How does one know the true systolic number of a blood pressure?

Hi, I want to ask a question about blood pressure sounds. When taking blood pressure I hear a heart beat at 140mmHg but just one heart beat and then it stops. Then I hear another heart beat start at 110mmHg and it is consistent. My question is this: Is the 140mmHg my systolic number or is the first beat of a consistent set of beats my systolic number?

I have been told the first sound, then in school I was told the first consistent heart beat sound is the systolic number. I am a little confused and considering there is a 30mmHg difference I feel this is a very important consideration for me to have made clear by a professional before I am considered a professional. Thank you for your time.

Submitted by Christopher from Indiana on 08/04/2014

Dear Christopher,
Below is a method that I use to measure blood pressure. You can find further information in most textbooks of Physical Diagnosis.

Technique of Measuring Blood Pressure

1. The subject should be sitting in chair with his feet on the floor (sitting with the legs hanging off of the examination table will falsely raise the blood pressure).
2. Apply the fully deflated cuff snugly around the upper arm and place the marked area over the inside (medial) aspect of the elbow which is over the brachial artery.
3. While palpating the radial pulse, inflate the cuff and note the pressure reading at the point the pulse is extinguished. This estimates the systolic blood pressure.
4. Apply the stethoscope over the brachial artery above the elbow joint just below the cuff.
5. Inflate the cuff to a reading which is at least 15 mmHg above where the pulse was extinguished. Inflating the cuff too rapidly to high pressures may cause discomfort and result in a temporary increase in the pressure over the baseline.
6. Listen for the onset of the Karotkoff sounds which is the systolic pressure.
7. Drop the pressure slowly (2 mmHg per beat) until the sounds disappear. This is the diastolic pressure.

Points to Remember:

An alternate method is to arbitrarily pump the cuff to 200 mmHg and listen for the sounds. This is not recommended because (1) It may cause pain. (2)The pressure may actually be higher than 200 and one could have inflated to the level of the ‘auscultatory gap’ which is a pressure range in some patients where the sounds may actually temporarily disappear which can cause significant underestimation of the systolic pressure.

If you hear an occasional sound at the beginning of step 6 above, it could be do to a variation of the pressure of a single beat which is common in the presence of an irregular heart beat. Repeat the measurement until you get a clear reading during a period regular rhythm (if possible). Accurate measurement of the blood pressure by this technique depends on the presence of a regular rhythm. In patients with frequent premature beats and atrial fibrillation, the pressure varies from beat to beat. By auscultation, one can better estimate the pressure. Digital devices essentially measure one systolic and one diastolic pressure and assume the rhythm is regular. The varying RR intervals will often lead to inaccurate readings of both the blood pressure and the pulse. The digital pressure recording should not be trusted in the presence of an irregular rhythm.

In patients with severe respiratory distress (eg., asthma) or pericardial tamponade, the pressure will vary significantly with the respiratory cycle (pulsus paradoxus). The degree of paradox is the pressure difference from the onset of all sounds to the appearance of sounds during the entire respiratory cycle (consistent sounds). A paradox reading of >10 mmHg is considered abnormal.

Finally, in some individuals, one can hear Karotkoff sounds close to zero. In this case, the point at which the sounds become muffled is considered the diastolic pressure. It is appropriate to give 3 readings in this situation. For example: 130/70/15 or 150/70/0.

One last point: When measuring the pressure in a patient for the first time, measure it in both arms. A consistent difference of >10 mmHg is a sign of possible arterial obstruction which may need to be investigated. The correct pressure is obviously in the arm with the highest reading.

I hope this answers your question. Sincerely.