Blood Pressure

Blood Pressure: Normal Examination
Parameters and Student Data

Blood Pressure Lab: How to Take a Blood Pressure Measurement

Using the Sphygmomanometer

Position the patient's arm so the anticubital fold (inside elbow area) is level with the heart. Support the patient's arm with your arm or a bedside table.
Center the bladder of the cuff over the brachial artery approximately 2 cm above the anticubital fold. The arrow should line up with the artery. Proper cuff size is essential to obtain an accurate reading. Be sure the index line falls between the size marks when you apply the cuff. Position the patient's arm so it is slightly flexed at the elbow.
Palpate the radial pulse and inflate the cuff until the pulse disappears. This is a rough estimate of the systolic pressure.
Place the stethescope diaphragm over the brachial artery and the earpieces in your ears.
Inflate the cuff to 30 mmHg above the estimated systolic pressure and hold it there by tightening the knurled knob.
Release the cuff pressure slowly by turning the knurled knob just until you hear the hiss of air being released (no greater than 5 mmHg per second).
The level at which you consistantly hear the heartbeats through the stethescope is the systolic pressure. The needle on the gauge should also start a pulsing movement at this point. Record this value as the systolic pressure.
Continue to release the cuff pressure until the sounds muffle and disappear. The point at which you no longer hear sounds and the needle on the gauge stops its pulsing movement is the diastolic pressure. Record the value from the gauge.
Record the blood pressure as systolic over diastolic ("120/70" for example).

What Do You Hear While Measuring Blood Pressure?

Phase 1
A loud, clear tapping (or snapping) sound is evident, which increases in intensity as the cuff is deflated. As an example, this phase begins at a cuff pressure of 120 millimeters of mercury and ends at a pressure of 106 mm Hg. The beginning of phase 1 is taken as systolic pressure.

Phase 2:
A succession of murmurs can be heard. Sometimes the sounds seem to disappear during this time (auscultatory gap). This may be a result of inflating or deflating the cuff too slowly. In our example, this phase begins at a cuff pressure of 106 mm Hg and ends at 86 mm Hg.

Phase 3:
A loud, thumping sound, similar to phase I but less clear, replaces the murmurs. This phase begins at a cuff pressure of 86 mm Hg and ends at 81 mm Hg.

Phase 4:
A muffled sound abruptly replaces the thumping sounds of phase 3. This phase begins at a cuff pressure of 81 mm Hg and ends at 76 mm Hg.

Phase 5:
All sounds disappear. This phase is absent in some people. The pressure at which the sound becomes muffled (beginning of phase 4) and the pressure at which the sound disappears (beginning of phase 5) are taken as measurements of diastolic pressure. Phase 5 is closer to the true value, however, phase 4 is easier to detect and the measurements are more reproducible.

Blood goes through the arteries in a laminar flow, that is, blood in the central axial stream moves faster than that in the peripheral layers, with little or no transverse flow (mixing) between layers. Therefore, at rest, the artery is silent when auscultated.

When the sphygmomanometer bag is inflated to a pressure above the systolic pressure, the flow of blood is stopped and the artery is again silent.

As pressure in the bag drops to levels between the systolic and diastolic pressures of the artery, the blood is pushed through the compressed walls of the artery, creating turbulent flow. Now, the layers of blood are mixed by eddies that flow at right angels to the axial stream, causing turbulence and vibrations in the artery that are heard as sound in the stethoscope.

Interpretation

Higher blood pressures are normal during exertion or other stress. Systolic blood pressures below 80 may be a sign of serious illness or shock.
Outliers in systolic pressure may be a result of a defense reaction, a rise in blood pressure associated with the anxiety of measurement. In a clinic setting, BP early in the visit may be higher due to the "white coat" effect. It's the same result, higher BP than expected, but for different reasons. Sometimes it helps to retake the blood pressure near the end of the patient's visit.
In a clinic setting, blood pressure should be taken in both arms on the first encounter. If there is more than 10 mmHg difference between the two arms, use the arm with the higher reading for subsequent measurements.
Always recheck "unexpected" blood pressures.
In children, pulse and blood pressure vary with the age. The following tables present a rough guide to BP in adults & children:

Blood Pressure Classification in Adults
Category	Systolic	Diastolic
Normal	<140	<90
Isolated Systolic Hypertension	>140	<90
Mild Hypertension	140-159	90-99
Moderate Hypertension	160-179	100-109
Severe Hypertension	180-209	110-119
Crisis Hypertension	>210	>120

Average Pulse and Blood Pressure in Normal Children
Age	Birth	6mo	1yr	2yr	6yr	8yr	10yr
Systolic BP	70	90	90	92	95	100	105

In the 2005 blood pressure lab, students practiced taking a rested blood pressure with each person measuring a partner's blood pressure. The results are shown in the chart below.

The above graph shows the average rested blood pressure to be approximately 118/74, correlating with normal arterial blood pressure for young adults. (Older adults would probably have an average systolic pressure that is even higher with an average diastolic pressure that is about the same).