Richard J Schwab

Southwestern PA Pulmonary & Sleep Medicine Ltd., Washington, Pennsylvania, United States

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Publications (63)353.97 Total impact

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    ABSTRACT: Rationale: Body habitus is a major determinant of obstructive sleep apnea (OSA). However, many individuals do not have OSA despite being overweight/obese (body mass index, BMI>25 kg/m2) for reasons that are not fully elucidated. Objectives: To determine the key physiological traits (upper-airway anatomy/collapsibility, upper-airway muscle responsiveness, chemoreflex control of ventilation, arousability from sleep) responsible for the absence of OSA in overweight/obese individuals. Methods: We compared key physiological traits in 18 overweight/obese non-apneics (apnea-hypopnea index, AHI<15 events/hr) to 25 overweight/obese matched OSA patients (AHI≥15 events/hr), and 11 normal-weight non-apneic controls. Traits were measured by repeatedly lowering continuous positive airway pressure to sub-therapeutic levels for 3 min during non-REM sleep. Measurements and Main Results: Overweight/obese non-apneics exhibited a less collapsible airway than overweight/obese apneics (Pcrit: -3.7±1.9 vs. 0.6±1.2 cmH2O, P=0.003; mean±95%CI.), but a more collapsible airway relative to normal-weight controls (-8.8±3.1 cmH2O, P<0.001). Notably, overweight/obese non-apneics exhibited a 3-fold greater upper-airway muscle responsiveness than both overweight/obese apneics (Δgenioglossus EMG/Δepiglottic pressure: -0.49[-0.22 to -0.79] vs. -0.15[-0.09 to -0.22] %/cmH2O, P=0.008; mean[95%CI]) and normal-weight controls (-0.16[-0.04 to -0.30] %/cmH2O; P=0.02). Loop gain was elevated (more-negative) in both overweight/obese groups vs. normal-weight controls (p=0.02). Model-based analysis demonstrated that overweight/obese non-apneics rely on both more favorable anatomy/collapsibility and enhanced upper-airway dilator muscle responses to avoid OSA. Conclusions: Overweight/obese non-apneics have a moderately-compromised upper-airway structure that is mitigated by highly-responsive upper-airway dilator muscles to avoid OSA. Elucidating the mechanisms underlying enhanced muscle responses in this population may provide clues for novel OSA interventions.
    American Journal of Respiratory and Critical Care Medicine 09/2014; · 11.04 Impact Factor
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    ABSTRACT: Obstructive sleep apnoea (OSA) is associated with cardiovascular disease. Dyslipidaemia has been implicated as a mechanism linking OSA with atherosclerosis, but no consistent associations with lipids exist for OSA or positive airway pressure treatment. We assessed the relationships between fasting lipid levels and obesity and OSA severity, and explored the impact of positive airway pressure treatment on 2-year fasting lipid level changes. Analyses included moderate-to-severe OSA patients from the Icelandic Sleep Apnoea Cohort. Fasting morning lipids were analysed in 613 untreated participants not on lipid-lowering medications at baseline. Patients were then initiated on positive airway pressure and followed for 2 years. Sub-classification using propensity score quintiles, which aimed to replicate covariate balance associated with randomised trials and, therefore, minimise selection bias and allow causal inference, was used to design the treatment group comparisons. 199 positive airway pressure adherent patients and 118 non-users were identified. At baseline, obesity was positively correlated with triglycerides and negatively correlated with total cholesterol, and low-density and high-density lipoprotein cholesterol. A small correlation was observed between the apnoea/hypopnoea index and high-density lipoprotein cholesterol. No effect of positive airway pressure adherence on 2-year fasting lipid changes was observed. Results do not support the concept of changes in fasting lipids as a primary mechanism for the increased risk of atherosclerotic cardiovascular disease in OSA.
