Sleep Apnea: Implications in Cardiovascular and Cerebrovascular Disease PDF

Preface

As Ovid proclaims, the onset of sleep should herald relaxation of the heart and the cardiovascular system. However, when this pacific state is disrupted by pauses in breathing, the heart and the sympathetic nervous system "waketh," denying the slumberer the full restorative effects of sleep. When apnea, a condition common in patients with cardiovascular and cerebrovascular disease, disrupts sleep, it places direct mechanical and neurohumoral stresses on the heart and vasculature. In some instances, these forces can exceed those experienced during vigorous mental and physical activity. However, until recently, the adverse implications of these pathophysiological effects of sleep apnea on the cardiovascular system have received little attention. Indeed, current evidencebased guidelines for the investigation and therapy of conditions such as hypertension and heart failure focus on the patient with hypertension or heart failure as he or she presents, in clinic, while awake. This clinical approach presupposes that any mechanisms that might contribute to the pathophysiology or progression of such conditions are quiescent 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 lifethreatening 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. Over the same period there has been increasing recognition of the limitations of conventional drug-based approaches to the therapy of cardiovascular conditions that fail to specifically address and treat coexisting sleep-related breathing disorders. As a result there has been a renewal of interest in concepts such as "refractory hypertension" and "limits to neurohumoral blockade in heart failure" in the cardiovascular literature.

These several considerations underscored the compelling need for a comprehensive reference text on the topic of sleep apnea and its implications for cardiovascular and cerebrovascular disease. For the last two decades, the editors, a respirologist and cardiologist, respectively, have shared the concern that cardiovascular turmoil triggered by sleep-related breathing disorders may participate in the initiation or progression of common and debilitating conditions such as heart failure, hypertension, stroke, arrhythmias, and nocturnal angina. We therefore accepted with great enthusiasm the invitation from Dr Claude Lenfant to develop and edit a comprehensive monograph specifically addressing the cardiovascular and cerebrovascular consequences of sleep apnea. 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.

Our objective in the first edition of this text was to assemble the available 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. We addressed, 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. We were gratified by the enthusiastic response to our first edition, in 2000, and by the subsequent acceleration of interest, among the broader medical research and clinical communities in this entire topic, and in related public health issues such as interactions between sleep apnea, obesity, and the metabolic-cardiovascular syndrome. With this success came the responsibility to ensure that important new advances in this field were not overlooked.

Our objective in preparing the second edition of this text was to ensure the critical synthesis, into the existing literature, of new information linking sleep apnea to the major disease burdens facing developed and developing nations. This includes both new basic and epidemiological data linking sleep apnea to inflammation, the metabolic syndrome, and stroke, in addition to hypertension and heart failure and, importantly, the results of recently published clinical trials. The majority of the studies reviewed in the first edition of this text were mechanistic or interventional studies, comprising small numbers of experimental or human subjects, performed in single centers. These investigations have since stimulated a number of single and multicenter randomized controlled trials of interventions specifically addressing the treatment of sleep apnea on clinically important outcomes. Because these trials have important implications for clinical practice, they therefore merit particular attention. 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. Our role as editors was to ensure that our readers would consider this volume transformative rather than simply evolutionary.

We thank our authors for the quality, comprehensiveness, and the timeliness of their contributions, and Dr Claude Lenfant of the World Hypertension League and Ms Sandra Beberman at Informa Healthcare for their patience and good humor during the editing and publishing process. We have enjoyed the opportunity to create this second edition and trust that our readers and the patients we treat will benefit from its contents.