Insights into puberty: the relationship between sleep stages and pulsatile LH secretion.

CONTEXT: During the pubertal transition, LH secretion initially increases only during sleep; however, its relationship to sleep stage is unknown. OBJECTIVES: Our objective was to determine whether the initiation of LH pulses is related to a specific sleep stage in pubertal children. DESIGN AND SETTING: Frequent blood sampling and polysomnographic studies were performed in a Clinical Research Center. SUBJECTS: Fourteen studies were performed in nine healthy pubertal children, ages 9.9-15.6 yr. INTERVENTIONS: Subjects underwent one to two overnight studies with polysomnography and blood sampling for LH at 10-min intervals. RESULTS: Alignment of polysomnographic records and LH pulses demonstrated that LH pulses (n = 58) occurred most frequently during slow-wave sleep (SWS) (1.1 pulse/h, n = 30) compared with all other sleep stages or periods of wake after sleep onset (P < 0.001). There was also a significant increase in the amount of SWS in the 15 min preceding and the 5 min following each pulse compared with the amount of SWS seen across the study night (P < 0.01). CONCLUSIONS: During puberty, the majority of LH pulses that occur after sleep onset are preceded by SWS, suggesting that SWS is intimately involved in the complex control of pubertal onset. These studies raise concerns about the potential hormonal repercussions of the increasing prevalence of sleep disturbances in adolescents.

Regression and recursive partition strategies in the analysis of medical survival data.

Regression and clustering methods have both been used to explore the effects of explanatory variables on survival times for patients with cancer or other chronic diseases. This paper discusses effective and computationally feasible approaches for this task in situations where there are fairly large and complex data sets; the techniques stressed are all-subsets regression and a kind of recursive partition clustering. We compare the two approaches in a rather general way, in part by examining some survival data for patients with ovarian carcinoma, and conclude that both have strong points to recommend them.