Asthma is characterized by airflow obstruction, chronic airway inflammation and remodeling. The investigators' report has shown directly the relationship between fibrocytes, and chronic airflow obstruction with rapid decline in FEV1 in asthma. Asthma concomitant of obstructive sleep apnea (OSA) may appear intermittent hypoxia and result in the frequent attack of asthma symptoms. In animal model, hypoxia may increase the circulating fibrocytes, thus play a role in pulmonary hypertension. The investigators' published paper also showed that an increased expression of EGFR, ETAR and Vascular endothelial growth factor receptor (VEGFR) in circulating fibrocytes in chronic obstructive asthmatics. It is unknown whether circulating fibrocytes from asthma with OSA have the higher expression of EGFR, connective tissue growth factor receptor, VEGFR and ETAR compared to asthma without OSA. The investigators are also interested in whether proliferation and differentiation of fibrocytes are different between asthmatics with or without concomitant of OSA. The investigators will study the correlation between the percentage of circulating fibrocytes and the oxygen desaturation index (ODI) and severity of sleep apnea to clarify the role of hypoxia, which contributing to chronic asthma.