EVALUATION OF SELF-SIMILAR FEATURES IN TIME-SERIES OF SERUM GROWTH-HORMONE AND PROLACTIN LEVELS BY FRACTAL ANALYSIS - EFFECT OF DELAYED SLEEP AND COMPLEXITY OF DIURNAL-VARIATION

We assayed the diurnal concentrations of growth hormone (GH) and prola ctin (PRL) in 6 healthy male volunteers to evaluate the self-similar f eatures in the time series of each hormone on the basis of fractal the ory and to determine the fractal dimension as an index of the complexi ty of the diurnal variation. Tn addition, we assessed the effects of a 6-hour delay in the sleep period on the complexity of the diurnal var iaton of these hormones. These was a statistically significant fractal feature in the serum levels of GR both under the nocturnal-sleep and delayed-sleep conditions in all subjects. The time series of the serum PRL concentrations also showed a statistically significant fractal fe ature under the nocturnal-sleep and delayed-sleep conditions in all su bjects. The fractal dimensions of the patterns of the GH or PRL levels were 1.879 and 1.929 or 1.754 and 1.785 under the nocturnal-sleep and delayed-sleep conditions, respectively. Two-way ANOVA revealed no sig nificant difference in the fractal dimension between the two sleep con ditions but did reveal a significant difference between the fractal di mensions of the GH and PRL levels. These results showed (l) that delay ed sleep had no significant effect on the complexity of the diurnal pa ttern of these hormones, and (2) that the diurnal pattern of the GH le vels was more complex than that of the PRL levels.