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CARDIODYNAMICS
Cardiac Cycle
Left ventricular pressure-volume changes during one
cardiac cycle
KEY
Left ventricular pressure (mm Hg)
EDV = End-diastolic volume
ESV = End-systolic volume
Stroke volume
120
D
ESV
80
C
One
cardiac
cycle
40
EDV
B
A
0
65
100
Left ventricular volume (mL)
135
Figure 14-25
Cardiac Cycle
KEY
EDV = End-diastolic volume
ESV = End-systolic volume
Left ventricular pressure (mm Hg)
120
80
40
A
0
65
100
Left ventricular volume (mL)
135
Figure 14-25 (1 of 4)
Cardiac Cycle
KEY
EDV = End-diastolic volume
ESV = End-systolic volume
Left ventricular pressure (mm Hg)
120
80
40
EDV
B
A
0
65
100
Left ventricular volume (mL)
135
Figure 14-25 (2 of 4)
Cardiac Cycle
KEY
EDV = End-diastolic volume
ESV = End-systolic volume
Left ventricular pressure (mm Hg)
120
80
C
40
EDV
B
A
0
65
100
Left ventricular volume (mL)
135
Figure 14-25 (3 of 4)
Cardiac Cycle
KEY
EDV = End-diastolic volume
ESV = End-systolic volume
Stroke volume
120
Left ventricular pressure (mm Hg)
D
ESV
80
C
One
cardiac
cycle
40
EDV
B
A
0
100
65
Left ventricular volume (mL)
135
Figure 14-25 (4 of 4)
Stroke Volume and Cardiac Output
• Stroke volume
– Amount of blood pumped by one ventricle during a
contraction
– EDV – ESV = stroke volume. (135 mL - 65 mL = 70 mL)
• Cardiac output(Cardiac Output Is a Measure of
Cardiac Performance)
– Volume of blood pumped by one ventricle in a given
period of time
– CO = HR  SV
•
•
CO = 72 beats/min x 70 mL/beat
= 5040 mL/min (or approx. 5/L min)
• Average = 5 L/min
Ejection Fraction – is the fraction of the enddiastolic volume that is ejected with each beat,
that is, it is stroke volume (SV) divided by enddiastolic volume (EDV),
is a commonly used measure of cardiac
performance.
stroke volume / end diastole volume X 100%,
normal range, 55-65%.
CO
Cardiac output
(ml/min)
=
HR
Heart rate
(beats/min)
10
X
SV
Stroke
volume
(ml/beat)
Factors Affecting Cardiac OutputAll factors that control HR and SV will influence CO
physiology
11
Factors Affecting Heart rate
1. Autonomic innervation
• Sympathetic stimulus increases heart rate
Ex. During fight or flight response
• Parasympathetic stimulation decreases
heart rate. Ex. Relaxation techniques
2. Hormones
– Epinephrine : Increases heart rate
Tachycardia= Resting HR> 100 beats/min
Bradycardia=Resting HR<60 beats/min
physiology
12
Stroke Volume
• Force of contraction
– Stroke volume
– Affected by length of muscle fiber and contractility of
heart
• Frank-Starling law
– Stroke volume increase as EDV increases
• EDV determined by venous return
– Skeletal muscle pump
– Respiratory pump
– Sympathetic innervation
Stroke Volume
Length-force relationships in intact heart: a Starling
curve
Figure 14-28
Factors that Affect Cardiac Output
Figure 14-31