Auscultation is the practice of listening to internal body sounds, often used in the physical examination to detect abnormal vascular sounds known as bruits. A bruit is a whooshing or blowing noise created by turbulent blood flow within an artery. Listening for these sounds over the kidneys provides a targeted assessment that offers early, non-invasive clues about vascular health. This physical assessment helps guide further testing when investigating the causes of elevated blood pressure.
The Purpose of Renal Artery Auscultation
A practitioner listens to the renal arteries primarily to screen for Renal Artery Stenosis (RAS), which is the narrowing of one or both arteries supplying blood to the kidneys. The most common cause is atherosclerosis, the buildup of fatty plaques, typically affecting the proximal segment of the vessel. A less common cause, often seen in younger individuals, is Fibromuscular Dysplasia, which affects the mid-to-distal segments.
The reduction in the artery’s diameter impedes the smooth passage of blood, forcing it through a smaller opening at a higher velocity. This turbulent flow creates the audible bruit. When the kidney senses this reduced blood flow, it triggers the renin-angiotensin-aldosterone system. This hormonal cascade leads to the retention of salt and water and systemic vasoconstriction, ultimately resulting in secondary hypertension.
Identifying the Anatomical Landmark
The physical location for placing the stethoscope involves both anterior and posterior sites. The most common location is the upper abdomen, specifically the epigastric region. The stethoscope should be placed one to three centimeters superior and slightly lateral to the umbilicus on both the left and right sides. This positioning targets the origin of the renal arteries as they branch off the abdominal aorta.
The renal arteries are deep structures, so the sound is often faint and may be obscured by overlying bowel sounds. Because the arteries are located retroperitoneally, a second location can be assessed over the flanks, specifically at the costovertebral angles (CVA). The CVA is the angle formed by the twelfth rib and the vertebral column on the back. Assessing both the abdominal and flank locations bilaterally provides the most comprehensive opportunity to detect turbulent flow.
Proper Auscultation Technique
The patient is positioned supine to relax the abdominal musculature and improve sound transmission. The bell of the stethoscope is the preferred headpiece for this assessment. The bell detects lower-pitched sounds, which is the frequency range where vascular bruits associated with significant stenosis are best heard.
To maximize the chance of hearing the deep-seated sound, firm pressure should be applied with the bell to suppress overlying bowel noise. The practitioner must listen carefully for several seconds at each location. To further reduce interference, the patient may be asked to hold their breath briefly. Comparing the sounds heard on the left and right sides is an important part of the technique to identify any asymmetry in blood flow.
Interpreting the Sounds
A positive finding is characterized as a harsh, blowing, or whooshing sound that coincides with the pulse. This sound is known as a systolic bruit, as it is heard only during the heart’s contraction phase. While a systolic bruit indicates turbulent flow, its presence alone is not definitive, as it can occasionally be heard in thin, healthy individuals without significant disease.
The presence of a continuous bruit is a much more significant finding. A continuous bruit begins in systole but extends through the entire cardiac cycle, audible during the diastolic, or resting, phase. This sound suggests a high-grade, severe narrowing of the artery, as the blood flow gradient is so pronounced that turbulence persists throughout both phases of the heartbeat.
A continuous bruit heard over the renal artery in a patient with hypertension is a strong indicator of significant renovascular disease. However, the absence of a bruit does not conclusively rule out renal artery stenosis, as the sound may be too faint or the artery may be completely blocked, meaning there is no flow to generate a sound.