Step 2 CK · Internal Medicine · Pulmonology

Sleep-Disordered Breathing & Pulmonary HTN

Name: Sleep-Disordered Breathing & Pulmonary HTN
Creator: Veli Bakalov, MD

From apnea to pulmonary pressures: CPAP, catheters, and vasodilators

Pulmonology·Pulmonary Vascular & Sleep Disorders·4 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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OSA = repetitive upper-airway collapse with continued respiratory effort; risk factors are obesity, large neck, male sex, retrognathia (tonsillar enlargement in children).
Diagnose OSA with polysomnography (or a home sleep test); AHI under 5 normal, 5–15 mild, 15–30 moderate, over 30 severe; the Epworth scale quantifies daytime sleepiness.
CPAP is first-line for OSA (plus weight loss, avoiding alcohol/sedatives, positional therapy); untreated OSA causes resistant hypertension, atrial fibrillation, pulmonary hypertension, stroke, MI, and crashes.
Central sleep apnea = apnea without effort (heart failure/stroke with Cheyne-Stokes breathing, opioids, altitude); adaptive servo-ventilation is avoided in low-EF HFrEF.
Obesity hypoventilation = BMI ≥30 with awake PaCO2 over 45 (raised bicarbonate) not explained otherwise; most also have OSA; treat with CPAP if severe OSA coexists, otherwise NIV (BiPAP), plus weight loss.
Pulmonary hypertension = mean PA pressure >20 mmHg (older definition ≥25); echo screens, right-heart catheterization confirms and measures wedge, PVR, and vasoreactivity.
WHO groups: 1 PAH (idiopathic, BMPR2, scleroderma, HIV, drugs, congenital), 2 left heart (most common, wedge over 15), 3 lung/hypoxia, 4 CTEPH (screen with V/Q; curable by thromboendarterectomy), 5 multifactorial.
PAH (group 1) drugs: endothelin antagonists (bosentan, ambrisentan), PDE-5 inhibitors (sildenafil, tadalafil), prostacyclins (epoprostenol, treprostinil), riociguat; start most with ERA plus PDE-5 inhibitor combination; CCBs only if vasoreactivity-positive; never for group 2.
Cor pulmonale = RV failure from lung-disease PH: raised JVP, loud P2, RV heave, tricuspid regurgitation, hepatomegaly, ascites, and edema.

Obstructive sleep apnea

Mechanism. In obstructive sleep apnea (OSA), the upper airway collapses repeatedly during sleep. The patient keeps trying to breathe against the closed airway, which causes apneas and hypopneas, intermittent hypoxemia, and repeated arousals that fragment sleep. Risk factors are obesity, a large neck circumference, male sex, and retrognathia; in children, enlarged tonsils and adenoids.

Presentation. Loud snoring, witnessed apneas, and gasping, with nonrestorative sleep. Daytime symptoms are excessive sleepiness (quantified by the Epworth Sleepiness Scale), morning headaches, and poor mood or concentration. The bed partner's history is key. Questionnaires such as STOP-BANG help screen for OSA.

Diagnosis. In-lab polysomnography, or a home sleep test in uncomplicated patients with high pretest probability. Severity is graded by the apnea-hypopnea index (AHI), the number of events per hour; each apnea or hypopnea lasts ≥10 seconds.

NormalAHI <5.
MildAHI 5–15.
ModerateAHI 15–30.
SevereAHI >30.

Treatment. CPAP, which splints the airway open, is first-line. Add weight loss, avoidance of alcohol and sedatives, and positional therapy (avoid sleeping supine). Alternatives for selected patients who cannot use CPAP are mandibular-advancement oral appliances, hypoglossal-nerve stimulation, and surgery such as uvulopalatopharyngoplasty. In children, adenotonsillectomy is first-line. Wake-promoting drugs such as modafinil are only adjuncts for sleepiness that persists despite adequate CPAP, never a replacement for it.

Untreated OSA causes systemic hypertension (often resistant to several drugs), atrial fibrillation and other arrhythmias, pulmonary hypertension with cor pulmonale, stroke, myocardial infarction, and motor-vehicle accidents from sleepiness. Treatment lowers blood pressure and cardiovascular risk.

Central apnea and obesity hypoventilation

Three sleep-related breathing disorders

Feature	Obstructive sleep apnea	Central sleep apnea	Obesity hypoventilation
Core problem	Airway collapse; effort continues	No respiratory effort during the apnea	Awake daytime hypercapnia in an obese patient
Key associations	Obesity, large neck, male sex, retrognathia	Heart failure and stroke (Cheyne-Stokes breathing), opioids, high altitude	BMI ≥30; most patients also have OSA
Diagnostic clue	AHI ≥5 on polysomnography	Apneas without chest or abdominal movement	PaCO2 >45 awake, not explained by another cause; raised bicarbonate
Treatment	CPAP plus weight loss	Treat the cause; adaptive servo-ventilation for selected patients	CPAP if severe OSA coexists; NIV (BiPAP) otherwise or if CPAP fails; weight loss

Effort without airflow means obstructive apnea; no airflow and no effort means central apnea. Cheyne-Stokes breathing is a crescendo-decrescendo pattern alternating with central apneas.

