Importance of the pulse oximeter averaging time when measuring oxygen desaturation in sleep apnea

Fast cycling of intermittent hypoxia in a physiomimetic 3D environment: A novel tool for the study of the parenchymal effects of sleep apnea

Background: Patients with obstructive sleep apnea (OSA) experience recurrent hypoxemic events with a frequency sometimes exceeding 60 events/h. These episodic events induce downstream transient hypoxia in the parenchymal tissue of all organs, thereby eliciting the pathological consequences of OSA. Whereas experimental models currently apply intermittent hypoxia to cells conventionally cultured in 2D plates, there is no well-characterized setting that will subject cells to well-controlled intermittent hypoxia in a 3D environment and enable the study of the effects of OSA on the cells of interest while preserving the underlying tissue environment. Aim: To design and characterize an experimental approach that exposes cells to high-frequency intermittent hypoxia mimicking OSA in 3D (hydrogels or tissue slices). Methods: Hydrogels made from lung extracellular matrix (L-ECM) or brain tissue slices (300-800-μm thickness) were placed on a well whose bottom consisted of a permeable silicone membrane. The chamber beneath the membrane was subjected to a square wave of hypoxic/normoxic air. The oxygen concentration at different depths within the hydrogel/tissue slice was measured with an oxygen microsensor. Results: 3D-seeded cells could be subjected to well-controlled and realistic intermittent hypoxia patterns mimicking 60 apneas/h when cultured in L-ECM hydrogels ≈500 μm-thick or ex-vivo in brain slices 300-500 μm-thick. Conclusion: This novel approach will facilitate the investigation of the effects of intermittent hypoxia simulating OSA in 3D-residing cells within the parenchyma of different tissues/organs.

Development of closed-loop modelling framework for adaptive respiratory pacemakers

OBJECTIVE

Ventilatory pacing by electrical stimulation of the phrenic nerve has many advantages compared to mechanical ventilation. However, commercially available respiratory pacing devices operate in an open-loop fashion, which require manual adjustment of stimulation parameters for a given patient. Here, we report the model development of a closed-loop respiratory pacemaker, which can automatically adapt to various pathological ventilation conditions and metabolic demands.

METHODS

To assist the model design, we have personalized a computational lung model, which incorporates the mechanics of ventilation and gas exchange. The model can respond to the device stimulation where the gas exchange model provides biofeedback signals to the device. We use a pacing device model with a proportional integral (PI) controller to illustrate our approach.

RESULTS

The closed-loop adaptive pacing model can provide superior treatment compared to open-loop operation. The adaptive pacing stimuli can maintain physiological oxygen levels in the blood under various simulated breathing disorders and metabolic demands.

CONCLUSION

We demonstrate that the respiratory pacing devices with the biofeedback can adapt to individual needs, while the lung model can be used to validate and parametrize the device.

SIGNIFICANCE

The closed-loop model-based framework paves the way towards an individualized and autonomous respiratory pacing device development.

Use of oximetry to screen for paediatric obstructive sleep apnoea: is one night enough and is 6 hours too much?

INTRODUCTION

Nocturnal pulse oximetry can be used to screen for obstructive sleep apnoea (OSA) using the McGill Oximetry Score (MOS). The MOS has a time threshold for a technically adequate study of 6 hours. It has been suggested that one night of oximetry is sufficient to screen for OSA using the MOS.

AIMS

(1) To evaluate night-to-night variation of the MOS. (2) To determine the impact of recording three nights of oximetry on the screening yield for OSA. (3) To explore whether useful MOS data are discarded when a threshold of 6 hours of oximetry recording is used.

METHODS

A retrospective study of nocturnal pulse oximetry done at home over three consecutive nights in paediatric patients with suspected OSA. Studies were scored (MOS) using thresholds of ≥6 and ≥4 hours of recording.

RESULTS

A total of 329 patients were studied. MOS scores over three nights showed only fair to moderate agreement. On the first night 126 patients (38%) screened positive for OSA. When three nights of oximetry were done 195 patients (59%) screened positive on at least one of the nights. There were 48 patients with studies of between 4 and 6 hours duration on one or more nights. If these studies are scored 20 patients (42%) would screen positive for OSA on at least one night based on scoring these studies alone.

CONCLUSION

One night of oximetry screening may not be sufficient to screen for OSA. Lowering the time threshold to ≥4 hours may increase the screening capability of nocturnal oximetry.

Pediatric polysomnography-A review of indications, technical aspects, and interpretation

Polysomnography is an elaborate diagnostic test composed of numerous data-collecting sensors working concomitantly to aid in the evaluation of varied sleep disorders in all age groups. Polysomnography is the study of choice for the assessment of pediatric sleep-disordered breathing, including obstructive sleep apnea syndrome, central apnea, and hypoventilation disorders, and is used to help determine treatment efficacy. Beyond the purview of snoring and breathing pauses, polysomnography can elucidate the etiology of hypersomnolence, when associated with a multiple sleep latency test, and abnormal movements or events, whether nocturnal seizure or complex parasomnia, when a thorough patient history cannot provide clear answers. This review will highlight the multitudinous indications for pediatric polysomnography and detail its technical aspects by describing the multiple neurophysiologic and respiratory parametric sources. Knowledge of these technical aspects will provide the practitioner with a thoughtful means to understand the limitations and interpretation of polysomnography.

Observational study on the influence of averaging time on oximetry results in infants and children

AIM

Oximetry values are influenced by the averaging time (AT) used. We aimed to evaluate the effect of different ATs on number, duration, mean single event and total integral of desaturations in preterm infants and children to convert between parameters obtained with different ATs.

METHODS

In a prospective observational study, 49 children underwent sleep laboratory-based polysomnography and 15 preterm infants were studied in the intensive care unit. Their raw red-to-infrared-saturation-data were reprocessed using seven different ATs (3-16 seconds). Desaturation thresholds were <80% (infants) and <90% (children), conversion formulas and their median percentage errors were calculated.

RESULTS

We found a linear relationship between the logarithms of the ATs and those of the desaturation parameters, leading to a conversion formula with different exponents. Based on this relationship, the number of desaturations decreased from AT = 3s to AT = 16s by factor 0.28 (children) and 0.18 (infants); total oxygen saturation integral decreased by factor 0.72 (children) and 0.48 (infants). The desaturation duration increased by factor 1.89 (children) and 3.34 (infants).

