A System for the Analysis of Snore Signals

AbstractSleep apnoea syndrome (SAS) is a disease consisting in the nocturnal cessation of oronasal airflow at least 10 seconds in duration. The standard method for SAS diagnosis is the polysomnographic exam (PSG). However it does not permit a mass screening because it has high cost and requires long term monitoring.This paper presents a preliminary software system prototype for snoring signal analysis, whose main goal is to support the doctor in SAS diagnosis and patient follow-up. The design of the system is modular to allow a future hardware implementation in a portable device for personal snore collection and monitoring

Models and Analysis of Vocal Emissions for Biomedical Applications

The MAVEBA Workshop proceedings, held on a biannual basis, collect the scientific papers presented both as oral and poster contributions, during the conference. The main subjects are: development of theoretical and mechanical models as an aid to the study of main phonatory dysfunctions, as well as the biomedical engineering methods for the analysis of voice signals and images, as a support to clinical diagnosis and classification of vocal pathologies

Enhancing the Diagnosis and Management of Obstructive Sleep Apnoea in Atrial Fibrillation Patients

Background: Atrial fibrillation (AF), is the most common sustained cardiac arrhythmia, and significantly increases the risk of stroke and cardiovascular mortality. It is strongly associated with obstructive sleep apnoea (OSA). Aims: 1. Examine the epidemiology of OSA in a hospital cohort with AF. 2. Compare the diagnostic accuracy of clinical screening tools for OSA in patients with AF. 3. Compare cardiac autonomic function in AF patients with and without OSA. 4. Conduct a pilot study of mandibular advancement splint (MAS) therapy for OSA in AF patients. Methods: 107 AF patients were recruited. The diagnostic accuracy of screening tools including a level 3 (portable) sleep study device as compared to polysomnography in AF patients was assessed. Cardiac autonomic function as a potential mechanistic link between OSA and AF was assessed using Heart Rate Variability (HRV). A pilot study of OSA treatment in AF patients using MAS therapy was conducted. Results: 62.6% of patients were newly diagnosed with OSA. Patients with moderate to severe OSA showed an increased BMI, neck circumference and Mallampati score, but were not significantly different in terms of daytime somnolence. Oxygen desaturation index (ODI) derived from a Level 3 portable sleep study device performed best for the diagnosis of moderate to severe and severe OSA, with excellent diagnostic accuracy (AUC 0.899, 95% CI 0.838 – 0.960 and AUC 0.925, 95% CI 0.859 – 0.991 respectively). We found a chronic increase in parasympathetic nervous activity in paroxysmal AF patients with OSA. MAS therapy showed high rates of acceptance, compliance and efficacy in AF patients. Conclusions: This thesis contributes to our understanding of the association between AF and OSA across a spectrum o

Sleep-disordered breathing in patients with implanted cardiac devices: validation of the ApneaScanTM algorithm and implications for prognosis

Aims Sleep-disordered breathing (SDB) is common in heart failure (HF) and frequently undiagnosed. The ApneaScanTM algorithm, available on certain ICD and CRT devices, uses changes in transthoracic impedance with breathing to quantify SDB. This research tests 3 hypotheses: 1) The ApneaScanTM algorithm can accurately detect moderate-to-severe SDB in patients with HF 2) There is minimal night-to-night variability in the ApneaScanTM-determined severity of SDB 3) Those with moderate-to-severe SDB, assessed by ApneaScanTM, have a higher rate of adverse cardiovascular events than those without. Methods Patients with EF≤40% and ICD or CRT devices incorporating ApneaScanTM were recruited. For hypothesis 1, 54 subjects underwent a successful sleep polygraphy study and simultaneous download of ApneaScanTM data. 22 subjects (44%) had undiagnosed moderate-to-severe SDB. The area under the ROC curve was 0.84 for the diagnosis of moderate-to-severe SDB. The optimal ApneaScan cut-off was 30.5/hour (sensitivity 95%, specificity 69%, positive predictive value 68%, negative predictive value 95%). For hypothesis 2, ApneaScanTM data over 28- and 92-nights in 35 patients was reviewed. There was minimal variability in SDB and no significant difference between durations. For hypothesis 3, 72 patients were followed up at a median of 532 (IQR 386-736) days.Mean event-free survival was 660±344 days (95% CI 535-785 days) in the insignificant SDB group and 854±413 days (95% CI 730-978 days) in the significant SDB group (p=0.25 by log rank test). Conclusions ApneaScanTM, with an optimal cut-off of 30.5 events/hour, is a sensitive means of screening for SDB in patients with HF with a high negative predictive value. Readings above 30.5/hour require further investigation with a sleep study. Night-to-night variability in SDB is minimal and repeat sleep studies should be reserved for those with ‘borderline’ AHI. In this cohort, the presence of SDB was not associated with adverse cardiovascular outcomes. Recruitment is on-going to test this further.Open Acces

