Evidence for sympatholysis at the onset of forearm exercise

2002 ◽  
Vol 93 (2) ◽  
pp. 555-560 ◽  
Author(s):  
Darren S. DeLorey ◽  
Simon S. Wang ◽  
J. Kevin Shoemaker
Keyword(s):  
Blood Flow ◽  
Forearm Blood Flow ◽  
Lower Body Negative Pressure ◽  
Voluntary Contraction ◽  
Dependent Manner ◽  
Vascular Conductance ◽  
Exercise Hyperemia ◽  
Forearm Vascular Conductance ◽  
Forearm Exercise ◽  
Handgrip Contractions

The effect of augmented sympathetic outflow on forearm vascular conductance after single handgrip contractions of graded intensity was examined to determine whether sympatholysis occurs early in exercise ( n = 7). While supine, subjects performed contractions that were 1 s in duration and 15, 30, and 60% of maximal voluntary contraction (MVC) in intensity. The contractions were repeated during control and lower body negative pressure (LBNP) (−40 mmHg) sessions. Forearm blood flow (FBF; Doppler ultrasound) and mean arterial pressure were measured continuously for 30 s before and 60 s after the single contractions. Vascular conductance (VC) was calculated. Total postcontraction blood flow increased in an exercise intensity-dependent manner. Compared with control, LBNP caused a reduction in baseline and postexercise FBF ( P < 0.05), VC ( P < 0.01), as well as total excess flow ( P < 0.01). Specifically, during LBNP, baseline FBF and VC were reduced by 29 and 34% of control, respectively ( P < 0.05). After the 15% MVC contraction, peak VC during LBNP was reduced by a magnitude similar to that during baseline (i.e., ∼30%), but it was only reduced by 15% during both the 30 and 60% MVC trials ( P < 0.01). It was concluded that the stimuli for exercise hyperemia during moderate and heavy, but not mild, handgrip exercise intensities, diminish the vasoconstrictor effects of LBNP. Furthermore, these data demonstrate that this sympatholysis occurs early in exercise.

Exogenous NO administration and α-adrenergic vasoconstriction in human limbs

2003 ◽  
Vol 95 (6) ◽  
pp. 2370-2374 ◽  
Author(s):  
Jaya B. Rosenmeier ◽  
Sandy J. Fritzlar ◽  
Frank A. Dinenno ◽  
Michael J. Joyner
Keyword(s):  
Blood Flow ◽  
Skeletal Muscles ◽  
Forearm Blood Flow ◽  
Norepinephrine Release ◽  
Vascular Conductance ◽  
No Donor ◽  
Exercise Hyperemia ◽  
Functional Sympatholysis ◽  
Human Forearm ◽  
Forearm Vascular Conductance

Nitric oxide (NO) is capable of blunting α-adrenergic vasoconstriction in contracting skeletal muscles of experimental animals (functional sympatholysis). We therefore tested the hypothesis that exogenous NO administration can blunt α-adrenergic vasoconstriction in resting human limbs by measuring forearm blood flow (FBF; Doppler ultrasound) and blood pressure in eight healthy males during brachial artery infusions of three α-adrenergic constrictors (tyramine, which evokes endogenous norepinephrine release; phenylephrine, an α1-agonist; and clonidine, an α2-agonist). To simulate exercise hyperemia, the vasoconstriction caused by the α-agonists was compared during adenosine-mediated (>50% NO independent) and sodium nitroprusside-mediated (SNP; NO donor) vasodilation of the forearm. Both adenosine and SNP increased FBF from ∼35–40 to ∼200–250 ml/min. All three α-adrenergic constrictor drugs caused marked reductions in FBF and calculated forearm vascular conductance ( P < 0.05). The relative reductions in forearm vascular conductance caused by the α-adrenergic constrictors during SNP infusion were similar (tyramine, –74 ± 3 vs. –65 ± 2%; clonidine, –44 ± 6 vs. –44 ± 6%; P > 0.05) or slightly greater (phenylephrine, –47 ± 6 vs. –33 ± 6%; P < 0.05) compared with the responses during adenosine. In conclusion, these results indicate that exogenous NO sufficient to raise blood flow to levels simulating those seen during exercise does not blunt α-adrenergic vasoconstriction in the resting human forearm.

