A comprehensive electrophysiological evaluation of phrenic nerve injury related to open-heart surgery

A prospective electrophysiological study of phrenic nerve was performed in 59 subjects undergoing open-heart surgery. The nerve was stimulated percutaneously at the neck and the diaphragmatic response was recorded with surface electrodes placed over the 8th intercostal space. The latency, amplitude, duration and area of the evoked response were measured before and after the operation. Post-operatively no response was elicited in 2 patients bilaterally, in 5 from the left and in 2 from the right. Comparison of the post-operative with the pre-operative group values in the remaining subjects showed that the amplitude and area of the left phrenic were lower in the post-operative study, indicating that some of the nerve fibres were not conducting. There were no statistically significant differences between pre and post-operative values of latency or duration on the left or any of the parameters on the right. Our findings suggest that the amplitude and area of the diaphragmatic response are more sensitive than latency in detecting phrenic nerve paresis associated with open-heart surgery.     

Transient phrenic nerve palsy after cardiac operation in infants.

OBJECTIVE: The aims of this study were to prove the presence of transient phrenic nerve palsy in children after cardiac surgery by successive recordings of diaphragmatic action potentials (DAPs), and to decide the indication of diaphragmatic plication in infants with postoperative phrenic nerve palsy. METHODS: The DAPs were recorded from 11 infants (age 0-54 months) under artificial ventilation after cardiac surgery. The successive DAP recordings were performed within 3-4 days (0W), 1 week (1W) and 2 weeks (2W) after operation to make a final decision for diaphragmatic plication to wean artificial ventilation. RESULTS: The patients were divided into 3 groups according to the DAP changes in successive recordings, namely, patients with normal DAPs at 0W, patients with transient depression of DAPs at 0W followed by recovery to normal DAPs by 1W and/or 2W, and patients with persistent depression of DAPs of the affected side necessitating plication of hemidiaphragm. CONCLUSIONS: In infants with phrenic nerve palsy after cardiothoracic surgery, persistently abnormal DAPs in repeated electrophysiologic examinations for at least 2 weeks after surgery are a useful guidance to support clinical and radiological evidence for an indication of diaphragmatic plication.     

A prospective evaluation of phrenic nerve conduction in multifocal motor neuropathy and chronic inflammatory demyelinating polyneuropathy

The purpose of the study was to evaluate electrophysiologically phrenic nerve involvement in multifocal motor neuropathy (MMN) and chronic inflammatory demyelinating polyneuropathy (CIDP). The response latencies following phrenic nerve stimulation were increased in 11 of 14 (80%) patients in the CIDP group but in only 1 of 14 (8%) patients in the MMN group. The mean diaphragmatic compound muscle action potential (CMAP) was significantly lower in amplitude in the CIDP group compared to the MMN group and to a control group of 8 subjects (P < 0.001). There were no significant differences between the MMN and control groups. Only the reduction in CMAP amplitude correlated with the presence of restrictive lung function. Phrenic nerve conduction measurement should be performed more systematically, especially in CIDP and, when diaphragmatic CMAPs are reduced in amplitude, pulmonary function tests should be performed to look for a restrictive lung syndrome.     

Respiratory electrophysiological studies in Guillain-Barré syndrome.

Respiratory failure is a common and potentially life threatening complication in patients with Guillain-Barré syndrome. The incidence of phrenic nerve involvement and the predictive value of phrenic nerve conduction and diaphragmatic needle EMG were studied in 40 patients with Guillain-Barré syndrome within the first three days of admission to hospital. The negative peak onset latency of the diaphragmatic compound muscle action potential (CMAP), and its amplitude, duration, and area were abnormal in 83%. The need for ventilation was correlated with diaphragmatic CMAP amplitude (P = 0.005), and area (P = 0.001), but not with latency or duration. Abnormalities in diaphragmatic needle EMG were found in 45%, mainly a decreased number of motor unit potentials. The abnormalities correlated with the need for ventilation (P = 0.013). Of the 40% who required ventilation, all had either abnormal phrenic conduction, abnormal diaphragmatic needle EMG, or both. Eighty one per cent of the ventilated patients had abnormal forced vital capacity on the day of the electrophysiological examination. The results indicate that phrenic nerve conduction studies and diaphragmatic EMG are useful in detecting respiratory involvement in patients with Guillain-Barré syndrome and in identifying those at risk of respiratory failure.     

