The Effect of Preexercise Expiratory Muscle Loading on Exercise Tolerance in Healthy Men.

PURPOSE: Acute nonfatiguing inspiratory muscle loading transiently increases diaphragm excitability and global inspiratory muscle strength and may improve subsequent exercise performance. We investigated the effect of acute expiratory muscle loading on expiratory muscle function and exercise tolerance in healthy men. METHODS: Ten males cycled at 90% of peak power output to the limit of tolerance (TLIM) after 1) 2 × 30 expiratory efforts against a pressure-threshold load of 40% maximal expiratory gastric pressure (PgaMAX) (EML-EX) and 2) 2 × 30 expiratory efforts against a pressure-threshold load of 10% PgaMAX (SHAM-EX). Changes in expiratory muscle function were assessed by measuring the mouth pressure (PEMAX) and PgaMAX responses to maximal expulsive efforts and magnetically evoked (1 Hz) gastric twitch pressure (Pgatw). RESULTS: Expiratory loading at 40% of PgaMAX increased PEMAX (10% ± 5%, P = 0.001) and PgaMAX (9% ± 5%, P = 0.004). Conversely, there was no change in PEMAX (166 ± 40 vs 165 ± 35 cm H2O, P = 1.000) or PgaMAX (196 ± 38 vs 192 ± 39 cm H2O, P = 0.215) from before to after expiratory loading at 10% of PgaMAX. Exercise time was not different in EML-EX versus SHAM-EX (7.91 ± 1.96 vs 8.09 ± 1.77 min, 95% CI = -1.02 to 0.67, P = 0.651). Similarly, exercise-induced expiratory muscle fatigue was not different in EML-EX versus SHAM-EX (-28% ± 12% vs -26% ± 7% reduction in Pgatw amplitude, P = 0.280). Perceptual ratings of dyspnea and leg discomfort were not different during EML-EX versus SHAM-EX. CONCLUSION: Acute expiratory muscle loading enhances expiratory muscle function but does not improve subsequent severe-intensity exercise tolerance in healthy men.

Regional anesthesia considerations for cardiac surgery.

Pain is a significant consequence of cardiac surgery and newer techniques in cardiac anesthesia have provided an impetus for the development of multimodal techniques to manage acute pain in this setting. In this regard, regional anesthesia techniques have been increasingly used in many cardiac surgical procedures, for the purposes of reducing perioperative consumption of opioid agents and enhanced recovery after surgery. The present investigation focuses on most currently used regional techniques in cardiac surgical procedures. These regional techniques include chest wall blocks (e.g., PECS I and II, SAP, ESB, PVB), sternal blocks (e.g., TTMPB, PSINB), and neuraxial blocks (e.g., TEA, high spinal anesthesia). The present investigation also summarizes indications, technique, complications, and potential clinical benefits of these evolving regional techniques. Cardiac surgery patients may benefit from application of these regional techniques with well controlled indications and careful patient selections.

Anatomical Variations of the Pectoralis Major Muscle: Notes on Their Impact on Pectoral Nerve Innervation Patterns and Discussion on Their Clinical Relevance.

BACKGROUND: The presented study attempts to classify individual anatomical variants of the pectoralis major muscle (PM), including rare and unusual findings. Rare cases of muscular anomalies involving the PM or its tendon have been presented. An attempt has also been made to determine whether anatomical variations of the PM may affect the innervation pattern of the lateral and medial pectoral nerves. MATERIAL AND METHODS: The research was carried out on 40 cadavers of both sexes (22 males, 18 females), owing to which 80 PM specimens were examined. RESULTS: Typical PM structure was observed in 63.75% of specimens. The most frequently observed variation was a separate clavicular portion of the PM. In one female cadaver (2.5% of specimens) the hypotrophy of the clavicular portion of the PM was noticed. In two male cadavers (5% of specimens) the fusion between the clavicular portion of the PM and the deltoid muscle was observed. In one of those cadavers, small sub-branches of the lateral pectoral nerve bilaterally joined the clavicular portion of the deltoid muscle. The detailed intramuscular distribution of certain nerve sub-branches was visualized by Sihler's stain. PM is mainly innervated by the lateral pectoral nerve. In all specimens stained by Sihler's technique, the contribution of the intercostal nerves in PM innervation was confirmed. CONCLUSIONS: Surgeons should be aware of anatomic variations of the PM both in planning and in conducting surgeries of the pectoral region.

