Use of the WatchPAT to detect occult residual sleep-disordered breathing in patients on CPAP for obstructive sleep apnea
2020; American Academy of Sleep Medicine; Volume: 16; Issue: 7 Linguagem: Inglês
10.5664/jcsm.8406
ISSN1550-9397
AutoresMatthew D. Epstein, Tariq Musa, Stephanie Chiu, Jacquelyn Costanzo, Christine Dunne, Federico Cerrone, Robert J. Capone,
Tópico(s)Cardiovascular and Diving-Related Complications
ResumoFree AccessScientific InvestigationsUse of the WatchPAT to detect occult residual sleep-disordered breathing in patients on CPAP for obstructive sleep apnea Matthew Epstein, MD, Tariq Musa, MD, Stephanie Chiu, MPH, Jacquelyn Costanzo, RRT, Christine Dunne, RRT, Federico Cerrone, MD, Robert Capone, MD Matthew Epstein, MD Atlantic Health Sleep Centers, Livingston, New Jersey; Atlantic Health System, Morristown, New Jersey; New Jersey Medical School, Newark, New Jersey Search for more papers by this author , Tariq Musa, MD Atlantic Health System, Morristown, New Jersey; Search for more papers by this author , Stephanie Chiu, MPH Atlantic Health System, Morristown, New Jersey; Search for more papers by this author , Jacquelyn Costanzo, RRT Atlantic Health System, Morristown, New Jersey; Search for more papers by this author , Christine Dunne, RRT Atlantic Health Sleep Centers, Livingston, New Jersey; Atlantic Health System, Morristown, New Jersey; Search for more papers by this author , Federico Cerrone, MD Atlantic Health Sleep Centers, Livingston, New Jersey; Atlantic Health System, Morristown, New Jersey; Search for more papers by this author , Robert Capone, MD Atlantic Health Sleep Centers, Livingston, New Jersey; Atlantic Health System, Morristown, New Jersey; Search for more papers by this author Published Online:July 15, 2020https://doi.org/10.5664/jcsm.8406Cited by:3SectionsAbstractPDF ShareShare onFacebookTwitterLinkedInRedditEmail ToolsAdd to favoritesDownload CitationsTrack Citations AboutABSTRACTStudy Objectives:To determine the accuracy of the apnea-hypopnea index (AHI) as measured by continuous positive airway pressure (CPAP) machines by simultaneously employing a home sleep apnea testing device (WatchPAT 200, Itamar Medical, Israel [WPAT]) in patients suspected of having residual sleep-disordered breathing (SDB).Methods:Patients with new, recurrent, or worsening signs, symptoms, or comorbidities associated with obstructive sleep apnea underwent home sleep apnea testing using WPAT while simultaneously using CPAP at their usual prescribed settings. CPAP AHI and WPAT AHI, respiratory disturbance index, and oximetry readings were then compared.Results:We identified an elevated AHI with WPAT testing in nearly half of patients with clinically suspected residual SDB and a normal CPAP AHI. WPAT detected additional respiratory events as well, including rapid eye movement-related apneas, respiratory effort-related arousals, and hypoxemia.Conclusions:WPAT AHI was significantly higher than simultaneous CPAP AHI in nearly half of those patients with clinically suspected residual SDB being treated with CPAP. Additional respiratory disturbances, including rapid eye movement-related respiratory events, respiratory effort-related arousals, and hypoxemia, were elucidated only with the use of the WPAT. Residual SDB may have potential clinical consequences, including reduced CPAP adherence, ongoing hypersomnolence, and other health-related sequelae. Simultaneous WPAT testing of patients with a normal CPAP AHI may represent a valuable tool to detect clinically suspected residual SDB or to ensure adequate treatment in high-risk patients with obstructive sleep apnea in general.Citation:Epstein M, Musa T, Chiu S, et al. Use of the WatchPAT to detect occult residual sleep-disordered breathing in patients on CPAP for obstructive sleep apnea. J Clin Sleep Med. 2020;16(7):1073–1080.BRIEF SUMMARYCurrent Knowledge/Study Rationale: We have observed patients with obstructive sleep apnea on CPAP treatment with a high clinical suspicion of occult residual