A Guide to Blood Pressure 210

7/31/2019 A Guide to Blood Pressure 210

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X. Blood Pressure

A. INTRODUCTION

When the ventricles contract (systole), the pressure inside the ventricles increases and this

closes the atrioventricular (mitral and tricuspid) valves. Further contraction increases theventricular pressure until it exceeds the aortic pressure. At this point, the arterial pressure isat its lowest point during the cardiac cycle (diastolic pressure), the semilunar (pulmonary

and aortic) valves are forced open, and blood flows into the arteries. Blood entering the

arterial system, slightly inflates the aorta and increases blood pressure to a maximum(systolic pressure). These pressure and volume changes are illustrated in Figure X-1.

Figure X-1. Wiggers diagram showing the relationship between pressure and volume changes in the leftheart and aorta. Adapted from Silverthorn Fig. 14-27.

Although the variation in arterial blood pressure during the cardiac cycle is smoothed by theelasticity of the major arteries, blood still exhibits pulsatile flow through the arteries. This

pulsatile arterial blood flow is measured using a stethoscope and a sphygmomanometer(blood pressure cuff). Blood is delivered to all tissues of the body by the maintenance of an

adequate arterial blood pressure, which is directly dependent on cardiac output (volume of

blood pumped by the heart per minute) and peripheral resistance (which is increased byconstriction and decreased by dilation of the arterioles).

A As explained above, this procedure involves stopping blood flow to the arm, which ispotentially dangerous. Subjects should be healthy individuals who do not have a personal

or family history of cardiovascular problems. If possible, use more than one subject duringthe course of the lab session. Please take the following precautions:

1. Know what you are doing ahead of time.

2. Do not leave the cuff inflated for a prolonged period of time (>30 seconds).3. Flex and extend fingers between experiments to maintain blood flow.


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B. MEASURING BLOOD PRESSURE

1. Measuring Blood Pressure using a Sphygmomanometer and Stethoscope

The routine clinical procedure for measuring arterial blood pressure is to use a deviceknown as a sphygmomanometer (Figure X-2). This instrument consists of an inflatable

rubber cuff connected by rubber hoses to a hand pump and to a pressure gauge

(manometer) graduated in millimeters of mercury. The cuff is wrapped around the upperarm and inflated to a pressure greater than the systolic pressure, which occludes blood flow

in the brachial artery. The examiner listens to the brachial artery with a stethoscope while

the pressure in the cuff is decreased. When thepressure in the cuff is lower than systolic

pressure but higher than diastolic pressure, bloodflow in the artery is partially occluded; this causes

a turbulence, which can be heard using a

stethoscope. These are called the Korotkoffsounds (or K-sounds), after the man who first

described them. The sounds of Korotkoff are

divided into the following five phases based onthe loudness and quality of the sounds (see

Figure X-3). The first appearance of the Korotkoffsounds indicates the systolic pressure. These

sounds continue to get quieter as pressure drops

and diastolic pressure is marked by theirdisappearance.

Figure X-2. Setup of sphygmomanometer

(a) Sounds of KorotkoffPhase 1: A loud, clear tapping (or snapping) sound is evident, which increases in

intensity as the cuff is deflated.

Phase 2: A succession of murmurs can be heard. Sometimes the sounds seem todisappear during this time, which may be a result of inflating or deflating the cuff too

slowly.Phase 3: A loud,

thumping

sound, similar tophase 1 but less

clear, replacesthe murmurs.

Phase 4: A

muffled soundabruptly

replaces thethumping

sounds of phase

3.Phase 5: All

sounds

disappear. Thisphase is absent in some people.

Figure X-3. Sounds of Korotkoff

Relative

intensity

of sounds

Cuff

pressure

mm Hg


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The cuff pressure at which the first sound is heard (that is, the beginning of phase 1) is

taken as the systolic pressure. The cuff pressure at which the sound disappears (thebeginning of phase 5) is taken as measurement of the diastolic pressure. In the example

shown in Figure X-3, the pressure would be indicated as 120/76.

(b) Procedure

1. Ask the subject to relax with their left hand resting on the table as before.2. Place the blood pressure cuff around the upper portion of the left arm, between the

elbow and shoulder, about 2-3 cm above the elbow.

3. Position the manometer so it is easy to read.4. Palpate the brachial artery just above the elbow, and place the head of the

stethoscope where the pulse is felt, and hold it firmly in place.5. Clean the ear pieces of the stethoscope with alcohol wipes before using them.

