Relationships between MRI fat distributions and sleep apnea and obesity hypoventilation syndrome in very obese patients.

PURPOSE: Obesity is associated with both obstructive sleep apnea (OSA) and obesity hypoventilation. Differences in adipose tissue distribution are thought to underlie the development of both OSA and hypoventilation. We explored the relationships between the distribution of upper airway, neck, chest, abdominal and muscle fat in very obese individuals. METHODS: We conducted a cross-sectional cohort study of individuals presenting to a tertiary sleep clinic or for assessment for bariatric surgery. Individuals underwent magnetic resonance (MR) imaging of their upper airway, neck, chest, abdomen and thighs; respiratory polygraphy; 1 week of autotitrating CPAP; and morning arterial blood gas to determine carbon dioxide partial pressure and base excess. RESULTS: Fifty-three individuals were included, with mean age of 51.6 ± 8.4 years and mean BMI of 44.3 ± 7.9 kg/m2; there were 27 males (51%). Soft palate, tongue and lateral wall volumes were significantly associated with the AHI in univariable analyses (p < 0.001). Gender was a significant confounder in these associations. No significant associations were found between MRI measures of adiposity and hypoventilation. CONCLUSIONS: In very obese individuals, our results indicate that increased volumes of upper airway structures are associated with increased severity of OSA, as previously reported in less obese individuals. Increasingly large upper airway structures that reduce pharyngeal lumen size are likely to lead to OSA by increasing the collapsibility of the upper airway. However, we did not show any significant association between regional fat distribution and propensity for hypoventilation, in this population.

Adhesion molecule increases in sleep apnea: beneficial effect of positive airway pressure and moderation by obesity.

BACKGROUND: Elevated levels of intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) may contribute to cardiovascular disease and are associated with obstructive sleep apnea (OSA) and obesity. The relationship between OSA and obesity in determining ICAM-1 and VCAM-1 levels, and the effect of treatment, is unclear. OBJECTIVE: Our aim was to study whether positive airway pressure (PAP) usage resulted in changes in ICAM-1 and VCAM-1 after 2 years within 309 OSA patients from the Icelandic Sleep Apnea Cohort, and determine how obesity affected such changes. SUBJECTS/METHODS: The mean body mass index (BMI) was 32.4±5.1 kg m(-2); subjects had moderate-to-severe OSA (apnea-hypopnea index=45.0±20.2) and 79% were male. There were 177 full PAP users (⩾4 h per night and ⩾20 of last 28 nights), 44 partial (<4 h per night or <20 nights) and 88 nonusers. RESULTS: ICAM-1 (P<0.001) and VCAM-1 (P=0.012) change was significantly different among the PAP groups. The largest ICAM-1 differences were among the most obese subjects (P<0.001). At follow-up, nonusers had increased ICAM-1 compared with decreased levels in full users. All groups had increased VCAM-1, but nonusers had a significantly larger increase than full users. CONCLUSIONS: Within moderate-to-severe OSA patients, PAP usage prevents increases in adhesion molecules observed in nonusers after 2 years. For ICAM-1, the largest effect is in the most obese subjects. As OSA and obesity commonly coexist, the usage of PAP to limit increases in adhesion molecules may decrease the rate of progression of OSA-related cardiovascular disease.

Hormone variations associated with quantitative fat measures in the menopausal transition.

OBJECTIVE: Reproductive hormone levels are associated with body size, and the association between estradiol and body size varies over the menopausal transition. This study aims to delineate these relationships using quantitative measures of visceral and subcutaneous fat. METHODS: Early follicular hormones (follicle stimulating hormone (FSH), estradiol, luteinizing hormone, dehydroepiandrosterone sulfate, testosterone) and T-1 weighted abdominal MRI images were obtained in a cross-sectional assessment of 77 women in the Penn Ovarian Aging Study. Fat volume (cm(3)) was quantified using validated software (Amira) and divided into tertiles of visceral and subcutaneous fat volume for analysis. Multivariable linear regression models compared hormone values between tertiles adjusting for race, age, and menopausal status. RESULTS: In adjusted models, estradiol was positively associated with visceral fat tertiles (geometric mean (GM) estradiol (pg/ml): Low 13.0, Mid 17.5, High 26.7, p = 0.006) while FSH was inversely associated with visceral fat tertiles (GM FSH (mIU/ml): Low 42.8, Mid 43.2, High 30.8, p = 0.03). The association of estradiol with visceral and subcutaneous fat tertiles varied by menopausal status (p < 0.001). In the early transition, estradiol was similar across tertiles of fat; postmenopause, estradiol was positively associated with visceral fat. Other hormones were not associated with fat measures. CONCLUSIONS: Estradiol was associated with quantitative measures of visceral fat and varies by menopausal status. This finding suggests that visceral fat may be an important mediator in hormone changes over the menopausal transition.

