Home Sleep Testing

1

Introduction

Testing for obstructive sleep apnea (OSA) outside of the sleep laboratory setting has become increasingly common in the United States. Since 2008, when the Centers for Medicare and Medicaid Services (CMS) began reimbursing for the use of home testing, many other insurance companies have accepted, and in many cases, demanded, that testing in the home be used as the preferred method of diagnosis. The preferred terminology is home sleep apnea testing (HSAT), which denotes that the devices utilized for this purpose should be solely used to diagnose OSA. The term home sleep testing is confusing, as in reality, most of these devices do not measure sleep. Another common term, portable monitoring, is also less accurate, as these devices are not “monitored” during acquisition. HSAT has both advantages and disadvantages compared with polysomnography (PSG), but overall should be viewed as adjunctive to our diagnostic capabilities.

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Types of HSAT Devices

Diagnostic testing devices were grouped in a 1994 article by the American Academy of Sleep Medicine (AASM) into four types. Types 1 and 2 represented PSG, with the differentiation being whether the study was attended (type 1) or unattended (type 2). Type 3 has a minimum of four channels which measured airflow, effort, and oximetry. Type 4 has one or two channels, typically oximetry and airflow. Although the literature is full of references to these types, ultimately, the designations were not particularly helpful as they did not provide specificity regarding what the devices actually measured. In 2011, the AASM published a technical evaluation of HSAT devices and developed a unique categorization scheme to help differentiate what signals individual HSAT devices could provide. This paper also reviewed validation literature for devices by category. Unfortunately, this evaluation has not been updated as newer and updated devices have been developed.

HSAT devices typically measure the same signals that are measured during PSG; however, unique devices have been developed as well. The standard HSAT will have an airflow signal, usually a nasal cannula pressure transducer (NCPT), and a respiratory effort measure along with a pulse oximeter. The respiratory effort measure is typically one or two respiratory inductance plethysmography (RIP) belts. The oximeter is usually placed on the patient's finger, and pulse is also derived from this signal. The actual receiver that the signals are plugged in to often contains movement and position detection elements ( Fig. 5.1 ). The software will usually provide an “automated” score, but studies consistently show that automated scoring is inferior to manual scoring, with most users utilizing the automated scoring as the first pass, then reviewing and correcting with a certified polysomnographic technologist.

There are some unique HSAT devices. The WatchPAT device utilizes a signal generated from vascular tone in a finger (usually the first digit) ( Fig. 5.2 ). This “peripheral arterial tonometry” (PAT) signal rises and falls with changes in the sympathetic nervous system and is linked to the oxygen saturation signal, actigraphy, and a snore microphone via a proprietary software algorithm that calculates a breathing disturbance index. The device is attached to the patient's wrist, like a watch.

Another unique device is the Apnea Risk Evaluation System (ARES), which is strapped to the patient's head ( Fig. 5.3 ). It has a sensor box that lies on the forehead and embedded in it are an oximeter, electroencephalogram leads, and a sensor that measures forehead venous impedance, which tracks ventilation. An NCPT attaches to the sensor box, which can also detect head position. Similar to WatchPAT, the device has proprietary software that integrates these signals and provides a breathing disturbance index.

There are several considerations when evaluating an HSAT device. Obviously, the more “leads” there are, the more complicated it becomes for the patient to apply the device. However, lack of redundancy in the data output increases the risk of failure. For instance, using a standard device that has an NCPT and two RIP belts, if you “lose” the NCPT signal, you can utilize the two RIP belts (sum of the belts) as a surrogate for the airflow signal. If you lose a RIP signal, you still have the other RIP belt to provide an effort measure.

Another consideration is if the device provides a “sleep” measure. Devices that only measure breathing parameters require use of the testing time as the denominator for the disordered breathing index. Devices that have a surrogate sleep measure, such as actigraphy or the PAT signal, allow further reduction in the denominator by excluding awake time, hence improving the accuracy of the disordered breathing index.

Regarding the disordered breathing index, there is a lot of confusion regarding the best terminology. The AASM has suggested that for HSAT, the preferred term is the respiratory event index, or REI. This index includes all apneas plus all hypopneas divided by the recording time or surrogate sleep time; it is often used with a subscript of 3 or 4 (REI ₃ or REI ₄ ), which distinguishes whether the hypopneas were scored using a 3% or 4% oxygen desaturation. This differentiates it from the respiratory disturbance index, or RDI, that is often used in PSG, which includes respiratory effort–related arousals (RERAs) plus apneas plus hypopneas divided by total sleep time, and from the Apnea/Hypopnea Index (AHI), which includes apneas plus hypopneas divided by total sleep time.