Phrenic nerve conduction study in demyelinating neuropathies and open-heart surgery.

OBJECTIVES: The aim of this study was to determine normal values of phrenic nerve conduction (PNC) in healthy individuals; to evaluate the subclinical extent of phrenic nerve involvement in Guillain-Barré syndrome (G-B) and hereditary motor and sensory neuropathy-I (HMSN-I), and to evaluate phrenic nerve damage after cardiac surgery. MATERIALS AND METHODS: PNC was performed by transcutaneous stimulation in the neck and recording the diaphragmatic potential from surface electrodes placed at the seventh and eight intercostal spaces. PNC was performed bilaterally in 25 healthy volunteers and 25 patients before and after open-heart surgery. Right PNC was also performed in 5 cases with G-B and 5 patients with HMNS-I. RESULTS: Latency and amplitude of the diaphragmatic potential were the same in controls and in patients with cardiac disease before surgery. After surgery, 28% of patients had left phrenic nerve inexcitability, and 8% had reduced amplitude of the response. These 9 patients demonstrated elevation of the left hemidiaphragm on chest radiography. Left PNC performed 1 year after the operation showed improvement in latency and amplitude of the responses in all except one patient. PNC was prolonged in 4 out of 5 cases with G-B and in all patients with HMNS-I. CONCLUSIONS: PNC is an easy and reliable method in evaluating phrenic nerve damage due to hypothermia or primary stretch injury in patients after cardiac surgery. PNC may be helpful in detecting diaphragmatic involvement before clinical ventilatory insufficiency in demyelinating neuropathies such as G-B and HMNS-I.     

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.     

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 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     

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.     

Phrenic nerve conduction studies: technical aspects and normative data

In our clinical work we have occasionally encountered difficulties (e.g., no response, concomitant brachial plexus stimulation) in performing phrenic nerve conduction studies. The aim of this study was to overcome these difficulties and obtain our own set of normative data. In 29 healthy volunteers (15 men), aged 21-65 years, phrenic nerve conduction studies were performed using bipolar surface stimulation electrodes and a standard recording montage. Stimulation just above the clavicle, between the sternal and clavicular heads of the sternocleidomastoid muscles, elicited responses at the lowest stimulation strength, without concomitant brachial plexus stimulation. M-wave amplitude and duration changed with respiration, whereas latency and area did not. The normative limit for M-wave latency was 8.0 ms (upper), for amplitude it was 0.46/0.33 mV (lower: inspiration/expiration), and for area it was 4.4 mVms (lower). We suggest a slight modification of the generally used position for phrenic nerve stimulation, and the use of M-wave latency and area (unaffected by the respiratory cycle) in future phrenic nerve conduction studies.     

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.     

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.     

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.     

Evaluation of phrenic nerve and pulmonary function in hereditary motor and sensory neuropathy, type I.

Phrenic nerve and diaphragmatic dysfunction has been assumed to be the cause of respiratory failure in hereditary motor and sensory neuropathy, type 1 (HMSN I). In order to determine the relationship between phrenic nerve and pulmonary function in this disease, 25 patients underwent a 4-step evaluation process consisting of: (1) bilateral phrenic nerve conduction study; (2) median, peroneal, and tibial motor conduction studies; (3) measurement of forced vital capacity (FVC) and maximal inspiratory and expiratory pressures (MIP, MEP); and (4) pulmonary-focused history and physical. Phrenic nerve motor latency was abnormally prolonged in 22 of the 23 (96%) subjects when a response was obtained. All had slowed velocity or absent peripheral motor conduction responses. Vital capacity was abnormally reduced in 6 of the 25 (24%) subjects. Eight (32%) had an abnormally reduced MIP, while 19 (76%) had an abnormally reduced MEP. Only 2 (8%) subjects had clinical evidence of pulmonary dysfunction. None of the dependent variables (FVC, MIP, MEP, peripheral nerve conduction, or clinical examination) correlated with phrenic nerve latencies. Although phrenic nerve latencies are markedly prolonged in HMSN I, these values are not useful in predicting respiratory dysfunction.     

