AJP - Regulatory, Integrative and Comparative Physiology, Vol 266, Issue 3 1052-R1060, Copyright © 1994 by American Physiological Society
A gradient-layer calorimeter for measurement of energy expenditure of infants
S. J. Meis, E. L. Dove, E. F. Bell, C. M. Thompson, M. A. Glatzl-Hawlik, A. L. Gants and W. K. Kim
Department of Pediatrics, University of Iowa, Iowa City 52242.
We have developed and validated a gradient-layer calorimeter for direct
measurement of energy expenditure of preterm infants. Infant calorimeters
must be operated and tested differently from adult calorimeters, because
the calorimeter must be warmed during operation to limit heat loss from the
infant, the calorimeter wall temperature (which is selected on the basis of
the infant's maturity) must be precisely controlled, and energy expenditure
(heat output) is typically < 10 W. We calibrated our calorimeter by
varying the heat produced by a dry source (manikin or light bulb) with
airflow (n = 42) and without airflow (n = 8) at various water jacket
temperatures (n = 7) and by a wet source (combustion of ethyl alcohol) with
airflow (n = 9). With no air moving, qc = 0.740 Vc + 0.029 Twj-0.697, where
qc (W) is the estimated output of the heat source measured by the
calorimeter, Vc (mV) is the gradient-layer voltage of the calorimeter, and
Twj (degree C) is the temperature of the water jacket surrounding the walls
of the device. From this equation and enthalpy calculations, the slope and
intercept of the regression line relating the estimated heat production to
the actual heat produced from alcohol combustion are 1.029 +/- 0.046 and
-0.549 +/- 0.484 (SE), respectively. The slope is not significantly
different from unity, and the intercept is not significantly different from
zero. Thus we can accurately estimate the energy expenditure of preterm
infants from the equations describing our calorimeter, and we can
accurately resolve the total heat output into a dry (nonevaporative)
component and a wet (evaporative) component.
