| With the growing obesity epidemic in the US, there is increasing interest in understanding the physiological aberrations in obese individuals. The focus of this dissertation is to investigate fluid distribution alterations in extremely obese women, and to examine the accuracy of clinical tools to assess it. Obese individuals have been shown to have an expanded extracellular fluid compartment. They have also been reported to have dysregulation of an important fluid regulatory system; specifically, obese individuals have increased systemic renin-angiotensin system hormone concentrations. Furthermore, there is also a growing need for convenient and accurate assessment tools capable of measuring body composition, and/or fluid compartments in obese individuals. In the current study, we first investigated the relationships between nutritional factors (sodium and fluid intake, and adiposity), renin-angiotensin system proteins (plasma renin activity, angiotensin II, and aldosterone), and extracellular fluid. We found that the renin-angiotensin system, specifically angiotensin II, may mediate the relationship evident between our nutritional factors (sodium and fluid intakes, and adiposity) and extracellular fluid. Second, we examined the accuracy of several field techniques, multiple frequency bioelectrical impedance analysis and bioimpedance spectroscopy, for the assessment of fluid compartments, and specifically, intracellular fluid (which provides an approximation of body cell mass) in obese women before and after bariatric surgery-induced weight loss. We found that several bioimpedance approaches provided estimates of fluid that compared reasonably well to our criterion-measured fluid volumes. However, accuracy was less convincing based on individual level comparisons. At this time, concern is warranted with use of bioimpedance devices for extremely obese individuals in the clinical setting. In summary, evaluation of the underlying mechanisms of expanded extracellular fluid, as well as the assessment tools capable of detecting it, are critical in making progress toward the management of obese individuals with alterations in fluid distribution. |
