A bruit of longer duration is associated with more severe stenosis especially if it extends into diastole. Venous hums can masquerade as continuous bruits. Intensity of the bruit has in one study been shown to correlate with degree of stenosis. In practice, the intensity of the bruit is related to the sixth power of the velocity of the blood flow and is the major determinant of intensity. One important clinical aspect of the Philips equation is that intensity is loudest with the bell distal to the site of the obstruction and directly facing the vessel.
Orbital auscultation is a useful adjunct to the method described above.
This technique involves gently placing the bell of the stethoscope on the orbit, lid closed, while the other eye remains open to reduce blinking sounds. Bruits heard should be documented as present or absent and not further graded. The finding of an ocular bruit suggests a contralateral internal carotid artery stenosis with augmented flow through the carotid ipsilateral to the bruit. This may be a feature of the populations studied as intracranial cerebrovascular disease is more common in Asian people. As with any diagnostic test, the predictive value of carotid bruit is dependent upon the prevalence of the disease in the population.