Differentiating obstructive and central sleep respiratory events through pulse transit time

Validation of Tracheal Sound-Based Respiratory Effort Monitoring for Obstructive Sleep Apnoea Diagnosis

Background: Respiratory effort is considered important in the context of the diagnosis of obstructive sleep apnoea (OSA), as well as other sleep disorders. However, current monitoring techniques can be obtrusive and interfere with a patient's natural sleep. This study examines the reliability of an unobtrusive tracheal sound-based approach to monitor respiratory effort in the context of OSA, using manually marked respiratory inductance plethysmography (RIP) signals as a gold standard for validation. Methods: In total, 150 patients were trained on the use of type III cardiorespiratory polygraphy, which they took to use at home, alongside a neck-worn AcuPebble system. The respiratory effort channels obtained from the tracheal sound recordings were compared to the effort measured by the RIP bands during automatic and manual marking experiments. A total of 133 central apnoeas, 218 obstructive apnoeas, 263 obstructive hypopneas, and 270 normal breathing randomly selected segments were shuffled and blindly marked by a Registered Polysomnographic Technologist (RPSGT) in both types of channels. The RIP signals had previously also been independently marked by another expert clinician in the context of diagnosing those patients, and without access to the effort channel of AcuPebble. The classification achieved with the acoustically obtained effort was assessed with statistical metrics and the average amplitude distributions per respiratory event type for each of the different channels were also studied to assess the overlap between event types. Results: The performance of the acoustic effort channel was evaluated for the events where both scorers were in agreement in the marking of the gold standard reference channel, showing an average sensitivity of 90.5%, a specificity of 98.6%, and an accuracy of 96.8% against the reference standard with blind expert marking. In addition, a comparison using the Embla Remlogic 4.0 automatic software of the reference standard for classification, as opposed to the expert marking, showed that the acoustic channels outperformed the RIP channels (acoustic sensitivity: 71.9%; acoustic specificity: 97.2%; RIP sensitivity: 70.1%; RIP specificity: 76.1%). The amplitude trends across different event types also showed that the acoustic channels exhibited a better differentiation between the amplitude distributions of different event types, which can help when doing manual interpretation. Conclusions: The results prove that the acoustically obtained effort channel extracted using AcuPebble is an accurate, reliable, and more patient-friendly alternative to RIP in the context of OSA.

Paediatric sleep diagnostics in the 21st century: the era of "sleep-omics"?

Paediatric sleep diagnostics is performed using complex multichannel tests in specialised centres, limiting access and availability and resulting in delayed diagnosis and management. Such investigations are often challenging due to patient size (prematurity), tolerability, and compliance with "gold standard" equipment. Children with sensory/behavioural issues, at increased risk of sleep disordered breathing (SDB), often find standard diagnostic equipment difficult.SDB can have implications for a child both in terms of physical health and neurocognitive development. Potential sequelae of untreated SDB includes failure to thrive, cardiopulmonary disease, impaired learning and behavioural issues. Prompt and accurate diagnosis of SDB is important to facilitate early intervention and improve outcomes.The current gold-standard diagnostic test for SDB is polysomnography (PSG), which is expensive, requiring the interpretation of a highly specialised physiologist. PSG is not feasible in low-income countries or outwith specialist sleep centres. During the coronavirus disease 2019 pandemic, efforts were made to improve remote monitoring and diagnostics in paediatric sleep medicine, resulting in a paradigm shift in SDB technology with a focus on automated diagnosis harnessing artificial intelligence (AI). AI enables interrogation of large datasets, setting the scene for an era of "sleep-omics", characterising the endotypic and phenotypic bedrock of SDB by drawing on genetic, lifestyle and demographic information. The National Institute for Health and Care Excellence recently announced a programme for the development of automated home-testing devices for SDB. Scorer-independent scalable diagnostic approaches for paediatric SDB have potential to improve diagnostic accuracy, accessibility and patient tolerability; reduce health inequalities; and yield downstream economic and environmental benefits.

A single-arm, open-label, multicenter, and comparative study of the ANNE sleep system vs polysomnography to diagnose obstructive sleep apnea

STUDY OBJECTIVES

Evaluate per-patient diagnostic performance of a wireless dual-sensor system (ANNE sleep) compared with reference standard polysomnography (PSG) for the diagnosis of moderate and severe obstructive sleep apnea (OSA) with a minimum prespecified threshold of 80% for both sensitivity and specificity.

METHODS

A multicenter clinical trial was conducted to evaluate ANNE sleep vs PSG to diagnose moderate and severe OSA in individuals 22 years or older. For each testing approach, apnea-hypopnea index (AHI) was manually scored and averaged by 3 registered sleep technologists blinded to the other system. Average variations > 15% were adjudicated by a sleep medicine physician.

RESULTS

In a total of n = 225 participants (mean age 53 years, range 22-88 years), PSG diagnosed 30% (n = 68) of participants with moderate or severe OSA (AHI ≥ 15 events/h) compared to 29% (n = 65) diagnosed by ANNE sleep (P = .55). The sensitivity and specificity for ANNE sleep were 90% (95% confidence interval: 80-96%) and 98% (95% confidence interval: 94-99%), respectively. Strong correlation was shown in terms of final AHI (r = .93), with an average AHI bias of 0.5 (95% limits of agreement: -12.8 to 11.8). The majority of users noted comfort with using the ANNE sleep in the home setting. No adverse events were noted.

CONCLUSIONS

Using PSG as the gold standard, ANNE sleep demonstrated high sensitivity and specificity for the diagnosis of moderate or severe OSA.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov; Name: Comparative Study of the ANNE™ One System to Diagnose Obstructive Sleep Apnea; URL: https://clinicaltrials.gov/ct2/show/NCT04643782; Identifier: NCT04643782.

CITATION

Davies C, Lee JY, Walter J et al. A single-arm, open-label, multicenter, and comparative study of the ANNE sleep system vs polysomnography to diagnose obstructive sleep apnea. J Clin Sleep Med. 2022;18(12):2703-2712.

Blood pressure wave propagation - a multisensor setup for cerebral autoregulation studies

OBJECTIVE

Cerebral autoregulation is critically important to maintain proper brain perfusion and supply the brain with oxygenated blood. Non-invasive measures of blood pressure (BP) are critical in assessing cerebral autoregulation. Wave propogation velocity may be a useful technique to estimate BP but the effect of the location of the sensors on the readings has not been thoroughly examined. In this paper, we were interested to study if propagation velocity of the pressure wave in the direction from the heart to the brain may differ compared with propagation from the heart to the periphery, as well as across different physiological tasks and/or health conditions. Using non-invasive sensors simultaneously placed on different locations of the human body allow for the study of how propagation velocity of the pressure wave, based on pulse transit time (PTT), varies across different directions.

APPROACH

We present multi-sensor BP wave propagation measurement setup aimed for cerebral autoregulation studies. The presented sensor setup consists of three sensors, one each placed on the neck, chest and finger, allowing simultaneous measurement of changes in BP propagation velocity towards the brain and to the periphery. We show how commonly tested physiological tasks affect the relative changes of PTT and correlations with BP.

