Identifying High-Attenuating and Low-Attenuating Muscle Using Computerized Tomography and Exploring Its Impact on Physical Function and Muscle Strength in Obese Critically Ill Patients.

Abstract

Computed tomography (CT) methods to estimate sarcopenia in obesity do not differentiate high-attenuating from low-attenuating muscle. The primary purpose of this study was to determine agreement between a CT method using general workstation-derived total and high-attenuating psoas muscle cross-sectional area (CSA) and a commercially available segmentation software-derived value. Secondary purpose was to explore the relationship between quantity of high-attenuating muscle to physical functioning in a pilot cohort of obese medical intensive care unit (MICU) patients. We conducted a prospective observational cross-sectional study. CT images of obese MICU patients were reconstructed to calculate total psoas muscle, low-attenuating muscle, and high-attenuating muscle within the third lumbar psoas CSA using a CT method and commercial software. We performed blinded outcome measures of CSA, physical function, and muscle strength in 28 patients. Concordance correlation coefficient for identifying total psoas muscle was 0.96 (95% confidence interval: 0.93-0.98, P-value < 0.0001) between CT method and commercial software. There was moderate correlation between modified Medical Research Council muscle strength scores and high-attenuating psoas muscle CSA (r = 0.47, P = 0.01) and lower extremity strength and high-attenuating psoas muscle CSA (r = 0.40, P = 0.04). There was strong agreement between our CT method and a commercial software method to identify total psoas muscle CSA in obesity. Greater total high-attenuating psoas CSA moderately correlated with muscle strength. Additional studies using more objective markers of muscle strength validating these findings are needed.