CONCLUSION

The number and total integral decreased, but the duration and mean single event integral increased with increasing AT. These changes were stronger in infants. Conversion formulas may facilitate comparisons between studies using different averaging times.

Validation of the Nox-T3 Portable Monitor for Diagnosis of Obstructive Sleep Apnea in Patients With Chronic Obstructive Pulmonary Disease

STUDY OBJECTIVES

Clinical practice guidelines recommend polysomnography (PSG) for diagnosis of obstructive sleep apnea (OSA) in patients with major comorbidities. We evaluated home sleep apnea testing (HSAT) using a type 3 portable monitor (PM, Nox-T3, Nox Medical, Reykjavik, Iceland) to diagnose OSA in adults with chronic obstructive pulmonary disease (COPD).

METHODS

Ninety adults with COPD (89.0% males, mean ± standard deviation age 66.5 ± 7.8 years, body mass index 27.5 ± 5.8 kg/m², forced expiratory volume in the first second/forced vital capacity [FEV₁/ FVC] 53.5 ± 12.4%, FEV₁ 54.0 ± 18.4% predicted) underwent unattended HSAT followed by an in-laboratory PSG with simultaneous PM recording.

RESULTS

Scoring hypopneas with a ≥ 4% oxygen desaturation, the apnea-hypopnea index (AHI) was 16.7 ± 20.6 events/h on HSAT, 20.0 ± 23.3 events/h on in-laboratory PM, and 21.2 ± 26.2 events/h on PSG (P < .0001). Bland-Altman analysis of AHI on HSAT versus PSG showed a mean difference (95% confidence interval) of -5.08 (-7.73, -2.42) events/h (P = .0003) and limits of agreement (± 2 standard deviations) of -30.00 to 19.85 events/h; HSAT underestimated AHI to a greater extent for more severe values (rho = -.529, P < .0001). Using an AHI ≥ 5 events/h to diagnose OSA, HSAT had 95% sensitivity, 78% specificity, 88% positive predictive value, and 89% negative predictive value compared to PSG. Mean oxygen saturation was 93.2 ± 3.7% on PSG, 91.0 ± 3.3% on in-laboratory PM, and 90.8 ± 4.0% on HSAT (P < .0001). Percentage time oxygen saturation ≤ 88% was 17.9 ± 26.4% on HSAT, 17.4 ± 25.5% on in-laboratory PM, and 10.0 ± 21.1% on PSG (P < .0001).

CONCLUSIONS

The Nox-T3 PM can be used to diagnose OSA in patients with COPD but, most likely due to differences among pulse oximeters, a greater number of patients with COPD and without OSA qualified for nocturnal oxygen treatment using this PM than PSG.

Gas Partial Pressure in Cultured Cells: Patho-Physiological Importance and Methodological Approaches

Gas partial pressures within the cell microenvironment are one of the key modulators of cell pathophysiology. Indeed, respiratory gases (O2 and CO2) are usually altered in respiratory diseases and gasotransmitters (CO, NO, H2S) have been proposed as potential therapeutic agents. Investigating the pathophysiology of respiratory diseases in vitro mandates that cultured cells are subjected to gas partial pressures similar to those experienced by each cell type in its native microenvironment. For instance, O2 partial pressures range from ∼13% in the arterial endothelium to values as low as 2-5% in cells of other healthy tissues and to less than 1% in solid tumor cells, clearly much lower values than those used in conventional cell culture research settings (∼19%). Moreover, actual cell O2 partial pressure in vivo changes with time, at considerably different timescales as illustrated by tumors, sleep apnea, or mechanical ventilation. Unfortunately, the conventional approach to modify gas concentrations at the above culture medium precludes the tight and exact control of intra-cellular gas levels to realistically mimic the natural cell microenvironment. Interestingly, well-controlled cellular application of gas partial pressures is currently possible through commercially available silicone-like material (PDMS) membranes, which are biocompatible and have a high permeability to gases. Cells are seeded on one side of the membrane and tailored gas concentrations are circulated on the other side of the membrane. Using thin membranes (50-100 μm) the value of gas concentration is instantaneously (<0.5 s) transmitted to the cell microenvironment. As PDMS is transparent, cells can be concurrently observed by conventional or advanced microscopy. This procedure can be implemented in specific-purpose microfluidic devices and in settings that do not require expensive or complex technologies, thus making the procedure readily implementable in any cell biology laboratory. This review describes the gas composition requirements for a cell culture in respiratory research, the limitations of current experimental settings, and also suggests new approaches to better control gas partial pressures in a cell culture.

Oxygen Desaturation Index Differs Significantly Between Types of Sleep Software

STUDY OBJECTIVES

The aim of this study was to compare the oxygen desaturation index (ODI) generated by two different sleep software systems.

METHODS

Participants undergoing diagnostic polysomnography for suspected obstructive sleep apnea underwent simultaneous oximetry recording using the ResMed ApneaLink Plus device (AL) and Compumedics Profusion PSG3 system (Comp). The ODI was calculated by the algorithms in the respective software of each system. To determine if differences were due to algorithm or recording devices, the Comp software was also used to generate ODI values using oximetry data from the AL.

RESULTS

In 106 participants, there was good correlation but poor agreement in the ODI generated by the two systems. AL ODI values tended to be higher than Comp ODI values, but with significant variability. For ODI4%, bias was 4.4 events/h (95% limits of agreement -5.8 to 14.6 events/h). There was excellent correlation and agreement when the same oximetry raw data was analyzed by both systems. For ODI4%, bias was 0.03 events/h (95% limits of agreement -2.7 to 2.8 events/h). Similar results were evident when the ODI3% was used.

CONCLUSIONS

There is a clinically significant difference in ODI values generated by the two systems, likely due to device signal processing, rather than difference in ODI calculation algorithms.

