PULMONARY HYPERTENSION: Elevated Pulmonary Arterial Pressure & Its Impact on the Right Heart
Pulmonary hypertension (PH) is a chronic condition characterised by abnormally high pressure in the pulmonary circulation. Unlike systemic hypertension, which affects the high-pressure arterial system, pulmonary hypertension occurs in a normally low-resistance, low-pressure vascular bed. Even small increases in pulmonary pressure therefore place a disproportionate strain on the right ventricle.
Pulmonary hypertension is not a single disease but a syndrome with multiple potential causes. It can arise from intrinsic pulmonary arterial disease, chronic lung pathology, left-sided heart disease, chronic thromboembolic disease or systemic conditions that affect pulmonary vasculature. Regardless of the cause, sustained elevation in pulmonary pressure leads to progressive right ventricular hypertrophy, dilation and, eventually, right-sided heart failure.
What You Need to Know
Pulmonary hypertension is a condition characterised by chronically elevated pressure within the pulmonary arterial system, driven by increased pulmonary vascular resistance. Under normal circumstances, the pulmonary circulation is a low-pressure, highly compliant system that allows the right ventricle to eject blood with minimal effort. When pulmonary vessels become narrowed, stiffened, obstructed, or exposed to persistently elevated downstream pressure from left-sided heart disease, resistance rises. The right ventricle must then generate much higher pressures to maintain pulmonary blood flow, fundamentally altering its workload.
Initially, the right ventricle adapts by hypertrophying, thickening its muscular wall to generate greater systolic pressure. This adaptation can preserve cardiac output for a time, but it comes at a cost. The hypertrophied right ventricle becomes less compliant and more oxygen-demanding, while coronary perfusion to the right ventricular myocardium may be compromised. As pulmonary vascular resistance continues to increase, contractile efficiency declines, right ventricular dilation develops, and forward flow into the pulmonary circulation falls.
Several key pathophysiological consequences emerge as the disease progresses:
Increased pulmonary vascular resistance that places sustained pressure overload on the right ventricle.
Right ventricular hypertrophy followed by dilation, reflecting transition from compensation to failure.
Reduced pulmonary and left-sided filling, contributing to fatigue and reduced exercise tolerance.
Clinically, pulmonary hypertension often presents late because the right ventricle compensates for a prolonged period before failing. Early symptoms such as exertional breathlessness and fatigue are nonspecific and easily overlooked. As right ventricular reserve is exhausted, patients may develop syncope during exertion, worsening exercise intolerance, and signs of systemic venous congestion including peripheral oedema, abdominal distension, and raised jugular venous pressure. Without treatment, progressive right-sided heart failure becomes the dominant feature and a major determinant of prognosis.
Beyond the Basics
Classifications and Mechanisms Behind Pulmonary Hypertension
Pulmonary hypertension is classified into five groups based on the dominant underlying mechanism. This classification reflects where resistance develops within the cardiopulmonary system and helps explain why pulmonary hypertension behaves differently across conditions. Although the initiating causes vary, all groups ultimately increase pulmonary vascular resistance and impose a sustained pressure load on the right ventricle.
1. Pulmonary arterial hypertension (PAH)
This group includes disorders that primarily affect the pulmonary arterioles. Endothelial dysfunction reduces production of vasodilators such as nitric oxide and prostacyclin while increasing vasoconstrictors like endothelin-1. The result is persistent vasoconstriction, smooth muscle hypertrophy, intimal fibrosis, and the formation of plexiform lesions, which are complex vascular structures that further obstruct flow. PAH may be idiopathic or associated with connective tissue disease, congenital heart defects, or exposure to certain drugs or toxins.
2. Pulmonary hypertension due to left heart disease
This is the most common cause of pulmonary hypertension. Left ventricular systolic or diastolic dysfunction, or mitral valve disease, elevates left atrial pressure. This pressure is transmitted backward into the pulmonary veins and capillaries, producing pulmonary venous congestion. Over time, chronic exposure to high pressure triggers secondary vasoconstriction and structural remodelling of pulmonary arteries, increasing resistance beyond the initial passive pressure rise.
3. Pulmonary hypertension due to lung disease or chronic hypoxia
Chronic lung conditions such as COPD, interstitial lung disease, or obstructive sleep apnoea expose the pulmonary circulation to persistent alveolar hypoxia. Hypoxia induces vasoconstriction of pulmonary arterioles as a physiological attempt to redirect blood flow, but when sustained, this response becomes maladaptive. Long-term hypoxic vasoconstriction leads to medial hypertrophy and structural narrowing of pulmonary vessels, permanently increasing resistance.
4. Chronic thromboembolic pulmonary hypertension (CTEPH)
CTEPH develops when pulmonary emboli fail to resolve completely. Organised thrombus becomes incorporated into the vessel wall, forming fibrotic obstructions that mechanically narrow or occlude pulmonary arteries. In addition to these fixed lesions, the remaining vascular bed undergoes compensatory microvascular remodelling, which further elevates pulmonary vascular resistance.
