Home sleep apnea testing for obstructive sleep apnea in adults

INTRODUCTION — Obstructive sleep apnea (OSA) is a disorder characterized by repetitive episodes of apnea or reduced inspiratory airflow due to upper airway obstruction during sleep. In select patients with OSA, home sleep apnea testing (HSAT; also referred to as out-of-center sleep testing or portable monitoring) can be used as an alternative to overnight, attended, in-laboratory polysomnography for both the diagnosis of OSA and for following the response to therapy.

The types of devices used for HSAT and the indications and limitations of HSAT are reviewed here. The selection of suitable candidates for HSAT during the evaluation of patients with suspected OSA is described separately. (See "Clinical presentation and diagnosis of obstructive sleep apnea in adults".)

SLEEP MONITORING DEVICES — Four types of sleep study monitoring devices have been defined [1,2]. Type 1 is an in-laboratory polysomnogram that cannot be performed at home. All others (types 2, 3, and 4) are portable devices (table 1).

In-laboratory devices

Type 1 devices (attended polysomnogram) — Type 1 monitoring devices are used for technician-attended, overnight polysomnography (PSG), typically done in a sleep laboratory setting (figure 1). These devices are not portable and cannot be used at home. They are the gold standard for sleep apnea testing, against which home/portable devices are compared. PSG is discussed separately. (See "Overview of polysomnography in adults".)

Home devices — Types 2, 3, and 4 devices are portable devices. The most common HSAT devices in use are type 3 and type 4 devices.

Advantages and disadvantages of HSAT are listed in the table (table 2). Advantages of HSAT include its convenience (it can be performed in the patient's home or in a hospital room) and its potential to lower costs, since most HSAT devices are less costly than complete polysomnography systems and the attendance of a technologist is not required. In addition, sleep data can be obtained over several nights of sleep in the comfort of the patient's home rather than one night in a laboratory setting where the patient may not sleep for prolonged periods. The main disadvantage of HSAT is that for most of these devices, particularly, type 3 and 4 devices, fewer physiologic variables are measured than with PSG, which can lead to misinterpretation of the results. These are discussed in greater detail below. (See 'Limitations' below.)

Type 2 devices (unattended polysomnography) — Type 2 devices (unattended polysomnography) are rarely used. Type 2 monitoring devices can record the same variables as type 1 devices. Leads for the equipment can either be placed in the sleep laboratory and the patient is sent home or setup in the home. However, a technologist is not present during the recording (ie, they are unattended studies) and data is frequently lost due to frequent lead detachment, thereby resulting in an inadequate study [3]. In addition, they are not significantly more convenient or less costly when compared with PSG.

Type 3 devices (portable devices) — Type 3 monitoring devices (portable HSAT devices) typically measure between four and seven physiologic variables, including two respiratory variables (eg, respiratory effort and airflow), a cardiac variable (eg, heart rate or an electrocardiogram), and arterial oxyhemoglobin saturation via pulse oximetry (figure 2). Some devices have additional signals that can detect snoring, determine body position, or detect movement. Sleep variables (eg, sleep stages, sleep continuity) are typically not measured by a type 3 device, since electroencephalography is not generally included in a type 3 device. However, some newer devices have methods for estimating sleep (eg, actigraphy monitors, which detect movement and assist with differentiating sleep from wake states). A technologist is typically not present during the recording and real-time visualization of the signals is usually not available.

Recordings from a typical type 3 portable monitoring device are shown in the figure (figure 3). In this example, respiratory effort is detected by a chest wall impedance monitor, airflow is detected by a nasal cannula pressure transducer, and oxyhemoglobin saturation is measured by a pulse oximeter. The heart rate is derived from the pulse oximetry signal. Measurement of these variables is generally sufficient to detect most apneas and hypopneas, although they are unable to adequately detect arousals. Additionally, many devices can also detect body position with a sensor embedded in the device. (See 'Limitations' below.)