Impact of obstructive sleep apnoea/hypopnoea and its treatment with continuous positive airway pressure on the outcome of stroke

BACKGROUND: The prevalence of sleep-disordered breathing (SDB) in stroke is high. One study showed SDB had a negative impact on the functional capacity of stroke patients on discharge and another that SDB was associated with a higher mortality rate. However, these findings are disputed. The impact of SDB in stroke patients on cognition and health-related quality of life is also not clear. The one randomized controlled trial of nasal continuous positive airway pressure (CPAP) in stroke patients with SDB showed CPAP improved wellbeing but not other outcomes. I hypothesised that: (1) SDB is related to stroke outcome and (2) treatment of SDB in stroke patients with CPAP would improve functional outcome.METHODS: There are three parts of the thesis: (1) a study of the prevalence of SDB after stroke; (2) a randomized controlled trial (RCT) of CPAP after stroke and (3) a longitudinal cohort study to investigate the impact of SDB on outcome after stroke. On day 14-19 after stroke, recruited patients underwent a limited sleep study using a validated system (Embletta PDS, Medcare Flaga, Iceland). Baseline assessments were performed on the morning following the sleep study. On day 21-25 following stroke, patients who had (A+H)-h⁻¹ ≥ 30 with < 30% of central events were randomized to 8 weeks of CPAP treatment with Autoset T (ResMed, SanDiego USA) or conservative treatment for SDB. All outcomes were recorded in the 8th week after randomization or 3 months after stroke for non-randomized patients. All recruited patients received follow-up at six months after stroke. If available, patients also received 12 months and 18 months follow-up until the last recruited patient had had his 6 months follow-up. The Nottingham Extended ADL Index (EADL) was chosen as the primary outcome measure. Secondary outcome measures included: Subscales of EADL, NIH Stroke Scale (NIHSS), Barthel Index (BI), Stanford Sleepiness Scale (SSS), Addenbrooke's Cognitive Examination (ACE) and Mini- Mental State Examination (MMSE), Hospital Anxiety and Depression Scale (HADS), MOS Short Form 36 Health Survey (SF-36) and ambulatory blood pressure - measured with Spacelabs 90207 (Spacelabs, Redmond, USA).RESULTS: We screened 658 patients with recent strokes and excluded those with dementia, confusion, severe dysphasia or insufficient hand function to use CPAP. Only 96 of 658 patients remained eligible of whom 25 declined to give informed consent. 71 patients were thus successfully recruited for overnight limited sleep study 14-19 days following stroke. Sixty-six patients with adequate recording were included in the study: 45 men and 21 women, median age 74yrs. The sleep study showed 50% of patients had more than 30 apnoeas + hypopnoeas per hour in bed [expressed as (A+H)-h⁻¹]. Pulse oximetry alone had lower sensitivity (70%) but high specificity (90%) to predict (A+H)-h⁻¹ ≥ 30. A combination of age, body mass index, snoring and excessive daytime sleepiness based on logistic regression model is useful as a screening tool at the bedside (sensitivity = 85%, specificity = 70%) to predict (A+H)-h⁻¹ ≥ 30 in stroke before referring patients for overnight sleep study. Interaction of lowest oxygen saturation and lowest heart rate is independently associated with stroke during sleep in patients with (A+H)-h⁻¹ < 30 (p = 0.023). Patients with (A+H)-h⁻¹ ≥ 30 more often had their stroke during daytime than patients with (A+H)-h⁻¹ < 30 (p = 0.006). Thirty patients who had (A+H)-h⁻¹ ≥ 30, with < 30% central apnoea or Cheyne-Stokes respiration, proceeded to a randomized controlled trial starting from the 4th week after stroke with 15 patients randomized to CPAP and 15 to conservative treatment for SDB. Conventional stroke treatment was maintained in all patients. Duration of treatment was 8 weeks and blind outcome assessment was performed at 3 months and 6 month after stroke. The result showed compliance with CPAP was poor with mean 1.40 hours and median 0.16 hours per night. There was no statistically significant difference in the outcomes, sleepiness and ambulatory blood pressure with CPAP therapy. Increased length of keeping CPAP was correlated with higher score of language subscale in the Addenbrooke's Cognitive Examination (Spearman's rho = 0.544, p = 0.036) and lower score in the depression subscale of the Hospital Anxiety and Depression Scale (HADS, Spearman's rho = -0.538, p = 0.039). All 66 patients with adequate sleep studies received longitudinal follow-up at 3, 6 12 and 18 months following stroke. The patients with (A+H)-h⁻¹ ≥ 30 had a trend to worse functional capacity in both Barthel Index and Nottingham Extended ADL Index (EADL) than patients with (A+H)-h⁻¹ < 30 but there was only a statistically significant difference in the mobility subscale of EADL. The negative influence of (A+H)-h⁻¹ ≥ 30 on functional capacity and health-related quality of life following stroke was only statistically significant in patients with mild stroke (NIH Stroke Scale, NIHSS < 7) at both 3 and 6 months, lesser emotional distress (HADS < 8) at both 3 and 6 months and lesser cognitive impairment (Mini Mental State Examination ≥ 28) at 6 months after stroke in subgroup analysis. The difference of Modified Rankin Scale between groups was significant at 6 months after stroke (p = 0.026). There was no difference in cognitive or emotional outcome. No significant difference of mortality rate was noted.CONCLUSIONS: We focused on a group of patients with mild to moderate stroke (median NIHSS = 6) within a narrow time span (14-19 days) and confirmed a high prevalence of SDB in stroke. CPAP compliance was a major problem but might be enhanced by selecting patients with higher functional capacity, higher cognitive function especially language and less depression in the acute or subacute phase of stroke. We also found that sleep-disordered breathing had little or no effect on cognitive and emotional outcomes, health-related quality of life and mortality in stroke patients. Many other factors resulting from brain damage or complications of stroke have stronger influences on stroke outcome than SDB

