Classification Of Methods For Diagnosis Of Sleepdisordered Breathing

The AASM, formerly known as the American Sleep Disorders Association, in 1994 (16,17) classified diagnostic sleep equipment into four levels (Table 1). Attended PSG has already been described and is Level I. Unattended PSG is Level II. Measurement of a minimum of four channels, which must include oximetry, one channel each of respiratory effort or movement and airflow or two channels of respiratory effort or movement, and heart rate is Level III. A single or two-channel system typically including oximetry is Level IV. For purposes of this review, traditional systems that do not

Sleep Apnea Rera Events

FIGURE 6 A respiratory effort-related arousal (RERA) with a crescendo increase in esophageal pressure (Pes) is depicted in the first half of the epoch. There is a decrease in nasal but not oral airflow, so the abnormal respiratory event does not meet criteria for a hypopnea. Snoring is observed, and the RERA culminates in an arousal, noted by an increase in chin and leg electromyogram tone and an increase in the electroencephalogram signal frequency. The RERA occurs in non-rapid eye movement stage 1 sleep, and the arterial oxygen desaturates to 90%. Following the RERA, there is a resumption of snoring and a crescendo increase in esophageal pressure, and the decrease in both the nasal and oral airflow is more compatible with a hypopnea. The epoch is two minutes in duration. Abbreviations: C3A2 and C4A1, left and right electroencephalogram electrodes placed centrally and referenced to the right (A2) and left (A1) ear, respectively; O1A2 and O2A1, left and right electroencephalogram electrodes placed occipitally and referenced to the right (A2) and left (A1) ear, respectively; Chin EMG, electromyogram recorded from chin muscles; LOCA2, left eye electro-oculogram referenced to the right (A2) ear; ROCA1, right eye electro-oculogram referenced to the left (A1) ear; EKG, electrocardiogram; LAT and RAT, leg movements measured from left and right anterior tibialis, respectively; SaO2, pulse oximetry from a finger sensor; Mic, snoring intensity by microphone; Nasal and Oral, airflow assessed by pressure transducer and thermistor, respectively; Chest and Abdomen, thoracic and abdominal movement, respectively, measured by impedance bands; Pes, esophageal pressure measurements. Source: Courtesy of Clete A. Kushida, M.D., Ph.D.

meet minimum criteria for a Level III will be classified as Level IV. The classification is essentially one of lesser and lesser channels that are typically part of the PSG.

Portable monitoring systems are generally designed to be used unattended usually in the patient's home. However, the systems can also be used attended in the sleep laboratory and this will also be reviewed. For purposes of this paper, attended PSG will be the reference for comparison of portable monitoring systems.

WHAT IS THE PROPER STUDY DESIGN TO VALIDATE A PORTABLE MONITOR?

As discussed in a review published in 2003 (18), validation of a particular device involves comparison to attended PSG with determination of the sensitivity and specificity of the portable monitor. This comparison should be made in a patient population that is representative of the population in which the method is to be

FIGURE 7 A series of increasing snores (noted as increasing duration of activity on the sonogram channel), followed by an arousal marked by an increase in the frequency of the electroencephalogram activity, a leg movement and an increase in chin electromyogram activity. The sleep stage is non-rapid eye movement stage 2 with K complexes prior to the arousal. There is no obvious reduction in airflow or a decrease in arterial oxygen saturation. The epoch is 30 seconds in duration. Abbreviations: LEOG, left eye electro-oculogram; REOG, right eye electro-oculogram; CHIN EMG, electromyogram recorded from chin muscles; C3A2, O2A1, electroencephalogram electrodes placed centrally or occipitally and referenced to the right (A2) or left (A1) ear, respectively; L&R LEGS, sensors placed on each leg and linked to provide a single signal for leg movement; EKG, electrocardiogram; SONOGRAM, snoring intensity by microphone; AIRFLOW, airflow measured by oronasal thermistor; THORACIC and ABDOMINAL, thoracic and abdominal movement, respectively, measured by strain gauges; OXIMETRY, pulse oximetry from a finger sensor.

FIGURE 7 A series of increasing snores (noted as increasing duration of activity on the sonogram channel), followed by an arousal marked by an increase in the frequency of the electroencephalogram activity, a leg movement and an increase in chin electromyogram activity. The sleep stage is non-rapid eye movement stage 2 with K complexes prior to the arousal. There is no obvious reduction in airflow or a decrease in arterial oxygen saturation. The epoch is 30 seconds in duration. Abbreviations: LEOG, left eye electro-oculogram; REOG, right eye electro-oculogram; CHIN EMG, electromyogram recorded from chin muscles; C3A2, O2A1, electroencephalogram electrodes placed centrally or occipitally and referenced to the right (A2) or left (A1) ear, respectively; L&R LEGS, sensors placed on each leg and linked to provide a single signal for leg movement; EKG, electrocardiogram; SONOGRAM, snoring intensity by microphone; AIRFLOW, airflow measured by oronasal thermistor; THORACIC and ABDOMINAL, thoracic and abdominal movement, respectively, measured by strain gauges; OXIMETRY, pulse oximetry from a finger sensor.

used. Patient selection should be consecutive without undue referral biases or at least with the referral bias clearly defined and uninfluenced by the investigator or a small group of providers. In addition, the prevalence of OSA in the study population should be typical of the population for which the device is ultimately to be used. For example, if a method tests only high probability patients for validation, the results cannot be confidently extrapolated to populations of moderate or low probability.

There are two approaches that should be used to validate a portable monitor. First, the sensitivity and specificity under ideal conditions should be determined in a simultaneous comparison with attended PSG. This must be done blinded. The question of whether a technician should intervene depends, in part, on the intended use of the portable monitor. If there is consideration to use the portable monitor with a technician to attend the study, then intervention is appropriate. If the consideration is only for unattended use, then there should be no intervention to repair or correct possible data loss from the portable monitor. This provides the sensitivity and specificity for the diagnosis in direct comparison during the same real-time period as the PSG. The

TABLE 1 American Academy of Sleep Medicine Classification of Levels of Sleep Apnea Testing (Modified)
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