Epidemiology and Classification

Epidemiology

• Most common sleep-related breathing disorder
• Incidence of approximately 20%–30% in men and 10%–15% in women (note that rates are similar between men and post-menopausal women)
• Prevalence increases with age with a plateau after the seventh decade.
• Obesity Obesity Obesity is a condition associated with excess body weight, specifically with the deposition of excessive adipose tissue. Obesity is considered a global epidemic. Major influences come from the western diet and sedentary lifestyles, but the exact mechanisms likely include a mixture of genetic and environmental factors. Obesity (body mass index [BMI] > 30) correlates strongly with obstructive sleep apnea (OSA).
• African Americans are more likely to develop OSA independent of age and BMI.
• Global prevalence more than doubled from 1990 to 2010 (may relate to increased detection and/or increased rates of obesity)

Classification

• Sleep Sleep Sleep is a reversible phase of diminished responsiveness, motor activity, and metabolism. This process is a complex and dynamic phenomenon, occurring in 4-5 cycles a night, and generally divided into non-rapid eye movement (NREM) sleep and REM sleep stages. Physiology of Sleep apnea:
  • Repeated cessation of breathing for > 10 seconds during sleep
  • Results in sleep interruption, fatigue, and daytime sleepiness 
• Obstructive sleep apnea:
  • Flaccid soft tissues obstruct airway, leading to hypoventilation during sleep
• Central sleep apnea (CSA):
  • Airflow limitation and/or ventilation problem mediated by aberrant central nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. General Structure of the Nervous System
  • May be hyper- or hypoventilation 
• Mixed sleep apnea:
  • Combination of both OSA and CSA
• Obesity Obesity Obesity is a condition associated with excess body weight, specifically with the deposition of excessive adipose tissue. Obesity is considered a global epidemic. Major influences come from the western diet and sedentary lifestyles, but the exact mechanisms likely include a mixture of genetic and environmental factors. Obesity hypoventilation syndrome (OHS):
  • Extra adipose tissue Adipose tissue Adipose tissue is a specialized type of connective tissue that has both structural and highly complex metabolic functions, including energy storage, glucose homeostasis, and a multitude of endocrine capabilities. There are three types of adipose tissue, white adipose tissue, brown adipose tissue, and beige or "brite" adipose tissue, which is a transitional form. Adipose Tissue in obese individuals leads to hypoventilation while awake.
  • Also known as Pickwickian syndrome

Risk Factors and Pathophysiology

Risk factors

• Obesity Obesity Obesity is a condition associated with excess body weight, specifically with the deposition of excessive adipose tissue. Obesity is considered a global epidemic. Major influences come from the western diet and sedentary lifestyles, but the exact mechanisms likely include a mixture of genetic and environmental factors. Obesity:
  • Condition of metabolic or nutritional nature
  • Characterized by accumulation of excess body fat
  • Assessed by BMI, ≥ 30 is considered obese
• Congenital or acquired craniofacial abnormalities: 
  • Abnormalities of the jaw Jaw The jaw is made up of the mandible, which comprises the lower jaw, and the maxilla, which comprises the upper jaw. The mandible articulates with the temporal bone via the temporomandibular joint (TMJ). The 4 muscles of mastication produce the movements of the TMJ to ensure the efficient chewing of food. Jaw and Temporomandibular Joint (micrognathia or retrognathia)
  • Tonsillar hyperplasia
  • Macroglossia
  • Neck circumference > 43 cm (17 in.)
  • Previous airway surgery
  • Nasal polyps (benign lesions of the nasal mucosa that typically present with postnasal drip and nasal obstruction; usually due to chronic inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation) or septal deviation
  • Hypertrophied pharyngeal muscles
• Advanced age: increased incidence > 65 years
• Alcohol consumption before sleep
• Use of sedatives
• Acromegaly Acromegaly Acromegaly and gigantism are caused by an excessive production of growth hormone (GH) by the pituitary gland. Acromegaly is usually produced by pituitary tumors secreting GH or, less commonly, by extrapituitary disorders. Acromegaly and Gigantism: excess production of growth hormone by the pituitary gland Pituitary gland The pituitary gland, also known as the hypophysis, is considered the "master endocrine gland" because it releases hormones that regulate the activity of multiple major endocrine organs in the body. The gland sits on the sella turcica, just below the hypothalamus, which is the primary regulator of the pituitary gland. Pituitary Gland
• Hypothyroidism Hypothyroidism Hypothyroidism is a condition characterized by a deficiency of thyroid hormones. Iodine deficiency is the most common cause worldwide, but Hashimoto's disease (autoimmune thyroiditis) is the leading cause in non-iodine-deficient regions. Hypothyroidism:
  • Deficiency of T3 and T4 hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview
  • Clinical features of hypothyroidism are primarily due to the accumulation of matrix substances and a decreased metabolic rate.
• Poor muscle tone due to brain injury or neuromuscular disease

