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Singh N, Hammam E, Macefield VG. Vestibular modulation of muscle sympathetic nerve activity assessed over a 100-fold frequency range of sinusoidal galvanic vestibular stimulation. J Neurophysiol 2019; 121:1644-1649. [PMID: 30811260 DOI: 10.1152/jn.00679.2018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have previously shown that sinusoidal galvanic vestibular stimulation (sGVS), delivered at 0.2-2.0 Hz, evokes a partial entrainment of muscle sympathetic nerve activity (MSNA). Moreover, at lower frequencies of stimulation (0.08-0.18 Hz) sGVS produces two peaks of modulation: one (primary) peak associated with the positive peak of the sinusoidal stimulus and a smaller (secondary) peak associated with the trough. Here we assessed whether sGVS delivered at 0.05 Hz causes a more marked modulation of MSNA than at higher frequencies and tested the hypothesis that the primary and secondary peaks are of identical amplitude because of the longer cycle length. MSNA was recorded via tungsten microelectrodes inserted into the left peroneal nerve in 11 seated subjects. Bipolar binaural sGVS (±2 mA, 100 cycles) was applied to the mastoid processes at 0.05, 0.5, and 5.0 Hz (500 cycles). Cross-correlation analysis revealed two bursts of modulation of MSNA for each cycle at 0.05 and 0.5 Hz but only one at 5 Hz. There was a significant inverse linear relationship between vestibular modulation (primary peak) and frequency (P < 0.0001), with the amplitudes of the peaks being highest at 0.05 Hz. Moreover, the secondary peak at this frequency was not significantly different from the primary peak. These results indicate that vestibular modulation of MSNA operates over a large range of frequencies but is greater at lower frequencies of sGVS. We conclude that the vestibular apparatus, through its influence on muscle sympathetic outflow, preferentially contributes to the control of blood pressure at low frequencies. NEW & NOTEWORTHY Vestibulosympathetic reflexes have been documented in experimental animals and humans. Here we show that sinusoidal galvanic vestibular stimulation, a means of selectively exciting vestibular afferents in humans, induces greater modulation of muscle sympathetic nerve activity when delivered at a very low frequency (0.05 Hz) than at 0.5 or 5.0 Hz.
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Affiliation(s)
- Natasha Singh
- School of Medicine, Western Sydney University , Sydney, New South Wales , Australia
| | - Elie Hammam
- School of Medicine, Western Sydney University , Sydney, New South Wales , Australia
| | - Vaughan G Macefield
- School of Medicine, Western Sydney University , Sydney, New South Wales , Australia.,Baker Heart and Diabetes Institute , Melbourne, Victoria , Australia
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Coleman Wood KA, Lowndes BR, Buus RJ, Hallbeck MS. Evidence-based intraoperative microbreak activities for reducing musculoskeletal injuries in the operating room. Work 2018; 60:649-659. [DOI: 10.3233/wor-182772] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Affiliation(s)
| | - Bethany R. Lowndes
- Robert D. and Patricia E. Kern Center for the Science of Health Care Delivery, Mayo Clinic, Rochester, MN, USA
- Department of Health Sciences Research, Mayo Clinic, Rochester, MN, USA
| | - Ryan J. Buus
- Department of Physical Medicine and Rehabilitation, Mayo Clinic, Rochester, MN, USA
| | - M. Susan Hallbeck
- Robert D. and Patricia E. Kern Center for the Science of Health Care Delivery, Mayo Clinic, Rochester, MN, USA
- Department of Health Sciences Research, Mayo Clinic, Rochester, MN, USA
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Bolton PS, Hammam E, Macefield VG. Neck movement but not neck position modulates skin sympathetic nerve activity supplying the lower limbs of humans. J Neurophysiol 2018; 119:1283-1290. [PMID: 29357457 DOI: 10.1152/jn.00043.2017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We previously showed that dynamic, but not static, neck displacement modulates muscle sympathetic nerve activity (MSNA) to lower limbs of humans. However, it is not known whether dynamic neck displacement modulates skin sympathetic nerve activity (SSNA). Tungsten microelectrodes inserted into the common peroneal