Assessment of skeletal muscle mass in critically ill patients: considerations for the utility of computed tomography imaging and ultrasonography

Purpose of review: Low muscularity and skeletal muscle atrophy are commonly exhibited in critically ill patients and have major implications on patient outcomes. Typically, in the ICU, body composition is assessed through anthropometrics or bioelectrical impedance analysis, but these modalities cannot specifically quantify skeletal muscle; thus, we evaluate the merits and challenges of using computed tomography (CT) and ultrasonography to specifically measure skeletal muscle in the ICU. Recent findings: CT-based cut points have been used to identify critically ill patients with low muscle mass, and low muscularity associates with poor clinical outcomes and function. Ultrasonography is emerging as a useful tool to quantify skeletal muscle loss and degradation in architecture, as well as prospectively track changes in these parameters over time. Rates of muscle atrophy and changes in muscle architecture has been quantified by ultrasonography and associated with poor clinical outcomes, but identification of critically ill patients with low muscularity is still in its infancy. Summary: CT imaging and ultrasonography require additional comprehensive validations against accurate measures of whole body muscle mass. As these validations begin to emerge, there will be a need to translate this knowledge into a simple tool that clinicians can apply as part of routine care

Development of a bedside-applicable ultrasound protocol to estimate fat mass index derived from whole body dual-energy x-ray absorptiometry scans

The final publication is available at Elsevier via https://doi.org/10.1016/j.nut.2018.04.012. © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Objectives: Precise measures of adiposity are difficult to obtain in clinical settings due to a lack of access to accurate and reliable techniques. The aim of this study was to develop and internally validate a bedside-applicable ultrasound protocol to estimate fat mass index. Methods: We conducted an observational cross-sectional study of 94 university and community dwelling adults who attended a single data-collection session. Adipose tissue thickness was quantified in a supine or prone position using the four-site protocol (images two anterior sites on each thigh) and the nine-site protocol (images nine anterior and posterior sites). Adipose tissue thicknesses from the four-site protocol were compared against the fat mass index that was derived from dual-energy x-ray absorptiometry scans. Subsequently, we optimized the accuracy of the four-site protocol with the addition of bedside-accessible adipose tissue thicknesses from the nine-site protocol and easily obtained covariates. Results: The four-site protocol was strongly associated (R2 = 0.65) with fat mass index but wide limits of agreement (-3.53 kg/m2 and 3.50 kg/m2) were observed using the Bland-Altman analysis. With the addition of the anterior upper arm and abdomen adipose tissue thicknesses as well as the covariates age, sex, and body mass index, the model accuracy improved (R2 = 0.93) and the Bland-Altman analysis displayed narrower limits of agreement (-1.57 kg/m2 and 1.60 kg/m2). Conclusions: This optimized protocol developed can be applied bedside and provide accurate assessments of fat mass index.This work was supported by Canada Graduate Scholarship (Master) - Canadian Institute of Health Research, Province of Ontario Ministry of Research and Innovation Early Researcher Award, Canada Foundation for Innovation, Natural Sciences and Engineering Research Council, and Canadian Institute of Health Research

Site-specific skeletal muscle echo intensity and thickness differences in subcutaneous adipose tissue matched older and younger adults