The role of obesity, different fat compartments and sleep apnea severity in circulating leptin levels: the Icelandic Sleep Apnea Cohort study.

OBJECTIVES: To assess whether sleep apnea severity has an independent relationship with leptin levels in blood after adjusting for different measures of obesity and whether the relationship between obstructive sleep apnea (OSA) severity and leptin levels differs depending on obesity level. METHODS: Cross-sectional study of 452 untreated OSA patients (377 males and 75 females), in the Icelandic Sleep Apnea Cohort (ISAC), age 54.3±10.6 (mean±s.d.), body mass index (BMI) 32.7±5.3 kg m(-2) and apnea-hypopnea index 40.2±16.1 events per h. A sleep study and magnetic resonance imaging of abdominal visceral and subcutaneous fat volume were performed, as well as fasting serum morning leptin levels were measured. RESULTS: Leptin levels were more highly correlated with BMI, total abdominal and subcutaneous fat volume than visceral fat volume per se. No relationship was found between sleep apnea severity and leptin levels, assessed within three BMI groups (BMI <30, BMI 30-35 and BMI > or =35 kg m(-2)). In a multiple linear regression model, adjusted for gender, BMI explained 38.7% of the variance in leptin levels, gender explained 21.2% but OSA severity did not have a significant role and no interaction was found between OSA severity and BMI on leptin levels. However, hypertension had a significant effect on the interaction between OSA severity and obesity (P=0.04). In post-hoc analysis for nonhypertensive OSA subjects (n=249), the association between leptin levels and OSA severity explained a minor but significant variance (3.2%) in leptin levels. This relationship was greatest for nonobese nonhypertensive subjects (significant interaction with obesity level). No relationship of OSA severity and leptin levels was found for hypertensive subjects (n=199). CONCLUSION: Obesity and gender are the dominant determinants of leptin levels. OSA severity is not related to leptin levels except to a minor degree in nonhypertensive nonobese OSA subjects.

Identification of craniofacial risk factors for obstructive sleep apnoea using three-dimensional MRI.

The alteration of craniofacial structures has been associated with obstructive sleep apnoea (OSA). We hypothesised that: 1) a smaller mandible is a risk factor for OSA; and 2) the previously observed inferiorly positioned hyoid bone in apnoeics is associated with enlarged tongue volume. This is a case-control study using three-dimensional magnetic resonance imaging cephalometry. 55 apneics and 55 controls were matched for age, sex and race. The analysis was stratified by sex and controlled for age, race, height, neck visceral fat, skeletal type and tongue volume. We found that a 1-sd increase in mandibular length and depth were associated with decreased risk of sleep apnoea (OR 0.52, 95% CI 0.28-0.99 and OR 0.46, 95% CI 0.23-0.91, respectively) in males but not in females. Greater hyoid-to-nasion (OR 2.64, 95% CI 1.19-5.89 in males and OR 5.01, 95% CI 2.00-12.52 in females) and supramentale-to-hyoid (OR 2.39, 95% CI 1.12-5.14) in males and OR 3.38, 95% CI 1.49-7.68 in females) distances were associated with increased risk of OSA. The difference for hyoid position between apnoeics and controls was lost after controlling for tongue volume. Enlargement of tongue is likely to be the pathogenic factor for inferior-posterior positioning of hyoid. A small and shallow mandible is an independent risk factor for OSA in males but not in females.

