MEASUREMENTS OF BLOOD PRESSURE

INTRODUCTION
An important measurable aspect of the circulatory system is blood pressure.  When the ventricles of the heart contract, blood pressure is increased throughout all the arteries.  Arterial blood pressure is directly dependent on the amount of blood pumped by the heart per minute and the resistance of blood flow through the arterioles.  The arterial blood pressure is measured by the use of a device known as a sphygmomanometer.  This device consists of an inflatable cuff connected by rubber hoses to a hand pump and to a pressure gauge graduated in millimeters of mercury.  The cuff is wrapped around the upper arm and inflated to a pressure that will shut off the brachial artery.  The examiner listens to the sounds of the brachial artery by placing the bell of a stethoscope in the inside of the elbow below the biceps; the pressure of the cuff is allowed to fall gradually by opening a screw valve located next to the hand pump.  The examiner then listens for the sounds of Korotkoff.

At rest, the blood normally goes through the arteries so that the blood in the central stream moves faster than the blood in the peripheral layers.  Under these conditions, the artery is silent when one listens.  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 the pressure in the cuff gradually drops to levels between the systolic and diastolic pressures of the artery, the blood is pushed through the compressed walls of the artery in a turbulent flow.  Under these conditions, the layers of blood are mixed by eddies that flow at right angles to the axial stream, and the turbulence sets up vibrations in the artery that are heard as sounds in the stethoscope.  These sounds are known as the sounds of Korotkoff.  The sounds are divided into five phases based on the loudness and quality of the sounds.
Phase 1.  A loud, clear tapping sound is evident that increases in intensity as the cuff is deflated.
Phase 2.  A succession of murmurs can be heard.  Sometimes the sounds seem to disappear during this time, which may be a result of inflating or deflating the cuff too slowly.
Phase 3.  A loud, thumping sound similar to Phase 1 but less clear, replaces the murmur.
Phase 4.  A muffled sound abruptly replaces the thumping sounds of Phase 3.
 Phase 5.  No sound.

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 becomes muffled (the beginning of Phase 4) and the pressure at which the sound disappears (the beginning of Phase 5) are taken as measurements of the diastolic pressure. Systolic pressure is written first and the diastolic pressure, e.g., 120/80.

The normal blood pressure measurement for a given individual depends on the person’s age, sex, heredity, and environment. It also varies depending on whether a person is lying, sitting, or standing, and is affected by such factors as time of day, fullness of bladder, amount of recent exercise, and recent intake of caffeine, nicotine or alcohol.  Blood pressure measurements that are chronically elevated may indicate a state deleterious to the health of the person.  This condition is called hypertension and is a major contributing factor in heart disease and stroke.  Some normal blood pressures for males and females at different ages are given in Table 1.  

Table 1.  Normal Blood Pressures for Males and Females at Different Ages
	Males	Females	
Age 	Pressure (systolic/diastolic)	Pressure (systolic/diastolic)	
10	103/69	103/70	
12	106/71	106/72	
14	110/73	110/74	
15	112/75	112/76	
16	118/73	116/72	
17	121/74	116/72	
18	120/74	116/72	
19	122/75	115/71	
20-24	123/76	116/72	
25-29	125/78	117/74	

PURPOSE
1. 	The student will demonstrate a competence in the correct and responsible usage of the stethoscope and sphygmomanometer.
2. 	The student will take blood pressure readings from a human subject.
3. 	The student will compare these blood pressure readings to normal blood pressure readings.
4. 	The student will calculate pulse pressure and cardiac output from blood pressure data.

SAFETY
1. 	When inflating the cuff, pressure should not exceed 180 mm Hg.
2. 	Rate of deflation of the cuff should be between 2 and 3 mm Hg per second.
3. 	Never leave the cuff inflated on the subject for more than a few seconds; severe bruising may occur.
4. 	The cuff should never be inflated unless being used on a subject.
5. 	Wipe the ends of the stethoscope with an alcohol pad before inserting them in the ears.
6. 	The stethoscope is a sensitive instrument which dramatically magnifies sound.  Once in place, the person using the stethoscope should never be exposed to loud noise, i.e. tapping, yelling, etc.

