title: Clinical Use of Loop Gain Measures to Determine Continuous Positive Airway Pressure Efficacy in Patients with Complex Sleep Apnea. A Pilot Study.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
  
  
  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.
authors.affiliation: 1 Pulmonary, Critical Care, and Sleep Medicine, Alpert Medical School at Brown University, Providence, Rhode Island.
authors.forename: Michael
authors.initials: M
authors.lastname: Stanchina
authors.affiliation: 1 Pulmonary, Critical Care, and Sleep Medicine, Alpert Medical School at Brown University, Providence, Rhode Island.
authors.forename: Kristen
authors.initials: K
authors.lastname: Robinson
authors.affiliation: 1 Pulmonary, Critical Care, and Sleep Medicine, Alpert Medical School at Brown University, Providence, Rhode Island.
authors.forename: William
authors.initials: W
authors.lastname: Corrao
authors.affiliation: 1 Pulmonary, Critical Care, and Sleep Medicine, Alpert Medical School at Brown University, Providence, Rhode Island.
authors.forename: Walter
authors.initials: W
authors.lastname: Donat
authors.affiliation: 2 Division of Sleep Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.|3 Central Clinical School, The Alfred Hospital and Monash University, Melbourne, Victoria, Australia; and.
authors.forename: Scott
authors.initials: S
authors.lastname: Sands
authors.affiliation: 4 Division of Pulmonary, Critical Care and Sleep Medicine, University of California at San Diego, La Jolla, California.
authors.forename: Atul
authors.initials: A
authors.lastname: Malhotra
mesh_terms: D000368:Aged; D002639:Cheyne-Stokes Respiration / Q000628:therapy*; D045422:Continuous Positive Airway Pressure / Q000379:methods*; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D010349:Patient Compliance; D010865:Pilot Projects; D017286:Polysomnography / Q000379:methods*; D012720:Severity of Illness Index; D020182:Sleep Apnea, Central / Q000628:therapy*; D020181:Sleep Apnea, Obstructive / Q000628:therapy*; D016896:Treatment Outcome
keywords: Cheyne-Stokes respiration; central sleep apnea; continuous positive airway pressure ventilation; mixed sleep apnea; obstructive sleep apnea