This article previously ran in the Q2 2023 issue of A2Zzz.
Obstructive sleep apnea (OSA) is estimated to be the most prevalent sleep disorder, with approximately 34% of middle-aged men and 17% of middle-aged women in the general population expected to meet the diagnostic criteria for it.1,2 Prevalence in patients with cardiovascular and cardiometabolic disease is higher, estimated as high as 40%-80%. In recent years there has been an increasing awareness of OSA but despite this, the disease remains frequently underdiagnosed or diagnosis is delayed, even in patients with moderate to severe symptoms.3,4
OSA is characterized by recurrent complete (apneas) and partial (hypopneas) obstruction of the upper airway, causing intermittent hypoxemia, autonomic fluctuation, arousals and sleep fragmentation, and is associated with consequences that negatively affect health and quality of life of undiagnosed patients. The most common consequences of untreated OSA are hypertension,5,6 cardiovascular and cardiometabolic disease7,8 and stroke,9,10 all included in the group of the costliest diseases in the U.S. Additionally, OSA increases allcause mortality,11,12 and patients with undiagnosed OSA have higher rates of health care utilization and increased hospital readmissions, adding substantially to medical costs annually.13-15 It is therefore of high importance to implement comprehensive, precision care in both diagnosis and treatment of OSA to improve patient outcomes.
Sleep is dynamic with sleep duration, the proportion of OSA severity and non-rapid eye movement (non-REM) and rapid eye movement (REM)-sleep changing from night to night.16 Polysomnography (PSG) is still the reference standard, recording sleep and breathing to calculate the apnea hypopnea index (AHI), defined as the average number of apnea and hypopnea events per hour during sleep, to diagnose and classify OSA severity. The limitations of PSG are well understood with high cost, complexity, lack of access and the requirement for a trained specialist to interpret results. It would be unreasonable to expect patients or payers to do a multi-night PSG for the purpose of OSA diagnosis or treatment tracking. Therefore, use of various, limited channel home sleep apnea testing (HSAT) devices has been increasing. These devices are simpler to use, patients can sleep in their natural sleep environment when tested for OSA and the output is simpler to analyze, making the process less costly and cumbersome.
Recent studies report a relevant night-to-night variability of apnea events that may lead to misdiagnosis of patients suspected of OSA in both adults and children when sleep is evaluated for only one night.17-19 A study by Punjabi et al., utilizing type-3 HSAT to calculate AHI reports a substantial within-patient variability and that “approximately 20% of patients with mild and moderate sleep apnea on the first night were misdiagnosed either as not having sleep apnea or as having mild disease.”20 A similar study by Tschopp et al. utilizing peripheral arterial tonometry (PAT) concluded that 24% of patients were misclassified when using devices for one night compared to AHI-average calculated from three-nights.21 A meta-analysis by Roeder et al. reported “on average 41% (95% CI 27% to 57%) of all participants showed changes of respiratory events >10/hour from night-to-night” and “49% of participants changed OSA severity class at least once in sequential sleep studies.”18
These results indicate that 1) misclassification and underdiagnosis of mild and moderate OSA are relatively common when based on a single-night study, and 2) single-night studies are imperfect, with multi-night testing possibly offering improvements in the diagnostic process. For this purpose, sleep-testing devices with a lower-cost structure offer more flexibility for multi-night testing for diagnosis and less burden for patients to use repeatedly if applicable for use for treatment tracking. Implementing multi-night testing should not only improve diagnostic accuracy, but additionally our understanding of the dynamics and variations of sleep and OSA severity over time. This will also offer the option to track responses to therapy that can be utilized as an adjunct to manage therapy for improvements in outcomes. While some single-patient, multi-use disposable devices improve the diagnosis by capturing intra-night variability of AHI, it is no less important to track treatment efficacy over time. Single-patient, non-disposable devices recently introduced to the market offer ease of use and cost-effectiveness.
The most novel of the disposable devices, Sunrise, is capable of recording three nights of sleep. The system utilizes mandibular jaw movements, pulse-rate and oxygen-saturation (SpO2) that is recorded during sleep with artificial intelligence (AI) powered algorithms to aid in evaluation of OSA.22 Sunrise can be utilized in patients 18 years and older with suspicion of OSA (FDA K222262).
Multiple photoplethysmogram (PPG) sensor devices are also on the market that use the plethysmography-signal (PLETH) to measure pulsatile volume changes in the arteries of peripheral vasculature of the fngers.23 These devices combine recordings of the PLETH signal with SpO2 and actigraphy to provide estimates of sleep and to calculate an AHI. The devices that are marketed in the group of using the PPG include WatchPAT,24,25 which uses a pressurized probe with a PPG sensor and offers a multi-patient reusable device with single-use disposable sensor and a single-patient disposable, one-night sleep-testing option. WatchPAT is intended for use with patients 12 years and older (for OSA) or 17 years and older (for central sleep apnea [CSA]) suspected to have sleep-related breathing disorders (FDA K183559).