6. Watch the manometer as you pump up the pressure in the cuff to about 180 mmHg.

7. While listening for the Korotkoff sounds, open the valve and allow the pressure in thecuff to decrease slowly.

8. Record the systolic pressure (beginning of phase 1, when the first sounds can be

heard).

9. Record the diastolic pressure (beginning of phases 4 and 5, when the soundsdisappear).

10. Repeat these steps a few times until you become comfortable with the procedure

and you obtain consistent readings.

2. Measuring Blood Pressure using iWorx

(a) Equipment Required

Plethysmograph Sphygmanometer/Blood pressure cuff

Event marker Stethoscope

(b) Equipment Setup

1. Connect the plethysmograph to Channel 3, and the subjects volar surface of the

distal segment of a middle finger or thumb.2. Connect the event marker to Channel 4.

3. Place the blood pressure cuff around the upper portion of the left arm, in the samemanner as in the previous exercise.

4. The subject should sit quietly.

5. Start LabScribe and select the "Heart #4" settings file.

(c) Procedure

1. Ask the subject to sit quietly and relax with their left hand resting on the table at the

level of the heart.2. Make sure to label your data trace appropriately and start recording.3. Inflate the cuff until the pressure is just above 200 mm Hg, notice that the finger

pulse disappears as in Figure IX-4 below.


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Figure X-4. Finger pulse during cuff

inflation and deflation

4. Slowly release the cuff pressure. When the pressure reaches 200, quickly press and

release the event marker to produce a signal on channel four (event). Repeat the

signal every time the pressure drops by an increment of 20 mmHg.5. When the cuff reaches 40 mmHg stop recording and remove the cuff. The subject

should flex and extend their fingers to enhance blood circulation.6. Save the file.

7. Repeat this whole procedure (including the data analysis) two more times.

(d) Data Analysis - Measuring Blood Pressure

Systolic Pressure1. Find when the finger pulse reappears and the pair of event markers closest to this

point (see Figure X-5). Move all this data to the Analysis window.

Figure X-5. Finger pulse reappearsbetween 120 and 100 mm Hg

2. Place one cursor on the peak of the smallest signal and the second cursor on the

event marker signal entered prior to the peak. Measure the time interval (T2-T1) and

call this time value#1 (shown above).3. Repeat with the second cursor on the Event marker signal entered after the peak--

call this time value#2 (shown above).

4. Calculate:2#1#

)20(2#

valuevalue

incrementpressurevalue

+

5. Add this number to the lowest value in the bracket (100 in the above example) to

give you the systolic pressure.


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Diastolic Pressure

Look at your recording and find where the amplitude of the finger pulse increases until itreaches (and stays at) its largest amplitude. Repeat the above for the largest peak to give

you the diastolic pressure.

3. Clinical Significance

Normal blood pressure for a given individual depends on the persons age, sex, heredity,

and environment. The traditionally accepted values for arterial blood pressure are given in

Table X-1. Chronic high blood pressure is called hypertension. Hypertension is a majorcontributing factor in heart disease and stroke. Hypertension may be divided into two

general categories. Primary hypertension, which comprises 95% of all cases, refers to

hypertension of unknown causes. This category is, in turn, divided into benign hypertension(also known as essential hypertension) and malignant hypertension. When the pathology

that produces the hypertension is known, it is referred to as secondary hypertension.

Table X-1 . Normal arterial blood pressure at different ages.

Recently, the conclusions of a major national study1 (JNC 7 report) of hypertension were

published in the Journal of the American Medical Association. This study recommended asignificant lowering of the blood pressure values used to define hypertension. The following

excerpts were taken from an accompanying summary of the article 2.

The World Health Organization has estimated that high blood

pressure causes 1 in every 8deaths worldwide, making hypertensionthe third leading killer in the world. The JNC 7reportsummarizes how the burden of hypertensioncan be decreased. Among the

1The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of

High Blood Pressure: The JNC 7 Report JAMA Vol. 289, No. 19, pp. 2560-2571. May 21, 2003.

2JNC 7 - It's More Than High Blood Pressure. JAMAVol. 289, No. 19, pp. 2573-2575. May 21, 2003.


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messages emphasized is that systolicblood pressure control should be the focus oftreatment. Cardiovascularrisk from systolic hypertension begins at 115 mm Hg and riskfromdiastolic hypertension begins at 75 mm Hglowering bloodpressure toward the new goallevel of 120/80 mm Hg will decreaseheart attacks, heart failure, stroke, kidney disease, andwillsave lives.