Cerebral Oximetry Monitoring Provides Early Warning of Hypercyanotic Spells in an Infant with Tetralogy of Fallot

A 3.6-kg, 3-month-old infant with a history of tetralogy of Fallot and increasing hypercyanotic spells was brought to the operating room for operative repair. Before the initiation of cardiopulmonary bypass, it was noted that an abrupt decrease in the cerebral oximetry value occurred before pulse oximetry measured the decrease in oxygen saturation. This happened 4 times, and during all 4 of the hypercyanotic spells, the decrease of the cerebral oximeter value occurred 15 to 30 seconds before a change registered in the pulse oximetry value. For the first time, this case illustrates that cerebral oximetry monitoring may be able to identify the onset of hypercyanotic spells and desaturation before standard pulse oximetry. Cerebral oximetry may provide a quicker identification of acute changes in the clinical status of infants and children by identifying hypoxemia before pulse oximetry.

The Impact of Averaging Window Length on the"Desaturation Indexes during Overnight Pulse Oximetry at High-Altitude"

STUDY OBJECTIVES

To determine the impact of averaging window-length on the "desaturation" indexes (DIs) obtained via overnight pulse oximetry (SpO2) at high altitude.

DESIGN

Overnight SpO2 data were collected during a 10-day sojourn at high altitude. SpO2 was obtained using a commercial wrist-worn finger oximeter whose firmware was modified to store unaveraged beat-to-beat data. Simple moving averages of window lengths spanning 2 to 20 cardiac beats were retrospectively applied to beat-to-beat SpO2 datasets. After SpO2 artifacts were removed, the following DIs were then calculated for each of the averaged datasets: oxygen desaturation index (ODI); total sleep time with SpO2 < 80% (TST < 80), and the lowest SpO2 observed during sleep (SpO2 low).

SETTING

South Base Camp, Mt. Everest (5,364 m elevation).

PARTICIPANTS

Five healthy, adult males (35 ± 5 y; 180 ± 1 cm; 85 ± 4 kg).

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

49 datasets were obtained from the 5 participants, totalling 239 hours of data. For all window lengths ≥ 2 beats, ODI and TST < 80 were lower, and SpO2 low was higher than those values obtained from the beat-to-beat SpO2 time series data (P < 0.05).

CONCLUSIONS

Our findings indicate that increasing oximeter averaging window length progressively underestimates the frequency and magnitude of sleep disordered breathing events at high altitude, as indirectly assessed via the desaturation indexes.

Could transient hypoxia be associated with rhythmic masticatory muscle activity in sleep bruxism in the absence of sleep-disordered breathing? A preliminary report

Sleep bruxism (SB) is a repetitive jaw-muscle activity characterised by clenching or grinding of the teeth during sleep. Sleep bruxism activity is characterised by rhythmic masticatory muscle activity (RMMA). Many but not all RMMA episodes are associated with sleep arousal. The aim of this study was to evaluate whether transient oxygen saturation level change can be temporally associated with genesis of RMMA/SB. Sleep laboratory or home recordings data from 22 SB (tooth grinding history in the absence of reported sleep-disordered breathing) and healthy subjects were analysed. A total of 143 RMMA/SB episodes were classified in four categories: (i) no arousal + no body movement; (ii) arousal + no body movement; (iii) no arousal + body movement; (iv) arousal + body movement. Blood oxygen levels (SaO2 ) were assessed from finger oximetry signal at the baseline (before RMMA), and during RMMA. Significant variation in SaO2 over time (P = 0·001) was found after RMMA onset (+7 to +9 s). No difference between categories (P = 0·91) and no interaction between categories and SaO2 variation over time (P = 0·10) were observed. SaO2 of six of 22 subjects (27%) remained equal or slight increase after the RMMA/SB onset (+8 s) compared to baseline; 10 subjects (45%) slightly decreased (drop 0·01-1%) and the remaining (27%) decreased between 1% and 2%. These preliminary findings suggest that a subgroup of SB subjects had (i) a minor transient hypoxia potentially associated with the onset of RMMA episodes, and this (ii) independently of concomitant sleep arousal or body movements.

Should All Congestive Heart Failure Patients Have a Routine Sleep Apnea Screening? Pro

Sleep-disordered breathing (SDB) is highly prevalent in heart failure (HF) patients. These breathing disturbances are independent predictors of increased morbidity and comorbid conditions that improve with SDB treatment. Considering the overlap between SDB-related and HF clinical symptoms reported by patients, objective tests need to be conducted for a diagnosis to be firmly established and to determine the type and severity of SDB that will dictate treatment alternatives. Considering the high success rate and diagnostic value of ambulatory monitoring techniques, they represent a practical, cost-effective, and accurate alternative to diagnosing SDB in HF patients.

A conversion formula for comparing pulse oximeter desaturation rates obtained with different averaging times

Objective

The number of desaturations determined in recordings of pulse oximeter saturation (SpO₂) primarily depends on the time over which values are averaged. As the averaging time in pulse oximeters is not standardized, it varies considerably between centers. To make SpO₂ data comparable, it is thus desirable to have a formula that allows conversion between desaturation rates obtained using different averaging times for various desaturation levels and minimal durations.

Methods

Oxygen saturation was measured for 170 hours in 12 preterm infants with a mean number of 65 desaturations <90% per hour of arbitrary duration by using a pulse oximeter in a 2–4 s averaging mode. Using 7 different averaging times between 3 and 16 seconds, the raw red-to-infrared data were reprocessed to determine the number of desaturations (D). The whole procedure was carried out for 7 different minimal desaturation durations (≥1, ≥5, ≥10, ≥15, ≥20, ≥25, ≥30 s) below SpO₂ threshold values of 80%, 85% or 90% to finally reach a conversion formula. The formula was validated by splitting the infants into two groups of six children each and using one group each as a training set and the other one as a test set.

Results

Based on the linear relationship found between the logarithm of the desaturation rate and the logarithm of the averaging time, the conversion formula is: D₂ = D₁ (T₂/T₁)^c, where D₂ is the desaturation rate for the desired averaging time T₂, and D₁ is the desaturation rate for the original averaging time T₁, with the exponent c depending on the desaturation threshold and the minimal desaturation duration. The median error when applying this formula was 2.6%.

Conclusion

This formula enables the conversion of desaturation rates between different averaging times for various desaturation thresholds and minimal desaturation durations.

