Obstructive Sleep Apnea in Adults

J. S. Borer

• Publisher: S. Karger
• Year: 2011
• ISBN:
  9783805596466
• Topic: Medicine
• Subtopic: Endocrinology & Metabolism

This book aims to provide a comprehensive and clear review of the current knowledge of the relationship between obstructive sleep apnea (OSA) and cardiovascular and metabolic diseases, a subject of concern to a wide range of specialists and general practitioners. Separate chapters describe: the definition, symptoms and sequelae of OSA, and the diagnostic strategies and treatment options for adults with OSA according to the American Academy of Sleep Medicine; pathogenic mechanisms, by which OSA may contribute to the development and progression of cardiovascular and metabolic disorders, including inflammation, oxidative stress and thrombosis; links between OSA and obesity, alterations in glucose metabolism, metabolic syndrome and liver injury; relationships between OSA, endothelial dysfunction, autonomic dysfunction and cardiovascular disorders, and the results of studies investigating the effect of treatment for OSA on the concomitant cardiovascular disease. Each chapter summarizes the essential information and is illustrated by tables and figures, which will aid the readers in their understanding of the complex systemic interactions involved in this disease.Reviewed by internationally recognized experts, this publication will be of benefit to clinicians and scientists in the fields of pulmonology, cardiology, endocrinology and neurology as well as to sleep specialists and general practitioners.

Chapter 1

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Obstructive Sleep Apnea in Adults: Epidemiology, Clinical Presentation, and Treatment Options

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Abstract

Obstructive sleep apnea (OSA) is characterized by repetitive episodes of complete and partial obstructions of the upper airway during sleep. The diagnosis of OSA requires the objective demonstration of abnormal breathing during sleep by measuring the respiratory disturbance index (RDI, events per hour of sleep), i.e. the frequency of apnea (complete upper airway obstruction), hypopnea (partial upper airway obstruction) and arousals from sleep related to respiratory efforts. OSA is defined by combining symptoms and an RDI ≥5 or by an RDI ≥15 without symptoms. The apnea-hypopnea index (AHI), the frequency of apnea and hypopnea events per hour of sleep, is widely used to define OSA (many clinical and epidemiological studies use this metric). In the general adult population, the prevalence of OSA defined by ≥5 apnea and hypopnea events per hour of sleep associated with excessive sleepiness is approximately 3-7% in men and 2-5% in women. The prevalence of OSA is much higher, e.g. ≥50%, in patients with cardiac or metabolic disorders than in the general population. Risk factors for OSA include obesity (the strongest risk factor), upper airway abnormalities, male gender, menopause and age (the prevalence of OSA associated with a higher risk of morbidity and mortality increases with age and peaks at approximately 55 years of age). OSA is associated with symptoms during sleep (snoring, choking and nocturia) and wakefulness (excessive sleepiness, fatigue and lack of energy) and with sequelae such as psychological changes, alterations in the quality of life, and social, familial and professional performance including vehicle and industrial accidents. The identification of OSA may be a difficult task for the clinician, even in populations in which OSA is highly prevalent such as patients with cardiovascular disorders because they may not present the cardinal signs of the disease, e.g. excessive sleepiness and obesity. Guidelines have been developed to tailor OSA therapy to patients according to the results of their disease evaluation and their preferences.

