scholarly journals The activity of a single muscle sympathetic vasoconstrictor nerve unit is affected by physiological stress in humans

2006 ◽  
Vol 290 (2) ◽  
pp. H853-H860 ◽  
Author(s):  
Hisayoshi Murai ◽  
Shigeo Takata ◽  
Michiro Maruyama ◽  
Manabu Nakano ◽  
Daisuke Kobayashi ◽  
...  
Keyword(s):  
Single Unit ◽  
Physiological Stress ◽  
Valsalva Maneuver ◽  
Muscle Sympathetic Nerve Activity ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Accurate Information ◽  
Neural Firing ◽  
Handgrip Exercise ◽  
New Strategy

Recording of neural firing from single-unit muscle sympathetic nerve activity (MSNA) is a new strategy offering information about the frequency of pure sympathetic firing. However, it is uncertain whether and when single-unit MSNA would be more useful than multiunit MSNA for analysis of various physiological stresses in humans. In 15 healthy subjects, we measured single-unit and multiunit MSNA before and during handgrip exercise at 30% of maximum voluntary contraction for 3 min and during the Valsalva maneuver at 40 mmHg expiratory pressure for 15 s. Shapes of individual single-unit MSNA were proved to be consistent and suitable for further evaluation. Single-unit and multiunit MSNA exhibited similar responses during handgrip exercise. However, acceleration of neural firing determined from single-unit MSNA became steeper than multiunit MSNA during the Valsalva maneuver. During the Valsalva maneuver, unlike handgrip exercise, the distribution of multiunit burst between 0, 1, 2, 3, and 4 spikes was significantly shifted toward multiple spikes within a given burst ( P < 0.05). These results indicated that evaluation of single-unit MSNA could provide more detailed and accurate information concerning the role and responses of neuronal discharges induced by various physiological stresses in humans, especially amid intense sympathetic activity.

Muscle sympathetic single-unit responses during rhythmic handgrip exercise and isocapnic hypoxia in males: the role of sympathoexcitation magnitude

2021 ◽  
Author(s):  
Anthony V. Incognito ◽  
André L. Teixeira ◽  
Brooke M. Shafer ◽  
Massimo Nardone ◽  
Tyler D. Vermeulen ◽  
...  
Keyword(s):  
Single Unit ◽  
Muscle Sympathetic Nerve Activity ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Spike Frequency ◽  
Single Units ◽  
Response Patterns ◽  
Handgrip Exercise ◽  
Young Males ◽  
End Tidal

A small proportion of postganglionic muscle sympathetic single units can be inhibited during sympathoexcitatory stressors in humans. However, whether these responses are dependent on the specific stressor or the level of sympathoexcitation remains unclear. We hypothesize that, when matched by sympathoexcitatory magnitude, different stressors can evoke similar proportions of inhibited single units. Multiunit and single-unit muscle sympathetic nerve activity (MSNA) were recorded in seven healthy, young males at baseline and during: 1) rhythmic handgrip exercise (40% of maximum voluntary contraction) and 2) acute isocapnic hypoxia (partial pressure of end-tidal O2: 47±3 mmHg). Single units were classified as activated, nonresponsive, or inhibited if the spike frequency was above, within, or below the baseline variability, respectively. By design, rhythmic handgrip and isocapnic hypoxia similarly increased multiunit total MSNA (D273±208 vs. D254±193 AU, P=0.84) and single-unit spike frequency (D8±10 vs. D12±13 spikes/min, P=0.12). Among 19 identified single units, the proportion of activated (47% vs. 68%) non-responsive (32% vs. 16%) and inhibited (21% vs. 16%) single units were not different between rhythmic handgrip and isocapnic hypoxia (P=0.42). However, only 9 (47%) single units behaved with concordant response patterns across both stressors (7 activated, 1 non-responsive, and 1 inhibited during both stressors). During the 1-min epoch with the highest increase in total MSNA during hypoxia (D595±282 AU, P<0.01) only 1 single unit was inhibited. These findings suggest that the proportion of muscle sympathetic single units inhibited during stress are associated with the level of sympathoexcitation and not the stressor per se in healthy young males.

