Biology 242 – Lab
LAB #7
(7th/19 Lab Sessions for Winter Quarter, 2008)
TOPICS TO BE COVERED:
»Review of the Principals of Hemodynamics: Physiology of Circulation
»Equations for Various Calculations
DESIRED OUTCOMES:
After completing the activities described for this lab session, students should:
»Be able to auscultate the sounds of the heart.
»Be able to palpate arterial pulses at various points.
»Be able to explain Sounds of Korotkoff and how they relate to blood flow.
»Be able to measure and record blood pressure using a stethoscope and syphgmomanometer.
»Be able to explain and calculate Pulse pressure (PP) and mean arterial pressure (MAP).
MATERIALS NEEDED:
»Anatomical Models: Heart and Torso
»Stethoscopes
»Watch (or clock) with a second hand
»Sphygomomanometers
»Alcohol wipes (for cleaning ear-pieces)
Introduction:
One complete heartbeat is called a cardiac cycle. During a cardiac cycle, the atria contract and
relax, and the ventricles contract and relax. The contraction phase of a chamber is called systole, and the
relaxation phase is termed diastole. The human heart averages 75 cardiac cycles (or heartbeats) per minute,
with each cardiac cycle occurring in 0.8 seconds. (Refer to Figure which illustrates the events of a cardic
cycle). The cycle begins with the brief systole of the atria, lasting 0.1 seconds, to fill the resting ventricles.
(Actually, most blood enters the ventricles during the quiescent period – see below. Atrial systole contributes only 30% of the blood volume in the ventricle prior to ventricular systole. 70% of the blood, gravity
and pressure passively feeds it into the ventricles from the atria.) Next, the ventricles enter their systolic
phase and contract for 0.3 seconds to eject blood out of the heart. The remaining 0.4 seconds of the cardiac
cycle is known as the quiescent period because all chambers are in diastole and fill with blood in preparation for the next heartbeat.
Each cardiac cycle is marked with an increase and a decrease in blood pressure, both within the
heart and in the arteries. When a chamber contracts, pressure increases as a result of the squeezing together
of the chamber walls. The increase in blood pressure forces blood to circulate into the next chamber or out
of the ventricle. As a ventricle relaxes, its walls move apart and pressure decreases. This drop in pressure
draws blood into the ventricle and refills it for the next systole.
When all chambers of the heart are in diastole, the atrioventricular (AV) valves are open and blood
passively flows from the atria into the ventricles. Both semilunar (SL) valves are closed to prevent backflow of blood from the aorta and pulmonary artery into the left and right ventricles, respectively. When the
left ventricle contracts, pressure increases to a point where it exceeds the pressure of the blood in the aorta
holding the aortic SL valve shut. (Remember, this is the “Afterload” component of the three factors that affect cardiac
output (HR x SV): Preload, Contractility, Afterload.) The ventricle forces blood through the valve, and arterial
blood pressure increases as a result of this increase in blood volume. When the ventricle relaxes, aortic and
arterial pressures drop and the aortic SL valve closes. At these same times, identical events occur on the
right side of the heart with the pulmonary SL valve.
Your Lecture Notes for Chapter 21: Blood Vessels (second page, Part III) describes Hemodynamics as:
“…the distribution of cardiac output to various tissues ….which depends on the interplay of the
pressure differences that drive blood flow and the resistance to blood flow.”
Even more simply stated: Blood Flow depends on Pressure differences and Resistance.
Let’s define each of the bolded terms above:
I. Blood Flow – Actual volume of blood flowing through the blood vessels of the tissues, organs,
(F)
systems in a given unit of time. (This is usually constant, but CAN vary greatly.)