Another type of HSAT is the "WatchPAT" device which measures peripheral arterial tonometry (PAT), oximetry, heart rate, snoring, actigraphy, and body position (picture 1 and figure 4). It uses an automated algorithm to detect breathing events based upon peripheral arterial tone [4-6]. This device provides an apnea hypopnea index (pAHI) and respiratory disturbance index (pRDI) corresponding with the validated algorithm that is utilized in calculating sleep disordered breathing events using the PAT signal. PAT provides an indirect indication of respiratory events by the detection of sympathetic activity that is increased along with an increase in heart rate and decrease in oxygen saturation at the termination of a respiratory event. PAT has been validated for the diagnosis of OSA [6-8] but alone is insensitive and not specific for the diagnosis of OSA [9]. The classification of devices that include PAT is challenging. While many experts consider them as type 3 devices (per the original American Academy of Sleep Medicine [AASM] classification), the Centers for Medicare and Medicaid Services (CMS) classify them as a type 4 device.

Type 4 devices (portable devices with limited monitoring) — Type 4 monitoring devices, that measure one to three variables, are defined differently by different organizations:

●The American Academy of Sleep Medicine (AASM) originally defined type 4 monitoring devices as devices that record one or two variables (eg, arterial oxyhemoglobin saturation and airflow) and can be used without a technician. These devices are called continuous single or dual bioparameter devices.

●In contrast, the United States Centers for Medicare and Medicaid Services (CMS) guidelines include devices that measure three variables as type 4 monitoring devices.

Type 4 devices that record one or two variables provide limited information. Pulse oximetry and airflow are the physiological variables that are most commonly measured. As a result, derived information typically includes the frequency of apneas, frequency of hypopneas, baseline oxyhemoglobin saturation (SpO₂), mean SpO₂, frequency of oxyhemoglobin desaturation, duration of oxyhemoglobin desaturation, degree of oxyhemoglobin desaturation, and nadirs of SpO₂.

Pulse oximetry is considered a type 4 device but is not adequate when used alone or with one other variable for sleep apnea testing. (See 'Pulse oximetry' below.)

Proposed alternative classification — An alternative classification scheme for HSAT devices has been proposed, the SCOPER categorization system [10]. The acronym SCOPER stands for Sleep, Cardiovascular, Oximetry, Position, Effort, and Respiration. The SCOPER categorization system provides a more detailed description of the type of physiologic parameters that are being measured and how they are being measured than traditional classification schemes. The system is described in detail in the table (table 3).

SCOPER allows the clinician to more easily assess whether the variable is being optimally measured or not. As an example, consider a device that measures actigraphy, derives the pulse rate from the oximetry, measures oximetry with an adequate sampling rate, uses a mercury position sensor, measures effort via a piezo belt, and measures respiration via a thermocouple; this device would have a SCOPER designation of S₃C₄O₁P₂E₄R₃.

CHOOSING AN ADEQUATE HOME DEVICE — Several devices for HSAT are available. Each device has different proprietary equipment that measures different variables and has different algorithms for the detection and definition of respiratory events. Thus, it behooves the clinician to know what variables are being measured by specific devices so that they can understand the limitations of the device used and select an alternate device or in-laboratory testing, if needed. The American Academy of Sleep Medicine (AASM) considers an "adequate" device as one that incorporates a minimum of the following sensors [10,11]:

●Nasal pressure

●Chest and abdominal respiratory inductance plethysmography

●Oximetry

Or

●Peripheral arterial tone (PAT)

●Actigraphy

●Oximetry

In essence, providers should choose HSAT devices that have been validated against PSG, utilize an oxygen saturation sensor, AND measure respiratory events with a minimum of one airflow and effort sensor or PAT or another validated measure of respiratory disturbance. As newer devices come on the market, assessing whether these minimal parameters are met by the device should be sought.

The United States Centers for Medicare and Medicaid Services (CMS) guidelines do not make any specific recommendations about which type of HSAT device should be used. However, they do indicate that positive airway pressure (PAP) therapy prescriptions will be covered by Medicare and Medicaid only if OSA is diagnosed using a type 1, 2, or 3 device, or Type 4 device that utilizes PAT technology [12]. (See 'Home devices' above.)

