Cardiopulmonary baroreflexes do not modulate exercise-induced sympathoexcitation

1988 ◽  
Vol 64 (5) ◽  
pp. 2197-2203 ◽  
Author(s):  
D. R. Seals
Keyword(s):  
Lower Body Negative Pressure ◽  
Voluntary Contraction ◽  
Voluntary Exercise ◽  
Sympathetic Outflow ◽  
Isometric Handgrip ◽  
General Hypothesis ◽  
Isometric Handgrip Exercise ◽  
Exercise Induced ◽  
The Right ◽  
Exercise In Humans

The purpose of this study was to test the general hypothesis that sympathoinhibitory cardiopulmonary baroreflexes modulate sympathetic outflow during voluntary exercise in humans. Direct (microneurographic) measurements of postganglionic sympathetic nerve activity to noncontracting muscle (MSNA) were made from the right peroneal nerve in the leg, and arterial pressure (AP) and heart rate (HR) were recorded in 10 healthy subjects before (control) and for 2.5 min during each of five interventions: 1) lower-body negative pressure at -10 mmHg (LBNP) alone, 2 and 3) isometric handgrip exercise at 15 and 30% of maximal voluntary contraction (MVC) alone, and 4 and 5) handgrip at 15 and 30% MVC performed during LBNP. During LBNP alone, which should have reduced cardiopulmonary baroreflex sympathoinhibition, AP and HR did not change from control, but MSNA increased 93 +/- 24% (P less than 0.05). Handgrip elicited contraction intensity-dependent increases in AP and HR (P less than 0.05), but MSNA increased above control only at the 30% MVC level (165 +/- 30%, P less than 0.05). The HR, AP, and MSNA responses to either level of handgrip performed during LBNP were not different from the algebraic sums of the corresponding responses to handgrip and LBNP performed separately (P greater than 0.05). Since there was no facilitation of the MSNA response to handgrip when performed during LBNP compared with algebraic sums of the separate responses, our results do not support the hypothesis that cardiopulmonary baroreflexes modulate (inhibit) sympathetic outflow during exercise in humans.

Autonomic mediation of the pressor responses to isometric exercise in humans

1988 ◽  
Vol 64 (5) ◽  
pp. 2190-2196 ◽  
Author(s):  
D. R. Seals ◽  
P. B. Chase ◽  
J. A. Taylor
Keyword(s):  
Sympathetic Nerve Activity ◽  
Isometric Exercise ◽  
Voluntary Contraction ◽  
Handgrip Exercise ◽  
Isometric Handgrip ◽  
Nerve Activity ◽  
Pressor Responses ◽  
Isometric Handgrip Exercise ◽  
The Right ◽  
Exercise In Humans

The purpose of this study was to determine the respective contributions of tachycardia and increases in sympathetic nerve activity (SNA) in mediating the pressor responses to fatiguing vs. nonfatiguing levels of isometric handgrip exercise (IHE) in humans. We performed direct (microneurographic) measurements of muscle SNA from the right peroneal nerve in the leg and recorded arterial pressure (AP) and heart rate (HR) in eight healthy subjects before (control), during, and after 2.5 min of IHE at 15, 25, or 35% of maximal voluntary contraction (MVC). At 15% MVC, AP increased during the initial 1.5 min of IHE (7 mmHg, P less than 0.05) and remained at this level; at 25 and 35% MVC, AP increased throughout IHE (22 and 34 mmHg vs. control, respectively, P less than 0.05). HR increased during the initial 1.5 min of IHE at all three levels (5, 12, and 19 beats/min, respectively, P less than 0.05) but did not increase further over the last minute. At 15% MVC, muscle SNA did not increase above control; during 25 and 35% MVC, muscle SNA did not increase during the 1st min of IHE but increased progressively thereafter (109 and 205% vs. control, respectively, P less than 0.05). The magnitudes of the average increases in AP and muscle SNA over the last minute of IHE were directly related (r = 0.99, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Splenic constriction during isometric handgrip exercise in humans

2008 ◽  
Vol 33 (5) ◽  
pp. 990-996 ◽  
Author(s):  
Maria F. Frances ◽  
Zeljko Dujic ◽  
J. Kevin Shoemaker
Keyword(s):  
Lower Body Negative Pressure ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Moderate Intensity ◽  
Isometric Handgrip ◽  
Human Spleen ◽  
Splenic Volume ◽  
Isometric Handgrip Exercise ◽  
Valsalva's Manoeuvre ◽  
Prolonged Apnea

