Epidemiology

Snoring is extremely common in both genders and in all age groups. It is reported to occur in nearly 50% of the adult population, with a higher prevalence among men.² Of note, however, estimates of its prevalence vary widely because detection methods rely heavily on subjective reports by bed partners or parents. Reported prevalence rates for snoring range between 5% and 86% in men and between 2% and 57% in women.³ Evidence suggests that the frequency of snoring increases with age until about age 60, at which time a decrease occurs.² In children, snoring is common, with a reported prevalence of 10%.⁴ It typically is associated with enlarged tonsils and adenoids, as well as obesity. Snoring also has been reported to increase markedly during pregnancy.^5,6

The reported prevalence of OSA varies widely because of differences in assessment methods and in the number of abnormal respiratory events per hour used to define abnormality. It is estimated that about 2% to 4% of the adult population 30 to 60 years of age is affected by OSA; however, 9% of women and 24% of men have signs or symptoms suggestive of sleep-disordered breathing.⁷ Different rates of occurrence have been reported for males and for females, with males affected more often. Variation among racial groups may be due to genetic differences. African Americans, Hispanics, and Asian Americans tend to have a somewhat higher prevalence than that in whites. About 3% of children are affected with OSA, with the highest prevalence reported between the ages of 2 and 5 years.⁸

Etiology and Pathophysiology

The underlying defect in sleep-related breathing disorders is an anatomically narrowed upper airway combined with pharyngeal dilator muscle collapsibility. The exact pathogenesis, however, is not well understood. Depending on the extent of narrowing, increased resistance to airflow may be clinically expressed as vibration of soft tissues (snoring), reduced ventilation (hypopnea), or complete obstruction (apnea).

Anatomic narrowing may occur at any site in the upper airway from the nasal cavity to the larynx. Within the nasal cavity, septal deviation and enlarged turbinates may cause narrowing. In the nasopharynx, hypertrophic adenoids and tonsils, an elongated soft palate, and an elongated and edematous uvula may be the cause. In the oropharynx, narrowing may be due to an enlarged tongue, retrognathia, excessive lymphoid tissue, palatine tonsils, or redundant parapharyngeal folds. The most common sites of airway narrowing or closure during sleep are the retropalatal and retroglossal regions.⁹ Most patients with OSA have more than one site of narrowing.¹⁰ It also has been demonstrated that the volume of the upper airway soft tissue structures (i.e., tongue, lateral pharyngeal walls, soft palate, parapharyngeal fat pads) is significantly greater in patients with OSA than in normal control subjects.¹¹ Factors that are thought to contribute to enlargement of the upper airway soft tissues in apneic patients include obesity, edema secondary to negative pressures, vibration trauma of the uvula, male gender, and possibly, genetics.⁹ Other anatomic risk factors for narrowing of the upper airway include retrognathia, large tongue, long soft palate, and enlarged uvula, tonsils, and adenoids.

In addition to anatomic narrowing of the airway, an abnormal degree of collapsibility is observed in the pharyngeal dilator muscles surrounding the airway. Patency of the airway depends on a balance between air pressure within the airway and pressure outside of the airway exerted by the parapharyngeal musculature. Muscles that surround the airway receive phasic activation during inspiration and tend to promote a patent pharyngeal lumen by dilating the airway and stiffening the airway walls.¹² Normally, the intraluminal pressure exceeds the external pressure, and the airway remains patent during inhalation and exhalation. Normal function requires coordinated timing and activity of agonists and antagonists, and of individual muscles or groups of muscles. The cause of abnormal pharyngeal airway collapse is complex, involving both dynamic and static factors. These factors may include tissue volume, changes in the adhesive character of mucosal surfaces, changes in neck and jaw posture, decreased tracheal tug, effects of gravity, and decreased intraluminal pressure resulting from increased upstream resistance in the nasal cavity or pharynx.⁹

Complications and Outcomes

To appreciate the consequences of sleep-related breathing disorders, it is necessary to review the aspects of normal sleep. Normal sleep patterns vary with age but are nevertheless similar across patient groups; thus, for illustrative purposes, the sleep of young adults is discussed here. Normal sleep occurs in two phases: non–rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep¹³ (Table 9-1).

TABLE 9-1 Percentage of Time Spent in the Various Stages of Sleep for Normal, Healthy Young Adults

EEG, Electroencephalogram.

