Physiology, Korotkoff Sound


Article Author:
Miles Campbell


Article Editor:
Leela Sharath Pillarisetty


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Updated:
3/31/2019 1:51:52 PM

Introduction

The medical practice of measuring blood pressure by constricting the upper arm and listening with a stethoscope to assess when the first sound and final sounds are audible dates back over 100 years ago. This method is still considered the gold standard for noninvasive blood pressure measurement. While there have been advancements in the technique for upper arm constriction, the quality of stethoscopes, and most recently fully automatic blood pressure devices – the overall process has not changed significantly. The discovery and utilization of Korotkoff sounds (KorS) are what allows physicians to check patient blood pressures and provide appropriate medical treatments. Understanding the underlying physiology and proper measurement techniques are important for quality patient care and appropriate medical therapy.

Issues of Concern

Korotkoff sounds (KorS) are the audible noises used to measure blood pressure. Throughout the short process of taking a blood pressure measurement, the sounds change a phenomenon which has undergone extensive study. Korotkoff sounds are broken down into five distinct phases, each with a distinct sound and waveform associated with the phase. Phase I has a clear tapping tone. Phase II is associated with a softening of the tapping and a swishing element. Phase III sounds like phase I but with distinct sharpening. Phase IV is noted to have abrupt muffling of the sounds, followed by Phase V which is the cessation of all sounds. When measuring blood pressure, a cuff is applied to the upper arm and inflated to the point that blood is no longer able to flow through the brachial artery. When pressure is released to point blood is again able to flow, phase I begins. As pressure continues to decrease the examiner can hear the different phases, ultimately concluding with phase V when no sound is audible. The first sound appears as the pressure approaches systolic blood pressure (SBP) and the diastolic blood pressure (DBP) measurement is by the disappearance of sound.[1] Despite 100 years of debate and research, the underlying physiology of Korotkoff sounds is not fully understood. There are several theories which are prominent in the literature trying to explain the underlying cause of Korotkoff sounds. There are two main schools of thought guiding the research of Korotkoff sounds; the sounds are a result of fluid turbulence or the result of arterial wall oscillations. Adding a layer of complexity, those who test the arterial walls are uncertain what the best method of experimentation is. For example, Dr. Charles Babbs used a primarily mathematical approach to analyze wall motion mechanics, while Drzewiecki et al. used an electrical analogy in attempts to postulate the equations governing the fluid dynamics and nonlinear compliance of arterial segments. While there are many ideas, two commonly speculated theories for the causation of the sounds heard in stethoscopes will be briefly discussed here.[2]

Dr. Nikolai Korotkov is the physician credited with discovering the sounds that carry his name. He speculated the sounds resulted from the closing and opening of the vessel. He suspected the net transmural pressure oscillating from positive to negative was responsible for the different phases of sound. Dr. Charles Babbs, conducted an experiment measuring blood pressure and the associated Korotkoff sounds, concluding the sounds were from the transition of the vessel from a buckled to fully expanded the state. The transient vibrations of the artery being the mechanism for actual sound production. The study, while not universally accepted as proof for the physiologic source of Korotkoff sounds. It was able to explain how venous engorgement downstream to the collapsed artery adds to the increased resistance, preventing artery collapse, as the cause of the muffling heard in phase IV.[2]

A study performed at Chengdu University in China demonstrated the importance of proper technique when measuring blood pressure (BP). The study concluded that different stethoscope positioning results in sounds being present sooner/later, resulting in higher/lower BP readings than the actual blood pressure. Over the last 100 years, it has been widely accepted that hearing the first sound is in direct correlation with SBP. However, there is still discourse regarding measurement of the DBP. It has actually become known as the “diastolic dilemma” since the argument is whether the DBP should be measured during phase IV when the sound muffles or in phase V when the sound disappears completely. The position of the stethoscope also affects auscultation and influences the DBP reading by up to 10 mm Hg. The study was able to recommend stethoscope positioning which most accurately represented the DBP, via comparison to an invasive blood pressure measurement simultaneously. The study concluded proper placement of the cuff, just above the elbow, with the stethoscope under the cuff provided the most accurate blood pressure readings. This study along with many others have demonstrated how a seemingly simple procedure can have extensive variability, dependent on multiple factors (cuff pressure, circumferential and longitudinal stethoscope positioning, and sound cutoff). Ongoing research and continued technological advancements will hopefully definitely pinpoint the true physiology responsible for Korotkoff sounds, enabling even more precise blood pressure readings and patient care.[2][1][3][4][5][1]

Clinical Significance

As medical technology continues to advance, machines are assuming on a more significant role in everyday patient care. One of the most prominent automated medical tests is blood pressure readings, whether in the clinic, the ICU, or labor deck. Patients are having their blood pressure (BP) measured using devices which rely on oscillometric methods to give medical providers information to guide treatment. Extensive data analyses of these machines have demonstrated an overestimation of hypotensive BPs and an underestimation of hypertensive BPs. The reading of BP within normal ranges have proven to be accurate and reliable.[6] However, in most scenarios, it is the abnormal BPs that are most important to medical providers. It is quintessential for accurate blood pressure readings in stroke, acute kidney injury, septic, etc., patients. Blood pressure is easy to assess and easy to correct to prevent further deterioration. A wise clinician will often advise staff to manually check the BP if the machine reading is suspicious compared to patient status.[7] Despite the advancement of technology, we still rely on human measurement for a second and more trusted blood pressure reading. It is for this reason, understanding KorS and how to properly obtain BP readings is crucial. Accurate blood pressure readings obtained manually via cuff and stethoscope are still a vital aspect of modern medicine, and with a greater understanding of Korotkoff sounds, we will more precisely measure BP and allow better clinical decision making.