During the first minute of a moderate-intensity isometric handgrip (HG) exercise, there is an increase in stroke volume and cardiac output that occurs without any change in systemic vascular conductance. Although the mechanism of increased venous return is not yet known, current focus has been placed on the constriction of visceral organs. The human spleen represents a compliant organ with high perfusion that constricts during the rather severe stresses of maximal exercise, a diving reflex, or prolonged apnea. This study tested the hypothesis that spleen constriction occurs during isometric HG exercise. Eight participants performed a 1 min isometric HG test at 40% maximum voluntary contraction. Splenic length and width were measured (with ultrasound imaging) after 1 min of exercise, and volume was calculated. To investigate the reflex specificity of this response, spleen dimensions were also measured during 4 min of lower-body negative pressure (LBNP; –20 mm Hg). To test the additional impact of altered breathing and intra-abdominal pressures during the HG, measures were also taken during Valsalva’s manoeuvre (VM) at 30 mm Hg. Compared with baseline, both length and width of the spleen were reduced by 0.20 to 0.55 cm (or 4.44%–6.09%; p < 0.05) during each test. This resulted in relative reductions in splenic volume of 13 ± 1% (HG), 9% ± 7% (LBNP) and 18% ± 7% (VM) (p < 0.05; all mean ± SD). It was concluded that the spleen can constrict during the first minute of isometric HG exercise.

Forearm endurance training attenuates sympathetic nerve response to isometric handgrip in normal humans

1992 ◽  
Vol 72 (3) ◽  
pp. 1039-1043 ◽  
Author(s):  
V. K. Somers ◽  
K. C. Leo ◽  
R. Shields ◽  
M. Clary ◽  
A. L. Mark
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Endurance Training ◽  
Sympathetic Nerve ◽  
Isometric Exercise ◽  
Voluntary Contraction ◽  
Isometric Handgrip ◽  
Nerve Response ◽  
The Right ◽  
Muscle Chemoreflex

Recent evidence indicates that muscle ischemia and activation of the muscle chemoreflex are the principal stimuli to sympathetic nerve activity (SNA) during isometric exercise. We postulated that physical training would decrease muscle chemoreflex stimulation during isometric exercise and thereby attenuate the SNA response to exercise. We investigated the effects of 6 wk of unilateral handgrip endurance training on the responses to isometric handgrip (IHG: 33% of maximal voluntary contraction maintained for 2 min). In eight normal subjects the right arm underwent exercise training and the left arm sham training. We measured muscle SNA (peroneal nerve), heart rate, and blood pressure during IHG before vs. after endurance training (right arm) and sham training (left arm). Maximum work to fatigue (an index of training efficacy) was increased by 1,146% in the endurance-trained arm and by only 40% in the sham-trained arm. During isometric exercise of the right arm, SNA increased by 111 +/- 27% (SE) before training and by only 38 +/- 9% after training (P less than 0.05). Endurance training did not significantly affect the heart rate and blood pressure responses to IHG. We also measured the SNA response to 2 min of forearm ischemia after IHG in five subjects. Endurance training also attenuated the SNA response to postexercise forearm ischemia (P = 0.057). Sham training did not significantly affect the SNA responses to IHG or forearm ischemia. We conclude that endurance training decreases muscle chemoreflex stimulation during isometric exercise and thereby attenuates the sympathetic nerve response to IHG.

scholarly journals Muscle metaboreceptors modulate postexercise sweating, but not cutaneous blood flow, independent of baroreceptor loading status

2015 ◽  
Vol 309 (11) ◽  
pp. R1415-R1424 ◽  
Author(s):  
Gabrielle Paull ◽  
Sheila Dervis ◽  
Ryan McGinn ◽  
Baies Haqani ◽  
Andreas D. Flouris ◽  
...  
Keyword(s):  
Sweat Rate ◽  
Pressure Control ◽  
Voluntary Contraction ◽  
Treadmill Running ◽  
Maximal Heart Rate ◽  
Isometric Handgrip ◽  
Young Males ◽  
Isometric Handgrip Exercise ◽  
Postexercise Recovery ◽  
Cutaneous Vascular Conductance

