Spirometry
Spirometry was performed by a portable spirometer, spirolab (Medical International Research, Rome, Italy) which is standardised for Indian children (based on height) in Paediatric OPD AIIMS, New Delhi during follow up visits. Forced expiratory volume in 1 second of predicted (FEV1), forced vital capacity (FVC), FEV1/FVC ratio were assessed after obtaining acceptable spirometry curves. Abnormal pulmonary function is determined as presence of obstructive, restrictive or mixed pattern on spirometry or abnormality in three minute step test. Obstructive pattern is defined as having forced vital capacity of percent predicted ≥80% and FEV1/FVC <85%. Restrictive pattern is defined as having forced vital capacity of percent predicted <80% and FEV1/FVC ≥85%. Mixed pattern is defined as having forced vital capacity of percent predicted <80% and FEV1/FVC <85%. Based on FEV1, severity of obstructive pattern was assessed as mild, moderate, moderately severe, severe or very severe obstruction if predicted FEV1 is >70%, between 60% to 69%, between 50% to 59%, between 35% to 49%, <35% respectively. Based on FVC, severity of restrictive pattern was assessed as mild, moderate, severe or very severe obstruction if predicted FVC is >70%, between 50% to 69%, between 35% to 49%, between, <35% respectively