sleep-disordered breathing despite having a normal CPAP machine-reported apnea-hypopnea index and adequate treatment adherence. We sought to determine the accuracy of the apnea-hypopnea index as measured by CPAP machines by testing patients with a home sleep apnea testing device (WatchPAT) while they simultaneously wore CPAP at their usual settings.Study Impact: WatchPAT detected a significant degree of residual sleep-disordered breathing in a substantial number of patients with a normal CPAP apnea-hypopnea index. Residual sleep-disordered breathing may have important clinical consequences, including hypersomnolence, adverse health related sequelae, and reduced treatment adherence, and WatchPAT testing on CPAP may represent a valuable tool in optimizing obstructive sleep apnea treatment.INTRODUCTIONObstructive sleep apnea syndrome (OSA) may affect more than 25% of the adult population and can lead to numerous health related consequences, impaired quality of life, and substantial economic burden.1–7 Treatment of OSA improves sleepiness and cognitive functioning, reduces medical sequelae, and decreases health care and societal costs, but maximal OSA reduction may be necessary to fully realize these benefits.8–18Despite the growing number of novel treatments for OSA, continuous positive airway pressure (CPAP) remains the gold standard. While the greatest obstacle to effective CPAP treatment is suboptimal adherence, residual sleep-disordered breathing (SDB) may be present despite adequate CPAP usage.19–22 CPAP machines utilize proprietary algorithms to detect and report residual, untreated apneas and hypopneas. Although some studies have found CPAP machine quantification of residual respiratory events to be accurate, there is growing concern that both fixed and auto-adjusting CPAP machine reporting may be subject to error.21, 23–28We have observed patients with an acceptable CPAP data report in terms of compliance and machine-reported residual apnea-hypopnea index (AHI) who nevertheless manifest new, recurrent or worsening signs, symptoms, or comorbidities associated with OSA. These patients have a high clinical suspicion for having occult, residual SDB.We sought to determine the accuracy of the AHI as measured by CPAP machines by simultaneously employing a home sleep apnea testing device in patients suspected of having residual SDB while using CPAP.METHODSOver a 12-month period, all patients actively using CPAP for OSA with clinically suspected residual SDB were included from 2 American Academy of Sleep Medicine-accredited sleep centers. Patients were tested because of clinical suspicion of incompletely treated OSA despite adequate CPAP use and an AHI of 5 or fewer events/h on their CPAP data report (CPAP AHI). This study was performed as a retrospective analysis and met criteria for “Activities that Do Not Represent Human Subject Research.” Hence, informed consent was not required and the study qualified for exemption from institutional review board review.Clinical criteria for suspected residual SDB included significant weight gain (more than 10 pounds), worsening or persistent daytime sleepiness, poor or worsening self-reported sleep quality or recurrent apneas, or new or worsening medical comorbidities, such as hypertension, diabetes, cardiac arrhythmias, or thromboembolic disease. All patients had baseline OSA ranging from mild to very severe and were compliant with CPAP (documented usage of 4 or more hours per night on at least 70% of nights for the prior 30 nights).Initial diagnostic testing for OSA was performed by either home sleep apnea testing or in-laboratory, overnight polysomnography (PSG). All patients were being treated with either auto-adjusting or fixed CPAP, bilevel positive airway pressure, or assisted servo ventilation, and CPAP machines were no more than 5 years old. Patients using fixed pressure CPAP had been evaluated by an in-laboratory overnight titration study. Patients with central sleep apnea and those taking alpha-adrenergic blockers