Pharmacokinetics and safety of multiple doses of daptomycin 6 mg/kg in noninfected adults undergoing hemodialysis or continuous ambulatory peritoneal dialysis.

AIMS: The purpose of this study was to characterize the pharmacokinetics and tolerability of daptomycin in subjects undergoing hemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD). METHOD: 16 noninfected adults on stable dialysis regimens were enrolled. Daptomycin 6 mg/kg was administered after HD during a 48 h - 48 h - 72 h dialysis week or before a CAPD dwell time over a 48 h - 48 h - 48 h dialysis week. Pharmacokinetic parameters were described, and adverse events were monitored. RESULTS: Daptomycin had mean half-lives in HD subjects of 28.0 and 35.9 h on Days 1 and 5, with corresponding values of 25.8 and 26.7 h in CAPD subjects. Steady state was reached by Day 5 in both groups. At steady state, HD subjects had a mean peak plasma concentration (Cmax) of 81.6 µg/ml and a mean trough concentration of 15.3 µg/ml (on Day 8). In CAPD subjects, Cmax was 93.9 µg/ml and the trough was 20.7 µg/ml (on Day 7). Adverse events were experienced by 71.4% and 66.7% of HD and CAPD subjects, respectively. Most of these were mild or moderate in intensity; however, 2 subjects experienced muscle spasms and mild creatine phosphokinase elevations although neither event was considered to be related to study drug. CONCLUSIONS: The pharmacokinetics of daptomycin 6 mg/kg support a dosing regimen of every 48 h in CAPD and thrice-weekly dosing in HD.

Imaging for the snoring and sleep apnea patient.

Upper airway imaging techniques have significantly advanced the understanding of the pathogenesis of obstructive sleep apnea and the biomechanical mechanisms by which therapeutic interventions for this disorder exert their effects. Both static and dynamic imaging studies have been used to examine the structure and function of the upper airway during wakefulness and sleep. These studies have highlighted the importance of the lateral pharyngeal walls in addition to the tongue and soft palate in modulating changes in upper airway caliber. Upper airway imaging has also been used to understand the changes in upper airway anatomy associated with weight loss, mandibular repositioning devices, and upper airway surgery. At present, upper airway imaging should be considered in patients undergoing upper airway surgery and possibly in patients being evaluated for oral appliances. MR imaging and nasopharyngoscopy are the imaging modalities of choice in patients undergoing a UPPP. Cephalometrics should be considered in patients being treated with mandibular repositioning devices. Upper airway imaging has provided an important framework to examine the pathogenesis of airway closure, and these investigations may, in time, lead to more effective treatment options for patients with sleep apnea.

Magnetic resonance imaging of the upper airway structure of children with obstructive sleep apnea syndrome.

The anatomical relationships between lymphoid, bony, and other tissues affecting the shape of the upper airway in children with obstructive sleep apnea syndrome (OSAS) have not been established. We therefore compared the upper airway structure in 18 young children with OSAS (age 4.8 +/- 2.1 yr; 12 males and 6 females) and an apnea index of 4.3 +/- 3.9, with 18 matched control subjects (age, 4.9 +/- 2.0 yr; 12 males and 6 females). All subjects underwent magnetic resonance imaging under sedation. Axial and sagittal T1- and T2-weighted sequences were obtained. Images were analyzed with image-processing software to obtain linear, area, and volumetric measurements of the upper airway and the tissues comprising the airway. The volume of the upper airway was smaller in subjects with OSAS in comparison with control subjects (1.5 +/- 0.8 versus 2.5 +/- 1.2 cm(3); p < 0.005) and the adenoid and tonsils were larger (9.9 +/- 3.9 and 9.1 +/- 2.9 cm(3) versus 6.4 +/- 2.3 and 5.8 +/- 2.2 cm(3); p < 0.005 and p < 0.0005, respectively). Volumes of the mandible and tongue were similar in both groups; however, the soft palate was larger in subjects with OSAS (3.5 +/- 1.1 versus 2.7 +/- 1.2 cm(3); p < 0.05). We conclude that in children with moderate OSAS, the upper airway is restricted both by the adenoid and tonsils; however, the soft palate is also larger in this group, adding further restriction.

