Use of home sleep studies for diagnosis of the sleep apnoea/hypopnoea syndrome

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1 68 Thorax 1997;52:68 73 Use of home sleep studies for diagnosis of the sleep apnoea/hypopnoea syndrome A T Whittle, S P Finch, I L Mortimore, T W MacKay, N J Douglas Abstract patients referred for investigation is rising rapidly. Background A study was undertaken to New referrals to the Edinburgh sleep clinic test the hypothesis that unsupervised dom- increased -fold between 199 and iciliary limited sleep studies do not impair Most require some form of sleep study for the accuracy of diagnosis when used to diagnosis, and this puts increasing strain on investigate the sleep apnoea/hypopnoea a service based on overnight studies in the syndrome (SAHS) and can be cheaper laboratory. We have therefore investigated the than laboratory polysomnography. validity and practicality of performing limited Methods For validation, 23 subjects with sleep studies unsupervised in the patients suspected SAHS underwent laboratory homes. polysomnography and a home study A number of portable sleep study systems (EdenTec 3711) on successive nights. All have been validated by recording simulsubjects with >15 apnoeas+hypopnoeas taneously with polysomnography in a sleep (A+H)/hour on polysomnography showed laboratory Portable systems have been used >3 A+H/hour on their home study. for epidemiological studies and are increasingly Thereafter, in a prospective trial 15 used routinely for diagnosis or ex- subjects had a home study as the initial clusion of SAHS by sleep services However, investigation and studies showing >3 sleep quality is not recorded in a limited home events/hour were regarded as diagnostic study; subjects may sleep better at home than of SAHS. Those showing fewer events were in a laboratory study 17 but, equally, patients investigated with polysomnography if with severe SAHS may sleep very little. It is necessary. Time to treatment, outcome, therefore important that the use of portable and costs of this protocol were compared systems in the home is validated by comparing with those of 75 patients investigated initially studies performed at home with poly- with polysomnography. somnography. Few of the groups using home Results Of the prospective trial subjects, studies have reported this; one group found 29% had >3 A+H/hour and proceeded that the portable system underestimated the directly from home study to treatment; severity of SAHS % without daytime sleepiness were not Our study had two aims. The first was to investigated further. Polysomnography validate the use of limited sleep studies in was undertaken to establish a diagnosis in the home, and to determine a criterion for a 56% of cases, including 18% whose home confident diagnosis of SAHS from a home studies were unsuccessful. Compared with study. The second was to test in a prospective the 75 control patients, this protocol gave trial whether home studies in clinical practice a diagnosis faster (median 18 (range 221) can maintain diagnostic accuracy and have benefits versus 47 ( 227) days, p<.1) and more in time and cost without affecting outversus cheaply (mean (SD) 164 (4) versus 2 come when compared with an investigative (), p<.1). The proportions offered protocol based on laboratory polysomno- CPAP (61% versus 67%) and subsequent graphy. For home sleep studies we used the objective CPAP usage (mean 4.7 (2.4) versus EdenTrace system which has been validated 5. (2.4) hours/night) were not differ- for laboratory use by simultaneous recording ent. with laboratory polysomnography 5 and is in Conclusions Use of home sleep studies clinical use in several centres. has benefits in time and cost. For diag- Sleep Laboratory, nostic reliability a further sleep study was Respiratory Medicine Unit, Royal Infirmary required in 56% of cases. Methods of Edinburgh, (Thorax 1997;52:68 73) Edinburgh EH3 9YW, SUBJECTS UK The subjects were patients newly referred to A T Whittle Keywords: sleep apnoea/hypopnoea syndrome, home sleep studies, polysomnography. our sleep clinic for investigation of suspected S P Finch SAHS between February 1994 and July 1996 I L Mortimore T W MacKay who lived within 3 miles of our laboratory. N J Douglas The alleged gold standard investigation for the All subjects were judged by NJD or TWM to Correspondence to: diagnosis of the sleep apnoea/hypopnoea syn- require a sleep study as an initial investigation Dr A T Whittle. drome (SAHS) is inpatient overnight poly- on the basis of at least two major symptoms of Received 6 March 1997 somnography 1 and this is recommended as SAHS. 19 Patients were excluded from the trial Returned to authors standard by American 2 and Australasian 3 if they were judged to be physically or mentally 6 May 1997 Revised version received guidelines. However, SAHS may occur in up incapable of using portable sleep study equip- 29 August 1997 to 4% of the middle aged male population 4 Accepted for publication ment unsupervised and no family assistance 3 September 1997 and, as awareness increases, the number of was available, or if there was a clinical suspicion

