CRC SLP APN: IMPLCTNS CARDIO CERBRO DIS PDF

PREFACE

As alluded to in the above passage, the onset of sleep should herald relaxation of the cardiovascular system, and autonomic neural quiescence. When this pacific state is disrupted, the heart and circulation may not enjoy fully the restorative effects of sleep. Apnea, a condition common in patients with cardiovascular and cerebrovascular disease, not only disrupts sleep but places direct mechanical and neurohumoral stresses on the heart and vasculature. In some instances, these can exceed those experienced during active wakefulness. Nevertheless, it is our impression that these pathophysiological effects of sleep apnea on the cardiovascular system are not fully appreciated in the broader medical research and clinical communities.

For these reasons, we accepted with great enthusiasm the invitation from Dr. Claude Lenfant to develop and edit this first comprehensive monograph to specifically address the cardiovascular and cerebrovascular consequences of sleep apnea. Since joining the faculty of the University of Toronto in 1985, as a respirologist and cardiologist, respectively, we have shared the concern that cardiovascular turmoil triggered by sleep-related breathing disorders may be fundamental to the initiation, exacerbation, and perhaps mortality of many patients with common and debilitating conditions such as heart failure, hypertension, and nocturnal angina and conduction disturbances. At the time this concept was not generally appreciated. There was a paucity of scholarly literature on this topic, and the majority of clinicians and investigators in the subspecialties of cardiology, neurology, respirology, and hypertension seemed indifferent to the potential adverse impact of sleep-related breathing disorders on their patients. Indeed, attention was focused on cardiovascular event rates during the first few hours after waking, rather than during sleep.

Over the last decade, the concerted efforts of many integrative physiologists, epidemiologists, and clinical investigators worldwide have transformed our understanding and appreciation of the many mechanisms by which apneas during sleep may contribute to the pathophysiology or complications of cardiovascular and cerebrovascular disease. These are the most common life-threatening and debilitating diseases affecting the adult Western population; as life expectancy in developed and developing countries extends, the number of individuals suffering from one or more of these conditions will increase greatly. These several considerations underscored the compelling need for a comprehensive reference text on this topic.

Our overall objective was to assemble the experimental and clinical literature on this topic into a single authoritative and timely monograph useful to basic and clinical scientists interested in these concepts, and to practicing physicians managing such patients. The text is divided into four parts, addressing, in turn, the influence of normal sleep and respiration on the cardiovascular system, the effects of sleep apnea on blood pressure, the relationship of sleep apnea to coronary and cerebrovascular disease, and the pathophysiological interactions between sleep apnea and congestive heart failure. Our contributors were invited to review critically the current literature in their area of expertise, and encouraged to highlight, whenever possible, those novel observations and important concepts arising from their laboratories with the greatest impact. Any success we have achieved toward this goal must be attributed to these authors, who are to be commended for the quality, comprehensiveness, and timeliness of their contributions.

Excitement in any new and emerging field of scientific endeavour is stimulated by the controversies that inevitably arise whenever investigators from different laboratories attempt to interpret and synthesize observations from a variety of experimental models (each with its own specific limitations) and relate these to human disease. Thus, the astute reader should not be surprised to discover that rigorous experiments by highly talented investigators have often yielded conflicting conclusions as to the mechanisms and impact of specific respiratory events on cardiac function and circulatory regulation. In our view, the intensity and sophistication of such debate render current sleep apnea research all the more interesting. We believe that our role as editors was not to adjudicate the relative merits of the assumptions, methods, or conclusions of individual authors, but rather to allow these experienced investigators to develop their points of view as they saw fit, and allow the critical reader to judge the validity of the arguments presented and their relevance for patients with sleep apnea. Our own experience, as clinician scientists focused on human disease, has enhanced our awareness of the difficulties inherent in application of the integrative approach to the identification of discrete mechanisms triggered by apnea during sleep, and its consequences. However, we have been gratified and stimulated by the positive impact of our research findings on the outcomes of our patients with these co-related conditions. Indeed, we undertook this project with the confidence that transmission of this information to a broader readership would ultimately benefit patients who suffer from sleep apnea and its complications.

We would like to thank Dr. Claude Lenfant of the National Heart, Lung, and Blood Institute and Ms. Sandra Beberman at Marcel Dekker, Inc., for their patience and good humor during the editing and publishing process. We have enjoyed the opportunity to create this volume and trust that our readers will profit from its contents.