Adaptive servo-ventilation (ASV). ASV helps selected patients with central apnea but is avoided in heart failure with a low ejection fraction (HFrEF), where it increased mortality.

Obesity hypoventilation syndrome (Pickwickian syndrome). Chronic hypercapnia leads to renal retention of bicarbonate, so a high serum bicarbonate in an obese, sleepy patient is a clue. Patients may develop polycythemia, pulmonary hypertension, and cor pulmonale. Treat with positive airway pressure: CPAP first when severe OSA coexists, as it does in most patients, and NIV (BiPAP) when severe OSA is absent or hypercapnia persists on CPAP; add weight loss, including bariatric surgery for selected patients.

Pulmonary hypertension: definition and diagnosis

Definition. Pulmonary hypertension (PH) is a mean pulmonary artery pressure >20 mmHg at rest (2022 ESC/ERS definition); the older threshold was ≥25 mmHg.

Clinical picture. Progressive exertional dyspnea and fatigue, with exertional syncope or chest pain as the disease advances. The exam shows a loud P2. Right-heart failure adds further signs (see cor pulmonale).

EchocardiogramScreening test: estimates RV systolic pressure and assesses RV size and function.
Right-heart catheterizationGold standard: confirms PH and measures wedge pressure, PVR, and vasoreactivity.
V/Q scanScreens for operable CTEPH.
PFTs, overnight oximetry or sleep study, serologiesFind lung disease, sleep-disordered breathing, or connective tissue disease.

A V/Q scan, not CT, is the preferred screen for chronic thromboembolic PH. A normal scan effectively excludes CTEPH.

The five WHO groups

WHO classification of pulmonary hypertension

Group	Causes	Hemodynamics	Treatment focus
1: Pulmonary arterial hypertension	Idiopathic, heritable (BMPR2), scleroderma and other connective tissue disease, HIV, drugs, congenital heart disease	Precapillary (wedge ≤15, high PVR)	PAH vasodilators
2: Left heart disease	HFrEF, HFpEF, mitral or aortic valve disease. Most common cause overall	Postcapillary (wedge >15)	Treat the heart; avoid PAH vasodilators
3: Lung disease or hypoxia	COPD, ILD, OSA	Precapillary	Treat the lung disease; oxygen
4: Chronic thromboembolic (CTEPH)	Unresolved organized emboli	Precapillary	Lifelong anticoagulation; pulmonary thromboendarterectomy is potentially curative
5: Multifactorial	Mixed or unclear mechanisms	Variable	Treat the cause

Do not give PAH vasodilators for group 2 PH. Opening the pulmonary arterioles in front of a failing left heart increases flow into a congested system and can precipitate pulmonary edema.

PAH therapy and cor pulmonale

Group 1 treatment. PAH drugs are for group 1 only. They target three pathways, and riociguat adds a fourth mechanism:

PAH drug classes

Class	Examples	Mechanism
Endothelin-receptor antagonists	Bosentan, ambrisentan	Block vasoconstrictor endothelin-1; teratogenic, and bosentan is hepatotoxic
PDE-5 inhibitors	Sildenafil, tadalafil	Prolong cGMP-mediated vasodilation
Prostacyclins	Epoprostenol, treprostinil	Vasodilate and inhibit platelets; IV epoprostenol for the sickest patients
Guanylate cyclase stimulator	Riociguat	Increases cGMP; also used for inoperable CTEPH; never combine with a PDE-5 inhibitor (hypotension)

Calcium-channel blockers. Use them only when the acute vasoreactivity test during right-heart catheterization is positive, which is true for a small minority of patients. Most patients are vasoreactivity-negative; start initial combination therapy with an endothelin-receptor antagonist plus a PDE-5 inhibitor (for example ambrisentan plus tadalafil), and add an IV or subcutaneous prostacyclin for high-risk disease.

Cor pulmonale. Right ventricular failure caused by pulmonary hypertension from lung disease or hypoxia, not from left heart disease. Signs:

Elevated JVP
Loud P2
Right parasternal (RV) heave
Tricuspid regurgitation murmur
Hepatomegaly, ascites, and peripheral edema

Treat the underlying lung disease, correct hypoxemia with oxygen (hypoxia drives pulmonary vasoconstriction), and use diuretics cautiously for volume overload.