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Role of portable sleep studies for diagnosis of obstructive sleep apnea

Suzanne Boyer and Vishesh Kapur

Purpose of review There is growing awareness of the significance of obstructive sleep apnea in the general population and in the medical community and, as a result, there is a growing demand for diagnosis and treatment. Attended, in-laboratory polysomnography is resource intensive and not readily available in some communities. Alternate diagnostic strategies have been proposed including the use of home sleep studies. Although these portable systems have been in use for many years, only in the past few years have a significant number of studies been performed to evaluate these systems in the home setting. The use of actigraphy and peripheral arterial tonometry for diagnostic purposes has also recently been investigated. Recent findings In the laboratory setting, measurements of sleep-disordered breathing with specific portable sleep systems correspond well with measurements provided by standard polysomnography. In the home setting, portable systems demonstrate several important limitations including lost or inadequate data collection, logistic concerns, and mildly reduced diagnostic accuracy. Data regarding the potential cost benefit of home studies is inconclusive. Summary Home polysomnography is a viable option for evaluating patients with moderate or high clinical suspicion for sleep-disordered breathing. However, patients with failed or equivocal home studies and those with negative studies but persistent symptoms should undergo standard polysomnography. Further investigations are needed to compare long-term outcomes in patients evaluated using portable devices versus standard polysomnography. Keywords obstructive sleep apnea, diagnosis, polysomnography, portable sleep study

Curr Opin Pulm Med 9:465­470. © 2003 Lippincott Williams & Wilkins.

EOG PAT PSG SDB UARS

electrooculogram peripheral arterial tonometry polysomnography sleep-disordered breathing upper airway resistance syndrome

© 2003 Lippincott Williams & Wilkins 1070-5287

Introduction

The American Academy of Sleep Medicine (AASM) classifies sleep study systems into four categories: level I, in-laboratory attended full polysomnography (PSG); level II, unattended home sleep study with comprehensive portable devices incorporating the same channels as the in-laboratory standard PSG; level III, unattended devices that measure at least four cardiorespiratory parameters; and level IV, unattended devices recording one or two parameters [1]. The "gold standard" level I study is monitored by a trained technician and consists of at least two channels of electroencephalogram (EEG), submental and tibialis electromyogram (EMG), two channels of electrooculogram (EOG), respiratory airflow (thermistor or pressure-flow transducer), respiratory effort (thoracic and abdominal breathing movements), oximetry, and electrocardiography. Body position and snoring (via microphone) are also typically recorded. Studies are manually scored and an index (apnea hypopnea index, AHI) of the number of apneas and hypopneas per hour of sleep is used to quantify severity of sleep-disordered breathing (SDB) [2]. With these studies, sleep architecture can be characterized, sleep stage and position-specific severity of SDB can be quantified, and the relation between SDB, leg movements, and arousals can be determined. Respiratory effort-related arousals, the hallmark of upper airway resistance syndrome (UARS), can be detected in particular if nasal pressure transducers or esophageal pressure monitors are used. Attendance by a technician allows for troubleshooting of technical difficulties and the potential initiation of CPAP, if the patient meets criteria for a splitnight study. On the other hand, there are issues that some argue make in-laboratory PSG an imperfect "gold standard". Although there are recent attempts to improve standardization, the literature contains considerable variability in

465

Pulmonary and Critical Care Medicine, University of Washington, Sleep Disorders Center, University of Washington, Seattle, Washington, USA Correspondence to Suzanne Boyer, MD, University of Washington, Sleep Disorders Center, Box 359803, Harborview Medical Center, 325 Ninth Ave., Seattle, WA 98104, USA E-mail: [email protected] Current Opinion in Pulmonary Medicine 2003, 9:465­470 Abbreviations AHI EEG EMG apnea hypopnea index electroencephalogram electromyogram