This is the peer reviewed version of the following article: Paris, M. T., Letofsky, N., &amp; Mourtzakis, M. (2020). Site‐specific skeletal muscle echo intensity and thickness differences in subcutaneous adipose tissue matched older and younger adults. Clinical Physiology and Functional Imaging, 41(2), 156–164, which has been published in final form at https://doi.org/10.1111/cpf.12679. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.Background: Age-related deterioration of muscle mass does not occur uniformly across the body. However, there is limited knowledge on the uniformity of age-related muscle composition changes across the body. Objective: Our primary objective was to evaluate muscle composition differences between younger and older adults across multiple muscle groups. Methods: We re-analysed data from a previously published cohort to evaluate differences in ultrasound muscle composition (echo intensity) between younger (60 years) adults, when matched for adipose tissue mass at the anterior upper arm, anterior upper leg and abdominal muscles. Analysis of echo intensity is confounded by subcutaneous adipose tissue (SAT) thickness overlaying the muscle; we accounted for these effects by matching older and younger adults (1:1), stratified by sex, for absolute SAT thickness at each landmark. Results: From 96 adults (n = females), 58 (n = 34) were SAT matched at the anterior upper arm, 52 (n = 30) at the anterior upper leg and 60 (n = 30) at the abdominal region; thus, there were no age group differences in SAT thickness at each landmark. In comparison with younger adults, older adults presented with greater echo intensity at the anterior upper leg (females:40.3 ± 6.8 vs. 52.4 ± 7.6; males:35.7 ± 8.0 vs. 54.3 ± 9.8, p < .01) and abdominal (females:38.7 ± 27.6 vs. 73.4 ± 31.0; males:18.7 ± 15.2 vs. 60.9 ± 23.4, p < .01) muscles, but not anterior upper arm muscles (females:47.0 ± 6.5 vs. 53.2 ± 13.1; males:43.4 ± 8.9 vs. 48.9 ± 10.1, p = .18). Conclusions: Distinct age-related differences in trunk and lower limb muscle composition were evident compared to upper limb muscles; highlighting the importance of quantifying specific muscle groups when evaluating age-associated muscle characteristics.This work was supported by Canada Graduate Scholarship - Canadian Institute of Health Research, Province of Ontario Ministry of Research and Innovation Early Researcher Award, Canada Foundation for Innovation, Natural Sciences and Engineering Research Council and Canadian Institute of Health Research

Myokines and adipokines in sarcopenia: understanding cross-talk between skeletal muscle and adipose tissue and the role of exercise

The final publication is available at Elsevier via https://doi.org/10.1016/j.coph.2020.06.003. © 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Detrimental age-associated changes in skeletal muscle and adipose tissue increase the risk of sarcopenia. Age-related changes in myokines, such as myostatin and irisin, as well as adipokines, such as leptin and adiponectin, contribute to cross-talk between muscle and adipose tissue. These age-related changes in myokines and adipokines have important implications for sarcopenia, however, recent literature highlights discrepancies in these relationships. Exercise may alter serum profiles and muscle receptor expression of these factors, but future work is needed to determine whether these changes in myokines and adipokines relate to improvements in muscle mass and function. Here, we describe myokine-mediated and adipokine-mediated interactions between muscle and adipose tissue, and discuss the fundamental importance of these cytokines to understanding the development of sarcopenia

Body size normalization of ultrasound measured anterior upper leg muscle thickness in younger and older males and females

This is a post-peer-review, pre-copyedit version of an article published in European Journal of Clinical Nutrition. The final authenticated version is available online at: https://doi.org/10.1038/s41430-022-01070-0BACKGROUND: Ultrasound measurements of the anterior upper leg muscle thickness are often used to quantify muscle mass; however, the ideal normalization approach is unclear. Our primary objective was to examine how the anterior upper leg muscle thickness scales with indices of body size in younger and older adults. Our secondary objectives were to examine how normalization with body size alters the identification of low muscle thickness and associations with strength and physical function. METHODS: Younger (<45 years) males (n = 38) and females (n = 24) and older (≥60 years) males (n = 53) and females (n = 24) were evaluated for anthropometrics and anterior upper leg muscle thickness. Allometric models were used to examine how body size metrics scale with anterior upper leg muscle thickness. A subset of older males was evaluated for strength and function. RESULTS: Weight and BMI scaled with anterior upper leg muscle thickness with coefficients less than 1 (0.58 to 0.82, r2 = 0.15 to 0.31, p < 0.05) for both younger and older males and females. Compared to absolute anterior upper leg thickness, normalized indices identified a greater proportion of older adults with low muscle thickness (p < 0.05). Absolute muscle thickness provided stronger associations with strength compared to weight normalized indices. CONCLUSIONS: Scaling exponents less than 1 for weight and BMI for the anterior upper leg muscle thickness indicate that allometric normalization is the ideal approach to develop body size independent metrics. However, allometric normalization of muscle thickness increases the proportion of older adults classified as low muscle mass but decreased the associations with strength