INDICATIONS — The American Academy of Sleep Medicine (AASM) has released clinical practice guidelines to guide clinicians in the use of HSAT [1,11,13,14]. The most common indications for HSAT are the diagnostic evaluation of OSA in patients with a high pretest probability of moderate to severe uncomplicated OSA and the follow-up assessment of OSA therapies (eg, positive airway pressure [PAP] therapy, oral appliance, surgery).

HSAT devices are not typically used for determining the initial level of PAP therapy, since many monitoring devices do not interface with PAP devices and third-party reimbursement for this indication is not standard. In addition, although some HSAT devices can be performed while on PAP (eg, WatchPAT devices), this mode for PAP titration has not been adequately validated and is not recommended. PAP titration is discussed separately. (See "Titration of positive airway pressure therapy for adults with obstructive sleep apnea" and "Mode selection for titration of positive airway pressure in adults with obstructive sleep apnea".)

Diagnosis — Many HSAT devices have been validated against standard polysomnography (PSG), typically by testing the same patient with both modalities in the sleep laboratory [15-19]. The sensitivity and specificity appear to be high in populations considered by sleep specialists to be at high risk of uncomplicated moderate to severe OSA on the basis of clinical symptoms, assuming there are no comorbid medical disorders or other suspected sleep disorders [1,20,21]. Patient selection for HSAT and patients in whom HSAT should be avoided are discussed separately (algorithm 1 and table 4). (See "Clinical presentation and diagnosis of obstructive sleep apnea in adults", section on 'Home sleep apnea testing'.)

Reassessment — Guideline from the American Academy of Sleep medicine support the use of HSAT for reassessment [14]. HSAT can be used to assess the adequacy of the prescribed PAP therapy within a patient's usual environment, provided the HSAT device can interface with the PAP device or run independently of the PAP device and to guide adjustment of the therapy, regardless of the mode of therapy (positive pressure ventilation, surgery, or an oral appliance) [22,23]. HSAT can also be used to reassess a patient with OSA after weight loss or weight gain and to assess patients with residual sleepiness despite therapy, including the possible detection of treatment emergent central sleep apnea (TECSA), although HSAT devices have not been validated for the detection of CSA and, if found, a polysomnogram is indicated. (See "Obstructive sleep apnea: Overview of management in adults" and "Evaluation and management of residual excessive sleepiness in adults with obstructive sleep apnea" and "Treatment-emergent central sleep apnea".)

LIMITATIONS — The main disadvantage of HSAT is that for particularly type 3 and 4 devices, fewer physiologic variables are measured than with in laboratory polysomnography (PSG), which can lead to misinterpretation of the results. Although type 2 devices measure similar variables to PSG, they are rarely used, cumbersome for in home testing, and do not have a technician on site to fix the equipment when leads become detached and data sensors are lost, which is not uncommon.

Important limitations typically include the following:

●Underestimation of the apnea hypopnea index (AHI) – Type 3 and type 4 devices often underestimate the AHI, increasing the likelihood of a false-negative result. The AHI is calculated during polysomnography by dividing the number of apneas and hypopneas by total sleep time, whereas the HSAT calculates the "respiratory event index" (REI) dividing the number of apneas and hypopneas by total recording time (which is a larger number). As a result, the REI derived from HSAT is usually lower than an AHI derived by PSG, thereby underestimating the severity of sleep-related events. Thus, if the suspicion remains for OSA and a HSAT study is negative, the threshold to test using an in-laboratory PSG should be low. One retrospective study showed that 24 percent of patients with a negative HSAT who were subsequently studied with PSG were positive for OSA, and those positive OSA patients tended to be over the age of 50 years [19]. Notably many of the missed events are arousals [24]. Of note, the WatchPAT device uses an algorithm that estimates sleep and divides it into "light sleep", "deep sleep," and REM sleep. This reduces the denominator and likely improves accuracy somewhat [25].