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.

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.

scholarly journals Exercise hyperemia and vasoconstrictor responses in humans with cystic fibrosis

2005 ◽  
Vol 99 (5) ◽  
pp. 1866-1871 ◽  
Author(s):  
William G. Schrage ◽  
Brad W. Wilkins ◽  
Vicki L. Dean ◽  
John P. Scott ◽  
Nancy K. Henry ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Cystic Fibrosis ◽  
Blood Flow ◽  
Forearm Blood Flow ◽  
Cold Pressor Test ◽  
Cold Pressor ◽  
Pressor Test ◽  
Sympathetic Vasoconstriction ◽  
Exercise Hyperemia ◽  
Forearm Exercise

ATP released from circulating erythrocytes is a potential signal regulating muscle blood flow during exercise (exercise hyperemia), and intravascular ATP appears to blunt sympathetic vasoconstriction during exercise. Erythrocytes from patients with cystic fibrosis (CF) do not release ATP. The goal of the present study was to determine whether increases in forearm blood flow during exercise are blunted in CF patients and whether CF patients exhibit greater vasoconstrictor responsiveness during exercise. Nine control subjects and 10 CF patients who were free of other disease complications (∼96% O2 saturation) performed incremental rhythmic forearm exercise at 5, 10, and 15% of maximum handgrip strength for 21 min (7 min at each workload). We used a cold pressor test to evoke sympathetic vasoconstriction under resting conditions and at each exercise workload. As a control, subjects performed a second exercise bout without the cold pressor test. Continuous brachial artery blood velocity was monitored beat-to-beat, and vessel diameter was assessed by Doppler ultrasound. Artery diameter, as well as blood pressure, heart rate, and O2 saturation, was measured at steady-state exercise and at 1 min into the cold pressor stimulus. Blood pressure and heart rate responses to the forearm exercise and each cold pressor test were similar in both groups ( P > 0.05). Contrary to our hypothesis, forearm blood flow ( P = 0.91) and forearm vascular conductance ( P = 0.82) were similar at rest and at each level of exercise between CF patients and controls. Additionally, there was no difference in the degree of sympathetic vasoconstriction between groups at rest and at each level of exercise ( P = 0.22). Our results suggest that ATP released from the deformation of erythrocytes is not an obligatory signal for exercise hyperemia in human skeletal muscle.

Hypohydration affects forearm vascular conductance independent of heart rate during exercise

1992 ◽  
Vol 73 (4) ◽  
pp. 1232-1237 ◽  
Author(s):  
C. G. Tankersley ◽  
D. H. Zappe ◽  
T. G. Meister ◽  
W. L. Kenney
Keyword(s):  
Heart Rate ◽  
Blood Flow ◽  
Mean Arterial Pressure ◽  
Forearm Blood Flow ◽  
Body Core Temperature ◽  
Esophageal Temperature ◽  
Vascular Conductance ◽  
Cutaneous Vasodilation ◽  
Forearm Vascular Conductance ◽  
Body Core

Elevated body core temperature stimulates cutaneous vasodilation, which can be modified by nonthermal factors. To test whether hypohydration affects forearm vascular conductance discretely from relative alterations in heart rate (HR), eight trained cyclists exercised progressively for 20 min each at 60, 120, and 180 W [approximately 22, 37, and 55% of maximal cycling O2 consumption (VO2peak), respectively] in a warm humid environment (dry bulb temperature 30 degrees C; wet bulb temperature 24 degrees C). Esophageal temperature and forearm blood flow were measured every 30 s, and mean arterial pressure and HR were measured at rest and during each exercise intensity (minutes 15, 35, and 55). In the hypovolemic (HP) compared with the euvolemic (EU) state, blood volume was contracted by 24-h fluid restriction an average of 510 ml, and this difference was sustained throughout exercise. The esophageal temperature and HR responses were similar between EU and HP states at 60 and 120 W but were significantly (P < 0.05) higher in HP by the end of 180 W. In contrast, the forearm blood flow response was significantly (P < 0.05) depressed during exercise at 120 and 180 W in HP, whereas mean arterial pressure remained similar between conditions. When body core temperature is elevated in a hypohydrated state, forearm vascular conductance is reduced at exercise intensities of approximately 37% VO2peak, which is independent of relative changes in HR. These findings are consistent with the notion that during exercise an attenuated cutaneous vasodilation is elicited by alterations in regionalized sympathetic outflow, which is unaccompanied by activation of cardiac pacemaker cells.