    European Respiratory Journal 05/2014; · 6.36 Impact Factor
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    ABSTRACT: Rationale: The metabolic activity of the tongue is unknown in patients with sleep apnea. Tongue EMG activity has been shown to be increased in apneics. This increase in tongue EMG activity is thought to be related to increased neuromuscular compensation or denervation/reinnervation of the muscle fibers. Increased glucose uptake in the tongue would support increased neuromuscular compensation, whereas decreased glucose uptake in the tongue would support denervation/reinnervation of the muscle fibers. Objectives: To investigate the metabolic activity of the genioglossus and control upper airway muscles in obese apneics compared to obese controls. Methods: Subjects underwent a standard overnight sleep study to determine an apnea-hypopnea index (AHI); positron emission tomography with [18F]-2-fluoro-2-deoxy-D-glucose (FDG) and magnetic resonance imaging. We quantified glucose uptake by obtaining the standardized uptake value (SUV) within upper airway tissues. Main Results: We recruited 30 obese control subjects (AHI: 4.7±3.1 events/hour) and 72 obese apneics (AHI: 43.5±28.0 events/hour). Independent of age, BMI, gender and race, apneics had significantly reduced glucose uptake in the genioglossus (p=0.03) in comparison to controls. No differences in SUV were found in the masseter (p=0.38), pterygoid (p=0.70) or in neck (p=0.44) and submental (p=0.95) fat deposits between apneics and controls. Conclusions: There was significantly reduced glucose uptake in the genioglossus of apneics in comparison to obese controls. The reduction in glucose uptake was likely secondary to alterations in tongue muscle fiber type or to chronic denervation. The reduced glucose uptake argues against the neuromuscular compensation hypothesis explaining the increase in tongue EMG activity in apneics.
    American Journal of Respiratory and Critical Care Medicine 04/2014; · 11.04 Impact Factor
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    ABSTRACT: 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 hours/night and ⩾20 of last 28 nights), 44 partial (<4 hours/night or <20 nights), and 88 non-users.ResultsICAM-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, non-users had increased ICAM-1 compared to decreased levels in full users. All groups had increased VCAM-1, but non-users had a significantly larger increase than full users.Conclusion Within moderate-to-severe OSA patients, PAP usage prevents increases in adhesion molecules observed in non-users after two 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.International Journal of Obesity accepted article preview online, 21 July 2014; doi:10.1038/ijo.2014.123.
    International Journal of Obesity 01/2014; · 5.22 Impact Factor
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    ABSTRACT: Accumulating evidence has shown that there is a genetic contribution to obstructive sleep apnea (OSA).The objectives were to use magnetic resonance imaging (MRI) cephalometry to (1) confirm heritability of craniofacial risk factors for OSA previously shown by cephalometrics; and (2) examine the heritability of new craniofacial structures that are measurable with MRI.
    Sleep 01/2014; 37(10). · 5.10 Impact Factor
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    ABSTRACT: The objective of this study was to determine whether tongue fat is increased in obese sleep apneics compared to obese subjects without sleep apnea. We hypothesized that excess fat is deposited in the tongue in obese patients with sleep apnea.
    Sleep 01/2014; 37(10). · 5.10 Impact Factor
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    ABSTRACT: (1) To determine whether facial phenotype, measured by quantitative photography, relates to underlying craniofacial obstructive sleep apnea (OSA) risk factors, measured with magnetic resonance imaging (MRI); (2) To assess whether these associations are independent of body size and obesity. Cross-sectional cohort. Landspitali, The National University Hospital, Iceland. One hundred forty patients (87.1% male) from the Icelandic Sleep Apnea Cohort who had both calibrated frontal and profile craniofacial photographs and upper airway MRI. Mean ± standard deviation age 56.1 ± 10.4 y, body mass index 33.5 ± 5.05 kg/m(2), with on-average severe OSA (apnea-hypopnea index 45.4 ± 19.7 h(-1)). N/A. Relationships between surface facial dimensions (photos) and facial bony dimensions and upper airway soft-tissue volumes (MRI) was assessed using canonical correlation analysis. Photo and MRI craniofacial datasets related in four significant canonical correlations, primarily driven by measurements of (1) maxillary-mandibular relationship (r = 0.8, P < 0.0001), (2) lower face height (r = 0.76, P < 0.0001), (3) mandibular length (r = 0.67, P < 0.0001), and (4) tongue volume (r = 0.52, P = 0.01). Correlations 1, 2, and 3 were unchanged when controlled for weight and neck and waist circumference. However, tongue volume was no longer significant, suggesting facial dimensions relate to tongue volume as a result of obesity. Significant associations were found between craniofacial variable sets from facial photography and MRI. This study confirms that facial photographic phenotype reflects underlying aspects of craniofacial skeletal abnormalities associated with OSA. Therefore, facial photographic phenotyping may be a useful tool to assess intermediate phenotypes for OSA, particularly in large-scale studies. Sutherland K, Schwab RJ, Maislin G, Lee RW, Benedikstdsottir B, Pack AI, Gislason T, Juliusson S, Cistulli PA. Facial phenotyping by quantitative photography reflects craniofacial morphology measured on magnetic resonance imaging in icelandic sleep apnea patients. SLEEP 2014;37(5):959-968.