scholarly journals Pre-Exercise Rehydration Attenuates Central Fatigability during 2-Min Maximum Voluntary Contraction in Hyperthermia

Medicina ◽  
2019 ◽  
Vol 55 (3) ◽  
pp. 66
Author(s):  
Kazys Vadopalas ◽  
Aivaras Ratkevičius ◽  
Albertas Skurvydas ◽  
Saulė Sipavičienė ◽  
Marius Brazaitis
Keyword(s):  
Body Weight ◽  
Physiological Stress ◽  
Maximum Voluntary Contraction ◽  
Thermal Strain ◽  
Plasma Osmolality ◽  
Voluntary Contraction ◽  
Whole Body ◽  
Knee Extensors ◽  
Lower Body ◽  
Whole Body Hyperthermia

Background and objectives: Hyperthermia with dehydration alters several brain structure volumes, mainly by changing plasma osmolality, thus strongly affecting neural functions (cognitive and motor). Here, we aimed to examine whether the prevention of significant dehydration caused by passively induced whole-body hyperthermia attenuates peripheral and/or central fatigability during a sustained 2-min isometric maximal voluntary contraction (MVC). Materials and Methods: Ten healthy and physically active adult men (21 ± 1 years of age) performed an isometric MVC of the knee extensors for 2 min (2-min MVC) under control (CON) conditions, after passive lower-body heating that induced severe whole-body hyperthermia (HT, Tre > 39 °C) with dehydration (HT-D) and after HT with rehydration (HT-RH). Results: In the HT-D trial, the subjects lost 0.94 ± 0.15 kg (1.33% ± 0.13%) of their body weight; in the HT-RH trial, their body weight increased by 0.1 ± 0.42 kg (0.1% ± 0.58%). After lower-body heating, the HT-RH trial (vs. HT-D trial) was accompanied by a significantly lower physiological stress index (6.77 ± 0.98 vs. 7.40 ± 1.46, respectively), heart rate (47.8 ± 9.8 vs. 60.8 ± 13.2 b min−1, respectively), and systolic blood pressure (−12.52 ± 5.1 vs. +2.3 ± 6.4, respectively). During 2-min MVC, hyperthermia (HT-D; HT-RH) resulted in greater central fatigability compared with the CON trial. The voluntary activation of exercising muscles was less depressed in the HT-RH trial compared with the HT-D trial. Over the exercise period, electrically (involuntary) induced torque decreased less in the HT-D trial than in the CON and HT-RH trials. Conclusions: Our results suggest that pre-exercise rehydration might have the immediate positive effect of reducing physiological thermal strain, thus attenuating central fatigability even when exercise is performed during severe (Tre > 39 °C) HT, induced by passive warming of the lower body.

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)

Ventilatory responses to static handgrip exercise

1983 ◽  
Vol 54 (6) ◽  
pp. 1457-1462 ◽  
Author(s):  
S. R. Muza ◽  
L. Y. Lee ◽  
R. L. Wiley ◽  
S. McDonald ◽  
F. W. Zechman
Keyword(s):  
Time Course ◽  
Ventilatory Response ◽  
Maximum Voluntary Contraction ◽  
Muscle Afferents ◽  
Voluntary Contraction ◽  
Static Exercise ◽  
Handgrip Exercise ◽  
Co2 Partial Pressure ◽  
Ventilatory Responses ◽  
End Tidal

