Extracellular water-to-total body water ratio and fluid volume impact skeletal muscle mass index and phase angle accuracy in physical function

Haruhiko Akiyama, Takahiro Ando, Takanobu Bito, Naoki Akazawa
Purpose:

This study aimed to investigate the impact of ECW/TBW on SMI and PhA, adjusted for the physical function parameter obtained through CPX in patients with chronic heart failure (CHF) and to examine the effects of differences in body fluid volume, in addition to differences in ECW/TBW, on SMI and PhA.

Methods:

Eighty-three patients (56 males, mean age 66.3 ± 15.7 years) with CHF underwent CPX and body composition measurement using direct segmental multi-frequency BIA method. The ECW/TBW was categorized into two groups: ≥0.4 and 0.4. Total body water (TBW) was adjusted for body size by using height squared and then divided into two groups: ≥12 L/m² and 12 L/m² based on the median value. Analysis of covariance (ANCOVA) was conducted with SMI and PhA as dependent variables, and peak work rate (peak WR) and ECW/TBW as independent variables. Additionally, multiple regression analysis was performed using peak WR, age, sex, and dummy variables based on ECW/TBW and TBW categories.

Results:

ANCOVA results showed that both ECW/TBW (p 0.001) and peak WR (p 0.001) significantly affected both SMI and PhA. In multiple regression analysis with SMI, the partial regression coefficients were 0.56 (p = 0.003) for high ECW/TBW & low TBW and 1.61(p = 0.001) for high ECW/TBW & high TBW. The standardized partial regression coefficient for high ECW/TBW & high TBW (0.63) was greater than that of peak WR (0.45). For PhA as the dependent variable, the partial regression coefficients were -0.39 (p = 0.042) for high ECW/TBW & low TBW, and -0.57 (p = 0.012) for high ECW/TBW & high TBW.

Conclusion(s):

The findings demonstrated that ECW/TBW was independently associated with SMI and PhA, indicating that high ECW/TBW led to the overestimation of SMI and underestimation of PhA compared to actual physical function. Notably, this effect was larger in high TBW than in low TBW.

Implications:

The conditions and extent of inaccurate assessment of SMI and PhA using the BIA device are indicated. These findings emphasize the potential to enhance the accuracy of skeletal muscle assessments with BIA and broaden the application of each indicator, leading to better-informed clinical decisions.

Funding acknowledgements:
This research received no funding.
Keywords:
Extracellular water-to-total body water ratio
Skeletal muscle index
Phase angle
Primary topic:
Cardiorespiratory
Did this work require ethics approval?:
Yes
Name the institution and ethics committee that approved your work:
The ethics committee of the Gifu University Graduate School of Medicine
Provide the ethics approval number:
2024-091
Has any of this material been/due to be published or presented at another national or international conference prior to the World Physiotherapy Congress 2025?:
No

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