Copyright © 2011 S. Karger AG, Basel

1 Definitions

Obstructive sleep apnea (OSA) is characterized by repetitive episodes of complete or partial obstructions of the upper airway during sleep [1]. The spectrum of these obstructive respiratory events during sleep occurs as a continuum ranging from flow limitation to full apnea. These all lead to an increase in airway resistance and respiratory effort, and may produce oxygen desaturation, central nervous system arousal and sleep fragmentation. According to the International Classification of Sleep Disorders [1, 2], alternate names include OSA syndrome, sleep apnea, sleep apnea syndrome, obstructive apnea, mixed sleep apnea, sleep-disordered breathing (SDB), sleep hypopnea syndrome and upper airway obstruction. Sleep-related breathing disorder is a widely used but rather imprecise term that applies to all types of breathing abnormalities that may occur during sleep, including central sleep apnea syndromes, OSA syndrome, sleep-related hypoventilation/hypoxemia syndromes and sleep-related hypoventilation/hypoxemia due to a medical condition. The International Classification of Sleep Disorders recommends that upper airway resistance syndrome be included as part of OSA and not considered as a separate entity [1]. The diagnosis of upper airway resistance syndrome is a proposed diagnosis for patients with respiratory effort-related arousal (RERA) episodes who do not also have events that fulfill the definitions of apnea and hypopnea [1]. RERA episodes may be responsible for unrefreshing sleep, excessive sleepiness and fatigue as they have the same underlying pathophysiology as apnea and hypopnea. The definitive treatment for OSA, i.e. continuous positive airway pressure (CPAP) treatment, has been shown to significantly improve excessive sleepiness and other outcomes in upper airway resistance syndrome patients [3].

The frequency of apnea, hypopnea and RERA episodes per hour of sleep (respiratory disturbance index, RDI; events per hour of sleep) is used to quantify the severity of OSA (table 1, fig. 1). According to the International Classification of Sleep Disorders, a diagnosis of OSA can be made for an RDI ≥15, independently of the occurrence of symptoms, or whenever an RDI >5 is associated with any of the symptoms described in table 2. The severity of OSA is defined as mild for an RDI ≥5 and <15, moderate for an RDI ≥15 and ≤30, and severe for an RDI >30 [4]. The apneahypopnea index (AHI), the frequency of apnea and hypopnea events per hour of sleep, is a widely used index to define OSA, including many epidemiological studies [5–7].

Obesity hypoventilation syndrome (OHS) is different from OSA [8]. It is defined as daytime hypercapnia and hypoxemia (arterial carbon dioxide pressure >45 mm Hg and arterial oxygen pressure < 70 mm Hg at sea level) in obese patients (body mass index, BMI, ≥30) with SDB in the absence of any other cause of hypoventilation, e.g. severe obstructive airways disease, severe interstitial lung disease, severe chest wall disorders such as kyphoscoliosis, severe hypothyroidism, neuromuscular disease and congenital central hypoventilation syndrome [8]. OSA is the SDB associated with OHS in approximately 90% of patients, while it is sleep hypoventilation in the remaining 10%. Sleep hypoventilation is defined by an increase in arterial carbon dioxide pressure of >10 mm Hg above that of wakefulness or significant oxygen desaturations, neither of which is the result of obstructive apneas or hypopneas [8]. Sleep hypoventilation patients are characterized by an AHI <5. Categorization of SDB in OHS patients is performed during an overnight polysomnography (PSG) examination.

Table 1. Definition of apnea, hypopnea and RERA according to the 2007 American Academy of Sleep Medicine recommendations [255]

Apnea	A respiratory event is scored as apnea when all of the following criteria are met: there is a drop in the peak oral and nasal thermal sensor excursion ≥90% of baseline, and at least 90% of the event's duration meets the amplitude reduction criteria for apnea
Obstructive apnea	Obstructive apnea meets the apnea criteria and is associated with continued or increased inspiratory effort throughout the entire period of absent airflow
Mixed apnea	Mixed apnea meets the apnea criteria and is associated with a lack of inspiratory effort in the initial portion of the event (no thoracic and abdominal movements), followed by the resumption of inspiratory effort in the second portion of the event (persistent thoracic and abdominal movements)
Central apnea	Central apnea meets the apnea criteria and is associated with absent inspiratory effort throughout the entire period of absent airflow
Hypopnea	A respiratory event is scored as hypopnea when nasal pressure excursion drops by (1) ≥30% of baseline and there is a ≥4% desaturation from the pre-event baseline, or (2) ≥50% of baseline and there is a ≥3% desaturation from the pre- event baseline or the event is associated with arousal. I...