Previous research indicates that fatiguing static exercise causes hyperventilation and a decrease of end-tidal CO2 partial pressure PETCO2. The objectives of this study were 1) to examine the changes in pattern of breathing during static exercise, and 2) to define the isocapnic ventilatory response. Six healthy males were studied once a week at one of three levels of static handgrip exercise: 15, 25, or 30% maximum voluntary contraction (MVC) was sustained for 5 min while holding PETCO2 constant or allowing it to run free. During 25 and 30% MVC, we observed 1) progressive increases in mean tidal volume (VT), inspiratory ventilation (VI), VT/TI, heart rate (HR), and arterial BP, 2) increased breath-to-breath variability of VT, 3) no significant changes in respiratory frequency (f), and 4) progressive decreases in PETCO2. Keeping PETCO2 constant at preexercise levels did not change the pattern or magnitude of the ventilatory response to exercise. The time course and magnitude of the subjects' perceived effort resembled the time course and magnitude of the ventilatory response. The variability of VT during the response to static exercise suggests an element of control instability. The identical ventilatory responses during hypocapnic and isocapnic conditions may result from the slow response of the central chemoreceptors; an overriding influence of muscle afferents; and/or increased central command arising with fatigue.

Impact of heart failure and exercise capacity on sympathetic response to handgrip exercise

2001 ◽  
Vol 280 (3) ◽  
pp. H969-H976 ◽  
Author(s):  
Catherine F. Notarius ◽  
Deborah J. Atchison ◽  
John S. Floras
Keyword(s):  
Heart Failure ◽  
Muscle Sympathetic Nerve Activity ◽  
Normal Subjects ◽  
Peak Oxygen Uptake ◽  
Voluntary Contraction ◽  
Handgrip Exercise ◽  
Muscle Metaboreflex ◽  
Sympathetic Response ◽  
Patients With Heart Failure ◽  
Rest And Exercise

Peak oxygen uptake (V˙o 2 peak) in patients with heart failure (HF) is inversely related to muscle sympathetic nerve activity (MSNA) at rest. We hypothesized that the MSNA response to handgrip exercise is augmented in HF patients and is greatest in those with lowV˙o 2 peak. We studied 14 HF patients and 10 age-matched normal subjects during isometric [30% of maximal voluntary contraction (MVC)] and isotonic (10%, 30%, and 50% MVC) handgrip exercise that was followed by 2 min of posthandgrip ischemia (PHGI). MSNA was significantly increased during exercise in HF but not normal subjects. Both MSNA and HF levels remained significantly elevated during PHGI after 30% isometric and 50% isotonic handgrip in HF but not normal subjects. HF patients with lower V˙o 2 peak (<56% predicted; n = 8) had significantly higher MSNA during rest and exercise than patients withV˙o 2 peak > 56% predicted ( n = 6) and normal subjects. The muscle metaboreflex contributes to the greater reflex increase in MSNA during ischemic or intense nonischemic exercise in HF. This occurs at a lower threshold than normal and is a function ofV˙o 2 peak.

Dynamic cerebral autoregulation during and after handgrip exercise in humans

2010 ◽  
Vol 108 (6) ◽  
pp. 1701-1705 ◽  
Author(s):  
Shigehiko Ogoh ◽  
Kohei Sato ◽  
Toshinari Akimoto ◽  
Anna Oue ◽  
Ai Hirasawa ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Cerebral Autoregulation ◽  
Valsalva Maneuver ◽  
Maximum Voluntary Contraction ◽  
Static Exercise ◽  
Handgrip Exercise ◽  
Arterial Blood ◽  
Significant Difference ◽  
Acute Hypotension ◽  
Dynamic Cerebral Autoregulation

The purpose of the present study was to examine the effect of static exercise on dynamic cerebral autoregulation (CA). In nine healthy subjects at rest before, during, and after static handgrip exercise at 30% maximum voluntary contraction, the response to an acute drop in mean arterial blood pressure and middle cerebral artery mean blood velocity was examined. Acute hypotension was induced nonpharmacologically via rapid release of bilateral thigh occlusion cuffs. Subjects were instructed to avoid executing a Valsalva maneuver during handgrip. To quantify dynamic CA, the rate of regulation (RoR) was calculated from the change in cerebral vascular conductance index during the transient fall in blood pressure. There was no significant difference in RoR between rest (mean ± SE; 0.278 ± 0.052/s), exercise (0.333 ± 0.053/s), and recovery (0.305 ± 0.059/s) conditions ( P = 0.747). In addition, there was no significant difference in the rate of absolute cerebral vasodilatory response to acute hypotension between three conditions ( P = 0.737). This finding indicates that static exercise and related elevations in blood pressure do not alter dynamic CA.

