Download AHS CVS Lecture 3

THE CARDIOVASCULAR SYSTEM
LECTURE 3:
THE CARDIAC CYCLE
Eamonn O’Connor
Allied Health Sciences
Lecture Outline
1
The Pump Cycle
  Atrial and Ventricular Pressure
  Aortic Pressure
  Ventricular Volume
  Heart Sounds
 
AHS Physiology - Cardiovascular System 11-12
1
The Cardiac Cycle
2
 
All the events associated with the flow of blood
through the heart during a single complete
heartbeat
  Avg
HR = 72 beats.min-1
  Therefore
 
cardiac cycle lasts 0.8 s
2 Main periods of cardiac cycle (72 beats.min-1)
  Systole
(0.3 s)
  Ventricular
  Diastole
contraction
(0.5 s)
  Ventricle
relaxation
AHS Physiology - Cardiovascular System 11-12
Opening of Valves During Cardiac Cycle
3
 
Valves open passively due to pressure gradients
  AV
  P
valves open when
atria > P ventricles
  Semilunar
  P
valves open when
ventricles > P arteries
AHS Physiology - Cardiovascular System 11-12
2
Four Phases of Cardiac Cycle
4
 
Phase 1: Ventricular filling (Venous return and atrial
contraction)
  Blood
returns to the heart via systemic and pulmonary veins
  AV valves open (Pressure atria > Pressure ventricles)
  Passive phase - no atria or ventricular contraction
  Sharp volume increase; levels off as pressure gradient
decreases
  Active phase - atria contract
  Pressure in ventricle increases because extra blood is forced
in
  Volume in ventricle increases
AHS Physiology - Cardiovascular System 11-12
Four Phases of Cardiac Cycle
5
 
Phase 2: Isovolumetric ventricular contraction
  Ventricle
contracts - increases pressure
  AV valve shut (pressure in ventricle > pressure in atria)
  Semilunar valve still closed
  No blood entering or exiting ventricle (isovolumetric)
AHS Physiology - Cardiovascular System 11-12
3
Four Phases of Cardiac Cycle
6
 
Phase 3: Ventricular ejection
  Ventricles
continue to contract
  Semilunar valves open (Pressure ventricles > Pressure
aorta)
  Pressure continues to increase in ventricles
  Peaks
then declines
  Aortic
pressure increases, peaks, then declines
  Blood volume decreases as ejection occurs
AHS Physiology - Cardiovascular System 11-12
Four Phases of Cardiac Cycle
7
 
Phase 4: Isovolumetric Ventricular Relaxation
  Ventricle
relaxes - decreases pressure
  Ventricular pressure drops as ventricle relaxes
  Aortic pressure decreases as pressure dissipates
through arterial system
  Semilunar valve closes
  Semilunar and AV valves are closed – no blood
movement – no volume change
AHS Physiology - Cardiovascular System 11-12
4
Cardiac Cycle
8
Figure 13.18
AHS Physiology - Cardiovascular System 11-12
Ventricular Systole (35% cardiac cycle)
9
 
Isovolumetric Ventricular Contraction
  AV
& aortic valves closed
  Ventricular pressure increases until it exceeds
atrial pressure
 
Ventricular Ejection
  Aortic
valve opens
  Blood moves from ventricle to aorta
AHS Physiology - Cardiovascular System 11-12
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Ventricular Diastole (65% cardiac cycle)
10
 
Isovolumetric Ventricular Relaxation
  Ventricle
muscle relaxes so that pressure is less
than aorta
  Aortic valve closes
  Pressure in ventricle continues dropping until it is less
than atrial pressure
 
Ventricular Filling
  AV
valve opens
  Blood moves from atria to ventricle
  Passive until atrium contracts
AHS Physiology - Cardiovascular System 11-12
Cardiac Cycle
11
AHS Physiology - Cardiovascular System 11-12
Figure 13.18
6
12
Ventricular & Atrial Pressure During the
Cardiac Cycle
Figure 13.19
AHS Physiology - Cardiovascular System 11-12
Aortic Pressure During the Cardiac Cycle
13
 
 
 
 
 
Rises and falls with each heartbeat: blood flow is
pulsatile
Normal value for systolic pressure is approx. 120mmHg
Normal value for diastolic pressure is approx. 80mmHg
Pulse pressure = Systolic – diastolic = approx. 40mmHg
Average aortic pressure throughout the cardiac cycle is
called mean arterial pressure – very important (later
lecture)
Figure 13.20
AHS Physiology - Cardiovascular System 11-12
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Continuous Blood Flow During Cardiac Cycle
14
 
Aorta (and large arteries) – elastic
  Pressure
 
reservoir
Store energy during systole as walls expand
  Release
energy during diastole as walls
recoil inward
  Maintains blood flow through entire
cardiac cycle
AHS Physiology - Cardiovascular System 11-12
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IV.Ventricular Volume and Stroke
Volume
 
 
 
 
EDV = end diastolic volume = volume of blood in ventricle at end of
diastole
ESV = end systolic volume = volume of blood in ventricle at end of
systole
SV = stroke volume = volume of blood ejected from heart each
cycle = SV = EDV - ESV (130 mL – 60 mL = 70 mL)
Ejection fraction: Fraction of end-diastolic volume ejected during a
heartbeat. Ejection fraction = stroke volume / end diastolic volume
= 70 mL / 130 mL = 0.54
AHS Physiology - Cardiovascular System 11-12
Figure 13.21
8
Heart Sounds
16
 
Sounds occur due to valve closure:
Figure 13.22
First sound = soft lubb
AV valves close
 
Second sound = louder dubb
Semilunar valves close
Sounds also referred to as ‘lup’ and ‘dup’
AHS Physiology - Cardiovascular System 11-12
ECG and Mechanical Events
17
ECG = measure of electrical
events
  Electrical events cause
mechanical events
 
  Precede
mechanical events
  P
wave precedes atrial contraction
  QRS complex precedes ventricular
contraction
  T wave precedes ventricular
relaxation
AHS Physiology - Cardiovascular System 11-12
Figure 13.18
9