Magnetic resonance imaging of the upper airway in children with Down syndrome.

As compared with control subjects, children with Down syndrome have different size and shape relationships among tissues composing the upper airway, which may predispose them to obstructive sleep apnea (OSA). We hypothesized that Down syndrome children without OSA have similar subclinical differences. We used magnetic resonance imaging to study the upper airway in 11 Down syndrome children without OSA (age, 3.2 +/- 1.4 yr) and in 14 control subjects (age, 3.3 +/- 1.1 yr). Sequential T1- and T2-weighted spin-echo axial and sagittal images were obtained. We found a smaller airway volume in subjects with Down syndrome (1.4 +/- 0.4 versus 2.3 +/- 0.8 cm(3) in controls, p < 0.005). Subjects with Down syndrome had a smaller mid- and lower face skeleton. They had a shorter mental spine-clivus distance (5.7 +/- 0.6 versus 6.2 +/- 0.4 cm, p < 0.05), hard palate length (3.2 +/- 0.4 versus 3.7 +/- 0.2 cm, p < 0.005), and mandible volume (11.5 +/- 3.7 versus 16.9 +/- 2.9 cm3, p < 0.0005). Adenoid and tonsil volume was significantly smaller in the subjects with Down syndrome. However, the tongue, soft-palate, pterygoid, and parapharyngeal fat pads were similar to those of control subjects. This study shows that Down syndrome children without OSA do not have increased adenoid or tonsillar volume; reduced upper airway size is caused by soft tissue crowding within a smaller mid- and lower face skeleton.

Abnormal sleep/wake cycles and the effect of environmental noise on sleep disruption in the intensive care unit.

UNLABELLED: Little is known about sleep/wake abnormalities in intensive care and less is known about the mechanisms responsible for these abnormalities. We studied 22 (20 mechanically ventilated) medical intensive care unit (ICU) patients with continuous polysomnography (PSG) and environmental noise measurements for 24-48 h to characterize sleep-wake patterns and objectively determine the effect of environmental noise on sleep disruption. All 22 patients demonstrated sleep-wake cycle abnormalities. There were large variations in total sleep time (TST) with the mean total sleep time per 24-h study period of 8.8 +/- 5.0 h. Sleep-wake cycles were fragmented and nonconsolidated with a mean of 57 +/- 18% and 43 +/- 18% of the TST occurring during the day and night, respectively. Environmental noise was responsible for 11.5 and 17% of the overall arousals and awakenings from sleep, respectively. The mean noise arousal index was 1.9 +/- 2.1 arousals/h sleep. CONCLUSIONS: (1) ICU patients are qualitatively, but not necessarily quantitatively, sleep deprived; and (2) although environmental noise is in part responsible for sleep-wake abnormalities, it is not responsible for the majority of the sleep fragmentation and may therefore not be as disruptive to sleep as the previous literature suggests.

Physical findings and the risk for obstructive sleep apnea. The importance of oropharyngeal structures.

In this study, we hypothesized that anatomic abnormalities of the oropharynx, particularly narrowing of the airway by the lateral pharyngeal walls, tonsils, and tongue, would be associated with an increased likelihood for obstructive apnea among patients presenting to a sleep disorders center. To test this hypothesis, we used data from a cohort of 420 patients presenting to the Penn Center for Sleep Disorders. Associations between individual variables in the clinical evaluation model and sleep apnea as defined by a respiratory disturbance index greater than or equal to 15 events per hour were characterized by odds ratios (ORs) with 95% confidence intervals (CIs). Multivariable logistic regression was used to simultaneously estimate ORs for multiple variables and to control for other relevant patient characteristics. Results showed that narrowing of the airway by the lateral pharyngeal walls (OR = 2.5; 95% CI, 1.6-3.9) had the highest association with obstructive sleep apnea (OSA) followed by tonsillar enlargement (OR = 2.0; 95% CI, 1.0-3.8), enlargement of the uvula (OR = 1.9; 95% CI, 1.2-2.9), and tongue enlargement (OR = 1.8; 95% CI, 1.0-3.1). Low-lying palate, retrognathia, and overjet were not found to be significantly associated with OSA. Controlling for BMI and neck circumference, only lateral narrowing and enlargement of the tonsils maintained their significant (OR = 2.0 and 2.6, respectively). A subgroup analysis examining differences between male and female subjects showed that no oropharyngeal risk factor achieved significance in women while lateral narrowing was the sole independent risk factor in men. These findings suggest that enlargement of the oropharyngeal soft tissue structures, particularly the lateral pharyngeal walls, is associated with an increased likelihood of OSA among patients presenting to sleep disorders centers.

