A bruit is an abnormal vascular sound heard when a healthcare provider listens to a patient’s arteries with a stethoscope (auscultation). It signals a disturbance in the smooth flow of blood, causing vibrations within the artery wall that are transmitted to the surface.
Defining the Sound: Auditory Characteristics
A bruit is commonly described using auditory terms like a “whooshing,” “blowing,” or “swishing” sound, similar to a rushing river or a gust of wind. This sound contrasts sharply with the silent or low-frequency laminar flow of blood in a healthy artery. The pitch and intensity of the bruit change based on the severity of the underlying arterial narrowing, or stenosis.
A mild blockage may produce a soft, low-pitched sound heard only during the systolic phase. As the blockage increases, the velocity of the blood flow speeds up, causing the pitch to rise and the intensity to become louder. A more severe obstruction, such as 60% narrowing, generates a high-pitched, intense sound that lasts throughout the entire systolic phase.
When arterial narrowing becomes severe (approaching 70% to 80% diameter reduction), the bruit may extend into the diastolic phase, heard as a continuous sound. The presence of a bruit in both systole and diastole indicates a substantial pressure difference across the narrowed segment. If the artery is almost completely blocked, the flow may be so diminished that the turbulence is insufficient to create an audible vibration, and the bruit may disappear entirely.
The Source of the Sound: Turbulent Blood Flow
The origin of the bruit is turbulent blood flow, which contrasts with the body’s usual laminar flow. In a healthy, unobstructed artery, blood moves in smooth, parallel layers, generating no sound that can be heard externally.
Turbulence occurs when blood flow becomes chaotic. This disruption is most often caused by a reduction in the inner diameter of the blood vessel, typically due to the buildup of atherosclerotic plaque (stenosis). As blood is forced through the constriction, its velocity dramatically increases, transforming the quiet laminar flow into noisy turbulent flow.
The chaotic movement of blood causes the artery walls to vibrate, which the stethoscope picks up as the whooshing sound. Beyond narrowing, other factors like vessel malformations (such as an aneurysm) or sharp turns in the artery’s path can also generate turbulent flow and an audible bruit.
Common Areas Where Bruits Are Heard
Bruits are sought out during a physical examination because their location often suggests a specific underlying vascular issue. Providers commonly listen over the carotid arteries in the neck, where a bruit suggests carotid artery disease—narrowing of the arteries that supply blood to the brain.
The presence of a bruit in the neck indicates potential for reduced blood flow to the brain, increasing the possibility of a transient ischemic attack or a stroke. Providers also listen over the abdomen, especially near the renal arteries (which supply the kidneys). A bruit here may suggest renal artery stenosis, where vessel narrowing can lead to secondary hypertension.
A bruit over the abdominal aorta may raise concern for an abdominal aortic aneurysm or peripheral artery disease. While a bruit is a significant finding, it is not a definitive diagnosis and requires additional testing to assess the extent of the vascular disease.