The effect of lateral pectoral nerve sparing technique and radiotherapy on the pectoralis major muscle applied with modified radical mastectomy.

BACKGROUND/OBJECTIVE: The aim of this study was to evaluate with electromyography (EMG) the effect of lateral pectoral nerve sparing technique (LPNST) and radiotherapy (RT) on the lateral pectoral nerve (LPN) in patients applied with modified radical mastectomy (MRM). METHODS: The study included 66 patients who underwent MRM surgery. The patients were separated into 2 groups as those applied with LPNST and those who underwent standard surgery (Control group). Within these 2 groups, patients were again separated as those who received or did not receive RT. The EMG evaluations were made by a neurology specialist blinded to the patient groups. RESULTS: The mean age of the patients was 53.3 ± 10.6 years. Standard surgery was applied to 33 (50%) patients and LPNST to 33 (50%) patients, RT was applied to 32 (48.5%) patients and not to 34 (51.5%) patients. In the EMG evaluation, latency was 2.1 ms (1.4-3.2) in the LPNST and 3.7 ms (1.9-12.4) in the control (p <0.001) and amplitude values were 9650 mV (3120-36900) in the LPNST and 4780 mV (510-12.4) in the control (p <0.001). The latency values in the Control receiving and not receiving RT were 4.0 ms (1.9-12.4) and 2.6 ms (1.9-6.2) respectively (p <0.05). The latency values of the patients receiving and not receiving RT in the LPNST were 2.2 ms (1.8-3.2) and 2.0 ms (1.4-2.4) respectively (p <0.05). In the Control and LPNST Group, no significant difference was determined between receiving and not receiving RT groups in respect of amplitude values (p >0.05). CONCLUSION: The results of this study demonstrated that electromyographically the latency and amplitude values were better protected in the LPNST group. It was also seen that RT increased the formation of nerve damage in both groups.

Efficacy of Pectoral Nerve Block Type II for Breast-Conserving Surgery and Sentinel Lymph Node Biopsy: A Prospective Randomized Controlled Study.

Objectives: The pectoral nerve block type II (PECS II block) is widely used for postoperative analgesia after breast surgery. This study evaluated the analgesic efficacy of PECS II block in patients undergoing breast-conserving surgery (BCS) and sentinel lymph node biopsy (SNB). Methods: Patients were randomized to the control group (n=40) and the PECS II group (n=40). An ultrasound-guided PECS II block was performed after induction of anesthesia. The primary outcome measure was opioid consumption, and the secondary outcome was pain at the breast and axillary measured using the Numerical Rating Scale (NRS) 24 hours after surgery. Opioid requirement was assessed according to tumor location. Results: Opioid requirement was lower in the PECS II than in the control group (43.8 ± 28.5 µg versus 77.0 ± 41.9 µg, p < 0.001). However, the frequency of rescue analgesics did not differ between these groups. Opioid consumption in the PECS II group was significantly lower in patients with tumors in the outer area than that in patients with tumors in the inner area (32.5 ± 23.0 µg versus 58.0 ± 29.3 µg, p=0.007). The axillary NRS was consistently lower through 24 hr in the PECS II group. Conclusion: Although the PECS II block seemed to reduce pain intensity and opioid requirements for 24 h after BCS and SNB, these reductions may not be clinically significant. This trial is registered with Clinical Research Information Service KCT0002509.

