Atlas of pathophysiology, 2 Edition

Part II - Disorders

Respiratory Disorders

Pulmonary Hypertension

Pulmonary hypertension is a mean systolic pulmonary artery pressure (PAP) above 25 mm Hg at rest and 30 mm Hg during exercise. Primary or idiopathic pulmonary hypertension is characterized by increased PAP and increased pulmonary vascular resistance.

Age Alert

Primary pulmonary hypertension is most common in women ages 20 to 40 and is usually fatal within 3 to 4 years.

Secondary pulmonary hypertension results from existing cardiac (patent ductus arteriosus or atrial or septal defect) or pulmonary disease (rheumatic valvular disease or mitral stenosis), or both. The prognosis in secondary pulmonary hypertension depends on the severity of the underlying disorder.

Causes

Primary pulmonary hypertension

·         Unknown, but may include:

§  hereditary factors

§  altered immune mechanisms.

Secondary pulmonary hypertension

·         Conditions causing alveolar hypoventilation include:

§  chronic obstructive pulmonary disease

§  sarcoidosis

§  diffuse interstitial pneumonia

§  malignant metastases

§  scleroderma

§  obesity

§  kyphoscoliosis.

·         Conditions causing vascular obstruction include:

§  pulmonary embolism

§  vasculitis

§  left atrial myxoma

§  idiopathic veno-occlusive disease

§  fibrosing mediastinitis

§  mediastinal neoplasm.

Pathophysiology

In primary pulmonary hypertension, the smooth muscle in the pulmonary artery wall hypertrophies for no known reason, narrowing or obliterating the artery or arteriole. Fibrous lesions form around the vessels, impairing distensibility and increasing vascular resistance. Pressures in the left ventricle, which receives blood from the lungs, remain normal. However, the increased pressures generated in the lungs are transmitted to the right ventricle, which supplies the pulmonary artery. Eventually, the right ventricle fails (cor pulmonale).

Alveolar hypoventilation can result from diseases caused by alveolar destruction or from disorders that prevent the chest wall from expanding to allow air into the alveoli. The resulting decreased ventilation increases pulmonary vascular resistance. Hypoxemia resulting from this ventilation-perfusion ([V with dot above]/[Q with dot above]) mismatch also causes vasoconstriction, further increasing vascular resistance and resulting in pulmonary hypertension.

Signs and symptoms

·         Shortness of breath, increasing dyspnea on exertion, fatigue and weakness, and chest pain

·         Cough and hemoptysis

·         Cyanosis, Raynaud's phenomenon, and syncope

·         Ascites

·         Jugular vein distention

·         Restlessness and agitation, decreased level of consciousness, confusion, and memory loss

·         Decreased diaphragmatic excursion and respiration

·         Possible displacement of point of maximal impulse

·         Peripheral edema

·         Easily palpable right ventricular lift

·         Reduced carotid pulse

·         Palpable and tender liver

·         Tachycardia

·         Systolic ejection murmur

·         Split S2; presence of S3 and S4 sounds

·         Decreased or loud, tubular breath sounds

Diagnostic test results

·         Arterial blood gas analysis reveals hypoxemia.

·         Chest X-ray shows enlargement of main and hilar pulmonary arteries, narrowing of peripheral arteries, and enlargement of right atrium and ventricle.

·         A chest computed tomography scan may show abnormal lung vessels or blood clots

·         Electrocardiography in right ventricular hypertrophy shows right axis deviation and tall or peaked P waves in inferior leads.

·         Cardiac catheterization reveals mean pulmonary artery pressure above 25 mm Hg or an increased pulmonary artery wedge pressure if the underlying cause is left atrial myxoma, mitral stenosis, or left-sided heart failure.

·         Pulmonary angiography detects filling defects in pulmonary vasculature.

·         Pulmonary function studies show decreased flow rates and increased residual volume (underlying obstructive disease) or reduced total lung capacity (underlying restrictive disease).

·         Radionuclide imaging detects abnormalities in right and left ventricular functioning.

·         Open lung biopsy determines the type of disorder.

·         Echocardiography shows ventricular wall motion and possible valvular dysfunction, right ventricular enlargement, abnormal septal configuration consistent with right ventricular pressure overload, and reduction in left ventricular cavity size.

·         Perfusion lung scanning shows multiple patchy and diffuse filling defects.

Treatment

·         Treatment of the underlying cause

·         Oxygen therapy

·         Fluid restriction

·         Digoxin, diuretics, vasodilators, pulmonary vasodilators, calcium channel blockers, beta-adrenergic blockers, bronchodilators, and anticoagulants; prostacyclin; endothelin receptor antagonists such as bosentan

·         Pulmonary thromboendarterectomy

·         Lung or heart-lung transplantation

P.109

NORMAL PULMONARY ARTERY

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EARLY PULMONARY HYPERTENSION

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LATE PULMONARY HYPERTENSION

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