Expiratory activity in transferred intercostal nerves in brachial plexus injury patients

Muscles of Breathing: Development, Function, and Patterns of Activation

This review is a comprehensive description of all muscles that assist lung inflation or deflation in any way. The developmental origin, anatomical orientation, mechanical action, innervation, and pattern of activation are described for each respiratory muscle fulfilling this broad definition. In addition, the circumstances in which each muscle is called upon to assist ventilation are discussed. The number of "respiratory" muscles is large, and the coordination of respiratory muscles with "nonrespiratory" muscles and in nonrespiratory activities is complex-commensurate with the diversity of activities that humans pursue, including sleep (8.27). The capacity for speech and adoption of the bipedal posture in human evolution has resulted in patterns of respiratory muscle activation that differ significantly from most other animals. A disproportionate number of respiratory muscles affect the nose, mouth, pharynx, and larynx, reflecting the vital importance of coordinated muscle activity to control upper airway patency during both wakefulness and sleep. The upright posture has freed the hands from locomotor functions, but the evolutionary history and ontogeny of forelimb muscles pervades the patterns of activation and the forces generated by these muscles during breathing. The distinction between respiratory and nonrespiratory muscles is artificial, as many "nonrespiratory" muscles can augment breathing under conditions of high ventilator demand. Understanding the ontogeny, innervation, activation patterns, and functions of respiratory muscles is clinically useful, particularly in sleep medicine. Detailed explorations of how the nervous system controls the multiple muscles required for successful completion of respiratory behaviors will continue to be a fruitful area of investigation. © 2019 American Physiological Society. Compr Physiol 9:1025-1080, 2019.

Electromyographic comparison of various exercises to improve elbow flexion following intercostal nerve transfer

We compared the quantitative electromyographic activity of the elbow flexors during four exercises (forced inspiration, forced expiration, trunk flexion and attempted elbow flexion), following intercostal nerve transfer to the musculocutaneous nerve in 32 patients who had sustained root avulsion brachial plexus injuries. Quantitative electromyographic evaluation of the mean and maximum amplitude was repeated three times for each exercise. We found that mean and maximum elbow flexor activity was highest during trunk flexion, followed by attempted elbow flexion, forced inspiration and finally forced expiration. The difference between each group was significant (p < 0.001), with the exception of the difference between trunk flexion and attempted elbow flexion. Consequently, we recommend trunk flexion exercises to aid rehabilitation following intercostal nerve transfer.

Analysis of activity of motor units in the biceps brachii muscle after intercostal-musculocutaneous nerve transfer

We examined respiratory activity of motor units (MUs) in the internal intercostal nerves (IICNs)-transferred biceps brachii muscle (IC-biceps) in cats. MUs of IC-biceps showed respiratory discharges in inspiratory and expiratory phases, and these were enhanced by CO2 inhalation. Narrowing the airway also enhanced inspiratory and expiratory MUs activity. A mechanical load to the thorax immediately enhanced inspiratory MUs activity and weakened expiratory MUs activity. We analyzed the cross-correlation of MUs activity in interchondral muscle and IC-biceps to characterize the respiratory spinal descending inputs to motoneurons. We confirmed the short-term synchronization from interchondral muscles indicating divergence of a single respiratory presynaptic axon to thoracic motoneurons, but could not find synchronization from IC-biceps. The motor axonal conduction velocity (axonal CV) of IC-biceps MUs was lower than that of interchondral muscles. There was no correlation between the respiratory recruitment order of IC-biceps MUs and their axonal CV. These results indicate that IC-biceps shows the respiratory activities and afferent inputs from intercostal muscle spindles in the neighboring segments remain influential on activity of IC-biceps. In addition, the short-term synchronization from IC-biceps could not be found, suggesting that the intercostal nerve transfer alters the respiratory spinal descending inputs to thoracic motoneurons.