MAIN RESULTS

We observed that during maximal blow, valsalva and breath hold breathing tasks, the relative changes of PTT were higher when PTT was measured in the direction from the heart to the brain than from the heart to the peripherals. In contrast, during a deep breathing task, the relative change in PTT from the heart to the brain was lower. In addition, we present a short literature review of PTT methods used in brain research.

SIGNIFICANCE

These preliminary data suggest that physiological task and direction of PTT measurement may affect relative PTT changes. Presented three-sensor setup provides an easy and neuroimaging compatible method for cerebral autoregulation studies by allowing to measure BP wave propagation velocity towards the brain vs. towards the periphery.

Pulse arrival time, a novel sleep cardiovascular marker: the multi-ethnic study of atherosclerosis

BACKGROUND

Pulse arrival time (PAT) is commonly used to estimate blood pressure response. We hypothesised that PAT response to obstructive respiratory events would be associated with increased cardiovascular risk in people with obstructive sleep apnoea.

METHODS

PAT, defined as the time interval between electrocardiography R wave and pulse arrival by photoplethysmography, was measured in the Multi-Ethnic Study of Atherosclerosis Sleep study participants. The PAT response to apnoeas/hypopnoeas was defined as the area under the PAT waveform following respiratory events. Cardiovascular outcomes included markers of subclinical cardiovascular disease (CVD): left ventricular mass, carotid plaque burden score and coronary artery calcification (CAC) (cross-sectional) and incident composite CVD events (prospective). Multivariable logistic and Cox proportional hazard regressions were performed.

RESULTS

A total of 1407 participants (mean age 68.4 years, female 47.5%) were included. Higher PAT response (per 1 SD increase) was associated with higher left ventricular mass (5.7 g/m2 higher in fourth vs first quartile, p<0.007), higher carotid plaque burden score (0.37 higher in fourth vs first quartile, p=0.02) and trended to greater odds of CAC (1.44, 95% CI 0.98 to 2.15, p=0.06). A total of 65 incident CVD events were observed over the mean of 4.1 (2.6) years follow-up period. Higher PAT response was associated with increased future CVD events (HR: 1.20, 95% CI 1.02 to 1.42, p=0.03).

CONCLUSION

PAT is independently associated with markers of subclinical CVD and incident CVD events. Respiratory-related PAT response is a novel and promising polysomnography metric with cardiovascular implications.

Quantification of airway conductance from noninvasive ventilatory drive in patients with sleep apnea

Upper airway conductance, the ratio of inspiratory airflow to inspiratory effort, quantifies the degree of airway obstruction in hypopneas observed in sleep apnea. We evaluated the ratio of ventilation to noninvasive ventilatory drive as a surrogate of conductance. Furthermore, we developed and tested a refinement of noninvasive drive to incorporate the interactions of inspiratory flow, pressure, and drive to better estimate conductance. Hypopneas were compiled from existing polysomnography studies with esophageal catheterization in 18 patients with known or suspected sleep apnea, totaling 1,517 hypopneas during NREM sleep. For each hypopnea, reference standard conductance was calculated as the ratio of peak inspiratory flow to esophageal pressure change during inspiration. Ventilatory drive was calculated using the algorithm developed by Terrill et al. and then mathematically modified according to the presence or absence of flow limitation to noninvasively estimate esophageal pressure. The ratio of ventilation to ventilatory drive and the ratio of peak inspiratory flow to estimated esophageal pressure were each compared with the reference standard for all hypopneas and for median values from individual patients. Hypopnea ventilation to drive ratios were of limited correlation with the reference standard (R2 = 0.17, individual hypopneas; R2 = 0.03, median patient values). Modification of drive to estimated pressure yielded estimated conductance, which strongly correlated with reference standard conductance (R2 = 0.49, individual hypopneas; R2 = 0.77, median patient values). We conclude that the severity of airway obstruction during hypopneas may be estimated from noninvasive drive by accounting for mechanical effects of flow on pressure. NEW & NOTEWORTHY Classification of hypopneas as obstructive (decreased upper airway conductance) or central (decreased inspiratory flow commensurate with decreased effort) is complicated by the requirement of invasive methods, such as esophageal manometry. Here, we demonstrate that using a few esophageal pressure measurements to account for the interactions between inspiratory flow, pressure, and noninvasive ventilatory drive allows estimation of upper airway conductance. Further studies may use these findings to quantify airway obstruction completely noninvasively.

A comparison of 2 visual methods for classifying obstructive vs central hypopneas

STUDY OBJECTIVES

Rules for classifying apneas as obstructive, central, or mixed are well established. Although hypopneas are given equal weight when calculating the apnea-hypopnea index, classification is not standardized. Visual methods for classifying hypopneas have been proposed by the American Academy of Sleep Medicine and by Randerath et al (Sleep. 2013;36[3]:363-368) but never compared. We evaluated the clinical suitability of the 2 visual methods for classifying hypopneas as central or obstructive.

METHODS

Fifty hypopnea-containing polysomnographic segments were selected from patients with clear obstructive or clear central physiology to serve as standard obstructive or central hypopneas. These 100 hypopnea-containing polysomnographic segments were deidentified, randomized, and scored by 2 groups. We assigned 1 group to use the American Academy of Sleep Medicine criteria and the other the Randerath algorithm. After a washout period, re-randomized hypopnea-containing polysomnographic segments were scored using the alternative method. We determined the accuracy (agreement with standard), interrater (Fleiss's κ), and intrarater agreement (Cohen's κ) for obtained scores.

RESULTS

Accuracy of the 2 methods was similar: 67% vs 69.3% for Randerath et al and the American Academy of Sleep Medicine, respectively. Cohen's κ was 0.01-0.75, showing that some raters scored similarly using the 2 methods, while others scored them markedly differently. Fleiss's κ for the American Academy of Sleep Medicine algorithm was 0.32 (95% confidence interval, 0.29-0.36) and for the Randerath algorithm was 0.27 (95% confidence interval, 0.23-0.30).

CONCLUSIONS

More work is needed to discover a noninvasive way to accurately characterize hypopneas. Studies like ours may lay the foundation for discovering the full spectrum of physiologic consequences of obstructive sleep apnea and central sleep apnea.

Photoplethysmography in Normal and Pathological Sleep

This article presents an overview of the advancements that have been made in the use of photoplethysmography (PPG) for unobtrusive sleep studies. PPG is included in the quickly evolving and very popular landscape of wearables but has specific interesting properties, particularly the ability to capture the modulation of the autonomic nervous system during sleep. Recent advances have been made in PPG signal acquisition and processing, including coupling it with accelerometry in order to construct hypnograms in normal and pathologic sleep and also to detect sleep-disordered breathing (SDB). The limitations of PPG (e.g., oxymetry signal failure, motion artefacts, signal processing) are reviewed as well as technical solutions to overcome these issues. The potential medical applications of PPG are numerous, including home-based detection of SDB (for triage purposes), and long-term monitoring of insomnia, circadian rhythm sleep disorders (to assess treatment effects), and treated SDB (to ensure disease control). New contact sensor combinations to improve future wearables seem promising, particularly tools that allow for the assessment of brain activity. In this way, in-ear EEG combined with PPG and actigraphy could be an interesting focus for future research.