For many,high blood pressure is just one manifestation of what may betermed the lifestylesyndrome, which is a cluster of conditions and diseases that result from consuming too manycalories; ingestingtoo much saturated fat, sodium, and alcohol; not expending enough

calories; and using tobacco or being exposed to tobacco smoke. In addition to hypertension,manifestations of the lifestylesyndrome include the metabolic syndrome, obesity,dyslipidemia,cardiovascular disease, cancer, osteoarthritis, depression,sexual dysfunction,and type 2 diabetes mellitus. To the extentthat the stakeholders in hypertension control-clinicians,patients, health services organizations, and the purchasersof health care services-act and are organized toprevent hypertension,the burden from the diseases and conditionsof the lifestylesyndrome also will be decreased.

C. BLOOD PRESSURE, BODY POSITION, AND GRAVITY

As you know, blood pressure is tightly regulated; however, most of this regulation isconcerned with blood reaching the brain and the heart. Blood pressure in the peripheralsystem is influenced by distance from the heart as well as other factors such as temperature

and gravity. This laboratory is meant to explore how some factors influence overall blood

pressure, but also to look at how pressure varies in different parts of the body and how it isinfluenced by body position and gravity. For instance, if you are lying down, by the time

blood reaches the capillaries in the foot, the systolic pressure is lower than it was when it leftthe heart. Now, if you stand up, gravity makes it more difficult for the blood to flow upward

to the brain and to return to the heart, because it tends to pull blood to the lower extremities.

So when standing, the pressure at the foot is much greater than when lying down. Thispressure is transmitted to the veins, which need to generate enough pressure to work

against gravity and propel the blood back to the heart.

Our bodies have several mechanisms to deal with gravity and changes in body position.

Baroreceptors quickly sense changes in blood flow to the brain and heart and makeadjustments to peripheral resistance and the heart to modulate overall blood pressure. Leg

muscles help in the process of venous return by functioning as pumps. During walking or

other leg movements, the muscles contract, forcing blood up through the veins back to theheart. Also, blood return is aided by valves in the veins, which do not allow blood to flow

backwards. For a demonstration of these valves, keep your hand below heart level, place a

finger on a vein to prevent blood from moving into it. Then push the remaining blood in thevein towards the heart. Because valves are preventing backflow, and you are not allowing

any blood to enter them, the vein will remain collapsed until you release your finger.

1. Effect of Body Position on Blood Pressure

1. Use one of the two methods above to measure blood pressure and enter these

values in Table X-2 under the sitting entry.

2. Compare your pressure with the range of normal values listed in Table 2.3. Calculate the subjects pulse pressure (systolic minus diastolic pressure) and enter

this value in Table X-2.4. Calculate the subjects mean arterial pressure. This is equal to the diastolic pressure

plus 1/3 of the pulse pressure. Enter this value in Table X-2.


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5. Repeat these measurements on the same subject after they have been lying down

for a few minutes (arms at sides), and again in a standing position for a few minutes(arms down). Enter these values in Table X-2.

Table X-2. Body position blood pressure data

Sitting Reclining Standing

Systolic pressure (Ps)

Diastolic pressure (P D)

Pulse pressure (P)

Mean arterial pressure(PA)

2. Effect of Gravity and Cardiac Return on Blood Pressure

1. Choose a new subject. Measure blood pressure in the left arm in the sitting positionand enter the same variables you calculated in Table X-2, in Table X-3.

2. Measure the subjects blood pressure in the left arm while their left hand is placed on

their head and repeat step 2.3. Repeat these measurements while the subject is sitting but holding their right arm on

their head, while in a prone position, and from the prone position immediately afterlifting both legs perpendicular to the bench.

Table X-3. Gravity and cardiac return blood pressure data

Sitting Left Arm Up Right Arm Up Prone Legs Up

Ps

PD

P

PA


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In order to see how blood flow to the extremities is affected by gravity, place the

plethsymograph on the left finger and monitor blood flow using Heart #3. Repeat thepositions used in the previous experiment and see how changes in gravity and cardiac

return change the blood flow to the left finger. An example of how the trace may changewhen the left hand is lifted above the head is shown in Figure X-6.

Figure X-6. Plethysmograph datarecorded with a change in thesubject's hand elevation

3. Blood Pressure and Distance from the Heart

The purpose of the experiments on this page is to examine blood pressure in different partsof the body. In this part of the lab we want to concentrate more on the effect of distance

from the heart, so to minimize other factors, make sure the subject is lying down for all the

measurements. Use the iWorx system for all these measurements.

Measure the blood pressure of the left arm using the iWorx system as before. Compare

these to measurements from the forearm, and measurements from the left leg (move theplethysmograph to the left big toe and wrap the cuff around the calf).