Pathophysiology

• Sleep Sleep Sleep is a reversible phase of diminished responsiveness, motor activity, and metabolism. This process is a complex and dynamic phenomenon, occurring in 4-5 cycles a night, and generally divided into non-rapid eye movement (NREM) sleep and REM sleep stages. Physiology of Sleep results in loss of the wakefulness drive to breathe, decreased motor output to respiratory muscles, decreased upper airway (UA) size, increased UA resistance. 
  • Leads to apneic and hypopneic episodes in susceptible individuals
• Apneic and hypopneic episodes → increased arterial carbon dioxide (CO₂) levels (hypercapnia) → stimulates respiratory efforts against the narrowed upper airway until the individual is awakened
  • Hypercapnia → respiratory acidosis Respiratory acidosis The respiratory system is responsible for eliminating the volatile acid carbon dioxide (CO2), which is produced via aerobic metabolism. In the setting of hypoventilation, this acid load is not adequately blown off, and respiratory acidosis occurs. Renal compensation occurs after 3-5 days, as the kidneys attempt to increase the serum bicarbonate levels. Respiratory Acidosis
  • Increased respiratory efforts are achieved by sympathetic effects → secondary tachycardia and hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension
  • Reduced airflow results in pulmonary hypoxia which triggers pulmonary vasoconstriction (Euler-Liljestrand mechanism) → pulmonary hypertension Pulmonary Hypertension Pulmonary hypertension (PH) or pulmonary arterial hypertension (PAH) is characterized by elevated pulmonary arterial pressure, which can lead to chronic progressive right heart failure. Pulmonary hypertension is grouped into 5 categories based on etiology, which include primary PAH, and PH due to cardiac disease, lung or hypoxic disease, chronic thromboembolic disease, and multifactorial or unclear etiologies. Pulmonary Hypertension → cor pulmonale Cor Pulmonale Cor pulmonale is right ventricular (RV) dysfunction caused by lung disease that results in pulmonary artery hypertension. The most common cause of cor pulmonale is chronic obstructive pulmonary disease. Dyspnea is the usual presenting symptom. Cor Pulmonale

Clinical Presentation

• Often, the patient is unaware of their symptoms and is brought in by their spouse or sleep partner.
• Symptoms may include:
  • Nocturnal restlessness 
  • Vivid, strange, or threatening dreams 
  • Interrupted sleep, frequent awakenings
  • Snoring, choking, or gasping while asleep
  • Nocturia
  • Diminished ability to concentrate
  • Cognitive deficits
  • Irritability and other changes in mood
  • Morning headaches
  • Daytime sleepiness

Diagnosis

• Suspicion is raised based on a thorough history, including information from bed partner/spouse. A common questionnaire to estimate pretest probability Probability Probability is a mathematical tool used to study randomness and provide predictions about the likelihood of something happening. There are several basic rules of probability that can be used to help determine the probability of multiple events happening together, separately, or sequentially. Basics of Probability of OSA is:
  • STOP-BANG
    • Do you Snore loud enough to be heard through closed doors, or your bed partner elbows you for snoring at night?
    • Do you often feel Tired, fatigued, or sleepy during the day?
    • Has anyone Observed you stop breathing, or choking/gasping during your sleep?
    • Do you have or are you being treated for high blood Pressure?
    • B MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction > 35 kg/m²
    • Age older than 50 years?
    • Neck size large: male > 17 inch shirt collar and female > 16 inch shirt collar
    • Gender: male?
  • Low risk of OSA: Yes to 0–2 questions
  • Intermediate risk of OSA: Yes to 3–4 questions
  • High risk of OSA: Yes to 5–8 questions
• Polysomnography (PSG): gold-standard diagnostic test for OSA
  • Patient is monitored on video overnight while hooked up to electrocardiogram Electrocardiogram An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) ( ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG)), electroencephalogram (EEG), pulse oximetry, and nasal prongs to assess snoring, sleep architecture, and physiologic changes during sleep. 
  • The severity of OSA can be determined from the Apnea/Hypopnea index (AHI), which is calculated as the number of apneic episodes per hour of sleep during a sleep study.
    • AHI > 5 = mild OSA
    • AHI > 15 = moderate OSA
    • AHI > 30 = severe OSA
  • If EEG monitoring is used, then the arousal index (AI) can be calculated as the number of arousals per hour of sleep.