Older males exhibit reduced anterior upper leg and anterior abdominal muscle thickness compared to younger males when matched for relative appendicular lean tissue

The final publication is available at Elsevier via https://doi.org/10.1016/j.archger.2021.104483. © 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Background Ageing-related muscle atrophy does not occur uniformly across the body; rather, atrophy occurs to a greater extent in specific muscle groups compared to others. However, site-specific comparisons of muscle mass between older and younger adults typically do not account for relative muscle mass (i.e., matched for age- and sex-specific percentiles), which may confound site-specific differences. Furthermore, the uniformity of ageing-related differences in muscle composition (e.g., intramuscular adipose tissue) across the body are not well characterized. Purpose To examine site-specific muscle mass and composition differences between younger and older males matched for relative muscle mass. Methods Younger (18-44 years old, n = 19) and older (≥65 years old, n = 19) males were matched for relative appendicular lean tissue index (NHANES age- and sex-specific Z-scores) measured using dual-energy x-ray absorptiometry. Site-specific differences in skeletal muscle size (thickness) and composition (echo-intensity) were evaluated using ultrasound for 8 distinct landmarks across the body. Results Relative appendicular lean tissue mass was well matched between younger and older males (Z-score difference: -0.02, p = 0.927). Compared with younger males, older males had smaller muscle thickness for the anterior upper leg (difference: -1.08 cm, p < 0.001) and anterior abdomen (difference: -0.53 cm, p < 0.001). However, older adults displayed higher echo intensity across all muscles (p < 0.05), except for the posterior upper arm (p = 0.377), in comparison to the younger males. Conclusions When matched for relative appendicular lean tissue, muscle thickness differences between younger and older males are not-uniform across the body, whereas echo intensity was more uniformly higher in the older males

Ultrasound image resolution influences analysis of skeletal muscle composition

This is the peer reviewed version of the following article: Paris, M. T., Bell, K. E., Avrutin, E., &amp; Mourtzakis, M. (2020). Ultrasound image resolution influences analysis of skeletal muscle composition. Clinical Physiology and Functional Imaging, 40(4), 277–283, which has been published in final form at https://doi.org/10.1111/cpf.12636. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.Introduction: Analysis of muscle composition using ultrasound requires standardization of several equipment settings (i.e. gain). However, the influence of image resolution, which is altered by imaging depth, on measures of muscle composition is unknown. Methods: We analysed rectus femoris muscle composition using ultrasound images captured from 32 males and females (aged 28 ± 5 years) at depths of 9.0, 7.3, 5.9 and 4.7 cm. The transducer's orientation was fixed using a clamp during image acquisition to minimize movement. Across each image resolution, a region of interest encompassing the same anatomical area within the muscle was used for muscle composition analysis. Muscle composition was analysed using a combination of first-, second- and higher-order texture features. Muscle composition agreement across image resolutions was evaluated using a one-way ANOVA and intraclass correlation coefficients (ICC). Results: Most muscle composition features displayed differences due to image resolution (p 0.90) compared to lower resolution images. Conclusions: Ultrasound image resolution influences muscle composition analysis. Image resolution should be fixed within and between individuals when evaluating muscle composition using ultrasound.This research was funded by the University of Waterloo's Network for Aging Researc

Expression of executive control in situational context: Effects of facilitating versus restraining cues on snack food consumption

Objectives: To examine the effects of executive function (EF) on objectively measured high-calorie snack food consumption in 2 age groups and to explore the moderating influence of environmental cues. Methods: In Study 1, 43 older adults (Mage = 74.81) and in Study 2, 79 younger adults (Mage = 18.71) completed measures of EF and subsequently participated in a bogus taste-test paradigm wherein they were required to rate 3 highly appetitive (but high-calorie) snack foods on taste and texture. Grams of snack food consumed was measured covertly in the presence randomly assigned contextual cues (explicit semantic cues in Study 1; implicit visual cues in Study 2) that were facilitating or restraining in nature. Results: Findings indicated that in both age groups, stronger EF predicted lower consumption of snack foods across conditions, and the effects of EF were most pronounced in the presence of facilitating cues. Conclusions: Older and younger adults with weaker EF tend to consume more high-calorie snack food compared with their stronger EF counterparts. These tendencies appear to be especially amplified in the presence of facilitating cues

