Neurophysiological changes in COPD patients with chronic respiratory insufficiency

Chronic hypoxemia is known to cause peripheral neuropathy (PNP) in chronic obstructive pulmonary disease (COPD) patients. We aimed to know how often PNP is encountered in such patients and the changes in the central nervous system (CNS) if any. We enrolled 32 patients (30 M, 2 F; mean age +/- SD: 61.5 +/- 8.8 years) with COPD into the study. PaO2 > or = 55 mmHg was considered as the cut-off value designating tissue hypoxia. According to this cut-off value the subjects were divided into two groups: Group I, n: 19, PaO2 < 55 mmHg and Group II, n: 13, PaO2 > or = 55 mmHg. All subjects were evaluated with motor and sensory nerve conduction studies (MNCV and SNCV, respectively), electromyography, visual and brainstem evoked potentials (VER and BAER, respectively). We detected PNP in 93.8% of the study subjects. Distal latency of sural nerve correlated significantly with cigarette consumption and reduction in PEFR. SNCV of median nerve was reduced as PaCO2 was elevated and pH was lowered. BAER wave III latency showed significant inverse correlation with PEFR, FEF25 and FEF25-75. Interpeak latency (IPL) of BAER I-III was also significantly and inversely correlated with FEV1/FVC and FEF25-75. IPL of BAER III-V too showed significant correlations with PaCO2, HCO3- and pH of the arterial blood. As BAER III and IPLs of it represent the pontomedullary portion of the brain, cigarette smoking and airways obstruction may not only cause peripheral neuropathy but also a delay in evoked responses of the brain stem by inducing chronic hypercapnia and respiratory acidosis in patients with COPD.