Regeneration of periodontal Ruffini endings of rat lower incisors following nerve cross-anastomosis with mental nerve

The present study utilized protein gene product 9.5 (PGP 9.5) and S-100 protein immunohistochemistry to examine if Ruffini endings, the primary mechanoreceptors in periodontal ligaments, can regenerate following nerve cross-anastomosis with an inappropriate nerve. Normally, axon terminals of periodontal Ruffini endings are extensively ramified, and terminal Schwann cells, identified by their S-100 immunoreactivity, are associated with axon terminals. Schwann cells are restricted to the alveolus-related part (ARP), but not tooth-related part (TRP) or the shear zone at the border between the ARP and the TRP of the lingual periodontal ligament of the lower incisor. When the central portion of the mental nerve (MN) was connected with the peripheral portion of the inferior alveolar nerve (IAN), regenerating MN fibers invaded the IAN around postoperative day 5 (PO 5). During the postoperative period, numerous S-100-immunoreactive (IR) cells, presumably terminal Schwann cells, began to migrate to the shear zone and the TRP. PGP 9.5-IR elements reappeared at PO 7 and gradually increased in number. Around PO 28, the terminal portion of the regenerating Ruffini endings appeared dendritic, but less expanded, and the rearrangement of terminal Schwann cells was noted. Regenerated periodontal Ruffini endings were slightly smaller in number. The number of trigeminal ganglion neurons sending peripheral processes beyond the site of injury was smaller compared to those of normal MN, but their cross-sectional areas were almost comparable. Expressions of calbindin D28k and calretinin, normally localized in axonal elements in Ruffini endings, were first detected around PO 56. The present results show that parts of periodontal Ruffini endings can regenerate following nerve cross-anastomosis with mental nerve.

Efficient reinnervation of hindlimb muscles by thoracic motor neurons after nerve cross-anastomosis in rats

Object. Peripheral motor axons can regenerate through motor endoneurial tubes of foreign nerves to reinnervate different target muscles. This regenerative capacity has been brought to clinical applications for restorative surgery after nerve or root injury. In this study the authors explore the extent to which nerve cross-anastomosis between lower intercostal nerves and lumbar ventral roots would be effective in inducing reinnervation of paralyzed hindlimb muscles after spinal cord hemisection at the thoracolumbar boundary in rats.

Methods. The proximal extremities of sectioned intercostal nerves T10–12 were surgically connected to the distal extremities of sectioned ipsilateral lumbar ventral roots L3–5, respectively. Motor activity reappeared 2 months postsurgery; however, locomotion was not restored and inappropriate motor patterns persisted at 9 months postsurgery. At that time, data from electrophysiological and histological studies and horseradish peroxidase retrograde labeling demonstrated efficient regrowth of thoracic motor neuron axons that reached hindlimb muscles. They also revealed a persistent maturation defect of regrown fibers, as shown by size heterogeneity and presumable extensive axonal branching. These features are consistent with reduced neural activity subsequent to continuing inappropriate motor patterns.

Conclusions. These results indicate that cross-anastomosis of intercostal nerves with lumbar ventral roots allows efficient reinnervation of paralyzed hindlimb muscles after spinal cord hemisection in rats. Stimulating the reorganization of the neuronal circuitry in the central nervous system by locomotion training or other methods would presumably result in both functional and anatomical improvements. This experimental setting provides a convenient animal model to investigate these processes.

Movement related cortical source for elbow flexion in patients with branchial plexus injury after intercostal-musculocutaneous nerve crossing

Nine patients with brachial plexus injury whose transected musculo-cutaneous nerves had been sutured with intercostal nerves were examined and the relationship between flexion of the operated elbow and the respiratory movement were shown. Three out of nine patients showed independent control of movement from respiration after regeneration. The primary motor cortex for either flexion of the elbow to the operated side or brisk voluntary inspiration was estimated in the medial vertex region of the frontal cortex by the dipole-tracing method in these three patients. The present results suggest that patients contract the biceps muscle reinnervated by the intercostal nerve independently from respiratory movements using the same primary motor cortex with trunk movements. Functional plasticity may occur in the patients using the primary trunk motor cortex for elbow flexion.