Should thoracic paravertebral blocks be used to prevent chronic postsurgical pain after breast cancer surgery? A systematic analysis of evidence in light of IMMPACT recommendations.

The role of thoracic paravertebral block (PVB) in preventing chronic postsurgical pain (CPSP) after breast cancer surgery (BCS) has gained interest, but existing evidence is conflicting, and its methodological quality is unclear. This meta-analysis evaluates efficacy of PVB, compared with Control group, in preventing CPSP after BCS, in light of the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) recommendations. Electronic databases were searched for randomized trials comparing PVB with Control group for CPSP prevention after BCS. Eligible trials were assessed for adherence to IMMPACT recommendations. The primary outcomes were CPSP at 3 and 6 months, whereas secondary outcomes were PVB-related complications. Data were pooled and analyzed using random-effects modelling. Trial sequential analysis was used to evaluate evidence conclusiveness. Data from 9 studies (604 patients) were analyzed. The median (range) of IMMPACT recommendations met in these trials was 9 (5, 15) of 21. Paravertebral block was not different from Control group in preventing CPSP at 3 months, but was protective at 6 months, with relative risk reduction (95% confidence interval) of 54% (0.24-0.88) (P = 0.02). Meta-regression suggested that the relative risk of CPSP was lower when single-injection (R = 1.00, P < 0.001) and multilevel (R = 0.71, P = 0.01) PVB were used. Trial sequential analysis revealed that 6-month analysis was underpowered by at least 312 patients. Evidence quality was moderate according to the GRADE system. Evidence suggests that multilevel single-injection PVB may be protective against CPSP at 6 months after BCS, but methodological limitations are present. Larger trials observing IMMPACT recommendations are needed to confirm this treatment effect and its magnitude.

Remote Postconditioning Induced by Trauma Protects the Mouse Heart against Ischemia Reperfusion Injury. Involvement of the Neural Pathway and Molecular Mechanisms.

PURPOSE: Abdominal superficial surgical incision elicits cardioprotection against myocardial ischemia reperfusion (I/R) injury in mice. This cardioprotective phenomenon, termed remote preconditioning of trauma (RPCT), results in an 80 to 85 % reduction in cardiac infarct size. We evaluated cardioprotection and the molecular mechanisms of remote postconditioning of trauma (RPostCT) in a murine I/R injury model. METHODS: Mice were analyzed using a previously established I/R injury model. An abdominal superficial surgical incision was made 45 min after myocardial ischemia at the end of coronary occlusion, and infarct size was determined 24 h after reperfusion. RESULTS: The results indicated that a strong cardioprotective effect occurred during RPostCT (56.94 ± 2.71 % sham vs. 15.58 ± 2.16 % RPostCT; the mean area of the infarct divided by the mean area of the region at risk; p ≤ 0.05; n = 10). Furthermore, pharmacological intervention revealed neurogenic signaling involvement in the beneficial effects of RPostCT via sensory and sympathetic thoracic nerves. Pharmacological experiments in transgenic mice demonstrated that bradykinin receptors, ß-adrenergic receptors (AR), and protein kinase C were implicated in the cardioprotective effects of RPostCT. CONCLUSIONS: RPostCT significantly decreased myocardial infarction size via neurogenic transmission and various signaling pathways. This study describes a new cardiac I/R injury prevention method that might lead to the development of therapies that are more clinically relevant for myocardial I/R injury.

Neurophysiological characteristics of human leg muscle action potentials evoked by transcutaneous magnetic stimulation of the spine.