466 Sleep and respiratory neurobiology

definitions used for hypopnea (primarily in regard to desaturation or arousal criteria) [3], technology used to measure airflow (thermistor versus pressure transducer) [3,4], and the definition of "clinically significant" OSA (AHI cut-points ranging from 5 to 30) [5]. It is also possible that the laboratory setting itself has an effect on the measurement of SDB. Several studies have confirmed a "first night effect" with longer sleep onset latency, reduced sleep efficiency, reduced REM and slow wave sleep, and an increased arousal index during the initial night in a laboratory, compared with subsequent nights or the home setting [6,7]. One study has demonstrated a similar effect on respiratory parameters, with a lower AHI on the first night [7]. Night-to-night variation in SDB may also occur, perhaps related to differences in posture, nasal congestion, medication, or alcohol use. In fact, in patients with high clinical suspicion of disease, several studies have demonstrated that a single negative laboratory PSG may not be adequate to exclude the diagnosis [7,8]. Despite these limitations, most outcome data for OSA is based on results drawn from level I studies and they remain our best standard for comparison. The following is a review of recent literature on the use of level II to level III studies for diagnosis of OSA (Table 1). The extensive literature concerning use of home oximetry (level IV) for diagnosis of SDB is beyond the scope of this review and has been well reviewed elsewhere [9].

Level II studies

Level II systems measure the same sleep and respiratory parameters as standard PSG and thus potentially provide the same amount of information about sleep, respiration, and limb movements [1]. The main disadvantage is the absence of a technician who can make observations about sleep-related phenomenon and detect and rectify technical difficulties, which otherwise may result in lost or inadequate data. Potential benefits for level II studies include reduced cost (ie, no technician or hospital fees), improved availability, and perhaps more "typical" sleep given that patients are sleeping in the home environment. Several level II devices have been validated under laboratory conditions. AHI measured with home systems correlates well with that measured simultaneously with standard PSG (rho = 0.93­0.99) [10­12]. Only one study compared the measurement of AHI in a level II system in the home setting (Minisomno by Mallinckrodt; Les Ulis Courtabouef, France) with that of a laboratory-based standard PSG [13]. This study found an AHI difference of more than 10 in 35% of subjects, though only 10% of subjects were discordantly classified as normal or abnormal (AHI >15 cut-off). A recent crossover study compared home-unattended PSG to nurse-attended PSG in a local hospital with telemonitoring by a sleep laboratory (both studies performed

Table 1. Published studies of portable sleep systems, 2002­2003 Authors Gagnadoux et al. [14··] Quan et al. [16··] Dingli et al. [19··] Equipment (AASM level) Minisomno (II) Compumedics (II) Embletta (III) Number of subjects, setting 99 home and telemonitored hospital setting Blinded 99 each w/two home studies Blinded 40 simult w/lab PSG 61 lab PSG and home test Blinded Signals EEG, EOG, EMG, SaO2, therm, EKG, ch/abd, BP EEG, EOG, EMG, SaO2, therm, EKG, ch/abd, BP Pflow, SaO2, ch/abd, BP Lost data 11.2% tele 23.4% home 8% 18% Results 89% diagnostic agreement Patients preferred telemonitored setting Good internight correlation (ICC = 0.77­0.81) 79­89% diagnostic agreement Very good correlation in lab (rho = 0.98) Good diagnostic agreement w/home study (kappa = 0.57) Manual superior to automatic scoring 36% studies non-diagnostic 42% cost reduction Very good accuracy (AUC ROC 0.93­0.98) Manual superior to automatic scoring 16% studies non-diagnostic Good accuracy (AUC ROC 0.89) Good correlation in lab (rho = 0.88) Good correlation w/home (rho = 0.89) Good accuracy (AUC ROC 0.82­0.87)

Calleja et al. [21·] Golpe et al. [27·] Bar et al. [36··]

MERLIN (III)

86 simult w/lab PSG Blinded 55 lab PSG and home test (28 tech, 27 patient setup) Blinded 102 simult w/lab PSG 14, lab PSG and 2 home studies Blinded

Therm, HR, SaLO2, ch/abd BP, snore Therm, HR, SaO2, BP, actigraphy PAT, HR, SaO2, actigraphy

8%

Apnoescreen I (III) WatchPAT100 (III ?)

7% tech setup 33% pt setup 10.7%

Therm, airflow via thermistor; ch/abd, chest/abdominal wall motion; BP, body position; pflow, airflow via pressure transducer; HR, heart rate.