Clinical use of pulse oximetry: official guidelines from the Thoracic Society of Australia and New Zealand

Pulse oximetry provides a simple, non-invasive approximation of arterial oxygenation in a wide variety of clinical settings including emergency and critical-care medicine, hospital-based and ambulatory care, perioperative monitoring, inpatient and outpatient settings, and for specific diagnostic applications. Pulse oximetry is of utility in perinatal, paediatric, adult and geriatric populations but may require use of age-specific sensors in these groups. It plays a role in the monitoring and treatment of respiratory dysfunction by detecting hypoxaemia and is effective in guiding oxygen therapy in both adult and paediatric populations. Pulse oximetry does not provide information about the adequacy of ventilation or about precise arterial oxygenation, particularly when arterial oxygen levels are very high or very low. Arterial blood gas analysis is the gold standard in these settings. Pulse oximetry may be inaccurate as a marker of oxygenation in the presence of dyshaemoglobinaemias such as carbon monoxide poisoning or methaemoglobinaemia where arterial oxygen saturation values will be overestimated. Technical considerations such as sensor position, signal averaging time and data sampling rates may influence clinical interpretation of pulse oximetry readings.

The relationship between patterns of intermittent hypoxia and retinopathy of prematurity in preterm infants

BACKGROUND

We have previously shown an increased incidence of intermittent hypoxemia (IH) events in preterm infants with severe retinopathy of prematurity (ROP). Animal models suggest that patterns of IH events may play a role in ROP severity as well. We hypothesize that specific IH event patterns are associated with ROP in preterm infants.

METHODS

Variability in IH event duration, severity, and the time interval between IH events (≤80%, ≥10 s, and ≤3 min) along with the frequency spectrum of the oxygen saturation (SpO2) waveform were assessed.

RESULTS

Severe ROP was associated with (i) an increased mean and SD of the duration of IH event (P < 0.005), (ii) more variability (histogram entropy) of the time interval between IH events (P < 0.005), (iii) a higher IH nadir (P < 0.05), (iv) a time interval between IH events of 1-20 min (P < 0.05), and (v) increased spectral power in the range of 0.002-0.008 Hz (P < 0.05), corresponding to SpO2 waveform oscillations of 2-8 min in duration. Spectral differences were detected as early as 14 d of life.

CONCLUSION

Severe ROP was associated with more variable, longer, and less severe IH events. Identification of specific spectral components in the SpO2 waveform may assist in early identification of infants at risk for severe ROP.

Pulse oximetry for the detection of obstructive sleep apnea syndrome: can the memory capacity of oxygen saturation influence their diagnostic accuracy?

Objective. To assess the diagnostic ability of WristOx 3100 using its three different recording settings in patients with suspected obstructive sleep apnea syndrome (OSAS). Methods. All participants (135) performed the oximetry (three oximeters WristOx 3100) and polysomnography (PSG) simultaneously in the sleep laboratory. Both recordings were interpreted blindly. Each oximeter was set to one of three different recording settings (memory capabilities 0.25, 0.5, and 1 Hz). The software (nVision 5.1) calculated the adjusted O₂ desaturation index-mean number of O₂ desaturation per hour of analyzed recording ≥2, 3, and 4% (ADI2, 3, and 4). The ADI2, 3, and 4 cutoff points that better discriminated between subjects with or without OSAS arose from the receiver-operator characteristics (ROCs) curve analysis. OSAS was defined as a respiratory disturbance index (RDI) ≥ 5. Results. 101 patients were included (77 men, mean age 52, median RDI 22.6, median BMI 27.4 kg/m²). The area under the ROCs curves (AUC-ROCs) of ADI2, 3, and 4 with different data storage rates were similar (AUC-ROCs with data storage rates of 0.25/0.5/1 Hz: ADI2: 0.958/0.948/0.965, ADI3: 0.961/0.95/0.966, and ADI4: 0.957/0.949/0.963, P NS). Conclusions. The ability of WristOx 3100 to detect patients with OSAS was not affected by the data storage rate of the oxygen saturation signal. Both memory capacity of 0.25, 0.5, or 1 Hz showed a similar performance for the diagnosis of OSAS.

A higher incidence of intermittent hypoxemic episodes is associated with severe retinopathy of prematurity

OBJECTIVE

Retinopathy of prematurity (ROP), a vasoproliferative disorder of the retina in preterm infants, is associated with multiple factors, including oxygenation level. We explored whether the common intermittent hypoxemic events in preterm infants are associated with the development of ROP.

STUDY DESIGN

Oxygen desaturation events were quantified in 79 preterm infants (gestational age, 24 to 27-6/7 weeks) during the first 8 weeks of life. Infants were classified as requiring laser treatment for ROP versus having less severe or no ROP. A linear mixed model was used to study the association between the incidence of intermittent hypoxia and laser treatment of ROP, controlling for gestational age, sex, race, multiple births, and initial severity of illness.

RESULTS

For all infants, hypoxemic events increased with postnatal age (P<.001). Controlling for all covariates, a higher incidence of oxygen desaturation events was found in the infants undergoing laser therapy for ROP (P<.001), males (P<.02), and infants of younger gestational age (P<.003).

CONCLUSIONS

The incidence of hypoxemic events was higher in infants with ROP requiring laser therapy. Therapeutic strategies to optimize oxygenation in preterm infants should include minimization of desaturation episodes, which may in turn decrease serious morbidity in this high-risk population.

Diagnosis of obstructive sleep apnea syndrome and its outcomes with home portable monitoring

BACKGROUND

The use of portable respiratory monitoring (PM) has been proposed for the diagnosis of obstructive sleep apnea syndrome (OSAS), but most studies that validate PM accuracy have not followed the best standards for diagnostic test validation. The objective of the present study was to evaluate the accuracy of PM performed at home to diagnose OSAS and its outcomes after first validating PM in the laboratory setting by comparing it to polysomnography (PSG).

METHODS

Patients with suspected OSAS were submitted, in random order, to PM at the sleep laboratory concurrently with PSG (lab-PM) or at home-PM. The diagnostic performance was assessed by sensitivity, specificity, positive and negative predictive values, positive likelihood ratio (+LR), negative likelihood ratio (-LR), intraclass correlation coefficients, kappa statistic, and Bland-Altman plot.

