1. Obstructive Sleep Apnoea

1.1 Epidemiology

• Definition
  • OSA is a sleep-disordered breathing syndrome in which pharyngeal collapse or partial narrowing during sleep leads to apnoeic/hypopnoeic episodes, resulting in intermittent hypoxia and arousal from sleep.
• Prevalence
  • Estimated 1–2% in men and 0.5–1% in women aged 30–65 years, though many cases remain undiagnosed.
• Significance
  • Increases the risk of road traffic accidents by 2–7 times.
  • Strong association with obesity and other comorbidities (cardiovascular disease, diabetes).

1.2 Aetiology

• Pathophysiology
  • Reduced tone in the upper pharyngeal muscles during sleep → partial or total airway collapse → snoring or apnoeic episodes.
  • Repeated hypoxia and partial awakenings fragment sleep, causing daytime somnolence and reduced cognitive performance.
• Risk Factors
  • Modifiable: BMI >30 kg/m², thick neck circumference (>43 cm in men, >41 cm in women), nasal obstruction, alcohol use, sedatives, hypothyroidism, diabetes.
  • Non-modifiable: Male sex, older age (>40 years), certain craniofacial traits (micrognathia, retrognathia), acromegaly, perimenopausal status, family history of OSA.

1.3 Clinical Features

• Night-Time Symptoms
  • Snoring (often loud or disruptive).
  • Choking or gasping episodes.
  • Witnessed apnoeas by a partner.
• Daytime Effects
  • Excessive daytime sleepiness (EDS), measured by Epworth Sleepiness Scale.
  • Unrefreshed upon waking.
  • Reduced concentration, short-term memory impairment, personality change.
  • Nocturia, morning headaches, possibly decreased libido.
• Complications
  • Hypertension, arrhythmias, coronary artery disease, stroke, type II diabetes, pulmonary hypertension, cor pulmonale, motor vehicle accidents from somnolence.

1.4 Diagnosis

1. Clinical Assessment
   • History of excessive daytime sleepiness, tiredness, and repeated nocturnal episodes of gasping or apnoea.
   • The Epworth Sleepiness Scale quantifies sleepiness (score >9 is abnormal).
2. Physical Examination
   • Weight: Obesity is a key risk factor.
   • Neck circumference: >43 cm (men), >41 cm (women).
   • Nasal patency, pharyngeal appearance (Mallampati score).
   • Check for hypothyroidism, acromegaly, or craniofacial abnormalities.
3. Investigations
   • Thyroid function tests: TSH for hypothyroidism.
   • Full blood count: Exclude polycythaemia.
   • Overnight oximetry: A screening method. Sawtooth desaturation pattern is suggestive of OSA but not definitive.
   • Polysomnography (gold standard): Measures EEG, ECG, EMG, airflow, oxygen saturation, thoracoabdominal movement.
     • An apnoea–hypopnoea index (AHI) ≥5 episodes/h indicates sleep apnoea; >30 is severe.

1.5 Immediate Management

• Lifestyle Modifications
  • Weight reduction (if obese) and exercise.
  • Reduce or eliminate alcohol and sedative medication usage.
  • Stop smoking to mitigate upper airway inflammation.
  • Driving: Advise patients not to drive if feeling sleepy; they must inform the DVLA if diagnosed with OSA and daytime somnolence, especially if they drive vocationally.

1.6 Long-Term Management

• Untreated OSA predisposes to hypertension, stroke, arrhythmias, and higher mortality, especially in obese individuals.
• Mechanical Therapy
  • Mandibular Advancement Device: For mild disease or those intolerant of CPAP. It advances the jaw anteriorly, increasing pharyngeal diameter.
  • CPAP (Continuous Positive Airway Pressure): First-line therapy for moderate to severe OSA. Keeps the upper airway open via positive pressure, improving oxygenation and sleep quality.
  • Potentially improves long-term cardiovascular outcomes.
• Surgical Interventions
  • Correctable upper airway lesions (deviated septum, nasal polyps, enlarged tonsils/adenoids).
  • Bariatric surgery if morbidly obese with severe OSA.
• Prognosis
  • Excellent if patients tolerate and adhere to CPAP or other interventions, with improvement in daytime alertness, potential reduction in cardiovascular mortality.