    Sleep 01/2014; 37(5):959-968. · 5.10 Impact Factor
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    ABSTRACT: Obesity is the most important risk factor for obstructive sleep apnea (OSA), and the effects of obesity may be mediated by tongue fat. Our objective was to examine the effects of obesity on upper airway structures in obese (OBZ) and non-obese (NBZ) Zucker rats.
    Sleep 01/2014; 37(6):1095-102. · 5.10 Impact Factor
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    ABSTRACT: The objective of this study was to explore the mechanism of action of the oral pressure therapy (OPT) device, a new treatment for sleep apnea.
    Sleep 01/2014; 37(7):1237-47. · 5.10 Impact Factor
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    ABSTRACT: Symptoms of sleep-disordered breathing (SDB) are common among pregnant women, and several studies link SDB symptoms with gestational hypertension and preeclampsia. However, few prospective studies objectively measuring SDB during pregnancy have been performed. We performed a prospective cohort study examining risk factors for third trimester SDB in pregnant women. 105 pregnant women from the Hospital of the University of Pennsylvania obstetrics practices completed first and third trimester overnight polysomnography studies. We examined whether the number of SDB events per hour of sleep increased during pregnancy. We performed unadjusted and multivariable logistic regression analyses to estimate the effects of usual and pregnancy-specific characteristics on development of third trimester obstructive sleep apnoea (OSA). In secondary analyses, we examined the relationship between objectively measured SDB, hypertensive disorders of pregnancy, and other adverse maternal-fetal outcomes. Mean Apnoea-Hypopnoea Index increased from 2.07 (SD 3.01) events/h at baseline (first trimester) to 3.74 (SD 5.97) in the third trimester (p=0.009). 10.5% of women had OSA in the first trimester. By the third trimester, 26.7% of women had OSA. In multivariable analyses, first trimester body mass index (BMI) and maternal age were significantly associated with third trimester OSA. Third trimester OSA is common. Risk factors for third trimester OSA among women without baseline SDB include higher baseline BMI and maternal age.
    Thorax 11/2013; · 8.38 Impact Factor
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    ABSTRACT: Background: Continuous positive airway pressure (CPAP) is considered the treatment of choice for obstructive sleep apnea (OSA), and studies have shown that there is a correlation between patient adherence and treatment outcomes. Newer CPAP machines can track adherence, hours of use, mask leak, and residual apnea-hypopnea index (AHI). Such data provide a strong platform to examine OSA outcomes in a chronic disease management model. However, there are no standards for capturing CPAP adherence data, scoring flow signals, or measuring mask leak, or for how clinicians should use these data. Methods: American Thoracic Society (ATS) committee members were invited, based on their expertise in OSA and CPAP monitoring. Their conclusions were based on both empirical evidence identified by a comprehensive literature review and clinical experience. Results: CPAP usage can be reliably determined from CPAP tracking systems, but the residual events (apnea/hypopnea) and leak data are not as easy to interpret as CPAP usage and the definitions of these parameters differ among CPAP manufacturers. Nonetheless, ends of the spectrum (very high or low values for residual events or mask leak) appear to be clinically meaningful. Conclusions: Providers need to understand how to interpret CPAP adherence tracking data. CPAP tracking systems are able to reliably track CPAP adherence. Nomenclature on the CPAP adherence tracking reports needs to be standardized between manufacturers and AHIFlow should be used to describe residual events. Studies should be performed examining the usefulness of the CPAP tracking systems and how these systems affect OSA outcomes.
