Upper airway distensibility and collapsibility in patients with obstructive sleep apnea

The size and behavior of the human upper airway during inhalation of aerosols

INTRODUCTION

The mouth, the pharynx and the larynx are potential sites of aerosol deposition in the upper airway during inhalation of aerosolized drugs. The right angle bend of the lumen at the back of the mouth, the position of the tongue, the variable size and shape of the lumen in the pharynx and the larynx, and the breathing pattern could increase aerosol deposition in the upper airway and decrease lung deposition. Areas covered: In this review, the anatomy of the upper airway from the oral cavity to the glottis and the impact of mandibular protrusion and incisal opening on the size of the upper airway are highlighted. In addition, the impact of inhalation maneuvers, inhaler mouthpiece geometries and a stepped mouthpiece on the size of the upper airway are discussed. Expert opinion: The structure of the upper airway lumen does not have a fixed cross sectional area and is susceptible to both constriction and distension during inhalation. The size of the upper airway can be enlarged through mandibular protrusion and/or incisal opening which might decrease aerosol deposition in the upper airway and increase lung deposition.

Upper airway structural changes induced by CPAP in OSAS patients: a study using drug-induced sleep endoscopy

We studied upper airway structural changes induced by continuous positive airway pressure (CPAP) in obstructive sleep apnea syndrome (OSAS) patients using drug-induced sleep endoscopy (DISE). This prospective study was conducted at an academic secondary referral center. In total, 28 male OSAS patients (mean age 41.1 years) with only retropalatal level obstructions were enrolled. Measurements of the obstruction site were obtained in two steps: first a measurement was taken of the obstruction site in accordance with sleep apnea, then, a measurement was taken of the obstruction site in accordance with DISE-assisted CPAP titration, including quantitative changes in the occlusion site before and after CPAP in pixel format using an area calculation program. There was a tendency for persistent closing in cases of antero-posterior (AP) obstruction versus cases of lateral (Lat) obstruction in the CPAP titration. Lat obstructions showed a tendency to be wider than AP obstructions in the quantitative analysis. These results show that the pattern and degree of airway expansion after CPAP differ in accordance with the obstruction site.

Upper airway volume segmentation analysis using cine MRI findings in children with tracheostomy tubes

OBJECTIVE

The purpose of this study is to evaluate the airway dynamics of the upper airway as depicted on cine MRI in children with tracheotomy tubes during two states of airflow through the upper airway.

MATERIALS AND METHODS

Sagittal fast gradient echo cine MR images of the supra-glottic airway were obtained with a 1.5T MRI scanner on seven children with tracheotomy tubes. Two sets of images were obtained with either the tubes capped or uncapped. The findings of the cine MRI were retrospectively reviewed. Volume segmentation of the cine images to compare the airway volume change over time (mean volume, standard deviation, normalized range, and coefficient of variance) was performed for the capped and uncapped tubes in both the nasopharynx and hypopharynx (Signed Rank Test).

RESULTS

Graphical representation of the airway volume over time demonstrates a qualitative increased fluctuation in patients with the tracheotomy tube capped as compared to uncapped in both the nasopharyngeal and hypopharyngeal regions of interest. In the nasopharynx, the mean airway volume (capped 2.72 mL, uncapped 2.09 mL, p = 0.0313), the airway volume standard deviation (capped 0.42 mL, uncapped 0.20 mL, p = 0.0156), and the airway volume range (capped 2.10 mL, uncapped 1.09 mL, p = 0.0156) were significantly larger in the capped group of patients. In the hypopharynx, the airway volume standard deviation (capped 1.54 mL, uncapped 0.67 mL, p = 0.0156), and the airway volume range (capped 6.44 mL, uncapped 2.93 mL, p = 0.0156) were significantly larger in the capped tubes. The coefficient of variance (capped 0.37, uncapped 0.26, p = 0.0469) and the normalized range (capped 1.52, uncapped 1.09, p = 0.0313) were significantly larger in the capped tubes.

CONCLUSION

There is a statistically significant change in airway dynamics in children with tracheotomy tubes when breathing via the airway as compared to breathing via the tracheotomy tube.