The objectives of this study were to establish the neurophysiological properties of the compound muscle action potentials (CMAPs) evoked by transcutaneous magnetic stimulation of the spine (tsMSS) and the effects of tsMSS on the soleus H-reflex. In semi-prone seated subjects with trunk semi-flexed, the epicenter of a figure-of-eight magnetic coil was placed at Thoracic 10 with the handle on the midline of the vertebral column. The magnetic stimulator was triggered by monophasic single pulses of 1 ms, and the intensity ranged from 90% to 100% of the stimulator output across subjects. CMAPs were recorded bilaterally from ankle and knee muscles at the interstimulus intervals of 1, 3, 5, 8, and 10 s. The CMAPs evoked were also conditioned by posterior tibial and common peroneal nerve stimulation at a conditioning-test (C-T) interval of 50 ms. The soleus H-reflex was conditioned by tsMSS at the C-T intervals of 50, 20, -20, and -50 ms. The amplitude of the CMAPs was not decreased when evoked at low stimulation frequencies, excitation of group I afferents from mixed peripheral nerves in the leg affected the CMAPs in a non-somatotopical neural organization pattern, and tsMSS depressed soleus H-reflex excitability. These CMAPs are likely due to orthodromic excitation of nerve motor fibers and antidromic depolarization of different types of afferents. The latency of these CMAPs may be utilized to establish the spine-to-muscle conduction time in central and peripheral nervous system disorders in humans. tsMSS may constitute a non-invasive modality to decrease spinal reflex hyperexcitability and treat hypertonia in neurological disorders.

Anatomical and radiological study of the thoracic paravertebral space in dogs: iohexol distribution pattern and use of the nerve stimulator.

OBJECTIVE: To describe the landmarks and methodology to approach the thoracic paravertebral space in dogs; to evaluate if intercostal muscular response could be evoked by a nerve-stimulator; to radiographically assess the distribution pattern of a radio-opaque contrast medium after thoracic paravertebral injections. STUDY DESIGN: Randomized, controlled, experimental trial. ANIMALS: Two mongrel dog cadavers (anatomical study) and 24 mongrel dogs (experimental study). METHODS: For the anatomic study 0.2 mL kg(-1) of new methylene blue (NMB) was injected at the 5th thoracic paravertebral space; for the experimental study dogs were divided into three groups and received 1 (T(5)), 2 (T(4) and T(6)) or 4 (T(4), T(5), T(6) and T(7)) paravertebral injections of iohexol. The paravertebral approach was performed with insulated needles using landmarks and a blind technique. When the needle tip reached the respective thoracic paravertebral space, the nerve-stimulator was switched-on and the presence/absence of intercostal muscular twitch was registered, thus a total volume of 0.2 mL kg(-1) of iohexol, divided into equal parts for each injection point, was administered. Radiological studies were performed with two orthogonal projections at different times. Positive injection was confirmed when the paravertebral space was occupied by iohexol in both projections. RESULTS: NMB was distributed in the T(5) paraverterbal space. In the experimental study, when the needle tip reached the respective paravertebral space, intercostal twitching was obtained in 80% of the total injections with a stimulating current of 0.5 mA. The incidence of positive cases when the intercostal twitch was obtained with 0.5 mA was 83.3%. The main distribution pattern observed was cloud like without longitudinal diffusion. CONCLUSION AND CLINICAL RELEVANCE: Intercostal muscular responses obtained with a stimulating current of 0.5 mA could be useful to locate thoracic spinal nerves in dogs and in our study the injected solution was confined to one thoracic paravertebral space.

Voltage-dependent amplification of synaptic inputs in respiratory motoneurones.

