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A1719 - Subcutaneous and Visceral Fat Differentially Associate with Emphysema and Airway Phenotypes in Smokers
Author Block: U. Shrestha1, J. K. Leader2, F. C. Sciurba3, Y. Zhang4, S. Nouraie5, N. Hyre6, J. M. Bon4; 1Internal Medicine, UPMC Mckesport, McKeesport, PA, United States, 2Radiology, Univ of Pittsburgh, Pittsburgh, PA, United States, 3Univ of Pittsburgh Med Ctr, Pittsburgh, PA, United States, 4Univ of Pittsburgh, Pittsburgh, PA, United States, 5Medicine, PACCM, University of Pittsburgh, Pittsburgh, PA, United States, 6Internal Medicine, UPMC Presbyterian, Pittsburgh, PA, United States.
Rationale: Chronic obstructive pulmonary disease (COPD) is characterized by airflow obstruction due to variable contributions of emphysema and small airway inflammation. Obesity is shown to have both positive and negative impacts in COPD, with recent studies demonstrating differential associations between fat location and outcomes. We assessed the relationship between subcutaneous and visceral fat volume and chest computed tomography (CT) measurements of emphysema and small airway disease in current and former smokers. Methods: Participants from the University of Pittsburgh SCCOR cohort (N=260) underwent chest CT imaging at baseline and six years. Emphysema was quantified as the fraction of segmented lung voxels with pixel values less than -950 Hounsfield Units (HU) (F-950). Airway remodeling was quantified by computing the airway wall area as a percentage of total wall area (WA%) for all small airways. Subcutaneous fat was quantified at a single slice at the aortic arch level. Visceral fat was quantified at the CT image level depicting the liver, spleen, and both kidneys. Subcutaneous and visceral fat were quantified as the volume of manually segmented tissue voxels with values between -190 and -30 HU. The association between baseline subcutaneous and visceral fat and baseline F-950, baseline WA%, and 6-year change in F-950 and WA% was assessed by robust linear regression with and without adjustment for covariates (age, sex, smoking status). The relationship between fat location and change in F-950 and WA% was adjusted for baseline F-950 and WA%, respectively. Standardized betas (SB) are reported. Results: Participants had a mean age of 64.6 (SD 6.1) years, were 50% male, and had a mean FEV1 of 85.1% (SD 20%) at study entry. Subcutaneous fat volume was inversely associated with baseline F-950 (SB -0.16, p=0.007, unadjusted; SB - 0.23, p = 0.01, adjusted) but not WA%. Subcutaneous fat was also inversely related to 6-year F-950 change (SB -0.09, p= 0.01, unadjusted; SB -0.12, p =0.01, adjusted). By contrast, visceral fat was directly associated with baseline WA% (SB 0.17, p =0.006, unadjusted; SB 0.18, p=0.02, adjusted) but not F-950. Baseline visceral fat volume was also directly related to 6-year WA% change in unadjusted (SB 0.16, p =0.008), but not adjusted, analyses. Conclusions: Fat type differentially associates with emphysema, small airway inflammation, and radiographic disease progression in smokers. These findings further illustrate the complex relationship between obesity and COPD phenotypes and complements the cardiovascular literature showing a negative impact of visceral fat on cardiovascular outcomes.