RESULTS

One hundred fifty-seven subjects (73% men, mean age +/- SD, 45 +/- 12 yr) with an apnea-hypopnea index (AHI) of 31 (SD +/- 29) events/h were studied. Excluding inadequate recordings, 149 valid comparisons with lab-PM and 121 with unattended home-PM were obtained. Compared to PSG for detecting AHI > 5, the lab-PM demonstrated sensitivity of 95.3%, specificity of 75%, +LR of 3.8, and -LR of 0.11; the home-PM exhibited sensitivity of 96%, specificity of 64%, +LR of 2.7, and -LR of 0.05. Kappa statistics indicated substantial correlation between PSG and PM results. Bland-Altman plot showed smaller dispersion for lab-PM than for home-PM. Pearson product moment correlation coefficients among the three AHIs and clinical outcomes were similar, denoting comparable diagnostic ability.

CONCLUSIONS

This study used all available comparison methods to demonstrate accuracy of PM in-home recordings similar to that of repeated PSGs. PM increases the possibility of correctly diagnosing and effectively treating OSAS in populations worldwide.

Cerebral Oximetry Monitoring with Near Infrared Spectroscopy Detects Alterations in Oxygenation Before Pulse Oximetry

Background: The monitoring of oxygenation may be imperative to ensure patient safety and optimal outcome. We anecdotally noted that monitoring cerebral oxygenation (rSO2) using near infrared spectroscopy may provide an earlier warning of changes in oxygenation than pulse oximetry. Methods: Patients scheduled for airway laser surgery requiring intermittent periods of apnea were monitored with both a cerebral oximeter and a pulse oximeter. Following inhalational induction and endotracheal intubation, anesthesia was maintained with propofol. After 3 minutes of ventilation with 100% oxygen, the endotracheal tube was removed and laser surgery performed on the airway during apnea. The time for a 5% and a 10% decrease in the cerebral oximeter and the pulse oximeter was noted. Results: The study cohort included 10 infants and children ranging in age from 1 month to 7 years. The time for a 5% decrease of the rSO2 was 94 + 8 seconds versus 146 + 49 seconds for a 5% decrease of the SaO 2 (P < .0001). During all 42 episodes of apnea, the rSO2 decreased by 5% before the SaO2 had decreased by 5%. When the SaO2 had decreased by 5% (down to 95% from the starting value of 100%), the rSO2 had decreased by 16 + 4%. The time for a 10% decrease of the rSO2 was 138 + 29 seconds versus 189 + 64 seconds for a 10% decrease of the SaO2 (P = .0009). In all 42 cases, the rSO2 decreased by 10% before the SaO2. Conclusions: Cerebral oxygenation monitoring using near infrared spectroscopy detects changes in oxygenation earlier than standard pulse oximetry.

Pulse-oximetery is useful in determining the indications for adeno-tonsillectomy in pediatric sleep-disordered breathing

OBJECTIVE

Although first line therapy of sleep-disordered breathing (SDB) in children is adeno-tonsillectomy, the indications for this operation have not yet been clearly established. We investigated whether pulse-oximetry is useful for determining the optional treatment modality for pediatric SDB.

METHOD

Two hundred and thirty-two children presenting with snoring and gasping had their oxygen saturation levels examined during sleep. Among them, 86 underwent on adeno-tonsillectomy and were evaluated pre- and post-surgery. We also examined 25 healthy children as controls.

RESULTS

Little desaturation was observed in healthy children. The difference in oxygen saturation levels of the patients between pre- and post-surgery was closely correlated with the pre-surgery levels. We examined the reaction operation characteristics and concluded that children with an oxygen desaturation index of 4% or more (ODI4) of more than 1.5 and/or ODI3 of more than 3.5 should undergo surgery.

CONCLUSION

Pulse-oximetry is useful in determining the indications for adeno-tonsillectomy.

Central periodic breathing observed on hospital admission is associated with an adverse prognosis in conscious acute stroke patients

BACKGROUND

Central periodic breathing (CPB) is common following acute stroke, but its prognostic significance is uncertain. We determined the frequency of CPB on admission with stroke and assessed whether it was related to outcome.

METHODS

We measured arterial oxygen saturation (SaO2), chest wall movements and nasal airflow continually with portable monitoring equipment in a large cohort of acute stroke patients, from arrival at hospital through acute assessment to reaching the ward. Baseline neurological examination and 3-month outcome (modified Rankin scale, MRS) were assessed blind to recordings. CPB was defined as cyclical rises and falls in ventilation, with intermittent reduced respiratory airflow or total apnoea.

RESULTS

CPB was common in acute stroke (33/138, 24%), but was poorly recognised by clinical staff. Patients with CPB were more likely to have a total anterior circulation syndrome and higher National Institutes of Health Stroke Scale scores than those without (both p<0.01). Patients with CPB had significantly higher median SaO2 than those without (p<0.01), unrelated to whether they received oxygen or not. At 3-month follow-up: 91% of patients with CPB were dead or dependent (MRS>or=3) compared with 53% of those without (OR 8.8; 95% CI 2.5-30.5); the association remained statistically significant after adjusting for covariates (OR 5.9; 95% CI 1.4-25.4).

CONCLUSION

CPB is independently associated with poor outcome after stroke, but is not by association with hypoxia. Further work is required to identify causes, effects and interventions that might improve effects of CPB.

Prospective evaluation of nocturnal oximetry for detection of sleep-related breathing disturbances in patients with chronic heart failure

BACKGROUND

Because patients with chronic heart failure (CHF) can benefit from specific treatment for coexisting obstructive and central sleep apnea (CSA), there is a need to develop accurate screening tools to identify or exclude these sleep-related breathing disturbances (SRBDs) in patients with CHF.

OBJECTIVES

To evaluate, prospectively, the diagnostic value of nocturnal home oximetry in identifying SRBD in CHF patients and in distinguishing central events from obstructive events.

DESIGN

Blinded comparison of hospital and home oximetry, and polysomnographic nocturnal recordings

SETTING

Cardiac heart failure and sleep clinics in three tertiary referral centers.

PATIENTS

Fifty consecutive patients who were investigated for participation in the Canadian Continuous Positive Airway Pressure Trial for Congestive Heart Failure with Central Sleep Apnea and were recruited from three different centers.