The role of persistent inward currents (PICs) in cat respiratory motoneurones (phrenic inspiratory and thoracic expiratory) was investigated by studying the voltage-dependent amplification of central respiratory drive potentials (CRDPs), recorded intracellularly, with action potentials blocked with the local anaesthetic derivative, QX-314. Decerebrate unanaesthetized or barbiturate-anaesthetized preparations were used. In expiratory motoneurones, plateau potentials were observed in the decerebrates, but not under anaesthesia. For phrenic motoneurones, no plateau potentials were observed in either state (except in one motoneurone after the abolition of the respiratory drive by means of a medullary lesion), but all motoneurones showed voltage-dependent amplification of the CRDPs, over a wide range of membrane potentials, too wide to result mainly from PIC activation. The measurements of the amplification were restricted to the phase of excitation, thus excluding the inhibitory phase. Amplification was found to be greatest for the smallest CRDPs in the lowest resistance motoneurones and was reduced or abolished following intracellular injection of the NMDA channel blocker, MK-801. Plateau potentials were readily evoked in non-phrenic cervical motoneurones in the same (decerebrate) preparations. We conclude that the voltage-dependent amplification of synaptic excitation in phrenic motoneurones is mainly the result of NMDA channel modulation rather than the activation of Ca2+ channel mediated PICs, despite phrenic motoneurones being strongly immunohistochemically labelled for CaV1.3 channels. The differential PIC activation in different motoneurones, all of which are CaV1.3 positive, leads us to postulate that the descending modulation of PICs is more selective than has hitherto been believed.

Does thoracic pump influence the cerebral venous return?

We assessed the hemodynamic effects induced by the thoracic pump in the intra- and extracranial veins of the cerebral venous system on healthy volunteers. Activation of the thoracic pump was standardized among subjects by setting the deep inspiration at 70% of individual vital capacity. Peak velocity (PV), time average velocity (TAV), vein area (VA), and flow quantification (Q) were assessed by means of echo color Doppler in supine posture. Deep respiration significantly increases PV, TAV, and Q, but it is limited to the extracranial veins. To the contrary, no significant hemodynamic changes were recorded at the level of the intracranial venous network. Moreover, at rest TAV in the jugular veins was significantly correlated with Q of the intracranial veins. We conclude that the modulation of the atmospheric pressure operated by the thoracic pump significantly modifies the hemodynamics of the jugular veins and of the reservoir of the neck and facial veins, with no effect on the vein network of the intracranial compartment.

Nerve stimulator-guided repetitive paravertebral block for thoracic myofascial pain syndrome.

Myofascial pain syndrome (MPS) may persist for many years and is often refractory to traditional therapeutic approaches including pharmacotherapy, focal tenderness infiltration by local anesthetic and corticosteroids, physical therapy and behavioral modification. This report describes three cases of MPS following coronary artery bypass graft, inadequate positioning during abdominal hysterectomy, and excessive physical effort refractory to conventional therapeutic approaches. Three patients were successfully treated with repeated nerve stimulator-guided paravertebral block using a mixture of bupivacaine and clonidine. Physical examinations including a complete neurological assessments were unremarkable. Relevant diagnostic imaging (X-ray, magnetic resonance imaging, computed tomography) and laboratory evaluations also failed to demonstrate any significant structural disorders or systemic diseases that might have been responsible for their pain. Nerve stimulator-guided paravertebral block was performed at the dermatomes corresponding to the thoracic myofascial pain region. Each point was injected with 4 mL of the local anesthetic solution. If the pain returned, a second paravertebral block was performed. The three patients were pain-free over a follow-up period up to 2 years. Our report suggests that nerve stimulator-guided paravertebral blockade could be a useful treatment for MPS refractory to traditional therapeutic approaches.

Pelvic nerve input mediates descending modulation of homovisceral processing in the thoracolumbar spinal cord of the rat.

