Skip to Main Content

++

Pulmonary hypertension (PH) is a hemodynamic abnormality common to a variety of conditions that is characterized by increased right ventricular (RV) afterload and work. The clinical manifestations, natural history, and reversibility of pulmonary hypertension depend heavily on the nature of the pulmonary vascular lesions and the etiology and severity of the hemodynamic disorder, although individual variability exists. For example, subacute or chronic hypoxia predominantly causes increased muscularization of the small muscular pulmonary arteries and arterioles with the intima relatively intact. Relief of the hypoxia improves or occasionally reverses the process with little or no pathologic residue.1,2 In contrast, the lesions of systemic sclerosis (scleroderma), mostly confined to the intima of the small pulmonary arteries and arterioles, are usually progressive and irreversible. Unlike these two examples, which spare the pulmonary capillary bed, the pulmonary capillaries are the primary site of involvement in pulmonary capillary hemangiomatosis.3

++

Because of its large capacity, its great distensibility, its low resistance to blood flow, and the modest amounts of smooth muscle in the small arteries and arterioles, the pulmonary circulation is not predisposed to become hypertensive. In normal individuals lying supine, systolic pressure is approximately 15 to 25 mm Hg; the corresponding diastolic pressure is 5 to 10 mm Hg. The mean driving pressure (ie, the difference between the mean blood pressure in the pulmonary artery and in the left atrium) is approximately 10 to 12 mm Hg. Because blood flow (cardiac output) is the same in both circulations in the absence of any systemic to pulmonary communications, the pulmonary vascular resistance (PVR) is approximately one-eighth of systemic vascular resistance. The large cross-sectional surface area of the pulmonary circulation, coupled with the distensibility of its thin-walled vessels and the large recruitable vascular reserve, account for these unique characteristics. During exercise, as pulmonary blood flow increases, new regions of the pulmonary vascular bed are open and existing vasculature dilates; accordingly, the pulmonary circulation is capable of accommodating a four-fold or greater increase in resting blood flow with virtually no change in pulmonary artery pressure, with a concomitant decrease in PVR.

++

When total cross-sectional area is decreased by destruction or obliteration of lung tissue or occlusive lesions in the resistance vessels, pulmonary arterial pressures increase. The degree of PH that develops is a function of the amount of the pulmonary vascular tree that has been eliminated. PH is most often associated with cardiac or pulmonary diseases. Although idiopathic pulmonary arterial hypertension (IPAH; formerly known as primary pulmonary hypertension [PPH]) is uncommon, it is well recognized as a distinctive clinical entity in which intrinsic pulmonary vascular disease is free of the complicating features of PH contributed by diseases of the heart and/or lungs. Mild PH can exist for a lifetime without becoming evident clinically. For example, native residents at high altitude, in whom mild to moderate PH is a natural result of sustained exposure to hypoxia, can adapt and function normally. When PH does become manifest clinically, ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessCardiology Full Site: One-Year Subscription

Connect to the full suite of AccessCardiology content and resources including textbooks such as Hurst's the Heart and Cardiology Clinical Questions, a unique library of multimedia, including heart imaging, an integrated drug database, and more.

$595 USD
Buy Now

Pay Per View: Timed Access to all of AccessCardiology

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.