MEASUREMENTS AND RESULTS

Patients underwent two oximetry recordings, one at home and one during a polysomnographic study. The criterion for an SRBD was the presence of > 15 apneas and hypopneas per hour of sleep during polysomnography or an oxygen desaturation index of > 10 events per hour during oximetry. The pattern of desaturation/resaturation during oximetry was also examined to distinguish obstructive events from central events. Using a 2% fall in pulse oximetric saturation as the criterion for oxygen desaturation, home oximetry had a 85% sensitivity and a 93% specificity (p < 0.001) for detecting an SRBD. However, the desaturation/resaturation pattern did not accurately distinguish between obstructive events and central events (eg, 100% sensitivity, 17% specificity for identifying CSA). The interpretation of the oximetry recording was highly consistent between scorers (p < 0.001).

CONCLUSIONS

Overnight home oximetry is a sensitive and specific tool for identifying SRBDs in patients with CHF, but not for distinguishing between obstructive and central events in such patients.

Choice of Oximeter Affects Apnea-Hypopnea Index

STUDY OBJECTIVES

Current Medicare guidelines include an apnea-hypopnea index (AHI) > or = 15 events per hour, in which all hypopneas must be associated with 4% desaturation, to qualify for reimbursement for therapy with continuous positive airway pressure (CPAP). The present data demonstrate the effect of pulse oximeter differences on AHI.

DESIGN

Prospective study, blinded analysis.

SETTING

Academic sleep disorder center.

PATIENTS

One hundred thirteen consecutive patients (84 men and 29 women) undergoing diagnostic sleep studies and being evaluated for CPAP based on the Medicare indications for reimbursement.

INTERVENTIONS

Patients had two of four commonly used oximeters with signal averaging times of 4 to 6 s placed on different digits of the same hand during nocturnal polysomnography.

MEASUREMENTS AND RESULTS

Apneas and candidate hypopneas (amplitude reduction, > 30%) were scored from the nasal cannula airflow signal without reference to oximetry. Candidate hypopneas then were reclassified as hypopneas by each oximeter if they were associated with a 4% desaturation. Although the use of three oximeters resulted in a similar AHI (bias, < 1 event per hour), the fourth oximeter showed an overall increase in AHI of 3.7 events per hour. This caused 7 of 113 patients to have an AHI of > or = 15 events per hour (meeting the Medicare criteria for treatment) by one oximeter but not when a different oximeter was used. More importantly, when our analysis was limited to those patients whose number of candidate hypopneas made them susceptible to the threshold value of 15 events per hour, 7 of 35 patients who did not meet the Medicare AHI standard for treatment by one oximeter were reclassified when a different oximeter was used.

CONCLUSION

In the present study, oximeter choice affected whether the AHI reached the critical cutoff of 15 events per hour, particularly in those with disease severity that was neither very mild nor very severe. As oximetry is not a technique that produces a generic result, there are significant limitations to basing the definition of hypopnea on a fixed percentage of desaturation in determining the eligibility for CPAP therapy.

Sleep desaturation: comparison of two oximeters

Oxygen saturation is measured by pulse oximetry during sleep studies. Body movements and peripheral vasoconstriction related to respiratory events may interfere with measurements by conventional oximeters. Our objective was to compare the detection rate of sleep desaturations by two oximeters, one of which used new motion-resistant technology. We studied 34 children (median age, 13 years; range, 3-18) with suspected sleep-disordered breathing. During polysomnography, oxygen saturation was measured by two oximeters set on fast mode: the motion-resistant Radical oximeter (2-sec averaging), and the conventional Nellcor N-200 oximeter (2-3-sec averaging). Respiratory events were identified based on airflow signal. The numbers of respiratory event-related desaturations > or =3% or > or =5% detected by each oximeter were determined. Valid desaturations were defined using the Nellcor plethysmographic waveform and the Radical signal-quality data. Hypoxemic respiratory events were those with associated valid desaturation. In total, 1,278 respiratory events were identified and pooled. Basal oxygen saturation measured just before event onset was not different between oximeters (Radical: 98%; range, 84-100; Nellcor: 97%; range, 86-100; P = ns). However, the Radical detected a greater number of valid desaturations than did the Nellcor for any level of desaturation (respectively, N = 651 and 476 desaturations > or =3%, P < 0.001; and N = 232 and 146 desaturations > or =5%, P = 0.01). Consequently, for each patient, the number of hypoxemic respiratory events per hour of sleep was greater using the Radical than using the Nellcor (P = 0.002, and P = 0.021, for desaturation > or =3% and > or =5%, respectively). In conclusion, standardized oximeter settings are required to achieve more accurate assessments of hypoxemia in children with sleep-disordered breathing.

State of home sleep studies

Many different portable monitors have been used to assess patients with suspected sleep apnea. There is limited evidence for the use of type 2 monitors, especially in the unattended setting in which there may be high rates of data loss. Type 3 monitors have low likelihood ratios for negative tests and can be used to "rule out" sleep apnea. The ability of type 3 monitors to "rule in" sleep apnea is less convincing, but this may improve with the use of improved technology, such as nasal pressure transducers. Type 4 monitors usually use oximetry and can be used to "rule out" sleep apnea. Higher sampling rates and improved analysis algorithms can improve the specificity of these monitors; hence, likelihood ratios for a positive test result can be high enough with some monitors to "rule in" sleep apnea as well. Not all monitors record and analyze signals in the same way; it is not possible to generalize results from one monitor across all monitors of a particular type. Limited evidence is available for many portable monitors in the unattended setting, and further research is required in this area. Clinicians should identify how they plan to use a portable monitor: as a mechanism to exclude disease in asymptomatic snorers, to confirm disease in [figure: see text] patients with a high clinical probability of disease, or to risk stratify patients so that proper priority for polysomnography can be determined. This determination allows them to select a portable monitor with signals most appropriate to their needs. The quality of the validation studies for each portable monitor also should be evaluated carefully before implementation in clinical practice. The ability for a clinician to review raw data manually and consider artifact is a necessary feature. Measurement of oxygen saturation also is important to identify patients with previously unsuspected serious desaturation that would indicate the need for more urgent treatment. In centers in which polysomnography is not readily available, a clinical decision algorithm that incorporates a clinical prediction rule with the use of portable monitors can guide clinicians toward institution of therapy or further investigations. Intuitively, this approach could reduce waiting times for polysomnography and delays in diagnosis, but additional evidence for the validity and cost effectiveness of this approach is required.

