Medical professionals use palpation (touch) and auscultation (hearing) during a physical examination to assess blood flow in vessels outside the heart. When this assessment reveals an unusual finding, it indicates an underlying change in blood flow dynamics. A thrill and a bruit are two distinct physical signs that provide direct evidence of these circulatory changes.
What is a Thrill
A thrill is a palpable vibration felt by the examiner over a blood vessel or the chest wall. It is often described as a fine, buzzing, or humming sensation, detected by placing the fingertips or the flat of the hand lightly over the affected area. It is often likened to the sensation of a cat purring underneath the skin. The detection of a thrill occurs during the palpation phase of an examination. Its presence signifies that blood is moving with enough force and irregularity to cause the vessel wall and surrounding tissue to vibrate.
What is a Bruit
A bruit (pronounced “broo-ee”) is an audible sound heard when listening with a stethoscope over an artery or an organ. This sound is often described as a whooshing, blowing, or buzzing noise, similar to the sound of rushing water. Auscultation is the specific technique used to detect a bruit. A bruit is specifically associated with blood flow through an artery, which distinguishes it from a heart murmur. A heart murmur originates from the heart valves, while a bruit occurs in a vessel away from the heart. The sound results from vibrations within the vessel that are loud enough to be transmitted through the body.
The Underlying Cause of Both
Both a thrill and a bruit are produced by the same underlying physiological event: turbulent blood flow. Normally, blood flows smoothly through the center of a vessel in an orderly fashion, a pattern called laminar flow. This smooth motion is quiet and generates no palpable vibration. When a vessel narrows, or when blood is forced to change direction abruptly, the flow pattern breaks down. This breakdown causes the blood to swirl chaotically, creating eddies and vortices. Turbulent flow generates both sound waves and physical vibrations. The physical vibration is felt as the thrill, and the sound waves are heard as the bruit. They are essentially two manifestations—one felt, one heard—of the same circulatory disturbance beneath the skin.
Why These Signs Matter
The detection of a thrill or a bruit is an important finding during a physical examination, as it prompts further investigation into the cause of the turbulent flow. In native blood vessels, such as the carotid or renal arteries, the presence of these signs typically indicates a problem.
Indications of Disease
They often suggest significant vessel narrowing, a condition called stenosis, frequently caused by plaque buildup. This narrowing restricts flow and forces the blood to accelerate, leading to the turbulent pattern. These signs can also be associated with an aneurysm, a balloon-like bulge in an artery wall that causes blood to swirl in the widened area.
Positive Function in Dialysis Access
However, in specific clinical situations, the presence of both a thrill and a bruit is a positive sign of proper function. For patients undergoing hemodialysis, an arteriovenous (AV) fistula or graft is surgically created. The resulting high-pressure flow through this connection is intended to be turbulent, meaning the presence of a strong, continuous thrill and a loud bruit confirms the access is open and functioning correctly for treatment.