Phrenic Nerve Conduction Abnormalities Correlate with Diaphragmatic Descent in Chronic Obstructive Pulmonary Disease

Differences between diaphragmatic compound muscle action potentials recorded from over the sternum and lateral chest wall in healthy subjects

To report normative data for diaphragmatic compound muscle action potentials (DCMAPs) recorded from over the sternum and lateral chest wall (LCW) and highlight factors that may contribute to variations in DCMAP parameters at the two sites. The phrenic nerve of seventy-three healthy subjects was bilaterally stimulated at the posterior border of the sternocleidomastoid muscle. DCMAPs from over the sternum and LCW were recorded (inspiration/expiration). Normative values of sternal and LCW DCMAPs were presented. The mean values of latency of LCW DCMAPs, duration of sternal DCMAPs and area from both recording sites are close to values reported by other studies. The mean values of latency of sternal DCMAPs are higher than that reported by other studies. Significant differences were found between sternal and LCW potentials in the mean latency, amplitude, and area (p < 0.001). The duration did not differ between the two sites. Differences were found between inspiration and expiration, right and left sides, and men and women. Regression analysis showed a relation between latency of sternal and LCW potentials and age. Latency (LCW potentials) and amplitude and area (sternal/LCW potentials) were related to gender. Amplitude (LCW potentials/inspiration) and area (sternal potentials/inspiration) were related to chest circumference (p = 0.023 and 0.013 respectively). Area (sternal potentials/expiration) was related to the BMI (p = 0.019). Our normative values for sternal and LCW DCMAPs are provided. Notable differences in the DCMAPs parameters were detected between the two recording sites, inspiration and expiration, right and left, and men and women. The technique of phrenic nerve should be standardized.

The Amplitude of Diaphragm Compound Muscle Action Potential Correlates With Diaphragmatic Excursion on Ultrasound and Pulmonary Function After Supraclavicular Brachial Plexus Block

Objective

This prospective, double-blind, randomized study assessed (1) the associations between diaphragm compound muscle action potential (CMAP), hemidiaphragmatic excursion, and pulmonary function after supraclavicular brachial plexus block (SCBPB) and (2) diagnostic efficacy of pulmonary function for hemidiaphragmatic paralysis evidenced by diaphragm CMAP as an assessment of diaphragm strength was evaluated.

Methods

Eighty-six patients were scheduled for the removal of hardware after healing of a right upper limb fracture distal to the shoulder who were randomly assigned in a 1:1 ratio to two groups: Group A (diaphragmatic excursion), or Group B (pulmonary function). Phrenic nerve conduction studies (PNCSs), M-mode ultrasonography of the diaphragm, and pulmonary function tests (PFTs) were performed before and 30 min after SCBPB. PNCSs were used to determine the latency and amplitude of diaphragm CMAP. Ultrasonography of the diaphragm was performed with patients in a supine position using a low-frequency probe over the subcostal space at the midclavicular line. The diaphragmatic excursion was measured during quiet breathing and deep breathing. Pulmonary function, i.e., forced vital capacity (FVC), predicted value of FVC, and forced expiratory flow in the first second (FEV1), was measured with spirometry. Receiver Operating Characteristic (ROC) curve analysis was used to assess the diagnostic efficacy of pulmonary function for hemidiaphragmatic paralysis evidenced by diaphragm CMAP as an assessment of diaphragm strength.

Results

There were significant associations between the reduction in amplitude of diaphragm CMAP and reductions in diaphragmatic excursion during quiet breathing (r = 0.70, p < 0.01) and deep breathing (r = 0.63, p < 0.01) when expressed as a percentage of baseline values. There were significant associations between the reduction in amplitude of diaphragm CMAP and reductions in FVC (r = 0.67, p < 0.01), FVC% (r = 0.67, p < 0.01), and FEV1 (r = 0.62, p < 0.01), when expressed as percentage of baseline values. The area under the ROC curve for FVC was 0.86. A decrease of >8.4% in FVC compared to pre-block predicted hemidiaphragmatic paralysis (determined by diaphragm CMAP) with sensitivity and specificity of 79.2 and 100%, respectively.

Conclusions

The relative reduction in diaphragm CMAP amplitude after SCBPB was correlated with relative reductions in diaphragmatic excursion and pulmonary function. FVC has potential as a useful diagnostic indicator of hemidiaphragmatic paralysis, evidenced by diaphragm CMAP, after SCBPB. These data establish diaphragm CMAP as a direct and objective index of diaphragmatic paralysis after SCBPB.

