A bruit is an abnormal vascular sound detected during a physical examination, typically heard when a healthcare provider uses a stethoscope over an artery. This sound indicates that blood flow within that vessel is not moving smoothly. The presence of a bruit is a physical sign that prompts further investigation into the condition of the blood vessel. Understanding the characteristics of this sound and its mechanism helps determine what it signifies for a person’s health.
Decoding the Sound: Acoustic Characteristics of a Bruit
The sound of a bruit is often described as a “whooshing,” “hissing,” or “blowing” noise. This characteristic sound is created by vibrations within the vessel wall as disorganized blood rushes past an obstruction. The pitch is generally low to medium, making the bell of the stethoscope the preferred tool for auscultation.
The timing of the bruit relative to the heartbeat is an important acoustic detail. Many bruits are heard primarily during systole, the phase when the heart is contracting. If the underlying blockage is severe, the sound may extend throughout the entire cardiac cycle, becoming a systolic-diastolic or continuous bruit.
The intensity and duration of the bruit are directly related to the severity of the underlying arterial narrowing, or stenosis. A soft, short bruit heard only in early systole suggests less severe narrowing. As the obstruction becomes more pronounced, the sound usually increases in loudness, becomes higher-pitched, and extends for a longer duration, sometimes into the diastolic phase.
The Underlying Cause: How Turbulent Flow Creates the Sound
The physiological mechanism that produces a bruit involves a change in how blood moves through an artery. Normally, blood flows through vessels in a smooth, organized pattern known as laminar flow, which is silent. This smooth motion is maintained as long as the blood vessel is wide and unobstructed.
When an artery becomes narrowed, most commonly due to the buildup of plaque from atherosclerosis, the space for blood flow is reduced. As the blood passes through this constricted area, its velocity dramatically increases. This high speed causes the smooth laminar flow to break down into chaotic, disorganized motion known as turbulent flow.
This turbulent movement generates the sound. The disorganized blood flow creates vibrations transmitted to the arterial wall and surrounding tissues, which the stethoscope detects. If the narrowing is extremely severe, the flow may be so minimal that the turbulence—and thus the bruit—diminishes or disappears entirely, which can be a misleading sign.
Where Bruits Are Heard and What They Indicate
The location where a bruit is heard offers important clues about the potential underlying vascular problem. A carotid bruit is heard over the carotid arteries in the neck, which supply blood to the brain. The presence of a carotid bruit is a specific sign for carotid artery stenosis, or narrowing, which is a major risk factor for ischemic stroke.
An abdominal bruit may be heard over several locations, each with clinical significance. A bruit heard in the upper abdomen, slightly lateral to the midline, may indicate renal artery stenosis, a narrowing of the arteries supplying the kidneys. This condition is a known cause of secondary hypertension.
Bruits heard over the midline of the upper abdomen may originate from the aorta or other visceral arteries. While abdominal bruits are sometimes found in young, healthy adults, a continuous or diastolic bruit is more concerning and suggests a significant arterial blockage. The presence of a continuous abdominal bruit can also indicate an abdominal aortic aneurysm, which is a localized enlargement of the aorta.