nerve were used to record SSNA in 5 female and 4 male subjects lying supine on a table that fixed their head in space but allowed trapezoidal ramp (8.1 ± 1.2°/s) and hold (17.5° for 53 s) or sinusoidal (35° peak to peak at 0.33-0.46 Hz) horizontal displacement of the body about the head. SSNA recordings were made before, during, and after trapezoidal and sinusoidal displacements of the body. Spike frequency analysis of trapezoidal displacements and cross-correlation analysis during sinusoidal displacements revealed that SSNA was not changed by trapezoid body-only displacement but was cyclically modulated during sinusoidal angular displacements (median, 95% CI: 27.9%, 19.6-48.0%). The magnitude of this modulation was not statistically ( P > 0.05) different from that of cardiac and respiratory modulation at rest (47.1%, 18.7-56.3% and 48.6%, 28.4-59.3%, respectively) or during sinusoidal displacement (10.3%, 6.2-32.1% and 26.9%, 13.6-43.3%, respectively). Respiratory frequency was entrained above its resting rate (0.26 Hz, 0.2-0.29 Hz) during sinusoidal neck displacement; there was no significant difference ( P > 0.05) between respiratory frequency (0.38 Hz, 0.25-0.49 Hz) and sinusoidal displacement frequency (0.39 Hz, 0.35-0.42 Hz). This study provides evidence that SSNA is modulated during neck movement, raising the possibility that neck mechanoreceptors may contribute to the cutaneous vasoconstriction and sweat release associated with motion sickness. NEW & NOTEWORTHY This study demonstrates that dynamic, but not static, stretching of the neck modulates skin sympathetic nerve activity in the lower limbs.
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Affiliation(s)
- Philip S Bolton
- School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan, Australia.,Hunter Medical Research Institute, Callaghan, Australia
| | - Elie Hammam
- School of Medicine, Western Sydney University , Sydney , Australia
| | - Vaughan G Macefield
- School of Medicine, Western Sydney University , Sydney , Australia.,Neuroscience Research Australia, Sydney , Australia
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Hammam E, Macefield VG. Vestibular Modulation of Sympathetic Nerve Activity to Muscle and Skin in Humans. Front Neurol 2017; 8:334. [PMID: 28798718 PMCID: PMC5526846 DOI: 10.3389/fneur.2017.00334] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2017] [Accepted: 06/26/2017] [Indexed: 12/19/2022] Open
Abstract
We review the existence of vestibulosympathetic reflexes in humans. While several methods to activate the human vestibular apparatus have been used, galvanic vestibular stimulation (GVS) is a means of selectively modulating vestibular afferent activity via electrodes over the mastoid processes, causing robust vestibular illusions of side-to-side movement. Sinusoidal GVS (sGVS) causes partial entrainment of sympathetic outflow to muscle and skin. Modulation of muscle sympathetic nerve activity (MSNA) from vestibular inputs competes with baroreceptor inputs, with stronger temporal coupling to the vestibular stimulus being observed at frequencies remote from the cardiac frequency; “super entrainment” was observed in some individuals. Low-frequency (<0.2 Hz) sGVS revealed two peaks of modulation per cycle, with bilateral recordings of MSNA or skin sympathetic nerve activity, providing evidence of lateralization of sympathetic outflow during vestibular stimulation. However, it should be noted that GVS influences the firing of afferents from the entire vestibular apparatus, including the semicircular canals. To identify the specific source of vestibular input responsible for the generation of vestibulosympathetic reflexes, we used low-frequency (<0.2 Hz) sinusoidal linear acceleration of seated or supine subjects to, respectively, target the utricular or saccular components of the otoliths. While others had discounted the semicircular canals, we showed that the contributions of the utricle and saccule to the vestibular modulation of MSNA are very similar. Moreover, that modulation of MSNA occurs at accelerations well below levels at which subjects are able to perceive any motion indicates that, like vestibulospinal control of posture, the vestibular system contributes to the control of blood pressure through potent reflexes in humans.
