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manual blood pressure question

Discussion in 'EMS Talk' started by emt seeking first job, Dec 21, 2010.

  1. Can anyone explain, in simple lay-person's words, the mechanics of what is happening when a manual blood pressure is being taken.

    The cuff squeezes the arm to the point where the provider hears no pulse. Then they hear a pulse. Then there is so little pressure they stop hearing a pulse.

    How does this make the top # being the systolic and the bottom being diastolic ?

    I do it with no problem, I just want to understand the science behind it.

    Thank you in advance.
    Last edited by a moderator: Dec 21, 2010
  2. JJR512

    JJR512 New Member

    Location:
    Maryland, USA
    EMS Training:
    EMT-Basic
    The cuff squeezes the arm until there is no blood flowing in the brachial artery. You release the pressure slowly until you hear a pulse; at this point, the pressure in the cuff has dropped enough that the systolic pressure—the pressure when the heart actually pumps—is enough to push blood past the cuff. At this point, blood is only moving in the artery when the heart is actually pumping. This produces turbulence in the blood, and that's what you hear. When you release more pressure from the cuff, the diastolic pressure becomes enough to keep keep the blood flowing even between pumps. Because the blood is now constantly flowing, without turbulence, you can't hear the variation in pressure.
  3. Thank you.

    I am re-reading the above several times to get it to "digest."

    If anyone else has another way of putting in, do not hesitate to post.

    :)
  4. emt_irl

    emt_irl Member

    Location:
    dublin, ireland
    no other way of putting it. jjr512 has typed it in one of the most clear and easy to read ways ive seen in along time!

    was good to read again whats going on inside! thanks
  5. JJR512

    JJR512 New Member

    Location:
    Maryland, USA
    EMS Training:
    EMT-Basic
    Wikipedia has an article on the sounds you hear, which includes another phrasing of why you hear nothing above systolic pressure or below diastolic pressure, but only at or in between them.

    http://en.wikipedia.org/wiki/Korotkoff_sounds
  6. Phlipper

    Phlipper New Member

    Location:
    VA
    Another question: when in a bit of a hurry, and you find your pt with big flabby arms who is fighting you has screwed the cuff around and moved the steth, does anyone guage Bp by just watching the dial - seeing when it starts jumping and stops jumping? Is this totally unreliable or just fine? I often resort to to just systolic/palp, but was curious.
  7. beano

    beano forum junky

    Location:
    USA
    EMS Training:
    EMT-Basic

    Do not resort to watching the needle bounce. To much artifact to be accurate. When in doubt do it again.or again if you have to. If you can't hear go for a palp. If all else fails just make it up.

    If you can't tell that the last part Was a joke then let me make it clear, DON'T MAKE IT UP and don't just watch the needle.

    When you hear the first noise that is when the pressure of the heart pumping overcomes the pursue of the cuff squeeze. When the sound goes away the the cuff is no longer squeezing so hard that the heart has to pump past it.
  8. medichopeful

    medichopeful Scientia est lux lucis

    Don't just go by what the needle says when it bounces. When the needle starts bouncing, it can be a sign you're getting close to the systolic. It is NOT, however, necessarily an accurate measurement.
  9. AnthonyM83

    AnthonyM83 New Member

    Location:
    Los Angeles
    First, understand that diastolic is the pressure of blood flow pushing against the sides of the arteries. There's always some pressure there from the natural constriction of the arteries (and residual flow of blood from the last time the ventricle contracted).

    Systolic is the the transient spike in the pressure of the blood pushing out against the artery that happens during each ventricular contraction.

    So, when you pump up your cuff and suprass the systolic pressure, you're basically putting a tourniquet on the patient. No blood flows past bladder of the cuff, so you don't hear a sound distal to the cuff with your stethoscope.

    Let's say a patient's BP is 120/80.

    When the cuff deflates to 120 (or I suppose technically 119 in a perfect system?), the peak pressure from the blood flow rushing from the heart after each ventricular contraction is stronger the pressure of the cuff squeezing in around the artery from the outside. The blood can now force through!

    As it forces through, there's some turbulance, from that pressure from the cuff squeezing down on the artery. So, when it gets past the distal side of the cuff where your stethoscope bell (or diaphragm...though bell is supposed to pick up the lower tones) is waiting. You now start hearing the transient peak in pressure (called systolic) each time the heart pumps. Even as you keep going down, there's still enough pressure to cause turbulance to make the rush of blood forward audible under your bell.

    THEN, as you hit 80, EVEN when there's not that transient preak in pressure during each heart beat, the blood flowing (at 80mmHg) is now able to maintain that push outward against the sides of the blood vessel. SO, your external BP cuff is no longer pushing down on the arteries enough to squeeze them in and disrupt the smooth path. You no longer have "smooshed" blood vessels, only normal blood flow. SO, your bell can't pick up those beats.

    Sometimes there's residual venous congestion that causes you to hear beating all the way down to 0. Usually, this is an effect of taking a blood pressure...and you wouldn't have heard the heart beat under your bell if you had put it in the same spot BEFORE taking the BP. This happens more in some patient conditions. You're technically supposed to record 3 blood pressures...when sound showed up, when it changed to muffled, and when it went away completely. 120/80/0 or 118/76/2. In some areas, they put a down arrow as the diastolic to symbolize you heard it "all the way down". Some right it 120/0. It depends on agency policy (or really often it's unregulated).


    So, that's how *I* think of the BP. There might be some physics stuff in there that's not explained 100% accurately. But that allows it to make sense in my head and lets me be able to analyze what each value means. I had a lot of trouble really understanding why each number was what and didn't have someone explain it to me better (despite a lot of asking) until 3 years later. Then, kind of filled in the extra holes.

  10. Could someone explain what the word "artifact" means in that context ?

  11. Training stethoscopes for BP have two ear pieces so the instructor or tester can listen in.
  12. Thank you everyone for your attention to my thread.

    :):):)
  13. emt_irl

    emt_irl Member

    Location:
    dublin, ireland
    outside noise, or lets say the patients is still waving arms around that will create the artifact or extra noise
  14. JJR512

    JJR512 New Member

    Location:
    Maryland, USA
    EMS Training:
    EMT-Basic
    I have never ever heard of recording three numbers for a BP before. Not three numbers that are heard, anyway. I have heard of calculating MAP or PP, but the third number you're talking about, specifically the idea of recording it, is new to me.

    I was taught in class that when a pulse can be heard all the way down to 0, to try again and this time listen intently for a specific change in the sound of the beat, and to note the number where that happened as the diastolic.
  15. Aprz

    Aprz Active Member

    Location:
    California
    I was never taught about that in class either, but it's in a lot of books that mention BP including Bates' guide. I don't work yet, but I could imagine that causing a lot of confusion if I did use that notation just because I got a lot of wtf-faces at school when talking about it.

    That middle number is a lot different than PP and MAP, but that makes me wonder now... Which mumber to use? The middle or last one? Haha.

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