Diagnostic Studies in Obstructive Sleep Apnea

The standard for the diagnosis of obstructive sleep apnea (OSA) is polysomnography (PSG). Although PSG helps identify individuals who have OSA and guides medical management, it does not identify the obstruction site or predict surgical results. Radiologic and diagnostic studies have been used to direct surgical intervention and predict outcomes of sleep apnea surgery. These studies include lateral cephalometric radiographs, CT, MRI, asleep fluoroscopy, asleep and awake endoscopy, upper airway manometry, and acoustic reflection techniques. The ideal diagnostic study would identify individuals who have OSA, be cost-effective and readily accessible, and guide therapeutic, site-specific intervention with predictable results. In this article, the various modalities are reviewed in terms of their capability to effectively diagnose and guide treatment of OSA.

The upper airway in sleep: physiology of the pharynx

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.

Upper airway assessment: radiographic and other imaging techniques

Upper airway imaging is a powerful technique to study the mechanisms underlying the pathogenesis and biomechanics of sleep apnea and the mechanisms underlying the efficacy of therapeutic interventions in patients with sleep disordered breathing. The primary upper airway imaging modalities include nasopharyngoscopy, cephalometrics, CT scanning, and MR imaging. Imaging studies using these modalities have provided important insights into the static and dynamic structure and function of the upper airway and surrounding soft-tissue structures during wakefulness and sleep. Such imaging studies have highlighted the importance of the lateral pharyngeal walls in mediating upper airway caliber. These imaging modalities have also been used to study the effect of respiration, weight loss, mandibular repositioning devices, and upper airway surgery on the upper airway. Three-dimensional reconstruction of the airway and surrounding soft-tissue structures can be performed with MR imaging and CT scanning. Clinical indications for upper airway imaging are evolving such that imaging studies should be considered in patients with sleep apnea who are being treated with dental appliances or upper airway surgery.

Upper airway imaging

Upper airway imaging is a powerful technique to study the mechanisms underlying the pathogenesis, biomechanics, and efficacy of treatment options in patients with obstructive sleep apnea. Imaging studies have provided significant insight into the static and dynamic structure, and function of the upper airway and surrounding soft-tissue structure during wakefulness and sleep. Upper airway imaging modalities primarily include nasopharyngoscopy, cephalometrics, computed tomography (CT), and magnetic resonance (MR) scanning. These imaging modalities have been used to study the effect of respiration, weight loss, dental appliances, and upper airway surgery on the upper airway. MR imaging and CT have allowed quantification of the airway and surrounding soft-tissue structures in three dimensions. Clinical indications for upper airway imaging are evolving for patients being treated with dental appliances and upper airway surgery.

Retropalatal airway characteristics in uvulopalatopharyngoplasty compared with transpalatal advancement pharyngoplasty

Uvulopalatopharyngoplasty (UPPP) is reported successful in treatment of obstructive sleep apnea for approximately 50% of patients. Several modifications of the procedure have been described, including transpalatal advancement pharyngoplasty, which resects a portion of posterior hard palate and advances the soft palate anteriorly. Comparing effectiveness of different techniques based on sleep and respiratory data is confounded by multiple variables including clinical failure at nonsurgical sites and imprecise patient selection techniques. Since pharyngeal surgical procedures prevent collapse and obstruction by structurally modifying the upper airway, measuring structural changes in size and collapsibility provides a method to compare techniques. To evaluate whether transpalatal advancement pharyngoplasty is more effective in modifying upper airway characteristics than UPPP, upper airway cross-sectional size and collapsibility were measured after UPPP and transpalatal advancement pharyngoplasty. Six patients were evaluated using a quantitative endoscopic technique. After transpalatal advancement pharyngoplasty maximal retropalatal airway size increased 321% from 29.7 +/- 9.9 to 95.3 +/- 16 mm2 (P < 0.01), and retropalatal closing pressure decreased from 4.7 +/- 1.6 to -3.8 +/- 0.7 cm/H2O (P < 0.01) compared with UPPP. Respiratory disturbance index decreased from 74.5 +/- 13.5 to 29.2 +/- 9 events/hour postoperatively (P < 0.05). Results support the conclusion that transpalatal advancement pharyngoplasty increases retropalatal size and decreases retropalatal collapsibility compared with UPPP. Since these characteristics are postulated to contribute to increased stability during sleep, transpalatal advancement pharyngoplasty may potentially improve UPPP outcome in selected patients with small retropalatal airway areas after traditional surgery.

