Derivation of prediction equations for RV in overweight men and women.

Abstract

The purpose of this research was to derive and compare regression equations for predicting residual volume (RV) in overweight and normal weight adults. RV was determined on land, in 311 men and women, following an overnight fast, using the nitrogen-dilution technique. Subjects were then weighed underwater at RV; 5-10 underwater weights were recorded; and the heaviest 3 measurements were averaged as the underwater weight. Percent body fat was calculated using the Siri equation. Group analyses were performed on overweight men (N = 59, body fat > 25%) and women (N = 126, body fat > 30%) compared with normal weight men (N = 68, body fat < or = 25%) and women (N = 58, body fat < or = 30%). A stepwise regression was performed for each group using the Systat Statistical Package (Evanston, IL). When RV was regressed on sex, age (yr), body weight (kg), and height (cm), sex was not found to be a significant predictor variable for RV. Subsequent regressions revealed that prediction equations for the overweight (RV = 0.0277 AGE + 0.0048 WT + 0.0138 HT - 2.3967, F = 44.0, P < 0.0000, SEE = 0.403) were different from those generated for normal weight men and women (RV = 0.0275 AGE + 0.0189 HT - 2.6139, F = 58.6, P < 0.0000, SEE = 0.405). Similar equations were obtained when a cross validation was performed on a separate sample of normal weight (N = 31) and overweight (N = 46) men and women. These data suggest that prediction equations for RV are separate and distinct for the overweight and normal weight populations.