The document provides an overview of cardiovascular physiology, including: 1. The components and chambers of the heart, cardiac cycle, heart sounds, and cardiac muscle. 2. Electrophysiology of the heart and how it relates to the electrocardiogram (ECG). 3. Regulation of cardiac output and factors that influence stroke volume such as preload, contractility, and afterload.

1. Cardiovascular physiology
By:- Demeke A

3. General out lines
1. General introduction
2. Electrophysiology of the heart muscle
3. Cardiac cycle
4. The heart sounds
5. The heart rate and its regulation
6. CO in normal heart and in failing heart
7. ECG
8. The ABP and its regulation
9. Coronary circulation

4. Components of the Cardiovascular System (CVS)
HEART: Driving force for CVS
 ARTERIES :Distribution channels to the organs
 MICROCIRCULATION: Exchange region
 VEINS: Blood reservoirs and path for return of
blood to the heart

5. The Heart
The heart is a dual pump that drives blood in two serial
circuits, pulmonary(lungs) and the systemic(the rest
of the body) circulations, and receives blood from
the rest of the body through the vena cavae

6. Gross Functional Structure
Size: The heart has the size of a clenched fist,
weighs about 320gm in males (0.5% of body
wt ) and about 250 gm in the female (0.45%
of body weight).

8. Surfaces/Layers of the heart
Pericardium
– Is a fibrous closed sac investing the entire
heart and cardiac portion of great vessels.
– Contains:
 visceral layer (epicardium)immediately lining
the outer surface of the heart and
 a parietal pericardial layer forming outer lining
of the pericardial sac
 a small amount of fluid (10-20mL of serous fluid
(pericardial fluid) secreted by the
membranes)is found b/n the two layers .
 The presence of this fluid reduces the friction
between the beating heart and the surrounding
tissues.

9. Surface of the heart cont’d
Endocardium-Inner surfaces of atria and ventricles
-it is an endothelial connective tissue
extending over valves and lining cavities of
heart.
The myocardium
– This is the muscular wall of the heart.
– It primarily consists of cardiac muscle, but
also contains blood vessels and nerves
– Lies between epicardium and endocardium

11. Chambers of the Heart
 The heart has four chambers
o The Atria: Two thin-walled overlying muscular
sheaths, serving as reservoirs and pumps
o The Ventricles: Thicker-walled portion of the heart
that pumps blood from the low-pressure venous
system into the higher pressure arterial system.
• The right atrium receives deoxygenated blood from
the systemic circuit and passes it into the right
ventricle, which discharges it into the pulmonary
circuit.
• The left atrium receives oxygenated blood from the
pulmonary circuit and passes it into the left
ventricle, which discharges it into the systemic
circuit.

12. Chambers of the Heart cont’d
• The right and left atrium are separated by
the Interatrial septum
• The thick interventricular septum
separates the left and right ventricles.
• The left ventricle is 2-4x as thick as the
right ventricle because of its greater
workload

13. Cardiac Valves
 Thin flaps of flexible, endothelium-covered
fibrous tissue firmly attached to fibrous rings
at the base of the heart
 Responsible for the unidirectional flow of blood
through the heart.
 They are opened or closed in response to
pressure gradient(difference)
Types of valves
A. The Mitral and Tricuspid (atrio-ventricular-AV) valves
 Thin-walled and located b/n the atria and the
ventricles.
 Mitral (two cusps) valve lies b/n left atrium and left
ventricle
 Tricuspid (three cusps) valve lies b/n Rt atrium and Rt
ventricle

15. Valves cont’d
 The AV valves become opened when
pressure in the atria is greater than in the
ventricles and they become closed when
pressure in the ventricles is greater than
pressure in the atria

17. The semilunar valves
 Constitute the aortic and pulmonary valves
located at the exits of the right and left
ventricles.
• Open and close passively
• Aortic valve is three-cusped and allows blood to
flow into the aorta
• Semilunar valves open when pressure in the
ventricles is greater than pressure in the
arteries (i.e., during ventricular systole) and
close when pressure in the pulmonary trunk and
aorta is greater than pressure in the ventricles
(i.e. during ventricular diastole).
• Pulmonary valve allows blood to flow into the
pulmonary artery.

18. Cardiac Muscle
 Cardiac muscle cells( the cardiac myocyte) are
short, fat, branching and uninucleated.
 Cardiac muscle is similar to skeletal muscle in that
they are both striated.
 Cardiac muscle cells are intricately linked to one
another by structures called intercalated discs.
 Intercalated discs have 2 components.
• gap junctions (which provide an electrical
link between all cardiac myocytes) and
• desmosomes (which provide a mechanical link
between all cardiac myocytes).