Monitoring respiration during sleep

The sleep-related breathing disorders have been categorized in various ways. The most basic schema divides them into obstructive or central apneic events. An American Academy of Sleep Medicine (AASM) Task Force Report published in 1999 defined four separate syndromes associated with abnormal respiratory events during sleep among adults, namely, obstructive sleep apnea-hypopnea syndrome (OSAHS), central sleep apnea-hypopnea syndrome, Cheyne-Stokes breathing syndrome, and sleep hypoventilation syndrome. In this classification, the upper airway resistance syndrome was not regarded as a distinct syndrome; instead, respiratory event-related arousals (RERAs) were considered part of the syndrome of OSAHS.

Combined index of heart rate variability and oximetry in screening for the sleep apnoea/hypopnoea syndrome

Many sleep centres employ a preliminary screening test in order to reduce the number of polysomnographies required in the routine diagnosis of the sleep apnoea/hypopnoea syndrome (SAHS). We investigated the combination of heart rate and oximetry information as a means of performing this test. A retrospective study of 100 patients with suspected SAHS was made. All patients had in-hospital polysomnography on one night. We estimated the number of respiratory event-related arousals by counting the number of autonomic arousals (assessed on the basis of changes in the heart interbeat interval) that were coincident with a rise in oximetry. The hourly index of such events was denoted the "cardiac-oximetry disturbance index" (CODI). The median apnoea/hypopnoea index (AHI) was 16.5 (range 1.0-93.6) h-1. The CODI correlated significantly with the AHI (Spearman correlation coefficient rs = 0.88, P < 0.01), and the area (+/- standard error) under the receiver operating characteristic (ROC) was 0.94 +/- 0.05. Oximetry alone (based on 4% dips) was a less effective screening test (rs = 0.80, P < 0.01; area under ROC 0.83 +/- 0.06). Using 2% dips in oximetry offered comparable performance with the CODI (rs = 0.91, P < 0.01; area under ROC 0.93 +/- 0.04). The CODI was better correlated with the electroencephalograph arousal index (rs = 0.84, P < 0.01) than was oximetry (2% dips, rs = 0.57, P < 0.01). The CODI algorithm also offers an informal measure of self-validation: a large discrepancy between the number of autonomic arousals and the number of rises in oximetry indicates the presence of autonomic arousals without changes in oximetry (or vice versa). This self-validation mechanism identified several patients in this study, and may be useful in identifying sleep disruption due to chronic pain or other causes.

Blood pressure in sleep disordered breathing

AIMS

To investigate blood pressure (BP) in children with sleep disordered breathing (SDB).

METHODS

BP was measured during single night polysomnography in 23 suspected SDB child patients with adenotonsillar hypertrophy, but without respiratory or heart failure, or coma. The age related changes of the observed BP were normalised to the BP index. The BP indices were examined in relation to SDB measures, such as the desaturation time (percentage of time with oxygen saturation (SaO2) <90% against the total sleep time), SaO2 nadir, apnoea-hypopnoea index (AHI), and arousal index, in addition to age and body mass index (BMI).

RESULTS

The systolic BP index during rapid eye movement sleep (REMS) tended to correlate with AHI, while the diastolic index during REM sleep showed a significant correlation with AHI. The BP indices during non-REMS and wakefulness showed no correlation with the parameters obtained. Patients with an AHI of 10 or more (n = 7, AHIhigh) had significantly higher systolic and diastolic BP indices during both wakefulness and REMS, compared with those with an AHI of less than 10 (n = 16, AHIlow). Two patients in AHIhigh showed no sleep related dip of diastolic BP, and three patients in AHIlow lacked the sleep related dip in systolic BP. By means of multiple regression analysis, age, BMI, and AHI were found to be significant predictor variables of the systolic BP index during REMS.

CONCLUSIONS

BP in paediatric SDB patients is positively correlated with the degree of SDB.

Oximeter performance: the influence of acquisition parameters

STUDY OBJECTIVE

This study was designed to determine whether different desaturation indexes (DIs) would be obtained in patients with sleep-disordered breathing by systematically altering two acquisition parameters: the recording setting and the display mode.

DESIGN

Prospective clinical study.

SETTING

Community sleep-disorders center.

PATIENTS

The study included 75 patients who were suspected of having sleep-disordered breathing.

INTERVENTIONS

Each patient had simultaneous pulse oxyhemoglobin saturation (SpO2) traces at three recording settings (3 s, 6 s, and 12 s) during the diagnostic phase of split-night polysomnography. On-line and memory displays of those data at each recording setting were obtained. DIs for > or = 3% desaturation events per hour were calculated for each of the six traces.

RESULTS

The mean on-line DIs significantly differed from each other, with slower (longer) recording settings resulting in lower values than faster (shorter) settings. The memory DIs all significantly underestimated the on-line DIs. Pearson correlations ranged from 0.82 to 0.90 between the on-line/memory DI pairs, but Bland-Altman analysis detected disagreement at higher levels of disordered breathing.

CONCLUSIONS

These findings confirm that significantly different SpO2 data are obtained at various acquisition options. The recording setting and display mode parameters should be disclosed in all reports employing oximetry with the fastest recording setting and on-line display mode preferable for case finding of sleep-disordered breathing.

Measurement variability in sleep disorders medicine: the Victorian experience

BACKGROUND

Surveys of laboratories in North America have documented significant diversity in the working definitions used for reporting respiratory events in sleep studies.

AIM

To assess sources of variability in the measurement of sleep-disordered breathing (as defined by the Apnoea-Hypopnoea Index) between sleep laboratories in Victoria, Australia.

METHODS

A self-complete written questionnaire was constructed following literature review and interviews with staff at three separate sleep laboratories. The survey was sent to all laboratories listed in Victoria by the Australasian Sleep Association. The first part of the survey related to the type of equipment used to record sleep and other variables during overnight polysomnography and the second part related to the definitions and methods used to report results.