Management

Conservative management

Improving modifiable risk factors:

• Weight loss 
• Cessation of consumption of sedatives/alcohol
• Oral appliances or splints during sleep to prevent airway collapse/obstruction

Positive airway pressure devices

• Continuous positive airway pressure (CPAP): most effective treatment method
  • Noninvasive ventilation that uses positive air pressure to keep airways open
  • Improves restlessness, snoring, cognition, daytime somnolence and quality of life
  • Low adherence rate
• Bilevel positive airway pressure (BiPAP): provides a higher pressure during inhalation and a lower one during exhalation

Surgery

• Resection of nasal polyps 
• Nasal septal deviation correction
• Reduction of enlarged tonsils or hypertrophied inferior turbinates
• Uvulopalatopharyngoplasty: resection of uvula, soft palate Palate The palate is the structure that forms the roof of the mouth and floor of the nasal cavity. This structure is divided into soft and hard palates. Oral Cavity: Palate, tonsils, and excess oropharyngeal tissue
• Maxillomandibular advancement for patients with retrognathia or micrognathia
• Tracheotomy: only used in severe refractory life-threatening OSA
• Bariatric surgery Bariatric surgery Bariatric surgery refers to a group of invasive procedures used to surgically reduce the size of the stomach to produce early satiety, decrease food intake (restrictive type) and/or alter digestion, and artificially induce malabsorption of nutrients (malabsorptive type). The ultimate goal of bariatric surgery is drastic weight loss. Bariatric Surgery

Clinical Relevance

Possible complications of obstructive sleep apnea:

• Hypertension: condition defined as a systolic blood pressure ≥ 130 mm Hg and/or a diastolic blood pressure ≥ 80 mm Hg
• Stroke: acute neurological condition characterized by an impairment in the arterial blood supply to brain tissue. Usually due to a focal vascular cause, such as an embolism or the rupture of an aneurysm Aneurysm An aneurysm is a bulging, weakened area of a blood vessel that causes an abnormal widening of its diameter > 1.5 times the size of the native vessel. Aneurysms occur more often in arteries than in veins and are at risk of dissection and rupture, which can be life-threatening. Extremity and Visceral Aneurysms 
• Dementia: term used to group diseases and conditions characterized by a decline in memory, language, problem-solving, and other executive functioning skills
• Pulmonary hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension: condition of chronically elevated mean pulmonary arterial pressure ≥ 20 mm Hg
• Cor pulmonale: also known as right-sided heart failure, a condition characterized by an alteration in the structure and function of the right ventricle of the heart due to a primary disorder of the respiratory system
• Respiratory failure Respiratory failure Respiratory failure is a syndrome that develops when the respiratory system is unable to maintain oxygenation and/or ventilation. Respiratory failure may be acute or chronic and is classified as hypoxemic, hypercapnic, or a combination of the two. Respiratory Failure: insufficient levels of oxygen in the systemic bloodstream, due to inadequate oxygenation of blood or inadequate ventilation or both
• Cardiac disorders:
  • Arrhythmia: abnormality in the rate or rhythm of the heartbeat
  • Myocardial infarction Myocardial infarction MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction: ischemic damage to the myocardium, which occurs when blood flow is reduced or completely obstructed to a part of the heart
  • Sudden cardiac death: sudden, unexpected death as a result of cardiac arrest Cardiac arrest Cardiac arrest is the sudden, complete cessation of cardiac output with hemodynamic collapse. Patients present as pulseless, unresponsive, and apneic. Rhythms associated with cardiac arrest are ventricular fibrillation/tachycardia, asystole, or pulseless electrical activity. Cardiac Arrest. This occurs within 1 hour of symptom onset. Usually caused by acute coronary syndrome