Rectus abdominis muscle thickness is a valid measure of cross-sectional area: implications for ultrasound

The final publication is available at Elsevier via https://doi.org/10.1016/j.acra.2021.06.005. © 2022. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Rationale and objectives: The rectus abdominis muscle exhibits early and significant muscle atrophy, which has largely been characterized using ultrasound measured muscle thickness. However, the validity of rectus abdominis muscle thickness as a metric of muscle size has not been established, limiting precise interpretation of age-related changes. In a heterogeneous cohort of women and men, our objectives were to: (1) evaluate the association between rectus abdominis muscle thickness and cross-sectional area (CSA), and (2) examine if the visceral adipose tissue (VAT) compartment confounds the validity of rectus abdominis muscle thickness. Materials and methods: Abdominal computed tomography scans of the third lumbar vertebrae from clinical and healthy populations were used to evaluate rectus abdominis thickness and CSA, and VAT CSA. Computed tomography scans were utilized due to the limited field of view of ultrasound imaging to capture the rectus abdominis CSA. Results: A total of 348 individuals (31% women) were included in this analysis, with a mean ± standard deviation age and body mass index of 51.2 ± 15.4 years and 28.0 ± 5.1 kg/m2, respectively. Significant correlations were observed between rectus abdominis thickness and CSA for women (r = 0.758; p < 0.001) and men (r = 0.688; p < 0.001). Independent of age, VAT CSA was negatively associated with rectus abdominis thickness in men (p = 0.011), but not women (p = 0.446). Conclusion: These data support the use of rectus abdominis muscle thickness as a measurement of muscle size in both women and men; however, the VAT compartment may confound its validity to a minor extent in men

Influence of subcutaneous adipose tissue and skeletal muscle thickness on rectus femurs echo intensity in younger and older males and females

This is the peer reviewed version of the following article: Paris, M. T., Bell, K. E., Avrutin, E., Rosati, K., &amp; Mourtzakis, M. (2021). Influence of subcutaneous adipose tissue and skeletal muscle thickness on rectus femoris echo intensity in younger and older males and females. Journal of Ultrasound in Medicine, 41(9), 2355–2364. , which has been published in final form at https://doi.org/10.1002/jum.15922. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.Objectives—Ultrasound measurements of muscle echo intensity are commonly used surrogates of muscle composition (eg, intramuscular adipose tissue). However, given that soundwaves are increasingly attenuated with tissue depth, the interpretation of echo intensity may be confounded by adipose and skeletal muscle thickness. Our objectives are to compare the associations between adipose or muscle tissue thickness and rectus femoris echo intensity in younger and older males and females. Methods—Participants included in this analysis were derived from 3 previously published cohorts of younger (<45 years) and older (≥60 years) males and females. Ultrasound images of the rectus femoris were evaluated for muscle thickness, echo intensity, and subcutaneous adipose tissue thickness. Results—Older adults (n: 49 males, 19 females) had a higher body mass index (P = .001) compared with younger adults (n: 37 males, 49 females). Muscle thickness was negatively associated with echo intensity in older males (r =  0.59) and females (r =  0.53), whereas no associations were observed in younger males (r = 0.00) or females (r =  0.11). Subcutaneous adipose tissue thickness displayed no associations with echo intensity in any group. Conclusions—Despite the known influence of subcutaneous adipose tissue thickness on beam attenuation, we observed no association with muscle echo intensity, indicating that adipose tissue correction may be required to better understand muscle echo intensity across differences in adiposity. The negative associations between muscle thickness and echo intensity in older, but not younger adults, suggests these associations may be related to the co-occurrence of skeletal muscle atrophy and intramuscular adipose tissue infiltration with advancing age.This research was funded by the Network for Aging Research at the University of Waterloo. MTP was supported by a CIHR Doctoral research award and KEB was supported by a CIHR Fellowship