Methods for Detecting and Monitoring of Sleep Disordered Breathing in Children using Overnight Polysomnography

Sleep is crucial for the health of every individual, especially children. One of the common causes of disturbed sleep in children is disordered breathing. Children who suffer from sleep disordered breathing are likely to have severe consequences for their physical growth, heart health and neuropsychological function. Sleep disordered breathing (SDB) comprises a spectrum of severity from a mild form of upper airway resistance syndrome (UARS) to severe form of obstructive sleep apnea syndrome (OSAS). While OSAS is considered clinically significant, UARS and its health consequences have been underestimated. The most common treatment for OSAS in children is adenotonsillectomy. However, breathing disturbances related to UARS may persist even after adenotonsillectomy. The current diagnostic marker for OSAS, the Apnea-Hypopnea Index (AHI) often overlooks the less severe conditions of breathing disturbances. Therefore, the research objective of this thesis is to investigate the new alternative markers for SDB in children using non-invasive physiological measurements, such as thoracoabdominal signals and the photoplethysmogram. As the body experiences an array of complex changes, specifically in respiratory and autonomic nervous system activation during breathing disturbances, advanced signal processing and analysis techniques were used to identify the physiological variables that could reflect changes in those systems in children with SDB. Thoraco-abdominal asynchrony (TAA), heart period (HP) and pulse wave amplitude (PWA) were the three physiological variables were investigated. A total of five studies were conducted on two high-quality clinical research datasets to test the potential of the proposed physiological variables to effectively identify children with SDB. In the thesis: 1) Hilbert transform was applied for TAA estimation on the childhood adenotonsillectomy trial (CHAT) dataset; 2) symbolic dynamic analysis on HP was used to assess the effect of adenotonsillectomy on autonomic activations in children with SDB; 3) the conventional method of estimating PWA was combined with joint symbolic analysis of PWA and HP to analyse the effect of SDB on autonomic activation compared to healthy controls; 4) to improve the performance of the previous PWA measurement technique, a more robust and simpler method was proposed to estimate PWA using a simple envelope method, and a more extensive dynamic analysis method was created to capture more complete information; and 5) adding TAA and HP information with AHI, unsupervised machine learning method K-means clustering and linear discriminant analysis were used to discover the pathophysiology nature difference of children with SDB in CHAT dataset. The main results from this thesis suggest that children with SDB have higher values in all three physiological variables, which indicates a high respiratory effort and elevated frequency of autonomic activation. Adenotonsillectomy showed to reverse the effects on these physiological variables, suggesting it assisted in the reduce of pathophysiological symptoms in those children. Interestingly, TAA was found inversely correlated with quality of life and unreported baseline difference in HP in children who had their AHI normalised spontaneously. These findings further indicate the limitation of AHI as the only marker for paediatric sleep disordered breathing. By combining the TAA and HP information with AHI, the alternative proposed diagnosing approach could help doctors predict who may benefit from adenotonsillectomy or not. In conclusion, this thesis provides new evidence that TAA, HP and PWA can provide additional information and may yield more effective markers for diagnosing paediatric sleep disordered breathing.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 201

Symbolic dynamics to enhance diagnostic ability of portable oximetry from the Phone Oximeter in the detection of paediatric sleep apnoea

Objective: This study is aimed at assessing symbolic dynamics as a reliable technique to characterize complex fluctuations of portable oximetry in the context of automated detection of childhood obstructive sleep apnoea-hypopnoea syndrome (OSAHS). Approach: Nocturnal oximetry signals from 142 children with suspected OSAHS were acquired using the Phone Oximeter: a portable device that integrates a pulse oximeter with a smartphone. An apnoea-hypopnoea index (AHI) ⩾ 5 events h−1 from simultaneous in-lab polysomnography was used to confirm moderate-to-severe childhood OSAHS. Symbolic dynamics was used to parameterise non-linear changes in the overnight oximetry profile. Conventional indices, anthropometric measures, and time-domain linear statistics were also considered. Forward stepwise logistic regression was used to obtain an optimum feature subset. Logistic regression (LR) was used to identify children with moderate-to-severe OSAHS. Main results: The histogram of 3-symbol words from symbolic dynamics showed significant differences (p < 0.01) between children with AHI < 5 events h−1 and moderate-to-severe patients (AHI ⩾ 5 events h−1). Words representing increasing oximetry values after apnoeic events (re-saturations) showed relevant diagnostic information. Regarding the performance of individual characterization approaches, the LR model composed of features from symbolic dynamics alone reached a maximum performance of 78.4% accuracy (65.2% sensitivity; 86.8% specificity) and 0.83 area under the ROC curve (AUC). The classification performance improved combining all features. The optimum model from feature selection achieved 83.3% accuracy (73.5% sensitivity; 89.5% specificity) and 0.89 AUC, significantly (p <0.01) outperforming the other models. Significance: Symbolic dynamics provides complementary information to conventional oximetry analysis enabling reliable detection of moderate-to-severe paediatric OSAHS from portable oximetry