MATERIALS
Sphygmomanometer
Stethoscope
Alcohol wipes
Digital Blood Pressure Monitor
AA batteries

PROCEDURE
PART I.  Measuring Blood Pressure with a Sphygmomanometer.
1. 	Work in pairs.  Those who are to have their blood pressure measured should be seated with their sleeves rolled up.
2. 	Attach the cuff of the sphygmomanometer snugly around the upper arm.
3. 	Place the stethoscope directly below the cuff in the well of the elbow joint.  NOTE:  The earpieces of the stethoscope should be cleaned with alcohol swabs before and after use.
4. 	Close the valve of the bulb by turning it clockwise.  Pump air into the cuff until the pressure gauge goes to 180 mm Hg.
5. 	Turn the valve of the bulb counterclockwise and slowly release air from the cuff.  Listen for a pulse.
6. 	When you first hear the sounds of Korotkoff, note the pressure on the gauge.  This is the systolic pressure.  (As the cuff is inflated, the brachial artery in the arm collapses.  When the pressure is released, the artery expands and you hear a pulse.  As more pressure on the artery is released, all sound ceases.)
7. 	Continue to listen until the clear thumping sound of the pulse becomes strong and then fades.  When you hear the full heart beat, note the pressure.  This is the diastolic pressure.
8. 	Repeat two more times, recording, in Table 1 on the student data sheet, the systolic and diastolic pressure after each trial.
      NOTE:  Allow the subject to rest 30-60 seconds with the cuff deflated at the end of 	each trial.
9. 	Determine and record the average systolic and diastolic pressure.
10. 	Trade places with your partner and repeat the procedure.

PART II.  Measuring Blood Pressure With the Automatic Digital Blood Pressure   Monitor
1. 	Work in pairs.  Those who are to have their blood pressure measured should be seated with their sleeves rolled up.
2. 	Attach the cuff of the sphygmomanometer snugly around the upper arm.
3. 	Turn on the blood pressure monitor and press the “start” button.  The cuff will automatically inflate to 180-200 mm Hg and then begin to deflate.
4. 	The blood pressure and pulse readings will be displayed on the monitor screen at the end of cuff deflation.  Record the blood pressure readings in Table 1 on the student data sheet.  Record the pulse readings in Table 2 on the student data sheet.
5. 	Repeat two more times, recording the blood pressure and pulse after each trial.  NOTE:  Allow the subject to rest 30-60 seconds with the cuff deflated at the end of each trial.
6. 	Determine and record the average blood pressure and average pulse.
7. 	Trade places with your partner and repeat the procedure.
8. 	Turn the blood pressure monitor off after completing Part II.

PART III.  Calculating Pulse Pressure and Cardiac Output
1. 	Pulse pressure is the difference between the systolic and diastolic readings and is a crude estimate of the stroke volume of the heart.  
Pulse pressure (estimated stroke volume) =  systolic pressure - diastolic pressure.
2. 	Calculate the pulse pressure using the average blood pressure reading obtained in Part II.  Record this value in Table 3 on the student data sheet.
3. 	The cardiac output is the amount of blood pumped by the heart per minute.  
Cardiac output  =  heart rate (in beats/minute)  x  stroke volume.
4. 	The average cardiac output when at rest is about 4.5 liters per minute.  Calculate your cardiac output by assuming that 1 mm Hg is equal to 1 cm3 of blood. Record this value in Table 3 on the student data sheet.

STUDENT DATA SHEET	Name:______________________
MEASUREMENTS OF BLOOD PRESSURE	Date: ______________________

DATA
Table 1.  Blood Pressure Readings
	Trial #1	Trial #2	Trial #3	Average	
Part I.  Sphygmomanometer

Part II.
Digital Automatic Blood Pressure Monitor					

Table 2.  Pulse Readings
Trial #1	Trial #2	Trial #3	Average	

				

Table 3.  Cardiac Output Data
Pulse pressure (estimated stroke volume)
		
Heart rate (average pulse reading)
		
Cardiac output
(heart rate  x  (stroke volume)		

ANALYSIS
1. 	Compare your blood pressure with the normal values listed in the introduction.

2. 	List several factors that may affect blood pressure on a short-term basis.

3. 	List several factors that may influence blood pressure on a long-term basis.

4.  Suppose a person’s pressure is 165/110.
A. 	What is his systolic pressure?     __________

B. 	What is his diastolic pressure?  ___________

C. 	What is his pulse pressure?      ___________

5. 	What condition does the person in question 4 have?  Explain the dangers of this condition.

6. 	We know that eating the typical American high fat diet can cause cholesterol to accumulate in your veins and arteries.  How will this influence blood pressure?  Explain your answer.