BACKGROUND & AIMS: Colonic afferents project to the lumbosacral and thoracolumbar spinal cord via the pelvic and hypogastric/lumbar colonic nerves, respectively. Both spinal regions process inflammatory colonic stimuli. The role of thoracolumbar segments in processing acute colorectal pain is questionable, however, because the lumbosacral spinal cord appears sufficient to process reflex responses to acute pain. Here, we show that activity in pelvic nerve colonic afferents actively modulates thoracolumbar dorsal horn neuron processing of the same colonic stimulus through a supraspinal loop: homovisceral descending modulation. METHODS: Dorsal horn neurons were recorded in the rat thoracolumbar spinal cord after acute or chronic pelvic neurectomy and cervical cold block. RESULTS: Acute pelvic neurectomy or lidocaine inhibition of lumbosacral dorsal roots facilitated the excitatory response of thoracolumbar dorsal horn neurons to colorectal distention (CRD) and decreased the percentage of neurons inhibited by CRD, suggesting colonic input over the pelvic nerve inhibits thoracolumbar processing of the same stimulus. Ectopic activity developed in the proximal pelvic nerve after chronic neurectomy reactivating the inhibitory circuit, inhibiting thoracolumbar neurons. Cervical cold block alleviated the inhibition in intact or chronic neurectomized rats. However, the facilitated response after acute pelvic neurectomy was inhibited by cervical cold block, exposing an underlying descending facilitation. Inhibiting pelvic nerve input after cervical cold block had minimal effect. CONCLUSIONS: These data demonstrate that input over the pelvic nerve modulates the response of thoracolumbar spinal neurons to CRD by a supraspinal loop and that increasing thoracolumbar processing increases visceral hyperalgesia.

Differential control of the scapulothoracic muscles in humans.

The control of the scapulothoracic muscles trapezius (Tr) and serratus anterior (SA) has been examined in normal human subjects. Electromyographic recordings were made from the SA and Tr muscles (upper trapezius UTr, lower trapezius LTr) using surface electrodes placed bilaterally. Magnetic stimulation of the motor cortex and electrical stimulation of peripheral nerves were used to examine their descending and reflex control. The average optimal site of cortical stimulation was found to be the same for SA, UTr and LTr (an approximate centre of gravity of -0.6 cm, 3.7 cm where the centre of gravity is expressed as the mean anterio-posterior position, the mean medio-lateral position). Some asymmetry in the cortical representation of UTr was found in each individual tested. Magnetic stimulation evoked bilateral MEPs in Tr (latency contralateral (c) UTr 8.5 +/- 1.6 ms, ipsilateral (i) UTr 19.0 +/- 2.7 ms) but only contralateral responses were evoked in SA (11.2 +/- 2.6 ms). Electrical stimulation of the long thoracic nerve at two sites was used to examine homonymous and heteronymous reflexes of SA, while electrical stimulation of cervical nerve of C3/4 was used to examine the heteronymous reflexes of Tr. Ipsilateral SA H reflexes were evoked at a latency of 9.9 +/- 0.8 ms (proximal site) and 10.8 +/- 1.2 ms (distal site). No group I reflexes were evoked from SA to its contralateral homologue. No group I reflexes were evoked between Tr and SA. Finally, cross-correlation of activity from the Tr muscle pairs and the SA muscle pair revealed that the motoneurones of the Tr muscles share some common presynaptic input whereas there was no detectable common presynaptic input to the SA muscle pair. This study extends and consolidates knowledge regarding the neural control of trapezius and for the first time explores the neural control of SA. The study demonstrates a contrasting bilateral control of Tr and SA. These patterns of connections are discussed in relation to the contrasting bilateral functional roles of these muscles.

The long thoracic nerve conduction study revisited in 2006.

OBJECTIVE: To compare the reliability and feasibility of recording long thoracic nerve (LTN) conductions either with surface or needle electrodes. METHODS: The nerve conduction studies were carried out bilaterally on 40 control subjects. The LTN was first stimulated at the axilla and recorded with surface electrodes located on the 7th or 8th digitations of the serratus anterior (SA), then stimulated at Erb's point and recorded with a needle inserted in the 6th or 7th digitations of the SA. For each method, the latency and amplitude of the motor action potential were recorded. RESULTS: Responses were recorded on both sides for each patient. With surface recording, the mean latency was 2.2 +/- 0.30 ms, and the mean amplitude was 5.3 +/- 2.4 mV. With needle recording, the mean latency was 3.65 +/- 0.45 ms, and the mean amplitude was 8.95 +/- 4 mV. CONCLUSIONS: This study demonstrates that both techniques are reliable, feasible, and correlate well. SIGNIFICANCE: Our study shows surface recording of nerve conduction should be favored because it is non-traumatic, less uncomfortable for the patient, and less prone to pitfalls. Nevertheless, in pathological cases, both techniques should be used at initial and follow-up examinations in order to better assess axonal loss and nerve conduction impairment.

