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  Pulmonary Hypertension

Pulmonary Hypertension (PH) is a boost in blood pressure in the pulmonary artery or lung vasculature, which leads to shortness of breath, fainting, dizziness and other symptoms, with physical exertion. Depending on the cause, pulmonary hypertension can be a grave disease with a distinctly decreased exercise ability and right-sided heart failure. It was first recognized by Dr Ernst von Romberg in 1891. It can be one of the following five different types, arterial, venous, hypoxic, thromboembolic, or miscellaneous.

Pulmonary Hypertension Lung diseases
Pulmonary Hypertension


Although the terms primary pulmonary hypertension (meaning of unidentified cause) and secondary pulmonary hypertension (meaning due to a different medical condition) still continue to be in material distributed to patients and the general public, these terms have mainly been abandoned in the medical literature. This modification has occurred because the older dichotomous classification did not reflect pathophysiology or outcome. It led to fallacious therapeutic decisions, i.e. treat "primary" pulmonary hypertension only. This led to therapeutic hopelessness for many patients labeled "secondary" pulmonary hypertension, and could have been a factor in their deaths. The term "primary pulmonary hypertension" has now been substituted with "idiopathic pulmonary arterial hypertension". The terms "primary" and "secondary" pulmonary hypertension should not be used in future.

Signs and symptoms

A history usually reveals gradual establishment of shortness of breath, fatigue, non-productive cough, angina pectoris, fainting or syncope, peripheral edema (swelling of the limbs, especially around the ankles and feet), and seldom hemoptysis (coughing up blood). Pulmonary arterial hypertension (PAH) usually does not exhibit orthopnea or paroxysmal nocturnal dyspnea, while pulmonary venous hypertension usually does.

In order to determine the cause, the doctor will conduct a detailed medical history. A complete family history is taken to asertain whether the disease might be familial. A history of exposure to cocaine, methamphetamine, alcohol leading to cirrhosis, and smoking leading to emphysema are considered important. Physical examination is conducted to look for usual signs of pulmonary hypertension including a loud P2 (pulmonic valve closure sound), (para)sternal heave, jugular venous distension, pedal edema, ascites, hepatojugular reflux, clubbing etc.

Causes

The most frequent cause of pulmonary hypertension is left heart failure leading to pulmonary venous hypertension. This may be due to systolic or diastolic failure of the left ventricle or due to valvular failure such as mitral regurgitation or mitral stenosis. It usually manifests as pulmonary edema.

The usual causes of pulmonary arterial hypertension (PAH) include HIV, scleroderma and other autoimmune disorders, cirrhosis and portal hypertension, sickle cell disease, congenital heart disease, thyroid diseases, and others. The ingestion of weight loss pills such as Fen-Phen, Aminorex, fenfluramine (Pondimin), and phentermine led to the development of PAH in the past. Other causes include sarcoidosis, histiocytosis X, and fibrosing mediastinitis. Pulmonary embolism also leads to pulmonary hypertension, acutely as well as chronically. When none of these causes can be found, the disease is termed idiopathic pulmonary arterial hypertension (IPAH).

Lung diseases that decrease oxygen in the blood (hypoxia) are well known causes of pulmonary hypertension, including COPD, interstitial lung disease, Pickwickian syndrome or obesity-hypoventilation syndrome, and possibly sleep apnea. Human herpesvirus 8, also linked with Kaposi's sarcoma, has been seen in patients with PAH, suggesting that this virus may play a participant in its development. Recent studies have been unable to find an association between human herpesvirus 8 and idiopathic pulmonary arterial hypertension.

Pathogenesis

Whatever the initial cause, pulmonary hypertension involves the tightening of blood vessels connected to and within the lungs. This makes it more difficult for the heart to pump blood through the lungs. Eventually, the affected blood vessels become both stiffer and thicker, further increasing the blood pressure within the lungs and weakening blood flow. In addition, the increased workload of the heart causes thickening and enlargement of the right ventricle, making the heart less able to pump blood through the lungs, causing right heart failure. As the blood flowing through the lungs diminishes, the left side of the heart receives less blood. This blood may also carry less oxygen than normal. Thus, it becomes more and more difficult for the left side of the heart to pump a sufficient supply of oxygen to the rest of the body, chiefly during physical activity.

Diagnosis

Because pulmonary hypertension can be of 5 major types, a succession of tests must be done to differentiate pulmonary arterial hypertension from venous, hypoxic, thomboembolic, or miscellaneous varieties.

A physical examination is done to look for usual signs of pulmonary hypertension. These include altered heart sounds, such as a widely split S2 or second heart sound, a loud P2 or pulmonic valve closure sound (part of the second heart sound), (para)sternal heave, possible S3 or third heart sound, and pulmonary regurgitation. More signs include jugular venous distension (enlargement of the jugular veins), peripheral edema (swelling of the ankles and feet), ascites (abdominal swelling due to the accumulation of fluid), hepatojugular reflux, and clubbing.

Further procedures are required to verify the presence of pulmonary hypertension and rule out other possible diagnoses. These generally include pulmonary function tests, blood tests, electrocardiography (ECG), arterial blood gas measurements, X-rays of the chest (followed by high-resolution CT scanning if interstitial lung disease is suspected), and ventilation-perfusion or V/Q scanning to exclude recurring thromboembolic pulmonary hypertension. Biopsy of the lung is usually not needed unless the pulmonary hypertension is thought to be due to an underlying interstitial lung disease. But lung biopsies are full of risks of bleeding due to the high intrapulmonary blood pressure. Clinical improvement is often measured by a "six-minute walk test", i.e. the distance a patient can walk in six minutes. Stability and improvement in this measurement tie to better survival.

Although pulmonary arterial pressure can be predictable on the basis of echocardiography, pressure sampling with a Swan-Ganz catheter provides a distinct measurement. PAOP and PVR can not be measured directly with echocardiography. Therefore diagnosis of PAH requires a cardiac catheterization. A Swan-Ganz catheter can also measure the cardiac output, which is far more vital in measuring disease severity than the pulmonary arterial pressure.

Normal pulmonary arterial pressure in a person living at sea level has a mean value of 12–16 mm Hg (1600–2100 Pa). Definite pulmonary hypertension occurs when mean pressures at rest exceed 25 mm Hg (3300 Pa). If mean pulmonary artery pressure rises above 30 mm Hg (4000 Pa) with exercise, that is also considered pulmonary hypertension.

Diagnosis of PAH requires the existence of pulmonary hypertension with two other conditions. Pulmonary artery occlusion pressure (PAOP or PCWP) must be less than 15 mm Hg (2000 Pa) and pulmonary vascular resistance (PVR) must be greater than 3 Wood units (240 dyn•s•cm-5 or 2.4 mN•s•cm-5).

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