●Inability to detect arousals – Type 3 and 4 devices do not typically detect arousals from sleep because they do not include electroencephalography (EEG). As a result, arousals related to sleep-disordered breathing events cannot be detected. The inability to detect arousals related to sleep-disordered breathing events may lead to underestimation of the respiratory disturbance index (RDI) and under-recognition of cases of OSA in which arousals related to sleep-disordered breathing events s are the predominant feature. (See "Polysomnography in the evaluation of sleep-disordered breathing in adults", section on 'Respiratory disturbance index' and "Clinical presentation and diagnosis of obstructive sleep apnea in adults", section on 'Criteria'.)

●Inability to detect seizures – Because most type 3 and 4 HSAT do not have EEG recordings, nocturnal seizures cannot be detected. Similarly, for devices without electrocardiography monitoring, nocturnal arrhythmias cannot be detected.

●Inability to record position – Some type 3 and type 4 devices do not record position, so they may not be able to detect when the patient is lying in the supine or lateral decubitus position. Thus, OSA that only develops (or worsens) in the supine position may not be detected. However, most devices now have a position detection sensor, so this may be less of an issue than in the past.

●Inability to distinguish rapid eye movement (REM) sleep from non-REM (NREM) – Most type 3 and type 4 devices cannot distinguish rapid eye movement REM sleep from NREM sleep because they do not include EEG monitoring. As a result, the interpreting clinician cannot be certain that a period of REM sleep was captured during the study. This is an important limitation because severe perturbations are most common during REM sleep and some patients only develop sleep apnea during REM sleep (especially females). As noted above, the WatchPAT device has a sleep staging algorithm which includes REM sleep detection.

●Inability to distinguish between obstructive and central events – Some type 3 and 4 HSAT devices cannot distinguish between obstructive and central events, in part because respiratory effort is not measured. Additionally, there are only limited validation studies for diagnosing central sleep apnea with an HSAT WatchPAT device [22,23]. Patients at risk for central apneas, hypopneas, or hypoventilation should not be tested with such devices. (See "Mode selection for titration of positive airway pressure in adults with obstructive sleep apnea", section on 'Complicated OSA'.)

●Proprietary differences – Different manufacturers use different sensors and potentially different algorithms to identify respiratory events. The scoring algorithm is proprietary and many manufacturers do not allow the components of the algorithm to be viewed or altered by the provider who ordered the test. This is problematic according to numerous studies that showed that manual scoring or manual editing of automated scoring improves diagnostic accuracy compared with automated scoring alone [26-31]. Clinical practice guidelines recommend manual scoring or manual editing of automated scoring [1,11,32].

The failure rate of HSAT devices ranges from as low as 3 percent to as high as 33 percent [33]. Failures are usually due to data loss meaning that information from the device is inadequate to determine a diagnosis of OSA. Technical failures can be reduced by adequately educating patients in the clinic setting (or by clear written or video-taped instructions) on how to apply the device, using a device that is simple to apply, and giving the patient the ability to call someone if they encounter a problem when setting up the device. Guidelines from the American Academy of Sleep Medicine (AASM) recommend that if a single HSAT is negative, inconclusive, or technically inadequate that attended in-laboratory polysomnography should be performed [11].

TECHNICAL CONSIDERATIONS AND INTERPRETATION — Technical considerations that should be assured include the following [34]:

●HSAT for diagnostic evaluation of suspected OSA should be performed only in conjunction with a comprehensive sleep evaluation, in an accredited sleep center under the supervision of a board-certified sleep medicine physician or a board-eligible sleep medicine provider and preferably by a sleep medicine specialist.

●An experienced sleep technician, sleep technologist, or appropriately trained provider must apply the HSAT sensors or directly educate the patient (through written or video-taped material) about the correct application of sensors. In addition, there should be a methodology in place to monitor the quality of recordings.

●Ideally, HSAT devices should be capable of displaying the raw data for review by the clinician, in order to allow assessment of the quality of the data (ie, data from the entire duration of the study, rather than an automated summary of the data).

