THE MEASUREMENT OF BODY VOLUME IN PRETERM INFANTS BY ACOUSTIC PLETHYSMOGRAPHY

Abstract

An accurate measurement of body volume is essential when body protein and fat are estimated by the densitometric method expanded to a four compartment system: total body water, protein, fat, and mineral. Total body fat and lean body mass comprise the usual two compartment system. The acoustic plethysmograph, based on the Helmholtz resonator principle, was tested with miniature pigs. Body volume was estimated with a reproducibility of 2.5% and no differences were noted between volumes estimated by that method and water displacement. That initial prototype was affected significantly by temperature; a 1° deviation at 35° C resulted in a 2.5% change in body volume estimates. A constant temperature chamber has been designed. The body volume of 8 preterm infants (postnatal age and body weight ranges were 2.5 - 11 wks and 1423 - 2425 g, respectively) was measured. Ten measurements, each of 1 min duration, were obtained on each subject. The mean coefficient of variation of the measurements was 1.43 ± 0.55%. Body volumes and densities ranged from 1382 - 2450 cc and 0.97 - 1.067 g/cc (mean = 1.028 ± 0.024 g/cc), respectively. The reproducibility also was tested from measurements obtained on the same infants on two consecutive days. The mean difference between measurements was 0.7 ± 0.6%. This method is rapid, noninvasive, has a low coefficient of variation, and is ideal to measure the body volumes of infants.