Cephalometric comparison of characteristics in chronically snoring patients with and without sleep apnea syndrome

OBJECTIVE

The purpose of this investigation is to cephalometrically study 50 snoring patients with and without sleep apnea and to determine whether cephalograms can be used as a diagnostic tool to differentiate persons who are chronic snorers from persons with sleep apnea.

STUDY DESIGN

A sample of 30 sleep apnea patients was compared with a sample of 20 chronic snorers without sleep apnea as documented by polysomnography. Forty cephalometric measurements were determined to study various skeletal, soft tissue, and airway abnormalities.

RESULTS

This study showed that both groups presented multiple cephalometric abnormalities. Only four measurements differed significantly between the two samples. In the sleep apnea group the maxilla was retropositioned and the hypoid bone displaced inferiorly and distally as compared to nonapneic snorers.

CONCLUSIONS

Because of the overall presence of abnormal cephalometric findings in both samples and given similar age and weight ranges, a differential diagnosis between chronic snorers with and without sleep apnea cannot be reliably based on standard cephalometric evaluation alone.

Facilitation of fiberoptic nasotracheal intubation in a morbidly obese patient by simultaneous use of nasal CPAP

A morbidly obese patient was emergently nasotracheally intubated using a fiberoptic bronchoscope. Simultaneous application of 20 cm H2O nasal continuous positive airway pressure (CPAP) to the contralateral naris using a nasal pillow helped maintain ventilation of the patient during intubation and greatly facilitated visualization of anatomic landmarks and translaryngeal passage of the bronchoscope. Fiberoptic video images of this patient's hypopharynx demonstrate the pharyngeal splinting action of nasal CPAP thus applied. This is a novel approach to difficult intubation of the obese patient.

[The dynamics of pharyngeal structures in obstructive sleep apnea (during spontaneous, continuous positive pressure and BiPAP ventilation)]

Obstructive sleep apnea results from a pharyngeal collapse. Upper airway can be investigated using either static or dynamic methods during wakefulness or when the patient is sleeping. Somnofluoroscopy is one of the dynamic methods allowing a visualization of the upper airway during sleep. A lateral projection of the pharynx is obtained during fluoroscopic examination which allows visualization of the upper airway dimensions and the bone structures (hyoid bone, cervical spine, mandible). Standard polygraphic parameters (EEG, EOG, flow rate, thoracic and abdominal movements) and fluoroscopic image are simultaneously acquired on the same videotape. Using this technique, we have described the typical pattern of events occurring during an episode of apnea: 1-beginning of airway occlusion in the oropharynx with anterior or posterior hooking of the soft palate, 2-suction on the uvula downwards and complete occlusion of the oropharynx with further extension to the hypopharynx, 3-active movements of the cervical spine and hyoid bone as if the patient is choking, 4-overcoming of the occlusion usually accompanied by opening of the jaw and occurring either as a sudden event throughout the length of the pharyngeal airway or as a progressive reopening from the hypopharynx. In a recent study, we have investigated upper airway dynamics when a continuous positive pressure with one level (CPAP) or two levels of pressure (BiPAP) was applied. When using CPAP with pressure below the optimal pressure, uvula movements were the first changes we observed, preceding the pharyngeal collapse. Lowering the expiratory pressure alone lead to a significant reduction in pharyngeal dimensions starting at expiration and extending also to inspiration when the expiratory pressure is further reduced. Using BiPAP may lead to upper airway instability. The frequency and the variability of this phenomenon need further studies to be established.

