Phrenic nerve conduction studies: normative data and technical aspects

Abstract

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.Keywords: electrodiagnosis; reference values; phrenic nerve; spirometry; neural conduction. RESUMOObjetivo: O objetivo do presente estudo foi definir os dados normativos de condução do nervo frênico de uma população saudável. Métodos: Foram realizados estudos de condução do nervo frênico em 27 voluntários saudáveis. Resultados: Os limites normais do potencial de ação muscular composto do nervo frênico durante a expiração foram: amplitude (0.47 mv -0.83 mv), latência (5.74 ms -7.10 ms), área (6.20 ms/mv -7.20 ms/mv) e duração (18.30 ms -20.96 ms). E durante a inspiração os limites normais foram: amplitude (0.67 mv -1.11 mv), latência (5.90 ms -6.34 ms), área (5.62 ms/mv -6.72 ms/mv) e duração (13.77 ms -15.37 ms). Conclusão: O melhor ponto de estímulo do nervo frênico no pescoço varia entre a borda medial e lateral da cabeça clavicular do músculo esternocleidomastóideo. Estimular ambos os locais e escolher a melhor resposta do nervo frênico parece ser o procedimento mais adequado.Palavras-chave: eletrodiagnóstico; valores de referência; nervo frênico; espirometria; condução nervosa.Phrenic nerve conduction has found increasing application in the diagnosis of respiratory dysfunction associated with surgical, neuromuscular, and pulmonary disorders 1,2,3,4,5,6 , which are important causes of respiratory failure and frequently contribute to difficulties in weaning patients off the ventilator in the critical care unit 7 . To determine a neuromuscular cause of hypercapnic respiratory failure, respiratory electrodiagnostic studies are often used 8 . Recently, many authors have correlated phrenic nerve conduction abnormalities with chronic obstructive pulmonary disease. These studies demonstrated abnormal phrenic compound motor action potential (CMAP) amplitudes and latencies in chronic obstructive pulmonary disease patients 9,10,11,12 .Innervated by the phrenic nerve, the diaphragm is the principal respiratory muscle in humans. The diaphragmatic CMAPs are recorded with chest surface electrodes following phrenic nerve stimulation in the neck. Amplitude, latency, and area are measures used to evaluate phrenic nerve integrity 1,2,3,4,5,...

Phrenic Nerve Conduction in Healthy Subjects

“…The mean PhrenLat and upper limit of normal values were shorter than those reported in some previous studies, but similar to those found by others . Like Chen et al ,20 we think that the observed differences can be explained by differences between sites of stimulation (at the level of the thyroid or cricoid cartilage for the former and at a more caudal location just over the clavicle for the latter) and signal recording (shorter latencies if recorded from the anterior versus lateral chest).…”

“…We found that PhrenAmp and the corresponding lower limit of normal were overall lower than in previous studies (0.38 mV versus 0.66 m, 0.70 mV, and 0.65 mV) …”

“…12,16,17,26 We found that PhrenAmp and the corresponding lower limit of normal were overall lower than in previous studies (0.38 mV versus 0.66 m, 0.70 mV, and 0.65 mV). 20,21,27 We found a slightly lower value of mean CMAP duration than in the studies of Chen, Resman-Gaspersc, and Podnar (16.05 versus 19.4 and 21 ms respectively). 20,21 These differences may be explained by the larger number of participants in our study.…”

“…1 Finally, Maranhão et al found a significant correlation between FEV1, FVC, and inspiratory latencies, but they incorrectly assumed that latencies of response to phrenic nerve stimulation followed a Gaussian distribution, so the statistical analysis they used is questionable. 27 All these data suggest that in healthy subjects, respiratory muscle strength and particularly SNIP also depend on the activity of other respiratory muscles. In ALS patients, the early involvement of respiratory muscles leads us to think that diaphragm plays a predominant role in maintaining respiratory muscle strength.…”

“…Moreover, Stewart et al found that MIP and MEP did not correlate with diaphragm needle EMG . Finally, Maranhão et al found a significant correlation between FEV1, FVC, and inspiratory latencies, but they incorrectly assumed that latencies of response to phrenic nerve stimulation followed a Gaussian distribution, so the statistical analysis they used is questionable . All these data suggest that in healthy subjects, respiratory muscle strength and particularly SNIP also depend on the activity of other respiratory muscles.…”