Useful for medical and biology students who want to study the cardiac cycle in a short time with big benefits !! CVS physiology - Wigger Diagram - ECG of cardiac cycle - Heart sounds

1. The Cardiac Cycle
Prepared & Presented by :Mohammed S. Elreishi

2. The Main Objectives
• Introduction tothecardiac cycle
• Whatis the cardiac cycle ?
• Carl J.Wigger’sDiagram!
• The mechanicaleventsandphases of cardiac cycle :
• ✔ Describe the cardiac cycle in terms of systole and diastole of the
atriaand ventricles.
• ✔ Explainhow the pressure differences within the heart chambers are
responsible for blood flow during the cardiaccycle.
• Heart sounds

3. Pressure Gradientsand volume
• A fluid flows only if it is subjected to more pressure at one
point thanatanother. The differencecreates apressure
gradient,and fluidsalways flow down theirpressure
gradients, from thehigh pressure point to the low-pressure
point
the greater the volume, the lower the pressure, and vice versa

4. Think aboutit, if you
pusha smaller amount
of fluidintoa larger
area, youhave less
pressure thanif you
push a large amount of
fluidintoa smaller area

5. • Theopeningand closingof the heart valves are
governed by these pressure changes !

6. Question ?
• Why there is a bicuspid valve in the left
side of the heart and a tricuspid valve in
the right side of the heart ?
• When did the First Cardiac cyclestart ?
And how ?

7. OverviewOn Fetal CardiacCycle
In a fetus, the resistance to blood
flow through the pulmonary
circulation is quite high, because
hypoxia (low oxygen) stimulates
smooth muscle contraction in
pulmonary arterioles, producing
vasoconstriction. (This differs
from systemic arterioles, which
dilate in response to hypoxia.)

8. • The high resistance in the fetal
pulmonary circulation causes blood
to pass from the higher pressure of
the right ventricle into the left
ventricle through an opening in the
interatrial septum calledthe
foramenovale . The pressure
difference also causes blood to be
shunted (diverted) from the
pulmonary to the systemic
circulation through a connection
between the pulmonary trunk and
aorta calledthe ductus arteriosus

9. • These shunts normally close after
birth. When the newborn breathes,
the blood oxygen levels suddenly
become higher. Because of
differing responses of the smooth
muscle cells to increased oxygen,
the rise in oxygen normally causes
vasodilation and thus increased
blood flow in the pulmonary
vessels, but contraction (and thus
closing) of the ductus arteriosus. If
the foramen ovale and ductus
arteriosus remain open (are patent)
after birth, murmurs can result.

10. Cardiac Cycle
the human heart has periodsof contraction(during which
bloodis pumped intothe large arteries)thatalternate
withperiods of relaxation(during whichbloodfills the
heart). These contractionand relaxationperiodsoccur in
cycles known as the cardiaccycles. each of which consist
ofaperiodofcontractioncalledsystole followedbya
periodofrelaxationcalleddiastole.

11. Cardiaccycle is defined as the sequence of
coordinatedevents taking place inthe heart during
each beat
Events of cardiaccycle are
classifiedinto two:
1. Atrialevents
2. Ventricularevents.

12. Durations inthe cardiac cycle
The total durationofthecardiaccycle,includingsystole and
diastole,is the reciprocal of the heart rate. For example, if heart
rate is72 beats/min, the duration of the cardiac cycle is 1/72
min/beat—about 0.0139 minutes per beat, or 0.833 second per
beat.

13. „VENTRICULAREVENTS
Ventricular events are dividedinto two
divisions:
1. Ventricular systole = (0.3) sec
2. Ventricular diastole = (0.5) sec
ATRIAL EVENTS
Atrial events are dividedinto two
divisions:
1. Atrial systole = (0.1) sec
2. Atrial diastole = (0.7) sec.
NOTE : In clinical practice, the term
‘systole’ refers to ventricular systole
and ‘diastole’ refers to ventricular
diastole.

14. Ventricular systole is divided into two
subdivisions and ventricular diastole is
divided intofivesubdivisions:
Ventricular Systole
Time (second)
1. Isometric contraction = 0.05
2. Ejection period = 0.22
Ventricular Diastole
1. Protodiastole = 0.04
2. Isometric relaxation= 0.08
3. Rapid filling= 0.11
4. Slow filling = 0.19
5. Last rapidfilling = 0.11

15. The Phases of The Cardiac Cycle
1) Atrial Systole (Last rapid filling phase )
2) Isometric ( Isovolumic ) contraction period
3) Ejection period ( Rapid , Slow )
4) Protodiastole
5) Isometric ( Isovolumic ) relaxation period
6) Rapid fillingphase
7) Slow ( reduced ) fillingphase

17. A Wiggers diagram is a
standard diagram used in
cardiac physiology named
after Dr. Carl J. Wiggers

18. Phase 1 : AtrialSystole (Presystole)
• Theatrialsystoleis thelastphaseofa
diastoleduring which theventricular
fillingis completed.( 0.11second)
• Theatrioventricular valves areopen;
thesemilunarvalves areclosed.
• rightatrialpressureincreases4to6
mmHgduringatrialcontraction,and
theleftatrialpressureincreases
about7 to 8mmHg. ?!