were excluded.Patients underwent a single night of home sleep apnea testing using the WatchPAT 200 (Itamar Medical, Israel [WPAT]) while simultaneously using CPAP at their usual prescribed settings. CPAP data collection included usage time, machine brand, pressure settings, expiratory pressure relief settings, adherence, AHI, degree of air leak, and mask interface type. An adjusted CPAP AHI was calculated based on the CPAP reported AHI and the total sleep time, the latter being measured by simultaneous WPAT testing.WPAT data included total recording time, total sleep time and sleep efficiency, sleep staging, total AHI (WPAT AHI), rapid eye movement (REM)-related AHI, respiratory disturbance index (RDI, which included apneas, hypopneas, and respiratory effort-related arousals), oxygen desaturation index (defined by 4% or greater drop in oxygen saturation), and nadir oxygen saturation. Patients were instructed to wear the WPAT only during the time that they were simultaneously using their CPAP.Statistical AnalysisThe primary analysis was designed to test the accuracy of the AHI measured by a CPAP machine compared with a WPAT in patients suspected of having residual SDB while using CPAP, as determined by correlating the AHI within each patient using both measures. On the basis of convenience sampling, we enrolled 100 patients during a 12-month period between 2014 and 2015.Data were collected for each patient and separated into 2 groups based on the WPAT AHI. Group 1 included patients with a WPAT AHI of 5 or fewer events/h, and group 2 included patients with a WPAT AHI of > 5 events/h.We used the chi-square test or Fisher's exact test to compare categorical variables and the independent t test or Mann-Whitney to compare continuous variables. A cutoff of .05 or less was used to determine statistical significance. All statistical analyses were performed with MINITAB software, version 17 (Minitab, State College, Pennsylvania).Bland-Altman plots were used to evaluate the agreement between WPAT and CPAP events by identifying any differences between the 2 methods studied and 95% limits of agreement are shown to identify any possible outliers.RESULTSDuring a 12-month period between 2014 and 2015, we identified 109 patients with clinically suspected residual OSA, a CPAP AHI of 5 or fewer events/h, and adequate CPAP adherence. Nine patients were excluded due to incomplete or missing information.Demographic and baseline OSA characteristics are listed in Table 1. Fifty-two patients were found to have a similar CPAP AHI and WPAT AHI (5 or fewer events/h) during simultaneous monitoring and constituted group 1. The remaining forty-eight patients were found to have a simultaneous WPAT AHI that was greater than their CPAP AHI (ie, > 5 events/h) and comprised group 2. Mean patient age, sex, and body mass index were similar for the 2 groups, as were baseline OSA characteristics, initial AHI and ESS, and duration of CPAP usage. Figure 1 shows a scatterplot comparing the CPAP usage time (range 301–607 minutes) and WPAT recording time (range 294–601 minutes). Of note, WPAT recording time and CPAP usage time were nearly identical for each patient and significantly associated (P < .001).Table 1 Clinical characteristics.CharacteristicGroup 1 (n = 52)Group 2 (n = 48)Age57.9 ± 11.257.7 ± 11.8Sex35 (67.3%)35 (72.9%)BMI33.9 ± 7.934.8 ± 5.4Initial AHI29.5 (5–113)27.5 (5–107)Initial ESS7.9 ± 4.98.5 ± 5.0Duration of CPAP (y)5 (1–15)5 (1–22)General characteristic variables using mean and standard deviation, count and percent, or median and range. Clinical characteristics were not significantly different between groups 1 and 2. AHI = apnea-hypopnea index, BMI = body mass index, CPAP = continuous positive airway pressure, ESS = Epworth Sleepiness Scale.Figure 1: CPAP usage time and WPAT recording time (minutes).Scatterplot showing the consistency between WPAT and CPAP usage times. Data are significantly associated (P < .001). CPAP = continuous positive airway pressure, WPAT = WatchPAT.Download