Obstructive sleep apnea

Obstructive sleep apnea (OSA) is the most common breathing-related sleep disorder and is typically associated with obesity. It is characterized by obstruction of the upper airways due to the collapse of the pharyngeal muscles. OSA results in multiple episodes of interrupted breathing (apnea and hypopnea) during sleep, which leads to alveolar hypoventilation. Affected individuals generally suffer from severe daytime sleepiness and impaired cognitive function (e.g., deficits in attention and/or memory) as a result of sleep disruption. Their partners commonly describe observing restless sleep associated with irregular snoring, gasping, or choking episodes. Diagnosis is based on the assessment of risk factors and polysomnography. Many patients with OSA (> 50%) are affected by secondary hypertension. The cardiovascular consequences of secondary hypertension reduce life expectancy. However, these effects can be counteracted with weight loss and nightly continuous positive airway pressure (CPAP). Other important aspects of management include avoidance of precipitating factors (e.g., alcohol) and improvement of sleep hygiene.

• Obstructive sleep apnea (OSA): breathing-related sleep disorder in which airflow significantly decreases or ceases because of upper airway obstruction (typically the oropharynx)
• Apnea: respiratory arrests of ≥ 10 seconds
• Hypopnea: reduction of airflow by ≥ 30% of pre-event baseline for ≥ 10 seconds in combination with reduction of blood oxygenation by ≥ 3% or EEG arousal

References:^[1]

• Sex: ♂ > ♀ (2:1)
• Prevalence: ∼ 20–30% in men and 10–15% in women

References:^[1][2][3][4]

Epidemiological data refers to the US, unless otherwise specified.

• Obstruction of the upper airways due to the collapse of the pharyngeal muscles during sleep
• Risk factors
  • Obesity, especially around the neck (short, wide “bull neck”)
  • Structural abnormalities that impair respiratory flow: adenotonsillar hyperplasia (especially in children), nasal septum deviation, previous upper airway surgery, enlarged uvula, tongue, or soft palate (especially in adults), overbite with a small chin; , hypertrophied pharyngeal muscles, nasal polyps
  • Alcohol consumption before sleep
  • Intake of sedatives and/or beta-blockers before sleep
  • Smoking
  • Family history
  • Acromegaly
  • Hypothyroidism

Obesity is the most important risk factor for OSA.

References:^[3][5]

• Obstruction of the upper airways → apnea → ↓ partial pressure of oxygen in arterial blood (PaO₂), ↑ partial pressure of carbon dioxide in arterial blood (PaCO₂, also known as hypercapnia)
  • → ↑ Hypoxic pulmonary vasoconstriction → ↑ pulmonary hypertension → cor pulmonale
  • → ↑ Sympathetic activity → secondary hypertension
  • → Respiratory acidosis; → renal compensation; → increased HCO₃ retention and decreased chloride reabsorption

References:^[1][6][7]

• Restless sleep with waking, gasping, or choking
• Loud, irregular snoring with apneic episodes (third-party reports)
• Excessive daytime sleepiness (e.g., patient falls asleep, microsleep during meetings or while watching TV)
• Impaired cognitive function; (e.g., impaired concentration, memory loss)
• Depression, decreased libido

References:^[1][3]

General considerations

• Initial assessment: standardized questionnaires and third-party reports; (interview sleeping partner regarding snoring and respiratory interruptions)
• Laboratory tests are not usually considered useful in the diagnosis of OSA, but may help identify underlying conditions or physiological consequences of OSA.
  • Polycythemia (↑ Hct, ↑ Hb): This occurs because hypoxia induces erythropoietin secretion by the kidneys, which stimulate the blood marrow, leading to increased RBC production.
  • TSH (thyroid-stimulating hormone) may be considered in patients with possible hypothyroidism.
  • PaO₂ is usually normal during the day.

Sleep studies

• Polysomnography: first-line method; a test that records physiologic variables during sleep (including sleep stages, respiratory flow, respiratory pauses, and oxygen saturation); it may also help to identify the type of sleep disorder and associated conditions (e.g., seizures)
  • Classic findings
    • Apnea and hypopnea events; cease on arousal
    • Oxygen desaturation
    • Arousal events on EEG
    • ↑ Pulse pressure
    • Bradycardia
    • Fragmentation of sleep with pathological reduction of REM-sleep phases and slow-wave sleep
• Home sleep apnea testing (less sensitive): ambulatory screening method based on the use of a device for monitoring cardiorespiratory parameters during the night.
  • Indicated in patients with a high pretest probability of moderate to severe OSA or when in-laboratory polysomnography is not feasible

Obstructive sleep apnea is a very frequent cause of secondary hypertension!

