This study was considered as a case–control study, including 40 patients with COPD and 30 healthy individuals, non-smoker, as a control group, the study was conducted at neurology, internal medicine, and chest departments,
Inclusion criteria: Patients with COPD are diagnosed according to the global initiative for chronic obstructive pulmonary disease (GOLD) criteria .
Exclusion criteria: Patients with unstable COPD, Patients with neurological complaints or manifestations suggestive of neuromuscular illness due to co-morbid conditions of COPD (as diabetes mellitus, chronic kidney disease, chronic hepatic disease, and chronic alcoholism).
All included individuals were submitted to the following: (1) complete medical history with an emphasis on the main complaint, age, sex, smoking behaviors, duration of disease, risk factors (pollution, occupation,
Inhabitant area) and medical history of additional systemic diseases. (2) Physical and neurological examination. (3) Arterial Blood Gases including partial arterial oxygen tension, partial arterial carbon dioxide tension, pH, and oxygen saturation all of which were presented in the arterial blood sample, at room air. (4) Spirometry examinations: all patients and control subjects underwent spirometry after the administration of 400 ug of salbutamol whereas the patient was stable; forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and FEV1/FVC ratio were obtained.
Spirometry evaluations were completed according to the American Thoracic Society  as follows: (a) Description of the technique to the patient in detail. (b) Making sure that the patient was upright or sitting vertically with feet fixed on the floor. (c) Put on a nasal clip to the patient's nose. (d) Advise the patient to breathe entirely. (e) Closing the lips of the patient around the mouthpiece. (f) Requesting the patient to blast air out as fast and as far as he can until the lungs were empty. (g) Asking the patient to breathe once more as forcibly and entirely as possible. (h) At minimum three technically accepted maneuvers were done  the parameters of spirometry were measured to approve the diagnosis and to measure the severity of COPD rendering to GOLD criteria, which categorize patients with COPD into four stages rendering to the value of FEV1; Mild stage of COPD: FEV1/FVC < 0.70 FEV1 ≥ 80% normal, Moderate stage of COPD: FEV1/FVC < 0.70 FEV1 50–79% normal, Severe stage of COPD: FEV1/FVC < 0.70 FEV1 30–49% normal and Very Severe stage of COPD when: FEV1/FVC < 0.70 FEV1 < 30% normal or FEV1 < 50% predicted in addition to chronic respiratory failure. .
Nerve conduction studies: were achieved via Nihon Kohden apparatus; Model UT- 0800 J. Box BOARD (2CH) For JB-942BK. Made in Tokyo, Japan. That includes:
Motor nerve conduction: nerve conduction study was operated by electrical stimulation of peripheral nerves (median, ulnar, radial, common peroneal, and posterior tibial nerves) and reporting amplitude, motor latency and conduction velocity from a muscle supplied by these nerves (abductor pollicis brevis, abductor digitiminimi muscle, extensor indices, extensor digitorum brevis, and abductor halluces, respectively) and the ground electrode: Positioned between the recording electrode and the stimulator.
Sensory nerve conduction (sensory NCS) (antidromic): was operated by electrical stimulation of peripheral nerves (median, ulnar, radial, and sural) and reporting the amplitude, sensory latency, and conduction velocity from a purely sensory part of the nerve, (2nd finger, 5th digit, dorsum of 1st web space and the part behind and under the lateral malleolus, respectively) and the ground electrode: Sited between the stimulator and recording electrode.
Diagnosis of peripheral neuropathy: As demyelinating, axonal and mixed according to the criteria in the following table 
Nerve conduction velocity
> 50% LLN
The cut off value for motor median, ulnar, radial, tibial and peroneal nerve studies, the least normal compound motor action potentials (CMAP) were 5.2 mv, 4.2 mv, 3.2 mv, 3.6 mv and 3.1 mv, respectively, and the least motor nerve conduction velocity of median, ulnar, radial, tibial and peroneal nerves were 49 m/s, 51.2 m/s, 62.9 m/s, 42.9 m/s and 48.4 m/s, respectively.
The cutoff value for the sensory median, ulnar, radial, and sural nerve studies, the least normal sensory nerve action potentials (SNAP) were 15 uv, 18.9 uv, 16.4 uv, and 10 uv, respectively, and the least sensory nerve conduction velocity of median, ulnar and sural nerves were 38.8 m/s, 37.9 m/s, and 34.4 m/s, respectively.
Statistical analysis: The obtained data were coded, and statistically studied by the SPSS program for Windows version 16 (SPSS Inc., USA). Parametric numerical data were stated as mean and standard deviation (SD); whereas qualitative data were stated as relative frequency (n) and percent distribution. For the correlation between two parameters, the Spearman's correlation coefficient (r) was used. P value ≤ 0.05 was considered significant for the interpretation of results. Independent samples (t) student test was used for comparison between two means for parametric variables and Mann–Whitney (U) test for non-parametric numerical variables, in adding, qualitative data were compared by Chi-square test (χ2).