2. Obesity Hypoventilation Syndrome

2.1 Epidemiology

• Definition
  • Obesity hypoventilation syndrome (OHS) is a sleep-related ventilatory disorder in people with severe obesity, characterised by night-time hypoventilation rather than upper airway obstruction (as in obstructive sleep apnoea).
• Prevalence
  • Exact prevalence is unknown.
  • Up to 15% of patients suspected to have obstructive sleep apnoea actually have OHS, either alone or in combination.
• Increasing Recognition
  • Growing awareness and the availability of diagnostic tests have led to more diagnoses in recent years.

2.2 Aetiology

• Pathophysiology
  • Excess adipose tissue around the chest and abdomen restricts normal chest wall expansion, contributing to hypoventilation during sleep.
  • This under-ventilation leads to chronic hypercapnia (raised PaCO₂) and type 2 respiratory failure, distinct from the intermittent airway obstruction seen in obstructive sleep apnoea.

2.3 Risk Factors

• Severe Obesity
  • Typically with a BMI in the high obese range.
• Overlap with OSA
  • Some patients have both obstructive sleep apnoea and obesity hypoventilation.

2.4 Symptoms

• Similar to Obstructive Sleep Apnoea
  • Daytime hypersomnolence, morning headaches, personality changes, memory and concentration difficulties.
• Daytime Hypercapnia
  • Waking hypercapnia leading to early morning headache and fatigue.
• Acute Decompensation
  • Patients can present with an acute exacerbation of type 2 respiratory failure, causing severe drowsiness or coma.

2.5 Diagnosis

1. Clinical Suspicion
   • Severe obesity plus daytime somnolence, hypercapnia, or repeated episodes of decompensation.
2. Sleep Study
   • Documents nocturnal hypoventilation (rather than apnoeic episodes).
3. Arterial Blood Gases
   • Raised PaCO₂ (>6 kPa) during the day is critical for diagnosis.
4. Pulmonary Function Tests
   • Restrictive defect (↓ lung volumes) with preserved transfer factor.
5. Additional Testing
   • Chest X-Ray, ECG, Echo: May reveal pulmonary hypertension or right-sided cardiac strain/failure (cor pulmonale).

2.6 Immediate Management

• Weight Loss
  • Primary, definitive intervention; bariatric surgery may be needed for sustained weight reduction.
• Ventilatory Support
  • Overnight CPAP can worsen hypercapnia in some patients.
  • Non-invasive ventilation (NIV) is typically required to correct the hypoventilation, especially during acute exacerbations of type 2 respiratory failure.
• Treat Associated Conditions
  • Address cor pulmonale if present, and manage any coexisting obstructive sleep apnoea, COPD, or cardiac failure.

2.7 Long-Term Management

• Lifestyle Interventions
  • Continued focus on weight management, exercise, diet.
• Monitoring
  • Serial arterial blood gas checks, sleep studies, and cardiovascular assessment to detect emerging complications.
• Prognosis
  • Generally good if OHS is recognised early and treated.
  • Untreated severe OHS can lead to progressive cor pulmonale, recurrent hospital admissions, and increased mortality.

3. Chest Wall and Neuromuscular Disorders

3.1 Epidemiology

• Definition
  • A group of conditions in which weakness of the respiratory muscles (due to neuromuscular disease) or chest wall abnormalities leads to hypoventilation, predominantly type 2 respiratory failure (high PaCO₂, low PaO₂).
• Prevalence
  • Precise prevalence varies because of the spectrum of neuromuscular disorders (e.g. motor neurone disease, muscular dystrophies, spinal cord lesions) and various chest wall deformities (kyphoscoliosis, severe obesity, etc.).