Sleep-time predictors of cardiovascular complications in surgical peripheral arterial disease

ABSTRACT Patients with peripheral arterial disease (PAD) undergoing surgical revascularisation are in high risk of postoperative cardiovascular complications and death, due to advancing age and multiple comorbidities in the population. In addition, PAD needing surgery represents a severe form of systemic atherosclerosis but the exact underlying pathophysiology of acute myocardial infarction (AMI) in these patients is unclear and predicting outcome especially in the long-term is challenging. Obstructive sleep apnoea (OSA) is increasingly common in the general population and independently associated with various manifestations of cardiovascular disease or their risk factors; OSA is highly prevalent in patients with coronary artery disease (CAD), stroke, hypertension and diabetes. To expand this knowledge, we determined the prevalence and severity (in terms of the apnoeahypopnoea index, AHI) of OSA in surgical PAD as well as its impact on the incidence of major adverse cardiovascular and cerebrovascular events (MACCE) in this patient group. Heart rate variability (HRV) reflects fluctuations in sympathetic and parasympathetic activation responsible for neurocirculatory control in various physiological and pathophysiological situations. Depressed HRV is associated with increased cardiovascular morbidity and mortality following AMI and major surgery. In this study, the alterations of nocturnal HRV and their association with the severity of OSA and incidence of MACCE in patients with PAD was assessed, including the fractal correlation properties of HRV. HRV in a control group of 15 healthy subjects was also examined. Patients scheduled for sub-inguinal vascular surgery (n=84, age 67±9 years) underwent polysomnography and HRV analyses. OSA was detected in 86% of patients and in 56% it was moderate or severe. Age, male gender, depressed left ventricular function and decreasing high density lipoprotein/cholesterol ratio (HDL/Chol) predicted the presence and severity of OSA. The latter two remained significant after adjusting for age and gender. OSA with AHI ≥20/hour, used as a cut-off in the outcome analyses, predicted a higher risk of MACCE (p=0.001) along with pre-existing CAD (p=0.001), decreasing HDL/Chol (p=0.048) and <4 years history of PAD (p=0.018). HRV was altered in patients with PAD when compared to controls but the time domain measures were mostly unchanged. In the frequency domain, low frequency power was generally lower, high frequency power was mostly higher and fractal correlation was consistently lower. Very low frequency power was increased the most in patients with AHI 10-20/hour when compared to <10/hour while those with AHI ≥20/hour had lower fractal correlation in the morning. Patients suffering a MACCE had lower high frequency power during S3-4 and rapid eye movement sleep. In conclusion, OSA is associated with worsening atherosclerosis and predicts MACCE after vascular surgery. HRV alterations, although associated with PAD, have limited predictive value. Keywords: atherosclerosis, peripheral arterial disease, sleep apnoea, heart rate variabilityTIIVISTELMÄ Unenaikaiset sydänkomplikaatioiden ennustetekijät kirurgista hoitoa vaativassa perifeerisessä valtimotaudissa Perifeeristä valtimotautia sairastavilla potilailla on suuri leikkauksenjälkeisten sydänkomplikaatioiden riski johtuen yhä iäkkäämmästä väestöstä sekä lukuisista rinnakkaissairauksista. Lisäksi perifeerinen valtimotauti merkitsee vaikea-asteista yleistynyttä ateroskleroosia, mutta sydäninfarktin tarkka syntymekanismi näillä potilailla on epäselvä ja erityisesti pitkän aikavälin ennusteen arviointi on haastavaa. Obstruktiivinen uniapnea yleistyy väestössä ja sillä on itsenäinen yhteys useisiin sydän- ja verisuonisairauksiin ja niiden riskitekijöihin; uniapnea on erittäin yleinen sepelvaltimotauti-, aivohalvaus-, verenpainetauti- ja diabetespotilailla. Tämän tietopohjan laajentamiseksi tässä tutkimuksessa määritettiin uniapnean esiintyvyys ja vaikeusaste (määrittäjänä apnea-hypopneaindeksi, AHI) vaikea-asteista yleistynyttä ateroskleroosia sairastavilla potilailla sekä sen vaikutus vakavien sydän- ja aivotapahtumien ilmaantuvuuteen. Sydämen sykevaihtelu kuvastaa autonomisen hermoston toiminnan muutoksia, jotka puolestaan vastaavat verenkierron säätelystä erilaisissa fysiologisissa ja patofysiologisissa tilanteissa. Alentunut sykevaihtelu on yhteydessä lisääntyneeseen kardiovaskulaariseen sairastuvuuteen ja kuolleisuuteen sairastetun sydäninfarktin tai suuren leikkauksen jälkeen. Tässä tutkimuksessa arvioitiin yöllisen sydämen sykevaihtelun muutosten yhteyttä uniapnean vaikeusasteeseen sekä vakavien sydän- ja aivotapahtumien ilmaantuvuuteen, mukaan lukien sykevaihtelun fraktaalikorrelaatio-ominaisuudet. Tutkimuksessa analysoitiin sykevaihtelu myös 15 terveen henkilön vertailuryhmältä. Nivustason alapuoliseen verisuonileikkaukseen meneville potilaille (n=84, ikä 67±9 vuotta) tehtiin unipolygrafia ja sykevaihteluanalyysi. Uniapnea todettiin 86 %:lla potilaista ja 56 %:lla se oli kohtalainen tai vaikea. Ikä, miessukupuoli, heikentynyt vasemman kammion toiminta ja alentunut HDL-kolesterolin suhde kokonaiskolesteroliin ennustivat uniapneaa ja sen vaikeutumista; 2 viimeksi mainittua säilyivät merkitsevinä ikä- ja sukupuolivakioinnin jälkeen. AHI ≥20/tunti, joka valittiin kynnysarvoksi päätetapahtumaanalyyseihin, ennusti merkitsevästi vakavia sydän- ja aivotapahtumia (p=0.001). Muita merkitseviä tekijöitä olivat sepelvaltimotauti (p=0.001), alentunut HDL-suhde (p=0.048) ja lyhyt (alle 4 vuotta) perifeerisen valtimotaudin kesto ennen leikkaushoidon tarvetta (p=0.018). Sykevaihtelu oli muuttunut valtimotautipotilailla verrattuna kontrolleihin, mutta aikakenttäparametrit säilyivät lähes ennallaan. Pienitaajuuksinen sykevaihtelu oli yleisesti vähäisempää, suuritaajuuksinen enimmäkseen voimakkaampaa ja fraktaalikorrelaatio johdonmukaisesti heikompaa. Hyvin pienitaajuuksinen vaihtelu oli eniten lisääntynyt AHI 10-20/tunti -alaryhmässä verrattuna AHI <10/tunti -ryhmään, mutta AHI ≥20/tunti -potilailla aamun fraktaalikorrelaatio oli heikompaa. Potilaiden, jotka saivat vakavia sydän- ja aivotapahtumia, suuritaajuusvaihtelu oli heikompaa syvän unen ja vilkeunen aikana. Johtopäätöksinä todetaan, että uniapnea on yhteydessä vaikeutuvaan valtimotautiin sekä ennustaa vakavia sydän- ja aivotapahtumia verisuonileikkauksen jälkeen sykevaihtelun muutosten ennustearvon ollessa tässä aineistossa hyvin rajallinen. Avainsanat: ateroskleroosi, perifeerinen valtimotauti, uniapnea, sykevaihtel

