Overnight oximetry is a simple tool for investigation of obstructive sleep apnoea (OSA) in children, but only severe cases will be detected, and children with obstructive events resulting in arousal, but not desaturation, will have a normal (inconclusive) result. We hypothesised that pulse rate rises using pulse rate indices per hour (PRI) and pulse rate standard deviation (PR-SD) automatically calculated from commercially available software would improve oximetry as a diagnostic tool. METHODS: Children having home overnight oximetry for suspected OSA were identified over 12 months, and those with a normal result who went on to have polysomnography (PSG) were included. Oximetry, including PR-SD and PRI (rises of 8, 10 and 15 beats/min per hour), was analyzed using commercially available software. PR parameters were compared between those with OSA (obstructive apnoea-hypopnoea index (OAHI) >1 event/h) and those without OSA. RESULTS: One hundred sixteen children had normal oximetry, of whom 93 (median age 4.5 years; 55 M) had PSG. Fifty-seven of 93 (61 ) children had OSA (median OAHI 4.5 events/h, range 1.1-24). PR-SD was not different between the OSA and non-OSA groups (p = 0.87). PRI tended to be higher in those with OSA, but there was considerable overlap between the groups: PRI-8 (mean +/- SD 58.5 +/- 29.0/h in OSA group vs 48.6 +/- 20.2/h in non-OSA group, p = 0.07), PRI-10 (45.1 +/- 25.0 vs 36.2 +/- 16.7, p = 0.06) and PRI-15 (24.4 +/- 14.5 vs 18.9 +/- 9.0, p = 0.04). A PRI-15 threshold of >35/h had specificity of 97 for OSA. CONCLUSION: The PRI-15 shows promise as an indicator of OSA in children with normal oximetry.