Prof Simon Gandevia

PUBLICATIONS

Effects of Four Weeks of Strength Training on the Corticomotoneuronal Pathway.

Nuzzo JL, Barry BK, Jones MD, Gandevia SC, Taylor JL

Four weeks of isometric strength training of the elbow flexors increased muscle strength and voluntary activation, without a change in the muscle. The improvement in activation suggests that voluntary output from the cortex was better able to recruit motoneurons and/or increase their firing rates. The lack of change in CMEPs indicates that neither corticospinal transmission nor motoneuron excitability was affected by training.

Comparison of measurements of medial gastrocnemius architectural parameters from ultrasound and diffusion tensor images.

Bolsterlee B, Veeger HE, van der Helm FC, Gandevia SC, Herbert RD

In vivo measurements of muscle architecture provide insight into inter-individual differences in muscle function and could be used to personalise musculoskeletal models. When muscle architecture is measured from ultrasound images, as is frequently done, it is assumed that fascicles are oriented in the image plane and, for some measurements, that the image plane is perpendicular to the aponeurosis at the intersection of fascicle and aponeurosis. This study presents an in vivo validation of these assumptions by comparing ultrasound image plane orientation to three-dimensional reconstructions of muscle fascicles and aponeuroses obtained with diffusion tensor imaging (DTI) and high-resolution anatomical MRI scans. It was found that muscle fascicles were oriented on average at 5.5±4.1° to the ultrasound image plane. On average, ultrasound yielded similar measurements of fascicle lengths to DTI (difference <3mm), suggesting that the measurements were unbiased. The absolute difference in length between any pair of measurements made with ultrasound and DTI was substantial (10mm or 20% of the mean), indicating that the measurements were imprecise. Pennation angles measured with ultrasound were significantly smaller than those measured with DTI (mean difference 6°). This difference was apparent only at the superficial insertion of the muscle fascicles so it was probably due to pressure on the skin applied by the ultrasound probes. It is concluded that ultrasound measurements of deep pennation angles and fascicle lengths in the medial gastrocnemius are unbiased but have a low precision and that superficial pennation angles are underestimated by approximately 10°. The low precision limits the use of ultrasound to personalise fascicle length in musculoskeletal models.

Neurogenic changes in the upper airway of obstructive sleep apnoea.

Saboisky JP, Butler JE, Luu BL, Gandevia SC

Obstructive sleep apnoea (OSA) is linked to local neural injury that evokes airway muscle remodelling. The upper airway muscles of patients with OSA are exposed to intermittent hypoxia as well as vibration induced by snoring. A range of electrophysiological and other studies have established altered motor and sensory function of the airway in OSA. The extent to which these changes impair upper airway muscle function and their relationship to the progression of OSA remains undefined. This review will collate the evidence for upper airway remodelling in OSA, particularly the electromyographic changes in upper airway muscles of patients with OSA.

Use of a physiological profile to document motor impairment in ageing and in clinical groups.

Lord SR, Delbaere K, Gandevia SC

Arm posture-dependent changes in corticospinal excitability are largely spinal in origin.

Nuzzo JL, Trajano GS, Barry BK, Gandevia SC, Taylor JL

Biceps brachii motor evoked potentials (MEPs) from cortical stimulation are influenced by arm posture. We used subcortical stimulation of corticospinal axons to determine whether this postural effect is spinal in origin. While seated at rest, 12 subjects assumed several static arm postures, which varied in upper-arm (shoulder flexed, shoulder abducted, arm hanging to side) and forearm orientation (pronated, neutral, supinated). Transcranial magnetic stimulation over the contralateral motor cortex elicited MEPs in resting biceps and triceps brachii, and electrical stimulation of corticospinal tract axons at the cervicomedullary junction elicited cervicomedullary motor evoked potentials (CMEPs). MEPs and CMEPs were normalized to the maximal compound muscle action potential (Mmax). Responses in biceps were influenced by upper-arm and forearm orientation. For upper-arm orientation, biceps CMEPs were 68% smaller (P= 0.001), and biceps MEPs 31% smaller (P= 0.012), with the arm hanging to the side compared with when the shoulder was flexed. For forearm orientation, both biceps CMEPs and MEPs were 34% smaller (bothP< 0.046) in pronation compared with supination. Responses in triceps were influenced by upper-arm, but not forearm, orientation. Triceps CMEPs were 46% smaller (P= 0.007) with the arm hanging to the side compared with when the shoulder was flexed. Triceps MEPs and biceps and triceps MEP/CMEP ratios were unaffected by arm posture. The novel finding is that arm posture-dependent changes in corticospinal excitability in humans are largely spinal in origin. An interplay of multiple reflex inputs to motoneurons likely explains the results.

Ultrasound imaging of the human medial gastrocnemius muscle: how to orient the transducer so that muscle fascicles lie in the image plane.

Bolsterlee B, Gandevia SC, Herbert RD

The length and pennation of muscle fascicles are frequently measured using ultrasonography. Conventional ultrasonography imaging methods only provide two-dimensional images of muscles, but muscles have complex three-dimensional arrangements. The most accurate measurements will be obtained when the ultrasound transducer is oriented so that endpoints of a fascicle lie on the ultrasound image plane and the image plane is oriented perpendicular to the aponeurosis, but little is known about how to find this optimal transducer orientation in the frequently-studied medial gastrocnemius muscle. In the current study, we determined the optimal transducer orientation at 9 sites in the medial gastrocnemius muscle of 8 human subjects by calculating the angle of misalignment between three-dimensional muscle fascicles, reconstructed from diffusion tensor images, and the plane of a virtual ultrasound image. The misalignment angle was calculated for a range of tilts and rotations of the ultrasound transducer relative to a reference orientation that was perpendicular to the skin and parallel to the tibia. With the transducer in the reference orientation, the misalignment was substantial (mean across sites and subjects of 6.5°, range 1.4 to 20.2°). However for all sites and subjects a near-optimal alignment (on average 2.6°, range 0.5° to 6.0°) could be achieved by maintaining 0° tilt and applying a small rotation (typically less than 10°). On the basis of these data we recommend that ultrasonographic measurements of medial gastrocnemius muscle fascicle architecture be obtained, at least for relaxed muscles under static conditions, with the transducer oriented perpendicular to the skin and nearly parallel to the tibia.