Portable sleep studies for diagnosis of OSA Boyer and Kapur 467

with the Minisomno) [14··]. Twice as many unattended studies as nurse-monitored studies were considered inadequate for interpretation (23.4 vs. 11.2%). Forty-three percent of subjects had an AHI difference of 10 or greater but the two tests showed discordant classification in only 11% of patients (AHI >10 cut-off). As expected, discordant studies primarily occurred in patients with mild OSA (AHI 10­20). Most studies of home systems focus on referral-based populations with high clinical suspicion for OSA. In contrast, the Sleep Heart Health Study (SHHS) used a level II system (Compumedics PS2, Compumedics Pty. Ltd, Abbotsville, Australia) to measure sleep and SDB in middle-aged adults in the general community. In 6697 participants, 90.6% of initial studies were of acceptable quality for assessing SDB; however, of the acceptable tests, 25% were not of sufficient quality for reliable sleep staging or arousal detection [15]. Ninety-nine subjects drawn from the SHHS participated in a separate study in which two home PSGs were performed within a 4-month period [16··]. This analysis demonstrated a high intraclass correlation for AHI (ICC = 0.77­0.81) for the two home PSGs; 79 to 88% of patients were consistently classified to the same SDB status (depending on AHI cutpoints of >5, >10, and >15). Several studies have highlighted some of the logistic and technical difficulties associated with home PSG. Transportation issues, inconvenience, and/or inability to cooperate with use of fairly complex equipment excluded 26 to 34% of patients initially screened for study inclusion in two trials [10,13]. As mentioned previously, a significant portion of home studies (8­23.4%) were inadequate for interpretation [13,14··,15,16··]. Patient preference was also examined in several studies and, although it was hypothesized that patients would prefer the comfort of having sleep studies performed in their own homes, the opposite was found [10,14··]. Patients reported better sleep quality in the lab and complained of the increased travel and cumbersome equipment required for home studies [10]. No cost-analysis studies have been performed with level II systems.

studies have found well-correlated AHI measurements with simultaneous recording of level III tests and standard PSG in the laboratory (rho = 0.72­0.98) [17­19··, 20]. It should be noted that, with most systems, manual scoring has been found to be superior to automatic scoring [19··,20,21·]. Fewer studies have evaluated level III systems in the home. Two such studies investigated the Edentrace II (model 3711 by Nellcor; Eden Prairie, Minnesota), which measures airflow, chest wall impedance, oximetry, heart rate, snore, and body position. In one study, 89 patients underwent both laboratory PSG and a home study with the Edentrace II within a 1-month period [22]. Diagnostic agreement between the two studies was 89%. Home testing reduced costs by 66%; however, there was no attempt to analyze costs due to inaccurate diagnoses. The second study using the Edentrace II had two phases [18]. In the initial validation phase, 23 patients underwent simultaneous readings with the Edentrace II and standard PSG in a laboratory setting. AHI measured by both techniques was well correlated (rho = 0.8); using this data, criteria were defined for positive (AHI > 30), negative (AHI < 30 and no daytime sleepiness), and nondiagnostic home studies (AHI < 30 with daytime sleepiness). In the second phase, these diagnostic criteria were prospectively applied to 150 subjects who underwent home studies. Positive and negative home tests were treated accordingly and patients with failed or nondiagnostic tests underwent full PSG. The outcomes were compared with those of a control group of 75 patients undergoing standard laboratory PSG in which an AHI greater than or equal to 15 indicated OSA. Of 150 home studies, 18% were technically inadequate, 29% were positive, 12% were negative, and 41% were nondiagnostic. CPAP was prescribed in equal proportions in the home study and standard PSG groups and CPAP compliance rates were similar. The home study protocol was associated with a shorter time to diagnosis and lower cost. The Embletta system (Flaga, Reykjavik, Iceland), which records airflow by nasal pressure transducer, chest/abdominal wall motion, body position, and oximetry, has been similarly evaluated with a two-phase study [19··]. Criteria were defined for positive (AHI 20), negative (AHI < 10), and nondiagnostic home studies (AHI 10­ 19) based on simultaneous home study and standard laboratory PSG in 40 subjects. A second group of 61 patients subsequently underwent home study and laboratory PSG on separate nights. Eleven (18%) of the home studies were technically inadequate. Using the previously mentioned criteria, all 23 (37.7%) patients with positive home studies and all 9 (14.8%) patients with negative home studies were correctly classified based on a PSG AHI less than 15 cut-off point. Eighteen patients (29.5%) had indeterminate tests, of which 15 (83%) had

Level III studies: cardiorespiratory monitoring

Level III sleep studies require a minimum of four channels including respiratory movement, airflow, oxygen saturation, and heart rate or EKG [1]. These studies do not record EEG, EOG, or chin EMG and, therefore, do not allow accurate determination of sleep efficiency or architecture. Without the ability to assess sleep versus wakefulness, the AHI cannot be accurately expressed as "events per hour of sleep" and instead is calculated as "events per hour in bed". For this reason, the AHI may be underestimated in subjects who are awake for a significant part of the night. Despite this concern, multiple

468 Sleep and respiratory neurobiology

PSG AHI greater than or equal to 15. A crude economic analysis suggested that the use of the Embletta system in this manner would reduce costs by 42%.

