Cardiac
Cardiac Cycle
Cycle (Mechanical)
(Mechanical)
Alternate periods of systole (contraction) &
diastole (relaxation and filling)
¾
Phases of cardiac cycle:
Early ventricular diastole
1.
•
Atrium also still in diastole
9 T to P interval on EKG
•
Atrial pressure slightly higher than ventricle
9 Continuous flow from venous system
Late ventricular diastole
2.
•
•
•
SA node reaches threshold & fires (P wave)
Atrial contraction
Corresponding increased ventricular pressure
End of ventricular diastole
3.
•
•
Onset of ventricular contraction
Blood in chambers referred to as end-diastolic
volume (EDV)
Ventricular excitation & onset of systole
4.
•
•
Impulse reaches AV node
QRS complex
Isovolumetric ventricular contraction
5.
•
Ventricular pressure continues to increase
9 Briefly all valves are closed (isovolumetric ventricular
contraction)
•
Eventually exceeds atrial pressure
Ventricular ejection
6.
•
•
Ventricular pressure exceeds aortic pressure
Ventricular systole
9 Includes both periods of isovolumetric contraction and
ejection
End of ventricular systole
7.
•
•
Does not empty completely (end systolic volume)
Amount of blood pumped called Stroke Volume
1
Ventricular repolarization
8.
•
T wave
Isovolumetric ventricular relaxation
9.
•
Aortic valves close but AV valves still not open
Ventricular filling
10.
•
Passive filling
Cardiac
Cardiac Output
Output
Regulation
Regulation
Stroke Volume x Heart rate
~ 5 L/min @ rest
2
Regulation
Regulation of
of Heart
Heart Rate
Rate
Autonomic Nervous System
¾ Increase in HR
• Sympathetic nervous system
9 Via cardiac accelerator nerves
• Increases HR by stimulating SA
node
9 Norepinephrine release (accelerates
depolarization of SA node)
¾
Decrease in HR
• Parasympathetic nervous system
9 Via vagus nerves
• Slows HR by inhibiting SA node
9 Acetylcholine release (slow sinus
discharge)
Figure 9.24
Figure 9.24
(1)
(1)
Page 327
Page 327
Threshold
potential
Threshold
potential
= Inherent SA node pacemaker activity
= SA node pacemaker activity on parasympathetic stimulation
= SA node pacemaker activity on sympathetic stimulation
Regulation
Regulation of
of Stroke
Stroke Volume
Volume
Factors affecting:
1. End Diastolic Volume
9 Frank-Starling mechanism
9 Greater preload results in stretch of ventricles
and in a more forceful contraction
1. Venoconstriction
2. Skeletal muscle pump
3. Respiratory pump
3
Regulation
Regulation of
of Stroke
Stroke Volume
Volume
Factors affecting (cont.):
2. Average aortic blood pressure
9 Pressure the heart must pump against to eject
blood (“afterload”)
3. Strength of the ventricular contraction
9 “Contractility”
9 Increased contractility results in higher stroke
volume
9 Circulating epinephrine and norepinephrine
9 Direct sympathetic stimulation of heart
Regulation
Regulation of
of Stroke
Stroke Volume
Volume
Factors affecting (Starling):
• The Skeletal Muscle Pump
9Rhythmic skeletal muscle
contractions force blood in
the extremities toward the
heart
9One-way valves in veins
prevent backflow of blood
Contractility
Contractility and
and Starling’s
Starling’s law
law
Increasing
contractility
Note that
the curves
represent
Starling’s
Law
4
Terms…
Terms…
¾
Cardiac cycle - the cycle of blood flow and related electrical and
mechanical events as blood is received and ejected by the heart
¾
Preload - the stretch on the ventricular myocardium at enddiastolic volume
¾
Afterload - the pressure that must be overcome by the ventricles
prior to ejection
¾
Frank-Starling Law - concerns the increase in the velocity/power
of myocardial contraction with increasing stretch/EDV (balloons)
¾
Contractility - concerns the increase in the velocity/power of
myocardial contraction at a given EDV
¾
Stroke volume - the volume of blood ejected from the
ventricles/beat
Terms…
Terms…
¾
Ejection fraction - the fraction of EDV that is the stroke volume
¾
Cardiac output (Q) - the volume of blood pumped by the heart
each minute
• Q (L/min) = SV (L) x HR (b/min)
• for example,
9 5 L/min = 0.010 L x 50 b/min (rest conditions)
Values…
Values…
¾
Cardiac output
• Rest: ~ 5 L/min
• Exercise: ~22 - 40 L/min
¾
Stroke volume
• Rest: 71 - 100 ml
• Exercise: 113 – 179 ml
¾
Ejection fraction: 0.6 or 60% (normal at rest)
5
Blood
Blood (Ch.10)
(Ch.10)
Hemodynamics
Hemodynamics
¾
Flow of blood through the circulatory system
¾
Based on interrelationships between:
• Pressure
• Resistance
• Flow
Hemodynamics:
Hemodynamics: Pressure
Pressure &
& Resistance
Resistance
¾
Pressure
• Blood flows from high → low pressure
¾
Resistance
• Length of the vessel
• Viscosity of the blood
• Radius of the vessel
9A small change in vessel diameter can have a dramatic
impact on resistance!
Resistance =
Length x viscosity
Radius4
6
Blood
Blood
Plasma
1.
•
•
Liquid portion of blood
Contains ions, proteins, hormones
Cells
2.
