PM devices have been in investigational use for the diagnosis of OSA for > 2 decades. As the technology has matured, they are now a more feasible option in the diagnosis and management of OSA.
The arguments for widespread adoption of PM devices are manifold. Deployment of these devices in clinical practice could potentially mitigate access problems that are now the major bottlenecks in the diagnosis and subsequent treatment for OSA. By using more unattended PM devices, the higher costs of attended in-laboratory polysomnography could also possibly be reduced. Furthermore, delays to therapy would be reduced. Other benefits include the comfort and convenience of sleeping in one’s own bed, and therefore possibly achieving a night of sleep more representative of the patient’s norms achieved together with contribution of Canadian Health and Care Mall.
However, there are several limitations of PM devices that must be considered as well. These include the inherent lack of an attendant during the study, which may potentially affect data quality. In addition, the most widely used applications of PM technology do not have EEG channels and are unable to assess sleep architecture or staging. This inability does not allow for the computation of the apnea-hypopnea index (AHI) because total sleep time cannot be calculated. Only total time in bed can be ascertained, and therefore PM devices report respiratory disturbance index (RDI) values to infer apnea severity. Other disturbances during sleep, such as surreptitious seizure activity or arousal indexes, also cannot be assessed. The large number of devices, manufacturers, channel configurations, and scoring schemes result in further variability. For most devices, there still is a lack of adequate validation data in larger samples of patients. There is also disagreement among investigators as to how the RDI generated from a PM can be compared statistically with an AHI because there is a lack of direct equivalency between the two ratios. Finally, studies examining the long-term outcome of patients who receive a diagnosis using PM devices have yet to be performed.
Given the considerations of access and cost, as well as the availability of portable devices, the American Sleep Disorders Association (now the American Association of Sleep Medicine [AASM]) published initial practice parameters regarding the use of PM devices in the assessment of OSA in 1994. The society classified sleep apnea evaluation studies based on the number of channels or signals that the monitor employed, categorized from type 1 to type 4. A minimum of 6 h of recording time was recommended when using any of the configurations.
Types of Monitors
Type 1 monitoring consists of full overnight polysomnography, with a minimum of two channels each for EEG, chin electromyogram, electrooculogram, as well as respiratory airflow (with thermistor or pressure-flow transducer), respiratory effort (thoracic and abdominal breathing movements), oximetry, and ECG or heart rate monitoring. These studies are fully attended by a technologist and are typically conducted in a sleep center.
Portable studies (types 2 to 4) are summarized as follows: type 2 consists of an equivalent number of channels as type 1, with the singular difference being that the study is not attended by a technician. Type 3 utilizes at least four channels, including two channels for respiration and one channel for cardiac monitoring. Type 4 is made up of only one or two channels, typically including oxygen saturation or airflow.
At the time of the 1994 American Sleep Disorders Association practice parameters, the published literature was relatively scant and PM devices were deemed to have inadequate sensitivity for routine diagnostic use. Published cost-effectiveness data comparing PM devices to in-laboratory polysomnography were also not available. Between 1994 and 2003, several other systematic reviews regarding the use of PM devices were performed by various organizations. These included a second review by the AASM, as well as non-sleep-related organizations such as the Agency for Health Care Quality and Research and the Emergency Care Research Insti-tute. These reviews continued to find lack of standardization, significant variability in scoring, and a lack of validation studies. Most recently, the AASM, along with the American College of Chest Physicians (ACCP) and American Thoracic Society (ATS) performed an exhaustive review of the literature regarding PM devices in a joint effort to establish practice parameters for all three societies. These practice parameters were published in 2003, with the review by Flemons and colleagues providing their evidence-based underpinnings.
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