Diseño y evaluación de metodologías de análisis automático de la oximetría nocturna como método simplificado de detección del síndrome de apnea-hipopnea obstructiva del sueño en niños. Validación en el hospital y en el domicilio.

El síndrome de apnea-hipopnea obstructiva del sueño (SAHOS) es una enfermedad de alta prevalencia en la población infantil, con una importante morbilidad y elevado impacto sociosanitario, en la que la detección precoz es esencial para iniciar un adecuado tratamiento, el cual debe ser siempre individualizado. El SAHOS es una alteración fisiopatológica compleja y multifactorial, en la que no sólo influye una susceptibilidad genética e individual (factores anatómicos y dinámicos), sino también de estilo de vida. Los factores de riesgo más frecuentes son la hipertrofia adenoamigdalar y la obesidad. Los síntomas en los niños son escasos, son principalmente nocturnos y requieren un alto nivel de sospecha. El SAHOS no diagnosticado o no tratado se relaciona con diferentes consecuencias metabólicas, cardiovasculares, neurocognitivas, inflamatorias, conductuales y falta de desarrollo estaturoponderal, lo que conduce a un empeoramiento del estado de salud en términos generales y disminución de calidad de vida.Departamento de Anatomía y RadiologíaDoctorado en Investigación en Ciencias de la Salu

