Lab-8
Dr. Twana A. Mustafa
Human Cardiovascular Physiology: Blood Pressure and Pulse Determinations
The cardiac cycle includes all the events related to the flow of blood through the heart during
one complete heartbeat.
Heart Valves
During the cardiac cycle, heart valves open and close in response to differences in blood
pressure on their two sides.
The Heart Valves:
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Pulmonary semilunar valve
Aortic Semilunar Valve
Left AV valve or Bicuspid valve or Mitral valve
Right AV valve or Tricuspid valve
2 mail phases:
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Systole – Contraction
Diastole - Relaxation
Phases of the Cardiac Cycle
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1 – Ventricular filling and atrial contraction
2a – Isovolumetric contraction phase
2b – Ventricular ejection phase
3 – Isovolumetric relaxation and ventricular filling
1. Ventricular Filling - Occurs during mid to late diastole.
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Ventricular Filling: Passive: occurs during mid to late diastole, when
the heart chambers are relaxed. Blood flows passively into the atria, through
open AV valves, and into the ventricles, where the pressure is lower.
Ventricular Filling: Atrial Contraction: Atria contract, forcing the
remaining blood into the ventricles. Blood flows through both sides of the
heart at the same time.
2. Ventricular Systole - Includes isovolumetric contraction and ventricular ejection.
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Isovolumetric contraction: Ventricles contract and intraventricular pressure
rises, closing the AV valves. Briefly, ventricles are completely closed chambers.
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Ventricular ejection: Rising ventricular pressure forces semilunar valves open.
Blood is ejected from the heart into the aorta and pulmonary trunk
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Dicrotic notch represents the interruption of smooth flow due to the brief
backflow of blood that closes the aortic semilunar valve when the ventricles relax.
3. Isovolumetric Relaxation - Occurs during early diastole.
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Isovolumetric Relaxation: Ventricles relax and ventricular pressure
drops. Blood backflows, closing semilunar valves. Ventricles are totally closed off again.
Atrial Filling: Meanwhile, the atria have been filling with blood. When
atrial pressure exceeds ventricular pressure, AV valves open and ventricular filling, phase
1 begins again.
Heart Sounds (lub-dup)
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S1 - 1st sound (lub) – closing of the AV valves. Louder and longer than the second
sound. Beginning of ventricular systole
S2 - 2nd sound (dup) – closing of the semilunar valves. Short, sharp sound. End of
ventricular systole.
 Murmur - an abnormal sound of the heart; sometimes a sign of abnormal
function of the heart valves
The Pulse
Pulse – alternating surges in arterial blood pressure due to ventricular systole and
diastole. Normally, the pulse rate equals the heart rate and averages 70-76 beats per
minute while at rest. Normally, the pulse rate equals the heart rate and averages 70-76
beats per minute while at rest, however this number will wary based on age and the
level physical fitness.
Pulse pressure – is the difference between the systolic and diastolic pressures.
Indicates the amount of blood forced out of the heart during systole.
Pulse Pressure = Systolic Pressure - Diastolic Pressure
Pulse deficit – is the difference between the apical and radial pulse often
associated with atrial fibrillation. Your pulse is taken by touching one of several "pulse
points" located on your body. These spots are areas where the arteries are near to the
surface of the skin that the movement of blood through them can be felt. You can actually
feel arteries expand and contract, since the artery keeps pace with the heart.
 Common carotid pulse – anterior neck.
 Facial pulse – anterior to angle of mandible.
 Superficial temporal pulse – anterior to tragus of ear.
 Axillary pulse – within axilla.
 Apical pulse – not taken over an artery. Instead, it is taken over the the apex of the
heart itself.
 Brachial pulse – medial arm, between biceps and triceps.
 Radial pulse – anterior, lateral wrist.
 Femoral pulse – inguinal region.
 Popliteal pulse – posterior knee.
 Posterior tibial pulse – ankle.
 Dorsalis pedis pulse – dorsal surface (top) of foot.
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Blood Pressure
Blood pressure is an important indicator of cardiovascular health. It is influenced by the
contractile activities of the heart and conditions and activities of the blood vessels.
Blood Pressure Defined:
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The pumping action of the heart generates blood flow.
Blood Pressure is the force that blood exerts against blood vessel walls.
Blood pressure results when that flow is met by resistance from vessel walls.
Blood pressure is expressed in millimeters of mercury (mm Hg). For example a blood
pressure of 120 mm Hg is equivalent to a pressure exerted by a column of mercury 120
mm high.
The blood pressure is determined by the rate of blood flow produced by the heart
(cardiac output – the amount of blood pumped by each ventricle in 1 minute), and the
resistance of the blood vessels to blood flow (Peripheral resistance).
 Laminar Flow: Blood flows faster in the center of a vessel than near the sides,
because the blood near the sides is hitting the walls of the vessels. This is called
laminar flow and it is due to the friction (resistance) between the blood and the
vessel walls. The greater the resistance, the slower the blood flow.
 Systolic Pressure is the maximum pressure exerted by the blood against the
artery walls. It is the result of ventricular systole or contraction. It is normally
about 120 mm Hg.
 Diastolic Pressure is the lowest pressure in the artery. It's a result of ventricular
diastole (relaxation) and is usually around 80 mm Hg.
Mean Arterial Pressure (MAP)
 A term used in medicine to describe a notional average blood pressure in an
individual.
 It is defined as the average arterial pressure during a single cardiac cycle.
 Mean Arterial Pressure (MAP) = Diastolic Pressure + 1/3 Pulse Pressure
 MAP is closer to the diastolic pressure than systolic pressure because the heart
stays longer in diastole.
How blood pressure is measured
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Korotkoff Sounds are the sounds heard through the stethoscope (acoustic medical
device) over an artery when blood pressure is determined by
the sphygmomanometer (blood pressure measuring device)
 As the pressure cuff deflates, first clear sound indicates systolic pressure; the last
clear sound indicates diastolic pressure. When sounds cease to be heard the cuff
has deflated past the diastolic pressure.
 It is generally accepted that there are five phases of Korotkoff sounds. Each
phase is characterised by the volume and quality of sound heard. The figure
below illustrates these phases.
 In this example, the systolic and diastolic pressures are 120mmHg and 80mmHg
respectively.
WHO Blood Pressure Classifications
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Standards for assessment of high or low blood pressure have been established by
the World Health Organization (WHO) as shown on the following chart: