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LSM 3212 Practical session 3

Have you ever felt faint (and see yellow stars) when you suddenly jump out of bed?

As you go from a lying down to a standing position, blood rushes down your body, due to the pull

of gravity, and this causes a slight drop in blood pressure. The body will compensate by

increasing blood pressure by stimulating the sympathetic nervous system, increasing heart rate,

and subsequently cardiac output and blood pressure.

This can be observed by a very simple procedure where you monitor your heart rate and blood

pressure and you do exactly that. Go from a lying down to a standing position.

Aims of P3 : Effects of posture on heart rate and blood pressure

1. To learn how to take blood pressure using a simple clinical sphygmomanometer.

2. To observe the effect of posture (lying down vs standing up) on blood pressure and heart rate

3. To observe the differences in changes in blood pressure in people who are physically fit vs

those who are not.

Practical details

1. Your group will have aclinical sphygmomanometer and a stethoscope to detect blood

pressure. You will first learn, and master how this works. (see page 3).

2. Next, pick the volunteer in your group to be the subject. Another person needs to be the blood

pressure master, and another needs to be the pulse reader.

3. Let the subject lie down on the bed and relax. Take his blood pressure on one arm and his

pulse on the other.

4. When you are ready for the standing up measurement, inflate the blood pressure cuff and

then ask him to stand up quickly. Take the blood pressure reading and pulse rate immediately

after he stands up, as well as 1 min and 5 min after he has stood up.

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Record your blood pressure and heart rate when lying down and standing up. Remember

to pump the blood pressure cuff before you stand up so you don't waste time pumping it up

when you stand up the compensation occurs very fast!

Lying down Immediately

Standing

1 min after

standing

5 min after

standing

Pulse (beats per

min)

Blood pressure

(mm/Hg)

How to measure pulse:- put your fingers, not your thumb on the wrist of the subject and

count the number of beats you feel in 30 sec. Multiply by 2 for beats per min.

How to measure blood pressure:- see next page.

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How to take blood pressure

From the website http://www.madsci.org/experiments/archive/859422898.Bi.html(for

secondary school kids in the US)

Overview:Take a blood pressure.. correlate the blood pressure to the heart's pumping of blood.

Equipment:

1. Sphygmomanometer (blood pressure cuff)

2. Stethoscope.

It would be helpful if someone who knows how to take a blood pressure is present to supervise,as the technique requires some practice.

Safety:Avoid keeping the cuff inflated on someone's arm for too long, other wise the arm will go purple.

How to do the experiment:

1. Deflate the bladder of the cuff and place it around the upper arm so it fits snugly, but not too

tightly. If you're right handed, you should hold the bulb/pump in your left hand to inflate the cuff.

Hold it in the palm so your fingers can easily reach the valve at the top to open/close the outlet to

the air bladder wrapped around the person's arm.

2. Put the head of the stethoscope just under the edge of the cuff, a little above the crease of the

person's elbow. Hold it there firmly with the thumb, or with a few fingers of your right hand. Put

the ear pieces of the stethoscope in your ears.

3. Inflate the cuff with brisk squeezes of the bulb. Watch the pressure gage as you do it. For most

kids, you shouldn't need to go over 150 (the markings indicate "pressure" in mm Hg or mercury).

4. At 150, slightly open the valve on the air pump (held in your left hand, as above). This part

takes practice. It's important that you don't let the air out too suddenly. Likewise, your friend will

be quite irritated with you if you let it out too slowly.

5. Now, pay attention *very carefully* to what you hear through the stethoscope as the needle on

the pressure gage falls. You will be listening for a slight "blrrpp" or a something that sounds like

"prrpshh." The first time you hear this sound, note what the reading was on the pressure gage.

This value represents the systolic blood pressure (described below).

6. The sounds should continue and become louder in intensity. Note the pressure reading when

you hear the sound for the last time. This value represents the diastolic blood pressure.

7. Afterwards, open the air valve completely to release any remaining pressure.

http://www.madsci.org/experiments/archive/859422898.Bi.htmlhttp://www.madsci.org/experiments/archive/859422898.Bi.htmlhttp://www.madsci.org/experiments/archive/859422898.Bi.html

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Explanation:

BACKGROUND

Blood pressure varies relative to heart's pumping of blood. The heart should be thought of as a

dual pump, with a right and left side. Systole represents the active pumping of blood from the

ventricles into the circulation. The right side of the heart takes venous/returning blood from the

body and sends it to the lungs to be oxygenated (pulmonary circulation). Measuring blood

pressures on the right side of the heart requires very complicated equipment. The left side of the

heart takes the oxygenated blood and sends it to the rest of the body. When you take a blood

pressure reading, you measure pressures in the systemic circulation.

The highest pressures occur during systole as blood is ejected into the aorta and subsequent

arteries of the body. Diastole, the heart's resting phase, follows systole. During diastole the

ventricles fill with more blood. Systemic pressures fall until more blood is ejected during systole.

THE EFFECTThe blood pressure cuff lets you apply external pressure to a circumferential ring around the

upper arm. When the pressure is great enough, it forcibly closes the main artery of the upper arm

- the brachial artery. The stethoscope allows you to hear when the underlying artery opens and

closes as you release the air in the bladder.

Example - Take a person with a blood pressure of 120/80. The first number always representssystolic pressure (120), and the second numberdiastolic pressure (80). When you apply a

pressure of 180mm Hg to the arm, the 120mm of pressure from the artery cannot overcome your

externally applied pressure; the artery stays shut.

As you release the air out of the cuff, the external pressure falls. At 150mm the artery is still

closed.. but at 119mm, it can open for just the slightest instant as the maximum/systolic pressure

exceeds the applied pressure. Once the arterial pressure falls below 119mm, however, the artery

shuts again. This opening and shutting produces the sounds you hear through the stethoscope(Korotkoff sounds). When the applied pressure falls below the diastolic/resting pressure, the

artery stays open all the time.

Useful References:The Human Heart, an online explorationThe American Heart Association

Further comments:

Having a low blood pressure is inidicative of a longer (presumably healthier) life. Eat right,

exercise, and stay away from cigarettes. In addition to the other damage it causes, nicotine in

cigarettes constricts arterial blood vessels, increasing blood pressure and your chances of

developing hypertension.

http://sln.fi.edu/biosci/heart.htmlhttp://www.amhrt.org/http://sln.fi.edu/biosci/heart.htmlhttp://www.amhrt.org/