We examined whether sustained changes in baroreceptor loading status during prolonged postexercise recovery can alter the metaboreceptors' influence on heat loss. Thirteen young males performed a 1-min isometric handgrip exercise (IHG) at 60% maximal voluntary contraction followed by 2 min of forearm ischemia (to activate metaboreceptors) before and 15, 30, 45, and 60 min after a 15-min intense treadmill running exercise (>90% maximal heart rate) in the heat (35°C). This was repeated on three separate days with continuous lower body positive (LBPP, +40 mmHg), negative (LBNP, −20 mmHg), or no pressure (Control) from 13- to 65-min postexercise. Sweat rate (ventilated capsule; forearm, chest, upper back) and cutaneous vascular conductance (CVC; forearm, upper back) were measured. Relative to pre-IHG levels, sweating at all sites increased during IHG and remained elevated during ischemia at baseline and similarly at 30, 45, and 60 min postexercise (site average sweat rate increase during ischemia: Control, 0.13 ± 0.02; LBPP, 0.12 ± 0.02; LBNP, 0.15 ± 0.02 mg·min−1·cm−2; all P < 0.01), but not at 15 min (all P > 0.10). LBPP and LBNP did not modulate the pattern of sweating to IHG and ischemia (all P > 0.05). At 15-min postexercise, forearm CVC was reduced from pre-IHG levels during both IHG and ischemia under LBNP only (ischemia: 3.9 ± 0.8% CVCmax; P < 0.02). Therefore, we show metaboreceptors increase postexercise sweating in the middle to late stages of recovery (30–60 min), independent of baroreceptor loading status and similarly between skin sites. In contrast, metaboreflex modulation of forearm but not upper back CVC occurs only in the early stages of recovery (15 min) and is dependent upon baroreceptor unloading.

Individual differences in cardiac and vascular components of the pressor response to isometric handgrip exercise in humans

2014 ◽  
Vol 306 (2) ◽  
pp. H251-H260 ◽  
Author(s):  
Kazuhito Watanabe ◽  
Masashi Ichinose ◽  
Rei Tahara ◽  
Takeshi Nishiyasu
Keyword(s):  
Individual Differences ◽  
Arterial Pressure ◽  
Pressor Response ◽  
Voluntary Contraction ◽  
Handgrip Exercise ◽  
Isometric Handgrip ◽  
Muscle Metaboreflex ◽  
Coefficients Of Variation ◽  
Isometric Handgrip Exercise ◽  
Induced Changes

We tested the hypotheses that, in humans, changes in cardiac output (CO) and total peripheral vascular resistance (TPR) occurring in response to isometric handgrip exercise vary considerably among individuals and that those individual differences are related to differences in muscle metaboreflex and arterial baroreflex function. Thirty-nine healthy subjects performed a 1-min isometric handgrip exercise at 50% of maximal voluntary contraction. This was followed by a 4-min postexercise muscle ischemia (PEMI) period to selectively maintain activation of the muscle metaboreflex. All subjects showed increases in arterial pressure during exercise. Interindividual coefficients of variation (CVs) for the changes in CO and TPR between rest and exercise periods (CO: 95.1% and TPR: 87.8%) were more than twofold greater than CVs for changes in mean arterial pressure (39.7%). There was a negative correlation between CO and TPR responses during exercise ( r = −0.751, P < 0.01), but these CO and TPR responses correlated positively with the corresponding responses during PEMI ( r = 0.568 and 0.512, respectively, P < 0.01). The CO response during exercise did not correlate with PEMI-induced changes in an index of cardiac parasympathetic tone and cardiac baroreflex sensitivity. These findings demonstrate that the changes in CO and TPR that occur in response to isometric handgrip exercise vary considerably among individuals and that the two responses have an inverse relationship. They also suggest that individual differences in components of the pressor response are attributable in part to variations in muscle metaboreflex-mediated cardioaccelerator and vasoconstrictor responses.

