Transcript Lecture 3 + 4 - Cardiac Cycle (2012).

CARDIC CYCLE
Prof. Sultan Ayoub Meo
MBBS, M.Phil, Ph.D (Pak), PG Dip Med Ed, M Med Ed (Scotland)
FRCP (London), FRCP (Dublin), FRCP (Glasgow), FRCP (Edinburgh)
Professor and Consultant, Department of Physiology,
College of Medicine, King Saud University, Riyadh, Saudi Arabia
LECTURE OUTLI NES / OBJECTIVES
STUDENTS ABLE TO UNDERSTAND:
 General principle of the cardiac cycle
 Identify events occurring during cardiac cycle:
mechanical,
electrical,
volume
&
pressure
changes, heart sounds.
 Understand the various phases of the cardiac cycle
CARDIAC CYCLE
The cardiac events that occur from the beginning of one heart
beat to the beginning of the next is called the cardiac cycle.
Cardiac cycle is a complete beat of the heart.
Each cycle is initiated by spontaneous generation of an action
potential in the sinus node.
The cardiac cycle consists of a period of relaxation called
diastole during which the heart fills with blood. This period is
followed by a period of contraction called systole.
CARDIAC CYCLE: CARDIAC
VALVES
CARDIAC CYCLE: CARDIAC
VALVES
CARDIAC CYCLE: CARDIAC
VALVES
PRESSURES IN THE CARDIAC
CHABERS
Aortic pressure (left ventricular pressure)
Maximum pressure (during systole):
Minimum pressure (during dystole):
Pulse pressure (difference between systolic and diastolic) :
Right ventricular pressure
Maximum pressure =
Minimum pressure =
Atrial pressure
Maximum right atrial pressure
Minimum right atrial pressure
Maximum left atrial pressure
Minimum left atrial pressure
Pulmonary pressure (mm Hg)
Systolic pulmonary arterial pressure:
Diastolic pulmonary arterial pressure :
120 mm Hg.
80 mm Hg.
120-80 = 40 mm Hg.
25mm Hg
0-2mm Hg
6-8 mm Hg
0-2 mm Hg
6-9 mm Hg
0-2 mm Hg
25
8
CARDIAC CYCLE
I. VENTRICULAR SYSTOLE
Iso-volumetric contraction of ventricles
Maximum ejection phase
Reduced ejection phase.
2. VENTRICULAR DIASTOLE
Protodiastole
Isovolumetric (isovolumic ) relaxation
Rapid inflow
Reduced inflow
Atrial systole
(0.05 sec )
(0.112sec)
(0.141 sec )
------------0.303 Sec
(0. 033 sec)
(0. 071 sec)
(0.110 sec)
(0.161 sec)
(0.12 sec )
-------------0.495 sec. [0.8 Sec]
CARDIAC CYCLE: DURATION
SYSTOLE AND DIASTOLE
OF
0.3Sec.
0.5 sec.
VS
VD
CARDIAC CYCLE: VENTRICULAR
SYSTOLE
Isovolumetric contraction: The left ventricle begins to contract,
at this stage the pressure in the ventricles is slightly above 02mm Hg.
As the intra-ventricular pressure rises, it pushes the cusps of the
A-V valve up and the A-V orifices are closed.
The pressure in the ventricular cavities continues to rise but
remains less than that in the large arteries. Thus, the semilunar
valves (aortic and pulmonary) also remain closed and no blood
enters or leaves the ventricles.
CARDIAC CYCLE: VENTRICULAR
SYSTOLE
CARDIAC CYCLE: VENTRICULAR
SYSTOLE
MAXIMUM EJECTION PHASE: The ventricles contract and
increase the pressure more than in the large arteries.
 The left ventricular pressure rises up to 120 mm Hg causes the
opening of the aortic valves
 Right ventiricular presssure rises more than 25 mm Hg and
causes the opening of pulmonary valves so blood leaves the
ventricles rapidly to the aorta and pulmonary artery
 At the end of this stage, intraventricular pressure reaches its
peak level.
CARDIAC CYCLE: VENTRICULAR
SYSTOLE
REDUCED EJECTION PHASE
 In this phase of the cardiac cycle, the force of contraction of
the ventricles becomes weaker than the force of contraction
during the maximum ejection phase. Now the pressure within
the ventricles also decreases, but is still higher than that of the
aorta so ventricular emptying continues.
