Elsevier

Sleep Medicine

Volume 8, Issue 4, June 2007, Pages 400-426
Sleep Medicine

Sleep apnea: Clinical investigations in humans

https://doi.org/10.1016/j.sleep.2007.03.003Get rights and content

Abstract

Sleep apnea syndrome (SAS), a common disorder, is characterized by repetitive episodes of cessation of breathing during sleep, resulting in hypoxemia and sleep disruption. The consequences of the abnormal breathing during sleep include daytime sleepiness, neurocognitive dysfunction, development of cardiovascular disorders, metabolic dysfunction, and impaired quality of life. There are two types of SAS: obstructive sleep apnea syndrome (OSAS) and central sleep apnea syndrome (CSAS). OSAS is a prevalent disorder in which there is snoring, repetitive apneic episodes, and daytime sleepiness. Anatomical conditions causing upper airway obstruction (obesity or craniofacial abnormalities such as retrognathia or micrognathia) can cause OSAS. CSAS, much less common than OSAS, is a disorder characterized by cessation of breathing which is caused by reduced respiratory drive from the central nervous system to the muscles of respiration. The latter condition is common in patients with heart failure and cerebral neurologic diseases. The diagnosis of SAS requires assessment of subjective symptoms and apneic episodes during sleep documented by polysomnography. Treatments of OSAS include continuous positive airway pressure (CPAP), oral appliances, and surgery; patients with CSAS are treated with oxygen, adaptive servo-ventilation, or CPAP. With assessment and treatment of the SAS, patients usually have resolution of their disabling symptoms, subsequently resulting in improved quality of life.

Introduction

Sleep apnea syndrome (SAS), a common disorder, is characterized by repetitive cessation of breathing during sleep (sleep apnea) and daytime consequences which include subjective daytime sleepiness, impaired cognitive function, including impaired memory [1], [2]. There are two types of SAS based on the pathophysiologic mechanisms causing the apneas [3]. Obstructive sleep apnea syndrome (OSAS) is a disorder which is caused by obstruction of the upper airway. Central sleep apnea syndrome (CSAS), much less common than OSAS, is caused by reduction of impulses from the central nervous system to the respiratory muscles. SAS may negatively affect several organ systems which subsequently may increase the risk for cardiovascular, neuropsychiatric, and metabolic disorders [4], [5]. In this article, we focus on OSAS in adults and describe clinical investigations on clinical presentation, diagnosis, and treatment. Because CSAS is common in patients with heart failure [6], this topic will be reviewed in the Section 6.1.

Section snippets

Definition and nosology

Sleep-related breathing disorder (SBD) is a term used to describe a spectrum of respiratory disturbances that occur during sleep. The International Classification of Sleep Disorders – 2nd edition (ICSD-2) has defined the two major categories of SBD: central sleep apnea syndrome (CSAS) and obstructive sleep apnea syndrome (OSAS) [1], [2]. CSAS includes some subcategories based on each cause. OSAS is subdivided into adult type or pediatric type based on the patient’s age, because the clinical

Prevalence

A wide range in the prevalence of OSAS has been reported because of inconsistencies in definitions, diagnostic methods, and sampling biases. The landmark study which clarified the prevalence of OSAS in the general middle-aged population showed that OSAS (apnea/hypopnea index (AHI) >5/h and excessive daytime sleepiness) affects about 2% of females and 4% of males [21]. A more recent report estimated that OSAS affects approximately 5% of adults [22]; however, the prevalence of OSAS may be

Daytime sleepiness

Common clinical presentations and subjective symptoms are presented in Table 5, Table 6. Most patients with OSAS have daytime sleepiness, which adversely affects cognitive function, memory, and work performance. Because of impaired neurocognitive function, patients with OSAS are at increased risk for having motor vehicle accidents [5]. Excessive daytime sleepiness has been considered to result from fragmented sleep due to recurrent arousals in the brain that precede resumption of ventilation.

Upper airway obstruction and intrathoracic pressure

Negative intrathoracic pressure is generated by diaphragmatic contraction which results in thoracic expansion and reduced pharyngeal intraluminal pressure [7]. The pressure decreases further in patients with OSAS because of the increased respiratory efforts required to maintain flow in the presence of a narrowed or collapsed pharyngeal passage. The negative intrathoracic pressures have influence on hemodynamics. These effects have been simulated experimentally in humans by use of the Müller

Systemic hypertension

Recurrent episodes of apneas and hypopneas during sleep cause hypoxemia, arousals, and increased sympathetic activity, which have been hypothesized to increase daytime blood pressure in OSAS patients [97]. The prevalence of hypertension in patients with OSAS has been reported to be 45%; the value may overestimate the effect of apnea because age and BMI were independent predictors of hypertension [107]. The Wisconsin Sleep Cohort Study showed that both systolic and diastolic blood pressure

Nocturnal sleep study

A full-night polysomnographic sleep study is considered to be the gold standard method for diagnosis of OSAS. Overnight polysomnography (PSG) is usually performed in an attended setting (level 1 sleep study). Classification of sleep study based on the montage monitoring is presented in Table 8. Polysomnography includes multichannel monitoring of electroencephalogram (EEG), chin electromyogram (EMG), electrooculogram (EOG), anterior tibialis EMG, and SpO2 (by oximeter). Two plethysmograph belts

Continuous positive airway pressure

CPAP is a device that prevents upper airway obstruction by positive airway pressure usually applied via a nasal mask. CPAP has been shown to decrease the frequency of apneic events and oxygen desaturation during sleep, and to reduce the severity of sleep disturbance and daytime sleepiness in patients with OSAS [5], [271]. CPAP prevents some cardiovascular morbidities and may reduce mortality due to cardiovascular causes [4], [40], [175], [272]. CPAP also improves the following neuropsychiatric

Conclusions

Sleep apnea is a common disorder which negatively affects multiple organ systems, and which may play a role in the development of cardiovascular diseases and neurocognitive abnormalities. Treatment of sleep apnea has been shown to improve neuropsychiatric abnormalities, cardiovascular function, and quality of life.

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