Distinguishing Obstructive Versus Central Apneas in Infrared Video of Sleep Using Deep Learning: Validation Study

Background

Sleep apnea is a respiratory disorder characterized by an intermittent reduction (hypopnea) or cessation (apnea) of breathing during sleep. Depending on the presence of a breathing effort, sleep apnea is divided into obstructive sleep apnea (OSA) and central sleep apnea (CSA) based on the different pathologies involved. If the majority of apneas in a person are obstructive, they will be diagnosed as OSA or otherwise as CSA. In addition, as it is challenging and highly controversial to divide hypopneas into central or obstructive, the decision about sleep apnea type (OSA vs CSA) is made based on apneas only. Choosing the appropriate treatment relies on distinguishing between obstructive apnea (OA) and central apnea (CA).

Objective

The objective of this study was to develop a noncontact method to distinguish between OAs and CAs.

Methods

Five different computer vision-based algorithms were used to process infrared (IR) video data to track and analyze body movements to differentiate different types of apnea (OA vs CA). In the first two methods, supervised classifiers were trained to process optical flow information. In the remaining three methods, a convolutional neural network (CNN) was designed to extract distinctive features from optical flow and to distinguish OA from CA.

Results

Overnight sleeping data of 42 participants (mean age 53, SD 15 years; mean BMI 30, SD 7 kg/m²; 27 men and 15 women; mean number of OA 16, SD 30; mean number of CA 3, SD 7; mean apnea-hypopnea index 27, SD 31 events/hour; mean sleep duration 5 hours, SD 1 hour) were collected for this study. The test and train data were recorded in two separate laboratory rooms. The best-performing model (3D-CNN) obtained 95% accuracy and an F₁ score of 89% in differentiating OA vs CA.

Conclusions

In this study, the first vision-based method was developed that differentiates apnea types (OA vs CA). The developed algorithm tracks and analyses chest and abdominal movements captured via an IR video camera. Unlike previously developed approaches, this method does not require any attachment to a user that could potentially alter the sleeping condition.

Pulse transit time in pregnancy: a new way to diagnose and classify sleep disordered breathing?

STUDY OBJECTIVES

There are significant discrepancies between the prevalence of snoring and that of objectively defined sleep disordered breathing among pregnant women, suggesting subtle airflow limitations that may not be captured by conventional scoring. This study examined the performance of pulse transit time, an indirect measure of arterial stiffness and sympathetic activation, in pregnancy.

METHODS

Pregnant women with obesity and snoring and a group of controls without symptoms of sleep disordered breathing were recruited in the first trimester. Women underwent a level III in-laboratory sleep monitoring study including an electrocardiogram and pulse oximetry, and pulse transit time was measured. Sleep disordered breathing was defined as an apnea-hypopnea index at least five events per hour of sleep. Statistical analysis was performed using Spearman correlation, Fisher's exact t-test, and univariate analysis.

RESULTS

Of the 222 women, 38 met criteria for sleep disordered breathing. Pulse transit time drops were very prevalent (95% of participants with snoring had > 5 drops per hour). Median apnea-hypopnea index was 0.7 (interquartile range [IQR]: 2.6) events per hour whereas median pulse transit time drop index was 20.70 (IQR: 35.90) events per hour. Pulse transit time index was significantly higher in snorers with apnea-hypopnea index less than five events per hours and participants with apnea-hypopnea index greater than five events per hour compared to controls. Examination of random epochs with pulse transit time drops showed that 95% of pulse transit time drops were associated with airflow limitation.

CONCLUSIONS

Pulse transit time ascertains frequent events of sympathetic activation in at-risk women with and without sleep disordered breathing beyond conventional apneas and hypopneas. Pulse transit time may be an important addition to the identification of clinically significant sleep disordered breathing in pregnant women, and may identify more sleep disordered breathing than apnea-hypopnea index.

Alterations in heart rate variability in patients with peripheral arterial disease requiring surgical revascularization have limited association with postoperative major adverse cardiovascular and cerebrovascular events

Objective

Obstructive sleep apnea (OSA) is common in peripheral arterial disease (PAD) and associates with high mortality after surgery. Since abnormal heart rate variability (HRV) is predictive of postoperative complications, we investigated the relations of HRV with PAD, OSA and major adverse cardiovascular and cerebrovascular events (MACCE).

Materials and methods

Seventy-five patients (67±9 years) scheduled for sub-inguinal revascularization and 15 controls (63±6 years) underwent polysomnography and HRV analyses. OSA with an apnea-hypopnea index (AHI) ≥20/hour was considered significant. HRV was measured during wakefulness, S2, S3-4 and rapid eye movement (REM) sleep with time and frequency domain methods including beat-to-beat variability, low frequency (LF) and high frequency (HF) power, and detrended fluctuation analysis (DFA). MACCE was defined as cardiac death, myocardial infarction, coronary revascularization, hospitalized angina pectoris and stroke.

Results

Thirty-six patients (48%) had AHI≥20/hour. During follow-up (median 52 months), 22 patients (29%) suffered a MACCE. Compared to controls, fractal correlation of HRV (scaling exponent alpha 1 measured with DFA) was weaker during S2 and evening wakefulness in all subgroups (+/-AHI≥20/hour, +/-MACCE) but only in patients with AHI≥20/hour during morning wakefulness. The LF/HF ratio was lower in all subgroups during S2 but only in patients with AHI ≥20/hour during evening or morning wake. In the covariance analysis adjusted for age, body mass index, coronary artery disease and PAD duration, the alpha 1 during morning wakefulness remained significantly lower in patients with AHI≥20/hour than in those without (1.12 vs. 1.45; p = 0.03). Decreased HF during REM (p = 0.04) and S3-4 sleep (p = 0.03) were predictive of MACCE. In analyses with all sleep stages combined, mean heart rate as well as very low frequency, LF, HF and total power were associated with OSA of mild-to-moderate severity (AHI 10-20/hour).

Conclusions

HRV is altered in patients with PAD. These alterations have a limited association with OSA and MACCE.

The effect of continuous positive airway pressure on heart rate variability during the night in patients with chronic heart failure and central sleep apnoea

Continuous positive airway pressure (CPAP) improves autonomic activity in patients with chronic heart failure (CHF) and central sleep apnoea (CSA), but its effect on heart rate variability (HRV) during therapy has not been reported. We hypothesized that CPAP may decrease HRV, despite its beneficial effects on sympathetic overactivation, due to the expected stabilization of breathing. Sixty-seven CHF patients underwent polysomnography (PSG). Ten of them presented with CSA (age 66.1±8.5 years, apnoea-hypopnea index [AHI]=57.6±23.3, central AHI [cAHI]=41.6±24.6 [mean±SD]) and were subjected to a second PSG with manual CPAP titration. Beat-to-beat heart intervals for a 6-hour period of sleep were extracted from each recording and HRV was analysed. CPAP significantly reduced AHI (AHI=23.1±18.3 P=.004). Standard deviation of normal-normal interbeat interval (SDNN) (61.5±29.0 vs 49.5±19.3 ms, P=.021), root mean square of successive differences (RMSSD) (21.8±9.2 vs 16.4±7.1 ms, P=.042), total power (lnTP=7.8±1.1 vs 7.4±0.8 ms² , P=.037), low frequency power (lnLF=5.5±1.5 vs 5.0±1.4 ms² , P=.003) and high frequency power (lnHF=4.6±1.0 vs 4.0±1.0 ms² , P=.024) were decreased. There was a strong correlation between the decrease in AHI and the decrease in lnHF (Spearman's ρ=.782). CPAP leads to a decrease in spectral and time domain parameters of HRV during therapy in CHF patients with CSA. These changes are best explained by the effect which CPAP-influenced breathing pattern and lowered AHI exert on HRV.