19. Pressure and volume changes
• Ventricles:
About 25 % of the ventricular filling volume is
ejected from the atrium to the ventricle. Intra-
ventricular pressure increase slightly .
end-diastolicvolume = 110 to 120 milliliters
• Atria
The atrial contraction causes a rise in the atrial
pressure which produces the a wave .
• Arteries
The pressure in arteries of both systemic and
pulmonary circulations decreases constantly

20. Electrocardiogram
• Theatrialdepolarization is completed and theend of theP
waveappears at the beginningof the atrial systole.
Subsequently,the depolarization spreads from theatria to
theatrioventricular node and thePR segment is visible in
theECG

21. Heart sound
• The fourthheart sound is a soft sound due to an increase in
theventricular pressure following anatrial systole. It very
rarely occurs in a healthyperson. Under pathological
conditions this sound is present owing to an increase in intra-
atrialpressure or lower compliance of theventricle (e.g.in
ventricular hypertrophy).

22. Phase 2 : Isovolumetric contraction Period
• is thefirstphaseofventricular systole.(
0.05second )
• Immediatelyaftera ventricular
contraction begins,thepressure in the
ventriclesexceedsthepressure in the
atriaand thus the atrioventricular
valves shut.The semilunarvalves are
closedbecause theventricular pressure
islowerthan thatinthe aortaand the
pulmonaryartery

23. Pressure and volume changes
• Ventricles
The ventricular pressure rises considerably
without any change in the ventricular blood
volume
• The blood volumein the ventricles equals
tothe end-diastolic volume
• Atria
The atrioventricular valves are bulged backward
into the atria because of increasing pressure in
the ventricles. This event causes the c wave
• Arteries
Pressures in arteries of both systemic and
pulmonary circulations decrease constantly

24. Electrocardiogram
• The depolarization spreads from theatrioventricular node to
theseptumand thewalls of both ventricles throughthe
bundle of His and Purkinjefibres . The ventricular
depolarization causes theQRS complex in the ECG

25. Heart sound
• During theisovolumic contraction, the first heart sound
appears . This sound is caused by vibrations of the
atrioventricularvalves, the adjacent myocardium and blood
due to the closure of theatrioventricular valves

26. Phase 3 : Ejection
• Due to the opening of semilunar
valves and isotonic contraction of
ventricles, blood is ejected out of both
the ventricles. Hence, this period is
called ejection period. ( 0.22 second )
• Ejection period is of two stages:
• 1) First Stage or Rapid Ejection Period
( 0.13 second )
• 2) Second Stage or Slow Ejection
Period ( 0.09 second )

27. Pressure and volume changes
• Ventricles
During the first part of the ejection, the ventricular pressure rises and blood
is intensively ejected to the arteries – rapid ejection. As the blood volume
in the ventricles decreases, the ventricular pressure starts to decline in the
second part of this phase . The pressure gradient between ventricles and
arteries decreases and blood is ejected more slowly – decreased or slow
ejection. The maximum ventricular pressure at the top of the ejection
reaches 120 mmHg and 25 mmHg in the left and right ventricles,
respectively. This peak value is calledsystolic pressure.

28. • Atria
Asthe ventriclescontract theyalsoshorten.
Theshortening ventricleselongate the
atriaand thebig veins, loweringtheir
pressure. This pressure decrease is
representedbythe x wave.
• Arteries
Theblood pressure inthe big arteriesrises
due to rapidejection toreachthe
maximum value of120 mmHgand 25
mmHg inthe aortaand the pulmonary
artery,respectivelyDuring the slow
ejection,the bloodpressure in the
systemic andpulmonary circulations
startstodropprogressively.

29. TheEnd –SystolicVolume
• as the ventriclesemptyduring systole, the
volume decreases about 70 milliliters,
whichiscalled the stroke volume output.
The remainingvolume ineachventricle,
about 40 to 50 milliliters,is calledthe end-
systolic volume. The fractionofthe end-
diastolic volume that isejectedis called the
ejection fraction—usually equal toabout
0.6(or 60percent). Whentheheart
contracts strongly,the end-systolic volume
maydecrease toas littleas 10 to 20
milliliters.Conversely, when largeamounts
ofblood flowinto the ventriclesduring
diastole, theventricularend-diastolic
volumescan become as greatas 150to
180millilitersin the healthyheart

30. Electrocardiogram
• The ventricles are completely depolarized at the beginningof
theejection– segmentST in theECG. The T wave appears
due to the ventricularrepolarization in thesecond half of this
phase

31. Phase 4 : Protodiastole
• Protodiastoleis thefirststage
ofventricular diastole,hence
thenameprotodiastole.
Durationofthis periodis
0.04second. Due tothe
ejectionofblood,the
pressure in aorta and
pulmonaryartery increases
and pressure in ventricles
drops.