*Considering the entire organism, this is the same as Cardiac Output (CO);
therefore: F = CO
Factors that affect (F) – or (CO) – are: 1. Heart Rate
a. Nervous System
b. Chemicals
c. Other factors
2. Stroke Volume (EDV-ESV)
a. Preload
b. Contractility
c. Afterload
II. Blood Pressure – Force (whose units are mmHg) per unit area exerted on the wall of any blood vessel
(BP) or (P)
and the usual Blood Pressure being referred to is systemic article BP in the
elastic, conducting arteries, such as the Brachial Arteries. Even more specifically,
it is the MABP (Mean Arterial Blood Pressure) that is used.
Factors that affect (P) are:
1. Total Blood Volume
2. CO
3. Resistance (R)
III. Resistance – Opposition to flow; the measure of the amount of friction the blood encounters within
(R)
the blood vessels. Also known as Systemic Vascular Resistance and/or Peripheral
Resistance.
Factors that affect (R) are:
1. Blood vessel length
2. Blood vessel lumen-size (ie, radius, r) 1/r4
3. Blood viscosity
IV. The overall relationship between factors I, II, and III above may be expressed mathematically as:
and thus one can see the two-fold relationship that Blood Flow has to Blood Pressure and Resistance:
a. Blood Flow (F) is DIRECTLY proportional to Blood Pressure (as BP increases, so does F;
as BP decreases, so does F)
b. Blood Flow (F) is INVERSELY proportional to Resistance (as R increases, F decreases;
as R decreases, F increases.)
Overview:
A part of every physical examination includes close inspection of the cardiovascular system, in
which the pulse is taken, heart sounds are auscultated (“examined by listening”), and the blood pressure is measured. Blood pressure (BP) is a measure of the force the blood exerts on the walls of the
systemic arteries. Blood pressure in arteries is not constant and increases when the left ventricle contracts and pumps blood into the aorta. When the left ventricle relaxes, less blood flows into the aorta
and so the pressure decreases until the next ventricular systole. Two pressures are therefore used to express blood pressure, a systolic pressure and a lower diastolic pressure. An average blood pressure is
considered to be 120/80 mmHg; but, do not be surprised when your blood pressure is taken during today’s lab session and you discover it is not “average”. Remember, cardiovascular physiology is a dynamic mechanism, and pressure regularly changes to adjust to the demands of the body. In today’s lab
session, you will learn how to perform several common procedures, as well as the basis for their interpretation.
Activity #1: Blood Pressure Measurement
In this exercise, we will be using a stechoscope to auscultate sounds of Korotkoff. Let’s first look at the
parts of a stethoscope:
Earpieces: these are gently inserted into the external auditory canal. (The “forward lean” of each earpiece goes forward – this pushes the clinicians auditory canal open to hear better!)
Diaphragm: this is the broad, flat side of the end of the stethoscope. It is used to auscultate higherpitched sounds and is the side used most often in auscultation of heart sounds.
Bell:
this is the concave, smaller side of the end of the stethoscope. It is used to auscultate
lower-pitched sounds, such as the sounds of Korotkoff.
(Note: sounds are not audible through both the bell and the diaphragm at the same time. Typically, the
end can be flipped from one side to the next. Before auscultating with either side, lightly tap the
end to ensure that you can hear sound through it. Note also that the ends of some stethoscopes
have only one side – the diaphragm. In this case, placing light pressure on the end as you are
auscultating yields sounds associated with the diaphragm; placing heavier pressure yields
sounds associated with the bell.)
Blood pressure is determined by using an instrument called a sphygmomanometer and a stethoscope.
The proper use of these two items yields two pressure readings:
1. Systolic pressure: the pressure in the arteries during ventricular systole and, naturally, the larger of
the two readings.
2. Diastoloic pressure: the pressure in the arteries during ventricular diastole, the smaller of the two
readings.
These readings are taken using the sphygmomanometer to compress the brachial artery, which cuts off
blood flow through that artery. The stethoscope is utilized to auscultate the brachial artery for sounds
known as sounds of Korotkoff, which result from the turbulent blood flow resuming through the
previously clamped-off artery. (Remember: under normal circumstances, you cannot “hear” blood
flowing in arteries and veins. It is only upon manipulation in the way taking a blood pressure does:
momentarily stopping the flow of blood by occluding a vessel, and then, upon re-opening of this
vessel, it is the turbulence of the backed-up blood re-entering the previously occluded vessel that is
now “heard”; and this and other sounds may be correlated to pressures and/or other characterizations.
