Home Oximetry Studies for Diagnosis of Sleep Apnea/Hypopnea Syndrome: Limitation of Memory Storage Capabilities

doi:10.1378/chest.120.2.384

Chest

Volume 120, Issue 2, August 2001, Pages 384-389

https://doi.org/10.1378/chest.120.2.384 Get rights and content

Background

Memory oximeters enable diagnostic studies for sleep apnea hypopnea syndrome (SAHS) to be performed in the home. However, memory capabilities may be limited.

Study Objectives

To compare a pulse oximeter used at home with an 8-h memory, storing data every 12 s, and in the laboratory, with on-line recording every 2 s.

Design

Prospective cohort study.

Setting

Patients' homes and a sleep laboratory.

Patients

One hundred patients with suspected SAHS.

Measurements

Home oximetry and a laboratory full polysomnography. The number of ≥ 4% dips in pulse oximetric saturation (Spo₂) was calculated for each study. Daytime sleepiness was assessed by the Epworth Sleepiness Scale (ESS) score.

Results

The mean dips per hour were 5.3/h (range, 0 to 53/h) for home studies and 13.4/h (range, 0 to 106/h) for laboratory studies; the relationship between home and laboratory studies was as follows: home = (0.4 × laboratory) − 0.01 ± 11.2; r² = 0.64. Mean difference was 8.4/h (− 2.5 to + 77.9/h), which correlated with the mean of the measurements. At a cutoff point of 10/h, 52 studies were both negative and 13 studies were both positive. Nineteen home studies were false-negatives. Sensitivity was 0.41, and specificity was 1.0. In these 19 studies, 7 patients had an ESS score > 10 and 4 patients had an ESS score > 14. To confirm that differences were due to different sampling rates, 16 additional patients had on-line data and stored data collected simultaneously in the laboratory. Mean dips per hour were 3.2/h (range, 0.1 to 18.3/h) for the stored data and 8.34/h (0.2 to 22.8/h) for on-line data; the relationship being stored was as follows: 0.5 on-line − 1.17 ± 2.6; r² = 0.69. Mean difference was 5.2/h (0.04 to 15.4 h), which correlated with the mean of the measurements.

Conclusion

Home studies using a memory storage pulse oximeter may underestimate the number of hypoxic dips, probably due to sampling rates. Clinically significant hypoxic SAHS may therefore be missed.

Section snippets

Patients

One hundred consecutive patients were studied. They were referred from ear, nose, and throat surgeons, primary-care physicians, and other chest physicians for assessment of suspected SAHS using full polysomnography. All completed an Epworth Sleepiness Score (ESS).⁸

Pulse Oximeter

The oximeters used in this study were the Biox 3740 (Ohmeda; UK). For the home and laboratory studies, the oximeters were identical, including the software version (version 9) and the default settings. Signal averaging defaulted to 6

Results

All subjects completed the studies without difficulty. None of the subjects consumed alcohol on either of the study nights.

Discussion

The results of this study show that home oximetry studies using the oximeters used in this study in patients with suspected SAHS significantly underestimate the number of episodes of hypoxemia during sleep, and may therefore miss more clinically significant SAHS than oximeter studies analyzed on-line in the hospital. The results suggest that this is due to the memory capability of the oximeter, in that a data point is stored every 12 s as compared to every 2 s when recordings are made on-line

