J Tod Olin1, James H Hull2. 1. Pediatric Exercise Tolerance Center, Department of Pediatrics, Division of Pediatric Pulmonology, National Jewish Health, 1400 Jackson Street, Denver, CO 80206, USA. Electronic address: OlinT@NJHealth.org. 2. Royal Brompton Hospital, Imperial College, Department of Respiratory Medicine, Royal Brompton Hospital, Fulham Road, London SW3 6HP, UK. Electronic address: j.hull@rbht.nhs.uk.