Electrically heated simulator for relative evaluation of alternative infant incubator environments

A 10.9-cm diameter, copper ellipsoid was electrically heated to provide a simulation of sensible heat transfer from a newborn infant. The use of this simulator to determine mean radiant temperature and convective heat-transfer coefficient was demonstrated in three commercial incubators: the Isolette (Model C-86, Narco/Air Shields); the Armstrong Care-ette (Ohio Medical Products); and the I. C. (Ohmeda). The relative performance of these environmental therapeutic devices in shielding an infant against radiant heat loss was judged by the deviation of mean radiant temperature from incubator air temperature, which was varied from 32-36 degrees C. Whereas the I. C. incubator exhibited a radiant temperature always 0.5 degrees C less than air temperature, the Care-ette incubator showed radiant temperatures of 4.0-5.5 degrees C below air temperature, and the Isolette displayed radiant temperatures of 2.7-4.7 degrees C (inner wall removed) and 2.0-3.8 degrees C (inner wall inserted) below air temperature. The relative performance of the incubators in preventing convective heat loss was judged from the magnitude of the convective heat-transfer coefficient, hv. The I. C. incubator had an hv = 4.52 W/m2/degrees C; the Care-ette, 5.55 W/m2/degrees C; and the Isolette 7.19 W/m2/degrees C (inner wall removed) and 6.23 W/m2/degrees C (inner wall inserted). Although an ellipsoid simulator is not an anatomically correct substitute for an infant, it does provide a reliable and convenient comparison of steady-state heat transfer characteristics of alternative environmental devices.