5. Pulmonary hypertension with multifactorial or unclear mechanisms
This group includes conditions such as sarcoidosis, haematological disorders, and metabolic diseases where pulmonary vascular involvement occurs indirectly. Inflammation, infiltration, altered blood viscosity, or extrinsic compression contribute to increased resistance without a single dominant mechanism.
How Pulmonary Vascular Remodelling Develops
Pulmonary hypertension is sustained by both functional and structural changes within the pulmonary circulation. Endothelial dysfunction plays a central role. Healthy pulmonary endothelium maintains low resistance through release of vasodilators, while inhibiting smooth muscle proliferation. In pulmonary hypertension, this balance is lost. Reduced nitric oxide and prostacyclin production combined with excess endothelin-1 creates a persistently constricted vascular state.
Chronic haemodynamic stress stimulates smooth muscle proliferation within the medial layer of pulmonary arteries. Vessel walls thicken, lumens narrow, and compliance is reduced. With progression, intimal fibrosis further limits flow. These changes transform the pulmonary circulation from a low-pressure, highly adaptable system into a stiff, high-resistance network that cannot accommodate increased blood flow during exertion.
Impact on the Right Ventricle
The right ventricle is anatomically suited to pump against low resistance. As pulmonary pressures rise, it must generate progressively higher systolic pressures to maintain flow. Initially, the ventricle adapts through hypertrophy, increasing wall thickness to reduce wall stress and preserve output.
Over time, this adaptation becomes maladaptive. The hypertrophied ventricle becomes less compliant, impairing diastolic filling. Coronary perfusion of the right ventricular myocardium may be compromised because oxygen demand increases while perfusion becomes limited during prolonged systole. As resistance continues to rise, the ventricle dilates, stroke volume falls, and right-sided heart failure develops.
Consequences for Gas Exchange and Cardiac Output
Pulmonary hypertension disrupts normal ventilation–perfusion matching within the lungs. Blood flow may be diverted away from well-ventilated regions due to fixed obstruction or uneven vasoconstriction, contributing to hypoxaemia. Reduced pulmonary blood flow also limits oxygenated blood returning to the left heart.
As right ventricular output declines, left ventricular preload falls, lowering overall cardiac output. This produces fatigue, dizziness, and exertional syncope, particularly when the cardiovascular system cannot increase flow to meet metabolic demand. In advanced disease, right ventricular ischaemia may occur because myocardial oxygen demand increases while coronary perfusion becomes inadequate, accelerating progression toward end-stage right-sided heart failure.
Clinical Connections
Pulmonary hypertension often presents insidiously, with early symptoms that are vague and easily attributed to deconditioning or lung disease. Exertional breathlessness and reduced exercise tolerance reflect the inability of the pulmonary circulation and right ventricle to increase flow during activity. Fatigue develops as cardiac output becomes limited, particularly during exertion. Because right ventricular compensation can mask haemodynamic deterioration for a prolonged period, diagnosis is frequently delayed until structural and functional changes are advanced.
As disease progresses, examination findings begin to reflect right ventricular pressure overload and failure. Elevated jugular venous pressure indicates impaired venous return to the heart, while a right parasternal heave reflects right ventricular hypertrophy. A loud or accentuated pulmonary component of the second heart sound (P2) suggests elevated pulmonary arterial pressure. Peripheral oedema, ascites, and hepatomegaly signal progression to right-sided heart failure and mark a significant turning point in prognosis.
Key clinical indicators that suggest advanced pulmonary hypertension include:
Progressive exertional dyspnoea or syncope, indicating limited ability to augment cardiac output.
Rising jugular venous pressure and peripheral oedema, reflecting right ventricular failure.
Prominent P2 or right parasternal heave, consistent with sustained pulmonary pressure overload.
Echocardiography is the primary noninvasive investigation used to estimate pulmonary artery pressures, assess right ventricular size and systolic function, and identify secondary causes such as left-sided heart disease. Definitive diagnosis and classification require right heart catheterisation, which directly measures pulmonary artery pressure, pulmonary capillary wedge pressure, and pulmonary vascular resistance, allowing differentiation between pre-capillary and post-capillary disease. Management is determined by the underlying mechanism and disease severity. Options include oxygen therapy for hypoxic lung disease, targeted pulmonary vasodilators such as prostacyclins, endothelin receptor antagonists, and phosphodiesterase-5 inhibitors in appropriate subtypes, anticoagulation in chronic thromboembolic pulmonary hypertension, and cautious diuretic use to relieve venous congestion without compromising preload. Ongoing assessment of symptoms, volume status, and right ventricular function is essential, as clinical deterioration can be subtle but rapid once compensatory mechanisms fail.
Concept Check
Why does even a mild increase in pulmonary vascular resistance place significant strain on the right ventricle?
How do endothelial dysfunction and smooth muscle proliferation contribute to pulmonary vascular remodelling?
Why is pulmonary hypertension commonly caused by chronic left-sided heart disease?
What makes chronic thromboembolic pulmonary hypertension different from other forms?
Why do patients with pulmonary hypertension often experience fatigue, dizziness or syncope during exertion?