FigureTable 2 compares WPAT and CPAP findings. Sleep time, recording time, and sleep efficiency for the night of testing were similar for groups 1 and 2. CPAP AHI was in the normal range (mean AHI 2.1, range 0–5) for all 100 patients. When adjusted for total sleep time as determined by the WPAT, the adjusted CPAP AHI was slightly higher for both groups, but not significantly different between groups 1 and 2.Table 2 Comparison of WPAT and CPAP report data.VariableGroup 1 (n = 52)Group 2 (n = 48)P ValueSleep time389.2 ± 83.7403.8 ± 66.4.335aRecord time466.8 ± 74.8475.4 ± 72.7.562aSleep efficiency.87 (.27–.95).86 (.69–.93).833bCPAP AHI1 (0–5)1 (0–5).260bAdjusted CPAP AHI1 (0–11)1 (0–7).358bWPAT AHI2.5 (0–5)11 (6–45)< .001bAHI difference1 (-4 to 4)9.5 (1–44)< .001bWPAT REM AHI4 (0–21)17.5 (6–55)< .001bWPAT RDI6.5 (1–22)17 (8–45)< .001bWPAT ODI1 (0 to –3)4 (0–39)< .001bWPAT O2 saturation.91 (.78–.96).875 (.73–.93)< .001bReport data are summarized using mean and standard deviation or median and range. a2-sample t test. bMann-Whitney. *P < .001 between Group 1 and Group 2 using Mann-Whitney U test. AHI = apnea-hypopnea index, CPAP = continuous positive airway pressure, ODI = oxygen desaturation index, RDI = respiratory disturbance index.For group 1 patients, the median WPAT AHI was 2.5 events/h (range 0–5), and for group 2 patients, the median WPAT AHI was significantly greater at 11 events/h (range 6–45). The median WPAT REM AHI was elevated in some group 1 patients (AHI 4 events/h, range 0–21), while in group 2, WPAT REM AHI was significantly higher (median 17.5 events/h, range 6–55). The WPAT RDI was also elevated in some patients in group 1 (median 6.5 events/h, range 1–22), but was significantly higher in group 2 (median 17 events/h, range of 8–45). The WPAT oxygen desaturation index was significantly higher (median 4 events/h, range 0–39) and the nadir oxygen saturation was significantly lower (median 88%, range 72–93%) in group 2 vs group 1 patients.Mask types, machine brands, and pressure settings are listed in Table 3. Between the 2 groups, there were similar numbers of ResMed (San Diego, California) and Respironics (Murrysville, Pennsylvania) brand CPAP machines, and there was one DeVilbiss (Somerset, Pennsylvania) brand machine. CPAP mask interface type, pressure settings and use of pressure relief (expiratory pressure relief, C-flex) were not significantly different for the 2 groups.Table 3 CPAP treatment information.VariableGroup 1 (n = 52)Group 2 (n = 48)Mask type FFM26 (50%)20 (41.7%) NM12 (23.1%)8 (16.7%) NP14 (26.9%)20 (41.7%)Machine type ASV0 (0%)1 (2.08%) AutoCPAP15 (28.9%)9 (18.9%) Bi-Level0 (0%)2 (4.17%) CPAP33 (63.5%)35 (72.9%) VPAP4 (7.7%)1 (2.1%)EPR/C-Flex0 (0–3)1 (0–3)Off (0)32 (61.5%)22 (45.8%)On (1, 2, 3)20 (38.5%)26 (54.2%)Pressure (cm H2O)*13.3 ± 3.412.3 ± 3.7There was no significant difference between group 1 and group 2 for any of the mask, machine, or treatment variables. *Fixed pressure used number, auto used max, bilevel used inspiratory pressure. ASV = adaptive servo ventilation, CPAP = continuous positive airway pressure, EPR = expiratory pressure relief, FFM = full face mask, NM = nasal mask, NP = nasal pillows, VPAP = variable positive airway pressure.Figure 2 shows a scatterplot comparing the CPAP AHI vs the adjusted CPAP AHI. While some patients’ adjusted CPAP AHI was numerically greater than their CPAP AHI, 97% of patients had no clinically significant difference (AHI difference < 3 events/h).Figure 2: CPAP vs adjusted CPAP AHI.Relationship between unadjusted CPAP AHI and adjusted CPAP AHI for group 1 and group 2 patients. AHI = apnea-hypopnea index, CPAP = continuous positive airway pressure.Download FigureFigure 3 shows a scatterplot comparing the unadjusted CPAP AHI and WPAT RDI. The WPAT detected a substantially greater number of SDB events in comparison to the CPAP AHI. Of note, there is little difference whether the unadjusted or adjusted CPAP AHI is compared to the WPAT RDI (not shown in the figure), demonstrating