The phases of sleep are characterized by distinctive patterns on the electroencephalogram (EEG), as well as by the presence or absence of eye movements. NREM sleep occurs in three (or four) stages and generally is characterized by synchronous brain waves, mental inactivity, and physiologic stability (Figure 9-2). The NREM sleep state sometimes is referred to as “a quiet brain in a quiet body.” Stage 1 NREM is a brief, transitional stage that lasts only a few minutes between wakefulness and sleep and from which the person can be easily aroused. Stage 2 NREM is the initial stage of true sleep, from which arousal is more difficult. The appearance of EEG waves called sleep spindles, or K-complexes, identifies this stage, which typically lasts 10 to 25 minutes. Stage 3 is characterized by the appearance on the EEG of high-voltage, high-amplitude slow waves that last for a few minutes and then undergo transition into stage 4, with more frequent and higher-amplitude slow waves. This stage lasts for 20 to 40 minutes. Stages 3 and 4 often are combined, and this combination is referred to as slow wave sleep (SWS).

FIGURE 9-2 Electroencephalographic tracings of non–rapid eye movement (NREM) sleep stages.

(From Carskadon MA, Dement WC: Normal human sleep: an overview. In Kryger MH, Roth T, Dement WC, editors: Principles and practice of sleep medicine, ed 5, St. Louis, 2011, Saunders.)

After a period of NREM sleep, a “lightening” occurs, marked by entry into REM sleep. REM sleep is very different from NREM sleep and is characterized by asynchronous brain waves, an active brain, and physiologic instability, and muscular inactivity. The REM sleeep state often is described as “an active brain in a paralyzed body.” A key feature is the presence of periodic rapid movement of the eyes with low-voltage EEG waves resembling those typical of wakefulness (Figure 9-3). Variations in blood pressure, heart rate, and respiration occur, along with general muscle atonia and poikilothermia. Dreaming also occurs during REM sleep. Sleep normally is entered through NREM sleep and progresses to REM. Over the course of a night, sleep cycles between NREM and REM, with each cycle averaging about 90 minutes. Depending on the length of the sleep period, the sleeper typically passes through four to six cycles per night. The length of time in each stage varies, with NREM predominating in the earlier part of the night and REM predominating in the later part of the night (Figure 9-4). It is difficult to define the “normal” length of sleep because of multiple variables, including age, environment, circadian rhythm, and medication effects; however, most young adults report that they sleep an average of 7.5 hours per weeknight and 8.5 hours on weekend nights.¹⁴

FIGURE 9-3 Phasic events in human rapid eye movement (REM) sleep. C3/A2 is an electrooculographic (EOG) lead. ROC/A1 is a lead from the outer canthus of the right eye, and LOC/A2 is another lead from the outer canthus of the left eye. Note the several bursts of activity in the eye lead tracings.

(From Carskadon MA, Dement WC: Normal human sleep: an overview. In Kryger MH, Roth T, Dement WC, editors: Principles and practice of sleep medicine, ed 5, St. Louis, 2011, Saunders.)

FIGURE 9-4 Histogram showing progression of sleep stages across a single night in a normal, healthy, young adult volunteer.

(From Carskadon MA, Dement WC: Normal human sleep: an overview. In Kryger MH, Roth T, Dement WC, editors: Principles and practice of sleep medicine, ed 5, St. Louis, 2011, Saunders.)

To gain the restorative benefits of sleep, it is necessary to cycle through the normal stages of sleep. NREM sleep provides physical restoration, whereas REM sleep provides psychic restoration. If such restoration does not occur because of sleep deprivation or sleep fragmentation, cognitive and physiologic disturbances will result. Within the spectrum of sleep-related breathing disorders, different outcomes may be seen. With primary snoring, the degree of airway resistance is such that vibration of the parapharyngeal soft tissues is the only result. No sleep fragmentation or disruption occurs, and no other impairment of airflow or oxygenation is noted. Generally accepted thought has been that primary snoring has no significant adverse health effects, but evidence now suggests that primary snoring may be a risk factor for type 2 diabetes, hypertension, carotid atherosclerosis, and stroke.^15–19

With OSA, increasing resistance to airflow occurs to the point of partial (hypopnea) obstruction or complete (apnea) obstruction and the cessation of breathing, despite efforts to continue to breathe. Depending on the degree and duration of the obstruction, hypoxia, anoxia, and hypercarbia may occur. These changes lead to CNS arousal and transition to a lighter stage of sleep (stage 1 or 2), stimulating partial awakening, relief of the obstruction, and resumption of breathing. Depending on the frequency of arousals during the night, sleep can be fragmented (Figure 9-5). Sleep quality is poor, and the restorative benefits of sleep are not achieved, leading to a variety of cognitive and physiologic abnormalities.

FIGURE 9-5 These sleep histograms show sleep study data for a 64-year-old male patient with obstructive sleep apnea syndrome. The left graph shows the sleep pattern before treatment. Note the absence of slow wave sleep (SWS), the preponderance of stage 1 (S1), and the very frequent disruptions. The right graph shows the sleep pattern in this patient during the second night of treatment with continuous positive airway pressure (CPAP). Note that sleep is much deeper (with more SWS) and more consolidated, and rapid eye movement (REM) sleep in particular is abnormally increased. The pretreatment REM percentage of sleep was only 10%, versus nearly 40% with treatment

(From Carskadon MA, Dement WC: Normal human sleep: an overview. In Kryger MH, Roth T, Dement WC, editors: Principles and practice of sleep medicine, ed 5, St. Louis, 2011, Saunders.)