Ultrasound imaging of the human medial gastrocnemius muscle: how to orient the transducer so that muscle fascicles lie in the image plane.

Bolsterlee B, Gandevia SC, Herbert RD

The length and pennation of muscle fascicles are frequently measured using ultrasonography. Conventional ultrasonography imaging methods only provide two-dimensional images of muscles, but muscles have complex three-dimensional arrangements. The most accurate measurements will be obtained when the ultrasound transducer is oriented so that endpoints of a fascicle lie on the ultrasound image plane and the image plane is oriented perpendicular to the aponeurosis, but little is known about how to find this optimal transducer orientation in the frequently-studied medial gastrocnemius muscle. In the current study, we determined the optimal transducer orientation at 9 sites in the medial gastrocnemius muscle of 8 human subjects by calculating the angle of misalignment between three-dimensional muscle fascicles, reconstructed from diffusion tensor images, and the plane of a virtual ultrasound image. The misalignment angle was calculated for a range of tilts and rotations of the ultrasound transducer relative to a reference orientation that was perpendicular to the skin and parallel to the tibia. With the transducer in the reference orientation, the misalignment was substantial (mean across sites and subjects of 6.5°, range 1.4 to 20.2°). However for all sites and subjects a near-optimal alignment (on average 2.6°, range 0.5° to 6.0°) could be achieved by maintaining 0° tilt and applying a small rotation (typically less than 10°). On the basis of these data we recommend that ultrasonographic measurements of medial gastrocnemius muscle fascicle architecture be obtained, at least for relaxed muscles under static conditions, with the transducer oriented perpendicular to the skin and nearly parallel to the tibia.

Arm posture-dependent changes in corticospinal excitability are largely spinal in origin.

Nuzzo JL, Trajano GS, Barry BK, Gandevia SC, Taylor JL

Biceps brachii motor evoked potentials (MEPs) from cortical stimulation are influenced by arm posture. We used subcortical stimulation of corticospinal axons to determine whether this postural effect is spinal in origin. While seated at rest, 12 subjects assumed several static arm postures, which varied in upper-arm (shoulder flexed, shoulder abducted, arm hanging to side) and forearm orientation (pronated, neutral, supinated). Transcranial magnetic stimulation over the contralateral motor cortex elicited MEPs in resting biceps and triceps brachii, and electrical stimulation of corticospinal tract axons at the cervicomedullary junction elicited cervicomedullary motor evoked potentials (CMEPs). MEPs and CMEPs were normalized to the maximal compound muscle action potential (Mmax). Responses in biceps were influenced by upper-arm and forearm orientation. For upper-arm orientation, biceps CMEPs were 68% smaller (P= 0.001), and biceps MEPs 31% smaller (P= 0.012), with the arm hanging to the side compared with when the shoulder was flexed. For forearm orientation, both biceps CMEPs and MEPs were 34% smaller (bothP< 0.046) in pronation compared with supination. Responses in triceps were influenced by upper-arm, but not forearm, orientation. Triceps CMEPs were 46% smaller (P= 0.007) with the arm hanging to the side compared with when the shoulder was flexed. Triceps MEPs and biceps and triceps MEP/CMEP ratios were unaffected by arm posture. The novel finding is that arm posture-dependent changes in corticospinal excitability in humans are largely spinal in origin. An interplay of multiple reflex inputs to motoneurons likely explains the results.

Unexpected factors affecting the excitability of human motoneurones in voluntary and stimulated contractions.

Khan SI, Taylor JL, Gandevia SC

Effects of a home-based step training programme on balance, stepping, cognition and functional performance in people with multiple sclerosis--a randomized controlled trial.

Hoang P, Schoene D, Gandevia S, Smith S, Lord SR

To determine if step training can improve physical and neuropsychological measures associated with falls in MS. The findings indicate that the step training programme is feasible, safe and effective in improving stepping, standing balance, coordination and functional performance in people with MS.

Use of a physiological profile to document motor impairment in ageing and in clinical groups.

Lord SR, Delbaere K, Gandevia SC

Functional role of neural injury in obstructive sleep apnea.

Saboisky JP, Butler JE, Gandevia SC, Eckert DJ

The causes of obstructive sleep apnea (OSA) are multifactorial. Neural injury affecting the upper airway muscles due to repetitive exposure to intermittent hypoxia and/or mechanical strain resulting from snoring and recurrent upper airway closure have been proposed to contribute to OSA disease progression. Multiple studies have demonstrated altered sensory and motor function in patients with OSA using a variety of neurophysiological and histological approaches. However, the extent to which the alterations contribute to impairments in upper airway muscle function, and thus OSA disease progression, remains uncertain. This brief review, primarily focused on data in humans, summarizes: (1) the evidence for upper airway sensorimotor injury in OSA and (2) current understanding of how these changes affect upper airway function and their potential to change OSA progression. Some unresolved questions including possible treatment targets are noted.