that the difference between the WPAT RDI and CPAP AHI is not accounted for by CPAP underestimation due to reduced sleep efficiency.Figure 3: Unadjusted CPAP AHI vs WPAT RDI.Relationship between unadjusted CPAP AHI and WPAT RDI for group 1 and group 2 patients. AHI = apnea-hypopnea index, CPAP = continuous positive airway pressure, RDI = respiratory disturbance index, WPAT = WatchPAT.Download FigureFigure 4 shows a box plot comparing unadjusted CPAP AHI, WPAT AHI, and WPAT RDI. The WPAT AHI and RDI are markedly higher than the CPAP AHI.Figure 4: Comparison of CPAP AHI and WPAT AHI and RDI.Distribution of unadjusted CPAP AHI and WPAT AHI and RDI. P < .001. AHI = apnea-hypopnea index, CPAP = continuous positive airway pressure, RDI = respiratory disturbance index, WPAT = WatchPAT.Download FigureFigure 5A shows a Bland-Altman plot for group 1 unadjusted CPAP and WPAT RDI. Figure 5B shows a Bland-Altman plot for group 2 unadjusted CPAP and WPAT RDI. Group 2 patients had a significantly higher WPAT RDI vs CPAP AHI, whereas there was no significant difference in group 1 patients between the CPAP AHI and WPAT RDI.Figure 5: Unadjusted CPAP and WPAT RDI.Bland Altman plots showing difference between CPAP AHI and WPAT RDI in group 1 (A) and group 2 (B) patients. AHI = apnea-hypopnea index, CPAP = continuous positive airway pressure, RDI = respiratory disturbance index, WPAT = WatchPAT.Download FigureDISCUSSIONNewer generation CPAP machines monitor adherence as well as residual AHI, and interrogation of this data is part of the routine follow-up evaluation of patients on CPAP. However, residual SDB may occur in patients receiving either fixed CPAP (based on in-laboratory CPAP titration) or auto-adjusting CPAP, and the ability of CPAP machines to detect and treat these events has been increasingly scrutinized.21,23–28 We identified an elevated AHI with WPAT testing in nearly half of patients with clinically suspected residual SDB and a normal CPAP AHI. While previous studies have evaluated patients on CPAP with concomitant PSG to detect residual OSA, ours is the first to assess patients by comparing the CPAP data report derived AHI and WPAT AHI obtained simultaneously in the ambulatory setting. In addition to residual OSA, WPAT detected other types of respiratory events as well. An elevated WPAT REM-related AHI was found in a number of patients, which also went undetected by the CPAP machine. REM-related apnea may lead to potentially greater health consequences than apnea occurring in non-REM sleep.29–31 Hence, it may be important to detect and eliminate REM-related respiratory events, even in the setting of a normal overall AHI. WPAT testing also detected respiratory effort-related arousals (RERAs), which lead to sleep fragmentation and increased sympathetic outflow and autonomic activation. Clinically, this may translate into daytime sleepiness and fatigue, reduced psychomotor performance, and potential cardiovascular and metabolic consequences.32 Finally, some patients were also found to have hypoxemia by WPAT. While oximetry is not routinely re-evaluated once patients begin CPAP, ongoing hypoxemia may be common and has been implicated in causing additional detrimental consequences.33,34Recent studies have demonstrated the potential for under detection of OSA by home sleep testing, simply because the AHI may be decreased falsely as sleep efficiency is reduced.35,36 We recalculated the CPAP AHI (adjusted CPAP AHI) based on total sleep time as measured by the WPAT, instead of total recording time. Most of our study patients had a relatively high sleep efficiency, so while the adjusted CPAP AHI was slightly higher, reduced sleep efficiency did not account for the differences between the CPAP AHI and WPAT AHI. If CPAP usage time was less than the WPAT recording time while a patient slept, this could lead to a difference between the WPAT and CPAP AHI measurements, as the WPAT would be detecting apneas while CPAP was not being worn. In fact, the CPAP usage and WPAT