B-type natriuretic peptide is a substance secreted by the heart in response to cardiac effort. Elevated levels are used to diagnose and monitor heart failure, and distinguish it from other diseases. BNP also helps to lower blood pressure and salt content, and can be used to evaluate patients with shortness of breath and rule out heart disease in asymptomatic patients. It can also be used to monitor responses to heart failure treatment regimens.
B-type natriuretic peptide is a substance secreted by the ventricles of the heart in response to cardiac effort. It has an important physiological role in decreasing blood pressure and the salt content of the body. Levels of B-type natriuretic peptide are elevated in the blood of patients with heart failure; therefore, these levels are commonly measured to diagnose heart failure, monitor heart failure, and distinguish heart failure from other disease states.
Also known as brain natriuretic peptide (BNP), B-type natriuretic peptide is a molecule produced by different parts of the human body in response to stress. It is composed of 32 amino acids and is created from the pro-BNP parent species. B-type natriuretic peptide was first discovered as a product of the brain, but was later identified as a substance produced by the ventricles of the heart. Normal serum BNP levels are less than 100 picograms per milliliter.
Understanding the physiological function of BNP helps to understand why measuring BNP levels can be used clinically for diagnostic purposes. The heart ventricles secrete BNP in response to high blood flow, high pressures, and strong contractions of the heart. The secreted BNP promotes lowering of blood pressure, relaxation of blood vessels, increased excretion of salt in the urine, and increased urination. This peptide has also been shown to reduce heart remodeling, a process that has been implicated in heart failure.
In patients with heart failure, BNP levels are high. Heart failure is associated with elevated ventricular filling pressure, elevated blood flow, and strong cardiac contractility; all of these states stimulate the ventricles to release BNP. Patients with symptomatic and asymptomatic heart failure typically have elevated blood levels of BNP.
One specific use of the BNP level is in the evaluation of patients presenting with shortness of breath. Without a strong medical history, it can be difficult to distinguish pulmonary causes of shortness of breath, such as chronic obstructive pulmonary disease, from cardiac causes of shortness of breath, such as heart failure. Elevated BNP levels indicate a cardiac cause of shortness of breath. It is important to distinguish between heart failure and lung disease because the treatment for the two types of diseases is very different.
Another specific use of B-type natriuretic peptide is to rule out heart disease in asymptomatic patients. Almost all heart failure patients, even if asymptomatic, have increased BNP. Patients with normal BNP levels, therefore, probably do not have heart failure, so this measurement can be used to rule this out.
B-type natriuretic peptide has also been used by some physicians to monitor responses to heart failure treatment regimens. With appropriate heart failure medications, patients’ BNP levels should decrease. Some research groups have argued that drug dosages can be effectively titrated, or adjusted, in response to serial BNP levels.
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