Reconstruction of tonic vibration reflex in the biceps brachii reinnervated by transferred intercostal nerves in patients with brachial plexus injury

The transfer of intercostal nerves to musculocutaneous nerves has been performed to reconstruct elbow flexion in patients with brachial plexus injury. In nine of 15 such patients, 2-3 Hz tapping of the distal tendon of the biceps muscle reinnervated by the transferred intercostal nerves (IC-biceps) induced a mode in the correlogram between tap and EMG pulse of IC-biceps. In five of the mode-positive patients, tapping of various frequencies induced gradual augmentation of integrated EMG of IC-biceps. This reflex was consistent with the tonic vibration reflex (TVR) in normal controls. Conduction velocity and frequency property of the reflex were compatible with the speculation that rapid-conducting muscle afferents (group Ia or II or both) reinnervate mechanoreceptors, such as muscle spindles. The clinical significance of muscle sensory reinnervation is not clear; however, the reconstruction of TVR following this operation is worthy in that it confirms the specific sensory reinnervation of denervated muscle in humans.

Sensory reinnervation of muscle receptor in human

This report describes sensory reinnervation of muscle receptors in humans. In this study, sensory function was investigated in fourteen patients with brachial plexus injury, whose musculocutaneous nerve was surgically sutured with intercostal nerves for reconstruction of elbow flexion. Tapping the intercostal nerve-reinnervated brachial biceps muscle (IC-biceps) induced somatosensory evoked potentials (IC-biceps SEP) in four patients. Tapping also induced reflex IC-biceps activity in all IC-biceps SEP (+) patients, but not in eight out of nine IC-biceps SEP (-) patients. Results show that muscle afferent fibers in the intercostal nerves reinnervated mechanoreceptors in IC-biceps, and induced both cortical sensory activity and muscle activity that indicated the classical stretch reflex.

Respiration-related activity in the biceps brachii muscle after intercostal-musculocutaneous nerve transfer

Needle EMG and polygraphic recordings of respiration and biceps activity were obtained in 7 patients who had undergone intercostal to musculocutaneous nerve transfer because of severe traumatic injury to the brachial plexus. EMG activity during expiration and inspiration was assessed during quiet breathing, deep breathing, and during sustained inspiration and expiration, and compared to the clinical strength of the biceps muscle. Biceps activity was consistently found during both expiration and inspiration, and in either case separately related to the flexion force levels. Initially this relationship appeared equally strong for both phases. With time, control over flexion changes from a completely respiratory-driven control to a conscious volitional control; however, involuntary effects of respiration always remained present in polygraphic recordings. Theoretical explanations for the change in control are put forward.

Motor recovery after cross-reinnervation of a forelimb nerve by the phrenic nerve in cats

Electromyographic (EMG) activities of forelimb muscles and the diaphragm following cross-reinnervation of the elbow flexor nerve by the phrenic nerve sampled simultaneously with cinematographic recording of forelimb movements, in order to examine whether the respiratory nervous system in adult cats is capable of compensation for movement disorders. The right phrenic and musculocutaneous nerves were cut preparatory to cross-union, the proximal stump of the phrenic nerve being joined to the peripheral stump of the musculocutaneous nerve. Reinnervation of the elbow flexor muscles (m. biceps brachii and m. brachialis) was confirmed in terminal experiments by observing muscular contractions induced by nerve stimulations and/or retrogradely labeled motoneurons in cervical (C5-C7) segments following treatment for horseradish peroxidase (HRP) which had been injected previously into the m. biceps brachii of both sides. Behavioral observations were made in the chronically cross-reinnervated cats. Bipolar EMG recording electrodes were implanted chronically in the right m. biceps brachii, m. triceps brachii and in the left intact diaphragm. In freely moving cats 3-22 months after cross-union surgery, EMG activities in the elbow flexor usually were synchronized with those of the left diaphragm. However, occasionally, in cats cross-reinnervated more than 6 months previously, EMG activities in the right biceps muscle were dissociated from those of the left diaphragm during voluntary movements. During walking, EMG activities in the cross-reinnervated biceps muscle were not coordinated with the walking cycle. By contrast, during voluntary goal directed movements, the cats were capable of reaching their right forepaws to the target in a smooth manner using elbow flexion that was associated with EMG activity of the biceps muscles.(ABSTRACT TRUNCATED AT 250 WORDS)