Pulmonary hypertension, an abnormal elevation in pulmonary artery pressure, may be the result of left heart failure, pulmonary parenchymal or vascular disease, thromboembolism, or a combination of these factors. Whether the pulmonary hypertension arises from cardiac, pulmonary, or intrinsic vascular disease, it generally is a feature of advanced disease. Because the causes of pulmonary hypertension are so diverse, it is essential that the etiology underlying the pulmonary hypertension be clearly determined before beginning treatment.
The right ventricle responds to an increase in pulmonary vascular resistance by increasing right ventricular (RV) systolic pressure to preserve cardiac output. In some patients, chronic changes occur in the pulmonary circulation, resulting in progressive remodeling of the vasculature, which can sustain or promote pulmonary hypertension even if the initiating factor is removed.
The ability of the RV to adapt to increased vascular resistance is influenced by several factors, including age and the rapidity of the development of pulmonary hypertension. For example, a large acute pulmonary thromboembolism can result in RV failure and shock, whereas chronic thromboembolic disease of equal severity may result in only mild exercise intolerance. Coexisting hypoxemia can impair the ability of the ventricle to compensate. Studies support the concept that RV failure occurs in pulmonary hypertension when the RV myocardium becomes ischemic as a result of excessive demands and inadequate RV coronary blood flow. The onset of RV failure, often manifest by peripheral edema, is associated with a poor outcome.
The most common symptom attributable to pulmonary hypertension is exertional dyspnea. Other common symptoms are fatigue, angina pectoris, syncope, near syncope, and peripheral edema.
The physical examination typically reveals increased jugular venous pressure, a reduced carotid pulse, and a palpable RV impulse. Most patients have an increased pulmonic component of the second heart sound, a right-sided fourth heart sound, and tricuspid regurgitation (Chap. 227). Peripheral cyanosis and/or edema tend to occur in later stages of the disease.
(Fig. 250-1) The chest x-ray generally shows enlarged central pulmonary arteries. The lung fields may reveal other pathology. The electrocardiogram usually shows right axis deviation and RV hypertrophy. The echocardiogram commonly demonstrates RV and right atrial enlargement, a reduction in left ventricular (LV) cavity size, and a tricuspid regurgitant jet that can be used to estimate RV systolic pressure by Doppler. Pulmonary function tests are helpful in documenting underlying obstructive airways disease, whereas high-resolution chest computed tomography (CT) is preferred to diagnose restrictive lung disease. Hypoxemia and an abnormal diffusing capacity for carbon monoxide occur with pulmonary hypertension of many causes. A perfusion lung scan is almost always abnormal in patients with thromboembolic pulmonary hypertension (Chap. 262). However, diffuse defects of a nonsegmental nature often can be seen in long-standing pulmonary hypertension in the absence of thromboemboli. Laboratory tests should include antinuclear antibody and HIV testing. Because of the high frequency of thyroid abnormalities in patients with idiopathic pulmonary hypertension, it is recommended that the thyroid-stimulating hormone level be determined periodically.
An algorithm for the workup of a patient with unexplained pulmonary hypertension. All potential etiologies and associated conditions must be investigated in a patient with clinical findings consistent with pulmonary hypertension. COLD, chronic obstructive lung disease; CBC, complete blood count; ANA, antinuclear antibodies; HIV, human immunodeficiency virus; TSH, thyroid-stimulating hormone; LFTs, liver function tests.
Cardiac catheterization is mandatory for accurate measurement of pulmonary artery pressure, cardiac output, and LV filling pressure as well as documentation of an underlying cardiac shunt. Care should be taken to record pressures only at end expiration. It is recommended that patients with pulmonary arterial hypertension undergo drug testing with a short-acting pulmonary vasodilator to determine the extent of pulmonary vasodilator reactivity. Inhaled nitric oxide, intravenous adenosine, and intravenous epoprostenol have comparable effects in reducing pulmonary artery pressure acutely. Nitric oxide is administered via inhalation in 10–20 parts per million. Adenosine is given in doses of 50 μg/kg per min and increased every 2 min until side effects develop. Epoprostenol is given in doses of 2 ng/kg per min and increased every 30 min until side effects develop. Patients who respond usually can be treated with calcium channel blockers and have a more favorable prognosis.
Pulmonary arterial hypertension (PAH) refers to a variety of diseases that include idiopathic PAH, as noted in Table 250-1. Patients with PAH have a common histopathology characterized by medial hypertrophy, eccentric and concentric intimal fibrosis, recanalized thrombi appearing as fibrous webs, and plexiform lesions.
Table 250–1. A Clinical Classification of Pulmonary Hypertension
| Save Table
Table 250–1. A Clinical Classification of Pulmonary Hypertension
|Category 1. Pulmonary arterial hypertension (PAH)|
|Key feature: elevation in pulmonary arterial pressure (PAP) with normal pulmonary capillary wedge pressure (pcwp)|
• Exposure to drugs or toxins
• Persistent pulmonary hypertension of the newborn
• Pulmonary capillary hemangiomatosis (PCH)
|Associated with other active conditions|
• Collagen vascular disease
• Congenital systemic-to-pulmonary shunts
• Portal hypertension
• HIV infection
|Category 2. Pulmonary venous hypertension |
|Key feature: elevation in PAP with elevation in pcwp|
• Left-sided atrial or ventricular heart disease
• Left-sided valvular heart disease
• Pulmonary venous obstruction
• Pulmonary venoocclusive disease (PVOD)
|Category 3. Pulmonary hypertension associated with hypoxemic lung disease|
|Key feature: chronic hypoxia with mild elevation of PAP|
• Chronic obstructive lung disease
• Interstitial lung disease
• Sleep-disordered breathing
• Alveolar hypoventilation disorders
• Chronic exposure to high altitude
• Developmental abnormalities
|Category 4. Pulmonary hypertension due to chronic thromboembolic disease|
|Key feature: elevation of PA pressure with documentation of pulmonary arterial obstruction ...|
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