A bruit is an abnormal sound heard over an artery, representing a vascular sound that is not typically present in a healthy individual. This sound is generated when the smooth, orderly movement of blood, known as laminar flow, becomes disorganized and chaotic. The resulting turbulence creates vibrations within the vessel wall that signal an underlying change in the blood vessel structure or blood flow dynamics.
Understanding the Sound Quality
The acoustic characteristic of a bruit is often described using terms like blowing, whooshing, or humming, which evoke the sensation of rushing fluid. When blood encounters a narrowing or irregularity inside an artery, the flow accelerates and changes from smooth to turbulent, producing the audible vibrations.
The pitch of a bruit is a significant indicator, as a higher pitch usually suggests a greater degree of vessel narrowing, or stenosis. As the artery’s diameter decreases, the velocity of the blood increases dramatically at the constricted point, generating vibrations at a higher frequency. The intensity of the sound also correlates with the severity of the obstruction, becoming louder as the turbulence increases.
Most bruits are heard primarily during systole, which is the phase of the cardiac cycle when the heart contracts and pushes blood into the arteries. If the obstruction is severe enough, or if the flow is exceptionally high, the turbulence can persist throughout the entire cycle.
A continuous bruit, which can be heard in both systole and diastole, suggests a pressure gradient remains across the lesion even when the heart is relaxed. This continuous sound implies a constantly high-velocity flow or a persistent pressure difference, making it a more concerning finding. In some cases, a bruit might be low-pitched and humming, particularly in situations of high blood flow without a fixed obstruction, such as in arteriovenous malformations or conditions that increase cardiac output.
Where Bruits Are Heard and What They Indicate
Bruits are listened for across various major arteries in the body, and the location of the sound offers a strong clue about the underlying pathology. One of the most frequently assessed sites is the carotid artery in the neck, where a bruit is often associated with carotid artery stenosis. This narrowing, typically caused by atherosclerotic plaque buildup, significantly limits blood flow to the brain and indicates an increased risk of ischemic stroke, prompting further diagnostic imaging.
Bruits heard over the aorta in the abdomen may raise suspicion for an abdominal aortic aneurysm, which is a localized dilation of the artery wall. The turbulent flow in this instance is not caused by narrowing but by the change in vessel geometry.
A bruit detected over the renal arteries, located on either side of the abdomen, points toward renal artery stenosis. This condition restricts blood supply to the kidneys, often leading to secondary hypertension as the kidneys attempt to compensate for the perceived low flow.
In the extremities, bruits are often assessed over the femoral and popliteal arteries to investigate peripheral artery disease. A bruit in a peripheral artery suggests localized plaque formation causing stenosis, which can lead to pain, cramping, and poor circulation in the limbs.
How Bruits Differ from Heart Murmurs
The distinction between a bruit and a heart murmur lies fundamentally in the anatomical source of the turbulent blood flow. Both sounds are generated by disorganized flow, but a bruit originates in a peripheral or major artery outside the heart.
In contrast, a heart murmur originates from within the heart chambers or across the heart valves. Murmurs are typically caused by blood flowing backward through an incompetent valve or rushing forward through a valve that is too narrow.
While a heart murmur can sometimes radiate, or travel, to the neck and be mistaken for a carotid bruit, careful auscultation can usually differentiate the two. A bruit will be loudest directly over the affected artery, whereas a radiating heart murmur is typically loudest over the precordium, the area of the chest overlying the heart. The clinical implications also differ, with bruits pointing toward localized vascular disease and murmurs indicating primary cardiac or valvular pathology.