EFFECT OF DIFFERENT PHOTOTHERAPY LIGHTS ON INCUBATOR CHARACTERISTICS AND DYNAMICS UNDER 3 MODES OF SERVOCONTROL

Phototherapy is one of the most common therapeutic interventions in mo dern neonatal medicine. Analysis of physiological responses to phototh erapy requires understanding the physical effects of incident light un der 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 servocon trol modes. Under conditions of air servocontrol, the initiation of ph ototherapy resulted in an abrupt sustained increase in the surface tem perature of an infant simulator (a blackened aluminum disc). In contra st, when the surface (skin) temperature was the controlled variable, t here was a profound drop in the incubator air temperature. An algorith m that simultaneously controlled both the skin and the air temperature s 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 c onclude that wide, abrupt, and sustained changes in the thermal enviro nment of an incubator occur after phototherapy is initiated. Such chan ges must be anticipated in physiological studies using phototherapy.