D. EFFECTS OF EXERCISE ON CARDIOVASCULAR DYNAMICS

During exercise, the distribution of blood to organs of the body may be very different fromthat seen at rest. For example, the blood flow to the gut decreases during exercise, while

blood flow to the skeletal muscles increases dramatically (how does this effect arterialresistance?); furthermore, the cardiac output (Q) may be increased several times. In this

laboratory you will record the heart rate and the blood pressure from a subject at rest and

immediately after exercise.

A NOTE: This experiment involves exercise and an elevation of heart rate. It should not

be performed by anyone who is not healthy or has a personal or family history ofcardiovascular or respiratory problems.

Monitor the subjects blood pressure in their left arm. To obtain the heart rate, you may usethe iWorx system to record the ECG of your subject, or you may take the subjects pulse (at

least 30 seconds for each reading). If you use the iWorx system, open a new Heart #1 file.If you take the subjects pulse, use their right wrist.

Have the subject lie down for 5 minutes and make baseline measurements of HR and BP.Calculate the pulse pressure (P = Ps PD) and the mean arterial pressure (PA = PD +

1/3 P). These will be your Time = 5 min readings.


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0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

-5 0 5 10 15 20 25 30

TIME

HR(Beats/min)

HR = Ps = PD = P = PA =

Have the subject exercise for 5 minutes, by either jumping-rope or running stairs. Make

sure the exercise is rigorous enough to raise their heart rate by a sizeable percentage

(preferably in most subjects it should reach over 140 beats/minute). Have them immediatelylay down on the table for the rest of their readings (have them stay in this position for the

duration of the experiment).

Be prepared to measure the BP and HR as quickly as possible after exercise. This will be

your time=0 reading.

Try to get 2-3 data points within the first 10 minutes. This may be difficult, but do your best.

Just be sure to note the time at which you take your readings. Take another reading at 10minutes and then another reading every 5 minutes for a total duration of 20 minutes.

Your readings should look something like the table below. Again, compute Pa for eachreading. The state of the organism has gone through a lot of changes. Q is almost certainly

no longer 5L, and many cardiovascular variables have almost certainly changed quite a bit.

Make a graph of HR, and Pa as a function of time. An un-normalized graph will looksomething like the one below.

TIME HR BP(s) BP(d)

-5 71.0 120 80

0 122.2 175 60

2 117.7 166 62

4 113.1 157 63

6 108.6 148 65

8 104.1 138 67

10 95.0 120 70

15 102.0 120 7020 86.0 123 80

In order to see how all the variables change over time in relation to each other, you can

normalize all the traces and re-plot them. The way to do this is to take all your data points

for a variable and divide them by your baseline value.

The purpose of this experiment is to understand how these variables are related to eachother. More than likely, most of these results will not be surprising to you. HR and BP

should all have increased and come back towards baseline over a fairly short period of time.

However, many other variables that were not measured probably changed more even morethan the ones we did measure. What most likely happened to stroke volume, total cardiac

output, and peripheral resistance?


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QUESTIONSMEASURING BLOOD PRESSUREHow similar are the values for blood pressure (systolic and diastolic) from these different

methods and trials within each method?

What may cause any variations you see?

Using the iWorx system, you are looking for changes in the volume pulse. How wouldchanging the rate of pressure released from the cuff influence the accuracy of your

readings?

The first sound of Korotkoff occurs when the cuff pressure equals the________________pressure, and the last sound occurs when the cuff pressure equals the ________________pressure.

Suppose a persons blood pressure is 165/110.

What is the pulse pressure?

What is the mean arterial pressure?

What condition does this person have?

Why is this dangerous if it is allowed to continue indefinitely?

Why cant you hear the sounds of Korotkoff in the brachial artery before you inflate the cuff?

EFFECT OF BODY POSITION ON BLOOD PRESSURE

How does body position affect overall blood pressure?

How does it affect the pulse pressure and mean arterial pressure?

Explain why you find these results.


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BLOOD PRESSURE AND DISTANCE FROM THE HEART

How does the blood pressure values compare in these areas?

Explain the reason behind the readings you obtained from these different areas.

EFFECTS OF EXERCISE ON CARDIOVASCULAR DYNAMICSWhat happened to HR after exercise? Pulse pressure? Mean arterial pressure?

Explain why you may be able to use pulse pressure changes as an indicator of stroke

volume changes.

Now, using pulse pressure as an indicator of stroke volume, would you guess that stroke

volume or heart rate changes more after this sort of exercise? (hint: look at yournormalized charts).

What happens to cardiac output after this type of exercise?

How about total peripheral resistance?

What other changes are occurring in your body?

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A Guide to Blood Pressure 210