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Affiliation(s)
- Elie Hammam
- School of Medicine, Western Sydney University, Sydney, NSW, Australia
| | - Vaughan G Macefield
- School of Medicine, Western Sydney University, Sydney, NSW, Australia.,Neuroscience Research Australia, Sydney, NSW, Australia
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Knellwolf TP, Hammam E, Macefield VG. The vestibular system does not modulate fusimotor drive to muscle spindles in relaxed leg muscles of subjects in a near-vertical position. J Neurophysiol 2016; 115:2529-35. [PMID: 26936989 DOI: 10.1152/jn.01125.2015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Accepted: 03/02/2016] [Indexed: 11/22/2022] Open
Abstract
It has been shown that sinusoidal galvanic vestibular stimulation (sGVS) has no effect on the firing of spontaneously active muscle spindles in either relaxed or voluntarily contracting human leg muscles. However, all previous studies have been conducted on subjects in a seated position. Given that independent vestibular control of muscle spindle firing would be more valuable during postural threat, we tested the hypothesis that this modulation would become apparent for subjects in a near-vertical position. Unitary recordings were made from 18 muscle spindle afferents via tungsten microelectrodes inserted percutaneously into the common peroneal nerve of awake human subjects laying supine on a motorized tilt table. All recorded spindle afferents were spontaneously active at rest, and each increased its firing rate during a weak static contraction. Sinusoidal bipolar binaural galvanic vestibular stimulation (±2 mA, 100 cycles) was applied to the mastoid processes at 0.8 Hz. This continuous stimulation produced a sustained illusion of "rocking in a boat" or "swinging in a hammock." The subject was then moved into a near-vertical position (75°), and the stimulation repeated. Despite robust vestibular illusions, none of the fusimotor-driven spindles exhibited phase-locked modulation of firing during sinusoidal GVS in either position. We conclude that this dynamic vestibular stimulus was insufficient to modulate the firing of fusimotor neurons in the near-vertical position. However, this does not mean that the vestibular system cannot modulate the sensitivity of muscle spindles via fusimotor neurons in free unsupported standing, when reliance on proprioceptive feedback is higher.
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Affiliation(s)
- T P Knellwolf
- School of Medicine, Western Sydney University, Sydney, Australia; and
| | - E Hammam
- School of Medicine, Western Sydney University, Sydney, Australia; and
| | - V G Macefield
- School of Medicine, Western Sydney University, Sydney, Australia; and Neuroscience Research Institute, Sydney, Australia
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Hammam E, Bolton PS, Kwok K, Macefield VG. Vestibular modulation of muscle sympathetic nerve activity during sinusoidal linear acceleration in supine humans. Front Neurosci 2014; 8:316. [PMID: 25346657 PMCID: PMC4191191 DOI: 10.3389/fnins.2014.00316] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Accepted: 09/18/2014] [Indexed: 12/18/2022] Open
Abstract
The utricle and saccular components of the vestibular apparatus preferentially detect linear displacements of the head in the horizontal and vertical planes, respectively. We previously showed that sinusoidal linear acceleration in the horizontal plane of seated humans causes a pronounced modulation of muscle sympathetic nerve activity (MSNA), supporting a significant role for the utricular component of the otolithic organs in the control of blood pressure. Here we tested the hypothesis that the saccule can also play a role in blood pressure regulation by modulating lower limb MSNA. Oligounitary MSNA was recorded via tungsten microelectrodes inserted into the common peroneal nerve in 12 subjects, laying supine on a motorized platform with the head aligned with the longitudinal axis of the body. Slow sinusoidal linear accelerations-decelerations (peak acceleration ±4 mG) were applied in the rostrocaudal axis (which predominantly stimulates the saccule) and in the mediolateral axis (which also engages the utricle) at 0.08 Hz. The modulation of MSNA in the rostrocaudal axis (29.4 ± 3.4%) was similar to that in the mediolateral axis (32.0 ± 3.9%), and comparable to that obtained by stimulation of the utricle alone in seated subjects with the head vertical. We conclude that both the saccular and utricular components of the otolithic organs play a role in the control of arterial pressure during postural challenges.
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Affiliation(s)
- Elie Hammam
- School of Medicine, University of Western Sydney Sydney, NSW, Australia
| | - Philip S Bolton
- School of Biomedical Sciences and Pharmacy, University of Newcastle Newcastle, NSW, Australia ; Hunter Medical Research Institute Newcastle, NSW, Australia
| | - Kenny Kwok
- Institute for Infrastructure Engineering, University of Western Sydney Sydney, NSW, Australia
| | - Vaughan G Macefield
- School of Medicine, University of Western Sydney Sydney, NSW, Australia ; Neuroscience Research Australia Sydney, NSW, Australia
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