Effect of adenosine receptor blockade with caffeine on sympathetic response to handgrip exercise in heart failure

2001 ◽  
Vol 281 (3) ◽  
pp. H1312-H1318 ◽  
Author(s):  
C. F. Notarius ◽  
D. J. Atchison ◽  
G. A. Rongen ◽  
J. S. Floras
Keyword(s):  
Heart Failure ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Normal Subjects ◽  
Voluntary Contraction ◽  
Receptor Blockade ◽  
Handgrip Exercise ◽  
Muscle Metaboreflex ◽  
Sympathetic Response ◽  
Isotonic Exercise

Adenosine (Ado) increases muscle sympathetic nerve activity (MSNA) reflexively. Plasma Ado and MSNA are elevated in heart failure (HF). We tested the hypothesis that Ado receptor blockade by caffeine would attenuate reflex MSNA responses to handgrip (HG) and posthandgrip ischemia (PHGI) and that this action would be more prominent in HF subjects than in normal subjects. We studied 12 HF subjects and 10 age-matched normal subjects after either saline or caffeine (4 mg/kg) infusion during isometric [30% of maximal voluntary contraction (MVC)] and isotonic (10%, 30%, and 50%) HG exercise, followed by 2 min of PHGI. In normal subjects, caffeine did not block increases in MSNA during PHGI after 50% HG. In HF subjects, caffeine abolished MSNA responses to PHGI after both isometric and 50% isotonic exercise ( P < 0.05) but MSNA responses during HG were unaffected. These findings are consistent with muscle metaboreflex stimulation by endogenous Ado during ischemic or intense nonischemic HG in HF and suggest an important sympathoexcitatory role for endogenous Ado during exercise in this condition.

scholarly journals Altered firing pattern of single-unit muscle sympathetic nerve activity during handgrip exercise in chronic heart failure

2009 ◽  
Vol 587 (11) ◽  
pp. 2613-2622 ◽  
Author(s):  
Hisayoshi Murai ◽  
Masayuki Takamura ◽  
Michirou Maruyama ◽  
Manabu Nakano ◽  
Tatsunori Ikeda ◽  
...  
Keyword(s):  
Heart Failure ◽  
Chronic Heart Failure ◽  
Sympathetic Nerve ◽  
Single Unit ◽  
Firing Pattern ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Handgrip Exercise ◽  
Nerve Activity

Forearm elevation augments sympathetic activation during handgrip exercise in humans

2002 ◽  
Vol 103 (3) ◽  
pp. 295-301 ◽  
Author(s):  
Daisaku MICHIKAMI ◽  
Atsunori KAMIYA ◽  
Qi FU ◽  
Yuki NIIMI ◽  
Satoshi IWASE ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Muscle Sympathetic Nerve Activity ◽  
Voluntary Contraction ◽  
Sympathetic Activation ◽  
Handgrip Exercise ◽  
Excitatory Effect ◽  
Muscle Metaboreflex ◽  
Forearm Exercise ◽  
Exercise In Humans

Although angina pectoris in patients with coronary heart disease often occurs when their forearms are in an elevated position for a prolonged period, and sympathetic activation is a major cause of this condition, little is known about the physiological effects of forearm elevation on sympathetic activity during forearm exercise. We hypothesized that forearm elevation augments sympathetic activation during the static handgrip exercise in humans. A total of 10 healthy male volunteers performed 2min of static handgrip exercise at 30% of maximal voluntary contraction followed by 2min of post-exercise muscle ischaemia (PEMI; specific activation of the muscle metaboreflex) with two forearm positions: the exercising forearm was elevated 50cm above the heart (forearm-elevated trial) or fixed at the level of the heart (heart-level trial). Muscle sympathetic nerve activity (MSNA), blood pressure and heart rate were monitored. MSNA increased during handgrip exercise in both forearm positions (P<0.001); the increase was 51% greater in the forearm-elevated trial (516±99 arbitrary units) than in the heart-level trial (346±44units; P<0.05). The increase in mean blood pressure was 8.4mmHg greater during exercise in the forearm-elevated trial (P<0.05), while changes in heart rate were similar in both forearm positions. The increase in MSNA during PEMI was 71% greater in the forearm-elevated trial (393±71 arbitrary units/min) than in the heart-level trial (229±29units/min; P<0.05). These results support the hypothesis that forearm elevation augments sympathetic activation during handgrip exercise. The excitatory effect of forearm elevation on exercising MSNA may be mediated primarily by increased activation of the muscle metaboreflex.

