Korotkoff sounds are auditory cues during a common medical procedure. These sounds provide valuable insights into the circulatory system. Understanding their nature and origin helps explain how routine health assessments yield important information.
What Are Korotkoff Sounds?
Korotkoff sounds are the specific arterial sounds medical professionals listen for when measuring blood pressure using a non-invasive method. These sounds are heard through a stethoscope placed over the brachial artery in the upper arm, while a blood pressure cuff (sphygmomanometer) is in use. The discovery of these sounds dates back to 1905, when Russian physician Nikolai Korotkoff first described them. His observations provided a simple yet precise technique for assessing arterial pressure, revolutionizing blood pressure measurement.
How Korotkoff Sounds Are Produced
Korotkoff sounds are generated by the turbulent flow of blood through a partially compressed artery. When a blood pressure cuff is inflated around the upper arm, it temporarily occludes blood flow in the brachial artery. As the pressure in the cuff is gradually released, blood begins to spurt through the constricted artery, creating vibrations audible through a stethoscope. The sounds only appear when cuff pressure is between systolic and diastolic pressures, causing arterial pressure to rise and fall with each heartbeat. Without cuff compression, blood flows smoothly (laminar flow) and silently.
Their Role in Blood Pressure Measurement
These sounds are used to determine a person’s systolic and diastolic blood pressure readings. The moment the first Korotkoff sound becomes audible signifies the systolic blood pressure. This represents the maximum pressure exerted in the arteries when the heart contracts and pumps blood. As the cuff continues to deflate and the sounds change, the point at which they eventually disappear marks the diastolic blood pressure. This indicates the minimum pressure in the arteries when the heart is at rest between beats. The auscultatory method, relying on these sounds, remains a widely accepted and accurate technique for blood pressure assessment.
The Five Distinct Phases of Korotkoff Sounds
The sounds heard as the blood pressure cuff deflates are categorized into five phases, known as Korotkoff phases (K1-K5).
Phase I (K1) marks the initial appearance of faint, clear, repetitive tapping sounds. These sounds gradually increase in intensity and indicate the systolic blood pressure.
Phase II (K2) follows with sounds that become softer and may acquire a swishing or murmuring quality. This phase occurs as more blood flows through the artery, though it is still partially compressed.
Phase III (K3) is characterized by the return of sharper, crisper sounds, often becoming louder than those in Phase I. Despite their increased intensity, these sounds still occur within the turbulent flow.
Phase IV (K4) involves a muffling of the sounds, which become softer and blowing in quality. This change signifies a significant reduction in turbulence as the artery opens further.
Phase V (K5) is the point where all sounds completely disappear. This silence indicates that blood flow has returned to a smooth, laminar pattern, and this point is used to determine the diastolic blood pressure.