19. Cardiac muscle cont’d
• The electrical and mechanical connection
created by the intercalated discs allow the
thousands of cardiac muscle cells to behave as if
they were one giant cell.
• Multiple cells that function as one entity are
often referred to as a functional syncytium.
• It should be noted that not all cardiac myocytes
are identical. 99% of them are the contractile
cardiac muscle cells. They generate the force
that pumps blood through the systemic and
pulmonary circuits.
• The remaining 1% lack the elaborate sarcomeres
and other contractile machinery and have a
separate specialized function. They are the
autorhythmic cells of the heart.

21. Autorhythmic Cells
• "Autorhythmic" literally equates to "self-rhythm" and
that is an apt name for these cells because they set
the rhythm of the heart without any input from any
external organs, tissues, or signals.
• Exhibit pacemaker potentials (on pacemaker cells)
• Autorhythmic cells have the ability to spontaneously
depolarize to threshold and generate action potentials.
• Depolarization is due to the inward diffusion of
calcium (not sodium as in contractile cells & nerve cell
membranes).

23. Spread cont’d
Summary of Spread of cardiac
excitation
• SA node AV node  AV bundle 
bundle branches Purkinje fibers 
ventricles
• Fastest propagation in the Purkinje
system

25. Innervations of the Heart
 The autonomic nervous system provides a large
influence on the activity of the heart.
 Increased activity of the sympathetic nervous
system (the "fight or flight" branch of the ANS)
increases both the rate and the force of
heartbeat.
 Increased activity of the parasympathetic
nervous system (the "rest and digest" branch of
the ANS) decreases heart rate but has little
effect on the force of contraction.
– The right vagus nerve has a strong influence on
SA node, while the left vagus has dominant
effect on AV node.
– Ventricles are not supplied by vagus nerve.

26. Innervations of the Heart

27. Ionic Basis of Cardiac Action Potential
– Various phases of cardiac AP are associated
with changes in the permeability of the cell
membrane to, mainly, Na, K, and Ca ions.

28. • Ionic Basis of Cardiac Action Potential

29. Ionic basis cont’d
– Phase-0: Rapid depolarization caused by rapid
Na-influx
– Phase-1: Early partial repolarization caused by
Cl- influx
– Phase-2: The plateau caused by Ca2+influx via L-
channels
– Phase-3: Repolarization caused by K+ efflux
– Phase-4: complete repolarization
– RMP re-established by Na-K-ATPase

30. Excitation-contraction-coupling
• Spread of excitation from cell-to cell via gap
junctions
• Also spread to interior via T-tubules
During plateau phase, Ca++ permeability increases
– This Ca++ triggers release of Ca++ from SR
Ca++ level increases in cytosol(Intracellular)
Ca++ binds to Troponin C
Ca++-Troponin complex interacts with tropomyosin
to unlock active site between actin and myosin
Cross bridge cycling=contraction (systole)

31. Relaxation (diastole):
• As result of Ca++ removal
o Ca++ removed by:
 Uptake by SR-by the action of ca++
ATPase
 Extrusion by Na+-Ca++ exchange(3Na+ :
1Ca+)
 Ca++ pump (to limited extent)

32. The Cardiac Cycle
• It is sequence of events between the
start of one heartbeat and the beginning
of the next.
• With in one cardiac cycle there is
– Systole = heart contraction and
– Diastole = heart relaxation.

33. Phases of the cardiac cycle
The cardiac cycle can be broken down into 4
phases:
• Ventricular Filling
• Isovolumetric Contraction
• Ventricular Ejection
• Isovolumetric Relaxation.

34. Ventricular filling
• During ventricular filling, the AV valves are
open, the semilunar valves are closed and
atrial pressure exceeds ventricular pressure.

35. Isovolumetric Contraction
• Both the semilunar and atrioventricular
valves are closed but the ventricles are
contracting.
• B/c all valves are closed no blood enter and
leave the ventricles during this phase(i.e
the ventricular volume is not changing). Thus
this period is known as isovolumetric
contraction.

36. Ventricular Ejection
• Ejection of blood begins when ventricular
pressure exceeds arterial pressure - about
120mmHg in the left ventricle and 25mmHg
in the right ventricle.
• The amount ejected (typically about 70mL)
is known as the stroke volume(SV)
•

37. Isovolumetric Relaxation
• ventricles are relaxing and pressure is dropping,
but the volume is not changing - thus we have
isovolumetric relaxation.
When ventricular pressure does drop below atrial
pressure, the AV valves open and ventricular filling
begins a new.