•
Red blood cells (Erythrocytes)
9 Contain hemoglobin to carry oxygen
•
•
White blood cells (Leukocytes)
Platelets
9 Important in blood clotting
Blood
Blood (terms)
(terms)
¾
Hematocrit
• Percent of blood composed of cells
¾
Polycythemia
• Excess production of red blood cells causing an
abnormal increase in red blood cells
¾
Anemia
• Abnormally low red blood cell count
Blood
Blood
Is a high or low
HEMATOCRIT a problem?
7
Blood
Blood
¾
Volume: ~5 liters
¾
Affected by:
9Body size
9Endurance training status
9Extreme environments
9 Hypobaria
9 Hyperbaria
9 Heat
5 L = plasma volume (PV) + cell volume (hematocrit)
= (0.55 x 5) + (0.45 x 5)
= 2.75 + 2.25
Blood
Blood Pressure
Pressure
¾
Function of:
• Cardiac output (Q)
• Total peripheral resistance
(TPR)
Blood Pressure = Q x TPR
Arterial
Arterial Blood
Blood Pressure
Pressure
¾
Expressed as systolic/diastolic
• Normal is 120/80 mmHg
• High is ≥140/90 mmHg
¾
Systolic pressure (top number)
• Pressure generated during ventricular contraction
(systole)
¾
Diastolic pressure
• Pressure in the arteries during cardiac relaxation
(diastole)
8
Blood
Blood Pressure
Pressure
¾
Pulse pressure
• Difference between systolic and diastolic pressures
Pulse Pressure = Systolic - Diastolic
¾
Mean arterial pressure (MAP)
• Average pressure in the arteries
MAP = Diastolic + 1/3(Systolic - Diastolic)
Factors
Factors That
That
Influence
Influence
Arterial
Arterial
Blood
Blood
Pressure
Pressure
CV
CV Adaptation/
Adaptation/ Response
Response to
to
Training
Training
9
Exercise
Exercise Anticipation
Anticipation
¾
Pre-exercise anticipatory response
• Activation of motor cortex
9Increased sympathetic outflow
9Inhibition of parasympathetic activity
9Results:
9 ↑ HR
9 ↑ contractility
9 Vasodilation
Acute
Acute Adaptations
Adaptations to
to Exercise
Exercise
↑ heart rate
↑ ejection fraction
‹ ↑ stroke volume
‹ ↑ cardiac output
‹ Redistribution of Q in favor of contracting skeletal
muscle
‹ ↓ vascular resistance
‹ ↑ muscle blood flow
‹
‹
Transition
Transition From
From Rest
Rest →
→ Exercise
Exercise and
and Exercise
Exercise →
→
Recovery
Recovery
¾ Rapid increase in HR, SV, cardiac output
¾ Plateau in submaximal exercise
¾ Recovery depends on:
• Duration and intensity of exercise
• Training state of subject
10
Transition From
Transition From
Rest → Exercise
Rest → Exercise
→ Recovery
→ Recovery
Changes
Changes in
in
HemoHemoconcentration
concentration
Intense
Moderate
Low
Note that the
greatest single
change occurs
from rest to
exercise
Rest
Standing
Supine
Changes
Changes in
in Cardiac
Cardiac Output
Output
¾
Cardiac output increases due to:
• Increased HR
9Linear increase to max
• Increased SV
9Plateau at ~40% VO2max (untrained)
¾
Oxygen uptake by the muscle also increases
• Higher arteriovenous O2 difference
11
¾
Changes in
Cardiovascular
Variables
During
Exercise
Why is there a break
point in the aa-vO2
difference ??
Fiber type (greater
FOG & FG);
increased
glycolysis…??
Circulatory
Circulatory Responses
Responses to
to Exercise
Exercise
¾
Heart rate and blood pressure
• Depend on:
9Type, intensity, and duration of exercise
9Environmental condition
9Emotional influence
12
Changes
Changes in
in Blood
Blood Flow
Flow
¾
¾
Increased blood flow to working skeletal muscle
Reduced blood flow to less active organs
• Liver, kidneys, GI tract…
Hyperemia - ↑ blood flow
Vasodilation - ↑ diameter of a blood vessel
Vasoconstriction - ↓ diameter of a blood vessel
Increased
Increased Blood
Blood Flow
Flow to
to Skeletal
Skeletal Muscle
Muscle
During
Exercise
During Exercise
Withdrawal of sympathetic
vasoconstriction
¾ Autoregulation
¾
• Blood flow increased to meet metabolic
demands of tissue
• O2 tension, CO2 tension, pH, potassium,
adenosine, nitric oxide
13
Chronic
Chronic Adaptations
Adaptations
¾
Cardiovascular adaptations
• Important for:
9Improving exercise performance
9Preventing cardiovascular disease
~
~
~
~
~
~
~
↑ plasma volume
↑ red cell mass
↑ total blood volume
↓ systolic and diastolic blood pressures
↑ end diastolic dimensions and ventricular volumes
↑ maximal stroke volume
↑ maximal cardiac output
Cardiac
Cardiac Adaptations
Adaptations
¾
Specific to training
¾
Cardiovascular
Cardiovascular Function
Function &
& Adaptations
Adaptations
to
Exercise
to Exercise
Components
• Heart
• Blood
• Vasculature
Regulation during exercise
¾ Adaptations to exercise
¾
• Acute
• Chronic
14