Persistent respiratory effort after adenotonsillectomy in children with sleep-disordered breathing

OBJECTIVES

Adenotonsillectomy (AT) markedly improves but does not necessarily normalize polysomnographic findings in children with adenotonsillar hypertrophy and related sleep-disordered breathing (SDB). Adenotonsillectomy efficacy should be evaluated by follow-up polysomnography (PSG), but this method may underestimate persistent respiratory effort (RE). Mandibular movement (MMas) monitoring is an innovative measurement that readily identifies RE during upper airway obstruction. We hypothesized that MMas indices would decrease in parallel of PSG indices and that children with persistent RE more reliably could be identified with MMas.

METHODS

Twenty-five children (3-12 years of age) with SDB were enrolled in this individual prospective-cohort study. Polysomnography was supplemented with a midsagittal movement magnetic sensor that measured MMas during each respiratory cycle before and > 3 months after AT.

RESULTS

Adenotonsillectomy significantly improved PSG indices, except for RE-related arousals (RERA). Mandibular movement index changes after AT significantly were correlated with corresponding decreases in sleep apnea-hypopnea index (AHI) and O₂ desaturation index (ODI) (Spearman's rho = 0.978 and 0.922, respectively), whereas changes in MMas duration significantly were associated with both RERA duration (rho = 0.475, P = 0.017) and index (rho = 0.564, P = 0.003). Conditional multivariate analysis showed that both AHI and RERA significantly contributed to the variance of MMas index after AT (P = 0.0003 and 0.0005, respectively), whereas MMas duration consistently was related to the duration of RERA regardless of AT.

CONCLUSION

Adenotonsillectomy significantly reduced AHI. However, persistent RERA were apparent in a significant proportion of children, and this was reflected by the remaining abnormal MMas pattern. Follow-up of children after AT can be recommended and readily achieved by monitoring MMas to identify persistent RE.

LEVEL OF EVIDENCE

4. Laryngoscope, 128:1230-1237, 2018.

Mandibular Movements As Accurate Reporters of Respiratory Effort during Sleep: Validation against Diaphragmatic Electromyography

Context

Mandibular movements (MM) are considered as reliable reporters of respiratory effort (RE) during sleep and sleep disordered breathing (SDB), but MM accuracy has never been validated against the gold standard diaphragmatic electromyography (EMG-d).

Objectives

To assess the degree of agreement between MM and EMG-d signals during different sleep stages and abnormal respiratory events.

Methods

Twenty-five consecutive adult patients with SDB were studied by polysomnography (PSG) that also included multipair esophageal diaphragm electromyography and a magnetometer to record MM. EMG-d activity (microvolt) and MM (millimeter) amplitudes were extracted by envelope processing. Agreement between signals amplitudes was evaluated by mixed linear regression and cross-correlation function and in segments of PSG including event-free and SDB periods.

Results

The average total sleep time was 370 ± 18 min and the apnea hypopnea index was 24.8 ± 5.2 events/h. MM and EMG-d amplitudes were significantly cross-correlated: median r (95% CI): 0.67 (0.23–0.96). A mixed linear model showed that for each 10 µV of increase in EMG-d activity, MM amplitude increased by 0.28 mm. The variations in MM amplitudes (median range: 0.11–0.84 mm) between normal breathing, respiratory effort-related arousal, obstructive, mixed, and central apnea periods closely corresponded to those observed with EMG-d activity (median range: 2.11–8.23 µV).

Conclusion

MM amplitudes change proportionally to diaphragmatic EMG activity and accurately identify variations of RE during normal sleep and SDB.

Pulse transit time as a tool to characterize obstructive and central apneas in children

PURPOSE

The characterization of apneas during polysomnography (PSG) as obstructive or central is a key element of a sleep study. Pulse transit time (PTT) has demonstrated its potential as a noninvasive surrogate marker for inspiratory efforts. The aim of the study was to assess the ability of PTT to classify apneas as central or obstructive, as compared to respiratory inductance plethysmography (RIP) in children.

METHODS

Overnight PSG with simultaneous PTT recording was performed on 11 consecutive children (mean age 8.9 years, range 1-18.2 years). The same observer scored the apneas using two blinded configurations: (1) the RIP scoring used the nasal pressure, thermistors, thoracic and abdominal movements, and pulse oximetry signals: (2) the PTT scoring used PTT in combination with all the other signals without the thoracic and abdominal movements.

RESULTS

One hundred fourteen apneas out of a total of 520 respiratory events were analyzed. With RIP, 58 (51%) apneas were scored as obstructive and 56 (49%) as central. Using PTT, 77 (68%) of the apneas were scored as obstructive and 37 (32%) as central. When using PTT, 30 apneas scored as central by RIP were scored as obstructive. PTT was highly sensitive (81%) but poorly specific (46%) in scoring 58 apneas as obstructive. PTT was less sensitive (46%) but highly specific (81%) to score 56 apneas as central.

CONCLUSION

PTT may be used as an additional tool to RIP to improve the scoring of apneas as obstructive or central in children. The high percentage of artifact is a limitation of PTT.

Distinguishing obstructive from central sleep apneas and hypopneas using linear SVM and acoustic features

Sleep Apnea (SA) is a very common but underdiagnosed respiratory disorder. SA has 2 main types, obstructive and central sleep apnea (OSA and CSA, respectively). The distinction between the 2 types is important for proper clinical management. Our aim in this study was to deploy acoustic analysis of breath sounds to distinguish central from obstructive events. We recorded breath sounds from 29 patients from which 45 segments with obstructive only and 40 segments with central only respiratory events were isolated. Subsequently, 10 acoustic features were extracted and used to identify basic breath sounds: inspiration, expiration, and snoring. A 2nd set of 6 sound-specific features were extracted from the basic sounds, designed based on SA pathophysiology. These 6 features were used to train and test a linear SVM classifier using a leave-one-out cross validation scheme. We achieved an excellent accuracy of 91.8%. In conclusion, this is the first study to demonstrate the ability to distinguish CSA from OSA with high reliability from breath sound recordings during sleep.

Blood Pressure Increases in OSA due to Maintained Neurovascular Sympathetic Transduction: Impact of CPAP

STUDY OBJECTIVES

To test the hypothesis that greater resting sympathetic activity in obstructive sleep apnea (OSA) syndrome would not induce a lesser sympathetic neurovascular transduction.

DESIGN

Case-controlled cohort study.

PARTICIPANTS

33 patients with newly diagnosed OSA without comorbidities and 14 healthy controls.