    American Journal of Respiratory and Critical Care Medicine 09/2013; 188(5):613-20. · 11.04 Impact Factor
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    ABSTRACT: Background: Sleepiness may account for up to 20% of crashes on monotonous roads, especially highways. Obstructive sleep apnea (OSA) is the most common medical disorder that causes excessive daytime sleepiness, increasing the risk for drowsy driving two to three times. The purpose of these guidelines is to update the 1994 American Thoracic Society Statement that described the relationships among sleepiness, sleep apnea, and driving risk. Methods: A multidisciplinary panel was convened to develop evidence-based clinical practice guidelines for the management of sleepy driving due to OSA. Pragmatic systematic reviews were performed, and the Grading of Recommendations, Assessment, Development, and Evaluation approach was used to formulate and grade the recommendations. Critical outcomes included crash-related mortality and real crashes, whereas important outcomes included near-miss crashes and driving performance. Results: A strong recommendation was made for treatment of confirmed OSA with continuous positive airway pressure to reduce driving risk, rather than no treatment, which was supported by moderate-quality evidence. Weak recommendations were made for expeditious diagnostic evaluation and initiation of treatment and against the use of stimulant medications or empiric continuous positive airway pressure to reduce driving risk. The weak recommendations were supported by very low-quality evidence. Additional suggestions included routinely determining the driving risk, inquiring about additional causes of sleepiness, educating patients about the risks of excessive sleepiness, and encouraging clinicians to become familiar with relevant laws. Discussion: The recommendations presented in this guideline are based on the current evidence, and will require an update as new evidence and/or technologies becomes available.
    American Journal of Respiratory and Critical Care Medicine 06/2013; 187(11):1259-1266. · 11.04 Impact Factor
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    ABSTRACT: BACKGROUND: Obesity and fat distribution patterns [subcutaneous vs. visceral adipose tissue (VAT)] are important predictors of future cardiometabolic risk. As accurate VAT measurement entails imaging, surrogate anthropometric measurements that would be cheaper and quicker to obtain would be highly desirable. Sagittal abdominal diameter (SAD) may be better than other VAT surrogate measures in adults, but the value of SAD to predict magnetic resonance imaging (MRI)-determined VAT in adolescents of different races, sexes, and pubertal stages has not been determined. AIM: To test the hypothesis that SAD correlates more strongly with volumetric VAT than other anthropometric measurements, independent of age, sex, race, and Tanner stage. SUBJECTS AND METHODS: Twenty-eight normal-weight and 44 obese adolescents underwent Tanner staging, anthropometric examinations, and abdominal MRI for volumetric partitioned fat calculation. RESULTS: VAT increased exponentially in the body mass index (BMI) > 97th percentile range. SAD, waist circumference (WC), BMI, and BMI Z-score correlated strongly with VAT (correlation coefficients of 0.85-0.86, all p-values < 0.0005); waist-hip ratio was less predictive of VAT (r = 0.68, p < 0.0005). On hierarchical regression, the strongest predictors of VAT in obese subjects were BMI Z-score and SAD (R(2) = 0.34 vs. 0.31, respectively, p < 0.0005); in normal-weight subjects, most anthropometric measures predicted VAT equally (R(2) = 0.16-0.18, p-values = 0.018-0.026). CONCLUSIONS: Unlike adults, in obese adolescents, SAD is not the strongest predictor of visceral adiposity. BMI Z-score is equivalently predictive and, together with BMI, provides sufficient information to assess visceral adiposity; more specialized anthropometric measurements (e.g., SAD and WC) do not add additional predictive value.
    Pediatric Diabetes 05/2013; · 2.08 Impact Factor
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    ABSTRACT: The obstructive sleep apnea syndrome (OSAS) is associated with increased visceral adipose tissue (VAT) in adults; however, few studies have evaluated VAT in relation to upper airway function in adolescents. We hypothesized that increased neck circumference (NC) and VAT would be associated with increased upper airway collapsibility. Adolescents (24 obese patients with OSAS, 22 obese control patients, and 29 lean control patients) underwent abdominal magnetic resonance imaging, and measurement of upper airway pressure-flow relationships in the activated and hypotonic upper airway states. Patients with OSAS had a greater activated slope of the pressure-flow relationship (SPF) than control groups (P < 0.001), whereas hypotonic SPF was greater in both obese groups compared with lean control patients (P = 0.01). NC and VAT were greater in obese control patients and those with OSAS than in lean control patients (P < 0.001), but did not differ between obese patients with OSAS and obese control patients. In lean control patients and those with OSAS, increased NC was associated with increased activated SPF, whereas in obese control patients it was associated with decreased activated SPF (P = 0.03). In contrast, increased NC was associated with increased hypotonic SPF in all groups (P < 0.001). There was no significant effect of VAT on either activated or hypotonic SPF for any of the three groups. Increased neck circumference was associated with increased upper airway collapsibility in adolescents in the hypotonic but not activated state. These data suggest that obese adolescents without OSAS, despite a narrowed upper airway from adipose tissue, are protected from developing OSAS by upper airway neuromotor activation. Neither neck circumference nor visceral adipose tissue is useful in predicting upper airway collapsibility in obese adolescents. Yuan H; Schwab RJ; Kim C; He J; Shults J; Bradford R; Huang J; Marcus CL. Relationship between body fat distribution and upper airway dynamic function during sleep in adolescents. SLEEP 2013;36(8):1199-1207.