Another PPG sensor device is NightOwl®,26,27 which is a reusable, single-patient, disposable device that offers the option of recording up to 10 nights of sleep testing. NightOwl is intended to aid in the evaluation of OSA in adult patients suspected of sleep apnea (FDA K213463).
A third option is the SleepImage System®,28,29 that the FDA cleared as a software as a medical device (SaMD) and utilizes a simple device for data collection. Both devices offered currently can be utilized for diagnostic purposes, a ring-device that can be utilized for multiple patients for testing (Figure 1) and a patient-centric finger-tip device. Patients who are diagnosed with OSA/CSA can then continue to utilize the patient-centric device as instructed by their health care provider to track treatment efficacy (Figure 2). The SleepImage System is intended to aid in the evaluation of sleep disorders as well as diagnosis and management of sleep-disordered breathing (SDB) in children, adolescents and adults (FDA K182618). The Sleep Quality Index (SQI), sleep fragmentation, sleep duration and sleep stage calculations are based on cardiopulmonary coupling (CPC)30,31 analysis of data derived from the PLETH-signal collected with the PPG sensor, including SpO2 information to calculate AHI.
Historically in OSA diagnosis and management, focus has been on defining and quantifying disease severity by calculating the AHI. OSA is characterized by repeated paused breathing, which causes transient hypoxemia and sleep fragmentation that may affect sleep quality at different severity levels like the hypoxemia. Alternative metrics have been proposed with the aim to better predict clinical consequences of OSA, including sleepiness, cardiovascular and cardiometabolic health and effects on quality of life.32 These metrics include methods to better quantify the transient hypoxemia, apnea hypopnea event duration and hypoxic burden calculating the area under the oxyhemoglobin saturation curve.33,34 Additionally they quantify sleep fragmentation by estimating arousal intensity,35 the odds ratio product (ORP) quantifying sleep depth from analysis of electroencephalogram signal (EEG)36 and the SQI calculated from automated CPC analysis of heart rate variability (HRV) and breathing.37-40
Insomnia is common in the general population, with estimated 30%-50% of adults experiencing short-term insomnia and 10% chronic insomnia,41 with prevalence of insomnia in patients with OSA higher or 46%-60%.42 Patients suffering from both disorders, comorbid insomnia and sleep apnea (COMISA), are at greater cardiovascular risk43,44 and higher impairments to daytime functioning and quality of life compared to those with either OSA or insomnia alone.45 Therapy for both OSA and insomnia is more complex in patients with COMISA and often less effective.46,47 Therefore, it is important to document both the hypoxemia as well as insomnia symptoms and sleep quality to optimize therapy outcomes. Diagnosis of insomnia is based on subjective self reported symptoms, and the Insomnia Severity Index (ISI) has been suggested to screen for insomnia in patients with OSA.48,49 However, sleep quality is a multidimensional construct with both subjective and objective components, which are not always concordant.
Complementary methods as mentioned in this article are available to assess sleep quality, as are objective methods like the SleepImage System SQI, which measures sleep quality presented on a scale of 0-100 with higher intra-individual variability of patterns of sleep stability in patients with insomnia.50
Having a defined unit of metric in medicine helps differentiate disease states from normal and categorize the severity of illness. It’s important to both define the state of disease and track therapy efficacy over time to improve outcomes. The SQI has demonstrated a direct relationship with health outcomes in clinical studies; improving SQI in adults has positive effects on hypertension and stroke,51,52 adiponectin levels39 glucose disposal53 and depressive symptoms.54 Healthy-weight children with high sleep quality have better cardiometabolic health than healthy-weight children with low sleep quality.39 Children with high SQI also have better quality of life, attention and executive function, and are more likely to have spontaneous remission of OSA than children with low SQI.38 Both AHI and SQI need to be treated successfully to improve cardiometabolic health, behavior and quality of life.40
Additional utility for longitudinal sleep tracking may add value in continuous positive airway pressure (CPAP) management. CPAP-machine-detected respiratory events remains the approach to tracking CPAP efficacy. Although clinically convenient, studies have shown the difference in manual events and machine detected events to be clinically significant, especially during periods of unstable breathing.55 The ability to identify such residual respiratory events could warrant further sleep evaluation and possibly improve outcomes. Using home sleep testing tools such as those noted in this article may unlock the potential for precise home CPAP optimization.
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