Korotkoff sounds

To reduce deviations in blood pressure measurement in the clinic, the patient and clinician should not talk during blood pressure readings. The measurement arm is supported and positioned at heart level with the blood pressure cuff encircling at least 80% of arm circumference. If a mercury or aneroid device is used, then the palpatory method must be used first to estimate the systolic blood pressure.18 If an automated device is used, this is not necessary. After the patient s cuff is inflated above the systolic pressure, the mercury column should drop at a rate of 2 to 3 mm per second. A stethoscope placed over the brachial artery in the antecubital fossa identifies the first and last audible Korotkoff sounds, which should be taken as systolic and diastolic pressure, respectively. A minimum of two readings at least 1 minute apart are then averaged. If measurements... 

Korotkoff sounds The noise heard over an artery by auscultation when pressure over the artery is reduced below the systolic arterial pressure. 

The clinician should listen for Korotkoff sounds with the stethoscope. The first phase of Korotkoff sounds is the initial presence of clear tapping sounds. Note the pressure at the first recognition of these sounds. This is the SBP. As pressure continues to deflate, note the pressure when all sounds disappear (also known as the fifth Korotkoff phase). This is the DBP... 

In all instances, using the stethoscope bell rather than the diaphragm is recommended. Low-frequency Korotkoff sounds may not be heard clearly and accurately with the diaphragm. This is especially problematic in patients with faint or distant sounds. 

Patients with an auscultatory gap may have either underestimated SBP or overestimated DBP measurements. In this situation, as the cuff pressure falls from the true SBP value, the Korotkoff sound may disappear (indicating a false DBP measurement), reappear (a false SBP measurement), and then disappear again at the true DBP value. This is often identified by using the palaptory method to estimate SBP and then inflating the cuff an additional 30 mm Hg above this estimate because the gap is usually less than 30 mm Hg. When an auscultatory gap is present, Korotkoff sounds usually are heard when pressure in the cuff first starts to decrease after inflation. 

Piezoelectric sensors are used in cardiovascular applications for external (body surface) and internal (intracardiac) phonocardiography. They are also used in the detection of Korotkoff sounds for indirect blood pressure... 

Further deflation of the cuff leads to several more Korotkoff sounds, ultimately ending in silence as the pressure in the cuff drops below the diastolic blood pressure. The disappearance of sound determines the lower of the two readings that comprise a blood pressure measurement—the diastolic reading. The diastolic reading corresponds to the cycle where the heart is relaxing following its contraction. 

The standard explanation for vascular sound found in most medical textbooks explains that vascular sound is produced by fluid vibrations due to turbulence of the blood in the region of the narrowed vessel or valve. In the case of sound in an artery the sound is referred to as the vascular bruit. In the case of valvular sound the sound is termed a murmur. In fact, turbulence is offered up as the most common explanation for the occurrence of most any vascular sound even if it does not match experimental observations. For example, it is commonly proposed that the KorotkofF sounds of blood pressure determination are turbulence. 

The turbulence mechanism for the KorotkofF sound has been excluded as a valid theory of KorotkofF by Drzewiecki et al. (1989), on the basis of the wide variety of observations available for the KorotkofF sounds. While a turbulence theory does not fit the KorotkofF sounds it maybe useful in explaining some sounds of vascular disease. Sound generation by turbulence maybe a popular theory for vascular sound because it is a very efficient sound-generating mechanism. For example, turbulence provides the sound source for the Woodwind type of musical instruments. 

The flow dynamics of flexible vascular stenosis differ greatly from the rigid concentric stenosis as the normal comphant free wall section of artery can respond to local blood pressure (Siebes and D Argennio, 1989). This permits blood pressure to affect the lumen area, resulting in a pressure-dependent flow resistance, so that the free wall may lead to blood vessel constriction for low lumen pressure conditions. The condition where a compliant vessel free wall reduces the lumen area to increase flow resistance has been studied extensively in collapsible vessels such as the veins and results in a phenomenon referred to as flow limitation. Flow limitation is also known as the Starhng resistance effect (Drzewiecki et al., 1997). It is proposed here that flow limitation of a diseased artery with a flexible free wall leads to vascular sound generation as in the case of the Korotkoff sounds (Drzewiecki et al., 1989). The free wall mechanism of vascular sound is distinctly different from the turbulence theory and results in a characteristically different sound. 

This type of sound-generation mechanism was described earliest by Drzewiecki et al (1989) where the Korotkoff sounds of blood pressure determination were modeled by a computational fluid dynamic model. In this model, the brachial artery was represented by a similar free wall artery structure that was found to be an efficient sound-generating process. 

Clinical usefulness ofvascular sound information for disease diagnosis has been reviewed. Theories and experiments in the analysis of the production and origin of vascular sounds in a blood vessel are several and it is found that the plaque dome structure associated vibrating mechanism favors such sound generation in diseased arteries. Coupled with the previously established Korotkoff sound theory, a new approach to a more accurate diagnosis of carotid artery disease via auscultation is plausible. 

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