Clinical Use of Loop Gain Measures to Determine Continuous Positive Airway Pressure Efficacy in Patients with Complex Sleep Apnea. A Pilot Study

Rationale: Measures of unstable ventilatory control (loop gain) can be obtained directly from the periodic breathing duty ratio on polysomnography in patients with Cheyne-Stokes respiration/central sleep apnea and can predict the efficacy of continuous positive airway pressure (CPAP) therapy.

Objectives: In this pilot study, we aimed to determine if this measure could also be applied to patients with complex sleep apnea (predominant obstructive sleep apnea, with worsening or emergent central apneas on CPAP). We hypothesized that loop gain was higher in patients whose central events persisted 1 month later despite CPAP treatment versus those whose events resolved over time.

Methods: We calculated the duty ratio of the periodic central apneas remaining on the CPAP titration (or second half of the split night) while patients were on optimal CPAP with the airway open (obstructive apnea index < 1/h). Loop gain was calculated by the formula: LG = 2π/[(2πDR - sin(2πDR)]. Patients were followed on CPAP for 1 month. Post-treatment apnea-hypopnea index and compliance data were recorded from smart cards.

Measurements and main results: Thirty-two patients with complex sleep apnea were identified, and 17 patients had full data sets. Eight patients continued to have a total of more than five events per hour (11.8 ± 0.5/h) (nonresponders). The remaining nine patients had an apnea-hypopnea index less than 5/h (2.2 ± 0.4/h) (responders). Loop gain was higher in the nonresponders versus responders (2.0 ± 0.1 vs. 1.7 ± 0.2, P = 0.026). Loop gain and the residual apnea-hypopnea index 1 month after CPAP were associated (r = 0.48, P = 0.02). CPAP compliance was similar between groups.

Conclusions: In this pilot study, loop gain was higher for patients with complex sleep apnea in whom central apneas persisted after 1 month of CPAP therapy (nonresponders). Loop gain measurement may enable an a priori determination of those who need alternative modes of positive airway pressure.