Investigating the impact of fluid status on the ultrasound assessment of muscle quantity and quality in the diagnosis of sarcopenia - a multidimensional cross-sectional study

Abstract

Background: Sarcopenia is a clinical manifestation of adverse ageing, characterised by progressive loss of muscle mass and function. Diagnosis requires assessment of muscle quantity and quality; ultrasound represents an emerging tool for this. However, ultrasound muscle assessment may be impacted by fluid balance. This is particularly important when assessing for acute sarcopenia in hospitalised patients, where fluid disturbance often occurs. The primary aim of this study was to characterise the impact of fluid status on ultrasound muscle assessment, such that this may be accounted for in sarcopenia diagnostics.

Methods: This Multidimensional Cross-sectional study involved 80 participants, who were inpatients at QEHB, a large UK tertiary centre. Fluid status was evaluated clinically and quantified using Bioelectrical Impedance Analysis (BIA). Muscle quantity was measured using Bilateral Anterior Thigh Thickness (BATT) with Rectus Femoris (RF) echogenicity used to assesses muscle adiposity and hence provide an inverse measure of muscle quality.

Results: A significant positive correlation was found between fluid status, measured using BIA, and BATT as a measure of muscle quantity, in males (rs = 0.662, p < 0.001) and females (rs = 0.638, p < 0.001). A significant negative correlation was found between fluid status and RF echogenicity (rs=-0.448, p < 0.001).

Conclusions: These findings demonstrate associations between fluid balance and ultrasound assessment of muscle quantity and quality. Given the emerging use of ultrasound muscle assessment in sarcopenia diagnosis, there is a need to account for this in clinical practice. Future research should focus on the development of a corrective equation allowing assessment of muscle quantity and quality which account for changes in fluid status, hence aiding accurate diagnosis of sarcopenia.

Keywords: Bioelectrical Impedance Analysis; Echogenicity; Sarcopenia; Ultrasound muscle assessment.

Fig. 1

Screening, recruitment, and follow-up rates for participants in all cohorts and reasons for non-participation

Fig. 2

A) measurement of BATT in transverse plane. B) measurement of echogenicity in longitudinal plane. (A) The thickness of the Rectus Femoris (1) and of the Vastus Intermedius (2) were measured and summed. Totalling of this value bilaterally gives an overall value for BATT, recorded in cm. (B) Subcutaneous (SC) tissue, Rectus Femoris (RF) muscle and Vastus Intermedius (VI) muscle are identified. Boxes were then drawn surrounding the SC and RF as shown, with greyscale analysis function within ImageJ used to calculate echogenicity

Fig. 3

Summary of data acquired at patient assessments across all visits, divided by clinical fluid status. Hypovolaemic n = 14, Euvolaemic n = 162, Hypervolaemic n = 29. Nominal variables (gender, ethnicity, patient group, nutritional status and Fried Frailty Phenotype) are presented as percentage values and raw n values. Clinical Frailty Score, an ordinal variable, is summarised using median and interquartile range. Continuous data was tested statistically for normality using the Shapiro-Wilk test. Data for age, BMI, Frailty Index and handgrip strength did not follow a normal distribution and are therefore summarised as median values with interquartile ranges. * = p-value generated using Kruskal-Wallis test, + = p-value generated using Pearson’s chi-squared test

Fig. 4

Box and Whisker plot demonstrating Total Body Water divided by clinical fluid status. Data acquired from BIA measurement and clinical assessment of fluid status across all patient assessments from all visits. Hypovolaemic n = 13, Euvolaemic n = 140, Hypervolaemic n = 25. The centre of each box represents the median value, with the box representing the IQR and the ‘whiskers’ representing minimum and maximum values. A non-parametric Kruskal-Wallis test was used to compare the differences between groups as the data was not normally distributed, with the Dunn’s test applied post-hoc. * = p < 0.05

Fig. 5

Bilateral Anterior Thigh Thickness (BATT) in comparison to Skeletal Muscle Mass (SMM) index. BATT values acquired from ultrasound assessment of quadriceps muscles. SMM index values obtained from BIA assessment. All patient assessments included. n = 180. Correlation coefficient calculated using non-parametric Spearman rank correlation

Fig. 6

Total Body Water and Bilateral Anterior Thigh Thickness in Males (A) and Females (B). TBW values acquired from BIA assessment. BATT values acquired from ultrasound assessment of quadriceps muscles. Patients across all patient groups and across all visits are included. (A) n = 107. (B) n = 73. Correlation coefficient calculated using non-parametric Spearman rank correlation

Fig. 7

Scatter plot of Total Body Water and Rectus Femoris echogenicity. TBW values acquired from BIA assessment. RF echogenicity calculated from ImageJ greyscale analysis of longitudinal ultrasound images. All patient assessments included. n = 162. Correlation coefficient calculated using non-parametric Spearman rank correlation