References:^[1][8][9]

Central sleep apnea (CSA)

• Definition: Breathing-related sleep disorder characterized by repetitive cessation or decrease of respiratory effort during sleep due to impaired function of the respiratory center. Airway obstruction is absent.
• Etiology: idiopathic or caused by an underlying disorder
• Risk factors
  • Age > 65 years
  • Male sex
  • Heart failure
  • Central nervous system disease; (e.g., trauma, brainstem tumor, stroke)
  • Certain drugs (e.g., chronic opioid use)
• Pathophysiology: lack of stimulation to the respiratory center with patent upper airways → periodic lack of respiratory muscle innervation → interruption of thoracic and/or abdominal respiratory movements
• Clinical features
  • Morning headaches
  • Repeated waking at night
  • Daytime sleepiness
  • Snoring
  • Association with OSA is very common
  • Possibly Cheyne-Stokes breathing (especially in patients with heart failure)
• Diagnosis
  • Based on clinical history (e.g., underlying conditions such as heart failure or stroke)
  • Polysomnography
• Treatment
  • Treat underlying disorder (if present)
  • CPAP

The 3 C’s of Central sleep apnea are Congestive heart failure, CNS trauma or toxicity, and Cheyne-Stokes breathing.

Obesity hypoventilation syndrome (Pickwickian syndrome)

• Definition: : a breathing disorder that only affects morbidly obese individuals; ; frequently accompanied by OSA, it is characterized by diurnal hypercapnia
• Etiology: obesity (BMI ≥ 30 kg/m²)
• Risk factors: identical to those of obesity
• Pathophysiology: obesity reduces inspiratory muscle strength and restricts respiratory excursions → alveolar hypoventilation, sleep-disordered breathing (e.g., OSA), and failure of ventilatory compensatory mechanisms → decreased PaO₂ and increased PaCO₂ during sleep (PaCO₂ retention extends to the waking hours)
• Clinical features
  • Same symptoms as those of OSA
  • Headaches and severe sleepiness
• Diagnostic criteria
  • BMI ≥ 30 kg/m²
  • Arterial blood gasses showing diurnal hypercapnia (PaCO₂ > 45 mm Hg) that cannot not be explained by another condition
  • Polysomnography shows hypoventilation during sleep with or without obstructive apnea events.
• Treatment
  • Weight loss
  • Nasal intermittent positive pressure ventilation

References:^{[10][11][12][13]}

The differential diagnoses listed here are not exhaustive.

• Mild to moderate OSA (mild symptoms and < 20 apneic episodes)

  • Weight loss
  • Reduce and/or avoid risk factors: alcohol, nicotine, sedatives (e.g., benzodiazepines)
  • Sleep hygiene: regular and sufficient sleep
  • Lateral as opposed to supine sleeping position
  • Blood pressure control
  • Oral appliances
• Severe OSA (> 20 apneic episodes and alterations in arterial oxygen saturation)
  • Surgery (uvulopalatopharyngoplasty)
    • Resection of the uvula and redundant retrolingual, soft palate, and tonsillar tissue
    • This procedure should only be considered as a supplementary treatment.
  • Bilevel positive airway pressure (BPAP)
  • Continuous positive airway pressure (CPAP)

Nocturnal positive pressure therapy via CPAP is the therapy of choice in symptomatic OSA. The success of therapy is highly dependent on patient adherence and regular monitoring with sleep studies!
References:^[14][15]

• Systemic hypertension
• Hypoxia-induced cardiac arrhythmia (e.g., (atrial fibrillation, atrial flutter)
• Pulmonary hypertension and cor pulmonale
• Global respiratory insufficiency
• Cardiac infarction, stroke, and sudden cardiac death (the risk of sudden death is high in infants and the elderly)
• Polycythemia
• Risk of accidents (e.g., car crashes, occupational accidents) due to microsleep
• Increased risk of developing vascular dementia
• Poor sleep leads to increased appetite and obesity.

References:^{[1][16][17][18][19][20]}

We list the most important complications. The selection is not exhaustive.

• The mortality rate is higher in patients with severe OSA who do not receive adequate treatment.
• CPAP ventilation can significantly lower the risk of mortality in OSA.

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