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24 Scoring Center: Polysomnographic Features of Sleep Disordered Breathing - UARS AND RERA By Nic Butkov, RPSGT T he preceding two articles in this series discussed the basic concepts of evaluating respiratory data within the context of sleep-wake physiology.1 This article continues with an exploration of other sleep disordered breathing (SDB) variants and a discussion regarding newly emerging event definitions. Upper Airway Resistance Syndrome The upper airway resistance syndrome (UARS) was described in 1993 by Christian Guilleminault and coworkers at Stanford University.2 The polysomnographic features of UARS include repetitive increases in respiratory effort with consequent EEG arousals, but without airway collapse, oxygen desaturation or hypoventilation. UARS is distinguished from the obstructive sleep apneahypopnea syndrome (OSAHS) by an apnea and hypopnea index (AHI) of less than 5 events per hour and by lack of O2 desaturation.3 Guilleminault describes three possible patterns of UARS based on esophageal pressure measurements (Pes): Pes Crescendo is a progressive, breath-by-breath increase in Pes, terminating in an EEG arousal or activation. Sustained continuous effort is a more stable, yet persistent increase in Pes over a period of several epochs, terminat ing in an EEG arousal. Pes reversal is an abrupt drop in Pes following a sequence of variable respiratory effort, independent of EEG arousal. The clinical symptoms of patients with UARS differ from those with OSAHS. In contrast to the latter, patients with UARS frequently complain of insomnia instead of hypersomnia, and are more likely to present with symptoms of fatigue rather than sleepiness. Patients with UARS are usually non-obese and are often hypotensive instead of hypertensive. Patients with UARS typically have particular craniofacial features, including a high and narrow hard palate and abnormal overbite. Other symptoms related to UARS include postural hypotension, cold hands and feet, history of fainting, anxiety, and complaints of fibromyalgia and chronic fatigue.4 At the present time, the classification of UARS as a distinct syndrome separate from OSAHS remains controversial; however, the constellation of symptoms associated with the polysomnographic features of UARS has been well-documented. Nic Butkov, RPSGT Nic Butkov, RPSGT, has been in the sleep field since 1984 and is Education Coordinator at Rogue Valley Sleep Center and Director of the School of Clinical Polysomnography in Medford, Ore. Respiratory Effort-Related Arousals The term respiratory effort-related arousal (RERA) was introduced by the American Academy of Sleep Medicine (AASM) in 1999, defined as “a sequence of breaths characterized by increasing respiratory effort leading to an arousal from sleep, but which does not meet criteria for an apnea or hypopnea.”5 This definition is similar to the Pes crescendo definition for UARS as described above, and has been used interchangeably with UARS scoring definitions; however, the scoring of RERAs alone does not define UARS. RERAs are more commonly regarded as part of the obstructive sleep apnea-hypopnea continuum, and the threshold at which RERAs are distinguished from obstructive hypopneas is generally based on the most recent hypopnea definition. The new AASM scoring manual has redefined RERA as “a sequence of breaths lasting at least 10 seconds characterized by increasing respiratory effort or flattening of the nasal pressure waveform leading to an arousal from sleep when the sequence of breaths does not meet criteria for an apnea or hypopnea.”6 The AASM manual notes that esophageal pressure measurement is the preferred method of assessing changes in respiratory effort, but allows for the use of nasal air pressure and inductance plethysmography. This differs from the manual’s specification for distinguishing obstructive hypopneas, which states: “Classification of a hypopnea as obstructive, central, or mixed should not be performed without a quantitative assessment of ventilatory effort (esophageal manometry, calibrated respiratory inductance plethysmography, or diaphragmatic EMG).” In actual practice, the only method that adequately provides a quantitative measure of respiratory effort is esophageal manometry. Inductance plethysmography, whether calibrated or noncalibrated, is a surrogate measure of effort that is susceptible to signal distortion caused by patient movement, postural changes, and/or belt displacement. Diaphragmatic EMG cannot provide quantitative ventilatory effort measures because it is a qualitative signal. Without the use of esophageal manometry, RERAs are usually recognized by relative changes in airflow and/or effort preceding an arousal. Essentially, a RERA can be described as a subtle form of obstructive hypopneas, without the requisite O2 desaturation (as currently defined by Medicare). Paradoxical Respiratory Effort Paradoxical respiratory effort refers to out-of-phase movements of the chest and abdomen during inspiration and expiration. This pattern is often regarded as indicative of upper airway obstruction and used to help differentiate between obstructive and central respiratory events. However, paradoxical movements recorded by respiratory belts are not always reliable indicators of airway obstruction. Phase shifts recorded by the belt sensors may be seen in normal individuals, especially during rapid eye movement (REM) sleep. The extent to which paradoxical movement is recorded is also dependent on the type of transducer used, the