Nerve Conduction Studies of Phrenic Nerve: Normative Data.

Introduction: In neuromuscular diseases, respiratory failure is a major complication. Pulmonary function tests are generally used to assess respiratory function but can be influenced by a number of factors. Nerve conduction studies of the phrenic nerve (PN) is a simple, noninvasive, and safe method to assess diaphragm compromise in neuromuscular diseases.

Methods: A group of 132 (78 males) healthy subjects, aged between 23 and 90 years, was studied, with bilateral stimulation of the PN, with recording of diaphragm motor responses. Anthropometric variables (sex, age, height, and weight) were collected, and their influence on diaphragm motor response was assessed. Side-to-side differences were also analyzed.

Results: PN compound muscle action potential (CMAP) had significantly higher amplitude and area on the left side. Men had longer latency, and higher amplitude and area when compared with women, on both sides. Age was a significant factor influencing CMAP latency, with an average increase of 0.25 ms per decade of life. In men, a latency longer than 9.5 ms and a CMAP amplitude lower than 0.62 mV should be considered abnormal, while in women, the values are 8.5 ms and 0.48 mV, respectively.

Conclusions: PN conduction studies offer a simple and reliable technique readily applicable in clinical settings. Diaphragm CMAP parameters are significantly influenced by the anthropometric variables of sex and age. Notably, CMAP amplitude and area are greater for the left PN.