    Sleep 01/2013; 36(8):1199-207. · 5.10 Impact Factor
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    ABSTRACT: 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 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.International Journal of Obesity advance online publication, 11 September 2012; doi:10.1038/ijo.2012.138.
    International journal of obesity (2005) 09/2012; · 5.22 Impact Factor
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    ABSTRACT: OBJECTIVES/HYPOTHESIS: To quantitatively measure changes in airway caliber at multiple anatomical levels during drug-induced sleep endoscopy (DISE) for evaluation of sleep apnea. We hypothesize that patients undergoing DISE will show: 1) collapse at multiple upper airway regions (retropalatal, retroglossal, and retroepiglottic), with greater collapse in the retropalatal region; and 2) greater anterior-posterior dimensional narrowing than the lateral. STUDY DESIGN: Case series. METHODS: Patients underwent DISE employing propofol as part of a nonrandomized prospective trial assessing candidacy for transoral robotic surgery intervention for sleep apnea. Images of the retropalatal, retroglossal, and retroepiglottic regions were captured during an initial period of light sedation and again in a period of deep sedation. Images were analyzed using software to measure the percent change in regional airway measurements as a result of DISE. RESULTS: Thirty-seven sleep endoscopy videos were analyzed from patients with obstructive sleep apnea (apnea-hypopnea index: 42.9 ± 27.0 events/hour). Analyzable images were in the retropalatal (n = 24), retroglossal (n = 27), and retroepiglottic (n = 29) regions. The patients demonstrated mean reductions in airway area in the retropalatal (84.1 ± 18.7%), retroglossal (39.3 ± 37.5%), and retroepiglottic region (44.6 ± 42.8%). No statistically significant differences were found between lateral and anterior-posterior airway dimensional changes. CONCLUSIONS: Patients undergoing DISE had significant reductions in airway area at multiple regions under deep sedation with propofol. We conclude that collapse in the retropalatal region is greater than the hypopharyngeal region. This method can be used to quantitatively measure DISE upper airway changes, which could potentially be used as a means for understanding surgical outcomes in patients with sleep apnea. Laryngoscope, 2012.
    The Laryngoscope 09/2012; · 1.98 Impact Factor
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    ABSTRACT: Visceral adipose tissue (VAT) is associated with abnormal cardiovascular and metabolic profiles. Total VAT volume of the abdominal compartment by magnetic resonance imaging (MRI) is the gold-standard measurement for VAT but is costly and time consuming. Prior studies suggest VAT area on a single slice MR image may serve as a surrogate for total VAT volume but it is unknown if this relationship is maintained in overweight and obese men and women. Untreated sleep apnea subjects enrolled into the Icelandic Sleep Apnea Cohort (ISAC) underwent abdominal MRI. VAT area and subcutaneous adipose tissue (SAT) area at the L2-L3 and L4-L5 interspaces and total VAT and SAT volumes were determined by manual examination using image analysis software; 539 men and 129 women with mean ages of 54.1 and 58.8 years and mean BMI of 32.2 kg/m(2) and 33.7 kg/m(2), respectively, were studied. Mean total VAT volume was 40% smaller and mean total SAT was 25% larger among females compared with males. The correlation with VAT volume was significantly larger for L2-L3 VAT area (r = 0.96) compared to L4-L5 VAT area (r = 0.83). The difference in correlation coefficients was statistically significant (nonparametric bootstrap P < 0.001 with 95% confidence interval (CI) for the difference from 0.11 to 0.15. VAT area at L2-L3 was also significantly better correlated with VAT volume than traditional anthropometric variables. Linear regression analyses demonstrated that L2-L3 area alone was sufficient for predicting total VAT volume and that the nature of the linear association was maintained across all levels of obesity and in both genders.