Level III: cardiorespiratory monitoring utilizing actigraphy

Some level III systems incorporate actigraphy to provide an indirect measure of sleep versus wakefulness. These devices record body movements using a piezoelectric accelerometer. Sleep is defined by periods of inactivity of a predefined duration and wakefulness by periods of increased movement. These systems may better approximate the AHI from standard PSG since the AHI can be expressed per hour of sleep rather than per hour in bed. Unlike PSG, actigraphy does not provide assessment of cortical arousals or sleep stages. Validation studies of actigraphy have demonstrated good correlations with simultaneous polysomnographic measurements for sleep efficiency in normal subjects (rho = 0.71­0.9) [23,24] and moderate correlations for sleep efficiency in sleep apnea patients (rho = 0.63­0.74) [24,25··,26]. The Apnoescreen-I (CNS-Jaëger; Höchberg, Germany), which measures airflow, heart rate, body position, actigraphy, and oximetry, has been evaluated in the home setting with results compared with laboratory-based standard PSG performed on a separate night [27·]. The home study failure rate was 33% in patients who performed self-set up and 7% for patients who were set up by a technician. Of the remaining 44 studies, seven (16%) were diagnostically inconclusive. Thirty-three of the 37 home studies (89%) that gave a "definitive" diagnosis showed agreement with standard PSG results. The authors performed an economic analysis in which it was assumed that technically inadequate or "inconclusive" studies (total of 32.7% of subjects) would be referred for PSG and "diagnostic" studies would be treated accordingly without further evaluation. According to this analysis, home study with technician set-up was least expensive followed by home study with patient set-up and finally full PSG. No head-to-head studies of level III devices with and without actigraphy have been performed. However, one study attempted to assess the added benefit of actigraphy. Patients underwent standard laboratory PSG with simultaneous actigraphy, and AHI was calculated in three ways: using only cardiorespiratory parameters (eg, airflow, chest/abdominal wall movement, oximetry), using cardiorespiratory parameters plus actigraphy, and using full data from PSG [25··]. The results suggested that the addition of actigraphy only modestly improved correlation with PSG AHI (rho = 0.98 with actigraphy vs. 0.94 without actigraphy). However, this study included only 20 subjects, of whom 40% had an AHI of less than 10.

Given the variety of level III systems available and the diversity in study design, methodology, and outcomes, it is difficult to make broad statements about this class of devices. As in level II studies, data loss is a problem (7­33% of home studies) [18,19··,21·,22,27]. To minimize false­positive and false­negative studies, conservative AHI cut-points must be chosen to determine the presence and absence of SDB, which may result in a large portion of "nondiagnostic" studies (11­41%) [18, 19··,27]. Despite these limitations, several of the previously mentioned studies suggest that strategies using level III studies may improve cost and time to diagnosis compared with standard PSG [18,19··,22,27·]. However, other studies using decision analysis models, which include costs related to missed diagnoses and the need for repeated studies, have reported that laboratorybased PSG is more cost effective [28]and offers favorable cost­utility as measured in quality-adjusted life-years gained [29].

Peripheral arterial tonometry: "autonomic arousals" as a surrogate for apnea hypopnea index