Phrenic nerve paralysis and phrenic nerve reconstruction surgery

Phrenic nerve injury results in paralysis of the diaphragm muscle, the primary generator of an inspiratory effort, as well as a stabilizing muscle involved in postural control and spinal alignment. Unilateral deficits often result in exertional dyspnea, orthopnea, and sleep-disordered breathing, whereas oxygen or ventilator dependency can occur with bilateral paralysis. Common etiologies of phrenic injuries include cervical trauma, iatrogenic injury in the neck or chest, and neuralgic amyotrophy. Many patients have no identifiable etiology and are considered to have idiopathic paralysis. Diagnostic evaluation requires radiographic and pulmonary function testing, as well as electrodiagnostic assessment to quantitate the nerve deficit and determine the extent of denervation atrophy. Treatment for symptomatic diaphragm paralysis has traditionally been limited. Medical therapies and nocturnal positive airway pressure may provide some benefit. Surgical repair of the nerve injury to restore functional diaphragmatic activity, termed phrenic nerve reconstruction, is a safe and effective alternative to static repositioning of the diaphragm (diaphragm plication), in properly selected patients. Phrenic nerve reconstruction has increasingly become a standard surgical treatment for diaphragm paralysis due to phrenic nerve injury. A multidisciplinary approach at specialty referral centers combining diagnostic evaluation, surgical treatment, and rehabilitation is required to achieve optimal long-term outcomes.

Effects of Chronic and Acute Pulmonary Hyperinflation on Phrenic Nerve Conduction in Patients with COPD

In patients with moderate-to-severe Chronic Obstructive Pulmonary Disorder (COPD), pulmonary hyperinflation can occur at rest and increase during episodes of exacerbation. Among other mechanical constraints, changes in position and configuration of the diaphragm are also induced by increased end-expiratory lung volume. Both descent and flattening of diaphragm might damage the phrenic nerves by stretching their fibers. The study aimed to investigate the phrenic nerve conduction in COPD patients in stable conditions and during COPD exacerbation. In a group of 11 COPD patients without relevant comorbidities in stable conditions and subsequently in another group of 10 COPD patients during in-hospital COPD exacerbation and recovery, measurements of functional respiratory parameters and assessment of phrenic nerves motor conduction by bilateral electric stimulation were performed concurrently. Significant increase in phrenic nerves latency (p < 0.05), but similar amplitude of motor compound muscle action potential (cMAP) was observed in stable COPD patients vs. matched controls (p < 0.05). However, in COPD patients with resting pulmonary hyperinflation as reliably detected by substantial Inspiratory Capacity reduction (<80% pred.), the mean bilateral latency was longer vs. COPD patients without pulmonary hyperinflation (p < 0.02). During COPD exacerbation, in contrast with mean latency, the mean amplitude of phrenic nerves cMAP improved at discharge when compared with in-hospital admission (p < 0.05). In stable COPD patients the velocity of phrenic nerve conduction was impaired mostly in the presence of pulmonary hyperinflation, while during COPD exacerbation where dynamic pulmonary hyperinflation abruptly occurs, the reversible decrease of cMAP amplitude does suggest a temporary, acute axonal damage of phrenic nerves, potentially contributing to diaphragmatic dysfunction in these circumstances.

Effect of local anesthetic volume (20 mL vs 30 mL ropivacaine) on electromyography of the diaphragm and pulmonary function after ultrasound-guided supraclavicular brachial plexus block: a randomized controlled trial

BACKGROUND AND OBJECTIVES

Diaphragmatic paralysis following supraclavicular brachial plexus block (SCBPB) is ascribed to phrenic nerve palsy. This study investigated the effect of 2 volumes of 0.375% ropivacaine on efficacy of block as a surgical anesthetic and as an analgesic and examined diaphragm compound muscle action potentials (CMAPs) and pulmonary function before and after SCBPB.

METHODS

Eighty patients scheduled for removal of hardware for internal fixation after healing of an upper limb fracture distal to the shoulder were randomized to receive ultrasound-guided SCBPC for surgical anesthesia with 20 mL (Group A) or 30 mL (Group B) 0.375% ropivacaine. The latency and amplitude of diaphragm CMAPs and forced vital capacity (FVC), FVC% predicted, and forced expiratory volume in 1 s (FEV1) were measured before and 30 min after SCBPB.