exact placement of the belts, and the patient’s sleeping position and body habitus. Phase shifts between the thoracic and abdominal respiratory A2Zzz 18.4 | December 2009 25 Figure 1. Respiratory effort-related arousal (2-minute window). This sample demonstrates a respiratory effort-related arousal (RERA), identified by progressive increase in negative esophageal pressures (Pes crescendo), coinciding with decrease in nasal airflow (flow limitation), and terminating with an EEG arousal. By some definitions, this event could be scored as an obstructive hypopnea, except it does not meet the requisite (Medicare) O2 desaturation criterion. Sample provided by Stanford Sleep Medicine Center in Redwood City, CA. A2Zzz 18.4 | December 2009 Continued on Page 26 Figure 2. Evidence of increased upper airway resistance (2-minute window). In this example, an EEG arousal is seen on the left side of the display, associated with a preceding event. Following the arousal, a new cycle begins with increase in negative esophageal pressures (Pes crescendo) and coinciding decrease in nasal airflow (flow limitation). However, the EEG activation (delta burst) seen at the end of this event does not meet current AASM criteria for arousal. (The AASM scoring manual defines arousal as an abrupt shift in EEG frequency including alpha, theta and/or frequencies above 16 Hz. The AASM definition does not include other forms of EEG activation, such as K-complex clusters or delta bursts.) Since it is difficult to adequately discern EEG patterns in a compressed time scale, the effects of any perceived event on the EEG also should be examined using a standard 30-second window display. Sample provided by Stanford Sleep Medicine Center in Redwood City, CA. Continued from Page 25 26 channels are only useful when the signals clearly shift in a cyclical fashion from out-of-phase during the respiratory event, back to in-phase during the recovery breaths. Should RERAs Be Scored? The most accurate method of measuring increased inspiratory effort is by esophageal pressure manometry. However, this method is invasive and is not routinely used by most clinical sleep centers. It has been suggested that nasal air pressure can be used as a measure of flow limitation, whereby the presence of increased airway resistance is represented by a flattening of the nasal air signal waveform. One problem with this approach is that minor changes in the waveform shape can easily be over-scored. While nasal airflow pressure detection is very sensitive to minor changes in airflow, it is also susceptible to artifacts caused by cannula displacement and mouth breathing. Thus, any perceived changes in the airflow pattern must be carefully examined within the context of the EEG to determine whether the changes are associated with EEG arousal or activation. Because of differences in sensor technology, filter configurations, and the manner in which the data are displayed, the airflow flattening effect may vary in appearance. The low-frequency filter should be set to a very low setting (preferably 0.05 Hz or less) to detect the flattening effect. Signal integrity must be verified and maintained by the attending technologist. In some instances, nasal airflow pressure detection may be counterproductive if signal loss is a frequent occurrence. The key feature of RERA is EEG arousal. Without the detection of arousal, changes in airflow shape alone are meaningless. Detection of EEG arousal or activation is contingent on flawlessly recorded EEG signals that are adequately sampled and displayed in an appropriate manner. It is also important to recognize that commonly used criteria for EEG arousals do not address other forms of EEG activation such as delta bursts or Kcomplex clusters. These are more often seen in younger patients with UARS or OSAHS. Because of the subjective nature of RERA recognition, it may be suggested that the presence of suspected RERA patterns should be described in written form rather than tabulated, unless esophageal pressure measurements are recorded and correlated with the EEG. A subjective assessment of the patterns can be clinically relevant, but scoring each individual event could potentially lead to an overestimation of SDB severity. At the present time, the scoring of RERAs does not meet most reimbursement criteria for the treatment of SDB. Clinical Versus Industry-Based Respiratory Event Definitions Sleep technologists should be aware of a growing trend toward industry-based respiratory event definitions, as used in home sleep testing (HST) and positive airway pressure (PAP) compliance data collection. These definitions rely on proprietary algorithms, with signals derived either from PAP flow/pressure sensors (in the case of PAP data collection), or from a limited number of respiratory parameters (in the case of HST devices). The ongoing development of new technologies is essential for the advancement of the field. However, sleep professionals are cautioned against the indiscriminate adoption of industry-based scoring definitions and diagnostic labels. Any claims pertaining to the diagnostic capabilities of these technologies should be carefully assessed in terms of scientific evidence, professional judgment and common sense. For the most part, limited channel HST and PAP data collection systems are useful for detecting unambiguous obstructive apnea. Advanced PAP sensor technology also may help discern between closed and open airway apneas – an important distinction in making titration decisions. However, the main limitation of these systems is