Quantitative magnetic resonance imaging demonstrates alterations of the lingual musculature in obstructive sleep apnea.

Upper airway musculature is important in the pathogenesis of obstructive sleep apnea. Electromyographic studies of patients with obstructive sleep apnea demonstrate increased activity of upper airway dilator muscles. Biopsy studies of these muscles show both adaptation and muscle injury. In this study we utilized quantitative magnetic resonance imaging to characterize changes in the upper airway musculature of patients with obstructive sleep apnea. This technique provides measurements of the T2 relaxation times of upper airway muscles (genioglossus, geniohyoid, sternohyoid/sternothyroid) spatially localized to submillimeter resolution. Our results demonstrate that the mean T2 values of genioglossus (p = 0.04) and geniohyoid (p = 0.06) differ between the apneic and control groups, while the values for the sternohyoid/sternothyroid muscles (p = 0.6) are similar between groups. In both apneics and normals respectively the T2 values for the genioglossus (p = 0.0003, 0.0001) and geniohyoid (p = 0.0054, 0.001) were significantly greater than for the sternohyoid/sternothyroid muscles. The changes observed are compatible with the hypothesis that there is increased edema and possibly increased fat content of the tongue muscles in patients with obstructive sleep apnea.

Quantitative evaluation of the upper airway during nasopharyngoscopy with the Müller maneuver.

OBJECTIVE: To quantitatively examine changes in the upper airway caliber of normal subjects at graded negative inspiratory pressures generated during nasopharyngoscopy with a Müller maneuver. STUDY DESIGN: Eighteen normal subjects prospectively underwent nasopharyngoscopy with Müller maneuvers. Subjects performed graded and maximal effort Müller maneuvers while sitting upright, and maximal-effort Müller maneuvers in the supine position. Two regions of the upper airway--the retropalatal and retroglossal--were examined. METHODS: Images from the endoscopic examination were objectively analyzed by adjusting manually traced airway contours using full-width, half-maximum edge detection algorithm software. The adjusted tracings' area and dimensions through the airway centroid were measured. RESULTS: Müller maneuvers performed at -40 cm H2O resulted in a 64%+/-17% (P = .0001) reduction in upper airway area that consisted of a 51%+/-20% (P = .0001) reduction in the lateral dimension and a 21%+/-24% (P = .0026) reduction in antero-posterior dimension. Müller maneuvers in the retroglossal region did not significantly reduce airway area (P = .575), but demonstrated an altered airway conformation that consisted of lateral narrowing and an increase in antero-posterior dimension. Changes in body position did not result in significant differences in either airway caliber or airway dimension. CONCLUSIONS: Airway caliber during forced inspiration is mediated primarily through changes in the lateral pharyngeal walls. This study has also shown that antero-posterior and lateral airway structures are largely independent in their response to Müller maneuvers. Similarly, the retropalatal and retroglossal regions of the upper airway respond differently to forced negative intraluminal pressure.

Patient perception of sleep quality and etiology of sleep disruption in the intensive care unit.