2 Home sleep studies for diagnosis of SAHS 69 electrocardiogram, chest wall movement by electrical impedance, and finger pulse oximetry. Studies were transferred to paper and scored manually. Apnoea was defined as a cessation of airflow for > seconds and hypopnoea was defined as a reduction of >5% in chest wall movement for > seconds. Frequencies of events were calculated per hour of recording. Studies without four hours of interpretable recording were regarded as technically un- satisfactory. of cataplexy or periodic leg movement disorder. Control patients were new patients living >3 miles from the laboratory who attended the same initial referral clinics as the subjects for the prospective trial (one control selected for every two trial patients at a clinic) and who followed our normal investigation protocol of laboratory polysomnography booked at the time of the clinic. Data from control patients were used for comparison of costs, duration of investigation, and outcome. VALIDATION TRIAL Subjects underwent inpatient polysomnography on night 1. The next morning a trained OUTCOMES sleep technician educated them in the use of All subjects or controls who later attended the portable sleep study system which they took for laboratory titration for nasal continuous home to record themselves unsupervised on positive airway pressure therapy (CPAP) were night 2 and then returned the next day for classified as having been offered CPAP therapy. analysis. Those still in possession of a CPAP system in November 1996 (4 2 months after diagnosis) were classified as continuing CPAP. Objective PROSPECTIVE TRIAL CPAP usage was calculated from the number The diagnostic criteria used in this protocol of hours running time registered on the CPAP were based on the results of the validation trial unit s in-built time clock documented at the (see results below). Subjects underwent a home most recent clinic attendance, averaged over study as an initial investigation after education the number of days since the previous recording in the use of the equipment. Home studies (median 94 days, range 372). showing >3 apnoeas+hypopnoeas (A+H) The cost of inpatient polysomnographic per hour of recording were regarded as diag- studies and home studies included capital depreciation nostic of SAHS and these subjects proceeded of equipment, disposable equipnostic to treatment without further investigation. Sub- ment, medical, technician and nursing time. jects whose home studies showed <3 A+H The cost of overnight hospital stay was included per hour and who denied daytime sleepiness in the cost of the laboratory studies. For the were not investigated further but were given portable system we assumed nights use appropriate advice. The remaining subjects, before replacement and allowed travel expenses including those in whom the home study was for the patient s additional journey to return unsuccessful, were further investigated with the equipment. overnight polysomnography in the laboratory Time to diagnosis was the number of days and managed thereafter according to our usual between the clinic attendance when the decision practice. Bookings for polysomnography were was taken to investigate with a sleep given the same priority as those for control and study, and the date of the study which provided non-trial patients. a diagnosis on which management could be based. Costs and times for subjects in the prospective protocol who underwent two sleep POLYSOMNOGRAPHY studies allow for both studies. Overnight laboratory polysomnography recorded an electroencephalogram (two channels), electro-oculogram (four channels), submental electromyogram, bilateral anterior tibial electromyogram, electrocardiogram, STATISTICAL ANALYSIS summed oronasal airflow by thermocouple, The two forms of sleep study were compared thoracic and abdominal movement by in- in the validation trial by the method of Bland ductive plethysmography, and ear pulse oximetry. and Altman for the assessment of agreement Data were collected on a computerised between methods of clinical measurement. 22 recording system (Compumedics, Melbourne, Normally distributed values are quoted as Australia) but all interpretation and scoring means with standard deviation, and the significance was performed manually by experienced technicians. of differences was assessed by the Sleep was scored on screen by con- two-tailed Student s t test. Other values are ventional criteria. 2 Apnoea was defined as the quoted as medians with range and compared cessation of airflow for > seconds, and hypopnoea as a reduction of >5% in thoracoabdominal movement for > seconds. 21 with the two-tailed Mann-Whitney U test. Where more than one set of variables was compared with control values (tables 1 and 4) the probabilities of significance have been adjusted by the Bonferroni technique. Correlations between non-parametric data are HOME SLEEP STUDIES The EdenTrace system (EdenTec 3711, quoted as Spearman s rank correlation coefficients, and category comparisons were made Nellcor, Eden Prairie, Minnesota, USA) records oronasal airflow by thermocouple, with the χ 2 test.