EFFECTS OF EXERCISE ON SOMATOSENSORY-EVOKED POTENTIALS

The aim of this study was to investigate the effect of acute and regular exercise on somatosensory-evoked potentials (SEP). The study group was designed as 9 female and 7 male volleyball players, and the control group as 9 female and 7 male sedentary students. The P1 and P2 latency and amplitude values were measured by tibial nerve stimulation on both lower extremities in the study groups before and after exercise on a treadmill. Intra-group comparison was made to evaluate the acute effects of exercise, and inter-group comparison for the chronic effects of it. Statistically significant difference was determined in pre-exercise right P2 amplitudes and post-exercise left P2 latencies of female volleyball players and sedentary girls. There was significant difference between only the pre-exercise left P2 latency when comparison was made between the sportsmen and sedentary male subject groups. There were significant differences between the pre-exercise left P1 and P2 latency values of sportswomen and right P2 amplitudes of sedentary female subjects. There was no significant difference between left P2 latency values of sportsmen and sedentary male subjects. In conclusion, it was determined that acute and regular exercise shortened the latency of sensory-evoked potentials while decreasing their amplitudes. When evaluating the sensory-evoked potentials in electrophysiology laboratories, the exercise capacity and physical activity levels of the subjects should be considered.     

Analysis of reflex activity in cardiac sympathetic nerve induced by myelinated phrenic nerve afferents

Electrical stimulation of the phrenic nerve afferents evoked excitatory responses in the right inferior cardiac sympathetic nerve in chloralose-anaesthetized cats. The reflex was recorded in intact and spinal cats. The latency and threshold of the volley recorded from the phrenic nerve as well as of the cord dorsum potentials evoked by electrical stimulation of the phrenic nerve indicated that group III afferents were responsible for this reflex. The phrenicocardiac sympathetic reflex recorded in intact cats was followed by a silent period. The maximum amplitude of the reflex discharges was 800 microV, the latency was 83 ms and the central transmission time 53 ms. Duration of the silent period lasted up to 0.83 s. In spinal cats the reflex was recorded 5.5-8 h after spinalization. The maximum amplitude of the spinal reflex discharges ranged from 22 to 91 microV and the latency from 36 to 66 ms.     

Differences between paranoid and nonparanoid schizophrenic patients on the somatosensory P300 event-related potential

Event-related potentials were recorded from schizophrenic patients (n = 30) and healthy controls (n = 30) using a somatosensory-reaction-time version of the oddball paradigm, by stimulating the right and the left median nerve. Latency, amplitude, duration and area of the P300 were measured. The patient group was subdivided into a paranoid (n = 16) and a nonparanoid (n = 14) subgroup and each was compared to controls. After stimulation of the right median nerve the nonparanoid group had a significantly prolonged P300 latency and a normal amplitude. The paranoid subgroup had a trend toward reduction of the P300 amplitude; its P300 latency was normal. After stimulation of the left median nerve, a prolongation of the P300 latency was observed in the paranoid subgroup. This subgroup had also a reduced P300 amplitude, while the nonparanoid patients had both values comparable to those of the controls. Duration and area were not significantly different between the two subgroups of patients and controls. Paranoid and nonparanoid patients showed a different behavior on reaction time parameters. No relationship was observed between P300 parameters and clinical ratings, neuroleptic dose and demographic data. The P300 parameters did not correlate with the reaction time measures. These results are discussed in terms of a disturbance of CNS inhibitory mechanisms in cognitive processes of paranoid schizophrenic patients and could be a further indication that different subtypes of schizophrenia may have different biological substrates.     

Characteristics of habituation of the sympathetic skin response to repeated electrical stimuli in man.

OBJECTIVES: To study the effect of repeating electrical peripheral nerve stimulation on latency, duration and amplitude of the sympathetic skin response (SSR). METHODS: SSRs were elicited in all limbs by median and peroneal nerves stimuli. In 10 subjects, 20 stimuli were applied at random time intervals (15-20 s). Another test was performed in 7 subjects using the same protocol, but switching the stimulation site every 5 or 10 stimuli without warning. RESULTS: The mean amplitude of right palmar response to right peroneal nerve stimulation decreased from 5.05+/-0.76 (SEM) mV at the first stimulus to 1.23+/-0.42 mV at the 20th stimulus (P<0.001). The latency did not change significantly (1473+/-82 to 1550+/-90 ms, P>0.1), while the duration increased (1872+/-356 to 3170+/-681 ms, P<0.001). Stimulation and recording at other sites showed similar trends. Changing the stimulation site failed to alter the adaptation process in terms of amplitude, latency or duration. CONCLUSIONS: Changes in amplitude and duration of the SSRs to repeated electrical stimuli can occur in presence of constant latency and appear to be independent of the source of sensory input. Peripheral sweat gland mechanisms may be involved in the loss of amplitude and increase in duration of the SSR during habituation.     

