Abstract
Recent work from our group has demonstrated that the use of supplemental oxygen (suppO2) in infants with OSA results in fewer respiratory events and improved oxygenation without adversely affecting alveolar ventilation. However, a common observation in our study was that suppO2 was effective in some, but not all, infants. Based on data for adult patients with OSA, the administration of suppO2 seems most effective in those with a hypersensitive ventilatory control system (i.e. high loop gain). Accordingly, we hypothesized that infants who respond well to suppO2 have a higher measured loop gain than those who respond poorly. We conducted a retrospective analysis of 10 infants with OSA treated with suppO2 from 2007–2013. Subjects underwent a room air, diagnostic sleep study (RA-PSG) followed by a study for suppO2 titration (O2-PSG) on a separate night. The five subjects who best responded to suppO2, defined as those that showed the largest percent reduction in obstructive apnea hypopnea index (O-AHI) and those five with the worst response to suppO2 were identified. Loop gain was estimated from spontaneous breathing using 3 minute windows of sleep containing at least one respiratory event. Square root transformed nasal pressure airflow was used to provide a surrogate of ventilation. A standard model of ventilatory control (gain, time-constant, delay) that best matched ventilation data during periods of unobstructed breathing was used to estimate loop gain at the natural ‘resonant’ frequency (LGn) by a scorer blinded to responder condition. SuppO2 significantly reduced the O-AHI in responders (22.2 ± 10.0 events.hr-1 vs. 2.1 ± 1.0 events.hr-1: p<0.05) whereas it remained unchanged in the non-responders (18.3 ± 14.1 events.hr-1 vs. 20.3 ± 18.1 events.hr-1: p=NS). Compared to non-responders, responders displayed an elevated LGn (0.48 ± 0.07 vs. 0.36 ± 0.06: p<0.05). Our preliminary evidence suggests that infants with OSA who respond to suppO2 therapy have a higher loop gain compared to non-responders. These data suggest that similar to adults with OSA, ventilatory instability is an important mechanism causing OSA in some infants.
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