INTERVENTIONS

6 months of continuous positive airway pressure (CPAP) treatment for OSA patients and follow-up for 9 healthy controls.

MEASUREMENTS AND RESULTS

We assessed resting sympathetic outflow and sympathetic neurovascular transduction. Sympathetic activity was directly measured (microneurography) at rest and in response to sustained isometric handgrip exercise. Neurovascular transduction was derived from the relationship of sympathetic activity and blood pressure to leg blood flow during exercise. Despite an elevated sympathetic activity of ∼50% in OSA compared to controls, neurovascular transduction was not different (i.e., absence of tachyphylaxis). After six months of CPAP, there were significant declines in diastolic pressure, averaging ∼4 mm Hg, and in sympathetic activity, averaging ∼20% with no change in transduction.

CONCLUSIONS

Greater sympathetic activity in obstructive sleep apnea does not appear to be associated with lesser neurovascular transduction. Hence, elevated sympathetic outflow without lesser transduction may underlie the prevalent development of hypertension in this population that is well controlled by continuous positive airway pressure treatment.

[The syndrome of increased upper airways resistance: What are the clinical features and diagnostic procedures?]

The upper airway resistance syndrome "UARS" is a poorly defined entity, often described as a moderate variant of the obstructive sleep apnea syndrome. It is associated with respiratory effort-related arousal, absence of obstructive sleep apnea, and absence of significant desaturation. It is a relatively common condition that predominantly affects non-obese young adults, with no predominance in either sex. The degree of upper airway collapsibility during sleep of patients with UARS is intermediate between that of normal subjects and that of patients with mild-to-moderate sleep apnea syndrome. Craniofacial and palatal abnormalities are often noted. Patients frequently complain of a functional somatic syndrome, especially daytime sleepiness and chronic fatigue. Polysomnography with esophageal pressure measurements remains the gold standard diagnostic test. The absence of any neurological abnormality gives UARS a good prognosis and it is potentially reversible if treated early. However, some studies suggest that untreated UARS has an increased risk of arterial hypertension. It can also evolve into obstructive sleep apnea.

Mandibular movements identify respiratory effort in pediatric obstructive sleep apnea

STUDY OBJECTIVES

Obstructive sleep apnea-hypopnea (OAH) diagnosis in children is based on the quantification of flow and respiratory effort (RE). Pulse transit time (PTT) is one validated tool to recognize RE. Pattern analysis of mandibular movements (MM) might be an alternative method to detect RE. We compared several patterns of MM to concomittant changes in PTT during OAH in children with adenotonsillar hypertrophy.

METHODS

PARTICIPANTS

33 consecutive children with snoring and symptoms/signs of OAH.

MEASUREMENTS

MMs were measured during polysomnography with a magnetometer device (Brizzy Nomics, Liege, Belgium) placed on the chin and forehead. Patterns of MM were evaluated representing peak to peak fluctuations > 0.3 mm in mandibular excursion (MML), mandibular opening (MMO), and sharp MM (MMS), which closed the mouth on cortical arousal (CAr).

RESULTS

The median (95% CI) hourly rate of at least 1 MM (MML, or MMO, or MMS) was 18.1 (13.2-36.3) and strongly correlated with OAHI (p = 0.003) but not with central apnea-hypopnea index (CAHI; p = 0.292). The durations when the MM amplitude was > 0.4 mm and PTT > 15 ms were strongly correlated (p < 0.001). The mean (SD) of MM peak to peak amplitude was larger during OAH than CAH (0.9 ± 0.7 mm and 0.2 ± 0.3 mm; p < 0.001, respectively). MMS at the termination of OAH had larger amplitude compared to MMS with CAH (1.5 ± 0.9 mm and 0.5 ± 0.7 mm, respectively, p < 0.001).

CONCLUSIONS

MM > 0.4 mm occurred frequently during periods of OAH and were frequently terminated by MMS corresponding to mouth closure on CAr. The MM findings strongly correlated with changes in PTT. MM analysis could be a simple and accurate promising tool for RE characterization and optimization of OAH diagnosis in children.

Altered in vitro endothelial repair and monocyte migration in obstructive sleep apnea: implication of VEGF and CRP

STUDY OBJECTIVES

Although obstructive sleep apnea (OSA) causes cardiovascular morbidities through atherosclerosis induced by inflammation and endothelial dysfunction, OSA patients exhibit elevated plasma vascular endothelial growth factor (VEGF), which may represent an adaptive response to intermittent hypoxia. The aims of this study were to investigate whether in vitro endothelial wound healing and monocyte migration are affected by patient serum, and to determine the implication of circulating factors (VEGF and C-reactive protein).

PATIENTS

Serum was collected from healthy controls (HC), "healthy" OSA, and metabolic syndrome (MS) patients with or without OSA.

MEASUREMENTS AND RESULTS

Along with the presence of OSA and/or MS, both VEGF and hsCRP were significantly elevated in patient serum. Their specific role was tested with blocking antibodies on primary endothelial cells for wound healing assay and on human monocytes for migration assay. Endothelial wound healing was reduced with OSA compared to HC serum, and even more significantly using MS+OSA patient serum. Altered wound healing with OSA serum was unmasked when blocking VEGF and restored when blocking CRP. Monocyte migration was activated with OSA serum, and further enhanced by MS+OSA patient serum. Blocking CRP in serum inhibited this migration.

CONCLUSIONS

Serum from OSA patient alters in vitro endothelial cell repair function and activates monocyte migration; this is further aggravated with the presence of metabolic syndrome. These effects are partly driven by VEGF and CRP, suggesting an unfavorable balance between the pro healing (VEGF) and pro injury (CRP) factors that may promote vascular injury in OSA with and without metabolic syndrome.

Nonalcoholic fatty liver disease, nocturnal hypoxia, and endothelial function in patients with sleep apnea

BACKGROUND

Nocturnal hypoxia, the hallmark of OSA, is a potential contributing factor for nonalcoholic fatty liver disease (NAFLD). NAFLD severity and its implication in OSA-related endothelial dysfunction have not been investigated in a large, unselected OSA population, including nonobese subjects.

METHODS

Noninvasive blood tests (SteatoTest, NashTest, and FibroTest) were used to evaluate steatosis, nonalcoholic steatohepatitis (NASH), and fibrosis in a large cohort of patients with OSA. In the same group, endothelial function and its links with NAFLD severity were assessed.

RESULTS

Of the 226 subjects included who were referred for suspicion of OSA (men, 55%; median age, 56 years; median BMI, 34.2 kg/m2 [33% with BMI<30 kg/m2]), 61.5% exhibited moderate or severe steatosis. By multivariate analysis, independent factors for liver steatosis were, as expected, triglyceride levels (P<.0001) and insulin resistance (P=.0004) as well as nocturnal cumulative time spent<90% of oxygen saturation (CT90) (P=.01). Thirty-eight percent had borderline or possible NASH (N1 or N2 with NashTest). CT90 was significantly associated with borderline or possible NASH (P=.035) in univariate but not in multivariate analysis. The dose-response relationship between the severity of nocturnal hypoxia and liver injury was established only in morbid obesity and not in lean. Multivariate models showed that steatosis was independently associated with endothelial dysfunction after adjustment for confounders.

