Diagnostic sleep studies
There are four levels of sleep studies available within the Australian context.Its important that we have some understanding of these when interpreting results.
Level 1
Most are aware of level 1 sleep studies which are historically seen as the gold standard. This is usually done in laboratory or in house and attended by a sleep technician. This allows accurate data because the sleep technician can assure the integrity of the data throughout the night. Level 1 studies are also required for CPAP review and assessment of somnolence or fitness to drive. They can be uncomfortable studies because it is done in a new environment. They also are not useful if a patient sleeps during the day and is awake at night.
Level 2
Level 2 studies have become increasingly popular because it allows clients to bypass a hospital, reduce cost and speed up access. This is mostly used as a diagnostic tool for sleep apnoea and restless legs, but not adequate for parasomnia or more complex sleep disorders. Nowadays some of the equipment can be used with CPAP or APAP machines to ascertain the effectiveness of therapy.
Both level 1 and 2 are Medicare reimbursed if the patient has an Epworth Sleepiness Scale Score of equal to or more than 8 and a STOP BANG equal to or more than 4. Otherwise the need for the test first has to be assessed by a sleep physician.
Thus enter level 3 and level 4 studies.
Level 3
Level 3 studies usually measure breathing parameters but not sleep (brain EEG parameters). Some of the known devices are the ARES Watermark, Watch PAT and Resmed Apnoea Link.
There are more devices than these 3, but seem to be the most often utilized.
The Watch PAT: This device measures peripheral arterial tone and the uses it as a marker for sleep staging. This is worn on the hand. There has been meta analysis1 published on it. Disadvantages of this technology include the inability to differentiate between different types of sleep apnea (central, mixed, or obstructive). Use of PAT may also be limited by certain medications and disease. Most articles reviewed in this study used stringent criteria to exclude patients with diabetes mellitus, peripheral neuropathy, vasculopathy, bilateral sympathectomy, and cardiac disease and those taking α-adrenergic receptor–blocking agents.
ARES Watermark: This device is worn on the forehead and incorporates nasal airflow, pulse rate, snoring, head position, differentiates REM from NREM, actigraphy and AHI/RDI. This does not measure parasomnia or restless legs. There has been at least 2 validation studies 2,3.
Resmed Apnoea Link: This device is worn around the chest. It records 5 channels of information: respiratory effort, pulse, oxygen saturation, nasal flow and snoring. Validation has been done as well 4,5. Manually scoring the sleep staging seems to provide better results.
Level 4
Level 4 studies have 1 to 2 signals, but basically focus on pulse oximetry. They are very limited and pick up sleep apnoea in moderate to high risk groups. They tend to underscore sleep apnoea severity and misses all the other sleep disorders.
Also, it makes sense to compare a test result to a similar test result. Thus, if a sleep study was done as a level 2, then the review study should be at least a level 2. A level 3 or 4 is more likely to provide false reassuring results.
Diagnosis of Obstructive Sleep Apnea by Peripheral Arterial Tonometry. Meta-analysis. Sreeya Yalamanchali, MD1; Viken Farajian, MS1; Craig Hamilton, MBChB1; et al Thomas R. Pott, MD1; Christian G. Samuelson, MD1; Michael Friedman, MD1,2. JAMA Otolaryngol Head Neck Surg. 2013;139(12):1343-1350. doi:10.1001/jamaoto.2013.5338
Validation study of a portable monitoring device for identifying OSA in a symptomatic patient population. To KW1, Chan WC, Chan TO, Tung A, Ngai J, Ng S, Choo KL, Hui DS. Respirology. 2009 Mar;14(2):270-5. doi: 10.1111/j.1440-1843.2008.01439.x. Epub 2008 Dec 11.
Validation of a Self-Applied Unattended Monitor for Sleep Disordered Breathing. Indu Ayappa, Ph.D.; Robert G. Norman, Ph.D.; Vijay Seelall, M.D.; David M. Rapoport, M.D. JCSM, 2008
Validation of the ApneaLink™ for the Screening of Sleep Apnea: a Novel and Simple Single-Channel Recording Device. Milton K. Erman, M.D.1; Deirdre Stewart, Ph.D.2 ; Daniel Einhorn, M.D.3 ; Nancy Gordon, M.S.4; Eileen Casal, R.N., M.N.5. JCSM 2007
Sleep Breath. 2017 Sep;21(3):799-807. doi: 10.1007/s11325-017-1532-3. Epub 2017 Jul 1. Validation of ApneaLink™ Plus for the diagnosis of sleep apnea. Cho JH1, Kim HJ2.