Abstract

The physiology section of this volume covers a wide spectrum of very precise concepts from molecular and behavioral genetics to system physiology (temperature control, cardiovascular and respiratory physiology, immune and endocrine functions, sensory motor neurophysiology), integrating functions such as mental performance, memory, mood, and wake time physical functioning. An important focus has been to highlight the relevance of these topics to the practice of sleep medicine. A keener understanding of physiological dysfunction helps clinicians to explain to patients how to cope with a sleep disorder, a process that is integral to patient satisfaction and well being. A wider knowledge of physiology will also assist clinicians in clarifying new and relevant research priorities for basic scientists or public health investigators. Overall, the development of enhanced communication between health workforces will promote the rapid transfer of relevant clinical issues to scientists, of new findings to the benefit of patients. At the same time, good communication will keep clinicians in step with the expanding field of sleep medicine and will make them well prepared to face the growing challenges in public health issues.

Why do doctors and scientists need to understand sleep physiology? A thorough knowledge of sleep physiology is central to improved accuracy and validity in the development of diagnostic tools, to making innovations in patient management, and to keeping abreast of leading edge developments in sleep medicine. For some clinicians, reading chapters in sleep physiology may recall early years of training, but these days physiology is an integral part of many advancements in clinical practice (e.g., breathing and cardiovascular measurements, brain imaging), and it forms the basis of translating genetics and proteomics into innovation in diagnosis and therapeutics.

The impact of poor sleep and of several sleep disorders on societal and economic health is interrelated¹; health governmental agencies are extremely sensitive to discoveries that may improve the population’s quality of life and reduce health care costs. A greater understanding of sleep physiology has resulted in innovations in the pharmaceutical industry and in the design of diagnostic and therapeutic devices (e.g., recording and scoring systems, continuous positive airway pressure, mandibular advancement appliances). But governmental agencies only grant permission to market a given product following epidemiological findings, explorations of physiological and pathological mechanisms, and randomized control trials demonstrating efficacy and safety. The absence of objective and valid measures to assess sleep improvement and safety can prevent developments and innovation from being integrated into sleep medicine practices. Although questionnaires are used to screen patients for many sleep disorders, it is the physiological (e.g., hormonal-endocrine release, heart rate by electrocardiogram, brain activity by electroencephalography) and psychophysiological (reaction time, multiple sleep latency test, sensory perception) measures that confirm the accuracy and validity of the concepts.

Clinical science progresses sequentially. For example, using questionnaires, the prevalence of nonrestorative sleep has been reported at 10% in the general population.² With polygraphy, the consequences of that nonrestorative sleep consequences are characterized,^3,4 interindividual trait differences may be identified,⁵ and phenotypic determinants of vulnerability also recognized.⁶

The identification of gene polymorphism related to specific sleep disorders is another domain of intense interest (see Section 3 of this volume). We are already in the postgenomic era with the advent of proteomics: the science of protein characterization in relation to biological activity or disorder/disease.⁷ Most sleep disorders, such as insomnia, sleep breathing disorders (e.g., sleep apnea), parasomnia (e.g., sleepwalking, enuresis, REM behavior disorder [RBD]), sleep-related movement disorders (e.g., restless leg syndrome/periodic limb movement), and circadian rhythm sleep disorders have genetic and/or molecular targets that provide possible new avenues in therapeutics.^8,9 Genetic epidemiology is a growing field that integrates all aspects of physiology to further identify targets (gene loci), and variance related to individuals and environments.^10,11 Physiology provides the tools with which sleep disorders may be phenotyped and genetics advances the clinical domain by identifying risk or vulnerability factors. The combination makes for innovative approaches to therapy.

This section updates some chapters from the previous edition related to cardiovascular, respiratory, immune, endocrine, gastrointestinal, and thermoregulatory mechanisms. In addition there are new chapters on the contribution of brain imaging to the understanding of sleep physiology (Chapter 18), a description of the relevance of autonomic-cardiovascular measures and their meaning in sleep medicine (Chapter 20), the mechanisms that regulate breathing and the relevance of respiratory measures in sleep medicine (Chapters 21 and 23), the extension of endocrinology to obesity and women’s sleep issues (Chapter 26), the potential impact of thermoregulation on nonrestorative sleep management (Chapter 28), the circular relationship between sleep and memory-learning (Chapter 29), the role of sensory-motor integration on the control of breathing and sleep breathing disorders, on motor parasomnia or movement disorders, and on ways in which sensory feedback interferes with sleep in relation to periodic limb movement, RBD, pain, and bruxism (Chapter 30).

These new chapters will prepare the reader to understand the pathophysiological mechanisms relevant in understanding the clinical disorders described in this volume. In other words, we hope they will provide some answers about how disease affects physiology, how interventions work, why they do not work, and what remains to be done. Future editions of this volume will probably integrate more knowledge on the relevance of nano information, such as molecular and synaptic homeostasis,¹² micro information, such as how tractography imaging is used to assess cortical and brainstem networking activity during sleep or using mathematical modelling,¹³ and macro information that integrates behavior with sleep disorders and addresses issues related to cognition and placebo influence on sleep.^14–17