Sleep apnea overview

# Overview
Sleep apnea was first described in literature in the 19th century. It was often misdiagnosed as either narcolepsy or skepticism. There are three types of sleep apnea: obstructive, central, and mixed. The pathogenesis of obstructive sleep apnea includes upper airway anatomy defects, the inability of the upper airway dilator muscles to respond to respiratory challenge during sleep, inadequate arousal threshold, loop gain, and potential for state-related changes in lung volume. The pathogenesis of central sleep apnea involves chemoreceptors that modulate ventilation. Sleep apnea may be commonly caused by a large neck/abodminal circumference, administration of medications, diseases that narrow the respiratory airways, diseases that affect the central nervous system, or infectious diseases. The diagnosis of sleep apnea is listed in the DSM-V guidelines using either either the Apnea Hyponea Index (AHI) or the Respiratory Disturbance Index (RDI). Common symptoms in patients with sleep apnea include loud, chronic snoring, interruptions in breathing while sleeping, and somnolence. Generally, the most common signs of sleep apnea are a large waist/neck circumference and facial deformities. Polysomnography is diagnostic of sleep apnea and is recommended among all patients who are suspected to have sleep apnea during history-taking. Treatment often starts with behavioral therapy. The most effective treatments help open the airway such as continuous positive airway pressure (CPAP) and oral appliances. Primary prevention of sleep apnea involves lifestyle changes such as weight loss and smoking cessation, reconstruction of facial anomalies, and treatment of underlying medical causes. Secondary prevention of sleep apnea involves lifestyle changes. These methods reduce the severity of sleep apnea on the patient.

# Historical Perspective
Sleep apnea was first described in literature in the 19th century. It was often misdiagnosed as either narcolepsy or skepticism. In 1981, Collin Sullivan invented the continuous positive airway pressure (CPAP) for the treatment of sleep apnea. Prior to its recognition as a unique disorder, sleep apnea was viewed as either a type of insomnia or an age-related phenomenon.

# Classification
There are three types of sleep apnea: obstructive, central, and mixed. The majority of patients have obstructive sleep apnea (OSA). Individuals of untreated sleep apnea stop breathing repeatedly during the night usually for a minute or longer, during their sleep. Most of the time, these individuals are unaware of these episodes because the episodes don't trigger an awakening. Obstructive sleep apnea results from the narrowing or total blockage of the airway. In central sleep apnea, there is failure of the central nervous system to send appropriate signals to the muscles of respiration. These signals control the individual's breathing. It is also possible for an individual to have a combination of these two types, referred to as mixed apnea.

# Pathophysiology
The pathogenesis of obstructive sleep apnea includes upper airway anatomy defects, the inability of the upper airway dilator muscles to respond to respiratory challenge during sleep, inadequate arousal threshold, loop gain, and potential for state-related changes in lung volume. The pathogenesis of central sleep apnea involves chemoreceptors that modulate ventilation.

# Causes
Sleep apnea may be commonly caused by a large neck/abodminal circumference (e.g. obese individuals), administration of medications, diseases that narrow the respiratory airways (e.g. enlarged adenoids, enlarged tonsils), diseases that affect the central nervous system (e.g. cerebrovascular accident, spinal cord injury), or infectious diseases (e.g. polio).

# Differential Diagnosis
Sleep apnea must be differentiated from other diseases that cause loud snoring, fatigue, choking, coughing, and daytime sleepiness. To differentiate obstructive sleep apnea (OSA) and central sleep apnea, a polysomnogram should be performed. OSA will demonstrate evidence of thoracoabdominal effort, whereas central sleep apnea will not.

# Epidemiology and Demographics
The true prevalence of sleep apnea is difficult to estimate because mild cases may remain undiagnosed, and the majority of patients only present following the development of clinical manifestations. Sleep apnea is a chronic disorder, and clinical manifestations often develop as the disease progresses. Accordingly, elderly patients are more commonly diagnosed with sleep apnea than younger adults. Male gender and African American race are associated with higher prevalence of sleep apnea compared with female gender and other ethnicities.

