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A1241 - Clinical Predictors of Respiratory System Loop Gain in Healthy Subjects and Patients with Obstructive Sleep Apnea
Author Block: L. Messineo1, L. T. Taranto-Montemurro2, A. Azarbarzin3, M. Marques4, N. Calianese1, D. P. White5, S. A. Sands6, A. Wellman7; 1Sleep and circadian disorders, Harvard Medical School, Boston, MA, United States, 2Medicine and Neurology, Brigham and Women's Hospital, Boston, MA, United States, 3Sleep Medicine, Boston, MA, United States, 4Pulmonary Division, University of Sao Paulo, Sao Paulo, Brazil, 5Harvard Medical School, Boston, MA, United States, 6Dept. of Med, Div of Sleep Med, Brigham and Women's Hosp, Cambridge, MA, United States, 7Harvard, Boston, MA, United States.
Background: Increased loop gain of the respiratory system contributes to obstructive sleep apnea (OSA) and offers an important target for intervention. Since gold standard techniques to measure loop gain are rarely available, clinicians are currently lacking diagnostic tools to estimate it in the clinical setting. Here we tested the hypothesis that loop gain during sleep can be estimated by performing breath hold tests during wakefulness (maximal duration and desaturation, and compensatory ventilation following timed 20 s breath holds).
Methods: Twenty individuals (10 OSA patients and 10 healthy controls) were studied during wakefulness and sleep. Dynamic loop gain was measured using brief (20 s) pulses of hypoxic-hypercapnic gas during sleep (6%CO2-14%O2 mixture, while on CPAP to maintain airway patency). Steady state loop gain was measured during sleep using the CPAP dial-up technique. To estimate loop gain in the clinical setting, two maneuvers were performed during wakefulness: (1) maximal breath holds and (2) recurrent 20 s breath holds.
Results: Univariate analysis illustrated that loop gain in non-REM was correlated with the duration of maximal breath hold (r=-0.70, p=0.001), degree of desaturation during the maximum breath hold (r=-0.53, p=0.019), and the compensatory ventilation after 20-second breath holds (r=0.70, p=0.001). Multivariate analysis using maximum duration and ventilatory compensation values yielded a model (r=0.80, p=0.025) with a sensitivity of 80% and a specificity of 90% to detect high loop gain (cutoff: XX). Maximum breath hold duration was also inversely correlated with steady state loop gain (r=-0.47, p=0.036). Moreover, we found that dynamic loop gain during non-REM and during wake (pulses, off CPAP) were equivalent (r=0.63, p=0.003, difference=0.06±0.12, mean±SD) confirming the view that loop gain during sleep can be explored with testing during wake.
Conclusions: Our study demonstrates that loop gain during sleep can be estimated using simple breath-holding maneuvers performed during wakefulness in a clinical setting. Thus, breath holding techniques may facilitate selection of patients suitable for loop gain lowering therapies for OSA.