Study Identifies Increased Residual Sleep-Disordered Breathing in Patients on CPAP

residual sleep disordered breathing

By Lindsey Nolen

A common misconception across sleep medicine is that continuous positive airway pressure (CPAP) machines fully resolve sleep-disordered breathing (SDB) in apnea patients showing a successful AHI. However, research has shown that residual SDB can still occur during the use of a CPAP machine, leading to the need for increased detection through new, innovative solutions.

To determine the accuracy of the apnea-hypopnea index (AHI) as measured by CPAP machines, researchers examined whether patients with new, recurrent, or worsening signs, symptoms, or comorbidities associated with obstructive sleep apnea using CPAP at their usual prescribed settings were experiencing elevated AHI. Published in the Journal of Clinical Sleep Medicine, the findings by researchers showed that Peripheral Arterial Tone (PAT) AHI was significantly higher than simultaneous CPAP AHI in nearly half of those patients with clinically suspected residual SDB being treated with CPAP.1 This was concluded by simultaneously employing a home sleep apnea testing device, the WatchPAT®, an innovative Home Sleep Apnea Test (HSAT) from Itamar.

One of the researchers, Matt Epstein, MD, associate director of the Atlantic Health Sleep Centers in Morristown, New Jersey, and a fellow of the American College of Chest Physicians and the American Academy of Sleep Medicine, explained that this study sheds important light on the general acceptance of CPAP treatment effectiveness. He explained that for many years, the norm has been to go to a sleep center to be manually titrated during an overnight study if sleep apnea was a concern. Over the past several years, sleep physicians and centers have been initiating more at-home treatments with automatically adjusting CPAP and assuming the machine is fully effective given a positive patient data report using internal sensors and monitors.

“If we assume those reports are accurate, we often are satisfied with things,” Epstein said. “We started to notice that patients would occasionally have ongoing sleepiness, or they would have persistent medical problems that the apnea was contributing to. It raised the question of whether their sleep apnea was actually being fully eliminated. And when you look in the literature, there have been studies showing that the CPAP machines are not always effective.”

He noted that his team’s study was unique in the sense that it was doing a simultaneous home test while patients were on their CPAP in their home environment. This eliminated the need for in-lab testing. They found that in about half of cases where there was clinical suspicion that residual SDB was persisting in CPAP patients, this suspicion was correct. This means the CPAP machine was not successfully registering the patient’s apnea.

“We were looking at patients whose sleep machines were saying, ‘No, everything’s perfect,’ and yet, clinically, it didn’t fit,” Epstein said. “On the one hand, we strive for patients to use CPAP and be compliant with it. But then we have patients who are compliant and who are using it well. But yet we may not be fully eliminating the apnea. That adds a whole new dimension to the question of are we fully treating apnea.”

He speculated that this SDB might be a result of patients being more responsive to CPAP initially, but then their body responds differently to it, being able to withstand higher pressure. Epstein recalled that there have been other studies conducted within the last decade showing that when patients were restudied several months after an in-lab titration with a fully effective CPAP setting in the lab, the pressure prescribed was no longer effective. Regardless of the cause, this research means that physicians can no longer assume apnea will be eliminated in patients using CPAP.

To help detect continued SDB, Epstein and his colleagues employed the use of Itamar’s WatchPAT®, a diagnostic device that measures and can diagnose sleep apnea. This device allows physicians to essentially double-check that their patient’s apnea is fully resolved. This verification can be useful after a patient has had surgery for apnea or if they are using a new dental appliance to treat their apnea.

“The unique thing about the WatchPAT® is that it measures apnea in a different, novel way by measuring changes in arterial tone. The WatchPAT® is worn on the wrist and the finger, whereas all the other home testing appliances rely on airflow using a modified nasal oxygen tube,” Epstein said. “When you’re wearing a CPAP mask, you can’t use the other home testing devices because you wouldn’t be able to put your CPAP on with them.”

The WatchPAT® is uniquely positioned to monitor residual SDB in CPAP patients because the device doesn’t interfere with the patient’s ability to use their mask. No other devices would have helped Epstein’s team achieve its goal of testing CPAP effectiveness and residual SBD together, he said.

Melih Alvo, senior marketing director at Itamar® Medical, also emphasized that it can be difficult looking for residual sleep-disordered breathing with traditional tests due to the CPAP mask. WatchPAT® is the only home sleep apnea test on the market using PAT® technology, which does not rely on airflow like other traditional sleep tests, and WatchPAT®’s use of the PAT® technology extends great capability to providers in terms of the number of signals, such as AHI, AHIc, RDI, and ODI based on true sleep time and sleep staging.

“The beauty of WatchPAT® is that CPAP effectiveness can be measured at the same time they are using the machine, and WatchPAT® detected additional respiratory events beyond those detected by the CPAP machines, including rapid eye movement-related apneas, respiratory effort-related arousals, and hypoxemia,” Alvo said. “It is critically important to measure the effectiveness of CPAP, and the WatchPAT® makes this possible.”

Moving forward, Epstein said his team of researchers might conduct additional studies on the topic of residual SDB in CPAP patients. He would like to look at other specific populations in terms of sleep apnea, as this existing study only looked at patients whose apnea the team suspected wasn’t fully gone.

“We don’t know what the entire population is doing,” Epstein said. “I’d like to look at the most severe sleep apnea patients and severe hypoxemia patients. We’re all making the assumption that the auto CPAP machines are doing their job, but we just don’t know that for sure.”


  1. 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.


Lindsey Nolen is a journalist living in Jacksonville, Florida. She has been covering healthcare, including sleep medicine, for six years.

This article first appeared in Sleep Lab Magazine, Jan/Feb 2021 issue. Click the button below to start your free subscription.

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