Dynamic upper airway imaging during awake respiration in normal subjects and patients with sleep disordered breathing

The effects of respiration on upper airway caliber were studied using cine computed tomography (CT) in 15 normal subjects, 14 snorer/mildly apneic subjects, and 13 patients with obstructive sleep apnea. All subjects were scanned in the supine position during awake nasal breathing. Eight-millimeter-thick axial slices were obtained at four anatomic levels from the nasopharynx to the retroglossal region every 0.4 s during a respiratory cycle. Tidal volume measured from an integrated pneumotachograph signal was correlated with slice acquisition during inspiration and expiration to generate loops comparing upper airway area and tidal volume. In all three subject groups and at all anatomic levels studied, there were significant dimensional changes in upper airway caliber during the respiratory cycle. The major findings in this investigation include: (1) the upper airway was significantly smaller in apneic than normal subjects, especially at the retropalatal low and retroglossal anatomic levels; in apneic patients the airway had an anterior-posterior configuration unlike the normal airway, which had a horizontal configuration with the major axis in the lateral direction; (2) in all three subject groups, little airway narrowing occurred in inspiration, suggesting that the action of the upper airway dilator muscles balanced the effects of negative intraluminal pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Size and mechanical properties of the pharynx in healthy men and women

Obstructive sleep apnea (OSA) has a marked male predominance. To determine whether there are differences in the mechanical properties of the pharynx of men and women that may contribute to the gender difference in disease incidence, we measured pharyngeal cross-sectional area during quiet breathing in 77 normal men and 98 normal women using the acoustic pulse technique. Standard pulmonary function tests were also performed. Pharyngeal mechanics were studied in 23 men and 34 women by measuring the change in pharyngeal area during a slow vital capacity maneuver. Gender was found to be the most important independent factor contributing to pharyngeal size. The men had a significantly larger pharynx than the women (3.63 +/- 0.10 versus 3.20 +/- 0.09 cm2, mean +/- SEM; p < 0.01). Pharyngeal mechanics were also different between men and women. The men had a larger change in pharyngeal area with changing lung volume than the women (0.60 +/- 0.14 versus 0.12 +/- 0.12 cm2, mean +/- SEM; p < 0.02). This difference persisted even after normalizing the data for pharyngeal size. We found that there are gender-related differences in the size and mechanical properties of the pharynx and speculate that the larger pharynx of men may be more than offset by greater changes in pharyngeal size with changing lung volume, contributing to the greater incidence of OSA in men.

Effect of reduced expiratory pressure on pharyngeal size during nasal positive airway pressure in patients with sleep apnoea: evaluation by continuous computed tomography

BACKGROUND

This study aimed to determine whether reducing the expiratory pressure during nasal positive airway pressure for reasons of comfort causes a substantial decrease in the upper airway calibre.

METHODS

Eight patients with obstructive sleep apnoea were studied. Continuous computed tomography (each run lasting 12 seconds) was used to measure minimum and maximum pharyngeal cross sectional areas at the velopharynx and the hypopharynx. Pharyngeal areas were measured while patients were awake and breathing without assistance, during the application of 12 cm H2O continuous positive airway pressure, and during bi-level positive airway pressure with an inspiratory pressure of 12 cm H2O and an expiratory pressure of 6 cm H2O.

RESULTS

Nasal continuous positive airway pressure significantly increased the mean minimum and maximum upper airway areas at both the velopharynx and the hypopharynx compared with normal unassisted breathing. Bi-level positive airway pressure did not show a statistically significant increase in the minimum upper airway area at either level compared with normal unassisted breathing. The minimum areas of the velopharynx and hypopharynx were smaller with bi-level than continuous positive airways pressure in six of eight and eight of eight patients respectively but these were still greater than during unassisted breathing in seven of eight and six of eight patients respectively.

CONCLUSIONS

Continuous positive airway pressure at 12 cm H2O is more effective in splinting the pharynx open than bi-level positive airway pressure with an inspiratory positive airway pressure of 12 cm H2O and an expiratory pressure of 6 cm H2O in patients with obstructive sleep apnoea during wakefulness, suggesting an important role for expiratory positive airway pressure. The clinical importance of this finding needs to be evaluated during sleep.