Abstract              Background: In diseases such as idiopathic pulmonary fibrosis, the diffusing capacity for carbon monoxide is often decreased out of proportion to the restrictive defect. A DLCO less than 35 to 40 percent predicted for idiopathic pulmonary fibrosis and less than 40 percent for systemic sclerosis has been shown to predict worse outcomes Aims and Objectives: To Study of relationship between DLCO and other Spiro metric parameters. Methodology: The present  prospective observational study in patients with obstructive and restrictive lung diseases was approved by the institute ethics committee. Our center has pulmonary unit in a tertiary care government hospital that caters to populations of diverse groups. This is a prospective observational study carried from January 2013 to August 2014. All patients presenting with symptoms of obstructive and restrictive lung diseases lung disease such as breathlessness, cough, chest tightness and wheeze were included. DLCO was done by Jones and Mead technique. Data was entered in the Excel sheets and analyzed. Result: Majority of patients having COPD were in the age group of 45-54 years and 55-64 years, 44.44% and 33.33% respectively. Majority of patients having bronchial asthma were in the age group of 35-44 years 50%. Majority of patients having bronchiectasis were in the age group of 45-64 years 70.00%. Mean age for COPD, Bronchiectasis, Asthma were 55.48yrs, 43.7yrs and 35.72yrs respectively. Amongst ILD patients 17(58.62%) were males and 12(41.38%) were females, male: female ratio in ILD was 1.4:1. Amongst 27 COPD patients 21(77.78%) had decreased DLCO. Amongst 22 Asthma patients 17(77.27%) had increased DLCO. Amongst 10 Bronchictasis patients 8(80%) had decreased DLCO. Amongst 29 ILD patients, 25(86.20%) had decreased DLCO. Amongst 27 COPD patients 21(77.78%) had decreased DLCO.  Amongst 22 Asthma patients 17(77.27%) had increased DLCO.  Amongst 10 Bronchictasis patients 8(80%). DLCO in patients with COPD decreased progressively with decrease in FEV1 and this graph showing the same. Correlation Coefficient (r=0.94, p<0.001). Conclusion: It can be concluded from our study that Male preponderance is seen in COPD, Asthma, Bronchiectasis and ILD. COPD is common after 35 years of age & as the age increases incidence of COPD increases. Mean age in present study of COPD patients was (55.48yrs). Asthma occurs mostly before 35 years of age. Mean age in present study of Asthma patients was (43.7yrs).DLCO is decreased in the patients with Chronic Obstructive Pulmonary Disease, may be normal or increased in the patients with Asthma and may be normal or decreased in the patients with Bronchiectasis. DLCO is decreased in the patients with ILD  FEV1 %predicted correlates positively with DLCO% predicted in patients with COPD.

Key Words: COPD, DLCO, ILD, FEV1, Spirometry.