Several studies have recently investigated devices that indirectly estimate AHI by identifying surges of sympathetic activation that are associated with termination of respiratory events. These "autonomic arousals" can be seen as variability in heart rate or blood pressure [30]. Peripheral arterial tonometry (PAT) is a noninvasive technique used to measure change in blood flow to the finger, an area that is nearly exclusively regulated by -adrenergic innervation. Several authors have demonstrated that changes in PAT signal occur in response to airway obstruction and arousal from sleep [31,32·,33]. Sympathetic activation may also be seen with spontaneous arousals or periodic leg movement [34,35]. Algorithms taking into account periodicity, duration, and association with heart rate or desaturation have been developed to improve specificity for SDB- related arousals. Peripheral vasculopathy, neuropathy, or autonomic nervous dysfunction related to disease or medication may also affect PAT signal. Potential advantages of such a system include simplicity of equipment for patient use and automatic scoring, which may reduce cost. The Watch PAT100 (Itamar Medical, Caesarea, Israel) is a system that scores respiratory events based on an algorithm including PAT, heart rate, and oxygen saturation; AHI is calculated using actigraphically determined total sleep time. One recent study showed good correlation between AHI measured with simultaneous PAT100 and standard PSG in the laboratory setting (rho = 0.88) [36··]. The mean AHI measured with the PAT100 in 14 patients who underwent two home tests was also highly correlated with PSG AHI (rho = 0.89). The accuracy in diagnosing OSA was good with an area under the ROC curve ranging from 0.82 to 0.87. Compared with many

Portable sleep studies for diagnosis of OSA Boyer and Kapur 469

home systems, the Watch PAT100 is a simple device that requires little patient training; however, the technical failure rate in the home setting was 10.7%.

Conclusion

The search for a simple, inexpensive, and accurate diagnostic test for OSA continues. There are both potential advantages and disadvantages to using home sleep studies for diagnosis of OSA (Table 2). In choosing a diagnostic strategy, local factors must be taken into consideration including population density, disease prevalence, local hospital fees and technician salaries, the ability to perform split-night studies, use of auto-titrating CPAP equipment, and other characteristics of regional health care systems. Accuracy remains a concern. In studies of level II and III systems in the home setting, at least 10% of patients had discordant diagnoses in comparison with "gold standard" PSG [13,14··,22,27]. Whether normal night-to-night variability in SDB or differences in the devices explain the discordance is not clear. It remains to be determined if this disparity has clinical significance. Ideally, future studies are needed to compare outcomes including costs, symptoms, quality of life, and morbidity and mortality of patients evaluated using portable devices versus standard PSG (with and without split-night protocols). This is a rapidly evolving area due to technological advances including miniaturization of recorders, better digital storage devices, and improved sensor design. The findings using one level II or III system may not apply to other similar systems. All devices should be validated with synchronous laboratory PSG and subsequently studied in the home setting to determine reproducibility, accuracy, and frequency of failed data acquisition. More studies are needed to determine if actigraphy or peripheral arterial tonometry will improve portable diagnostic systems. In 1994, the AASM recommended that diagnostic portable studies (level II and III) be used only in patients without access to PSG and in patients with suspected

Table 2. Potential advantages and disadvantages Potential benefits of home studies for OSA diagnosis Lower cost Improve access to OSA evaluation More "typical" sleep in home setting Simplified scoring and interpretation (level III) Potential disadvantages of home studies for OSA diagnosis Data loss and inconclusive studies Inaccurate diagnosis Inability to recognize sleep stage/body position dependent SDB Inability to diagnose other sleep disorders (PLMD, RLS, narcolepsy) Inability to perform split-night study OSA, obstructive sleep apnea; SDB, sleep-disodered breathing; RLS, restless leg syndrome.

severe OSA requiring urgent therapy who do not have timely access to PSG [37]. In 1997, the recommendation was modified to include patients with a high pre-test probability of disease and severe symptoms [38]. In these situations, all negative tests would warrant further evaluation with standard PSG. Based on current literature, it seems reasonable to expand the indications for portable sleep studies to medically stable patients with moderate to high clinical suspicion of disease. Patients with positive home studies should proceed to CPAP titration and treatment. Patients with negative studies but persistent symptoms or failed or equivocal studies should undergo standard PSG. There is not enough data to assess the role of home studies in patients with low clinical suspicion of SDB. Patients with atypical symptoms or who are suspected of having narcolepsy, UARS, parasomnia, or periodic limb movement disorder should have standard PSG as the primary diagnostic test.