# Risk Factors
The most common risk factor for the development of sleep apnea is large neck circumference. Other risk factors of  sleep apnea  include smoking, alcohol, sedatives, tranquilizers, males, a positive family history, certain ethnic backgrounds such as African Americans, and individuals over 60-65 years. Continuous positive airway pressure (CPAP) is a risk factor for complex sleep apnea (also known as mixed sleep apnea).

# Screening
There are no guidelines to screen for either obstructive or central sleep apnea among the general population. However, commercial drivers, operators of heavy equipment, pilots, and other occupations at risk of diurnal sleepiness should be screened by history and physical exam using standardizes questionnaires.

# Natural History, Complications, and Prognosis
Sleep apnea can begin with loud snoring and eventually lead to serious complications. Common symptoms include somnolence, depression, and headaches. More serious complications include cardiovascular diseases, stroke,  and hypertension. If sleep apnea is adequately treated, the prognosis is very good. If it is left untreated, patients can develop serious complications and have a poor prognosis.

# Diagnosis
The diagnosis of sleep apnea is listed in the DSM-V guidelines using either either the Apnea Hyponea Index (AHI) or the Respiratory Disturbance Index (RDI).

# History and Symptoms
Common symptoms in patients with sleep apnea include loud, chronic snoring, interruptions in breathing while sleeping, and somnolence. There are many non-specific symptoms that include morning headaches, mood changes, lack of concentration, and history of diseases such as CHF. Children have specific symptoms such as hyperactivity and behavior problems.

# Physical Examination
Generally, the most common signs of sleep apnea are a large waist/neck circumference and facial deformities. If sleep apnea is left untreated, signs of for pulmonale, stroke, hypoxemia, and pulmonary hypertension are evident.

# Diagnostic Studies

## Laboratory Findings
Laboratory tests are not diagnostic of sleep apnea. Occasionally evidence of anemia, polycythemia, proteinuria, hypercapnia, or low T4 may be found.

## Polysomnography
Polysomnography is diagnostic of sleep apnea and is recommended among all patients who are suspected to have sleep apnea during history-taking.

## Oximetry
Home oximetry is a portable monitor that records similar information to a polysomnogram. The results of home oximetry are not diagnostic, but may determine the need for polysomnography to either confirm or rule out sleep apnea.

## CT
Computed tomography (CT) is not diagnostic of sleep apnea, but can help visualize abnormal airway structures and crania-facial anomalies.

## MRI
Magnetic Resonance Imagine (MRI) is not diagnostic of sleep apnea, but can be used to identify anatomical structures that may be associated with the development of sleep apnea.

## Ultrasound
Ultrasound is not diagnostic of sleep apnea. Cor pulmonale and pulmonary hypertension may be evident among patients with severe sleep apnea on echocardiography.

## Other Diagnostic Studies
Other tests for sleep apnea include EEG, EMG, EOG, ECG, a nasal airflow sensor, and a snore microphone.

# Medical Therapy
If left untreated, sleep apnea can have serious and life-threatening consequences such heart disease, hypertension, automobile accidents due to somnolence, and many other ailments.  Treatment often starts with behavioral therapy. Medical treatment involves the treatment of the underlying cause and somnolence. Medications, such as acetazolamide and oxygen are not routinely used for the treatment of sleep apnea. The most effective treatments help open the airway such as continuous positive airway pressure (CPAP) and oral appliances.

# Surgery
Surgery, usually the second line of treatment, is usually very effective in treating snoring.  It could either be an inpatient or an outpatient procedure.  Several surgical options exist depending on the site of the obstruction in the airway.

# Primary Prevention
Primary prevention of sleep apnea involves lifestyle changes such as weight loss and smoking cessation, reconstruction of facial anomalies, and treatment of underlying medical causes.

# Secondary Prevention
Secondary prevention of sleep apnea involves lifestyle changes. These methods reduce the severity of sleep apnea on the patient.