Phrenic nerve conduction in the early stage of Guillain-Barre syndrome might predict the respiratory failure

OBJECTIVE: To investigate whether phrenic nerve conduction in the early phase of Guillain- Barre syndrome (GBS) predicts the need for respiratory assistance during the subsequent clinical course. MATERIAL AND METHODS: We performed electrophysiological examinations of conventional peripheral nerve conduction and phrenic nerve conduction for GBS patients within 14 days from the onset. We excluded patients who had already been treated with immuno-related therapy and respiratory assistance. RESULTS: Fifteen patients were enrolled. Three patients with the sum of phrenic nerve latency longer than 30 ms and the sum of bilateral diaphragmatic compound muscle action potential amplitude smaller than 0.3 mV required respiratory assistance after the conduction test. CONCLUSION: Our findings showed that not only delayed distal latency but also decreased amplitude may predict the need for respiratory assistance during the subsequent disease course.     

Repetitive phrenic nerve stimulation in myasthenia gravis.

OBJECTIVE: In patients with MG it may be difficult to determine whether respiratory insufficiency is due to a defect in neuromuscular transmission. We therefore studied the clinical value of repetitive electrical stimulation of the phrenic nerve. METHODS: Repetitive phrenic nerve stimulation at 3 Hz was performed in 25 patients with MG. We recorded from the ipsilateral hemidiaphragm with surface electrodes before and after exercising the diaphragm for 10 and 90 seconds. The percent decrement of the negative peak (NP) area between the first and the fifth or sixth diaphragmatic compound muscle action potential (DCMAP) was analyzed and results compared with those from 10 healthy individuals. RESULTS: The mean +/- standard deviation percent change of the NP area in healthy individuals was -2.1 +/- 4.2%, with a normal cutoff of > or = 11%. Twelve patients (48%) had an abnormal decrement of DCMAP--9 had a decrement when the diaphragm was rested, 3 only after fatiguing of the diaphragm. The mean percent change in the 12 patients was 20% at rest, -18% after 10 seconds of exercise, and -23% after 90 seconds of exercise-a pattern consistent with MG. Repetitive stimulation of the accessory nerve with recording of the trapezius CMAP (TCMAP) was abnormal in nine patients (36%). The three patients with abnormal decrement of the DCMAP despite normal TCMAP had symptoms of dyspnea. CONCLUSIONS: Repetitive phrenic nerve stimulation studies are a promising tool in the diagnosis of respiratory muscle weakness in MG and should be part of electrophysiologic studies in patients with undiagnosed respiratory failure.     

Neuralgic amyotrophy with phrenic nerve involvement

Phrenic nerve involvement is a rare feature in patients with neuralgic amyotrophy (Parsonage-Turner syndrome). We report four patients who initially presented with severe dyspnea in the absence of lung disease. All patients had a history of infectious disease or surgery and of pain of sudden onset in the shoulder region. Weakness of the proximal arm was observed in only one. Radiographic and pulmonary function studies, phrenic nerve conduction studies, and needle electromyogram (EMG) of the diaphragm documented diaphragmatic paralysis which was unilateral in one patient, bilateral in two patients, and recurrent on alternating sides in another one. Follow-up studies remained abnormal for up to 4 years. Neuralgic amyotrophy with phrenic nerve involvement should be considered in patients presenting with severe, unexplained dyspnea of sudden onset.     

Contralateral diaphragmatic palsy after subcortical middle cerebral artery infarction without capsular involvement

Diaphragmatic palsy after acute stroke is a novel clinical entity and may result in a high incidence of respiratory dysfunction and pneumonia, which especially cause greater morbidity and mortality. Generally, internal capsule and complete middle cerebral artery (MCA) infarctions are major risk-factors for developing diaphragmatic palsy. Herein, we present a case with contralateral diaphragmatic palsy after a subcortical MCA infarction without capsular involvement. Dyspnea occurred after stroke, while a chest X-ray and CT study disclosed an elevated right hemidiaphragm without significant infiltration or patch of pneumonia. A phrenic nerve conduction study showed bilateral mild prolonged onset-latency without any significant right–left difference. This suggested a lesion causing diaphragmatic palsy was not in the phrenic nerve itself, but could possibly originate from an above central location (subcortical MCA infarction). We also discussed the role of transcranial magnetic stimulation study in the survey of central pathway and demonstrated diaphragmatic palsy-related orthopnea.     