Neurocognitive effects of OSA include sleepiness, decreased alertness, irritability, poor concentration, lack of libido, and memory loss. These deficits can lead to poor job performance, marital discord, interpersonal conflicts, and driving impairment. Up to 30% of traffic accidents involve sleepy drivers.²⁰ A systematic review investigating the relationship of crash risk and OSA found that drivers with OSA have a mean crash risk–to–OSA ratio of between 1.21 and 4.89.²¹

In addition to neurocognitive impairment, OSA is associated with numerous cardiovascular effects, including hypertension, stroke, congestive heart failure, pulmonary hypertension, and cardiac arrhythmia. OSA, which is now recognized as one of the treatable causes of hypertension,²² also has been shown to significantly increase the risks of stroke and death.²³ Patients with OSA have two- to four-fold greater odds of experiencing complex arrhythmias over those without the sleep disorder.²⁴ It also is thought that treatment of OSA may increase the survival rate among patients with heart failure.²⁵ In addition, a relationship between OSA, obesity, and metabolic syndrome has been noted.²⁶ Recent data from the Sleep Heart Health Study provide evidence for an independent relationship among sleep apnea, glucose intolerance, and insulin resistance that may lead to type 2 diabetes.²⁷ Overall, the mortality rate from all causes is significantly increased among people with untreated OSA and is proportional to the severity.²⁸

Signs and Symptoms

The signs and symptoms of sleep-related breathing disorders are those most often described by the bed partner or parent of a patient; they include snoring, snorting, gasping, and breath holding. Snoring is very common, as was previously indicated, and is the most common symptom in patients with OSA. However, most people who snore do not have OSA, but almost all patients with OSA snore. In the Wisconsin Sleep Cohort Study of subjects aged 30 to 60 years, 44% of men and 28% of women were habitual snorers, but only 4% of the men and 2% of the women had OSA.²⁹

Snoring may be very loud and disruptive to other members of the household. When snoring is the only complaint, the problem most often is primary snoring. If snoring is accompanied by daytime sleepiness and no breathing changes during sleep, UARS must be considered. Snoring accompanied by snorting, choking, gasping, or a complete cessation of breathing is likely to be a sign of OSA. Of note, however, definitive diagnosis of sleep-related breathing disorders cannot be made on the basis of clinical signs and symptoms alone.

Complaints of excessive daytime sleepiness are common in patients with OSA but are not specific, and the problem may be multifactorial. A commonly used subjective measure of sleepiness is the Epworth Sleepiness Scale³⁰ (Figure 9-6). This assessment tool has been validated in clinical studies and correlates with objective measures of sleepiness. It is composed of eight questions or situations in which patients are asked how likely they are to fall asleep. Each question is answered on a scale of 0 to 3, with 0 meaning no likelihood of falling asleep and 3 indicating 100% likelihood of falling asleep in that situation. The maximum possible score is 24. A score greater than 10 is indicative of significant daytime sleepiness but is not specific for sleep-related breathing disorders. Other complaints that may be associated with OSA are nocturia or enuresis, mood changes, memory or learning difficulties, erectile dysfunction, morning headache, and dry mouth noted upon awakening.

FIGURE 9-6 Epworth Sleepiness Scale.

(Redrawn from Johns MW: A new method for measuring daytime sleepiness: the Epworth sleepiness scale, Sleep 14:540-545, 1991.)

Obesity is common among patients with OSA. Obesity increases the risk of OSA several-fold; the most marked effects are observed during middle age.³¹ Approximately 70% of patients with OSA are obese.³² One measure of obesity is the body mass index (BMI), which is calculated by dividing weight in kilograms by the height in meters squared. Adults with a BMI greater than 25 are considered overweight, and those with a BMI over 30 are considered to be obese. Of interest, however, is that neck circumference has been found to be more closely related to severity of OSA than is BMI.³³ A neck circumference greater than 17 inches (43 cm) in men and greater than 16 inches (41 cm) in women is predictive of OSA.³⁴ Along with obesity and collar size, other physical features associated with OSA include mandibular retrognathia, long soft palate, large edematous uvula, large tongue, tonsillar and adenoidal hypertrophy, and a high-arched palate. In summary, the most useful predictors of OSA are witnessed apneas, excessive daytime sleepiness, male gender, BMI above 30, and neck circumference greater than 17 and 16 inches, respectively, for men and women.

Laboratory Diagnosis

Definitive diagnosis of a sleep-related breathing disorder is made by polysomnography, in which the patient’s brain waves, br/>