Aerospace medicine and biology: A continuing bibliography with indexes

This bibliography lists 187 reports, articles, and other documents introduced into the NASA scientific and technical information system in October, 1987

Quality and safety of inter-hospital transfers care of critically ill patients from rural community hospitals to the Tertiary Regional Hospital in Thailand: a focused ethnographic study

Background: The safety of critically ill patients during inter-hospital transfer is recognised as a globally important issue. However, little evidence exists pertaining to the care provided by transfer nurses throughout the processes of inter-hospital transfer in rural community hospitals where there is a high risk of adverse clinical events occurring during transportation. Aim: The overall aim of the study was to explore transfer nurses’ understanding of the delivery of quality of care during the transfer of critically ill patients from rural community hospitals to a tertiary regional hospital in Thailand. Design and Methods: The theory of symbolic interactionism (Blumer, 1986) and focused ethnography methodology were used. Data were collected using multiple qualitative methods including sixteen semi-structured interviews with transfer nurses, fourteen observations of critically ill patients’ transfers from three rural community hospitals to a tertiary centre and twenty-three subsequent handover events and the analysis of transfer documents from four hospital settings (e.g. one regional hospital and three rural community hospitals) in Thailand. Translation from Thai into English and back translation into vernacular language was required. Inductive, thematic analysis was conducted to identify major themes by using qualitative data analysis software, NVivo 10 to assist data management during the analysis. Results: Five major themes emerged including (i) protective factors influencing safe transfer care, (ii) barrier factors influencing safe transfer care, (iii) behavioural patterns in transfer care processes, (iv) maintaining the health condition of the patients, and (v) overcoming adverse events. These particular themes elaborate the meaning of the quality and patient safety of transfer care, the provision of care for safe transfer care, and significant contextual factors that influence the quality of inter-hospital transfer care for critically ill patients. In addition, Donabedian’s model (Donabedian, 1966, 1988) incorporated within the concept of context and culture was utilised to assist in conceptualising the framework for the quality of inter-hospital transfer care of critically ill patients in Thailand. Conclusion: The Donabedian model is useful as it is simple, but it does not include detail of the organisational context and culture as determinants of care quality. A conceptual framework for the quality of inter-hospital transfer care of critically ill patients in Thailand was therefore proposed. This study has expanded on current theoretical knowledge of the quality of inter-hospital transfer care by elaborating the patterns of thought and the behaviour of transfer nurses during provision of care throughout the processes of the inter-hospital transfer. It also highlights the limitations of organisational structure and the environment in which transfer work takes place, including issues on handover processes in hospital transfer care. The results can be useful to transfer nurses in that they facilitate greater understanding of the provision of better quality of care. They also help to inform hospital policy makers how to ensure safety of critically ill patients being transferred from community hospital settings

Technegas easy breather accessory (TEBA: a new concept in lung ventilation scintigraphy

The findings of this thesis represent a novel aspect in lung ventilation imaging involving a series of experiments with a new apparatus known as the Technegas Easy Breather Accessory (TEBA). The investigations were undertaken with both normal and Chronic Airways Limitation (CAL) volunteers and with Intubated Intensive Care patients. The data presented in this research were collected from 144 patients in total. In experiment one there were 25 normal volunteers who underwent conventional ventilation imaging and 25 normal volunteers who underwent TEBA assisted ventilation imaging, while in experiment two, there were 25 volunteers with CAL for conventional ventilation and 25 for TEBA; in experiment three, 25 intubated Intensive Care Patients successfully completed ventilation scintigraphy using TEBA. For experiment four, 20 patients volunteered to complete a Technegas ventilation study prior to their bronchoscopy procedure. Experiments one and two demonstrated that TEBA was effective in distinguishing normal lung ventilation from ventilation defects found in Chronic Airways Limitation (CAL) and Pulmonary Embolism (PE). Experiment three showed TEBA ventilation imaging could be successfully undertaken by intubated and unconscious patients. This has significant implications for the diagnosis and treatment for patients in ICU who formerly could not undergo this procedure. The results of this experiment will have implications for improving the diagnosis and treatment of patients in critical care. The findings of this thesis provide further evidence for the first line role of lung scintigraphy in the diagnosis of Pulmonary Embolism (PE). This is of vital importance to the large number of patients who are at risk from the life-threatening diseases of PE and Deep Venous Thrombosis (DVT). This is because timely lung ventilation imaging in the diagnosis and follow-up phase of these diseases will reduce the clinical uncertainty in directing treatment and consequently lower health care costs