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Pulse oximetry is currently used in many clinical applications. Usually reliable and accurate, a good knowledge of the limitations in measurement is necessary before use. This paper describes technical principles and limitations of pulse oximetry.
Long-term screening for sleep apnoea in paced patients: Preliminary assessment of a novel patient management flowchart by using automatic pacemaker indexes and sleep lab polygraphy
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Alternative techniques are being developed, which need fewer sensors and in some cases rely on single parameters. However, most current alternatives tend to be less reliable than conventional PSG [6–11] although nasal pressure and heart-rate variability (HRV) have shown promise in preliminary studies [12,13]. OSAS is highly prevalent among patients indicated for cardiac pacemakers [14].
The primary aim of this pilot study was to prospectively assess a flowchart to screen and diagnose paced patients (pts) affected by sleep apnoeas, by crosschecking indexes derived from pacemakers (minute ventilation sensor on-board) with Sleep-Lab Polygraphy (PG) outcomes. Secondarily, “smoothed” long-term pacemaker indexes (all the information between two consecutive follow-up visits) have been retrospectively compared vs. standard short-term pacemaker indexes (last 24 h) at each follow-up (FU) visit, to test their correlation and diagnostic concordance.
Data from long-term FU of 61 paced pts were collected. At each visit, the standard short-term apnoea+hypopnoea (PM_AHI) index was retrieved from the pacemaker memory. Patients showing PM_AHI ≥ 30 at least once during FU were proposed to undergo a PG for diagnostic confirmation. Smoothed pacemaker (PM_SAHI) indexes were calculated by averaging the overall number of apnoeas/hypopnoeas over the period between two FU visits, and retrospectively compared with standard PM_AHI.
Data were available from 609 consecutive visits (overall 4.64±1.78 years FU). PM_AHI indexes were positive during FU in 40/61 pts (65.6%); 26/40 pts (65%) accepted to undergo a PG recording; Sleep-Lab confirmed positivity in 22/26 pts (84.6% positive predictive value for PM_AHI). A strong correlation (r=0.73) and a high level of concordance were found between smoothed and standard indexes (multivariate analysis, Cohen's-k and Z-score tests).
Pacemaker-derived indexes may help in screening paced pts potentially affected by sleep apnoeas. Long-term “smoothed” apnoea indexes could improve the accuracy of pacemaker screening capability, even though this hypothesis must be prospectively confirmed by larger studies.
Pediatric Polysomnography
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Pediatric polysomnography is the diagnostic study of choice to evaluate for obstructive sleep apnea in children, and to evaluate cardiorespiratory function in infants and children with chronic lung disease, or neuromuscular disease when indicated. It is helpful to investigate atypical cases of parasomnias. It is important to understand that children are not just small adults when being studied in a sleep laboratory; they require a child friendly atmosphere and approach, need smaller and specialized equipment, and because of developmental and physiologic differences from adults, have age-adjusted rules for the scoring and interpretation of polysomnograms.
Association of sleep-disordered breathing with postoperative complications
2008, Chest
Citation Excerpt :
Overnight polysomnography is the “gold standard” for the diagnosis of OSA but may be impractical during preoperative assessment. Home nocturnal oximetry has been studied as a potential screening tool, although a wide range of sensitivity and specificity for OSA has been reported.789101112131415161718192021 Furthermore, prior studies using this modality did not correlate the results of home oximetry testing with perioperative outcomes.
Obstructive sleep apnea (OSA) is associated with increased perioperative risk, but the incidence of postoperative complications and the severity of OSA associated with increased risk have not been established. We investigated the relationship between intermittent hypoxemia measured by home nocturnal oximetry with the occurrence of postoperative complications in patients with clinical signs of OSA identified during preoperative assessment for elective surgery.
This study was performed at a tertiary care hospital. Home nocturnal oximetry was performed on elective surgical patients with clinical features of OSA. The number of episodes per hour of oxygen desaturation (or oxygen desaturation index) of ≥ 4% (ODI4%) was determined. Subjects with five or more desaturations per hour (ODI4%≥ 5) were compared to those with less than five desaturations per hour (ODI4%< 5). Hospital records were reviewed to assess the incidence and type of postoperative complications.
