Pulmonary Hypertension

Overview

Pulmonary hypertension (PH) is a hemodynamic state defined by elevated pressure in the pulmonary circulation. Left untreated, the sustained pressure overload causes the right ventricle (RV) to hypertrophy, dilate, and ultimately fail — a process known as cor pulmonale. PH is not a single disease but a final common pathway shared by a heterogeneous group of conditions. This distinction matters profoundly: the World Health Organization’s five-group classification guides treatment, and therapies appropriate for one group can be dangerous in another.

For respiratory therapists, the key responsibilities are correcting hypoxemia (a potent pulmonary vasoconstrictor), avoiding ventilatory strategies that raise pulmonary vascular resistance (PVR), and understanding the pharmacologic landscape well enough to support safe drug administration and recognize contraindications.

Key Concepts

Hemodynamic definition.PH is defined as a mean pulmonary arterial pressure (mPAP) >20 mmHg at rest. The 2018 6th World Symposium on Pulmonary Hypertension lowered this threshold from the older ≥25 mmHg cutoff, capturing an earlier, clinically significant disease state. Precapillary PH (the form affecting the pulmonary vasculature itself, as in Group 1 and Group 4) additionally requires a pulmonary artery wedge pressure (PAWP) ≤15 mmHg and a pulmonary vascular resistance (PVR) ≥2 Wood units, distinguishing it from the postcapillary form driven by left heart disease.

WHO classification — 5 groups.

• Group 1 — Pulmonary Arterial Hypertension (PAH): intrinsic pulmonary vascular disease. Subtypes include idiopathic, heritable (BMPR2 mutation), drug/toxin-induced, and PAH associated with connective-tissue disease, HIV, or portal hypertension.
• Group 2 — PH due to left heart disease: the most common cause of PH overall. Left ventricular systolic or diastolic dysfunction, valvular disease, and congenital cardiomyopathies all raise left-sided filling pressures that back up into the pulmonary vasculature.
• Group 3 — PH due to lung disease or hypoxia: COPD, interstitial lung disease (ILD), obstructive sleep apnea (OSA), and high-altitude exposure drive PH primarily through chronic hypoxic pulmonary vasoconstriction.
• Group 4 — Chronic thromboembolic PH (CTEPH): organized thrombi obstruct major pulmonary arteries after PE, raising PVR mechanically rather than vasomotorically. Potentially surgically curable.
• Group 5 — PH with unclear or multifactorial mechanisms:sarcoidosis, systemic disorders, metabolic diseases, and others.

Pathophysiology.In all groups, increased PVR imposes a pressure afterload on the thin-walled RV. Unlike the LV, the RV is poorly adapted to pressure overload. It compensates initially with hypertrophy but eventually dilates, displacing the interventricular septum leftward (“D-sign” on echo), reducing LV filling, and dropping cardiac output. In Group 3, hypoxic pulmonary vasoconstriction is the dominant mechanism and is partially reversible with oxygen.

Assessment & Findings

Symptoms. Early PH is often insidious. Exertional dyspnea and fatigue are the most common presenting complaints. As disease progresses, patients develop exertional syncope (a red flag for severely limited cardiac output) and chest pain from RV ischemia. Late-stage disease brings the signs of right heart failure: peripheral edema, ascites, and elevated jugular venous pressure (JVP).

Physical examination. Cardinal findings include:

• A loud, accentuated P₂ (pulmonic component of S₂) from forceful pulmonary valve closure
• A palpable RV heave along the left sternal border
• A holosystolic murmur of tricuspid regurgitation (TR) at the lower left sternal border, increasing with inspiration
• Right heart failure signs: elevated JVP, hepatojugular reflux, peripheral pitting edema, ascites

Diagnostic workup.Echocardiography is the standard screening test: it estimates RV systolic pressure via the TR jet velocity using the Bernoulli equation and provides important functional information about RV size, wall motion, and septal morphology. However, echo alone cannot confirm PH — it can only raise suspicion. Right heart catheterization (RHC) is the diagnostic gold standard, directly and simultaneously measuring mPAP, PAWP, PVR, and cardiac output. RHC also identifies the precapillary vs. postcapillary pattern and allows vasoreactivity testing in Group 1 patients. See the hemodynamic parameters reference for normal RHC values.

ECG findings.Right axis deviation, RV hypertrophy pattern (R > S in V₁, deep S in V₅–V₆), right atrial enlargement (P pulmonale: peaked P waves >2.5 mm in lead II), and incomplete or complete right bundle branch block may all be present, though none is sensitive or specific enough to diagnose PH.