3 7 Whittle, Finch, Mortimore, MacKay, Douglas interpretable recordings. All polysomnographic studies were interpretable. The 2 home studies showed a median of 25 A+H/hour of recording (range 6 45). Poly- somnography showed a median of 27 A+H/ hour of sleep (range 2 67) (fig 1A). The mean (SD) difference between these scores (polysomnographic minus home study) was +8 (12). A Bland-Altman plot 22 comparing the difference between each pair of results with the mean value of each pair (fig 1B) showed a bias to lower scores on home studies at higher A+H values. The home study A+H/hour recording did, however, correlate significantly with the polysomnography A+H/hour asleep (r=.8, p<.1, fig 1A). When the home study scores were compared with the polysomnographic frequency of A+H/ hour in bed (median 2 A+H/hour, range 2 5) rather than A+H/hour asleep, the Bland-Altman plot showed no bias (fig 1C). The mean (SD) difference was 1 (11) giving limits of agreement 22 (mean difference± 1.96SD between which 95% of differences should lie) of 22 to +21. To obtain a criterion for diagnosis of SAHS from a home sleep study for use in the prospective trial we examined the paired results from the validation trial (fig 1A). A frequency of >15 A+H/hour asleep on polysomnography defines a group of patients who are known to benefit from CPAP therapy 23 and is used in our laboratory as the criterion for a diagnosis of SAHS. All subjects who had a home study score of >2 A+H/hour recording showed >15 A+H/hour asleep on polysomnography. However, the scatter of the paired results suggested that a home study diagnostic cut off of >2 A+H/hour might result in false positive diagnoses when larger numbers were studied so a more conservative criterion for diagnosis of SAHS from a home study of >3 A+H/hour recording was adopted for use in the prospective trial. Results VALIDATION TRIAL Twenty three subjects (19 men) of mean (SD) age 5 (9) years and mean (SD) body mass index (BMI) 3 (4) kg/m 2 completed the protocol. Twenty of the 23 home studies produced HS A+H/hour Difference: PSG A+H/hour asleep HS A+H/hour Difference: PSG A+H/hour in bed HS A+H/hour A Line of identity PSG A+H/hour asleep B Mean outcome: [HS A+H/hour + PSG A+H/hour asleep]/2 C PROSPECTIVE TRIAL Mean outcome: [HS A+H/hour + PSG A+H/hour in bed]/2 Of an initial 15 subjects (table 1) 149 completed the protocol. One subject defaulted after Figure 1 Validation trial. (A) Home sleep studies (HS) an unsuccessful home study. Twenty seven compared with polysomnographic (PSG) apnoeas+hypopnoeas (A+H)/hour asleep: raw data. (18%) home studies produced no interpretable (B) Home sleep studies compared with polysomnographic data. In cases (7%) this was clearly due to A+H/hour asleep: Bland-Altman plot of difference the subject s failure to operate the equipment. against mean value. Horizontal line is the mean Several of the other failures were due to techdifference. (C) Home sleep studies compared with polysomnographic A+H/hour in bed: Bland-Altman plot nical problems inherent in the design of the of difference against mean value. Horizontal lines are equipment which have now been resolved. Submean difference and limits of agreement at the 95% level jects with unsuccessful studies did not differ (mean±1.96 SD). in terms of age, BMI, or subjective daytime sleepiness (Epworth Sleepiness Scale (ESS) 24 Table 1 Characteristics of control patients, prospective trial subjects, and the subset of at time of initial clinic attendance) from those subjects given CPAP titration following a home study as their sole investigation with successful studies, but women were overrepresented in the unsuccessful group (table Control patients Subjects (all) Subjects (direct to CPAP) (n=75) (n=15) (n=4) 2). Mean (SD) age (years) 49 (14) 48 (13) 5 (13) One hundred and twenty three (82%) home (p>.5) (p>.5) studies produced interpretable data (median 19 Sex (% female) 25% 13% 8% A+H/hour recording, range 2 91); 43 (29%) (p=.3) (p=.4) Mean (SD) BMI (kg/m 2 ) 33 () 31 (5) 32 (7) showed >3 A+H/hour recording confirming (p=.1) (p>.5) a diagnosis of SAHS. Of these, 4 subjects Significances refer to differences from control group. commenced CPAP therapy (characteristics in

