothesis that the rapid increases in blood flow at the exercise onsetare exclusively due to the mechanical effects of the muscle pump was tested in six volunteersduring dynamic handgrip exercise. While supine, each subject completed a series of eightdifferent exercise tests in which brachial artery blood pressure (BP) was altered by25–30 mmHg (1 mmHg = 133.3 Pa) by positioning the arm above or below the heart.Two different weights, corresponding to 4.9 and 9.7% of maximal voluntary isometriccontraction, were raised and lowered at two different contraction rate schedules (1s:1s and 2s:2swork–rest) each with a 50% duty cycle. Beat-by-beat measures of mean blood velocity (MBV)(pulsed Doppler) were obtained at rest and for 5 min following step increases in work ratewith emphasis on the first 24 s. MBV was increased 50–100% above rest following the firstcontraction in both arm positions (p < 0.05). The increase in MBV from rest was greaterin the below position compared with above, and this effect was observed following the first andsubsequent contractions (p < 0.05). However, the positional effect on the increase inMBV could not be explained entirely by the ~40% greater BP in this position. Also, the greaterworkload resulted in greater increases in MBV as early as the first contraction, compared withthe light workload (p < 0.05) despite similar reductions in forearm volume followingsingle contractions. MBV was greater with faster contraction rate tests by 8 s of exercise. Itwas concluded that microvascular vasodilation must act in concert with a reduction in venouspressure to increase forearm blood flow within the initial 2–4 s of exercise.Key words: Doppler, mean blood velocity, arterial diameter,handgrip exercise, perfusion pressure.

Effect of two methods of hand heating on body temperature, forearm blood flow, and deep venous oxygen saturation

1990 ◽  
Vol 259 (5) ◽  
pp. E639-E643 ◽  
Author(s):  
I. W. Gallen ◽  
I. A. Macdonald
Keyword(s):  
Blood Flow ◽  
Body Temperature ◽  
Oxygen Content ◽  
Forearm Blood Flow ◽  
Venous Blood ◽  
Blood Oxygen ◽  
Left Hand ◽  
Venous Oxygen Saturation ◽  
Baseline Values ◽  
Healthy Females

Two methods of hand heating [warmed blanket 40 degrees C (WB) and warm-air box 55 degrees C (WA)] were compared with the effect of no heating (control) in six healthy females. After 30 min baseline, the left hand was either heated for 1 h or not heated. Measurements were made of skin temperature (ST), core temperature (CT), right forearm (FBF) and skin blood flow (SBF), and right forearm deep venous blood oxygen content with and without occlusion of the hand circulation. CT rose above baseline in WB (by +0.2 degrees C, P less than 0.01) but not with control or WA. Abdominal ST rose only with WB (by +0.66 degrees C above baseline, P less than 0.01). FBF increased above baseline values with both WA (by +10 ml.l forearm-1.min-1) and WB (by +12 ml.l forearm-1.min-1), but neither was significantly greater than the control. SBF increased above baseline only with WB (by +202 mV, P less than 0.01), and this was significantly greater than control SBF. With an occluded hand circulation, deep venous oxygen content rose above baseline values with WB only (+6.0%, P less than 0.01) but was not greater than control with either method of hand heating. We conclude that using a warm-air box has less effect than a heated blanket on the measured variables.

Effects of forearm bier block with bretylium on the hemodynamic and metabolic responses to handgrip

2000 ◽  
Vol 279 (2) ◽  
pp. H586-H593 ◽  
Author(s):  
Frank Lee ◽  
J. Kevin Shoemaker ◽  
Patrick M. McQuillan ◽  
Allen R. Kunselman ◽  
Michael B. Smith ◽  
...  
Keyword(s):  
Blood Flow ◽  
Forearm Blood Flow ◽  
Muscle Blood Flow ◽  
Reflex Responses ◽  
Muscle Ph ◽  
Before And After ◽  
Autonomic Reflex ◽  
Bier Block ◽  
Forearm Muscle ◽  
Increased Blood Flow

We tested the hypothesis that a reduction in sympathetic tone to exercising forearm muscle would increase blood flow, reduce muscle acidosis, and attenuate reflex responses. Subjects performed a progressive, four-stage rhythmic handgrip protocol before and after forearm bier block with bretylium as forearm blood flow (Doppler) and metabolic (venous effluent metabolite concentration and 31P-NMR indexes) and autonomic reflex responses (heart rate, blood pressure, and sympathetic nerve traffic) were measured. Bretylium inhibits the release of norepinephrine at the neurovascular junction. Bier block increased blood flow as well as oxygen consumption in the exercising forearm ( P < 0.03 and P < 0.02, respectively). However, despite this increase in flow, venous K+ release and H+release were both increased during exercise ( P < 0.002 for both indexes). Additionally, minimal muscle pH measured during the first minute of recovery with NMR was lower after bier block (6.41 ± 0.08 vs. 6.20 ± 0.06; P < 0.036, simple effects). Meanwhile, reflex effects were unaffected by the bretylium bier block. The results support the conclusion that sympathetic stimulation to muscle during exercise not only limits muscle blood flow but also appears to limit anaerobiosis and H+ release, presumably through a preferential recruitment of oxidative fibers.

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