●All patients undergoing HSAT should receive a follow-up visit with an appropriately trained provider to discuss the results of the test.

●Recording should take place over at least one full night and include a minimum of four hours of technically adequate oximetry and flow data obtained during a habitual sleep period. Although data can be derived from several nights, a full night’s sleep is typically sufficient and most third party payers will only reimburse for one night [35].

●Formal scoring rules are published by the American Academy of Sleep Medicine (AASM) [36]. According to this manual, HSAT reports that do not include electroencephalography (EEG) monitoring should include a respiratory event index (REI), which is the number of respiratory events divided by monitoring time (in hours; applies to type 3 and 4 devices), or an apnea hypopnea index (AHI) if the device records sleep with EEG (eg, type 1 and 2 devices). When using devices that measure airflow and effort, the scoring of events is the same as for PSG, including [37]:

•Apnea: ≥90 percent reduction in peak signal excursion of the airflow sensor for ≥10 seconds

•Hypopnea: ≥30 percent reduction in airflow sensor lasting for ≥10 seconds and associated with a 3 percent oxygen desaturation (The United States Centers for Medicare and Medicaid Services [CMS] rule for hypopnea requires a 4 percent oxygen desaturation)

For devices measuring peripheral arterial tone (PAT), identification of events should be based on the PAT, oxygen desaturation, and heart rate changes [37]. These devices report a "pAHI" and "pRDI" utilizing the PAT signal and the sleep time as estimated with their algorithm. These devices can also be used with continuous positive airway pressure (CPAP), since there are no sensors measuring airflow.

MODES NOT RECOMMENDED FOR HOME SLEEP APNEA TESTING

Digital devices — Several digital devices have become increasingly available to consumers as potential tools to screen for OSA. One meta-analysis of 18 studies found that compared with polysomnography, devices that were bed/mattress-based had the best sensitivity (92 percent) [38]. While contactless devices (eg, a smartphone) could potentially detect mild OSA with a sensitivity of 97 percent, the false positive rate was high (49 percent). All other devices were poorly sensitive. These devices should remain investigational until robust studies demonstrate diagnostic benefit.

Pulse oximetry — Pulse oximetry is a widely accepted and important component of both polysomnography (PSG) and HSAT. However, when it is measured alone or with only one other variable, it is not recommended for the diagnostic evaluation of suspected OSA [1,12,39]. However, review of pulse oximetry during sleep can be a useful adjunct to the history and physical examination in selected settings, such as in children who are not able to comply with formal sleep testing or in the inpatient setting. (See "Evaluation of suspected obstructive sleep apnea in children", section on 'Alternatives to polysomnography' and "Sleep-related breathing disorders and stroke", section on 'Diagnosis'.)

The rationale for this approach is based on data which suggest that overnight pulse oximetry alone can be either a sensitive or a specific test for OSA, but not both. As a result, either false-positive or false-negative tests will be common, depending on the criteria chosen to define a positive test. The sensitivity and specificity of pulse oximetry during sleep as a diagnostic test for OSA are dependent upon whether the criteria used to define a positive test are quantitative or qualitative:

●Overnight pulse oximetry when used for OSA should report an "oxygen desaturation index" (ODI), which is the number of oxygen desaturations (typically 3 or 4 percent drops) divided by the total recording time. Pulse oximetry tends to have a high specificity but a low sensitivity for OSA when quantitative criteria such as the ODI are used [40-42]. As an example, a study of 200 patients with suspected OSA compared overnight pulse oximetry versus polysomnography [41]. Positive overnight pulse oximetry was defined as a decrease in the oxyhemoglobin saturation (SpO₂) of 4 percent or greater from baseline, to a value 90 percent or lower greater than five times an hour. Overnight pulse oximetry had a sensitivity of 41 percent and a specificity of 97 percent.