    Obesity 03/2012; 20(10):2124-32. · 3.92 Impact Factor
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    ABSTRACT: To assess the relative roles and interaction of obstructive sleep apnea (OSA) severity and obesity on interleukin-6 (IL-6) and C-reactive protein (CRP) levels. Cross-sectional cohort. The Icelandic Sleep Apnea Cohort. 454 untreated OSA patients (380 males and 74 females), mean ± standard deviation age 54.4 ± 10.6 yr. N/A. Participants underwent a sleep study, abdominal magnetic resonance imaging to measure total abdominal and visceral fat volume, and had fasting morning IL-6 and CRP levels measured in serum. A significantly higher correlation was found for BMI than visceral fat volume with CRP and IL-6 levels. Oxygen desaturation index, hypoxia time, and minimum oxygen saturation (SaO₂) significantly correlated with IL-6 and CRP levels, but apnea-hypopnea index did not. When stratified by body mass index (BMI) category, OSA severity was associated with IL-6 levels in obese participants only (BMI > 30 kg/m²). A multiple linear regression model with interaction terms showed an independent association of OSA severity with IL-6 levels and an interaction between OSA severity and BMI, i.e., degree of obesity altered the relationship between OSA and IL-6 levels. An independent association of OSA severity with CRP levels was found for minimum SaO₂ only. A similar interaction of OSA severity and BMI on CRP levels was found for males and postmenopausal women. OSA severity is an independent predictor of levels of IL-6 and CRP but interacts with obesity such that this association is found only in obese patients.
    Sleep 01/2012; 35(7):921-32. · 5.10 Impact Factor
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    ABSTRACT: Obesity is an important risk factor for pharyngeal airway collapse in obstructive sleep apnea (OSA). To examine the effect of obesity on pharyngeal airway size on inspiration and expiration, respiratory-gated MRI of the pharynx was compared in New Zealand obese (NZO) and New Zealand white (NZW) mice (weights: 50.4g vs. 34.7g, p<0.0001). Results: (1) pharyngeal airway cross-sectional area was greater during inspiration than expiration in NZO mice, but in NZW mice airway area was greater in expiration than inspiration; (2) inspiratory-to-expiratory changes in both mouse strains were largest in the caudal pharynx; and (3) during expiration, airway size tended to be larger, though non-significantly, in NZW than NZO mice. The respiratory pattern differences are likely attributable to obesity that is the main difference between NZO and NZW mice. The data support an hypothesis that pharyngeal airway patency in obesity is dependent on inspiratory dilation and may be vulnerable to loss of neuromuscular pharyngeal activation.
    Respiratory Physiology & Neurobiology 02/2011; 175(2):296-302. · 2.05 Impact Factor
  • American Thoracic Society International Conference; 01/2011

Publication Stats

2k Citations
353.97 Total Impact Points


  • 2014
    • Southwestern PA Pulmonary & Sleep Medicine Ltd.
      Washington, Pennsylvania, United States
  • 1996–2013
    • Hospital of the University of Pennsylvania
      • • Department of Medicine
      • • Division of Pulmonary Allergy and Critical Care
      Philadelphia, Pennsylvania, United States
  • 2012
    • National University Hospital of Iceland
      Reikiavik, Capital Region, Iceland
  • 2010–2011
    • Royal North Shore Hospital
      Sydney, New South Wales, Australia
  • 1993–2011
    • University of Pennsylvania
      • • Department of Medicine
      • • Division of Gastrointestinal Surgery
      • • Division of Pulmonary, Allergy and Critical Care
      • • Division of Sleep Medicine
      • • Department of Radiology
      Philadelphia, PA, United States
  • 2006
    • Brigham and Women's Hospital
      • Division of Pulmonary and Critical Care Medicine
      Boston, MA, United States
  • 2001–2002
    • The Children's Hospital of Philadelphia
      • Division of Pulmonary Medicine
      Philadelphia, PA, United States