Factors affecting daytime function in the sleep apnoea/hypopnoea syndrome

The sleep apnoea/hypopnoea syndrome (SAHS) is characterised by repetitive upper airway obstructions during sleep, which lead to recurrent hypoxaemia and brief arousals from sleep. SAHS patients suffer from excessive daytime sleepiness (EDS), cognitive impairments and decreased psychological well -being. Previous studies have examined relationships between the nocturnal events of SAHS and a limited number of daytime function measures, frequently in small, non -consecutive patient samples. Relationships found have been either weak or non -significant. This thesis examines the relationships between a wide range of nocturnal sleep and breathing variables and daytime function. Additionally, this thesis examines the use of subjective and objective measures of daytime sleepiness, to determine which tests provide the most useful information for SAHS patients.A pilot study found that neither the 103 patients' nor their partners' Epworth rating of sleepiness were strong predictors of SAHS severity. In 150 patients with a wide range of SAHS severity, relationships between nocturnal events and daytime function were examined using newer definitions of arousal and measures of sleep continuity. A broad battery of daytime tests were used including the maintenance of wakefulness test (MWT) and the short form (SF) -36. Unlike previous studies, all correlations were controlled for age and awake oxygen saturation, known to influence the variables measured. The current study also examined these correlations in an unselected patient sample with a range of disease severity. The study found a lack of strong relationships between conventional nocturnal sleep and breathing variables and daytime function. Few baseline variables significantly predicted CPAP use.Daytime function measures were compared within the 150 patients. The multiple sleep latency test (MSLT) and the MWT displayed a moderate, discordant relationship. Measures of cognitive function, psychological well -being and subjective sleepiness ii better related to the MWT than MSLT, suggesting that the MWT may be a more useful tool in assessing functional impairment in sleep apnoea.A randomised cross -over study, on 12 SANS patients, compared daytime sleepiness measured following a night's sleep at home (as performed in this thesis) versus a night in the sleep centre (standard protocol). Preliminary results indicated that daytime sleepiness, as measured by the MSLT and MWT, was not significantly different between the two study limbs. This suggests that the non -standard method of conducting the MSLT and MWT in this thesis does not explain the lack of correlational relationships between nocturnal measures and daytime sleepiness.The studies presented in this thesis demonstrate a lack of identified factors affecting daytime function in a group of unselected SANS patients. This may be due to inter - individual patient variability. Also, more sophisticated nocturnal SANS measures should be examined, as should more `real -life' daytime assessments, such as ambulatory EEG recorded during a patient's normal daily routine

Improving automatic detection of obstructive sleep apnea through nonlinear analysis of sustained speech

We present a novel approach for the detection of severe obstructive sleep apnea (OSA) based on patients' voices introducing nonlinear measures to describe sustained speech dynamics. Nonlinear features were combined with state-of-the-art speech recognition systems using statistical modeling techniques (Gaussian mixture models, GMMs) over cepstral parameterization (MFCC) for both continuous and sustained speech. Tests were performed on a database including speech records from both severe OSA and control speakers. A 10 % relative reduction in classification error was obtained for sustained speech when combining MFCC-GMM and nonlinear features, and 33 % when fusing nonlinear features with both sustained and continuous MFCC-GMM. Accuracy reached 88.5 % allowing the system to be used in OSA early detection. Tests showed that nonlinear features and MFCCs are lightly correlated on sustained speech, but uncorrelated on continuous speech. Results also suggest the existence of nonlinear effects in OSA patients' voices, which should be found in continuous speech