Prognosis of phrenic nerve injury following thoracic interventions: four new cases and a review

Introduction

Phrenic nerve lesion is a known complication of thoracic surgical intervention, but it is rarely described following thymectomy and lung surgery.

Objective

To review the literature on thoracic intervention and phrenic nerve lesion and to describe four new cases, in which regular neurophysiological studies were performed.

Methods

We reviewed the literature concerning phrenic nerve lesion after cardiac, lung and thymus surgical interventions. We described four cases of phrenic nerve lesion, three associated with thymectomy and one in lung surgery.

Results

The review shows that cryogenic or thermal injuries during cardiac surgeries are associated with good prognosis. The information on the outcome of phrenic nerve lesion in thymectomy or lung surgery is insufficient. Our cases and this review suggest that phrenic lesion in the last two interventions are associated with a poor recovery.

Conclusion

Our data suggests that the prognosis of phrenic nerve lesion following thoracic intervention depends on the nature of the damage. Probably, in thymectomy and lung surgery, nerve stretch or laceration are involved, consequently the outcome is poorer in comparison with cardiac surgery, where cold lesion is more frequent. Neurophysiological tests give a direct, quantified and reliable assessment of nerve regeneration.     

Diaphragmatic weakness related to radiotherapy: 2 cases and a review

Post-radiation diaphragmatic weakness have rarely been described. We report two cases of post-radiation diaphragmatic weakness from our center, and review the other published cases, computing clinical, electromyography and magnetic resonance imaging data. Including our two cases, seven cases of post-radiation diaphragmatic weakness have been described. Most occurred after mantle-field radiotherapy for Hodgkin lymphoma (5/7), often in associations with chemotherapy (4/7). Other radiations-induced complications were found (5/7) such as brachial plexopathy, cardiac involvement or hypothyroidy. When studied, phrenic nerve conduction studies revealed different profiles, from clearly abnormal responses to limit amplitudes. Imaging can be a useful diagnostic tool, displaying abnormalities with sharp limits matching the radiation field. Data is limited about long-term evolution. Presentation of post-radiation diaphragmatic weakness seems relatively homogeneous. We propose a diagnosis work-up for post-radiation diaphragmatic weakness, to exclude potentially treatable differential diagnoses.     

Experimental study of a late response recorded from the thoracic wall after phrenic nerve stimulation

ObjectivesThe phrenic nerve cervical stimulation induces an early motor diaphragmatic M response that may be recorded from the 7th ipsilateral intercostal space (ICS). Some responses with prolonged latency and of unclear origin can be recorded from the same recording site. The aim of the study was to determine the electrophysiological characteristics and the neuroanatomical pathways underlying the long-latency responses (LLRs) recorded from the 7th ICS.MethodsWe studied seven healthy volunteers, five patients with spinal cord injury and five patients with diaphragmatic palsy. All underwent phrenic nerve conduction study. An LLR was sought for at different stimulation sites using various stimulus intensities.ResultsA polyphasic LLR was recorded from the 7th ICS in all healthy subjects. It was mainly elicited by nociceptive stimulations, not only of the phrenic, but also of the median nerves. Its latency was longer than 70 ms, with a wide inter- and intra-individual variability. Amplitude was highly variable and some habituation phenomenon occurred. The LLR was retained in most tetraplegic patients after phrenic nerve stimulation, but absent otherwise. It was present in all patients with diaphragmatic palsy after phrenic nerve stimulation.ConclusionThe LLR is likely to be produced by both intercostal and diaphragm muscles. It is a polysynaptic and multisegmental spinal response, probably conveyed by small-diameter nociceptive A-δ and/or C fibres and modulated by a supraspinal control.SignificanceThe LLR recorded from the chest wall may constitute, by analogy with the nociceptive component of the lower limb flexion reflex in humans, a protective and withdrawal spinal reflex response.     