●In contrast, overnight pulse oximetry tends to have a high sensitivity but a low specificity when qualitative criteria are used [17]. Qualitative criteria emphasize pattern recognition. The overnight pulse oximetry strip is printed and visually analyzed for a pattern of multiple, short-duration fluctuations of the SpO₂. No specific level of desaturation is required for a positive study. As an example, a study of 240 patients with suspected OSA compared overnight pulse oximetry versus polysomnography. Positive overnight pulse oximetry was defined as greater than 10 fluctuations of SpO₂ per hour of sleep. The sensitivity and specificity of overnight pulse oximetry were 98 and 48 percent, respectively.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Sleep-related breathing disorders in adults".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: What is a sleep study? (The Basics)")

SUMMARY AND RECOMMENDATIONS

●In select patients with obstructive sleep apnea (OSA), home sleep apnea testing (HSAT; also referred to as out-of-center sleep testing or portable monitoring) can be used as an alternative to overnight, attended, in-laboratory polysomnography (PSG) for both the diagnosis of OSA and for following the response to therapy. Advantages of HSAT include its convenience (it can be performed in the patient's home or in a hospital room) and lower cost. (See 'Introduction' above.)

●Types 2, 3, and 4 devices are HSAT devices. A type 1 device is an in-laboratory PSG that is not a HSAT but is the gold standard against which all HSAT devices should be compared. (See 'Sleep monitoring devices' above.)

•While a type 2 device measures all the same variables as a type 1 device, it is performed at home and in the absence of a technologist; type 2 devices are not typically used since they are cumbersome at home, the studies are frequently inadequate due to data loss, and the cost savings are minimal compared with PSG.

•Type 3 monitoring devices typically measure between four and seven physiologic variables, including two respiratory variables (eg, respiratory effort and airflow), a cardiac variable (eg, heart rate or an electrocardiogram), and arterial oxyhemoglobin saturation via pulse oximetry (figure 2 and picture 1 and figure 4). Newer devices include the measurement of peripheral arterial tonometry (PAT), oximetry, heart rate, snoring, actigraphy, and body position and have been validated for the diagnosis of OSA.

•Type 4 devices are variably defined as measuring between one and two variables (eg, oxygen saturation, airflow, actigraphy).

●There are several types of HSAT devices available. Each device has different proprietary equipment that measures different variables using different sensors and has different algorithms for the detection and definition of respiratory events. An "adequate" device is defined as one that, at minimum, measures nasal pressure, chest and abdominal respiratory inductance plethysmography, and oximetry. Alternatively, devices that use PAT with oximetry and actigraphy are also appropriate. Thus, the clinician should know what variables are being measured by specific devices so that they can understand the diagnostic limitations of the device used and select an alternate device or in-laboratory testing, if needed. (See 'Choosing an adequate home device' above.)

●The most common indications for HSAT include the diagnostic evaluation of suspected OSA and the follow-up assessment of OSA therapies (eg, positive airway pressure therapy [PAP], oral appliance, surgery). We do not recommend that HSAT be used for positive airway pressure titration since this function has not been well validated and is not available on many devices. (See 'Indications' above and "Clinical presentation and diagnosis of obstructive sleep apnea in adults", section on 'Selecting home or in-laboratory testing' and "Mode selection for titration of positive airway pressure in adults with obstructive sleep apnea".)

●Type 3 and 4 devices have several limitations when compared with PSG including limited ability to detect arousals, underestimation of the apnea hypopnea index (and therefore the severity of OSA), and limited detection of positional OSA, nocturnal seizures, and nocturnal arrhythmias. In addition, type 3 and 4 devices typically cannot adequately examine sleep architecture; thus, HSAT devices should not be used when sleep disorders other than OSA are suspected. (See 'Limitations' above.)

●Several technical considerations need to be present for HSAT to be used successfully as a diagnostic tool. The application, interpretation, and follow-up of HSAT is best handled by experienced sleep healthcare providers. (See 'Technical considerations and interpretation' above.)

●Digital devices are available but are not well-validated. Pulse oximetry is a widely accepted and important component of both polysomnography and HSAT. However, it should not be used alone for the diagnostic evaluation of suspected OSA. (See 'Modes not recommended for home sleep apnea testing' above.)