Original Contribution to Bioimpedance Spectroscopy Theory for Body Composition Assessment in Nigerian Tropical Climate Populations

Bioimpedance spectroscopy for body composition assessment uses electrical impedance measurements across a frequency spectrum to estimate tissue compartment volumes, but the theoretical models relating impedance to composition were derived from studies in temperate populations whose hydration status, body morphometry, and skin impedance characteristics differ systematically from Nigerian tropical climate populations, creating biologically meaningful prediction errors. This dissertation makes original contributions to bioimpedance spectroscopy theory for body composition assessment by developing population-specific models incorporating physiological variables that differ systematically in Nigerian tropical conditions. The empirical foundation comprises multi-frequency bioimpedance spectroscopy measurements from five hundred and forty participants across three Nigerian climatic zones, North West arid, South West humid subtropical, and South South equatorial, with concurrent gold standard body composition measurements by deuterium dilution for total body water and by dual-energy X-ray absorptiometry for fat mass. Novel theoretical contributions include a revised Cole-Cole impedance arc model incorporating sweat-modified skin stratum corneum resistance terms parameterized from measured skin impedance data under ambient temperature conditions from 25 to 40 degrees Celsius. A population-specific regression model for extracellular water estimation incorporating Nigerian-derived anthropometric coefficients demonstrates significantly reduced prediction error relative to existing North American-derived prediction equations. A climate zone stratification variable was found to significantly improve prediction accuracy beyond ethnic stratification alone. Monte Carlo uncertainty propagation analysis establishes clinically meaningful measurement uncertainty limits for the revised model. The dissertation provides a theoretical basis for developing validated, climate-adapted bioimpedance spectroscopy equations for Nigerian clinical and nutritional research applications. Keywords: bioimpedance spectroscopy, body composition, theoretical modelling, tropical climate, Nigeria.