4 Home sleep studies for diagnosis of SAHS 71 Table 2 Technical success or failure of home studies in the prospective trial: comparison daytime sleepiness. In this selected group the of subject characteristics home study A+H/hour recording and the Successful Unsuccessful Significance A+H/hour asleep from polysomnography cor- (n=123) (n=27) related significantly (r=.38, p<.1, fig 2). Mean (SD) age (years) 47 (13) 51 (12) p=.1 Eighteen subjects (12% of study population) Sex (% female) 7% 37% p=.3 with severe SAHS (polysomnography >3 Mean (SD) BMI (kg/m 2 ) 31 (6) 31 (5) p=.7 Median (range) ESS ( 23) 12 ( 18) p=.7 A+H/hour asleep) had home studies showing <3 A+H/hour recording and four (3%) of these showed <15 A+H/hour recording (table 3). Home study A+H/hour recording 3 2 Line of identity COSTS AND DURATION OF INVESTIGATION The cost of a home study was calculated as 46 and the cost of a laboratory study as 2. The mean cost and median duration of investigation in the 15 prospective trial Polysomnography A+H/hour asleep subjects, allowing for both studies in those who required polysomnography after their home Figure 2 Prospective trial. Home sleep studies compared with polysomnographic A+H/hour asleep in subjects who underwent both investigations (58 subjects with study, were lower than those of the controls daytime sleepiness and home study score <3 A+H/hour). (table 4). The reduction in duration of investigation was due to the avoidance of waiting times for laboratory investigation. Table 3 Prospective trial: comparison between home study and polysomnography results To see whether a lower diagnostic cut off on in subjects undergoing both investigations (58 subjects with daytime sleepiness and home home study scores could have reduced the study scores <3 A+H/hour). Figures are numbers of subjects number of laboratory studies without impairing Polysomnography Home study A+H/hour recording Total diagnostic accuracy we analysed the data from A+H/hour slept the 58 prospective trial subjects who had both < home and laboratory studies. If the criterion < for diagnosis of SAHS from a home study had > been >2 A+H/hour, then 15 subjects with Total home study scores of 2 3 A+H/hour recording would not have undergone polysomnography and would have proceeded table 1), two were referred for tonsillectomy, directly to treatment. Three of these subjects and one declined treatment. in fact had polysomnography scores of <15 Eighty subjects had successful home studies A+H/hour slept and have not been treated (54%) showing <3 A+H/hour recording of with CPAP under our standard protocols, so whom 18 (with studies showing a median of 8 the reduced inconvenience to 15 patients A+H/hour, range 3 19) denied troublesome through avoiding inpatient studies must be set daytime sleepiness (median ESS 4.5, range against the possibly inappropriate initiation of 12) and four others declined further in- CPAP therapy in three patients. The relative vestigation. These subjects were not investigated inconvenience to patients cannot be quantified, further but were given advice but the financial effects can be calculated. The appropriate to their complaints. The remaining minimum initial cost for CPAP therapy for 58 subjects (median 16 A+H/hour, range 2 three patients is 2121 ( 77 per patient for 29) proceeded to overnight laboratory polysomnography. CPAP education, CPAP titration study, and Including 26 whose home provision of CPAP system). The financial sav- studies were unsuccessful, a total of 84 subjects ings from avoiding 15 laboratory studies would (56%) required polysomnography under this be 315 (15 2) giving a potential overall protocol. saving of 29 or 6.86 per subject in the Scores from polysomnography and home prospective trial. studies can therefore be compared in 58 subjects Similarly, a diagnostic threshold of 25 A+H/ who, by definition, had home studies hour on home studies could have reduced the showing <3 A+H/hour but complained of number of subjects undergoing laboratory stud- Table 4 Final outcome of control patients, prospective trial subjects, and the subset of subjects given CPAP titration following a home study as their sole investigation Control patients All subjects Subjects direct to CPAP (n=75) (n=15) (n=4) Median (range) days to diagnosis 47 ( 228) 18 ( 221) 7 ( 98) (p<.1) (p<.1) Mean (SD) cost of sleep studies per patient 2 () 164 (4) 46 () (p<.1) (p<.1) Number offered CPAP (% of total) 5 (67%) 92 (61%) 4 (%) (p>.5) (by definition) Number continuing CPAP (% of those offered CPAP) 4 (8%) 81 (88%) 36 (9%) (p=.4) (p=.4) Mean (SD) CPAP usage (hours/night) 5. (2.4) 4.7 (2.4) 4.9 (2.3) (p>.5) (p>.5) Significance refers to difference from control group.

