ABSTRACT
Phototherapy is one of the most common therapeutic interventions in modern neonatal
medicine. Analysis of physiological responses to phototherapy requires understanding
the physical effects of incident light under different modes of environmental control.
In this study, we tested the effect of initiation of phototherapy under laboratory
conditions in a convective incubator maintained in three clinically used servocontrol
modes. Under conditions of air servocontrol, the initiation of phototherapy resulted
in an abrupt sustained increase in the surface temperature of an infant simulator
(a blackened aluminum disc). In contrast, when the surface (skin) temperature was
the controlled variable, there was a profound drop in the incubator air temperature.
An algorithm that simultaneously controlled both the skin and the air temperatures
showed intermediate effects. Under conditions of skin servocontrol, fluctuations in
air and environmental temperatures were observed for a period of 3 hours before steady
state was reached. These findings are most clearly demonstrated using phase plane
plotting techniques. We conclude that wide, abrupt, and sustained changes in the thermal
environment of an incubator occur after phototherapy is initiated. Such changes must
be anticipated in physiological studies using phototherapy.
Keywords
Phototherapy - incubator - infant simulator - phase plane plots