recording times were almost identical for all study patients (P < .001).Other factors have been implicated in potentially reducing CPAP efficacy, such as mask interface type and expiratory pressure reduction. Use of an oronasal mask may require higher CPAP levels in comparison to a nasal mask, potentially leading to greater air leak, and CPAP efficacy with different masks may also be subject to effects of body position.37–39 Zhu et al40 showed that a pressure relief feature on both fixed and autoCPAP may reduce treatment efficacy, with a bench model demonstrating increased residual AHI when this modality is in use. Although our overall numbers were relatively small, there were no differences in mask type or pressure relief settings between the group 1 and group 2 patients in our study. There were no patient characteristics, baseline OSA findings, or other treatment parameters that correlated with the differences between the WPAT and CPAP data report findings.There is increasing evidence that treatment of OSA may reduce health consequences and daytime sleepiness and improve quality of life, even for mild OSA.41 Nevertheless, maximal treatment benefit may not be fully achieved in the setting of suboptimal CPAP effectiveness.14,42 While the greatest obstacle to CPAP therapy is suboptimal adherence, it is less well appreciated that CPAP may not always be fully effective, even when compliance is satisfactory18, and a number of studies have found residual SDB in patients using CPAP. Baltzan et al19 reported that suboptimal CPAP treatment of OSA was common, despite good CPAP compliance and a lack of subjective suspicion by OSA patients or their physicians. They examined 101 consecutive patients with OSA on fixed pressure CPAP (following in laboratory titration) and found 17% had a residual AHI > 10 events/h, using simultaneous PSG and CPAP. Pittman et al20 performed a multicenter study of 70 patients on fixed CPAP for at least 3 months following initiation of CPAP by in lab titration and found that nearly 1 in 5 patients (19%) had moderate to severe residual OSA on simultaneous WPAT and PSG. A study by Desai et al21 found 26% of their study subjects had an AHI of 5 events/h or greater on autoCPAP. Mulgrew et al22 examined patients with moderate to severe OSA on CPAP for 3 months of fixed CPAP treatment, and found 15 of 61 patients (25%) had residual OSA with an AHI > 10 events/h on CPAP.OSA severity may vary from night to night and over time, and hence autoCPAP may confer a potential treatment advantage over CPAP at a fixed pressure. Algorithms whereby CPAP machines detect and respond to residual SDB events are proprietary and brand-specific and have been shown to have a variety of inherent inaccuracies. Ueno et al23 found autoCPAP machine overestimation of hypopneas, but good correlation between the overall AHI measured by autoCPAP and that derived during simultaneous PSG with manual CPAP titration. Denotti et al24 compared airflow measured via nasal CPAP mask during PSG with the autoCPAP flow signal in 34 patients with OSA during CPAP treatment. AutoCPAP was purposely set to a subtherapeutic pressure in some patients, and the CPAP AHI was compared to a manually scored AHI from airflow measured at the CPAP mask. Nearly one-quarter of patients were inadequately treated by the autoCPAP machines based on manually scored AHI. Approximately three-fourths of patients were undertreated when respiratory events included flow limitation, ie, RERAs. They concluded that autoCPAP had inaccuracies in both detecting and responding to residual SDB events. Interestingly, those patients having greater residual SDB also had worse CPAP adherence. Cilli et al25 performed a retrospective study of 137 patients with OSA comparing autoCPAP AHI with the AHI during simultaneous PSG. CPAP machine AHI was found to be accurate, but only 2 patients had AHI > 10 events/h on therapy. Nigro et al27 found a slight underestimation of autoCPAP AHI vs PSG in 148 patients with OSA on CPAP, and absolute