RT Priorities / Interventions

Oxygen therapy.Hypoxemia is a potent stimulus for hypoxic pulmonary vasoconstriction (HPV), which increases PVR and worsens PH — especially in Group 3 patients whose disease is driven by chronic hypoxia. Correcting hypoxemia with supplemental O₂ is a primary RT intervention. Nocturnal and exertional desaturation should be identified and treated proactively; target normoxia (SpO₂ ≥90–92% at minimum, per guideline thresholds).

Avoid PVR-raising conditions.Hypercapnia and acidosis — both respiratory and metabolic — independently increase PVR by causing pulmonary vasoconstriction. During mechanical ventilation, avoid hypoventilation, air-trapping, and high intrathoracic pressures (which also impede RV outflow). Minimize sedation-induced respiratory depression.

Group 1 PAH-specific pharmacotherapy (RT awareness). Four drug classes target the PAH vascular pathways:

• Prostacyclin pathway agonists:epoprostenol (IV, continuous infusion; extremely short half-life — never interrupt), treprostinil (IV, subcutaneous, inhaled, oral), iloprost (inhaled)
• Endothelin receptor antagonists (ERAs):bosentan, ambrisentan, macitentan (all oral; teratogenic — REMS program)
• PDE5 inhibitors: sildenafil, tadalafil (oral; reduce cGMP breakdown, promoting pulmonary vasodilation)
• Soluble guanylate cyclase (sGC) stimulator: riociguat (also approved for CTEPH; contraindicated with PDE5 inhibitors)

Critical caveat. These agents are indicated for Group 1 PAH and selected Group 4 CTEPH patients. They are contraindicated or harmful in Group 2 and Group 3 (see Common Pitfalls below).

Group 4 CTEPH. Pulmonary endarterectomy (PEA) is potentially curative for surgically accessible chronic clot burden. For inoperable or residual disease, balloon pulmonary angioplasty (BPA) and riociguat are guideline-supported alternatives.

Inhaled pulmonary vasodilators in acute RV failure. Inhaled nitric oxide (iNO) and inhaled epoprostenol are used in the ICU setting for acute decompensated RV failure. Because they are inhaled, they preferentially vasodilate ventilated lung units and carry lower risk of systemic hypotension compared with IV agents. RTs are central to their administration and monitoring.

Common Pitfalls

• Giving PAH-specific vasodilators to Group 2 or Group 3 patients. In Group 2 (left heart disease), systemic pulmonary vasodilation without fixing the upstream problem can precipitate acute pulmonary edema. In Group 3 (lung disease), vasodilators blunt hypoxic pulmonary vasoconstriction, worsening V/Q mismatch and deepening hypoxemia. Classify the group before any vasodilator is considered.
• Allowing hypoxemia or hypercapnia.Both are potent pulmonary vasoconstrictors. Undertreated desaturation or CO₂ retention in a PH patient actively worsens pulmonary vascular resistance and can precipitate acute RV decompensation.
• Diagnosing PH severity on echocardiography alone. Echo-derived RV systolic pressure estimates are unreliable in the presence of TR grading limitations or suboptimal windows. RHC is required to confirm the diagnosis, measure true mPAP and PVR, and guide treatment.
• Aggressive diuresis or systemic vasodilation collapsing RV preload.The failing RV depends on adequate preload to maintain stroke volume. Overly aggressive diuresis or a vasodilator causing systemic hypotension can abruptly drop RV filling pressure, precipitating obstructive shock. Volume management in PH requires careful titration.

Board Exam Pearls

• mPAP >20 mmHg at rest is the updated definition of PH (lowered from the older ≥25 mmHg threshold at the 2018 World Symposium).
• Right heart catheterization is the diagnostic gold standard; echocardiography is the screening tool.
• Group 2 (left heart disease) is the most common cause of PH overall.
• Hypoxia causes hypoxic pulmonary vasoconstriction → increases PVR → worsens PH. Correct it with oxygen.
• PAH-specific vasodilators are for Group 1 (and riociguat for Group 4). They are contraindicated in Group 2 and Group 3.
• Loud P₂ + RV heave + TR murmur on exam = classic PH triad. Exertional syncope signals severely reduced cardiac output.
• Group 4 CTEPH: pulmonary endarterectomy is potentially curative.

FAQ

Related Resources

Sources

1. Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021.
2. Humbert M, Kovacs G, Hoeper MM, et al. 2022 ESC/ERS Guidelines for the diagnosis and treatment of pulmonary hypertension. Eur Heart J. 2022;43(38):3618-3731.
3. Simonneau G, Montani D, Celermajer DS, et al. Haemodynamic definitions and updated clinical classification of pulmonary hypertension. Eur Respir J. 2019;53(1):1801913.