5 72 Whittle, Finch, Mortimore, MacKay, Douglas ies by nine, of whom two had <15 A+H/hour by this criterion will tend to reduce the practical on polysomnography and have not proceeded benefits shown by the home studies protocol. routinely to CPAP. The overall cost saving The prospective trial confirms the practicality comes to 476 ( 3.17 per subject), again without of an investigative protocol based on quantifying the inconvenience to the home studies for local patients, with an acceptably patients. low rate of technically unsuccessful studies once patients with obvious relevant disabilities are excluded. The results suggest, however, that home studies alone cannot exclude FINAL OUTCOME OF PROSPECTIVE TRIAL a diagnosis of SAHS in patients with daytime SUBJECTS sleepiness. In the group most likely to present When the subjects who had followed the home diagnostic problems that is, those with daystudy protocol were compared with the control time sleepiness but a low or normal home study patients there was no difference in the proscore (<3 A+H/hour recording) the limited portion offered CPAP, the proportion conhome studies failed to identify several subjects tinuing CPAP, or their nightly usage of CPAP. who had severe SAHS on polysomnography. CPAP usage was also identical in the subset The reason for the discrepancy is likely to be whose only investigation was a home study a combination of factors including the night- (table 4). to-night variation in respiratory abnormality seen in any sleep study 25 which is more marked in those with mild SAHS, 26 the tendency of Discussion the limited home study to underestimate the This study shows that an investigative protocol frequency of sleep-related abnormalities in subjects based on home sleep studies can be used to who spend a significant part of the night diagnose SAHS with similar treatment out- awake since actual sleep time is not recorded, come compared with a protocol using laboratory and the different techniques for recording res- polysomnography alone and with reduced piratory variables. This illustrates the potential costs. There is also a benefit in reduced investigation for diagnostic error suggested by the validation time that is dependent on the wait- study and suggests that sleep services or re- ing time for laboratory investigation and will search trials depending solely on home limited vary between different centres. In our centre sleep studies may underestimate the severity of use of this investigative protocol reduced the SAHS or miss the diagnosis in an important demand for laboratory polysomnography by group of patients. 44% and so cut the waiting time for all sleep Debate continues as to whether CPAP treatlaboratory investigations. The reduced contact ment should be guided by the frequency of with laboratory staff and loss of some opportunities respiratory irregularity alone. Pressure for cri- for patient education did not affect terion based therapy from purchasers in the the final outcome in terms of the subjects UK and evidence based approaches overseas 27 uptake or nightly usage of CPAP. We would, are demanding strict definitions as to which however, emphasise the importance of expert SAHS patients should receive CPAP. The technical support for explanation of the use of standard protocol in our laboratory is to offer the portable equipment, CPAP education and CPAP to all those with a polysomnographic mask fitting, and particularly for interpretation AHI of >15/hour who have troublesome sleepiness. of the raw home study data which was all To make a positive diagnosis of SAHS performed manually. from a home study we continue to use the The validation trial shows that, in our clinic conservative criterion of >3 A+H/hour repopulation, the EdenTrace sleep study system cording which was derived from the validation used at home produces a score that correlates trial. The prospective trial indicates that a lower with the polysomnographic A+H averaged cut off would result in a small number of over sleep time (also known as the apnoea/ false positive diagnoses and give a small initial hypopnoea index, AHI) and is thus potentially benefit in financial terms through reducing the usable as a diagnostic test for SAHS. However, number of laboratory studies. Given the in- in terms of actual agreement of recording convenience for patients of an inappropriate methods rather than correlation, the variable trial of CPAP therapy as well as the psycho- measured during a home study (A+H averaged logical and legal consequences of a false diagnosis, over recording time) is equivalent to the polysomnographic we have concluded that in our future frequency of respiratory events practice the diagnostic criterion for home studies averaged over time spent recording, not over should not be changed. time asleep, as the home study gives no information about sleep time. This agreement The authors would like to thank the nursing, administrative, shows wide limits, demonstrating considerable technical, and research staff of the Edinburgh Sleep Laboratory variation in both tests. The home study score is therefore not identical to the polysomnography AHI, and diagnostic criteria derived from polysomnography should be applied with caution. For the design of the prospective part of this trial the diagnostic criterion of >3 A+H/hour on home study which we derived from the validation trial was deliberately conservative. Any bias introduced into the prospective trial for assistance and support. Dr Whittle and Dr Mortimore were supported by the Wellcome Trust. We are not aware of any conflicts of interest. 1 Douglas NJ, Thomas S, Jan MA. Clinical value of polysomnography. Lancet 1992;339: Phillipson EA, Remmers JE. American Thoracic Society Consensus Conference on indications and standards for cardiopulmonary sleep studies. Am Rev Respir Dis 1989; 139: McAvoy RD. Guidelines for respiratory sleep studies. Sydney: Thoracic Society of Australia and New Zealand, 1988.

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