Transcript Cardiac cycle

Cardiac cycle
Lecture by
Dr.Mohammed Sharique Ahmed Quadri
Assistant professor ,Physiology
‫بسم هللا الرحمن الرحيم‬
Objectives



To know about different phases of cardiac
cycle
To understand the volume, pressure and
electrical changes during the cardiac cycle
To emphasize the inter-relationship between
all these changes
Functional anatomy of heart
Cardiac cycle



Cardiac events that occur from beginning of one
heart beat to beginning of next are called the
cardiac cycle .
Cardiac cycle consist of alternate period of systole(
contraction/emptying)
&
diastole(relaxation /filling )
Contraction results from spread of excitation
across the heart & relaxation follows subsequent
repolarisation of cardiac musculature.
CARDIAC CYCLE

Cardiac cycle time : 0.8 second when heart rate
is 75 beats per minute.

Atria and Ventricle go through separate cycles
of systole and diastole.

When we use the term Systole and Diastole, we
refer to ventricles, until unless specified for
atria.
6
We will discuss mechanical & electrical
changes during Cardiac Cycle
Mechanical changes:
1.
Phases of cardiac cycle
2.
Pressure changes during cardiac cycle
3.
Volume changes during cardiac cycle
4.
Heart sounds
Electrical Changes
5.
Electrocardiogram (ECG)
7
CARDIAC CYCLE
0.7 Sec.
0.1 sec.
AD
AS
Atrial Cycle (0.8 Sec.)
0.3Sec.
0.5 sec.
VS
VD
Ventricular Cycle (0.8 Sec.)
AS – Atrial Systole;
AD – Atrial Diastole ;
VS – Ventricular systole;
VD – Ventricular diastole
ECG




ECG ( Electrocardiogram) – These electrical events can be
recorded by putting electrodes on the surface of body
P wave – Atrial depolarization
QRS - Ventricular Depolarization
T wave – Ventricular Repolarization
We will discuss
ECG in detail in
coming lectures.
9
Events during cardiac cycle




Atrial systole 0.1 second
Atrial diastole 0.7 second
Ventricular systole 0.3 second
 Isovolumic contraction 0.01 seconds
 Rapid ejection period
 Slow ejection period
Ventricular diastole 0.5 seconds
 Isovoumic relaxation 0.02 seconds
 Rapid filling
 Slow filling (Diastasis)
 Atrial contraction
Events during cardiac cycle
(continued)

Ventricular filling:



When ventricular pressure
falls below atrial pressure
AV valves opens &
ventricular filling begins
The first part of this period
is known as first ventricular
filling phase (3rd heart
sound)
Large part of ventricular
filling takes place during
this period
Semilunar
valves closed
AV valves
opened
Events during cardiac cycle
(continued)

Ventricular filling:




In the next phase of diastole
ventricular filling slows down .
As the ventricles are already
full to large a large extent &
ventricular pressure slowly
rises
This phase is known as
diastasis or slow inflow phase
Amount of filling during this
period is minimum
Semilunar
valves closed
AV valves
opened
Events during cardiac cycle
(continued)

Ventricular filling:


Than comes the last
phase of ventricular
filling known as last
rapid filling
This phase
corresponds with
atrial systole
(contributes to 2030% of ventricular
filling)
Semilunar
valves closed
AV valves
opened
Events during cardiac cycle

Atrial systole:





Caused by atrial
depolarization
Left ventricle is relaxed
As AV valves are open
,ventricles are filling with
blood even prior to atrial
systole
Atrial systole causes
further increase in
ventricular volume
Through out atrial
contraction atrial
pressure exceeds
ventricular pressure so
AV valves remain open
Semilunar
valves closed
AV valves
opened
Events during cardiac cycle
(continued)

Ventricular systole :


After the atrial contraction impulse travels
through AV node & specialized conduction
system to excite the ventricle.
As the ventricular contraction begins
pressure in the ventricles exceeds that of
atria and this backwards pressure forces
the AV valves to close
Events during cardiac cycle
(continued)

Isovolumetric
ventricular contraction:



To open the semilunar
valves ventricular pressure
must exceeds that of aortic
& pulmonary pressure
After closing of AV valves &
before opening of Semlunar
valves ,a brief period of time
when ventricles contracts as
a closed chamber
Ventricular pressure
continues to increase
Events during cardiac cycle
(continued)
Semilunar
valves
opened
Semilunar
valves closed
AV valves
closed
AV valves
closed
Systole: Period
venticular ejection.
Events during cardiac cycle
(continued)

Ventricular diastole (repolarization):

As the ventricles starts to relax on
repolarisation ,ventricular pressure falls
below aortic & pulmonary pressure &
semilunar valves closes .
Events during cardiac cycle
(continued)

Isovolumetric
relaxation:


when semilunar valves
closes AV valves is not yet
open because pressure in
vetricles still exceeeds that
of atria.
Therefore all valves are
once again closed for short
period of time when
ventricles are relaxing
Semilunar
valves closed
AV valves
closed
Tachycardia, Effect on
Cardiac Cycle


During Tachycardia, when heart rate is
increased, both systole and diastole
time decreases.
Diastole length (time) is shortened
much more than systole length.
Therefore it
reduces the time for ventricular
relaxation and filling.
21
Summary of events during
cardiac cycle
23
2. PRESSURE CHANGES DURING
CARDIAC CYCLE
24
Events of cardiac cycle
Rt- Atrium = 0-7mm Hg.
Lt- Atrium = 2-10 mm Hg.
Rt – Ventricle = 25 / 6(2-8) mm Hg.
Lt – ventricle = 120 / 8(2-10) mm Hg.
Aorta = 120 / 80 mm Hg.
Pul. Artery = 25 / 10 mm Hg.
Pressure changes during cardiac cycle
26
3. VOLUME CHANGES DURING
CARDIAC CYCLE
27

Define Stroke Volume (SV)

Define End Diastolic Volume (EDV)

Define End Systolic Volume (ESV)

Define Ejection Fraction (EF)
28



Stroke Volume: It is a volume of blood pumped out
by each ventricle per beat. It is about 70 - 80 ml.
Stroke volume (SV) = EDV – ESV
End Diastolic Volume: Volume of blood in each
ventricle at the end of diastole.
It is about 120 – 130 ml.
End Systolic Volume: Volume of blood in each
ventricle at the end of Systole. It is about 50 to 60 ml
29
Volume changes during cardiac
cycle
30
Events of cardiac cycle showing left ventricular pressure, volume
changes, & phonocardiogram
31

Ejection fraction (EF) is the percentage
of ventricular end diastolic volume (EDV)
which is ejected with each stroke.
EF =
SV (EDV – ESV)
X 100
EDV
75
X 100 = 62.5%
120
Normal ejection fraction is about 60 – 65 %.
Ejection fraction is good index of ventricular function.32
Relation Of Heart Sounds With Phases
Of Cardiac Cycle
0.7 Sec.
0.1 sec.
AD
AS
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;
33
VD – Ventricular diastole
Relation ship of heart sounds
with events of cardiac cycle


1st heart sound = closure of AV valves at start
of ventricular systole
2nd heart sound= closure of semi lunar valves
at end of ventricular systole

3rd heart sound = first rapid filling phase

4th heart sound = last rapid filling phase
Heart Sounds

We will discuss Heart Sounds in next
lecture.
35
References



Text book of physiology by Linda .S
.Costanzo third edition
Text book of physiology by Guyton &
Hall
review of medical physiology by
william F.Ganang