32. Phase 5 : Isovolumetricrelaxationperiod
• At theend of systole, the
ventricles relax and the
ventricular pressure decreases
rapidly. Due to theblood inertia,
theblood flows out of the
ventricles (for a short time) even
whenthe pressure in large
arteries exceeds the ventricular
pressure. 0.08 second

33. Pressure and volume changes
• Ventricles
The ventricles relaxwithoutchangingbloodvolume
in ventricles –theisovolumicrelaxation.The
bloodvolumein each ventricle equalstothe
end-systolicvolume (about60ml).
• Atria
Bloodflowsfromthe veins totheatriawhile the
atrioventricularvalves areclosed.Theatrial
pressureincreases toproducethe vwave.
• Arteries
The decreasein thearterialpressureis interruptedby
thedicroticnotchthatis seen in the aorticpulse.
It is amomentarypressure increasecausedbya
shortperiodofbackwardbloodflow
immediately beforetheclosureofthe semilunar
valves

34. Electrocardiogram
• The ventricularrepolarization is being completed and theend
of theT wave appears in theECG

35. Heart sound
• During theisovolumic relaxation, thesecond heart sound
appears . This sound is caused by vibrations of thesemilunar
valves, theadjacent myocardium and blood due to theclosure
of thesemilunarvalves.

36. Phase 6 : Rapid Ventricular Filling
• As soon as theventricular
pressure fallsbellow the atrial
pressure, the atrioventricular
valves open. Blood flows rapidly
from the atria to the ventricles.
The semilunarvalves are closed
( 0.11 second )

37. Pressure and volume changes
• Ventricle
Although the ventricular volume increases, the
ventricular pressure is not changed
significantly due to the ventricular
relaxation .
• Atria
The negative y wave is caused by the blood
evacuation from the atria to the ventricles.
Arteries
The minimum pressure within one cardiac cycle
called diastolic pressure is about 80 mmHg
and 8 mmHgin the systemic and the
pulmonary circulations, respectively

38. Electrocardiogram
• No electrical activity is produced by cardiac cells thusthe
isoelectriclineis present in theECG

39. Heart Sound
• Thethird heart sound, which occurs rarely, is probably caused
by therapid blood flow

40. Phase 7 : Slow Ventricular Filling
• Theatrioventricular valves remain open whilethesemilunar
valves are closed.

41. Pressure and Volumechanges
• Ventricles
During the middle part of a diastole a
small volume of blood flows into the
ventricles. This is the blood flowing
from veins and passing the atria to fill
the ventricles. The pressure in both
ventricles is close to zero .
• Arteries
The pressures in arteries of both systemic
and pulmonary circulations decrease
constantly

42. Electrocardiogram
• At theend of slow ventricular filling,depolarization spreads
from sino-atrialnode in all directions over the atria to
produce theP wave in ECG

43. Factors that affectthe cardiaccycle!
• ValvularDiseases
1 – Stenosis
2- Incompetence
• Variations
1-„Physiologicalvariations
2- Pathologicalvariations

44. • 1. Stenosis
• Stenosismeans narrowing of heart valve. Bloodflows
rapidlywith turbulence throughthe narrow orificeof the
valve, resultingin murmur.
• 2.incompetence
• Incompetence refers to weakening of the heart valve.
When the valve becomes weak, it cannotclose properly. It
causes back flow of blood,resultingin turbulence. This
diseaseisalsocalledregurgitationor valvularinsufficiency.

45. • PHYSIOLOGICAL VARIATIONS
• 1. Age
• 2. Sex
• 3. Body build
• 4. Diurnal variation
• 5. Environmental temperature
• 6. Emotional conditions
• 7. After meals
• 8. Exercise
• 9. High altitude
• 10. Posture
• 11. Pregnancy
• 12. Sleep
PATHOLOGICAL VARIATIONS
1. Fever: Due to increased oxidative
processes
2. Anemia: Due to hypoxia
3. Atrial fibrillation: Because of
incomplete fillingof ventricles
4. Congestive cardiac failure: Because of
weak contractions of heart
5. Shock: Due to poor pumping and
circulation
6. Hemorrhage: Because of decreased
blood volume.

46. The END