References and recommended reading

Papers of particular interest, published within the annual period of review, have been highlighted as: · ·· 1 Of special interest Of outstanding interest Ferber R, Millman R, Coppoly M, et al.: American Sleep Disorders Association Review: portable recording in the assessment of obstructive sleep apnea. Sleep 1994, 17:378­392. Chesson AL, Ferber RA, Fry JM, et al.: American Sleep Disorders Association Review: the indications for polysomnography and related procedures. Sleep 1997, 20:423­487. Redline S, Sanders M: Hypopnea, a floating metric: implications for prevalence, morbidity estimates and case finding. Sleep 1997, 20:1209­1217. Hernandez L, Ballester E, Farre R, et al.: Performance of nasal prongs in sleep studies. Spectrum of flow-related events. Chest 2001, 119:442­450. Hosselet J, Ayappa I, Norman RG, et al.: Classification os sleep-disordered breathing. Am J Resp Crit Care Med 2001, 163:398­405. Kingshott RN, Douglas NJ: The effect of in-laboratory polysomnography on sleep and objective daytime sleepiness. Sleep 2000, 23:1109­1113. LeBon O, Hoffman G, Tecco J, et al.: Mild to moderate sleep respiratory events. One negative might not be enough. Chest 2000, 118:353­359. Meyer TJ, Eveloff SE, Kline LR, et al.: One negative polysomnogram does not exclude obstructive sleep apnea. Chest 1993, 103:756­760. Netzer N, Eliasson AH, Netzer C, et al.: Overnight pulse oximetry for sleepdisordered breathing in adults: a review. Chest 2001, 120:625­633. Fry JM, DiPhillipo MA, Curran K, et al.: Full polysomnography in the home. Sleep 1998, 21:635­642. Mykytyn IJ, Sajkov D, Neill AM, et al.: Portable computerized polysomnography in attended and unattended settings. Chest 1999, 115:114­122. Orr WC, Eiken T, Pegram V, et al.: A laboratory validation stud of a portable system fr remote recording of sleep-related respiratory disorders. Chest 1994, 105:160­162. Portier F, Portmann A, Czernichow P, et al.: Evaluation of home versus laboratory polysomnography in the diagnosis of sleep apnea syndrome. Am J Respir Crit Care Med 2000, 162:814­818. Gagnadoux F, Pelletier-Fleury N, Philippe C, et al.: Home unattended vs hospital telemonitored polysomnography in suspected obstructive sleep apnea syndrome: a randomized crossover trial. Chest 2002, 121:753­758.

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470 Sleep and respiratory neurobiology

Novel approach utilizing nurse-attended PSG in a local hospital with telemonitoring by a sleep laboratory versus unattended home PSG. High technical failure rate in unattended studies. Good diagnostic agreement. Patients preferred hospitalbased testing. 15 Redline S, Sanders M, Lind B, et al.: Methods for obtaining and analyzing unattended polysomnography data for a multicenter study. Sleep 1998, 21:759­767. 26 Kushida C, Chang A, Gadkary C, et al.: Comparison study of actigraphic, polysomnographic, and subjective assessment of sleep parameters in sleepdisordered patients. Sleep Medicine 2001, 2:389­396.

16 ··

Quan SF, Griswold ME, Iber C, et al.: Short-term variability of respiration and sleep during unattended nonlaboratory polysomnography--the Sleep Heart Health Study. Sleep 2002, 25:8­14. Subgroup of 99 participants of Sleep Heart Health Study underwent two level II sleep studies demonstrating high internight correlation of AHI measurement and good agreement in diagnostic classification. The SHHS is the only study evaluating a level II device applied to a general community (rather than sleep clinic referralbased population). 17 18 Claman D, Murr A, Trotter K: Clinical validation of the Bedbugg in detection of obstructive sleep apnea. Otolaryngol Head Neck Surg 2001, 125:227­230. Whittle AT, Finch SP, Mortimore IL, et al.: Use of home sleep studies for diagnosis of the sleep apnoea/hypopnoea syndrome. Thorax 1997, 52:1068­1073.

27 Golpe R, Jimenez A, Carpizo R: Home sleep studies in the assessment of sleep apnea/hypopnea syndrome. Chest 2002, 122:1156­1161. · Compared home study with level III system including actigraphy to standard PSG and demonstrated good diagnostic agreement. One third of home studies were "inconclusive" or technical failures. 28 Reuven H, Schweitzer E, Tarasiuk A: A cost-effectiveness analysis of alternative at-home or in-laboratory technologies for the diagnosis of obstructive sleep apnea syndrome. Med Decis Making 2001, 21:451­458. Chervin RD, Murman DL, Malow BW, et al.: Cost-utility of three approaches to the diagnosis of sleep apnea: polysomnography, home testing and empirical therapy. Ann Intern Med 1999, 130:496­505. Pitson DJ, Stradling JR: Autonomic markers of arousal during sleep in patients undergoing investigation for obstructive sleep apnea, their relationship to EEG arousals, respiratory events and subjective sleepiness. J Sleep Res 1998, 7:53­59. Schnall RP, Shlitner A, Sheffy J, et al.: Periodic, profound peripheral vasoconstriction-a new marker of obstructive sleep apnea. Sleep 1999, 22:939­946.

