A detailed interval pulmonary history was taken. Pulmonary abnormalities were determined by pulmonary angiography and lateral chest x-ray and pulmonary function tests for small airway obstruction, reversible bronchial hyperreactivity, distribution of ventilation, air trapping and hyperinflation, residual interstitial disease or edema, vascular bed loss, and gas exchange. Right and left ventricular hypertrophy were evaluated by electrocardiogram. Elevated right ventricular pressure was estimated by echocardiography with doppler ultrasound. The atopic status of the children was determined. Other abnormalities, including growth retardation, developmental delay, hearing loss, retrolental fibroplasia, and neurologic disability seen in BPD were assessed by history and physical examination.