this is from wikipedia, pretty good definition of it. about your question for palpating a blood pressure, saying "110/palpation" is only getting the systolic bp. you're not concerned with the diastolic at that point. it's a good way of checking someone's bp quickly, then comparing it to one taken with a stethoscope. for example, someone is at a 5k race and feeling dehydrated, you can quickly palpate their pressure and if you palpate 120, it's a whole lot different than if you palpated 80. still you almost always want to confirm a palpated pressure with an auscultated one.
you can even take palpation a step further, in critically ill and injured patients we will often just palpate the presence and quality of pulses as a quick initial impression on distal perfusion. if a patient has a strong carotid but absent radial, then i can quickly figure that my systolic pressure might be around 70-give or take. it's a rough estimate and always confirmed but it's helpful in a bad situation for a baseline assessment.
the sounds heard during measurement of blood pressure are not the same as the heart sounds 'lub' and 'dub' that are due to the closing of the hearts valves. if a stethoscope
is placed over the brachial artery
in the antecubital fossa
in a normal person (without arterial disease), no sound should be audible. as the heart
beats, these pulses are transmitted smoothly via laminar (non-turbulent) blood flow throughout the arteries and no sound is produced. also, if the cuff of a sphygmomanometer
is placed around a patient's upper arm and inflated to a pressure above the patient's systolic blood pressure
, there will be no sound audible. this is because the pressure in the cuff is high enough such that it completely occludes the blood flow
. it is similar to a flexible tube or pipe with fluid in it that is being pinched shut.
if the pressure is dropped to a level equal to that of the patient's systolic blood pressure, the first korotkoff sound will be heard. as the pressure in the cuff is the same as the pressure produced by the heart, some blood will be able to pass through the upper arm when the pressure in the artery rises during systole
. this blood
flows in spurts as the pressure in the artery rises above the pressure in the cuff and then drops back down beyond the cuffed region, resulting in turbulence
that results in audible sound.
as the pressure in the cuff is allowed to fall further, thumping sounds continue to be heard as long as the pressure in the cuff is between the systolic and diastolic pressures, as the arterial pressure keeps on rising above and dropping back below the pressure in the cuff.
eventually, as the pressure in the cuff drops further, the sounds change in quality, then become muted, then disappear altogether. as the pressure in the cuff drops below the diastolic blood pressure, the cuff no longer provides any restriction to blood flow allowing the blood flow to become smooth again with no turbulence and thus produce no further audible sound.
korotkoff actually described five types of korotkoff sounds:
- the first korotkoff sound is the snapping sound first heard at the systolic pressure. a clear tapping sound; onset of the sound for two consecutive beats is considered systolic.
- the second sounds are the murmurs heard for most of the area between the systolic and diastolic pressures.
- the third = a loud, crisp tapping sound.
- the fourth sound, at pressures within 10 mmhg above the diastolic blood pressure, were described as "thumping" and "muting".
- the fifth korotkoff sound is silence as the cuff pressure drops below the diastolic blood pressure. the disappearance of sound is considered diastolic blood pressure- two points below the last sound heard.