scholarly journals Aging is associated with altered vasodilator kinetics in dynamically contracting muscle: role of nitric oxide

2015 ◽  
Vol 119 (3) ◽  
pp. 232-241 ◽  
Author(s):  
Darren P. Casey ◽  
Sushant M. Ranadive ◽  
Michael J. Joyner
Keyword(s):  
Nitric Oxide ◽  
Blood Flow ◽  
Young Adults ◽  
Voluntary Contraction ◽  
Brachial Artery Diameter ◽  
Contracting Muscle ◽  
Duty Cycles ◽  
Forearm Vascular Conductance ◽  
Monoexponential Model ◽  
Forearm Exercise

We tested the hypothesis that aging would be associated with slowed vasodilator kinetics in contracting muscle in part due to a reduced nitric oxide (NO) bioavailability. Young ( n = 10; 24 ± 2 yr) and older ( n = 10; 67 ± 2 yr) adults performed rhythmic forearm exercise (4 min each) at 10, 20, and 30% of max during saline infusion (control) and NO synthase (NOS) inhibition. Brachial artery diameter and velocities were measured using Doppler ultrasound. Forearm vascular conductance (FVC) was calculated for each duty cycle (1 s contraction/2 s relaxation) from forearm blood flow (FBF; ml/min) and blood pressure (mmHg) and fit with a monoexponential model. The main parameters derived from the model were the amplitude of the FBF and FVC response and the number of duty cycles for FBF and FVC to change 63% of the steady-state amplitude (τFBF and τFVC). Under control conditions 1) the amplitude of the FVC response at 30% maximal voluntary contraction (MVC) was lower in older compared with young adults (319 ± 33 vs. 462 ± 52 ml·min−1·100 mmHg−1; P < 0.05) and 2) τFVC was slower in older (10 ± 1, 13 ± 1, and 15 ± 1 duty cycles) compared with young (6 ± 1, 9 ± 1, and 11 ± 1 duty cycles) adults at all intensities ( P < 0.05). In young adults, NOS inhibition blunted the amplitude of the FVC response at 30% MVC and prolonged the τFVC at all intensities (10 ± 2, 12 ± 1, and 16 ± 2 duty cycles; P < 0.05), whereas it did not change in older adults. Our data indicate that the blood flow and vasodilator kinetics in exercising muscle are altered with aging possibly due to blunted NO signaling.

Aging and the skin blood flow response to the unloading of baroreceptors during heat and cold stress

2004 ◽  
Vol 96 (3) ◽  
pp. 1019-1025 ◽  
Author(s):  
Glaucio Scremin ◽  
W. Larry Kenney
Keyword(s):  
Blood Flow ◽  
Heat Stress ◽  
Cold Stress ◽  
Skin Blood Flow ◽  
Forearm Blood Flow ◽  
Lower Body Negative Pressure ◽  
Older Men ◽  
Stress Conditions ◽  
Vascular Conductance ◽  
Heat And Cold Stress