Procedure: Resting Blood Pressure
1. The lab needs to be fairly quiet (and all extraneous conversations amongst students should cease) in
order to maximize the capturing and correlating of these hard-to-hear sounds.
2. Obtain a stethoscope and sphygmomanometer. The latter needs to be the appropriate size (ie, it
needs to be at least 80% of the circumference of the arm. Note: there are pediatric, adult, and extralarge sizes. If the cuff of the sphygmomanometer is either too small or too large, the readings will not
be accurate.)
3. Clean the earpieces and diaphragm of the stethoscope with alcohol wipes. Then, position the earpieces of the stethoscope in your ears.
4. It is best if the subject is wearing a short sleeved blouse or shirt; or is able to roll up a long sleeve
sufficiently to expose the brachium. Wrap the cuff around your partner’s arm. It should be about 1½
inches proximal to the antecubital fossa. Also, it should not be noticeably tight, but it should stay in
place when you are not holding it. If the cuff has orientation arrows on it, line the arrows up with the
antecubitis; otherwise, position the rubber tubing over the antecubital region and the pressure gauge (or
“meter” part of the instrument) should be lined up where it is easily visible to you.
5. Insert the diaphragm or your stethoscope under the leading edge of the cuff and in a position that is
over the brachial artery. You should not hear anything at this point.
6. Be sure that your partner’s upper extremity is relaxed and supported on the lab bench or resting on
your arm.
7. On the bulb of the sphygmomanometer is a screw mechanism: be sure that this is CLOSED, and
inflate the cuff by squeezing the bulb several times. Pay attention to the level of pressure being applied by watching the pressure gauge. You should inflate it to approximately 150 mmHg, unless your
partner knows that he/she has had a previous systolic reading of 140 mmHg or higher – then inflate to
approximately 180 mmHg. Clinically, the “rule of thumb” is to inflate no more that 30 mmHg above
a high of 150 mmHg systolic pressure.) DO NOT leave the cuff inflated for more than 1 minute, since
the inflated cuff prevents blood flow to the forearm, and the disruption in blood flow COULD lead to
fainting.
8. Now, slowly open the screw, watching the pressure gauge, and listening to the brachial artery with
your stethoscope. (You may want to have one finger over the diaphragm of the stethoscope to insure
that there is complete capturing of the sounds.) When the first tapping sound (sound of Korotkoff) is
heard, note the pressure reading on the gauge. The pressure at which this first tapping sound is heard
is the systolic pressure. (This is the point at which the pressure in the cuff exactly equals the pressure
in the brachial artery and blood spurts through the artery. The “spurts” are the “taps” which are audible
through the stethoscope.)
9. You will also see the needle on the pressure gauge begin to bounce; at about the same time, you
will continue to hear the pulse in the brachial artery. These are the Phase II – Phase IV of Korotkoff
sounds and they will lessen as you continue to vent pressure (still slowly and carefully) from the cuff.
10. Continue to listen and watch the gauge until you can no longer hear any sound. (The sounds will
become fainter and fainter, but it is only at the point of no sound that corresponds to the diastolic pres-
sure. At this point, the needle on the gauge will stop rhythmically bounding. The pressure at which
you no longer hear any sound is the diastolic pressure.
11. Open the pressure valve completely, quickly finish deflating the cuff, and remove it from your
partner’s arm.
12. Record the observed blood pressures. Finally, repeat the above procedures and averaging the
readings may yield a more accurate overall blood pressure determination.