Long-term in vivo modulation of synaptic efficacy at the neuromuscular junction of Rana pipiens frogs.

Prolonged changes in motor neurone activity can result in long-term changes in synaptic transmission. We investigated whether mechanisms commonly thought to be involved in determining synaptic efficacy of vertebrate motor neurones are involved in these long-term changes. The nerve supplying the cutaneous pectoris muscle was chronically stimulated via skin surface electrodes in freely moving frogs for 5-7 days. Chronic stimulation induced a 50% reduction in evoked endplate potential (EPP) amplitude at stimulated neuromuscular junctions (NMJs). These changes appear to be presynaptic since miniature EPP (mEPP) amplitude was unchanged while mEPP frequency was decreased by 46% and paired-pulse facilitation was increased by 26%. High frequency facilitation (40 Hz, 2 s) was also increased by 89%. Moreover, stimulated NMJs presented a 92% decrease in synaptic depression (40 Hz, 2 s). An increase in mitochondrial metabolism was observed as indicated by a more pronounced labelling of active mitochondria (Mitotracker) in stimulated nerve terminals, which could account for their greater resistance to synaptic depression. NMJ length visualized by alpha-bungarotoxin staining of nAChRs was not affected. Presynaptic calcium signals measured with Calcium Green-1 were larger in stimulated NMJs at low frequency (0.2 Hz) and not different from control NMJs at higher frequency (40 Hz, 2 s and 30 s). These results suggest that some mechanisms downstream of calcium entry are responsible for the determination of synaptic output, such as a down-regulation of some calcium-binding proteins, which could explain the observed results. The possibility of a change in frequenin expression, a calcium-binding protein that is more prominently expressed in phasic synapses, was, however, refuted by our results.

Long thoracic nerve: anatomy and functional assessment.

BACKGROUND: The anatomy and function of the long thoracic nerve are not fully understood. The purposes of this study were to clarify the anatomy of the long thoracic nerve and to propose a clinical test to assess the function of the upper division of the long thoracic nerve. METHODS: The long thoracic nerve and the serratus anterior muscle were studied in fifteen fresh cadavera. Six patients had an operation to treat a brachial plexus injury, and the long thoracic nerve was electrically stimulated. The resulting shoulder motion was then observed. RESULTS: The long thoracic nerve was formed by branches arising from the C5, C6, and C7 nerve roots. The C5 and C6 branches joined beneath the scalenus medius muscle to form the upper division of the long thoracic nerve, which was located 1 cm posteriorly and superiorly to the upper trunk origin. The union of the upper division with the branch from C7 occurred caudally, in the axillary region. Two branches from the upper division of the long thoracic nerve to the upper portion of the serratus anterior muscle were consistently identified. After electrical stimulation of the upper division branches, shoulder protraction was observed. CONCLUSIONS AND CLINICAL RELEVANCE: In the supraclavicular region, the long thoracic nerve has a trajectory parallel to the brachial plexus, which is contrary to the schematic representation in most textbooks. The upper division of the long thoracic nerve can be assessed by the shoulder protraction test.

A novel technique for recording from the serratus anterior.

