Properties of tissues surrounding the upper airway.
ABSTRACT The pathogenesis of obstructive sleep apnea (OSA) remains unknown. However, we are beginning to understand the mechanisms leading to sleep apnea by evaluating the structure and function of the upper airway (UA) and the surrounding soft-tissue structures using sophisticated magnetic-resonance-imaging techniques. Knowledge of the morphology and mechanical behavior of the soft-tissue structures is essential for a complete understanding of the physiology of the UA. Although the tongue and soft palate have been considered the most important UA soft-tissue structures, our data have highlighted the importance of the lateral pharyngeal walls in the mediating UA caliber. We have demonstrated that: (1) during wakefulness, the predominant anatomic abnormality underlying UA narrowing in patients with OSA is thickening of the lateral pharyngeal walls; (2) during respiration, there are significant changes in lateral airway dimensions as well as in the thickness of the lateral walls; and (3) incremental levels of continuous positive airway pressure (CPAP) result in progressive thinning of the lateral pharyngeal walls. The dynamic biomechanical behavior of the lateral pharyngeal walls during wakefulness, sleep, and during apneas needs to be investigated.
Article: Novel retrospective, respiratory-gating method enables 3D, high resolution, dynamic imaging of the upper airway during tidal breathing.[show abstract] [hide abstract]
ABSTRACT: PURPOSE: A retrospective, respiratory-gated technique for measuring dynamic changes in the upper airway over the respiratory cycle was developed, with the ultimate goal of constructing anatomically and functionally accurate upper airway models in obstructive sleep apnea patients. METHODS: Three-dimensional cine, retrospective respiratory-gated, gradient echo imaging was performed in six adolescents being evaluated for polycystic ovary syndrome, a disorder with a high obstructive sleep apnea prevalence. A novel retrospective gating scheme, synchronized to flow from a nasal cannula, limited image acquisition to predefined physiological ranges. Images were evaluated with respect to contrast, airway signal leakage, and demonstration of dynamic airway area changes. RESULTS: Two patients were diagnosed with obstructive sleep apnea. Motion artifacts were absent in all image sets. Scan efficiency ranged from 48 to 88%. Soft tissue-to-airway contrast-to-noise ratio varied from 6.1 to 9.6. Airway signal leakage varied between 10 and 17% of soft tissue signal. Automated segmentation allowed calculation of airway area changes over the respiratory cycle. In one severe apnea patient, the technique allowed demonstration of asynchronous airway expansion and contraction above and below a severe constriction. CONCLUSIONS: Retrospective, respiratory gated imaging of the upper airway has been demonstrated, utilizing a gating algorithm to ensure acquisition over specified ranges of respiratory rate and tidal volume. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.Magnetic Resonance in Medicine 02/2013; · 2.96 Impact Factor
[show abstract] [hide abstract]
ABSTRACT: The upper airway is the primary conduit for passage of air into the lungs. Its physiology has been the subject of intensive study: both passive mechanical and active neural influences contribute to its patency and collapsibility. Different models can be used to explain behavior of the upper airway, including the "balance of forces" (airway suction pressure during inspiration versus upper airway dilator tone) and the Starling resistor mechanical model. As sleep is the primary state change responsible for sleep disordered breathing (SDB) and the obstructive apnea/hypopnea syndrome (OSAHS), understanding its effects on the upper airway is critical. These include changes in upper airway muscle dilator activity and associated changes in mechanics and reflex activity of the muscles. Currently SDB is thought to result from a combination of anatomical upper airway predisposition and changes in neural activation mechanisms intrinsic to sleep. Detection of SDB is based on identifying abnormal (high resistance) breaths and events, but the clinical tools used to detect these events and an understanding of their impact on symptoms is still evolving. Outcomes research to define which events are most important, and a better understanding of how events lead to physiologic consequences of the syndrome, including excessive daytime somnolence (EDS), will allow physiologic testing to objectively differentiate between "normal" subjects and those with disease.Sleep Medicine Reviews 03/2003; 7(1):9-33. · 6.93 Impact Factor
[show abstract] [hide abstract]
ABSTRACT: We utilized novel three-dimensional volumetric analysis techniques with magnetic resonance imaging (MRI) to study the upper airway and surrounding soft-tissue structures. These MRI techniques allowed us to objectively quantify the volume of the tongue, soft palate, parapharyngeal fat pads, and lateral pharyngeal walls. We first validated our volumetric imaging techniques on a phantom and then demonstrated that our results were reliable and reproducible in normal subjects who did not lose weight. Finally, we studied 12 obese, nonapneic women during wakefulness before and after weight loss. We hypothesized that our novel magnetic-resonance computer-reconstruction techniques would allow us to detect small reductions in the volume of the tongue, soft palate, lateral pharyngeal walls, and parapharyngeal fat pads and increases in the volume of the upper airway with weight loss. University medical center. Normal controls and 12 obese nonapneic women. Weight loss. Following a mean 17.1+/-8.62 kg (17.3%) reduction in weight, upper airway volume increased (p = 0.06) in both the retropalatal and retroglossal regions. This increase in upper airway volume was mediated by significant reductions in the volume of the lateral pharyngeal wall (p = 0.0001) and parapharyngeal fat pads (p = 0.001). However, the volume of the tongue (p = 0.35) and soft palate (p = 0.39) were not reduced significantly with weight loss. These data indicate that volumetric MRI is a powerful tool to study anatomic changes in the upper airway and surrounding soft-tissue structures and is sensitive enough to detect changes in these structures.Sleep 09/2002; 25(5):532-42. · 5.05 Impact Factor