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Influence of diffusion on estimations of protein reflection coefficient by double-indicator method
P White1, R G Brower, J T Sylvester
1Department of Medicine, Johns Hopkins Medical Institutions, Baltimore 21205.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|October 1, 1993
Summary
Diffusion significantly underestimates vascular protein reflection coefficients (sigma) in perfused organs. This error is substantial when fluid flux is low and true sigma is high, impacting edema research.
Area of Science:
- Physiology
- Biophysics
- Renal and Vascular Physiology
Background:
- Vascular protein reflection coefficients (sigma) are crucial for understanding fluid dynamics in perfused organs.
- Current methods for calculating sigma assume negligible transvascular protein diffusion, a potentially flawed assumption.
- Edema formation studies rely on accurate sigma measurements, necessitating an evaluation of diffusion's impact.
Purpose of the Study:
- To derive and assess an expression for perfusate protein concentration (CP) that incorporates diffusive protein flux.
- To quantify the error in measured sigma caused by transvascular protein diffusion under various experimental conditions.
- To determine the conditions under which diffusion-induced errors in sigma calculations become substantial.
Main Methods:
- Derived a mathematical expression for CP including protein permeability-surface area product (PS), fluid flux (J), true sigma, and protein concentration.
- Calculated measured sigma values using the derived CP expression under simulated experimental conditions.
- Analyzed the relationship between J/PS, true sigma, edema formation, and the magnitude of diffusion-induced errors.
Main Results:
- Diffusion consistently causes an underestimation of the true vascular protein reflection coefficient (sigma).
- The diffusion-induced error in measured sigma increases with greater edema formation and higher true sigma values.
- Significant underestimation occurs when the ratio of fluid flux to permeability-surface area product (J/PS) is low (<5) and true sigma exceeds 0.5.
Conclusions:
- Transvascular protein diffusion leads to a systematic underestimation of the true vascular protein reflection coefficient (sigma).
- The calculated sigma is significantly lower than the true sigma when J/PS is < 5 and true sigma is > 0.5.
- Researchers must consider diffusion-induced errors, especially in studies involving significant edema or low J/PS ratios, to ensure accurate physiological interpretations.