RESULTS

Block success as primary anesthetic in addition to analgesia was 81% in Group A and 91% in Group B. There were no obvious differences in the effectiveness of analgesia between the two groups. The mean time to onset of motor block was significantly longer in Group A (8.1±2.7 min) than in Group B (5.4 ± 2.8 min; p<0.05). The mean amplitude of the diaphragm CMAP was significantly lower in Group B than in Group A (p=0.03). The changes in FVC (Group A, - 8.1% vs Group B, -16.5%), FVC% (Group A, -8.0% vs Group B, -17.1%), and FEV1 (Group A, -9.5% vs Group B, -15.2%) from pre-SCBPB to post-SCBPB were significantly less in Group A than in Group B (all p=0.03).

CONCLUSIONS

The incidence rates of phrenic nerve palsy and diaphragm paralysis were reduced, and lung function was less impaired in patients who received 20 mL vs 30 mL of 0.375% ropivacaine without any differences in block success. Selecting a lower volume of anesthetic for nerve block may be especially beneficial in obese patients or patients with cardiopulmonary disease.

TRIAL REGISTRATION NUMBER

ChiCTR-IND-17012166.

Diaphragmatic motor cortex hyperexcitability in patients with chronic obstructive pulmonary disease

Background and objectives

Respiratory muscles dysfunction has been reported in COPD. Transcranial magnetic stimulation (TMS) has been used for assessing the respiratory corticospinal pathways particularly of diaphragm. We aimed to study the cortico-diaphragmatic motor system changes in COPD using TMS and to correlate the findings with the pulmonary function.

Methods

A case control study recruited 30 stable COPD from the out-patient respiratory clinic of Main Alexandria University hospital- Egypt and 17 healthy control subjects who were subjected to spirometry. Cortical conduction of the diaphragm was performed by TMS to all participants followed by cervical magnetic stimulation of the phrenic nerve roots. Diaphragmatic resting motor threshold (DRMT), cortical motor evoked potential latency (CMEPL), CMEP amplitude (CMEPA), peripheral motor evoked potential latency (PMEPL), PMEP amplitude (PMEPA) and central motor conduction time (CMCT) were measured.

Results

66.7% of COPD patients had severe and very severe COPD with median age of 59 (55–63) years. There was statistically significant bilateral decrease in DRMT, CMEPA and PMEPA in COPD group versus healthy subjects and significant increase in CMEPL and PMEPL (p <0.01). Left CMCT was significantly prolonged in COPD group versus healthy subjects (p <0.0001) but not right CMCT. Further, there was significant increase in CMEPL and CMCT of left versus right diaphragm in COPD group (p = 0.003 and 0.001 respectively) that inversely correlated with FEV₁% and FVC% predicted. Right and left DRMT were insignificantly different in COPD group (p >0.05) but positively correlated with FEV₁/FVC, FEV₁% and FVC% predicted.

Conclusion

Central cortico-diaphragmatic motor system is affected in COPD patients with heterogeneity of both sides that is correlated with pulmonary function.

Significance

Coticospinal pathway affection could be a factor for development of diaphragmatic dysfunction in COPD patients accordingly its evaluation could help in personalization of COPD management especially pulmonary rehabilitation programs.

Diaphragm quantitative electromyography in difficult-to-treat asthmatic patients

Quantitative electromyography is an important tool to evaluate myopathies, and some difficult-to-treat asthmatic patients may have a subclinical corticosteroid myopathic process, using only inhaled corticosteroid, according to some studies. In this report, diaphragm quantitative electromyography was used to evaluate asthmatic difficult-to-treat patients, comparing them with a control group. Significant differences were obtained in amplitude, duration and size index of motor unit action potentials, with lower parameters in the asthmatic patients, which may indicate a myopathic process.

Is phrenic nerve conduction affected in patients with difficult-to-treat asthma?

Objective The aim of this study was to obtain data on phrenic neuroconduction and electromyography of the diaphragm muscle in difficult-to-treat asthmatic patients and compare the results to those obtained in controls. Methods The study consisted of 20 difficult-to-treat asthmatic patients compared with 27 controls. Spirometry, maximal inspiratory and expiratory pressure, chest X-ray, phrenic neuroconduction and diaphragm electromyography data were obtained. Results The phrenic compound motor action potential area was reduced, compared with controls, and all the patients had normal diaphragm electromyography. Conclusion It is possible that a reduced phrenic compound motor action potential area, without electromyography abnormalities, could be related to diaphragm muscle fiber abnormalities due to overload activity.