The etiology of sleep disruption in patients in intensive care units (ICUs) is poorly understood, but is thought to be related to environmental stimuli, especially noise. We sampled 203 patients (121 males and 82 females) from different ICUs (cardiac [CCU], cardiac stepdown [CICU], medical [MICU], and surgical [SICU]) by questionnaire on the day of their discharge from the unit, to determine the perceived effect of environmental stimuli on sleep disturbances in the ICU. Perceived ICU sleep quality was significantly poorer than baseline sleep at home (p = 0.0001). Perceived sleep quality and daytime sleepiness did not change over the course of the patients' stays in the ICU, nor were there any significant differences (p > 0.05) in these parameters among respective units. Disruption from human interventions and diagnostic testing were perceived to be as disruptive to sleep as was environmental noise. In general, patients in the MICU appeared to be more susceptible to sleep disruptions from environmental factors than patients in the other ICUs. Our data show that: (1) poor sleep quality and daytime sleepiness are problems common to all types of ICUs, and affect a broad spectrum of patients; and (2) the environmental etiologies of sleep disruption in the ICU are multifactorial.

Identifying the patient with sleep apnea: upper airway assessment and physical examination.

Since the final common pathway for obstructive sleep apnea is obstruction of the upper airway during nocturnal respiration, examination and assessment of the anatomy of the upper airway plays a central role in patient evaluation. Since the upper airway begins at the nose and lips and ends at the larynx, a complete assessment of the upper airway evaluates this entire length of this anatomic region including the bony framework and soft tissue. Though office assessment of these structures does not necessarily mimic the appearance of behavior of these structures during physiologic sleep, the office examination can give important information as to the site of obstruction during sleep that can help direct therapy.

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.

State-related changes in upper airway caliber and surrounding soft-tissue structures in normal subjects.

State-dependent changes in upper airway caliber were studied with magnetic resonance imaging (MRI) techniques. We hypothesized that changes in airway caliber during sleep in normal subjects would result from positional and dimensional changes in upper airway soft-tissue structures, including the lateral pharyngeal walls, tongue, and soft palate. We used MRI to study 15 normal subjects during wakefulness and sleep. Sleep was facilitated by one night of sleep deprivation prior to MRI. During sleep, the volume of the retropalatal (RP) airway was reduced by 19% (p = 0.03). The volume of the retroglossal (RG) airway was not significantly reduced during sleep, suggesting that the RP region may be more likely to collapse. The mean minimal cross-sectional airway area was reduced by 228% (p = 0.004) in the RP and by 22% (p = 0.02) in the RG region during sleep as compared with values in anatomically matched axial images during wakefulness. Airway anteroposterior (AP) and lateral dimensions were also significantly reduced in the RP region. Airway narrowing in the RP region was associated with a 7% increase in thickness of the lateral pharyngeal walls (p = 0.04). In nine subjects, sagittal data showed significant posterior displacement of the soft palate during sleep as compared with wakefulness. Multiple linear regression analyses indicated that reduction in the RP airway area during sleep resulted from posterior movement of the soft palate, thickening of the lateral pharyngeal walls, and an increase in tongue oblique distance. We conclude that the lateral pharyngeal walls play an important role in upper airway narrowing during sleep in normal subjects.

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.

Properties of tissues surrounding the upper airway.

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.

Upper airway and soft tissue structural changes induced by CPAP in normal subjects.

Nasal continuous positive airway pressure (CPAP) is the treatment of choice for adults with obstructive sleep apnea. CPAP is known to increase upper airway size; however, the direct effects of CPAP on soft tissue structures surrounding the upper airway are less well understood. Magnetic resonance imaging was used to study the effect of incremental levels (0, 5, 10, and 15 cm H2O) of CPAP on the upper airway and surrounding soft tissue structures in 10 normal subjects. Progressive increases in CPAP resulted in the following major findings: (1) airway volume and airway area (measured at several different locations [midregion, minimal, maximal]) within the retropalatal and retroglossal regions increased; (2) lateral airway dimensional changes were greater than anterior-posterior changes; (3) lateral upper airway soft tissue structural changes were significantly greater than anterior-posterior changes; (4) lateral pharyngeal wall thickness decreased and the distance between the lateral parapharyngeal fat pads increased. An inverse relationship was demonstrated between CPAP level and pharyngeal wall thickness; (5) minimal changes were noted in the soft palate and tongue. These data suggest that the lateral pharyngeal walls are more "compliant" than the soft palate and tongue. This investigation provides further evidence that the lateral pharyngeal walls play an important role in mediating upper airway caliber.