Central and peripheral diaphragmatic neural function in chronic obstructive pulmonary disease assessed by magnetic stimulation

In chronic obstructive pulmonary disease [COPD], the diaphragm may contribute to respiratory decompensation. Factors responsible for such impairment are complex and not completely studied. Little is known about the state of neural diaphragmatic pathways particularly in milder grades of the disease. This study aimed to evaluate the cortical and peripheral diaphragmatic neuronal function in COPD using magnetic stimulation. Twenty patients with mild/moderate COPD with mean age of 52.5 +/- 8.5 years, were included. Diaphragmatic function was assessed by transcranial magnetic stimulation of the motor cortex followed by stimulation of the cervical roots of the phrenic nerves. The following parameters were measured: diaphragmatic resting motor threshold, cortical motor evoked potential [MEP] latency and amplitude, phrenic nerve latency and amplitude and central conduction time [CMCT]. Correlations were done between different electrophysiological parameters and age, duration of illness and variables of pulmonary function testing. Compared to controls, patients demonstrated significant prolongation of cortical [n=9] and cervical [n=3] MEP latencies and CMCT [n=9], reduced phrenic nerve amplitude [n=5] and increased resting motor threshold [n=11]. Significant correlations were identified between different electrophysiological parameters and age, duration, severity of disease and degree of hypoxemia. All patients with phrenic nerve abnormalities had cortical abnormalities [n=9]. We concluded that diaphragmatic neural dysfunction occurs in early stages of COPD. Central impairment [cortico-spinal] seems to occur earlier than peripheral [neuropathy of the phrenic nerve]. This information has important clinical and therapeutic implications. It will be important to study the effect of therapies as non-invasive ventilation and specific pharmacological interventions on these changes