Aims of this study is to explore the change of the concentration Exhaled Nitric Oxide (eNO) and the relationship between concentration eNO with FEV1 (Forced expiratory volume in 1 second) in the patients affected chronic obstructive pulmonary disease (COPD). Study was conducted at the Hospital of University Medical Hai Phong on 99 patients affected COPD having an average age of 40.5 + or - 5.7 (38 females, 61 males) and 99 normal people (52 males, 47 females) with the same age, in period from February 2011 to august 201l. Methods: eNO concentrations measured by the meter NO breath (Bed Font-USA). FEV1 was measured by automatic ventilator design type Analyser ST 250 (Fukuda Sangyo-Japan). Results: Concentration eNO of COPD is 27.00 + or - 5.61 ppb, that is higher than in normal people (27.00 + or - 5.61 ppb and 15.25 + or - 5.58 ppb
p 0.05) but lower in patients with bronchial asthma (eNO concentrations in patients with bronchial asthma were reported in previous studies by the same author is 34.54 + or - 9.16 ppb). There isn't difference about eNO levels between men and women, between aged and young people. No correlation between eNO levels and severity of COPD. No relationship between eNO levels and FEY1 in patients with COPD.