CONCLUSIONS

In a large, unselected OSA population, the severity of nocturnal hypoxia was independently associated with steatosis. Preexisting obesity exacerbated the effects of nocturnal hypoxemia. NAFLD is a potential mechanism of endothelial dysfunction in OSA.

Guidelines for the recording and evaluation of pharmaco-sleep studies in man: the International Pharmaco-EEG Society (IPEG)

The International Pharmaco-EEG Society (IPEG) presents guidelines summarising the requirements for the recording and computerised evaluation of pharmaco-sleep data in man. Over the past years, technical and data-processing methods have advanced steadily, thus enhancing data quality and expanding the palette of sleep assessment tools that can be used to investigate the activity of drugs on the central nervous system (CNS), determine the time course of effects and pharmacodynamic properties of novel therapeutics, hence enabling the study of the pharmacokinetic/pharmacodynamic relationship, and evaluate the CNS penetration or toxicity of compounds. However, despite the presence of robust guidelines on the scoring of polysomnography -recordings, a review of the literature reveals inconsistent -aspects in the operating procedures from one study to another. While this fact does not invalidate results, the lack of standardisation constitutes a regrettable shortcoming, especially in the context of drug development programmes. The present guidelines are intended to assist investigators, who are using pharmaco-sleep measures in clinical research, in an effort to provide clear and concise recommendations and thereby to standardise methodology and facilitate comparability of data across laboratories.

Profile of circulating cytokines: impact of OSA, obesity and acute cardiovascular events

Obstructive sleep apnea (OSA) is inducing oxidative stress and consequently promotes systemic inflammation and cardiovascular morbidity. The respective impact of obesity, sleep apnea and acute cardiovascular events on the profile of inflammatory cytokines has not been extensively evaluated. We examined the profile of circulating cytokines in a case-control study comparing nonobese or obese patients with or without sleep apnea and with or without an acute cardiovascular event. Patients were assessed by sleep studies and inflammatory (hs-CRP, Leptin, RANTES, MCP1, IL6, IL8, TNF-α) and anti-inflammatory (adiponectin, IL1-Ra) cytokines profile. A cardiovascular phenotyping was performed including carotid intima-media thickness, pulse wave velocity and 24h blood pressure monitoring. In comparison with patients without sleep apnea or without comorbidities, patients with the combination of an acute cardiovascular event and pre-existing sleep apnea showed a higher burden of systemic inflammation with significant increase in serum levels of hs-CRP, IL1-Ra, IL-8, IL-6, TNF-α, Rantes and sICAM. Rantes and sICAM serum levels were independently associated with AHI after an acute cardiovascular event. Serum levels of different inflammatory markers were significantly increased in patients with the combination of sleep apnea and an acute cardiovascular event. Since these biomarkers could be associated with worsened cardiovascular outcome, diagnosing and treating associated sleep apnea is potentially important in patients after an acute cardiovascular event.

A critical review of peripheral arterial tone and pulse transit time as indirect diagnostic methods for detecting sleep disordered breathing and characterizing sleep structure

PURPOSE OF REVIEW

Sympathetic activity varies continuously across sleep stages. During rapid eye movement sleep, sympathetic tone increases substantially but is highly variable. Microarousals are associated with momentary bursts of sympathetic activity. Abnormal respiratory events progressively elevate sympathetic activity in proportion to the severity of oxyhemoglobin desaturation. These phenomena imply that cardiovascular markers of sympathetic activity such as peripheral arterial tone (PAT) and pulse transit time could be indirect tools for diagnosing sleep disordered breathing and characterizing sleep structure and fragmentation.

RECENT FINDINGS

Measurement of variations in PAT coupled with pulse rate accelerations and desaturations in oximetry can be used to diagnose sleep apnea. Good agreement between both manually and automatically analyzed PAT recordings and polysomnography has been demonstrated during in-laboratory or at-home studies. Numerous validation studies against esophageal pressure have demonstrated that pulse transit time is the best noninvasive method for measurement of respiratory effort. Pulse transit time and PAT are sensitive techniques for arousal recognition, particularly in children and infants. There are specific sleep stage-dependent PAT patterns that allow for the recognition of rapid eye movement sleep and, in the case of nonrapid eye movement sleep, the separation of lighter stages from deeper, slow wave sleep. Elevated nocturnal sympathetic activity as documented by PAT attenuations is linked with chronically elevated blood pressure in humans.

SUMMARY

Cardiovascular markers of autonomic control during sleep permit not only the diagnosis of obstructive sleep apnea and estimation of sleep structure but are also linked with the prevalence of daytime hypertension.

Pulse transit time in screening sleep disordered breathing in an elderly population: the PROOF-SYNAPSE study

STUDY OBJECTIVES

Pulse transit time (PPT) has been introduced as a useful screening tool to diagnose sleep disordered breathing (SDB). Since the prevalence of SDB increases with age, the question is whether PTT could be used to diagnose SDB in the elderly. We assess the effectiveness of PTT for SDB screening in a large healthy elderly population.

SETTING

Community-based sample in home and research clinical settings.

INTERVENTION

N/A.

PARTICIPANTS

Seven hundred eighty volunteers, free of cardiac and neurologic disease, aged 68.6 ± 1.0 years, underwent ambulatory polygraphy to measure the apnea-hypopnea index (AHI). The presence of SDB was defined as an AHI of 15 or greater. The PTT was continuously monitored during the nocturnal study, and the overall autonomic arousal index (AAI) was calculated.

RESULTS

SDB was diagnosed in 447 (57.3%) subjects. In these subjects, the Bland-Altman plot for AAI revealed an underestimation with a bias of -8.04 ± 16.55 events per hour (mean ± 95% confidence interval). Receiver operating characteristic curves constructed for an AHI of 15 or greater defined an area under the curve of 0.67 and a cutoff point to AAI 32.3 events per hour, giving a sensitivity of 70.5% and a specificity of 54.7%. For prediction of an AHI of at least 30, the area under the curve was equal to 0.74 for a cutoff point of 56.3 events per hour, giving a better specificity (94.7%) but a lower sensitivity (32.2%).

CONCLUSIONS

In a healthy older population, the AAI showed moderate sensitivity for predicting SDB. This data does not allow us to use PTT as a screening tool for the diagnosis of SDB in the elderly.

CLINICAL TRIAL REGISTRATION

NCT 00759304 and NCT 00766584.

Automatic non-invasive differentiation of obstructive and central hypopneas with nasal airflow compared to esophageal pressure

The differentiation of obstructive and central respiratory events is a major challenge in the diagnosis of sleep disordered breathing. Esophageal pressure (Pes) measurement is the gold-standard method to identify these events but its invasiveness deters its usage in clinical routine. Flattening patterns appear in the airflow signal during episodes of inspiratory flow limitation (IFL) and have been shown with invasive techniques to be useful to differentiate between central and obstructive hypopneas. In this study we present a new method for the automatic non-invasive differentiation of obstructive and central hypopneas solely with nasal airflow. An overall of 36 patients underwent full night polysomnography with systematic Pes recording and a total of 1069 hypopneas were manually scored by human experts to create a gold-standard annotation set. Features were automatically extracted from the nasal airflow signal to train and test our automatic classifier (Discriminant Analysis). Flattening patterns were non-invasively assessed in the airflow signal using spectral and time analysis. The automatic non-invasive classifier obtained a sensitivity of 0.71 and an accuracy of 0.69, similar to the results obtained with a manual non-invasive classification algorithm. Hence, flattening airflow patterns seem promising for the non-invasive differentiation of obstructive and central hypopneas.