38. Heart sounds
Sounds associated (usually) with valve closure
• First heart sound(lub sound)
 is due to closure of AV valves
 Occurs at beginning of isovolumic contraction
• It is the loudest and longest of the heart sounds
• it is heard best over the apical region of the heart.
• The tricuspid valve sounds are heard best in the fifth
intercostal space, just to the left of the sternum;
• the mitral sounds are heard best in the fifth intercostal
space at the cardiac apex

39. • Second heart sound(dub sound)
 Closure of Aortic & Pulmonic valves (Semilunar valves)
 Occur at end of ejection (at onset of diastole)
 Sometimes splitted, since Aortic valve closes slightly before
Pulmonic valve
• is composed of higher-frequency vibrations (higher pitch), and
it is of shorter duration and lower intensity.
• closure of the pulmonic valve is heard best in the second
thoracic interspace just to the left of the sternum,
• closure of the aortic valve is heard best in the same
intercostal space but to the right of the sternum.
• The aortic valve sound is usually louder than the pulmonic,
but in cases of pulmonary hypertension the reverse is true.
• Third heart sound (sometimes)-due to rapid ventricular
filling
• Fourth heart sound (occasionally)- during atrial contraction

40. Areas for auscultating heart sounds

41. Cardiac Output
• It is the volume of blood pumped by each ventricle per
minute
• The cardiac output(CO) is the product of stroke volume(SV)
and heart (HR).
• CO = HR x SV
L/min = beats/min. L/beat.
 CO (at rest) = 5-6 L/min
 HR=72 beats/min , SV=0.07L/min (70ml)
 SV is the volume of blood pumped by each ventricle per
beat.

42. Factors affecting the cardiac out put(CO)
• Any thing which affects the heart rate
and the stroke volume indirectly can
affect the CO

43. Factors Affecting Stroke Volume
• Stroke volume is primarily governed by 3 factors:
1. Preload
• is the end diastolic volume(EDV)
2. Contractility
• refers to the contraction force at any given preload.
• It is independent of how stretched the myocardium
is.
• It's governed by neural, hormonal and chemical
factors.
3. After load
• Refers to the blood pressure just outside the
semilunar valves (in the aorta and pulmonary trunk).

44. Electrocardiography(ECG)
• Is a recording of electrical activity of heart conducted
through ions in body to surface
• The electrical activity of the heart is recorded by
electrocardiograph and the tracing is electrocardiogram
• ECG was developed by W. Einthoven in Leiden and
A. Waller in London in 1909

45. ELECTROCARDIOGRAPHY
• ECG of the heart is recorded from specific sites of
the body in graphic form relating voltage (vertical
axis) with time (horizontal axis).

46. Information obtained from ECG:
• Anatomical orientation of the heart
• Relative size of chambers
• Rhythm and conduction disturbance
• Extent, location and progress of ischemic
damage.
• Electrolyte disturbance
• Influence of drugs
• HR
• Origin of excitation

47. ECG Conventions
1. 1mV input→10mm deflection
2. Paper speed =25mm/sec.
3. Recording points =wrist, ankle, skin on chest
4. Right leg = ground(earth)

48. Relation b/n cardiac AP and ECG waves
As shown below, there are three main deflections per
cardiac cycle:
• The P wave represents atria depolarization
• The QRS complex represents ventricular depolarization,
atrial repolarization also occur during this period.
• QRS complex is useful in diagnosing cardiac arrhythmias,
ventricular hypertrophy, MI, electrolyte derangement, etc
• The T wave represents ventricular repolarization

49. Characteristics of the Normal
Electrocardiogram
• The normal electrocardiogram is composed of a P
wave, a QRS complex, and a T wave.
• The QRS complex is often, but not always, three
separate waves: the Q wave, the R wave, and the S
wave.

52. Electrocardiogram (ECG). Typical recording from lead II, showing ECG waves,
segments, and intervals, and standard calibrations for time and voltage.

53. Atrial repolarization is obscured by
the QRS complex.

54. Electrical activity in nodal and conducting tissue is not
seen on an ECG because the amount of tissue is too
small to produce measurable voltage differences at
the body surface.

56. ECG Intervals and segments
P-Q or P-R Interval.
• The time between the beginning of the P wave and
the beginning of the QRS complex
• Is the interval between the beginning of electrical
excitation of the atria and the beginning of excitation
of the ventricles.
• The normal P-Q interval is about 0.16 second.
• Prolonged PR interval may indicate a 1st degree
heart block.
• represents atria depolarization

57. ECG cont’d
Q-T Interval.
• The time between the beginning of the Q wave
to the end of the T wave.
• ordinarily is about 0.35 second.
S-T Interval
The time between the end of S wave to the end of
the T wave.
• represents ventricular repolarization

58. ECG Recording techniques(EKG Leads)
• Leads are electrodes which measure the difference
in electrical potential between either:
1. Two different points on the body (bipolar leads)
2. One point on the body and a virtual reference
point with zero electrical potential, located in the
center of the heart (unipolar leads)

59. ECG leads cont’d
The standard EKG has 12 leads:
• 3 Standard Limb Leads(bipolar limb leads)
• 3 Augmented Limb Leads(unipolar limb leads)
six limb leads mentioned above have frontal
(vertical) plane.
• 6 Precordial chest Leads(unipolar leads)
• Have transverse plane which is perpendicular to
the frontal plane.