What are sleep-related pulmonary diseases, classified according to American Academy of Sleep Medicine (AASM) guidelines, and how are they managed?

Sleep-Related Pulmonary Diseases: AASM Classification and Management

Overview

Sleep-related pulmonary diseases encompass three major categories according to the American Academy of Sleep Medicine: obstructive sleep apnea (OSA), central sleep apnea (CSA), and sleep-related hypoventilation syndromes. 1 These disorders represent distinct pathophysiologic mechanisms affecting ventilation during sleep, each requiring specific diagnostic and therapeutic approaches.

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1. Obstructive Sleep Apnea (OSA)

Definition and Pathophysiology

OSA is characterized by recurrent episodes of upper airway narrowing or collapse during sleep that impairs normal ventilation, resulting in repetitive apneas and hypopneas despite continued respiratory effort. 1 The ICSD-3 defines OSA as either: (1) an obstructive respiratory disturbance index (RDI) ≥5 events/hour with typical symptoms (unrefreshing sleep, daytime sleepiness, fatigue, insomnia, gasping/choking sensations, loud snoring, or witnessed apneas), or (2) an obstructive RDI ≥15 events/hour even without symptoms. 1

Prevalence and Risk Factors

• The prevalence is approximately 14% in men and 5% in women using an AHI cutoff ≥5 events/hour with symptoms. 1
• Substantially higher rates occur in specific populations: 70-80% in bariatric surgery candidates, 60-70% in stroke/TIA patients, and elevated rates in coronary artery disease, heart failure, arrhythmias, refractory hypertension, type 2 diabetes, and polycystic ovarian disease. 1
• Obesity and recent weight gain are strongly associated but not required for OSA presence. 1

Clinical Consequences

• Untreated OSA causes fragmented sleep, intermittent hypoxia and hypercapnia, intrathoracic pressure swings, and increased sympathetic activity, leading to daytime sleepiness, fatigue, impaired cognition, reduced quality of life, and increased motor vehicle accidents. 1
• OSA is an independent risk factor for hypertension, myocardial infarction, heart failure, and stroke. 1
• Healthcare utilization and costs are significantly elevated in untreated OSA. 1

Diagnostic Approach

• Polysomnography (PSG) is the standard diagnostic test for OSA, measuring sleep EEG, electromyography, eye movements, oronasal airflow, ECG, respiratory effort, and oxygen saturation. 1
• Home sleep apnea testing (HSAT) with technically adequate devices can be used for diagnosis in uncomplicated adult patients with signs/symptoms indicating increased risk of moderate to severe OSA. 1
• If a single HSAT is negative, inconclusive, or technically inadequate, PSG must be performed. 1
• PSG (not HSAT) is required for patients with significant cardiorespiratory disease, potential respiratory muscle weakness from neuromuscular conditions, awake hypoventilation or suspected sleep-related hypoventilation, chronic opioid use, history of stroke, or severe insomnia. 1
• Clinical tools, questionnaires, and prediction algorithms should not be used alone to diagnose OSA without PSG or HSAT. 1

Management

• Positive airway pressure (PAP) therapy is recommended for adult OSA patients with excessive sleepiness to improve this critical outcome. 1
• PAP therapy is suggested for adult OSA patients with impaired sleep-related quality of life (including snoring, nocturnal choking, insomnia, bed partner sleep disruption, morning headaches, nocturia, impaired productivity/social functioning, and daytime fatigue). 1
• Randomized controlled trials demonstrate PAP therapy lowers systolic blood pressure and improves quality of life. 1
• Nasal interfaces are preferred over oral or oronasal interfaces, and heated humidification should be used to minimize side effects. 1
• PAP therapy requires adequate follow-up to ensure treatment efficacy and adherence. 1

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2. Central Sleep Apnea (CSA)

Definition and Pathophysiology

CSA involves recurrent episodes of apnea during sleep resulting from temporary loss of ventilatory effort due to central nervous system or cardiac dysfunction, with complete cessation of both airflow and respiratory effort (distinguishing it from OSA where respiratory effort continues). 2 This represents a failure of respiratory drive rather than upper airway obstruction. 2

Clinical Presentations and Etiologies

• Congestive heart failure is a critical cause of CSA, manifesting through Cheyne-Stokes breathing and paroxysmal nocturnal dyspnea. 2
• Neuromuscular conditions causing respiratory muscle weakness can present as CSA due to hypoventilation during sleep. 2
• Other causes include structural brain lesions affecting respiratory control centers (particularly brainstem and cerebellum), chronic opioid or sedative use, renal failure, and treatment-emergent CSA from CPAP therapy. 3
• Patients may present with nocturnal gasping upon arousal, witnessed apneas, choking sensations, morning headaches, and daytime sleepiness. 2

Diagnostic Approach

• Polysomnography is mandatory to distinguish CSA from OSA, as both present with similar nocturnal symptoms including gasping. 2
• A comprehensive sleep evaluation with PSG is essential when nocturnal gasping occurs without confirmed OSA. 2
• In patients with ≥5 central apneas per hour, brain MRI should be performed to evaluate for structural lesions affecting respiratory control centers. 3
• Before attributing CSA to structural brain lesions, exclude more common etiologies: heart failure, atrial fibrillation, chronic opioid/sedative use, renal failure, and treatment-emergent CSA. 3

