ACTIGRAPHIC ASSESSMENT OF SLEEP-ACTIVITY CYCLE IN PHYSIOPATHOLOGY: EXPERIMENTAL AND METHODOLOGICAL STUDIES

The principal objective of my research during my PhD has been the investigation of the rest-activity circadian rhythms in physiopathology, dealing with both experimental and methodological issues. On the experimental side, the focus of my research program was centered on the investigation of the rest-activity circadian rhythms in patients with binge eating disorders. On the methodological side, my activity was aimed at exploring the relationships between the actigraphy-based assessment of circadian rhythmicity and the questionnaire-based assessment of circadian typology. The thesis is organized in 11 Chapters. Chapter 1 provides a short introduction to chronobiology and to the components of a circadian rhythm. Chapter 2 describes the two most common methods used to evaluate the circadian rhythmicity, namely actigraphy and self-administered questionnaires. These two approaches have remarkable strengths and weaknesses. Actigraphy is a non-invasive method (usually based on a small, wearable actigraphic unit) that allows one to monitor the activity levels during the 24 hours, to detect the rest-activity circadian rhythm, to evaluate the activity levels during the nocturnal sleep and to assess the quality and quantity of sleep by specific sleep parameters. One alternative approach to assessment of the circadian typology of a subject is based on self-administered questionnaires. Questionnaires are obviously less objective than actigraphy-based assessments, but have the advantage of being simple and cost-effective. Chapter 3 provides a general overview of all the research projects I have taken part in throughout my PhD course. This chapter has been written with the reader in mind and aims to succinctly describe the structure and function of the subsequent chapters, 4 through 11. In Chapters 4 to 7, I will focus on the experimental core of my research activity during my PhD course, which is the chronobiological investigation of obese patients suffering from binge eating disorder. First, I will provide an overview of the features characterizing this disorder. Then, I will describe three experimental studies that were carried out in these patients with the purpose of i): quantifying their rest-activity circadian rhythm (RARs); ii) describing their sleep behaviour; iii) evaluating the effectiveness of a physical activity program as an auxiliary therapeutic approach to the traditional treatment for BED. In Chapters 8 to 10, I will illustrate the methodological core of my research activity during my PhD which aims to develop predictive formulas - based on linear regression - enabling investigators to use the questionnaire-based assessment of circadian typology (Morningness-Eveningness Questionnaire, MEQ) as a surrogate of the actigraphy-based assessment of circadian rhythmicity. A methodological project of this kind was successful is showing that both MEQ and its reduced version rMEQ are appropriate for the prediction of the actigraphy-based acrophase and this may prove useful when actigraphy-based measurements are not applicable, in so far as they result either too complex or time-consuming. Chapter 11, the final chapter, is concerned with providing concise summaries of the other studies I have been involved in during my PhD course. Seven experimental studies are described in relation to: i) the influence of chronotype on circadian rhythm (RARs), on sleep, on physical activity and on cardiac autonomic function; ii) the effects of aerobic physical activity on sleep and on markers of insulin resistance in breast cancer women; iii) the effects of short and prolonged exposure to cave environments on human physiology. The thesis also comprises an appendix containing the list of all the scientific papers that I co-authored in the course of my PhD thesis. The list reports both the published and the submitted articles.