scholarly journals Global Reach 2018: reduced flow-mediated dilation stimulated by sustained increases in shear stress in high-altitude excessive erythrocytosis

2019 ◽  
Vol 317 (5) ◽  
pp. H991-H1001 ◽  
Author(s):  
Joshua C. Tremblay ◽  
Geoff B. Coombs ◽  
Connor A. Howe ◽  
Gustavo A. Vizcardo-Galindo ◽  
Rómulo J. Figueroa-Mujíca ◽  
...  
Keyword(s):  
Shear Stress ◽  
Cardiovascular Risk ◽  
High Altitude ◽  
Reactive Hyperemia ◽  
Maximum Voluntary Contraction ◽  
Duplex Ultrasound ◽  
Hemoglobin Concentration ◽  
Voluntary Contraction ◽  
Flow Mediated Dilation ◽  
Handgrip Exercise

Excessive erythrocytosis [EE; hemoglobin concentration (Hb) ≥ 21 g/dL in adult men] is a maladaptive high-altitude pathology associated with increased cardiovascular risk and reduced reactive hyperemia flow-mediated dilation (FMD); however, whether a similar impairment occurs in response to more commonly encountered sustained increases in shear stress [sustained stimulus (SS)-FMD] over a range of overlapping stimuli is unknown. We characterized SS-FMD in response to handgrip exercise in Andeans with and without EE in Cerro de Pasco, Peru (4,330 m). Andean highlanders with EE ( n = 17, Hb = 23.2 ± 1.2 g/dL) and without EE ( n = 23, Hb = 18.7 ± 1.9 g/dL) performed 3 min of rhythmic handgrip exercise at 20, 35, and 50% of maximum voluntary contraction (MVC). Duplex ultrasound was used to continuously record blood velocity and diameter in the brachial artery, and blood viscosity was measured to accurately calculate shear stress. Although baseline shear stress did not differ, Andeans with EE had 22% lower shear stress than Andeans without at 50% MVC ( P = 0.004). At 35 and 50% MVC, SS-FMD was 2.1 ± 2.0 and 2.8 ± 2.7% in Andeans with EE compared with 4.1 ± 3.4 and 7.5 ± 4.5% in those without ( P = 0.048 and P < 0.001). The stimulus-response slope (∆shear stress vs. ∆diameter) was lower in Andeans with EE compared with Andeans without ( P = 0.028). This slope was inversely related to Hb in Andeans with EE ( r2 = 0.396, P = 0.007). A reduced SS-FMD in response to small muscle mass exercise in Andeans with EE indicates a generalized reduction in endothelial sensitivity to shear stress, which may contribute to increased cardiovascular risk in this population. NEW & NOTEWORTHY High-altitude excessive erythrocytosis (EE; hemoglobin concentration ≥ 21 g/dL) is a maladaptation to chronic hypoxia exposure and is associated with increased cardiovascular risk. We examined flow-mediated dilation (FMD) in response to sustained elevations in shear stress achieved using progressive handgrip exercise [sustained stimulus (SS)-FMD] in Andean highlanders with and without EE at 4,330 m. Andeans with EE demonstrated lower SS-FMD compared with those without. Heightened hemoglobin concentration was related to lower SS-FMD in Andeans with EE.

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