Control of skin blood flow (SkBF) is on the efferent arm of both thermoregulatory and nonthermoregulatory reflexes. To what extent aging may affect the SkBF response when these two reflex systems interact is unknown. To determine the response of aged skin to the unloading of baroreceptors in thermoneutral, cold stress, and heat stress conditions, sequential bouts of nonhypotensive lower body negative pressure (LBNP) were applied at -10, -20, and -30 mmHg in 14 young (18–25 yr) and 14 older (63–78 yr) men. SkBF was measured by laser-Doppler velocimetry (averaged over 2 forearm sites), and data are expressed as percentage of maximal cutaneous vascular conductance (%CVCmax). Total forearm blood flow was measured by venous occlusion plethysmography, and forearm vascular conductance (FVC) was calculated as the ratio of forearm blood flow to mean arterial pressure. In young men, all three intensities of LBNP in thermoneutrality decreased FVC significantly ( P < 0.05), but FVC at -10 mmHg did not change in the older men. There were no significant LBNP effects on %CVCmax. Application of LBNP during cold stress did not significantly change %CVCmax or FVC in either age group. During heat stress, -10 to -30 mmHg of LBNP decreased FVC significantly ( P < 0.05) in both age groups, but these decreases were attenuated in the older men ( P < 0.05). %CVCmax decreased at -30 mmHg in the younger men only. These results suggest that older men have an attenuated skin vasoconstrictor response to the unloading of baroreceptors in heat stress conditions. Furthermore, the forearm vasoconstriction elicited by LBNP in older men reflects that of underlying tissue (i.e., muscle) rather than that of skin, whereas -30 mmHg LBNP also decreases SkBF in young hyperthermic men.

Evidence for a rapid vasodilatory contribution to immediate hyperemia in rest-to-mild and mild-to-moderate forearm exercise transitions in humans

2004 ◽  
Vol 97 (3) ◽  
pp. 1143-1151 ◽  
Author(s):  
Natasha R. Saunders ◽  
Michael E. Tschakovsky
Keyword(s):  
Maximal Voluntary Contraction ◽  
Voluntary Contraction ◽  
Arterial Blood Flow ◽  
Vascular Conductance ◽  
Muscle Pump ◽  
Arterial Blood ◽  
Exercise Hyperemia ◽  
Forearm Vascular Conductance ◽  
Condition B

Controversy exists regarding the contribution of a rapid vasodilatory mechanism(s) to immediate exercise hyperemia. Previous in vivo investigations have exclusively examined rest-to-exercise (R-E) transitions where both the muscle pump and early vasodilator mechanisms may be activated. To isolate vasodilatory onset, the present study investigated the onset of exercise hyperemia in an exercise-to-exercise (E-E) transition, where no further increase in muscle pump contribution would occur. Eleven subjects lay supine and performed a step increase from rest to 3 min of mild (10% maximal voluntary contraction), rhythmic, dynamic forearm handgrip exercise, followed by a further step to moderate exercise (20% maximal voluntary contraction) in each of arm above ( condition A) or below ( condition B) heart level. Beat-by-beat measures of brachial arterial blood flow (Doppler ultrasound) and blood pressure (arterial tonometry) were performed. We observed an immediate increase in forearm vascular conductance in E-E transitions, and the magnitude of this increase matched that of the R-E transitions within each of the arm positions ( condition A: E-E, 52.8 ± 10.7 vs. R-E, 60.3 ± 11.7 ml·min−1·100 mmHg−1, P = 0.66; condition B: E-E, 43.2 ± 12.8 vs. R-E, 33.9 ± 8.2 ml·min−1·100 mmHg−1, P = 0.52). Furthermore, changes in forearm vascular conductance were identical between R-E and E-E transitions over the first nine contraction-relaxation cycles in condition A. The immediate and identical increase in forearm vascular conductance in R-E and E-E transitions within arm positions provides strong evidence that rapid vasodilation contributes to immediate exercise hyperemia in humans. Specific vasodilatory mechanisms responsible remain to be determined.

