Download Cardiac Cycle and Heart Sounds

Cardiac Cycle and Heart Sounds
Cardiac Cycle
• Cardiac Cycle: the events of one complete
heart beat, both atria and ventricles contract
and then relax
• Systole: When the heart is contracting
• Diastole: When the heart is relaxing
• Since most of the pumping work is done by
the ventricles, these terms always refer to the
ventricles
Cardiac Cycle
• We will consider the cardiac cycle in terms of
events during 3 period: mid-late diastole,
ventricular systole, early diastole
Mid-late diastole
• At the beginning, the pressure in
the heart is low
• Blood is flowing passively into
and through the atria into the
ventricles from the pulmonary
and systemic circulation
• The semilunar valves are closed
and the AV valves are open
• Then the atria contract and
force the blood remaining in
their chambers into the
ventricles
Ventricular Systole
• Ventricular contraction
begins and the pressure
within the ventricles
increases rapidly, closing the
AV valves
• The semilunar valves are
forced open and blood
rushes through them out of
the ventricles
• The atria are relaxed and
their chambers are again
filling with blood
Early Diastole
• At the end of systole, the
ventricle relax, the semilunar
valves snap shut (preventing
backflow) and for a moment,
the ventricles are completely
closed chambers
• During early diastole, the AV
valves are forced open and
the ventricles again, begin to
refill rapidly with blood,
completing the cycle
Heart sounds
• The heart sounds are often described by the
two syllables “lub” and “ dup”
• The first sound “lub” is caused by the closing
of the AV valves
• The second heart sound “dup” occurs when
the semilunar valves close at the end of
systole
Cardiac Output (CO)
• It is the amount of blood pumped out by each
side of the heart (actually each ventricle) in 1
minute
• It is the product of heart rate (HR) and Stroke
volume (SV): CO = HR X SV
• Stroke volume is the volume of blood pumped
out by a ventricle with each heartbeat:
- In general, stroke volume increase as the force
of ventricular contraction increase
Regulation of Stroke Volume
• A healthy heart pumps out about 60% of the
blood that enters it
• The critical factor controlling stroke volume is
how much the cardiac muscle cells are stretched
just before they contract: the more they are
stretched, the stronger the contraction will be
• The important factor stretching the heart muscle
is venous return, the amount of blood entering
the heart and swell out its ventricles
• Anything that increase the volume or speed of
venous return also increase stroke volume and
force of contraction
Regulation of Heart Rate
• Although heart contraction does not depend
on the nervous system, its rate can be
changed temporarily by the autonomic nerves
- Sympathetic nervous system: speeds up heart
rate
- Parasympathetic nervous system: slows down
heart rate
Regulation of Heart Rate
• The heart rate is also modified by various
chemicals, hormones and ions
- Epinephrine/ thyroxine: increases heart rate
- Deficit Potassium ions: cause the heart to
beat without strength and abnormal heart
rhythms
• The average heart rate in female is 72-80
beats per min
• The average heart rate in male is 64-72 beats
per min