Systolic pressure #1_______________________
Diastolic pressure #1_____________________
Systolic pressure #2_______________________
Diastolic pressure #2_____________________
Average Systolic pressure:__________________
Average Diastolic pressure:________________
Expression of Blood Pressure (at rest)_________________________
Although we do not take the time to do the following corollary blood pressure determination tests, you
should be aware that posture, temperature, emotion(s) and exercise have quite marked effects on one’s
blood pressure reading. Changing posture affect the influence of gravity on blood pressure. (This is
readily apparent when standing on one’s head!) What if you had your partner lie in the supine position
for approximately 5 minutes to allow for cardiovascular adjustments, performed a blood pressure determination, and compared it to the pressure obtained while your partner was seated. How might the
two readings be different?
Or, what if you had your partner immerse one hand into a bucket of ice water for 2 – 3 minutes,
and performed a blood pressure determination. How might the two readings be different?
Or, what if you had your partner jog in place for 5 minutes (without stopping if possible) and
performed a blood pressure determination. How might this reading vary from the at-rest reading?
Definition and Description of the Phases of the Sounds of Korotkoff:
You may have noticed that hen taking someone’s blood pressure the sounds change in character
as you deflate the cuff. The following information describes those changes and explains how they
relate to the systolic and diastolic pressures.
The series of sounds heard through a stethoscope placed over an artery that has been occluded
by a compression cuff are called the Korotkoff Sounds. These sounds, by which arterial blood pressure
is determined, were first described over 100 years ago (in 1905) by a Russian physician (and physiologist, Nicolai Korotkoff (1874 – 19 ). He divided the sounds into five phases:
Phase I
Phase II
Phase III
Phase IV
Phase V
That period marked by the first appearance of clear, tapping sounds which
gradually increase in intensity.
That period during which the sounds change to a murmur and have a swishing
quality.
That period during which the sounds have a firm, knocking quality, but are not
quite as clear as those in Phase I.
That period when the sounds suddenly are muffled and again have a faint,
swishing quality.
That period when all sounds disappear.
As the pressure in the compression cuff decreases, so does the pressure on the artery. When the pressure on the artery equals that in the compression cuff, the occluded artery opens and the first spurt of
blood enters the collapsed artery below the cuff. This produces the tapping sounds of Phase I and represents the systolic pressure. When the cuff no longer compresses the artery (ie no longer puts any
back pressure on the artery) the sounds will disappear all together – because remember, you cannot
hear blood flowing in its normal circulatory route. This is Phase V and represents the diastolic pressure. The current guidelines state that the diastolic blood pressure should be recorded at the disappearance of sound, Phase V.
Activity #2: Determination of Pulse
Heart rate is usually determined by measuring the pulse or pressure wave in an artery. During
ventricular systole, blood pressure increases and stretches the walls of arteries. During ventricular
diastole, blood pressure decreases and the arterial walls rebound to their relaxed diameter. This change
in vessel diameter is felt as a throb at the pressure point. The most commonly used pressure point is
the radial artery on the anteroateral forearm just superior to the thumb. Other points include the common carotid artery in the neck and the popliteal artery of the posterior knee, or the dorsalis pedis artery at the ankle.
Procedure: Pulse Determination
1. Have your partner relax in a lab seat for several minutes.
2. Locate your subject’s pulse in the right radial artery located just above the thumb. Use your index
finger or index and middle fingers to palpitate and identify the pulse. Do not use your thumb for pulse
measurements.
3. Gently apply light pressure to the pulse point and count the pulse rate for 15 seconds and then multiply this number by 4 to obtain the rate per minute. (Or, count the pulse rate for 30 seconds and multiply by 2. Either of these methods SHOULD yield the same rate.) Record your data as a table in the
format suggested below.
4. Repeat the pulse determination at the carotid artery, the popliteal artery, and the dosalis pedis
artery. Record your data.
5. Is there a difference between the pulse at the various pulse points? Give an explanation.
TABLE for PULSE MEASUREMENTS
Pulse Point
1.
Radial
2.
Carotid
3.
Popliteal
4. Dorsalis Pedis
Pulse Rate
_____________________________
_____________________________
_____________________________
_____________________________