OBJECTIVE: To design an electrodiagnostic technique by which to accurately record the serratus anterior compound muscle action potential (CMAP). DESIGN: Observational study. SETTING: Academic electromyography laboratory. PARTICIPANTS: Fifteen healthy volunteers. INTERVENTIONS: The long thoracic nerve was stimulated by using a standard bipolar surface electrode in the axilla, just anterior to the midaxillary line. The serratus anterior CMAP was recorded by using a self-adhesive, 8.0 x 0.5 cm, ring electrode as the E1 placed across the serratus anterior interdigitations starting at the nipple level. A self-adhesive, motor (1 x 1 cm) electrode was used as E2 and placed over the seventh rib. A standard self-adhesive ground electrode was placed over the inferior region of the latissimus dorsi. MAIN OUTCOME MEASURES: Distal motor latency (DML), and CMAP amplitude and duration. RESULTS: After removing 2 outliers, the results are reported as the mean +/- 1.96 standard deviations. Right long thoracic DML was 2.2+/-1.0ms and the left was 2.3+/-0.9ms, with a side-to-side mean difference of 0.3+/-0.4ms. The right serratus CMAP amplitude was 3.8+/-3.9mV and the left was 3.9+/-3.7mV, with a side-to-side mean difference of 0.6+/-1.2mV. Statistical analysis did not reveal a significant side-to-side difference for DML or CMAP amplitude. Both sides were combined to form a single set of trials for DML and CMAP amplitude. The mean DML became 2.2+/-0.7ms, and the CMAP amplitude was 3.5+/-1.9mV. The CMAP duration was 14.5+/-4.3ms on the right and 14.5+/-4.1ms on the left. A significant, positive correlation existed between height and DML ( P <.02). The 95% confidence intervals for DML and CMAP amplitudes were 2.1 to 2.5ms and 1.5 to 3.1mV, respectively. CONCLUSIONS: Our latency, side-to-side comparisons and amplitude data were consistent with other motor nerve conduction findings in the literature. Stimulating the long thoracic nerve in the axilla will provide a reliable technique to aid in the diagnosis and treatment of long thoracic neuropathy.

Histamine contributes to ischemia-related activation of cardiac spinal afferents: role of H1 receptors and PKC.

Myocardial ischemia activates cardiac spinal afferents that transmit the nociceptive information leading to chest pain and elicit excitatory cardiovascular reflexes. Previous studies have shown that histamine is increased in coronary sinus blood during myocardial ischemia and that this autacoid stimulates abdominal visceral afferents. The present investigation evaluated the role of endogenous histamine in stimulation of ischemically sensitive cardiac spinal afferents. Nerve activity of single-unit cardiac afferents was recorded from the left sympathetic chain or rami communicans (T2-T5) in anesthetized cats. Sixty-four cardiac afferents were identified. Injection (5-30 microg/kg) of histamine into the left atrium (LA) stimulated 7 ischemically sensitive cardiac afferents resulting in a significant increase in their activity in a dose-dependent manner. Also, LA injection of histamine (10 microg/kg) stimulated 7 of 8 ischemically insensitive cardiac spinal afferents. Administrations of 2-(3-chlorophenyl)histamine (250 microg/kg, LA), a specific H1 receptor agonist and histamine (10 microg/kg, LA), stimulated 9 other ischemically sensitive cardiac afferents (0.48 +/- 0.10 to 1.40 +/- 0.20 imp/s). In contrast, dimaprit (500 microg/kg, LA), an H2 receptor agonist, stimulated only one of the 9 afferents and thus did not alter their overall activity (0.40 +/- 0.09 to 0.54 +/- 0.09 imp/s). (R)alpha-Methyl-histamine (500 microg/kg, LA), an H3 receptor agonist, did not stimulate any of the 9 afferents. Pyrilamine (300 microg/kg, i.v.), a selective H1 receptor antagonist, attenuated the activity of 8 afferents during 5 min of ischemia from 3.32 +/- 0.38 to 1.87 +/- 0.28 imp/s and abolished the response of 9 other cardiac afferents to histamine. Finally, administration of PKC-(19-36) (30 microg/kg, i.v.), a selective inhibitor of protein kinase C, attenuated the response of 8 cardiac afferents to histamine by 32%. These data indicate that endogenous histamine contributes to activation of cardiac sympathetic afferents during myocardial ischemia through H1 receptors and that the action of histamine on these cardiac afferents is partially dependent on the intracellular PKC pathway.