Pediatric obstructive sleep apnea assessment using pulse oximetry and dual RIP bands

The diagnosis of Obstructive Sleep Apnea (OSA) in children presents a challenging diagnostic problem given the high prevalence (2-3%), the resource intensity of the overnight polysomnography investigation, and the realisation that OSA poses a serious threat to the healthy growth and development of children. Previous attempts to develop OSA diagnostic systems using home pulse oximetry studies have failed to meet the accuracy requirements - particularly the low false normal rate (FNR) - required for a pre-PSG screening test. Thus the aim of this study is to investigate the feasibility of an OSA severity diagnostic system based on both oximetry and dual respiratory inductance plethysmography (RIP) bands. A total of 90 PSG studies (30 each of normal, mild/moderate and severe OSA) were retrospectively analyzed. Quantifications of oxygen desaturations (S), respiratory events (E) and heart rate arousals (A) were calculated and extracted and an empirical rule-based SEA classifier model for normal, mild/moderate and severe OSA defined and developed. In addition, an automated classifier using a decision tree algorithm was trained and tested using a 10-fold cross-validation. The empirical classification system showed a correct classification rate (CCR) of 0.83 (Cohen's Kappa κ=0.81, FNR=0.08), and the decision tree classifier achieved a CCR of 0.79 (κ=0.73, FNR=0.08) when compared to gold standard PSG assessment. The relatively high CCR, and low FNR indicate that a OSA severity system based on dual RIP and oximetry is feasible for application as a pre-PSG screening tool.

An invasive and a noninvasive approach for the automatic differentiation of obstructive and central hypopneas

The automatic differentiation of obstructive and central respiratory events is a major challenge in the diagnosis of sleep-disordered breathing. Esophageal pressure (Pes) measurement is the gold-standard method to identify these events. This study presents a new classifier that automatically differentiates obstructive and central hypopneas with the Pes signal and a new approach for an automatic noninvasive classifier with nasal airflow. An overall of 28 patients underwent night polysomnography with Pes recording, and a total of 769 hypopneas were manually scored by human experts to create a gold-standard annotation set. Features were automatically extracted from the Pes signal to train and test the classifiers (discriminant analysis, support vector machines, and adaboost). After a significantly (p < 0.01) higher incidence of inspiratory flow limitation episodes in obstructive hypopneas was objectively, invasively assessed compared to central hypopneas, the feasibility of an automatic noninvasive classifier with features extracted from the airflow signal was demonstrated. The automatic invasive classifier achieved a mean sensitivity, specificity, and accuracy of 0.90 after a 100-fold cross validation. The automatic noninvasive feasibility study obtained similar hypopnea differentiation results as a manual noninvasive classification algorithm. Hence, both systems seem promising for the automatic differentiation of obstructive and central hypopneas.

PTT variability for discrimination of sleep apnea related decreases in the amplitude fluctuations of PPG signal in children

In this paper, an analysis of pulse transit time variability (PTTV) during decreases in the amplitude fluctuations of pulse photoplethysmography signal (PPG) (DAP) events for obstructive sleep apnea syndrome (OSAS) screening is presented. The temporal evolution of time-frequency PTTV parameters during DAP was analyzed. The results show an increase in the sympathetic activity index low-frequency component (LF) during DAP for PTTV (85%) significantly higher than for heart rate variability (HRV) (33%), (p < 10(-13)). However, decreases in parasympathetic activity produce lower decrements in high-frequency component (HF) indexes for PTTV (18%) than for HRV (22%). Thus, PTTV reflects sympathetic changes more clearly than HRV. A clinical study was carried out. DAP events were classified as apneic or nonapneic using a linear discriminant analysis from the PTTV indexes. The ratio of DAP events per hour r (DAP), the ratio after filtering based on HRV indexes r (HRV) (DAP), or on PTTV indexes r (PTTV) (DAP), were computed. The results show an accuracy of 75% for r (PTTV) (DAP) (14% increase with respect to r (DAP) and 5% increase with respect to r (HRV) (DAP)), a sensitivity of 81.8%, and a specificity of 73.9% when classifying 1-h polysomnographic excerpts as OSAS or normal. These results suggest that the combination of DAP and PTTV could be better alternative for sleep apnea screening using PPG with the added benefit of its low cost and simplicity.

Automatic differentiation of obstructive and central hypopneas with esophageal pressure measurement during sleep

The differentiation between obstructive and central respiratory events is one of the most recurrent tasks in the diagnosis of sleep disordered breathing. Esophageal pressure measurement is the gold-standard method to assess respiratory effort and identify these events. But as its invasiveness discourages its use in clinical routine, non-invasisve systems have been proposed for differentiation. However, their adoption has been slow due to their limited clinical validation, as the creation of manual, gold-standard validation sets by human experts is a cumbersome procedure. In this study, a new system is proposed for an objective automatic, gold-standard differentiation between obstructive and central hypopneas with the esophageal pressure signal. First, an overall of 356 hypopneas of 16 patients were manually scored by a human expert to create a gold-standard validation set. Then, features were extracted from each hypopnea to train and test classifiers (Discriminant Analysis, Support Vector Machines and adaboost classifiers) to differentiate between central and obstructive hypopneas with the gold-standard esophageal pressure signal. The automatic differentiation system achieved promising results, with a sensitivity of 0.88, a specificity of 0.93 and an accuracy of 0.90. Hence, this system seems promising for an automatic, gold-standard differentiation between obstructive and central hypopneas.

[Management of central sleep apnea]

Central sleep apnea is highly prevalent in association with heart failure, some neurological diseases and chronic opioids use. There are two main categories of central sleep apnea respectively related with different underlying conditions. Some hypocapnic patients exhibit respiratory control system instability and central apnea occurs when PaCO(2) falls below the threshold for apnea during sleep. The other group are patients with chronic hypercapnia mainly in the context of neuromuscular disorders or obesity hypoventilation syndrome. All these patients should be assessed by recording blood gases, polysomnography and ventilatory responses to CO(2). Cardiologic assessment should include pro-brain natriuretic factor (pro-BNP) and cardiac echography whereas neurological examination requires brain imaging and/or electromyography. Ventilatory supports used for treating central sleep apnea are non-invasive ventilation and servo-assisted ventilation in hypercapnic and hypocapnic patients respectively.

Psychological variables as predictors of adherence to treatment by continuous positive airway pressure

STUDY OBJECTIVES

We examined whether psychological variables enable us to predict adherence to CPAP in order to construct a predictive model to identify patients at risk of abandoning treatment.