Management

• Adaptive servo-ventilation (ASV) is CONTRAINDICATED in patients with heart failure and reduced ejection fraction due to increased cardiovascular mortality demonstrated in the SERVE-HF trial. 1
• ASV provides dynamic breath-by-breath adjustment of inspiratory pressure support and auto-backup rate to normalize breathing. 1
• Do not treat central apnea and Cheyne-Stokes respiration with ASV in patients with chronic right-heart failure due to potential serious adverse effects. 4
• Treatment should focus on addressing underlying etiologies (optimizing heart failure management, discontinuing/reducing opioids when possible, treating renal disease). 3

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3. Sleep-Related Hypoventilation Syndromes

Definition and Pathophysiology

Sleep-related hypoventilation involves inadequate ventilation during sleep leading to elevated arterial CO2 levels, which can occur without discrete obstructive or central apneic events. 2 Sleep has well-recognized effects on breathing including changes in central respiratory control, airway resistance, and muscular contractility. 5

Specific Syndromes

Obesity Hypoventilation Syndrome (OHS)

• OHS presents with daytime hypoventilation that worsens during sleep, causing nocturnal dyspnea and gasping. 2
• Nocturnal respiratory events in OHS contribute to development of pulmonary hypertension, which is often severe. 4
• Treatment of sleep-disordered breathing is essential to improve pulmonary hemodynamics in OHS. 4

Overlap Syndrome (COPD + OSA)

• The combination of COPD and OSA causes more severe nocturnal hypoxemia than either disease alone and substantially greater risk of morbidity and mortality compared to either condition alone. 6
• Increased inflammatory markers are noted in overlap syndrome versus COPD alone. 7
• Treatment consists of continuous positive airway pressure and oxygen as needed; noninvasive ventilation may be helpful but requires further study. 6

COPD-Related Sleep Disorders

• Sleep-related hypoxemia and hypercapnia in COPD are most pronounced during REM sleep and may occur despite adequate awake oxygenation. 5
• Sleep studies are indicated in COPD patients when sleep apnea is suspected or when cor pulmonale/polycythemia are not explained by awake PaO2 levels. 5
• Supplemental oxygen therapy can acutely worsen hypoventilation in COPD and lead to disastrous consequences—recognition of hypoventilation is vital. 8
• Management includes optimizing COPD therapy, physiotherapy, prompt treatment of infections, supplemental oxygen (with caution), bronchodilators (particularly ipratropium bromide), theophylline, and noninvasive positive pressure ventilation. 5

Neuromuscular Disease-Related Hypoventilation

• Patients with respiratory muscle weakness exhibit rapid shallow breathing patterns during sleep and nocturnal hypoventilation commonly precedes daytime respiratory failure. 1, 2
• Disproportionate diaphragmatic involvement may cause nocturnal hypoventilation while upright vital capacity remains only moderately abnormal. 1
• Impaired ability to compensate for any coexisting obstructive sleep apnea leads to worsened hypercapnia and hypoxemia, with possible progression to cor pulmonale and cardiorespiratory failure. 1
• All patients should undergo polysomnography at diagnosis regardless of symptom history to objectively assess for obstructive sleep apnea or hypoventilation. 1

Diagnostic Evaluation

• Pulse oximetry and capnography should be routinely performed; if normal, arterial blood gas analysis is usually unnecessary. 1
• If capnography is unavailable, obtain venous bicarbonate and/or pCO2 or capillary blood pCO2 to assess for alveolar hypoventilation. 1
• Pulmonary function testing should include spirometric measurement of vital capacity, FEV1, maximal inspiratory pressure (MIP), and maximal expiratory pressure (MEP). 1
• Supine vital capacity measurement further evaluates diaphragm weakness. 1

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4. Pulmonary Hypertension in Sleep-Related Breathing Disorders

OSA and Pulmonary Hypertension

• "Pure" OSA is responsible for only a small increase in pulmonary arterial pressure whose clinical impact has not been demonstrated. 4
• Evidence suggests pulmonary arterial hypertension may occur with sleep-disordered breathing, although prevalence is low. 1
• Pulmonary hypertension in sleep-disordered breathing is most strongly associated with other risk factors: left-sided heart disease, parenchymal lung disease, nocturnal desaturation, and obesity. 1
• Treatment of sleep-disordered breathing with CPAP may lower pulmonary artery pressures when the degree of pulmonary hypertension is mild. 1

Sleep Disorders in Pulmonary Arterial Hypertension

• Patients with pulmonary arterial hypertension (PAH) or chronic thromboembolic pulmonary hypertension (CTEPH) are at risk of developing sleep-disordered breathing. 4
• Obstructive and central apnea, as well as worsening ventilation-perfusion mismatch, can occur during sleep in these patients. 4
• Diagnosis of OSA in patients with PAH or CTEPH should prompt treatment with CPAP, and isolated nocturnal hypoxemia should prompt long-term oxygen therapy to avoid worsening pulmonary hypertension. 4

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Key Clinical Pitfalls

• Do not assume all apneas are obstructive—PSG with assessment of respiratory effort is mandatory to distinguish central from obstructive events. 3
• In patients with marked respiratory muscle weakness, true obstructive events may be misscored as "central" on external sensors, requiring esophageal pressure monitoring. 3
• Vigorous arousals during respiratory events in OSA can produce behaviors clinically resembling REM behavior disorder; polysomnography is mandatory to establish RBD diagnosis and exclude other causes. 9
• Comorbid insomnia is frequently encountered in OSA patients and requires concurrent management. 1
• A comprehensive sleep evaluation is essential when OSA is suspected to identify or exclude other comorbid sleep complaints. 1, 9