Augmented Muscle Vasodilatory Responses in Obese Children with Glu27 β2-Adrenoceptor Polymorphism

2008 ◽  
Vol 20 (2) ◽  
pp. 157-168 ◽  
Author(s):  
Alexandre G. da Silva ◽  
Mauricio M. Ribeiro ◽  
Ivani C. Trombetta ◽  
Christiane Nicolau ◽  
Eliana Frazzatto ◽  
...  
Keyword(s):  
Blood Flow ◽  
Forearm Blood Flow ◽  
Color Word ◽  
Isometric Exercise ◽  
Obese Children ◽  
Vascular Conductance ◽  
Word Test ◽  
Forearm Vascular Conductance ◽  
Stroop Color Word Test

This study examined forearm vasodilatation during mental challenge and exercise in 72 obese children (OC; age = 10 ± 0.1 years) homozygous with polymorphism in the allele 27 of the β2-adrenoceptors: Gln27 (n = 61) and Glu27 (n = 11). Forearm blood flow was recorded during 3 min of each using the Stroop color-word test (MS) and handgrip isometric exercise. Baseline hemodynamic and vascular measurements were similar. During the MS, peak forearm vascular conductance was significantly greater in group Glu27 (Δ = 0.35 ± 0.4 vs. 0.12 ± 0.1 units, respectively, p = .042). Similar results were found during exercise (Δ = 0.64 ± 0.1 vs. 0.13 ± 0.1 units, respectively, p = .035). Glu27 OC increased muscle vasodilatory responsiveness upon the MS and exercise.

Gly16 + Glu27 β2-adrenoceptor polymorphisms cause increased forearm blood flow responses to mental stress and handgrip in humans

2005 ◽  
Vol 98 (3) ◽  
pp. 787-794 ◽  
Author(s):  
Ivani C. Trombetta ◽  
Luciana T. Batalha ◽  
Maria U. P. B. Rondon ◽  
Mateus C. Laterza ◽  
Eliana Frazzatto ◽  
...  
Keyword(s):  
Blood Flow ◽  
Sympathetic Nerve ◽  
Mental Stress ◽  
Sympathetic Nerve Activity ◽  
Forearm Blood Flow ◽  
Muscle Sympathetic Nerve Activity ◽  
Isometric Exercise ◽  
Vascular Conductance ◽  
Nerve Activity ◽  
Forearm Vascular Conductance

We hypothesized that the muscle vasodilatation during mental stress and exercise would vary among humans who are polymorphic at alleles 16 and 27 of the β2-adrenoceptors. From 216 preselected volunteers, we studied 64 healthy, middle-aged normotensive women selected to represent three genotypes: homozygous for the alleles Arg16 and Gln27 (Arg16/Gln27, n = 34), Gly16 and Gln27 (Gly16/Gln27, n = 20), and Gly16 and Glu27 (Gly16/Glu27, n = 10). Forearm blood flow (plethysmography) and muscle sympathetic nerve activity (microneurography) were recorded during 3-min Stroop color-word test and 3-min handgrip isometric exercise (30% maximal voluntary contraction). Baseline muscle sympathetic nerve activity, forearm vascular conductance, mean blood pressure, and heart rate were not different among groups. During mental stress, the peak forearm vascular conductance responses were greater in Gly16/Glu27 group than in Gly16/Gln27 and Arg16/Gln27 groups (1.79 ± 0.66 vs. 0.70 ± 0.11 and 0.58 ± 0.12 units, P = 0.03). Similar results were found during exercise (0.80 ± 0.25 vs. 0.28 ± 0.08 and 0.31 ± 0.08 units, P = 0.02). Further analysis in a subset of subjects showed that brachial intra-arterial propranolol infusion abolished the difference in vasodilatory response between Gly16/Glu27 ( n = 6) and Arg16/Gln27 ( n = 7) groups during mental stress (0.33 ± 0.20 vs. 0.46 ± 0.21 units, P = 0.50) and exercise (0.08 ± 0.06 vs. 0.03 ± 0.03 units, P = 0.21). Plasma epinephrine concentration in Arg16/Gln27 and Gly16/Glu27 groups was similar. In conclusion, women who are homozygous for Gly16/Glu27 of the β2-adrenoceptors have augmented muscle vasodilatory responsiveness to mental stress and exercise.

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