Chest pain in patients with COPD: the fascia's subtle silence

COPD is a progressive condition that leads to a pathological degeneration of the respiratory system. It represents one of the most important causes of mortality and morbidity in the world, and it is characterized by the presence of many associated comorbidities. Recent studies emphasize the thoracic area as one of the areas of the body concerned by the presence of pain with percentages between 22% and 54% in patients with COPD. This article analyzes the possible causes of mediastinal pain, including those less frequently taken into consideration, which concern the role of the fascial system of the mediastinum. The latter can be a source of pain especially when a chronic pathology is altering the structure of the connective tissue. We conclude that to consider the fascia in daily clinical activity may improve the therapeutic approach toward the patient.

Phrenic nerve conduction studies: normative data and technical aspects

OBJECTIVE

The aim of the present study was to define normative data of phrenic nerve conduction parameters of a healthy population.

METHODS

Phrenic nerve conduction studies were performed in 27 healthy volunteers.

RESULTS

The normative limits for expiratory phrenic nerve compound muscle action potential were: amplitude (0.47 mv - 0.83 mv), latency (5.74 ms - 7.10 ms), area (6.20 ms/mv - 7.20 ms/mv) and duration (18.30 ms - 20.96 ms). Inspiratory normative limits were: amplitude (0.67 mv - 1.11 mv), latency (5.90 ms - 6.34 ms), area (5.62 ms/mv - 6.72 ms/mv) and duration (13.77 ms - 15.37 ms).

CONCLUSION

The best point of phrenic nerve stimulus in the neck varies among individuals between the medial and lateral border of the clavicular head of the sternocleidomastoid muscle and stimulation of both sites, then choosing the best phrenic nerve response, seems to be the appropriate procedure.

Manual evaluation of the diaphragm muscle

The respiratory diaphragm is the most important muscle for breathing. It contributes to various processes such as expectoration, vomiting, swallowing, urination, and defecation. It facilitates the venous and lymphatic return and helps viscera located above and below the diaphragm to work properly. Its activity is fundamental in the maintenance of posture and body position changes. It can affect the pain perception and emotional state. Many authors reported on diaphragmatic training by using special instruments, whereas only a few studies focused on manual therapy approaches. To the knowledge of the authors, the existing scientific literature does not exhaustively examines the manual evaluation of the diaphragm in its different portions. A complete evaluation of the diaphragm is mandatory for several professional subjects, such as physiotherapists, osteopaths, and chiropractors not only to elaborate a treatment strategy but also to obtain information on the validity of the training performed on the patient. This article aims to describe a strategy of manual evaluation of the diaphragm, with particular attention to anatomical fundamentals, in order to stimulate further research on this less explored field.

Laryngeal and phrenic nerve involvement in a patient with hereditary neuropathy with liability to pressure palsies (HNPP)

Lower cranial and phrenic nerve involvement is exceptional in hereditary neuropathy with liability to pressure palsies (HNPP). Here we report the occurrence of reversible laryngeal and phrenic nerve involvement in a patient with HNPP. The patient recalled several episodes of reversible weakness and numbness of his feet and hands since the age of 30 years. His medical history was uneventful, apart from chronic obstructive pulmonary disease (COPD). At age 44, following severe weight loss, he presented with progressive dysphonia and hoarseness. EMG of cricoarytenoid and thyroarytenoid muscles and laryngeal fibroscopy confirmed vocal cord paralysis. These speech disturbances gradually regressed. Two years later, he reported rapidly worsening dyspnea. Electroneurography showed increased distal latency of the right phrenic nerve and diaphragm ultrasonography documented reduced right hemi-diaphragm excursion. Six months later and after optimization of CODP treatment, his respiratory function had improved and both phrenic nerve conduction and diaphragm excursion were completely restored. We hypothesize that chronic cough and nerve stretching in the context of CODP, together with severe weight loss, may have triggered the nerve paralysis in this patient. Our report highlights the need for optimal management of comorbidities such as CODP as well as careful control of weight in HNPP patients to avoid potentially harmful complications.