RESULTS

Seventeen out of 18 laboratories returned the surveys. There were variations identified in the types of sensors used to measure particular signals. There were also inconsistencies identified in the criteria used to score arousals, apnoeas and hypopnoeas by different laboratories. The variability was greatest for hypopnoea definitions.

CONCLUSIONS

There is considerable variation in the methods used to measure and define sleep-disordered breathing between sleep laboratories in Victoria. The extent to which these variations influence the comparability of reported results between laboratories requires further evaluation. The survey findings may assist the process of developing and implementing local guidelines for the performance and reporting of polysomnography.

Pulseoximetry: sufficient to diagnose severe sleep apnea

OBJECTIVES

To assess the clinical value of pulseoximetry in the diagnosis of sleep apnea when satisfactory agreement with polysomnography is obtained.

METHODS

This was a prospective clinical study, set in the Department of Otorhinolaryngology, Ullevaal University Hospital, Oslo, Norway. One hundred consecutive patients were investigated for sleep related breathing disorders. The main outcome measurements were: measurement success rate, oxygen desaturation thresholds, sensitivity and specificity at apnea-hypopnea-index (AHI) thresholds of 5 and 15.

RESULTS

Pulseoximetry was successfully performed in 93%. When different oxygen desaturation thresholds were calculated, optimal agreement with polysomnography was found at a 3% oxygen desaturation level. The sensitivity and specificity of diagnosing moderate/severe sleep apnea (AHI above 15) were 0.86 and 0.88, respectively. The corresponding figures for milder sleep apnea (AHI above 5) were 0.91 and 0.67. Good agreement was found between the AHI and the oxygen desaturation index (ODI) at the 3% level, with a mean AHI-ODI difference of 2.6 (SD, 7.3), a Pearson correlation of 0.95 and a weighted kappa of 0.86. The best agreement was found for AHI values below 15, where the estimated AHI-ODI difference was only -0.4 (SD, 3.3).

CONCLUSIONS

Pulseoximetry is a simple, non-invasive procedure, which is easy to perform and well suited for outpatient registration. When adjusted to polysomnography with high sensitivity of hypopnea registrations, an ODI at the 3% level is optimal to diagnose sleep apnea. In patients with moderate/severe sleep apnea with AHI values above 15, it is sufficient to establish the diagnosis and subsequent treatment. A negative pulseoximetry does not rule out sleep disorders; the patients should complete a full examination.

Overnight pulse oximetry for sleep-disordered breathing in adults: a review

Pulse oximetry is a well-established tool routinely used in many settings of modern medicine to determine a patient's arterial oxygen saturation and heart rate. The decreasing size of pulse oximeters over recent years has broadened their spectrum of use. For diagnosis and treatment of sleep-disordered breathing, overnight pulse oximetry helps determine the severity of disease and is used as an economical means to detect sleep apnea. In this article, we outline the clinical utility and economical benefit of overnight pulse oximetry in sleep and breathing disorders in adults and highlight the controversies regarding its limitations as presented in published studies.

Asynchronous breathing during sleep

BACKGROUND

Children rarely complain of symptoms associated with sleep disordered breathing (SDB). Paradoxical inward rib cage movement (PIRCM) during sleep might prove useful for detecting SDB.

AIMS

(1) To determine the correlation between the degree of PIRCM and other measures of disordered breathing during sleep. PIRCM occurs physiologically throughout rapid eye movement sleep in neonates, while no PIRCM has been reported during sleep in adolescents. (2) To determine the chronological changes in the degree of PIRCM.

METHODS

PIRCM was quantified by means of the laboured breathing index (LBI). LBI was determined by respiratory inductive plethysmography; PIRCM accompanies a high LBI. Sleep recordings obtained for 101 subjects for various reasons (aged from 3.5 months to 19 years) were analysed.

RESULTS

In 22 records, the minimum SaO2 value was 90% or more and no obstructive apnoea of more than 10 seconds was observed. In these 22 records, LBI during rapid eye movement sleep decreased significantly with age, reaching the mature low level at 3.3 years of age. In the other 79 records, LBI correlated well with measures of obstructed breathing during sleep.

CONCLUSIONS

By paying more attention to PIRCM, more obstructed breathing during sleep might be found among children aged 3 years or more.

Nocturnal oximetry for the diagnosis of the sleep apnoea hypopnoea syndrome: a method to reduce the number of polysomnographies?

BACKGROUND

Polysomnography (PSG) is currently the "gold standard" for the diagnosis of the sleep apnoea hypopnoea syndrome (SAHS). Nocturnal oximetry (NO) has been used with contradictory results. A prospective study was performed to determine the accuracy of NO as a diagnostic tool and to evaluate the reduction in the number of PSGs if the diagnosis of SAHS had been established by this method.

METHODS

Two hundred and seventy five patients with a clinical suspicion of SAHS were admitted to undergo, in the same night, full PSG and NO. Desaturation was defined as a fall in the haemoglobin saturation level (SaO(2)) to lower than 4% from the baseline level and an oxygen desaturation index per hour (ODI) was obtained in each patient with three cut off points: >/= 5 (ODI-5), >/= 10 (ODI-10), and >/= 15 (ODI-15).

RESULTS

SAHS was diagnosed in 216 patients (194 men). After withdrawing patients with abnormal lung function (forced expiratory volume in one second (FEV(1)) lower than 80% predicted), sensitivity (SE), specificity (SP), positive and negative predictive values (PPV and NPV) of NO were: ODI-5 (80%, 89%, 97%, 48%); ODI-10 (71%, 93%, 97%, 42%); ODI-15 (63%, 96%, 99%, 38%). The accuracy for each ODI was 0.81, 0.75, and 0.70, respectively. If NO had been considered as a diagnostic tool and PSG had been performed only in patients with a negative NO (false negative and true negative) and those with a positive NO and abnormal pulmonary function tests, 135/275 (ODI-5), 156/275 (ODI-10), and 170/275 (ODI-15) PSGs would have been performed, a reduction of 140, 119, and 105, respectively.

CONCLUSION

Nocturnal oximetry in patients with suspected SAHS and normal spirometric values permits the institution of therapeutic measures in most patients.