Electrophysiologic evaluation of diaphragm by transcutaneous phrenic nerve stimulation

Phrenic nerve function was evaluated by transcutaneous stimulation in the neck and recording the diaphragmatic potential from surface electrodes placed at the ipsilateral seventh intercostal space (7CS) and the xiphoid process (XP). Simultaneous recordings from 7CS and XP electrodes connected together (XP-7CS) and each connected to a remote reference (knee-7CS and knee-XP) disclosed that the 7CS electrode was always more active and showed electropositive activity, whereas the XP electrode, which was only minimally active, showed electronegative response. Out-of-phase summation of opposite polarity activity at the two electrodes resulted in a higher amplitude response in XP-7CS derivation. Phrenic nerve studies are useful in establishing phrenic nerve injury following cardiothoracic operation. They may also provide evidence of phrenic nerve or diaphragmatic involvement in demyelinative neuropathies, motor neuron disease, and muscular dystrophies.     

Visualization of the diaphragm muscle with ultrasound improves diagnostic accuracy of phrenic nerve conduction studies

Introduction: Evaluation of phrenic neuropathy (PN) with phrenic nerve conduction studies (PNCS) is associated with false negatives. Visualization of diaphragmatic muscle twitch with diaphragm ultrasound (DUS) when performing PNCS may help to solve this problem. Methods: We performed bilateral, simultaneous DUS–PNCS in 10 healthy adults and 12 patients with PN. The amplitude of the diaphragm compound muscle action potential (CMAP) (on PNCS) and twitch (on DUS) was calculated. Results: Control subjects had <38% side‐to‐side asymmetry in twitch amplitude (on DUS) and 53% asymmetry in phrenic CMAP (on PCNS). In the 12 patients with PN, 12 phrenic neuropathies were detected. Three of these patients had either significant side‐to‐side asymmetry or absolute reduction in diaphragm movement that was not detected with PNCS. There were no cases in which the PNCS showed an abnormality but the DUS did not. Conclusions: The addition of DUS to PNCS enhances diagnostic accuracy in PN. Muscle Nerve 49 : 669–675, 2014     

Phrenic and intercostal nerves with rhythmic discharge can promote early nerve regeneration after brachial plexus repair in rats

Exogenous discharge can positively promote nerve repair. We, therefore, hypothesized that endogenous discharges may have similar effects. The phrenic nerve and intercostal nerve, controlled by the respiratory center, can emit regular nerve impulses; therefore these endogenous automatically discharging nerves might promote nerve regeneration. Action potential discharge patterns were examined in the diaphragm, external intercostal and latissimus dorsi muscles of rats. The phrenic and intercostal nerves showed rhythmic clusters of discharge, which were consistent with breathing frequency. From the first to the third intercostal nerves, spontaneous discharge amplitude was gradually increased. There was no obvious rhythmic discharge in the thoracodorsal nerve. Four animal groups were performed in rats as the musculocutaneous nerve cut and repaired was bland control. The other three groups were followed by a side-to-side anastomosis with the phrenic nerve, intercostal nerve and thoracodorsal nerve. Compound muscle action potentials in the biceps muscle innervated by the musculocutaneous nerve were recorded with electrodes. The tetanic forces of ipsilateral and contralateral biceps muscles were detected by a force displacement transducer. Wet muscle weight recovery rate was measured and pathological changes were observed using hematoxylin-eosin staining. The number of nerve fibers was observed using toluidine blue staining and changes in nerve ultrastructure were observed using transmission electron microscopy. The compound muscle action potential amplitude was significantly higher at 1 month after surgery in phrenic and intercostal nerve groups compared with the thoracodorsal nerve and blank control groups. The recovery rate of tetanic tension and wet weight of the right biceps were significantly lower at 2 months after surgery in the phrenic nerve, intercostal nerve, and thoracodorsal nerve groups compared with the negative control group. The number of myelinated axons distal to the coaptation site of the musculocutaneous nerve at 1 month after surgery was significantly higher in phrenic and intercostal nerve groups than in thoracodorsal nerve and negative control groups. These results indicate that endogenous autonomic discharge from phrenic and intercostal nerves can promote nerve regeneration in early stages after brachial plexus injury.     

