Arousal and breathing responses to airway occlusion in healthy sleeping adults.
ABSTRACT The arousal and breathing responses to total airway occlusion during sleep were measured in 12 normal subjects (7 males and 5 females) aged 25-36 yr. Subjects slept while breathing through a specially designed nosemask, which was glued to the nose with medical-grade silicon rubber. The lips were sealed together with a thin layer of Silastic. The nosemask was attached to a wide-bore (20 mm ID) rigid tube to allow a constant-bias flow of room air from a blower. Total airway occlusion was achieved by simultaneously inflating two rubber balloons fixed in the inspiratory and expiratory pipes. A total of 39 tests were done in stage III/IV nonrapid-eye movement (NREM) sleep in 11 subjects and 10 tests in rapid-eye-movement (REM) sleep in 5 subjects. The duration of total occlusion tolerated before arousal from NREM sleep varied widely (range 0.9-67.0 s) with a mean duration of 20.4 +/- 2.3 (SE) s. The breathing response to occlusion in NREM sleep was characterised by a breath-by-breath progressive increase in suction pressure achieved by an increase in the rate of inspiratory pressure generation during inspiration. In contrast, during REM sleep, arousal invariably occurred after a short duration of airway occlusion (mean duration 6.2 +/- 1.2 s, maximum duration 11.8 s), and the occlusion induced a rapid shallow breathing pattern. Our results indicate that total nasal occlusion during sleep causes arousal with the response during REM sleep being more predictable and with a generally shorter latency than that in NREM sleep.
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ABSTRACT: Obstructive sleep apnea syndrome (OSAS) is a sleep disorder in which the complete occlusion of the upper airway accompanies the cessation of airflow repeatedly during sleep, due to collapse of the soft tissues that surround and support the pharyngeal airway. As an under-diagnosed problem, OSAS affects 2% of the children population. The goal of this thesis is to investigate new computational tools for understanding normal upper airway mechanics and OSAS pathogenesis. In this thesis firstly 3D patient-specific computational fluid dynamics (CFD) models were developed to investigate the contributions of airway anatomical restrictions to the airflow and resistance in children with OSAS and matched control subjects. Modeling methods were validated by in-vitro experiments. Normal controls had significantly less pressure drop in the pharynx than the nasal passages, but in the OSAS cases maximum pressure drop in the nasopharynx ranged from 30% to 1700% higher than nasal pressure drop. These new findings suggest that the shape of pharynx is an important factor in driving internal pressure toward the collapse pressure. Simplification and verification for studying a large number of patients using simple lumped-parameter or axisymmetric models of pharynx were discussed. Pressure distribution and resistance in pharynx have been shown strongly correlated with the airway cross-section area profile, and the accuracy is also influenced by the length of the narrowed segment and the pressure recovery coefficient. Contributions of anatomical restriction on airway collapse are also investigated using a two-dimensional fluid structure interaction (FSI) model. The model couples internal flow with upper airway mechanics, and reveals that airway narrowing (percent of stenosis) could be also an important factor determining airway patency, besides clinical measurements Pcrit. The effects of upper airway muscle activation in response to negative pharyngeal pressure to maintain airway patency are impaired by the anatomical restriction. A lumped parameter model was developed to explore the effects of airway narrowing and nasal resistance on upper airway performance To study the structure and intrinsic tissue properties of the airway non-invasively, a modeling method was developed that extends published methods to determine material properties of passive diastolic myocardium. Spin-echo MR imaging, MRI tissue tagging, finite element analysis (FEA), and nonlinear optimization, are used to identify model structure and tissue properties of the deformable upper airway. The model incorporates airway architecture and intrinsic material properties, and has been validated by noninvasive MR tagging techniques. Baseline studies demonstrate correct qualitative response, and quantitative accuracy of the model desplacements. A parameter sensitivity study indicates that the airway collapsibility is most sensitive to the tongue mechanical property.
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ABSTRACT: ObjectivesThe occurrence of mask leakages during the administration of nasal continuous positive airway pressure (CPAP) therapy for treating obstructive sleep apnoea syndrome (OSAS) leads to decreased compliance. Because of exhalation valves, all mask systems have a predefined amount of systematic mask leakage, thereby complicating measurement of any additional spontaneous leakage occurring during the night. In fact, relatively few studies have investigated the impact and amount of mask leakage in patients using CPAP. MethodsUsing a fourth-order polynomial, systematic leakage was modelled as the nonlinear relationship between mask pressure and leakage through the exhalation valves. The total leakage was measured in 22patients, and additional leakage was calculated by subtracting the systematic from the measured total leakage during the night. ResultsA mean additional leakage of 6.9±7.4l/min was found; however, some patients showed rather high mask leakages (up to 37.4 l/min) with high mask pressures, possibly indicating that not all nasal masks are equally suited for higher CPAP pressures. ConclusionsThe relevant mask leakages that were observed in some cases stress the importance of thorough monitoring of patients receiving CPAP therapy. Furthermore, all investigated patients were trained very extensively in our sleep lab, possibly indicating that intensive training may be an important factor for the rather low additional mask leakages. ZielMaskenleckagen während der Anwendung der nasalen kontinuierlichen Überdrucktherapie (CPAP) zur Behandlung der obstruktiven Schlafapnoe (OSAS) können zu verminderter Compliance führen. Alle Maskensysteme weisen eine vordefinierte systematische Maskenleckage aufgrund der Ausatemventile auf, was eine Messung der zusätzlichen spontanen Leckage während der Nacht erschwert. Daher gibt es nur wenige Studien, die den Einfluss und die Größe der Maskenleckage bei CPAP-Patienten untersucht haben. MethodenDie systematische Leckage wurde als nichtlinearer Zusammenhang zwischen Maskendruck und Leckage durch das Ausatemventil mit Hilfe eines Polynoms 4.Ordnung modelliert. Die Gesamtleckage wurde bei 22 Patienten gemessen und dann die zusätzliche Leckage durch Subtraktion der systematischen von der Gesamtleckage berechnet. ErgebnisseEine mittlere zusätzliche Leckage von 6,9±7,4l/min wurde gefunden, jedoch zeigten einige Patienten auch höhere Leckagen (bis zu 37,4l/min) bei hohen Maskendrücken, was ein Hinweis dafür sein kann, dass nicht alle Masken gleich gut bei hohen CPAP-Drücken brauchbar sind. FazitDie gefundenen, teilweise relevanten Maskenleckagen betonen die Wichtigkeit des gewissenhaften Monitorings von CPAP-Patienten. Jedoch wurden alle Patienten in unserem Labor sehr ausführlich geschult, was möglicherweise ein Hinweis sein kann, dass intensives Training ein wichtiger Faktor für die insgesamt eher niedrigen Leckagen bei der CPAP-Therapie sein kann.Somnologie - Schlafforschung und Schlafmedizin 03/2008; 13(1):18-23. DOI:10.1007/s11818-008-0357-5