Abstract not available

Doctor of Philosophy (Medicine) / Sleepiness is an important source of morbidity in the community, with potentially catastrophic consequences of occupational or driving injuries or accidents. Although many measures of sleepiness exist, there is no gold standard. The electroencephalograph (EEG) has been studied as an indicator of sleep pressure in the waking organism, or sleep depth. A mathematical model has been developed, relating the observed EEG to interactions between groups of neurons in the cortex and thalamus (Robinson, Rennie, Rowe, O'Connor, & Gordon, 2005; Robinson, Rennie, & Wright, 1997). These interactions are thought to be important in the transition from wake to sleep. Sleepiness is common in obstructive sleep apnea (OSA). The measurement of sleepiness would have great utility in quantifying the disease burden, measuring treatment response, or determining fitness for work or driving. This study will evaluate parameters derived from the EEG mathematical model as a measure of sleepiness. It is divided into the following four parts: 1. Subjects with likely OSA based on symptoms and demographics from an international database were compared with matched non-OSA controls. The OSA group showed deficits in executive function and abnormalities on evoked response potential testing. 2. Outcomes from a cross-sectional study in a sleep-clinic OSA population were aggregated by factor analysis into a five summary variables relevant to sleepiness: subjective sleepiness, mood & anxiety, memory & learning, driving, and executive functioning. 3. EEG mathematical model parameters from wake EEG recordings were related to the five summary outcomes. Executive function correlated with a parameter Z, representing the negative feedback loop between the thalamic reticular nucleus and the thalamocortical relay nuclei. 4. EEG model parameters during first NREM sleep cycle of 8 subjects with regular sleep architecture were studied. Net cortical excitation (parameter X) is predicted to increase across the cycle, while there was, as predicted, a greater inhibitory effect of the thalamic reticular nucleus upon thalamocortical relay cells (parameter Z). In this preliminary assessment, EEG model parameters reflecting thalamocortical interactions are sensitive to prefrontal lobe tasks such as executive function, which are known to be vulnerable to sleep loss and sleepiness, and these parameters also show variation with increasing sleep depth.

Accumulating evidence suggests that volume overload in drug-resistant hypertension (RH) may contribute to the high prevalence of obstructive sleep apnea-hypopnea (OSAH). Upon recumbency, leg fluid volume moves rostrally causing an increase in nuchal and peripharyngeal fluid content, subsequently obstructing airflow. Rostral fluid displacement following lower body positive pressure (LBPP) application and occurring spontaneously overnight were evaluated in subjects with RH (n = 25) and controlled hypertension (n = 15). In both groups, the reduction in mean upper airway cross-sectional area with LBPP strongly related to the amount of fluid displaced from the legs (R2 = 0.41; p<0.0001), although its magnitude was greater in the RH group (p=0.001; adjusted for propensity score). In both groups, the apnea-hypopnea index strongly related to the amount of fluid spontaneously displaced from the legs during sleep (R2 = 0.56; p<0.0001), although its magnitude was greater in the RH group (p=0.01; adjusted for propensity score).

Accumulating evidence suggests that volume overload in drug-resistant hypertension (RH) may contribute to the high prevalence of obstructive sleep apnea-hypopnea (OSAH). Upon recumbency, leg fluid volume moves rostrally causing an increase in nuchal and peripharyngeal fluid content, subsequently obstructing airflow. Rostral fluid displacement following lower body positive pressure (LBPP) application and occurring spontaneously overnight were evaluated in subjects with RH (n = 25) and controlled hypertension (n = 15). In both groups, the reduction in mean upper airway cross-sectional area with LBPP strongly related to the amount of fluid displaced from the legs (R2 = 0.41; p<0.0001), although its magnitude was greater in the RH group (p=0.001; adjusted for propensity score). In both groups, the apnea-hypopnea index strongly related to the amount of fluid spontaneously displaced from the legs during sleep (R2 = 0.56; p<0.0001), although its magnitude was greater in the RH group (p=0.01; adjusted for propensity score).

Even though the sleep apnea breathing occurs during the sleep,but it also affects the daytime's physiological status.Since sleep apnea breathing increases the risk of getting cardiovascular diseases,sleep disordered breathing has attracted significant amount attention.Conventional diagnosis processes for sleep disorder breathing is complex and time-consuming,therefore many efforts have been made in developing simplified physiological signal feature to detect sleep disorder breathing.To simplify the process of diagnosis,this study uses the ECG signals to differentiate patients and healthy subjects.In addition to traditional HRV features,this study also test a newly proposed ECG feature called degree of spectrum concentration which characterizes the degree of periodicity of the ECG waveform. Our experimental results show that sleep apnea patients have higher degree of spectrum concentration than healthy subjects.This work also tests the mutliscale entropy of this degree of spectrum concentration signal.The results demonstrate that complexity of the degree of spectrum concentration signal of the patients is higher than that of the healthy subjects.Finally,our results also detect differences between different age groups.

SAS has become an increasingly important public-health problem in recent years. It can adversely affect neurocognitive, cardiovascular, respiratory diseases and can also cause behavior disorder. Since up to 90% of these cases are obstructive sleep apnea (OSA), therefore, the study of how to diagnose, detect and treat OSA is becoming a significant issue, academically and medically. Polysomnography (PSG) can monitor the OSA with relatively fewer invasive techniques. However, PSG-based sleep studies are expansive and time-consuming because they require overnight evaluation in sleep laboratories with dedicated systems and attending personnel. This work develops a flow rate based detection method for apneas. In particular, via signal processing, feature extraction and neural network, this thesis introduces a flow rate based detective system. The goal is to detect OSA with less time and reduced financial costs.

The diagnosis of obstructive sleep apnea (OSA) syndrome is overnight PSG (mutli-channel system). But it¡¦s hard to be popularized for the general population (about twenty channel signals). In recent decades, several researches were devoted to a replacement system with only one channel signal (oxyhemoglobin saturation). However, it¡¦s hard to match PSG system¡¦s report without EEG wake information. Consequently, two channels (oxyhemoglobin saturation and EEG) were used of this study to enhance the AHI (estimation index for sleep apnea) prediction performance. After surveying the most recent studies, this work proposes a new basleline removal technique for oxygen saturation signal (SpO2) by using median filter. It was proved this technique improves the diagnostic accuracy for OSA. Furthermore, it is also found that by removing the wake periods, diagnostic accuracy can be improved further. By counting the number of times that the desaturation level has dropped more than 2% for at least 3 seconds, the correlation coefficient between AHI and proposed feature is 0.9218. In addition, by removing the wake period, this correlation increases to 0.9425. By using this feature to classify patients with AHI value larger than 5, the proposed approach achieves 93.78% accuracy, 95.94% sensitivity, 78.87% specificity f. Such results demonstrate the feasibility of using single SpO2 channel system for OSA diagnosis.

Thesis (M. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 168-215). Also available in print.

Thesis (M.S.)--University of Delaware, 2009. / Principal faculty advisor: William B. Farquhar, Dept. of Health, Nutrition, & Exercise Sciences. Includes bibliographical references.

published_or_final_version / Medicine / Master / Doctor of Medicine