A total of 172 patients were investigated as part of this study. No significant differences were observed between groups in terms of age, body mass index, number of medical comorbidities, or smoking history. Patients with an ODI4%≥ 5 had a significantly higher rate of postoperative complications than those with ODI4%< 5 (15.3% vs 2.7%, respectively [p < 0.01]; adjusted odds ratio, 7.2; 95% confidence interval, 1.5 to 33.3 [p = 0.012]). The complication rate also increased with increasing ODI severity (patients with an ODI4% of 5 to 15 events per hour, 13.8%; patients with an ODI4% of ≥ 15 events per hour, 17.5%; p = 0.01) Complications were respiratory (nine patients), cardiovascular (five patients), GI (one patient), and bleeding (two patients). The hospital length of stay was similar in both groups.
An ODI4%≥ 5, determined by home nocturnal oximetry, in patients with clinical features of OSA is associated with an increased rate of postoperative complications.
Improving diagnostic ability of blood oxygen saturation from overnight pulse oximetry in obstructive sleep apnea detection by means of central tendency measure
2007, Artificial Intelligence in Medicine
Nocturnal pulse oximetry is a widely used alternative to polysomnography (PSG) in screening for obstructive sleep apnea (OSA) syndrome. Several oximetric indexes have been derived from nocturnal blood oxygen saturation (SaO₂). However, they suffer from several limitations. The present study is focused on the usefulness of nonlinear methods in deriving new measures from oximetry signals to improve the diagnostic accuracy of classical oximetric indexes. Specifically, we assessed the validity of central tendency measure (CTM) as a screening test for OSA in patients clinically suspected of suffering from this disease.
We studied 187 subjects suspected of suffering from OSA referred to the sleep unit. A nocturnal pulse oximetry study was applied simultaneously to a conventional PSG. Three different index groups were compared. The first one was composed by classical indexes provided by our oximeter: oxygen desaturation indexes (ODIs) and cumulative time spent below a saturation of 90% (CT90). The second one was formed by indexes derived from a nonlinear method previously studied by our group: approximate entropy (ApEn). The last one was composed by indexes derived from a CTM analysis.
For a radius in the scatter plot equal to 1, CTM values corresponding to OSA positive patients (0.30 ± 0.20, mean ± S.D.) were significantly lower (p ≪ 0.001) than those values from OSA negative subjects (0.71 ± 0.18, mean ± S.D.). CTM was significantly correlated with classical indexes and indexes from ApEn analysis. CTM provided the highest correlation with the apnea–hipopnea index AHI (r = −0.74, p < 0.0001). Moreover, it reached the best results from the receiver operating characteristics (ROC) curve analysis, with 90.1% sensitivity, 82.9% specificity, 88.5% positive predictive value, 85.1% negative predictive value, 87.2% accuracy and an area under the ROC curve of 0.924. Finally, the AHI derived from the quadratic regression curve for the CTM showed better agreement with the AHI from PSG than classical and ApEn derived indexes.
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All original diagnostic accuracy studies published in 1993 in a predefined set of journals were selected. Validation of these studies was assessed in the original article and in articles published within a period of 10 years, through a literature search and contacting the authors.
None of the original studies reported any form of validation. Validation studies published later could be identified for 7 of the 11 original studies. Test characteristics were difficult to compare. Despite what was generally believed, not every validation study showed results inferior to the original. We found more studies that evaluated the test in a different population than in a similar one.
Not every diagnostic accuracy study is validated. Diagnostic tests are more often repeated in different populations.

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Chest

Clinical InvestigationsSleep And BreathingHome Oximetry Studies for Diagnosis of Sleep Apnea/Hypopnea Syndrome: Limitation of Memory Storage Capabilities

Background

Study Objectives

Design

Setting

Patients

Measurements

Results

Conclusion

Section snippets

Patients

Pulse Oximeter

Results

Discussion

Chest

Lancet

Chest

Quantification of sleep disordered breathing by computerized analysis of oximetry, heart rate and snoring

Eur Respir J

Utility of nocturnal home oximetry for case finding in patients with suspected sleep apnea hypopnea syndrome

Ann Intern Med

A comparison of clinical assessment and home oximetry in the diagnosis of obstructive sleep apnea

Am Rev Respir Dis

Evaluation of the Ohmeda 3700 pulse oximeter

Thorax

A new method of measuring daytime sleepiness: the Epworth Sleepiness Scale

Sleep

Monitoring and staging human sleep

Minitab

Clinical Investigations
Sleep And Breathing
Home Oximetry Studies for Diagnosis of Sleep Apnea/Hypopnea Syndrome: Limitation of Memory Storage Capabilities