 In this phase less volume of blood flows into the aorta and
pulmonary artery due to weaker contraction of the ventricles.
CARDIAC CYCLE: VENTRICULAR
SYSTOLE
CARDIAC CYCLE: VENTRICULAR
SYSTOLE
CARDIAC CYCLE: VENTRICULAR
DIASTOLE
VENTRICULAR DIASTOLE [PROTO DIASTOLE]
 In this stage, the ventricles relax and the intraventricular
pressure decreases, becoming less than the aortic and
pulmonary artery pressures.
 Blood present in the aorta and pulmonary artery tends to
move back into the ventricles.
 At this stage the semilunar valves ( aortic and pulmonary )
are closed and do not allow entry of blood into the ventricles
CARDIAC CYCLE: VENTRICULAR
DIASTOLE
ISOVOLUMETRIC RELAXATION
•In this stage the ventricles relax further and intraventricular
pressure falls.
•The semilunar valves remain closed due to higher pressure in
the large arteries as compared to intraventricular pressure.
•The pressure within the ventricles is still higher than the atria,
so the A-V valves remain closed and no blood enters or leaves
the ventricles.
CARDIAC CYCLE: VENTRICULAR
DIASTOLE
CARDIAC CYCLE: VENTRICULAR
DIASTOLE
RAPID INFLOW
The ventricular volume increases, the pressure within the
ventricles is further decreased to lower than intra atrial
pressure. The left ventricular pressure decreases up to 2-4 mm
Hg. This pressure is less than the maximum left atrial pressure
(6-9mm Hg). This change in pressure causes the opening of
left AV (biscuspid / mitral) valve. So blood which was
accumulate in the left atrium rush into the left ventricle.
CARDIAC CYCLE: VENTRICULAR
DIASTOLE
RAPID INFLOW
Right ventricular pressure decreased up to 0-2mm Hg. This
pressure is less than the maximum right atrial pressure (6-8mm
Hg). This change in pressure causes the opening of right AV
(tricuspid) valve. So the blood which was accumulate in the
right atrium rush into the right ventricle.
CARDIAC CYCLE: VENTRICULAR
DIASTOLE
CARDIAC CYCLE
CARDIAC CYCLE: VENTRICULAR
DIASTOLE
Reduced inflow
At the beginning of this phase most of the blood has already
entered the ventricles.
Remaining blood in the atria also flows into the ventricles.
Atrial systole
Once again the atrial muscle fibers start to contract, indicating
the beginning of a new cardiac cycle.
SUMMARY CARDIAC
CYCLE
EVENTS:
OPENING AND CLSOSING OF VAVLVES
CARDIAC CYCLE: ASSOCIATION WITH
HEART SOUNDS
CARDIAC CYCLE: ASSOCIATION WITH
HEART SOUNDS
CARDIAC CYCLE: ASSOCIATION WITH
HEART SOUNDS
CARDIAC CYCLE: ASSOCIATION WITH
HEART SOUNDS
VS
VD
0.3Sec.
0.5 sec.
1 st Heart Sound
2 nd Heart Sound
3 rd Heart Sound
4 th Heart Sound
HEART SOUNDS
AS – Atrial Systole;
AD – Atrial Diastole ;
VS – Ventricular systole;
VD – Ventricular diastole
CARDIAC CYCLE: ASSOCIATION WITH
HEART SOUNDS
0.3Sec.
1 st Heart Sound
Isovolumetric
contraction
2 nd Heart Sound
Maximum
ejection
Reduced ejection
period
period
period
Ventricular Systole
AS – Atrial Systole;
AD – Atrial Diastole ;
VS – Ventricular systole;
VD – Ventricular diastole
CARDIAC CYCLE: ASSOCIATION WITH
HEART SOUNDS
0.5Sec.
3 rd HS
2 nd HS
Isovolumetric
Relaxation
Maximum Filling
Reduced Filling
Phase
Phase
Protodiastolic Period
HS – Heart Sound
Ventricular Diastole
Phase
4 th HS
1 st HS
TAKE HOME MESSAGE
Beginning of one heart beat to the beginning of the next is
called the cardiac cycle. consists of a period of relaxation called
diastole followed by a period of contraction called systole.
Cycle duration is 0.8 Sec [Systole 0.3 sec and Diastole 0.5 Sec]
THANK YOU
College of Medicine, King Khalid University
Hospital, King Saud University, Riyadh,
Saudi Arabia