Continuous positive airway pressure treatment for the sleep apnoea/hypopnoea syndrome

The preferred form of treatment for the sleep apnoea/hypopnoea syndrome (SAHS) is continuous positive airway pressure (CPAP). This thesis investigates the usage, benefits to patients and partners, and method of initiation of CPAP therapy.A database of all 1,211 patients booked for CPAP between 1986-1997 was constructed, with 95.4% follow-up at a median of 22 months. Fifty-two (4.5%) patients refused CPAP treatment; these were more often female and current smokers. The methods of survival analysis found 68% of patients continued treatment at 5 years and the independent baseline predictors of continued CPAP use were snoring history, apnoea/hypopnoea index (AHI), and Epworth sleepiness score (ESS). CPAP use at 3 years was > 92% in sleepy patients with severe disease (ESS>10, AHI>60) but only 40% in non-sleepy mild severity patients (ESS<10, AHI<15). Average nightly use within 3 months was strongly predictive of longterm use.Using the above database the independent predictors of long-term use were used to match (AHI+/-15%, ESS +/-3) 46 patients prescribed split-night (diagnostic + CPAP titration studies in 1 night) studies with 92 full night patients. Classical symptoms of SAHS were the main reason for split-night studies (n=27). There was no difference between these split and full night studies in long-term CPAP use, median (IQR) nightly CPAP use [split 6.0 (3.8-7.4)hr/night, full 6.2 (3.7- 7.0)hr/night, p=0.9], post-treatment ESS, or frequency of nursing interventions/clinic visits required. Split-night patients received treatment quicker [median (IQR) time from referral to treatment 13 (11-20) versus 22 (12-34) months, p=0.003].In a randomised crossover study 22 unselected SAHS patients [median (IQR) AHI = 40(25-65)] events/hr had 1 month limbs on CPAP and placebo capsules, and home polysomnography was performed at the end of each month. During CPAP patients had a lower arousal index, less stage 1 and more stage 3+4 sleep (all; p<0.03), but no increase in stage REM sleep. In the above study the partners' sleep quality was also monitored while the patient received CPAP and placebo. There was no difference in the partners' objective sleep quality between CPAP and placebo. However partners reported improved subjective sleep quality (p=0.05) and less disturbance to sleep (p=0.03) during the patients' use of CPAP compared to placebo.Thus long-term CPAP use is related to disease severity and subjective sleepiness and can be predicted within 3 months. Low usage in mild patients with few symptoms suggests alternative treatments are needed. These studies also show that treatment waiting time and cost can be reduced, with no loss of effectiveness, by performing split-night studies in selected patients. Patients with SAHS have better objective sleep quality and their partners have improved subjective sleep quality when the patient is treated with CPAP

Pattern recognition applied to airflow recordings to help in sleep Apnea-Hypopnea Syndrome diagnosis

El Síndrome de la Apnea Hipopnea del Sueño (SAHS) es un trastorno caracterizado por pausas respiratorias durante el sueño. Se considera un grave problema de salud que afecta muy negativamente a la calidad de vida y está relacionada con las principales causas de mortalidad, como los accidentes cardiovasculares y cerebrovasculares. A pesar de su elevada prevalencia (2–7%) se considera una enfermedad infradiagnosticada. El diagnóstico estándar se realiza mediante polisomnografía (PSG) nocturna, que es un método complejo y de alto coste. Estas limitaciones han originado largas listas de espera. Esta Tesis Doctoral tiene como principal objetivo simplificar la metodología de diagnóstico del SAHS . Para ello, se propone el análisis exhaustivo de la señal de flujo aéreo monocanal. La metodología propuesta se basa en tres fases (i) extracción de características, (ii) selección de características, y (iii) procesado de la señal mediante métodos de reconocimiento de patrones. Los resultados obtenidos muestran un alto rendimiento diagnóstico de la propuesta tanto en la detección como en la determinación del grado de severidad del SAHS. Por ello, la principal conclusión de la Tesis Doctoral es que los métodos de reconocimiento automático de patrones aplicados sobre la señal de flujo aéreo monocanal resultan de utilidad para reducir la complejidad del proceso de diagnóstico del SAHS.Departamento de Teoría de la Señal y Comunicaciones e Ingeniería Telemátic