The sound comes from the cuffed artery.
Your heart creates a pressure pulse with each beat. Systolic pressure is the peak arterial pressure during a heartbeat. Diastolic pressure is the lower arterial pressure between beats. Blood pressure is usually reported as systolic over diastolic, in millimeters of mercury (mmHg).
Korotkoff sounds are the taps and other sounds heard over a compressed artery as a cuff slowly deflates. Cuff compression changes how pulse waves move the arterial wall and nearby tissue. These vibrations reach the stethoscope while blood passes through the partly compressed artery. These are different sounds from the heart-valve “lub-dub” heard on the chest. Sources 1, 2, and 4
Above systolic
The cuff pressure is high enough to block blood flow through the compressed artery. There are no Korotkoff taps.
Between the two pressures
As pressure falls, blood passes through the partly compressed artery during each beat. Recurring sounds begin. The onset of repeated taps, phase I, marks systolic pressure.
Near the lower boundary
Sounds can become muffled, called phase IV. Muffling is a change in sound, not the usual adult diastolic endpoint.
Below diastolic
Korotkoff sounds disappear, called phase V. This is the usual adult diastolic endpoint. Blood continues to flow; silence does not mean flow has stopped.
One pressure scale.
One beat at a time.
In fictional case BP-A, the model's arterial pressures are 118/76 mmHg. The cuff begins at 150 mmHg and falls by 2 mmHg each second. A modeled heartbeat occurs once per second. First, predict when the first tap will occur. Then play the model and compare the sound, text, and gauge.
Sound is optional and starts only after you choose it. Begin with low device volume. Every pulse and silent beat also has a text and visual equivalent.
A digital control, not a measured dB level.
Audio is off. The complete visual model is available.
The cuff is above the model's systolic pressure. Flow is blocked through the compressed artery; no Korotkoff sound is expected.
No beat observed yet.
Moving the time control pauses playback. Arrow keys move by 0.1 second. “Jump before first tap” goes to 14 seconds; “Jump before last tap” goes to 34 seconds.
First-tap observation: not marked.
Disappearance observation: not marked.
Your marks record the current simulated gauge pressure. Reaction time and the interval between beats affect a click; this activity gives no clinical score. Use the evidence review to explain your observations. Reset clears these temporary marks.
Listen for a repeated event
A single tap can be noise. In a real manual measurement, verify the start with repeated beats and use the instructor's full procedure. In this model, taps at 118 and 116 mmHg establish the repeated onset. Sounds become softer near the end. The last modeled sound occurs at 78 mmHg; the next expected beat, at 76 mmHg, is silent.
The model sets a sharp boundary for learning. Real observations have finite beat spacing, variable sound quality, and measurement uncertainty. This model does not claim 1 mmHg clinical accuracy.
Read the change.
Explain the endpoint.
Use the model's known values to connect what you heard or saw with a reported blood pressure. You can inspect the complete case with audio off.
| Time | Cuff pressure | Observation | Meaning in this model |
|---|---|---|---|
| 0 to 15 s | 150 to 120 mmHg at beats | No Korotkoff sound | Cuff above systolic |
| 16 s, then 17 s | 118, then 116 mmHg | First tap, confirmed by another tap | Repeated onset supports systolic = 118 |
| 18 to 33 s | 114 to 84 mmHg at beats | Recurring synthetic taps | Compressed-artery sound continues |
| 34 to 36 s | 82, 80, 78 mmHg | Softer, muffled synthetic pulses | Illustrative phase IV, not the usual adult diastolic endpoint |
| 37 s | 76 mmHg | First expected beat without a sound | Programmed phase V endpoint = 76 |
| 38 to 40 s | 74 to 70 mmHg | Korotkoff sounds remain absent | Blood flow continues without these sounds |
The exact pressures assigned to muffling are invented teaching choices. Real Korotkoff phases do not occur at universal fixed pressure intervals. A single last sound does not establish an exact boundary in a real measurement; the observer checks the disappearance and follows the full measurement protocol.
Choose “Show the model's evidence” above to reveal the labeled timeline, exact event table, and worked report. The evidence can be opened before, during, or after playback.
Make the listening conditions work.
A more expensive stethoscope cannot correct every listening problem. Before repeating a supervised classroom measurement, check the setup with your teacher. A quiet, well-placed chestpiece matters.
- Fit and activate the stethoscope. Earpieces point forward toward the nose. If the model has a selectable chestpiece side, verify the intended side is active. Follow its manufacturer's directions.
- Locate the listening site. Place the chestpiece, the round listening end, lightly over the brachial artery just below the cuff, in the inner elbow region. Keep it out from under the cuff. Avoid pressing hard or rubbing tubing, clothing, or the chestpiece.
- Set the conditions. Use the correct cuff size for the arm. Support the arm with the cuff at heart level. Keep the listener, subject, and room quiet. See the illustrated guide for the full preparation sequence.
- Slow the release. Deflate at about 2 mmHg per second. Listen through the whole sequence: first repeated taps, changing sounds, then disappearance. Fast release can skip the useful events.
- Stop and ask. If there is discomfort, or you cannot hear the expected sounds, fully deflate the cuff and ask the teacher to check placement, equipment, and technique. Do not keep pumping higher to search for a sound.
Record and explain
Play BP-A with audio off. Use the visual and text signals to mark the first tap and sound disappearance. Confirm that the first tap is followed by another tap. Review the evidence table. Explain why the last audible beat at 78 is different from the programmed silent boundary at 76.
Reflect and revise
If you wish, repeat with the synthetic sound enabled. Describe the recurring tap and the muffled ending. State why hearing silence alone cannot distinguish an overinflated cuff from cuff pressure below diastolic.
Quick vocabulary
Cuff pressure: pressure applied by the inflatable arm cuff. Brachial artery: the upper-arm artery used for this listening method. Korotkoff sounds: sounds from the compressed artery and surrounding tissues as the cuff deflates. Systolic: peak arterial pressure during a heartbeat. Diastolic: lower arterial pressure between beats. mmHg: millimeters of mercury, a pressure unit. Phase I: repeated sound onset. Phase IV: muffling. Phase V: sound disappearance.
The evidence behind the model.
Clinical measurement sources support the procedure and endpoints. The 40-second timeline, 118/76 values, and synthetic sound timbre are original fictional teaching choices.
- American Heart Association scientific statement (2019) · Measurement of Blood Pressure in Humans. Preparation, cuff and stethoscope technique, slow deflation, and auscultatory endpoints.
- New England Journal of Medicine · Videos in Clinical Medicine: Blood Pressure Measurement. Korotkoff phases and measurement technique.
- CDC · Measuring Your Blood Pressure. Positioning and measurement preparation.
- Primary research (2023) · The fundamental mechanisms of the Korotkoff sounds generation. Arterial-wall and tissue motion underlying recorded Korotkoff sounds. The synthesized taps here are illustrative and do not reproduce that study's measurements.