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Physiology, Korotkoff Sound - Questions

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After interviewing an 86-year-old African American female for a recent admission for syncopal episodes her vital signs are evaluated. The blood pressure cuff is appropriate applied and the stethoscope head placed under the cuff and above her brachial artery. The cuff is inflated and allowed to slowly deflate. Listening for the Korotkoff sounds shows phase I at 124 mm Hg, phase II at 110 mm Hg, phase III at 95 mm Hg, phase IV at 86 mm Hg, and finally, phase IV at 78 mm Hg. What is the patient's blood pressure?



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A 21-year-old male patient comes in for a sports physical before returning to college. He does not have a significant medical history and states he feels well. His heart rate is 65/min, respiratory rate 13/ min, and temperature 98.8 F. The blood pressure cuff is placed over his upper arm and the stethoscope is properly positioned under the cuff and above the brachial artery. The first Korotkoff sound is heard at 121 mm Hg, phase 2 at 106 mm Hg, phase 3 at 93 mm Hg, phase IV at 79 mm Hg, and phase V at 71 mm Hg. What sound is associated with phase IV and what is the physiologic reason for this sound?



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The automatic sphygmomanometer is not functioning so the blood pressure is checked manually. What are the Korotkoff sounds heard in each phase which one will hear as you check blood pressures?



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Which of the following is true regarding Korotkoff sounds? Select all that apply.



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A 23-year-old female presents to the emergency department after a motor vehicle accident. The patient was an unrestrained passenger who was ejected from the car and found unconscious, several yards away from the vehicle. She was intubated on the scene and rushed to the hospital. Her vitals on arrival are: blood pressure of 76/41, heart rate of 151/ min, respiratory rate of 11/min, and oxygen saturation of 98%. Physical exam reveals regular heart rate and rhythm without murmurs and the chest is clear to auscultation bilaterally without wheezes or rales. Reflexes are intact throughout, and the patient has intact rectal tone. The patient is most likely suffering from what? Also, what is the most immediate first step of treatment?



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A 47-year-old female presents to her primary care provider for her annual physical. Her past medical history is only significant for peripheral vascular disease, which is controlled with antihypertensive medications. She was a former smoker of 15 years before quitting three years ago. She denies having any current complaints and states she is doing well. You decide to take her vital signs before stepping out to discuss the case with the attending. Her heart rate is 71 bpm, respiratory rate 12/min, and temperature 98.7 F. You place a blood pressure cuff over her left arm and then place your stethoscope underneath the cuff and above the brachial artery. You inflate the cuff and slowly begin to release the pressure. Phase I is auscultated at 134 mm Hg, phase II is auscultated at 120 mm Hg, phase III is auscultated at 104 mm Hg, phase IV is auscultated at 91 mm Hg. You note as the cuff continues to completely deflate the quiet muffling sound persists. You are unable to appreciate a true phase V Korotkoff sound. Based on this reading, what blood pressure would you write down before rechecking in five minutes?



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Physiology, Korotkoff Sound - References

References

Pan F,Chen F,Liu C,Yang Z,Liu Z,Zheng D, Quantitative Comparison of Korotkoff Sound Waveform Characteristics: Effects of Static Cuff Pressures and Stethoscope Positions. Annals of biomedical engineering. 2018 Nov;     [PubMed]
Babbs CF, The origin of Korotkoff sounds and the accuracy of auscultatory blood pressure measurements. Journal of the American Society of Hypertension : JASH. 2015 Dec;     [PubMed]
Meidert AS,Saugel B, Techniques for Non-Invasive Monitoring of Arterial Blood Pressure. Frontiers in medicine. 2017;     [PubMed]
Liu C,Griffiths C,Murray A,Zheng D, Comparison of stethoscope bell and diaphragm, and of stethoscope tube length, for clinical blood pressure measurement. Blood pressure monitoring. 2016 Jun     [PubMed]
Xiang H,Liu Y,Qin Y,Cao Z,Guo T,Yu M, A pilot application of Korotkoff sound delay time in evaluating cardiovascular status. Technology and health care : official journal of the European Society for Engineering and Medicine. 2015     [PubMed]
Trigg SA,Abreu D,Bitton-Foronda B,Foley FC,Gibson AL, Comparison of Systolic Blood Pressure Measurements by Auscultation and Visual Manometer Needle Jump. International journal of exercise science. 2019     [PubMed]
    [PubMed]

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