Cutaneous vascular responses to isometric handgrip exercise

1989 ◽  
Vol 66 (4) ◽  
pp. 1586-1592 ◽  
Author(s):  
W. F. Taylor ◽  
J. M. Johnson ◽  
W. A. Kosiba ◽  
C. M. Kwan
Keyword(s):  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Dynamic Exercise ◽  
Laser Doppler ◽  
Handgrip Exercise ◽  
Isometric Handgrip ◽  
Local Skin ◽  
Vascular Responses ◽  
Arterial Blood ◽  
Isometric Handgrip Exercise

Cutaneous vascular responses to dynamic exercise have been well characterized, but it is not known whether that response pattern applies to isometric handgrip exercise. We examined cutaneous vascular responses to isometric handgrip and dynamic leg exercise in five supine men. Skin blood flow was measured by laser-Doppler velocimetry and expressed as laser-Doppler flow (LDF). Arterial blood pressure was measured noninvasively once each minute. Cutaneous vascular conductance (CVC) was calculated as LDF/mean arterial pressure. LDF and CVC responses were measured at the forearm and chest during two 3-min periods of isometric handgrip at 30% of maximum voluntary contraction and expressed as percent changes from the preexercise levels. The skin was normothermic (32 degrees C) for the first period of handgrip and was locally warmed to 39 degrees C for the second handgrip. Finally, responses were observed during 5 min of dynamic two-leg bicycle exercise (150–175 W) at a local skin temperature of 39 degrees C. Arm LDF increased 24.5 +/- 18.9% during isometric handgrip in normothermia and 64.8 +/- 14.1% during isometric handgrip at 39 degrees C (P less than 0.05). Arm CVC did not significantly change at 32 degrees C but significantly increased 18.1 +/- 6.5% during isometric handgrip at 39 degrees C (P less than 0.05). Arm LDF decreased 12.2 +/- 7.9% during dynamic exercise at 39 degrees C, whereas arm CVC fell by 35.3 +/- 4.6% (in each case P less than 0.05). Chest LDF and CVC showed similar responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Augmentation of exercise-induced muscle sympathetic nerve activity during muscle heating

1997 ◽  
Vol 82 (6) ◽  
pp. 1719-1733 ◽  
Author(s):  
Chester A. Ray ◽  
Kathryn H. Gracey
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Local Heating ◽  
Muscle Afferents ◽  
Voluntary Contraction ◽  
Muscle Temperature ◽  
Isometric Handgrip ◽  
Nerve Activity ◽  
Exercise Induced

Ray, Chester A., and Kathryn H. Gracey. Augmentation of exercise-induced muscle sympathetic nerve activity during muscle heating. J. Appl. Physiol. 82(6): 1719–1725, 1997.—The muscle metabo- and mechanoreflexes have been shown to increase muscle sympathetic nerve activity (MSNA) during exercise. Group III and IV muscle afferents, which are believed to mediate this response, have been shown to be thermosensitive in animals. The purpose of the present study was to evaluate the effect of muscle temperature on MSNA responses during exercise. Eleven subjects performed ischemic isometric handgrip at 30% of maximal voluntary contraction to fatigue, followed by 2 min of postexercise muscle ischemia (PEMI), with and without local heating of the forearm. Local heating of the forearm increased forearm muscle temperature from 34.4 ± 0.2 to 38.9 ± 0.3°C ( P = 0.001). Diastolic and mean arterial pressures were augmented during exercise in the heat. MSNA responses were greater during ischemic handgrip with local heating compared with control (no heating) after the first 30 s. MSNA responses at fatigue were greater during local heating. MSNA increased by 16 ± 2 and 20 ± 2 bursts per 30 s for control and heating, respectively ( P = 0.03). When expressed as a percent change in total activity (total burst amplitude), MSNA increased 531 ± 159 and 941 ± 237% for control and heating, respectively ( P = 0.001). However, MSNA was not different during PEMI between trials. This finding suggests that the augmentation of MSNA during exercise with heat was due to the stimulation of mechanically sensitive muscle afferents. These results suggest that heat sensitizes skeletal muscle afferents during muscle contraction in humans and may play a role in the regulation of MSNA during exercise.