Reliability of phrenic nerve conduction study: In healthy controls and in patients with primary lateral sclerosis

ObjectivePhrenic nerve conduction study is a marker of hypoventilation in amyotrophic lateral sclerosis. We aimed to evaluate its intra-rater reliability in healthy subjects and in a cohort of Primary Lateral Sclerosis (PLS) patients.MethodsEighteen healthy subjects and 16 PLS patients were included. All subjects underwent three phrenic nerve conduction evaluations (time interval: 1 week for healthy controls; 1 year for PLS patients). We analyzed intra-rater reliability for five parameters of the diaphragmatic motor response: latency; negative-peak duration, area and amplitude; peak-to-peak amplitude.ResultsHealthy subjects showed excellent inter-test reliability for most parameters (coefficients of variation <10%). In PLS patients coefficients of variation resulted <10% for latency and peak-to-peak amplitude, <20% for remaining parameters. Inter-test reliability was excellent for latency and peak-to-peak amplitude [intra-class correlation coefficient (ICC) > 0.9] and good for negative-peak amplitude and area (ICC 0.75 ≥ 0.9); duration was not reliable (ICC = 0.383). Negative peak and peak-to-peak amplitude had the least random error (respectively ±0.136 mV and ± 0.177 mV). All parameters showed homoscedasticity (R2 < 0.1).ConclusionsIntra-rater reliability is high for phrenic nerve study, especially for latency, peak-to-peak and negative-peak amplitude.SignificancePhrenic nerve conduction study is a reliable method to monitor respiratory function.     

Phrenic nerve conduction study in normal subjects

Phrenic nerve conduction studies were performed in 50 phrenic nerves from 25 normal subjects using a technique modified from previously described methods. The normal ranges for latency, amplitude, negative peak area, and duration were established. The latency correlates with age and the amplitude increases with chest circumference. With our method, the amplitude increases and the duration decreases with lung volume. We found good right-left agreement and reproducibility. Therefore, the unaffected side can be used as a reference in unilateral phrenic nerve lesions and previous studies can be used for comparison in serial studies. We recommend that phrenic nerve conduction studies be used routinely to diagnose and monitor patients with respiratory involvement from neuromuscular diseases.© 1995 John Wiley &Sons, Inc.     

Character of diaphragm compound muscle action potential and phrenic nerve conduction time in patients with obstructive sleep apnea-hypopnea syndrome☆◇

BACKGROUND： Both hypoxia and.carbon dioxide retention can damage phrenic nerve and muscle conduction, as well as diaphragm function. Diaphragm compound muscle action potential and phrenic nerve conduction time are reliable indicators for measuring phrenic nerve and diaphragm function. OBJECTIVES： To verify the hypothesis that changes of phrenic nerve conduction time （PNCT） and diaphragm compound muscle action potential （CMAP） in obstructive sleep apnea-hypopnea syndrome （OSAHS） patients might contribute to the decline of phrenic nerve and diaphragm function. PNCT and CMAP were measured with multipair esophageal electrodes combined with unilateral magnetic stimulation. DESIGN, TIME AND SETTING： Case controlled study. The experiment was carried out in Guangzhou Institute of Respiratory Disease, Guangzhou MediCal College, from June 2005 to April 2006. PARTICIPANTS： Twenty seven OSAHS patients and eight primary snoring subjects from Guangzhou Institute of Respiratory Disease, Guangzhou Medical College were recruited and all subjects were diagnosed by polysomnography （PSG）. Sixteen healthy, non-snoring subjects in the hospital for medical examination during the same time period were selected as the control group. METHODS： Esophageal electrodes, made by Guangzhou Institute of Respiratory Disease, combined with unilateral magnetic stimulation, were used to measure PNCT and CMAP of all subjects. PNCT was defined as the time from stimulation artifact to the onset of CMAP and diaphragm CMAP amplitude was measured from peak to peak. Oxygen desaturation index and apnea-hypopnea index were measured using PSG, and their relevance to PNCT and CMAP were analyzed. PNCT and CMAP in five OSAHS patients were repeatedly measured after effective nasal continuous positive airway pressure treatment for more than 2 months. MAIN OUTCOME MEASURES： （1） PNCT and diaphragm CMAP of subjects in each group. （2） Relevance of oxygen desaturation index and apnea-hypopnea index to PNCT and CMAP. （3） Changes of     

Phrenic Nerve Conduction in Healthy Subjects

Introduction: Assessment of diaphragm compound muscle action potential by noninvasive phrenic nerve stimulation at the neck is well described. However, normal values in a large cohort of healthy subjects are lacking. Our objective was to determine reference values of phrenic nerve conduction in healthy subjects. Methods: We recruited 155 healthy subjects (25–79 years old) and measured mean amplitude (PhrenAmp) and latency (PhrenLat) of motor responses according to Bolton's method. Results: The lower limit for PhrenAmp was 0.28 and 0.25 mV and the upper limit for PhrenLat was 8.41 and 8.56 ms for right and left side, respectively. PhrenLat was correlated with age. PhrenAmp, PhrenLat and area were significantly higher in men. Tolerance to phrenic nerve stimulation was excellent. Conclusions: Our study provides normative values of phrenic nerve motor responses in a large cohort of healthy subjects and identifies age and sex as factors of variation. Muscle Nerve 59:451–456, 2019     

