Poorly reversible obstructive airway disease means Post Bronchodilator FEV1/FVC< 0.7 and Post bronchodilator reversibility of FEV1 <12% OR 400ML. Patients with poorly reversible obstructive airway disease can be ashtmatic or Reversible Chronic obstructive pulmonary disease(COPD). In Asthmatic patient may be poorly reversible due to improper treatment, due to exposure to Noxious particles, Smoking , Biomass Exposure. Reversible COPD may be COPD in non smokers, may be due to significant eosinophilia (>3%) or concomitant for asthma. They all exhibit more or less similar clinical presentation. There are different phenotypes which include poorly controlled Asthma, Asthma with exposure to Smoking and biomass fuel. The Phenotypes in COPD includes COPD in Nonsmokers,COPD with eosinophilia, COPD  concomitant with Bronchial Asthma. Obstructive airway disease (OAD) includes mainly Asthma, Chronic obstructive airway disease(COPD) or Asthma chronic obstructive pulmonary disease overlap (ACO)

Asthma is defined as a “heterogeneous disease characterized by chronic airway inflammation with history of respiratory symptoms like wheeze, shortness of breath, chest tightness and cough that vary for a period in severity, along with changing expiratory airflow limitation¹.

Chronic obstructive pulmonary disease is a common, preventable and treatable disease. It is characterized by persistent respiratory symptoms and airflow limitation which is caused due to airway and / or alveolar abnormalities caused by significant exposure to harmful particles or gases.

When patients possess characteristic features of both asthma and COPD, they are often thought to have asthma-Chronic obstructive pulmonary disease overlap (ACO)².

—  Airway diseases are caused mostly by inflammation and its nature differs in asthma and also in chronic obstructive airway disease (COPD). It is eosinophilic and CD4-driven in asthma, where as in chronic obstructive pulmonary disease (COPD) neutrophilic and CD8-driven inflammation.

—  Patients with Asthma chronic obstructive pulmonary disease overlap(ACO) have an asthmatic factor and therefore may exhibit the same characteristics to some extent as patients with asthma. Therefore, studying the clinical and pathological differences between Asthma chronic obstructive pulmonary disease overlap(ACO )and Chronic obstructive pulmonary disease (COPD )patients is essential.

—  This study is conducted to study the differences in the respiratory physiology of patients with chronic obstructive pulmonary disease (COPD), asthma-COPD overlap  (ACO), and asthma with airflow limitation (asthma FL⁺).