Pre-term infant volume measurements by acoustic plethysmography

An acoustic plethysmograph has been developed to provide routine total body volume measurements of pre-term (1.5-3.0 kg) infants. It operates near 50 Hz and is excited by band-limited 25 Hz span noise. Excitation, measurement, analysis, and environment are computer controlled for greater accuracy, speed, and objectivity in volume determinations. Performance tests produced volume measurements with a mean per cent error (+/- SD) of 0.77 +/- 0.66% for two phantoms with volumes of 2880 and 2130 cm3. Ten, one-minute volume measurements were obtained for 14 infants over a 20 to 30 min period. Their mean density was 1.061 +/- 0.028 g cm-3 and their weight ranged from 1294 to 2025 g.