Sympathetic activation is associated with increases in EMG during fatiguing exercise

1989 ◽  
Vol 66 (1) ◽  
pp. 88-95 ◽  
Author(s):  
D. R. Seals ◽  
R. M. Enoka
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fatigue ◽  
Muscle Sympathetic Nerve Activity ◽  
Isometric Exercise ◽  
Voluntary Exercise ◽  
Emg Activity ◽  
Sympathetic Activation ◽  
Isometric Handgrip ◽  
Arterial Blood ◽  
Exercise In Humans

The purpose of this study was to test the hypothesis that efferent sympathetic neural discharge is coupled with the development of muscle fatigue during voluntary exercise in humans. In 12 healthy subjects (aged 20–34 yr) we measured heart rate (HR), arterial blood pressure (AP), and noncontracting, skeletal muscle sympathetic nerve activity (MSNA) in the leg (peroneal nerve) before (control) and during each of three trials of submaximal (30% of maximum) isometric handgrip exercise performed to exhaustion. In six of the subjects of eletromyographic (EMG) activity of the exercising forearm was also measured. HR and AP increased significantly (P less than 0.05) in the 1st min of exercise in all trials. In contrast, neither MSNA nor EMG activity increased significantly above control during the 1st min of exercise, but both parameters subsequently increased in a progressive and parallel manner (P less than 0.05). The overall correlation coefficient between MSNA and EMG activity (144 observations) was 0.85 (P less than 0.001). With successive trials the magnitudes of the increases in HR, AP, MSNA, and EMG activity were greater at any absolute point in time during exercise. These results indicate that sympathetic activation to noncontracting skeletal muscle is directly related to the development of muscle fatigue (as assessed by the change in EMG) during prolonged isometric exercise in humans. Furthermore, our findings demonstrate that previous fatiguing contractions alter the time course of the sympathetic neural adjustments to exercise.

scholarly journals Platelet ADP-Hypersensitivity by Aging and Isometric Exercise in Diabetics and its Prevention by EG-626

1977 ◽  
Author(s):  
T. Sano ◽  
T. Motomiya ◽  
Y. Itoh ◽  
N. Mashimo ◽  
H. Yamazaki ◽  
...  
Keyword(s):  
Healthy Subjects ◽  
Isometric Exercise ◽  
Voluntary Contraction ◽  
Handgrip Exercise ◽  
Isometric Handgrip ◽  
Camp Phosphodiesterase ◽  
Minimum Effective Concentration ◽  
Isometric Handgrip Exercise ◽  
Thrombotic Tendency

The important role of platelet aggregation in the pathophysiology of diabetic vascular disease has been emphasized. The authors devised a new method to assess platelet sensitivity to aggregation performed without centrifugation (Sano et al. Thrombos. Haemostasis April '77 issue, in press). Using this technique, platelet aggregability in diabetics was assessed concerning to age and to. the effect of isometric exercise. The effect of EG-626, a potent cAMP phosphodiesterase inhibiting and thromboxane A2-antagonistic substance, administered prior to exercise was also observed.In 52 diabetics without macroangiopathy, platelet sensitivity to ADP-aggregation was assessed. The sensitivity was expressed by ‘n’ of the minimum effective concentration of serially two-fold diluted ADP, 2-n mg/ml, to give aggregation. In males, both diabetics and healthy, the sensitivity correlated significantly with age. The regression lines obtained were Y=2.15+0,13X (Y: sensitivity, X:age in years) in the diabetics and Y=6.58+0.04X in the healthy subjects respectively. The value of the slope was significantly higher in the diabetics comparing to the healthy subjects. An enhancement of the platelet sensitivity was disclosed significantly in the diabetics but not in the healthy subjects, after isometric handgrip exercise at 50% maximal voluntary contraction for 2 minutes.. This enhancement was prevented when the patients were treated orally with 300 mg of EG-626, 1.5 hours before exercise. These findings would suggest the thrombotic tendency in diabetics and anti-thrombotic effect of this compound.

Physical ischaemia induced by isometric exercise facilitated collateral development in the remote ischaemic myocardium of humans

2014 ◽  
Vol 127 (10) ◽  
pp. 581-588 ◽  
Author(s):  
Song Lin ◽  
Yan Chen ◽  
Yongxue Li ◽  
Jianan Li ◽  
Xiao Lu
Keyword(s):  
Coronary Artery Disease ◽  
Isometric Exercise ◽  
Handgrip Exercise ◽  
Isometric Handgrip ◽  
Ischaemic Myocardium ◽  
Collateral Development ◽  
Collateral Growth ◽  
Isometric Handgrip Exercise ◽  
Artery Disease ◽  
Exercise Induced

Isometric-handgrip-exercise-induced local ischaemia in the normal limb facilitated collateral recruitment in acutely occluded vessels in patients with coronary artery disease. Ischaemic-handgrip-exercise-induced physical ischaemic training for 3 months facilitated myocardial collateral growth.

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