lack of information regarding the patient’s physiological state. The estimation of hypopneas, RERAs, flow limitation, or other less obvious forms of SDB may be inaccurate because of normal variants of sleep/wake physiology, movement artifacts, mask leaks, mouth breathing, or sensor displacement. Without having access to the neurophysiological aspects of sleep, it is often difficult to assess the validity or the clinical significance of events tabulated by these devices. Automated Event Scoring and Tabulation Despite the many complexities and ambiguities associated with accurate SDB evaluation, software-based automated scoring options are continually marketed to the sleep field. The algorithms used for automated scoring are usually oversimplified and do not take into account normal variants of sleep/wake physiology, artifacts, or SDB patterns that do not fit common scoring criteria. In most instances, automated scoring functions tend to overestimate respiratory events, leading to misdiagnoses in patients whose symptoms may not even be related to sleep disordered breathing. Attempts have been made to validate automated scoring functions by comparing visual and automated scores, but these are typically conducted within the narrow boundaries of rulebased definitions that have been sufficiently simplified to yield similar results by both methods. Using this approach, the scoring process, whether visual or automated, becomes a perfunctory exercise that is reproducible but does not necessarily reflect clinical reality. A Practical Approach to Accurate SDB Evaluation As discussed in the previous articles, a meaningful interpretation of SDB relies on recognizing clinically significant respiratory phenomena relative to the patient’s physiological state. Accurate event scoring relies on multiple factors, including the quality of the recorded signals, the scorer’s ability to differentiate potentially detrimental events from normal variants of sleep/ wake physiology and from recording artifacts, and the implementation of pattern recognition skills relative to each individual recording. There are no simple scoring formulae that can encompass all the different variants of SDB. The ability to rapidly assess and accurately describe the nature and significance of any suspected respiratory anomaly during sleep largely depends on scorer’s level of experience. Sleep technologists are encouraged to continually seek to improve their skills in this area, not by merely relying on a “cookbook” scoring style, but by careful observation, ongoing practice, and by balancing existing scoring rules with sound professional judgment. A2Zzz 18.4 | December 2009 27 References: 1. Butkov N. Scoring center: polysomnographic features of sleep disordered breathing. A2Zzz. 2009 June;18(2):25-27 and Sept;18(3):26-30. 2. Guilleminault C, Stoohs R, Clerk A, Cetel M, Maistros P. A cause of excessive daytime sleepiness: the upper airway resistance syndrome. Chest. 1993 Sep;104(3):781-7. 3. Guilleminault C, Bassiri A. Clinical features and evaluation of obstructive sleep apnea-hypopnea syndrome and upper airway resistance syndrome. In: Kryger M, Roth T, Dement WC, editors. Principles and practice of sleep medicine. 4th ed. Philadelphia: Elsevier Saunders;2005. p. 1043-1052. 4. 5. 6. Guilleminault C, Chowdhuri S. Upper airway resistance syndrome is a distinct syndrome. Am J Respir Crit Care Med. 2000 May;161(5):1412-13. American Academy of Sleep Medicine. Task Force Report. Sleep-related breathing disorders in adults: recommendations for syndrome definition and measurement techniques in clinical research..Sleep. 1999 Aug 1;22(5):667-89. The AAST acknowledges and thanks the following organizations for their generous support and for investing in the future of the sleep technology profession as ResMed & Respironics, Inc. American American Associatio Associatio nn Sleep TTechnologists echnologists of of Sleep AAST 2009 Cadwell Laboratories, Inc. American Associatio Associatio nn American of Sleep Sleep TT echnologists echnologists of AAST 2009 American Associatio Associatio nn American of Sleep Sleep TT echnologists echnologists of AAST 2009 AAST Supporter Members: Cardinal Health & MVAP Medical Supplies, Inc. American Academy of Sleep Medicine. The AASM manual for the scoring of sleep and associated events: rules, terminology and technical specifications. Westchester, Ill: American Academy of Sleep Medicine; 2007. Ambu/Sleepmate DO YOU NEED A TRANSCRIPT OF YOUR CECs? DON’T WANT TO WAIT UNTIL MARCH? Enjoy your newest member benefit and check your Continuing Education Credits online! IS YOUR RECERTIFICATION DATE COMING UP? IS YOUR SLEEP CENTER UNDERGOING ACCREDITATION? Now you can print transcripts or individual CECs any time of the year, day or night! The AAST has taken your paper transcripts and, instead of mailing them on a yearly basis, moved them online. Simply go to www.AASTweb.org and log in to your account. Click My CEC Credits at the top, and view a transcript of your CECs to date. *Only AAST CECs are listed. AAST CECs will be current as of 90 days prior. Only AAST CECs earned by AAST members while they are active members will be listed. AAST CECs are updated based solely on the attendance rosters that list the names of persons who registered for and participated in AAST-accredited educational programs offered by various educational providers. AAST CECs may not be displayed in a timely manner if attendance rosters are received late or without sufficient information to match AAST CECs to an active AAST member. A2Zzz 18.4 | December 2009