Effective Apnea-Hypopnea Index ('Effective AHI'): A New Measure of Effectiveness for Positive Airway Pressure Therapy

STUDY OBJECTIVES To assess a new measure of positive airway pressure (PAP) effectiveness, the Effective AHI, which accounts for sleep disordered breathing events during the time PAP is (PAP On) and is not (PAP Off) being used. A secondary aim was to test the accuracy of the Watch-PAT 200 (WP) portable monitor for measurement of the Effective AHI. METHODS A prospective two-center cohort study design was used to evaluate patients who had been prescribed PAP therapy for ≥ 2 months. The primary outcome measure was the Effective AHI as determined by an in-laboratory polysomnogram (PSG) where patients used their PAP machine as they did at home, and concomitantly wore the WP. The Effective AHI equals the sum of apneas and hypopneas with PAP On and PAP Off divided by hours of total sleep time. RESULTS Twenty-eight adult patients (75% men, age 51.4 ± 10.8 years [mean ± SD]) comprised the study sample. The mean Effective AHI of 18.3, was significantly lower than the mean Diagnostic AHI of 67.9 (P < 0.0001). All patients using PAP ≥ 6 h had an Effective AHI < 5. For patients using PAP < 6 h, Effective AHI scores < 5 only occurred in patients who slept in a non-supine position during PAP Off time; leaving 63.6% of patients with residual moderate-to-severe OSA. There was a high correlation between the PSG and WP for the Effective AHI (r = 0.871). CONCLUSIONS Significant disease burden, as objectively measured by the Effective AHI, may still exist in many patients with severe OSA in whom PAP therapy is not utilized for the entire sleep period. The WP is a reasonably accurate device to measure the Effective AHI.