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Dingli K, Coleman EL, Vennelle M, et al.: Evaluation of a portable device for diagnosing the sleep apnoea/hypopnoea syndrome. Eur Respir J 2003, 21:253­259. Phase one, validation study showed high correlation between simultaneous standard PSG and Embletta. Phase two prospectively applied diagnostic strategy using Embletta compared with standard PSG on the second night. Good diagnostic agreement, though nearly half of studies were "inconclusive" or technical failures. 19 ·· 20 Esnaola S, Duran J, Infante-Rivard C, et al.: Diagnostic accuracy of a portable recording device (MESAM IV) in suspected obstructive sleep apnoea. Eur Respir J 1996, 9:2597­2605.

32 Pillar G, Bar A, Shlitner A, et al.: Autonomic arousal index: an automated detection based on peripheral arterial tonometry. Sleep 2002, 25:543­549. · The "autonomic arousal index" measured via peripheral arterial tonometry is well correlated with cortical arousals measured on simultaneous EEG. O'Donnell CP, Allan L, Atkinson P, et al.: The effect of upper airway obstruction and arousal on peripheral arterial tonometry in obstructive sleep apnea. Am J Respir Crit Care Med 2002, 166:965­971. Both airflow obstruction and arousal from sleep result in increased sympathetic activation causing digital vasoconstriction, which can be reliably measured as a change in peripheral arterial tonometry (PAT) signal. 33 · 34 35 36 ·· Sforza E: EEG and cardiac activation during periodic leg movements in sleep: support for a hierarchy of arousal responses. Neurology 1999, 52:786­791. Winkelman W: The evoked heart rate response to periodic leg movements of sleep. Sleep 1999, 22:575­580.

Calleja JM, Esnaola S, Rubio R, et al.: Comparison of a cardiorespiratory device versus polysomnography for diagnosis of sleep apnoea. Eur Respir J 2002, 20:1505­1510. Validation study testing "unattended" MERLIN versus simultaneous PSG in laboratory setting; 8% failure rate, good accuracy, manual scoring superior to automatic. 21 · 22 Parra O, Garcia-Esclasans N, Montserrat JM, et al.: Should patients with sleep apnoea/hypopnoea syndrome be diagnosed and managed on the basis of home sleep studies? Eur Respir J 1997, 10:1720­1724. Cole RJ, Kripke DF, Gruen W, et al.: Automatic sleep/wake identification from wrist actigraphy. Sleep 1992, 15:461­469. Sadeh A, Hauri P, Kripke D, et al.: The role of actigraphy I the evaluation of sleep disorders. Sleep 1995, 18:288­302.

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Bar A, Pillar G, Dvir I, et al.: Evaluation of a portable device based on peripheral arterial tone for unattended home sleep studies. Chest 2003, 123:695­ 703. The first study to validate peripheral arterial tonometry as a tool to indirectly estimate AHI. The WatchPAT100, using PAT signal, oxygen saturation, heart rate, and actigraphy, provides highly correlated AHI measurements (rho = 0.88) and accurate diagnosis of OSA (AUC ROC 0.82 for AHI >10) in comparison with standard PSG. 37 Thorpy M, Chesson A, Ferber R, et al.: American Sleep Disorders Association Standards of Practice: practice parameters for the use of portable recording in the assessment of obstructive sleep apnea. Sleep 1994, 17:372­377. Chesson AL, Ferber RA, Fry JM, et al.: American Sleep Disorders Association Standards of Practice: practice parameters for the indications for polysomnography and related procedures. Sleep 1997, 20:406­422.

25 Elbez M, Roue GM, Lofaso F, et al.: Utility of actigraphy in the diagnosis of obstructive sleep apnea. Sleep 2002, 25:527­531. ·· The addition of actigraphy to cardiorespiratory parameters offered slight benefit over cardiorespiratory parameters alone (comparison of AHI based on "sleep time" vs. "time in bed").

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