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

Diaphragmatic weakness in chronic obstructive pulmonary disease (COPD) is ascribed to hyperinflation-induced diaphragm shortening as well as impairment in cellular and subcellular structures. Although phrenic neuropathy is known to cause diaphragmatic weakness, phrenic neuropathy is rarely considered in COPD. This work aimed at assessing phrenic nerve conduction in COPD and its relation to radiographic hyperinflation and pulmonary function. Patients and methods: Forty COPD patients were evaluated. Radiographic parameters of lung hyperinflation were measured on postero-anterior and lateral chest x-ray films. Flow volume loop parameters were obtained from all patients. Motor conduction study of the phrenic nerves was performed and potentials were recorded over the xiphoid process and the ipsilateral 7th intercostal space. Twenty-seven healthy subjects were enrolled as controls. Results: Parameters of phrenic nerve conduction differed significantly in patients compared to controls. Phrenic nerve abnormalities were detected in 17 patients (42.5%). Electrophysiological measures correlated with diaphragmatic angle of depression on lateral view films and with lung height on postero-anterior films. They did not correlate with the flow volume loop data or disease severity score. Conclusion: Phrenic nerve conduction abnormality is an appreciated finding in COPD. Nerve stretching associated with diaphragmatic descent can be a suggested mechanism for nerve lesion. The presence of phrenic neuropathy may be an additional contributing factor to diaphragmatic dysfunction in COPD patients.