Body composition and its measurement in vivo

Thoroughly Calibrated Modular Agent-Based Model of the Human Cardiovascular and Renal Systems for Blood Pressure Regulation in Health and Disease

Here we present a modular agent-based mathematical model of the human cardiovascular and renal systems. It integrates the previous models primarily developed by A. C. Guyton, F. Karaaslan, K. M. Hallow, and Y. V. Solodyannikov. We performed the model calibration to find an equilibrium state within the normal vital sign ranges for a healthy adult. We verified the model's abilities to reproduce equilibrium states with abnormal physiological values related to different combinations of cardiovascular diseases (such as systemic hypertension, chronic heart failure, pulmonary hypertension, etc.). For the model creation and validation, we involved over 200 scientific studies covering known models of the human cardiovascular and renal functions, biosimulation platforms, and clinical measurements of physiological quantities in normal and pathological conditions. We compiled detailed documentation describing all equations, parameters and variables of the model with justification of all formulas and values. The model is implemented in BioUML and available in the web-version of the software.

Extracellular water across the adult lifespan: reference values for adults

Extracellular water (ECW) is a large and clinically important body compartment that varies widely in volume both in health and disease. Interpretation of ECW measurements in the clinical setting requires consideration of potential influencing factors such as age, race, sex and other variables that influence fluid status. An important gap in physiological research is a lack of normative ECW values against which to reference perturbations in fluid homeostasis. The current study's aim was to develop conditional quantile equations for ECW based on weight, height, age, sex and race using a large (n = 1538, 854 females and 684 males) healthy adult multi-ethnic (African American, Asian, European American, Hispanic) sample. ECW was derived from total body water and potassium measured by isotope dilution and whole-body 40K counting, respectively. Quantile regression methods were used to identify five percentile levels (10th, 25th, 50th, 75th, 90th). Weight and height were significant variables at each quantile in both males and females; age made a significant contribution in the male but not the female sample. These regression equations provide ECW quantile reference values based on a large multi-ethnic adult population that should not only prove useful in clinical settings and physiological research, but serve as a model approach for developing body composition normative ranges.

Total exchangeable sodium related to body composition in patients with conventional or reservoir ileostomy

Decreased exchangeable body sodium might be a consequence of proctocolectomy and construction of an ileal reservoir. To investigate this, 35 patients with ulcerative colitis and conventional ileostomy were studied before and after conversion to continent ileostomy and compared with 25 unoperated subjects as reference. The sodium urinary excretion varied between 7 and 229 and 1 and 217 mmol/24 h in patients with conventional and reservoir ileostomy, respectively. The total exchangeable sodium was measured and related to body composition estimated from body weight, total body water, and total body potassium. No effect on exchangeable sodium was observed after conversion: 3100 mmol and 2990 mmol, respectively. Patients with ileostomy, regardless of type, did not differ from reference subjects in their exchangeable sodium when related to total body water. A larger variation of total exchangeable sodium related to total body water suggests unstable sodium homeostasis in patients with ileal reservoir compared with reference subjects.

Body composition. Prediction of normal body potassium, body water and body fat in adults on the basis of body height, body weight and age

In 134 males and 242 females, aged 20-70 years, most of them randomly selected from population studies, the body composition was estimated from the measurements of body height (BH), body weight (BW), total body potassium (TBK) and total body water (TBW). TBK was measured with isotope dilution technique using 42K or determined as 40K in a whole body counter. TBW was determined with an isotope dilution technique using tritiated water, assayed in urine or plasma. From these data, body cell mass (BCM), intra- and extra-cellular water (ICW and ECW, resp.) and body fat (BF) were calculated for each individual. Significant correlations were found between age versus TBK, ECW, BF and ECW/ICW; between BW versus TBK, TBW, ECW, BF and ECW/ICW; (females only) and between BH versus TBK, TBW, ECW (females only) and ECW/ICW. For the prediction of TBK, TBW and BF, multiple regression equations based on BW, BH and age are given. These equations are also presented diagrammatically. The problems with the methods used are considered as well as the applicability of the formulas for the calculation of BCM etc. The predictive value of the results when both TBW and TBK are used for the calculation of body composition data is discussed and compared with similar results, based on TBW or TBK only. It is concluded, that the most reliable method for calculation of BF is to estimate both TBW and TBK.

Intracellular electrolyte depletion in patients with ileostomies

Fourteen apparently healthy patients with ileostomies were found to be depleted of total exchangeable sodium and potassium, but had normal serum electrolyte concentrations and normal extracellular fluid and total body water volumes. The low exchangeable sodium and potassiums were thus primarily due to depletion of the intracellular compartment. There was no evidence of renal or intestinal conservation of these ions and plasma aldosterone, renin activity, and prolactin concentrations were normal in most and only moderately raised in a few. This apparent lack of any hormonal compensatory change to the electrolyte depletion may be due to the normality of the extracellular fluid volume and electrolyte concentrations. These patients seem to have adapted to a stable but depleted intracellular sodium and potassium state.