agreement between the 2 methodologies was low for obstructive apneas and hypopneas. In a bench model assessing 11 different commercially available autoCPAP devices in the treatment of simulated SDB, Zhu et al28 demonstrated significant variability in bench-measured and CPAP device-reported residual AHI. They found that each autoCPAP behaved differently and there were large differences in treatment efficacy and accuracy of the device report between different device models.Reiter et al43 demonstrated that direct manual analysis of device-derived flow/waveform information from CPAP machines was more accurate in determining residual AHI than when the machines did so using an automated algorithm. They found automated scoring missed half of patients with mild residual OSA and detected less than a quarter of those with moderate to severe residual OSA. A recent study by Gagnadoux et al44 evaluated a new automatic positive airway pressure device and found it to be accurate in detecting and treating residual OSA. However, there was a high rate of patient exclusion, including those with difficult or incomplete in-lab CPAP titrations, and the median and high range of pressures to treat OSA were relatively low (< 8–9cm H2O), raising the possibility that greater inaccuracy might occur at higher pressures.The main limitation to our study is that CPAP testing was performed using WPAT rather than PSG. The WPAT is a simple, well-tolerated, and accurate device that has been well-validated in different patient populations for measuring SDB as well as sleep staging.45–50 WPAT has also been shown to have good clinical agreement with PSG in evaluating patients for residual OSA on CPAP, with a mean AHI difference of only 3 events/h.20 Another potential weakness is that the number of patients with different mask interface and machine types was not large enough for more robust statistical analyses. Finally, our study is unique in that we studied only those patients with clinically suspected residual SDB. Although we did find a surprisingly high prevalence of residual SDB, this prevalence in unselected patients treated with CPAP could be less, but remains unknown.In summary, we found WPAT AHI was significantly higher than simultaneous CPAP AHI in nearly half of those patients with clinically suspected residual SDB being treated with CPAP. There were additional respiratory disturbances in these patients, including REM-related respiratory disturbances, RERAs, and hypoxemia, all of which were elucidated only with the use of the WPAT. Residual SDB may have potential clinical consequences, including reduced CPAP compliance, ongoing hypersomnolence, and other health-related sequelae. Simultaneous WPAT testing of patients wearing CPAP may represent a valuable tool to evaluate clinically suspected residual SDB, or in high-risk patients with OSA in general, in the setting of a normal CPAP AHI in the ambulatory setting.DISCLOSURESAll authors have seen and approve the manuscript. Work for this study was performed at Atlantic Health Sleep Centers, Atlantic Health System, Morristown, NJ.ABBREVIATIONSAHIapnea-hypopnea indexautoCPAPautomatically adjusting CPAPCPAPcontinuous positive airway pressureOSAobstructive sleep apneaPSGpolysomnographyREMrapid eye movementRERArespiratory effort related arousalSDBsleep-disordered breathingWPATWatchPATREFERENCES1. Punjabi NM, Caffo BS, Goodwin JL, et al.. Sleep-disordered breathing and mortality: a prospective cohort study. PLoS Med. 2009;6(8):e1000132. https://doi.org/10.1371/journal.pmed.1000132 CrossrefGoogle Scholar2. Marin JM, Agusti A, Villar I, et al.. Association between treated and untreated obstructive sleep apnea and risk of hypertension. JAMA. 2012;307(20):2169–2176. https://doi.org/10.1001/jama.2012.3418 CrossrefGoogle Scholar3. Basner RC. Cardiovascular morbidity and obstructive sleep apnea. N Engl J Med. 2014;370(24):2339–2341. https://doi.org/10.1056/NEJMe1404501 CrossrefGoogle Scholar4. 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