Research Article: A real-world comparison of apnea–hypopnea indices of positive airway pressure device and polysomnography

Date Published: April 5, 2017

Publisher: Public Library of Science

Author(s): Ritwick Agrawal, Julie A. Wang, Anita G. Ko, Joanne E. Getsy, Andrea Romigi.


The apnea hypopnea index (AHI) reported by positive airway pressure (PAP) device is widely used in clinical practice, yet its correlation with standardized AHI obtained during the sleep study is not established. The current study was conducted to investigate the correlation between AHI estimated by the PAP device and reported on the smart card with the AHI found during the PAP polysomnography (PSG) in the “real world” setting at an academic sleep center. We retrospectively reviewed the medical records of 280 patients who underwent a PAP titration PSG at Drexel sleep center, and were later prescribed a PAP device. The AHI was categorized in clinically relevant subgroups (as AHI ≤5 and AHI >5). The AHI at the final pressure on the PSG and the average AHI from the prescribed PAP device were compared. The results showed that in the majority (77.3%) of patients (126 of 163), the AHI from both PAP device and PSG correlated well and were in the same category (AHI ≤5 and AHI >5 respectively). The majority of patients (80.7%) with PSG AHI of <5 had PAP device AHI <5 as well. By contrast, if PSG AHI was >5, 61.5% patients reported good control, with AHI <5 on PAP device AHI. We conclude that in a majority of patients who were optimally titrated in the sleep laboratory, the PAP device continued to show optimal control at home.

Partial Text

Positive airway pressure (PAP) devices are the cornerstone of obstructive sleep apnea syndrome (OSAS) management. In addition to providing therapy for OSAS, they also assess the PAP efficacy and adherence. These devices monitor the hours of usage of device, mask leakage and efficacy of PAP therapy[1]. The efficacy of PAP therapy is usually reported as “residual” apnea hypopnea index (AHI). While the nomenclature of apnea hypopnea index is same for both PAP device AHI and the polysomnography (PSG) AHI, the definitions vary significantly. The AHI determined during a PSG is based on standardized definitions recommended by the American Academy of Sleep Medicine, while the AHI reported by the PAP device, usually with the “smart card” from the machine, is based on a non-standard proprietary definition of the device manufacturer[2]. A consensus statement from American Thoracic Society noted that the AHI data from the PAP device tracking systems are not easy to interpret due to differences in the definition of AHI across various manufacturers[1], and the need for further studies was noted. Furthermore, it has been shown that when PAP AHI from automatic and manual scoring was correlated; it was high for apneic events while the correlation for hypopnea was poor[3].

This study examined two main questions relevant to an AHI reported by a PAP device when used in a constant pressure setting. First, it looked at the real world AHI statistics in patients who have been using the CPAP machine and second, the study evaluated the correlation of the AHI between in-lab CPAP titration and the average AHI reported by the PAP device.