Effects of exercise on somatosensory-evoked potentials

The aim of this study was to investigate the effect of acute and regular exercise on somatosensory-evoked potentials (SEP). The study group was designed as 9 female and 7 male volleyball players, and the control group as 9 female and 7 male sedentary students. The P1 and P2 latency and amplitude values were measured by tibial nerve stimulation on both lower extremities in the study groups before and after exercise on a treadmill. Intra-group comparison was made to evaluate the acute effects of exercise, and inter-group comparison for the chronic effects of it. Statistically significant difference was determined in pre-exercise right P2 amplitudes and post-exercise left P2 latencies of female volleyball players and sedentary girls. There was significant difference between only the pre-exercise left P2 latency when comparison was made between the sportsmen and sedentary male subject groups. There were significant differences between the pre-exercise left P1 and P2 latency values of sportswomen and right P2 amplitudes of sedentary female subjects. There was no significant difference between left P2 latency values of sportsmen and sedentary male subjects. In conclusion, it was determined that acute and regular exercise shortened the latency of sensory-evoked potentials while decreasing their amplitudes. When evaluating the sensory-evoked potentials in electrophysiology laboratories, the exercise capacity and physical activity levels of the subjects should be considered.     

Diaphragm motor responses to phrenic nerve stimulation in ALS: Surface and needle recordings

Objective

In studies of phrenic nerve (PN) conduction in amyotrophic lateral sclerosis (ALS) both motor response amplitude and latency have been reported as abnormal. However, correlation with diaphragm motor unit loss, and with diaphragmatic function has not been fully evaluated.

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.     

Sensitivities of sensory nerve conduction study parameters in carpal tunnel syndrome.

It is generally accepted that median sensory nerve conduction studies are more sensitive than motor nerve conduction studies in the electrodiagnostic evidence of carpal tunnel syndrome (CTS). This study was conducted to compare the sensitivities of various parameters of sensory nerve conduction studies in the diagnosis of CTS.This prospective study included 88 consecutive patients (151 hands) with CTS and 106 control subjects. CTS was diagnosed clinically by two neurologists. Median sensory nerve responses with wrist stimulation were determined. The onset and peak latencies, peak-to-peak amplitudes, negative peak duration, and area were measured. The differences between the peak and onset latencies were also calculated as a measure of waveform temporal dispersion. Among each measured parameter, values between the 2.5th and the 97.5th percentile range of the control subjects served as the normal limits.Among the 151 hands with suspected CTS, five (3.3%) had normal electrodiagnostic studies and 146 (96.7%) had at least one abnormal electrodiagnostic study. Among the 146 hands with an abnormality, 138 had abnormal onset latency, 143 had abnormal peak latency, and 88 had abnormal difference between peak and onset latency. In addition, 87 had abnormal amplitude, 70 had abnormal duration, and 59 had abnormal area. The sensitivity was 91.4% for onset latency, 94.7% for peak latency, 58.3% for difference between peak and onset latency, 57.6% for amplitude, 46.4% for duration, and 39.1% for area.Our study shows that in patients with CTS, the most sensitive sensory nerve conduction parameter is the peak latency. Studying various additional sensory nerve conduction parameters did not significantly increase the diagnostic yield.     

Aging of phrenic nerve conduction in the elderly.

OBJECTIVE: We elucidated the possible relationship between age and conduction parameters of phrenic nerve in subjects above the sixth decade, comparing with the data from middle-age controls. METHODS: Diaphragmatic action potentials (DAPs) were recorded on bilateral hemithoraces of 41 volunteers aged 60-101 years (old group) and 25 volunteers aged 35-55 years (middle-age group). Statistical analyses were performed to assess the effects of aging on latency, latency corrected by size (Lat/Dist), amplitude, and the right-left difference of these DAP parameters. RESULTS: In all 61 subjects, age showed a significant quadratic correlation with latency and with Lat/Dist, and a linear correlation with amplitude. The right-left differences ranged from 0.0 to 14.5% for latency and from 6.5 to 112.4% for amplitude in the elderly. CONCLUSIONS: The normal ranges of DAP parameters should be determined according to age. The left-right difference may be a useful reference in diagnosing unilateral phrenic nerve lesion. SIGNIFICANCE: The precise normal ranges of phrenic nerve conduction parameters presented will encourage investigations of neuropathies in subjects aged above 60.     

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.