METHOD

One hundred and twenty-two Obstructive Sleep Apnoea (OSA) patients were studied before and one month after beginning CPAP treatment. All patients completed four psychological evaluation instruments before CPAP treatment: a health perception questionnaire (Nottingham Health Profile: NHP), a mental health rating scale (Hospital Anxiety and Depression Scale: HADS) and two disease-specific questionnaires that measure the patient's understanding of OSA and its treatment (Apnea Knowledge Test: AKT) and his attitudes to OSA and CPAP (Apnea Beliefs Scale: ABS).

RESULTS

Thirty percent of the participants were non-adherent at one month. Decision-tree analysis indicated that it was possible to correctly classify 85.7% of non-adherent patients using three baseline factors (Emotional reactions score [NHP], age, and total score on ABS). Logistic regression analyses confirmed these two psychological variables as independent predictors of adherence.

CONCLUSION

Assessing psychological well-being and subjective health status at onset of CPAP enables the identification of patients at risk of abandoning CPAP treatment. This subgroup could then be targeted early to receive supportive and educational measures to improve adherence rates.

Effects of continuous positive airway pressure on quality of life in patients with moderate to severe obstructive sleep apnea: data from a randomized controlled trial

STUDY OBJECTIVES

Previous studies have shown that CPAP has a substantial impact on daytime symptoms and quality of life (QOL). It remains unclear which outcome measures best identify real CPAP effects and carry independent information.

METHODS

One hundred-two men with moderate-severe obstructive sleep apnea were randomized to either "real" or "sham" CPAP for one month. Outcome measures were subjective sleepiness (Epworth Sleepiness Scale [ESS]) and QOL measures includiig SF-36/SF-12 and Calgary Sleep Apnea Quality of Life Index (SAQLI). The bed partner's QOL and rating of patient's response to CPAP were assessed with the Dublin questionnaire. All data were standardized using effect sizes and expressed as real minus sham to remove the nonspecific effects of placebo.

RESULTS

Real CPAP was superior to sham CPAP in almost all outcome measures. ESS, patient's component from Dublin, and social interactions from SAQLI showed the largest differences in effect sizes between real and sham (1.33, 0.98, and 0.92 respectively). ESS carried the highest predictive power of real CPAP response (P < 0.0001, r2 = 0.21). Question number 5 from Dublin (partner assessed patient's sleep quality) and question 6 from ESS (dozing while talking) were the best single item predictors of real CPAP response.

CONCLUSIONS

Real CPAP reduces subjective sleepiness and improves QOL of both patients and bed partners. ESS is the best score; question number 5 from Dublin and question number 6 from ESS are the best single item predictors of real CPAP response. This information should allow the selection of appropriate questions in clinical practice and research protocols.

Distinguishing obstructive from central sleep apnea events: diaphragm electromyogram and esophageal pressure compared

BACKGROUND

Distinguishing central sleep apnea (CSA) from obstructive sleep apnea (OSA) can be clinically important because different types of apnea may require different treatment approaches. Academically, this distinction is important for investigating the pathological mechanism of different types of sleep apnea. Conventional polysomnography (PSG) with recording of chest and abdominal movement may overestimate the frequency of CSA, leading to inappropriate treatment of sleep-disordered breathing. We hypothesized that diaphragm electromyogram (EMGdi) could be a useful technique to assess neural respiratory drive and respiratory effort and, therefore, to distinguish accurately CSA from OSA.

METHODS

A multipair esophageal electrode catheter mounted with a balloon was used to record the EMGdi and esophageal pressure (Pes) during overnight PSG. Nineteen patients were included in the study, 12 of whom had previously been identified as having central apnea-hypopnea on a diagnostic PSG undertaken for symptoms that suggest OSA and 7 of whom were known to have heart failure.

RESULTS

A good relationship was found between the swing of Pes and the root mean (+/- SD) square of the EMGdi during OSA events (0.89 +/- 0.10). About one third of CSA events diagnosed by uncalibrated respiratory inductance plethysmography could not be confirmed by Pes or EMGdi. No difference was found in the number of CSAs diagnosed by Pes (1,319) vs EMGdi (1,293; p > 0.01).

CONCLUSIONS

We conclude that both Pes and EMGdi measurements are useful in accurately differentiating central from obstructive respiratory events. Conventional PSG with recording of chest and abdominal movement overestimates the frequency of CSA events.

Validation of forehead venous pressure as a measure of respiratory effort for the diagnosis of sleep apnea

OBJECTIVES

The aim of the study was to validate the measurement of Forehead Venous Pressure derived from a single site on the forehead as an alternative to esophageal manometry and respiratory effort bands in the differential diagnosis of sleep apnea.

METHODS

Fourteen subjects underwent a laboratory polysomnography concurrently with ARES Unicorder at Walter Reed Army Medical Center. Two-hundred respiratory events were selected by a scorer boarded in sleep medicine and classified into six event categories used in the differential diagnosis of sleep disordered breathing. Four sets of events were prepared, each containing airflow and one of four measures of respiratory effort (i.e., esophageal manometer, chest and abdomen bands, and forehead venous pressure). A second board-certified scorer scored each set of events twice while blinded to the type of the effort signal.

RESULTS

The inter-rater Kappa scores across all event types indicated all four effort signals provided moderate agreement (kappa = 0.43-0.47). When comparing the intra-rater Kappa scores, the chest belt was superior (kappa = 0.88) to the esophageal manometry, FVP and abdomen belt (kappa = 0.78-0.82). The Kappa scores for the intra-rater comparison with the esophageal serving as the gold standard, FVP abdomen and chest all showed near perfect agreement (kappa = 0.81-0.86). The esophageal manometer and FVP provided slightly better inter-rater agreement in the detection of both obstructive hypopneas and apneas as compared to the chest and abdomen belts. There was a 20-30% drop in inter-rater reliability in the detection of flow-limitation and ventilation-change events compared to obstructive events, and all effort signals showed poor inter-rater agreement for central and mixed events.

CONCLUSIONS

The results of the study suggest that the FVP can serve as an alternative to respiratory bands in the differential diagnosis of sleep disordered breathing, and in the recognition of patients appropriate for bilevel continuous positive airway pressure devices.

Use of the pulse transit time trend to relate tidal breathing and central respiratory events

Central sleep apnoea (CSA) is a respiratory event where cessation of breathing effort and airflow occurs. Numerous lumped models have related the physical phenomena in the arterial tree to properties of the arterial wall. However, a limited model is available that describes pulse transit time (PTT) oscillations during CSA and tidal breathing. Data from 28 children (22 males; aged 6.2 +/- 3.6 years) were obtained during overnight polysomnography. Using a lumped-element model, PTT fluctuations during both respiratory events were described and compared with actual experimental data. 222 valid CSA and 222 tidal breathing events were acquired and analysed. For the tidal breathing, undamped PTT oscillations of 3.89 s were predicted while actual data showed a mean value of 3.68 +/- 0.83 s. Conversely, a damped PTT trend was observed during CSA as predicted by the model. The results attained showed that clustered CSA occurrences led to an increase of 7.23 +/- 3.34 per cent in PTT baseline value while the model predicted 7.86 +/- 2.63 per cent. The marginal increase in PTT baseline was expected since the blood pressure and heart rate decreased during such occurrences. The findings herein suggest that the described model has the potential to describe respiratory event characteristics of a sleeping child.