EFFECT OF VARIATION OF LINE VOLTAGE OF PHOTOTHERAPY LAMPS ON BILIRUBIN DEGRADATION IN VITRO AND IN VIVO

Abstract

Previously we reported that irradiance from phototherapy lamps vary linearly with change in line voltage (Ped. Res. 9:373, 1975). The effect of this variation of line voltage on bilirubin photo-oxidation in vitro was studied by observing the rate of bilirubin degradation in test tubes containing bilirubin in concentrations of 20 and 10 mg/100 ml standard solution (Hyland), placed 45 cm below an Air Shield Phototherapy Unit with daylight fluorescent lamps. Line voltage to the unit was controlled by a Variac Autotransformer W20MT 3A and varied to provide 110, 115, 120 and 125 volts. The rate of bilirubin degradation was found to vary linearly with line voltage - t½ of bilirubin at 1, 2, 3 and 4 hours varied linearly with line voltage. Effect of variation of line voltage on bilirubin degradation was also studied in vivo in 7 infants who required phototherapy for clinical reasons. The line voltage to phototherapy unit was alternated at 110 and 125 volts at 24 hour intervals. Fall in serum bilirubin after 24 hours of phototherapy was found to be 13% and 31% for line voltage of 110 and 125 volts, respectively. Since line voltage varies from place to place and at different times from the same outlet, the irradiance from phototherapy units will also vary depending upon variations in line voltage. These data underscore the need to define line voltage in photoirradiation studies.