3.2 Aetiology

• Neuromuscular Weakness
  • Examples include motor neurone disease, muscular dystrophy, myasthenia gravis, polio, Guillain–Barré syndrome, cervical spinal cord lesions.
  • Diaphragmatic paralysis from phrenic nerve damage.
• Chest Wall Abnormalities
  • Kyphoscoliosis, severe obesity (see obesity hypoventilation syndrome), chest deformities from congenital or traumatic causes.
• Pathophysiology
  • The mechanical inefficiency of breathing (due to muscle weakness or rigid chest wall) → inadequate ventilation, especially at night, leading to chronic CO₂ retention (type 2 respiratory failure).
  • Hypoventilation worsens during sleep because accessory muscle use and neural drive to breathe are reduced.

3.3 Risk Factors

• Underlying Neuromuscular Conditions
  • Hereditary myopathies, progressive neurological diseases, autoimmune disorders (e.g. myasthenia gravis).
• Severe Chest Wall Deformities
  • Long-standing kyphoscoliosis or chest trauma.
• Coexisting Obesity
  • Compounds hypoventilation, as in obesity hypoventilation syndrome.

3.4 Symptoms

• Nocturnal Hypoventilation
  • Sleep disruption, morning headaches (due to overnight CO₂ retention), unrefreshing sleep.
• Daytime Somnolence
  • Fatigue, excessive daytime sleepiness.
• Signs of Type 2 Respiratory Failure
  • Dyspnoea on exertion, potential confusion, drowsiness.
  • In advanced cases, cor pulmonale (raised JVP, peripheral oedema).
• Potential Overlap
  • Some patients with neuromuscular disease or severe chest wall issues may also have components of obstructive sleep apnoea.

3.5 Diagnosis

1. Clinical Assessment
   • History of neuromuscular disease, chest wall deformity, or progressive muscle weakness.
   • Reports of morning headache, daytime hypersomnolence, or repeated chest infections.
2. Arterial Blood Gases (ABG)
   • Type 2 respiratory failure: PaO₂ <8 kPa with PaCO₂ >6 kPa.
   • Often normal or near-normal pH initially if chronic compensation, but can decompensate with acute exacerbations.
3. Pulmonary Function Tests
   • Restrictive pattern (reduced lung volumes), but alveolar–arterial gradient or transfer factor may be relatively preserved if lung parenchyma itself is unaffected.
4. Sleep Studies
   • Might show hypoventilation throughout sleep, distinct from apnoeic episodes typical of OSA. Nocturnal oximetry or polysomnography documents persistent hypercapnia.
5. Other Tests
   • Imaging (chest X-ray) to identify severe spinal curvature or other chest wall deformities.
   • Neurological investigations (electromyography, nerve conduction studies) if indicated.

3.6 Immediate Management

1. Treatment of Acute Decompensation
   • If a patient presents with acute on chronic type 2 respiratory failure (elevated CO₂ and low pH), manage with non-invasive ventilation (NIV) in hospital.
   • Treat any triggering factor such as infection or sedation that has worsened their ventilatory compromise.
2. Supportive Oxygen
   • Cautious use of controlled oxygen therapy to maintain target saturations, avoiding overtreatment that may further increase CO₂ retention.
3. Identify Reversible Elements
   • Stop any sedative medications.
   • Monitor for hypothyroidism or other correctable causes of hypoventilation.

3.7 Long-Term Management

1. Nocturnal Non-Invasive Ventilation (NIV)
   • Essential once chronic type 2 respiratory failure develops.
   • Significantly reduces hospital admissions and extends survival in non-progressive disorders.
2. Address Underlying Disease
   • Physical therapy, disease-specific treatments (e.g. immunosuppressants for myasthenia gravis), spine surgery if feasible for severe kyphoscoliosis.
3. Lifestyle Modification
   • Weight reduction if obesity coexists, smoking cessation.
   • Vaccinations (influenza, pneumococcal) to reduce infection risk.
4. Prognosis
   • Varies based on the nature of the underlying neuromuscular disease or chest wall deformity.
   • In stable or slowly progressive conditions, NIV can significantly prolong life and improve quality of life.