Idiopathic bilateral diaphragmatic paralysis

A 41-year-old man complained of subacute onset of dyspnea and pain in the neck and chest. He was diagnosed with bilateral diaphragmatic paralysis, based on clinical inspection of the breathing pattern and transdiaphragmatic pressure recording, and was trained to use a portable bi-level positive airway pressure apparatus (BiPAP). Needle electromyography showed profuse fibrillation potentials and positive waves in the diaphragm, more abundant on the right than left side, and no response to phrenic nerve stimulation. Other muscles were not involved. Follow-up examinations, performed at 9 and 12 months after onset of paralysis, demonstrated a slow but progressive improvement of the patient's respiratory function, together with the appearance of reinnervation potentials in the diaphragm, and polyphasic, long-latency responses to phrenic nerve stimulation. The subacute onset of the paralysis associated with local pain, and its subsequent recovery, suggest bilateral proximal lesions in the phrenic nerves. In the absence of traumatic or metabolic causes, these findings suggest that the phrenic nerve can be a target in idiopathic neuritis.     

Character of diaphragm compound muscle action potential and phrenic nerve conduction time in patients with obstructive sleep apnea-hypopnea syndrome

BACKGROUND: Both hypoxia and carbon dioxide retention can damage phrenic nerve and muscle conduction, as well as diaphragm function. Diaphragm compound muscle action potential and phrenic nerve conduction time are reliable indicators for measuring phrenic nerve and diaphragm function.OBJECTIVES: To verify the hypothesis that changes of phrenic nerve conduction time (PNCT) and diaphragm compound muscle action potential (CMAP) in obstructive sleep apnea-hypopnea syndrome (OSAHS) patients might contribute to the decline of phrenic nerve and diaphragm function. PNCT and CMAP were measured with multipair esophageal electrodes combined with unilateral magnetic stimulation.DESIGN, TIME AND SETTING: Case controlled study. The experiment was carried out in Guangzhou Institute of Respiratory Disease, Guangzhou Medical College, from June 2005 to April 2006.PARTICIPANTS: Twenty seven OSAHS patients and eight primary snoring subjects from Guangzhou Institute of Respiratory Disease, Guangzhou Medical College were recruited and all subjects were diagnosed by polysomnography (PSG). Sixteen healthy, non-snoring subjects in the hospital for medical examination during the same time period were selected as the control group.METHODS: Esophageal electrodes, made by Guangzhou Institute of Respiratory Disease, combined with unilateral magnetic stimulation, were used to measure PNCT and CMAP of all subjects. PNCT was defined as the time from stimulation artifact to the onset of CMAP and diaphragm CMAP amplitude was measured from peak to peak. Oxygen desaturation index and apnea-hypopnea index were measured using PSG, and their relevance to PNCT and CMAP were analyzed. PNCT and CMAP in five OSAHS patients were repeatedly measured after effective nasal continuous positive airway pressure treatment for more than 2 months.MAIN OUTCOME MEAAURES: (1) PNCT and diaphragm CMAP of suhjects in each group. (2) Relevance of oxygen desaturation index and apnea-hypopnea index to PNCT and CMAP. (3) Changes of PNCT and CMAP of OSAHS patients before and after treatment.RESULTS: All subjects were included in the analyzed results. (1) PNCT of the OSAHS group was significantly longer compared to that of the control and primary snore groups, while CMAP of the OSAHS group was significantly lower (P<0.05). (2) PNCT and CMAP recorded from both sides correlated significantly with oxygen desaturation index and with apnea-hypopnea index (P<0.01). (3) PNCT shortened signiticantly after effective nasal continuous positive airway pressure treatment for more than 2 months (P<0.05).CONCLUSION: Prolongation of PNCT and decrease of CMAP might contribute to the decline of phrenic nerve and diaphragm function caused by repeated nocturnal hypoxia and carbon dioxide retention. The impairment of the phrenic nerve might also decrease diaphragm function.