CHAPTER II: CARDIAC MECHANICS
Asst. Prof. Dr. Emre Hamurtekin
EMU Faculty of Pharmacy
1.
2.
3.
4.
CARDIAC CYCLE
CARDIAC OUTPUT
DETERMINANTS of CARDIAC OUTPUT
CARDIAC WORK
encyclopedia.lubopitko-bg.com
medical-dictionary.thefreedictionary.com
• Cardiac cycle can be divided into seven phases:
1. Atrial systole
2. Isovolumic ventricular contraction
3. Rapid ventricular ejection
4. Reduced ventricular ejection
5. Isovolumic ventricular relaxation
6. Rapid ventricular filling
7. Reduced ventricular filling
• Atrial systole is initiated by …………………...
atrial excitation
• Atrial systole follows the crest of P wave on the ECG.
• Atrial contraction forces a small additional blood into the
venticular chamber (atrial kick).
• Ventricular systole begins with isovolumic ventricular contraction.
• In isovolumic ventricular contraction, when intraventricular
pressure rises, mitral valve closes.
• In isovolumic ventricular contraction, aortic valve is still held
closed by higher aortic pressure.
www.studyblue.com
hypocaffeinic.pbworks.com
• In Rapid Ventricular Ejection phase, aortic valve finally opens
and blood exits the ventricle.
• In this phase, atrium relaxes and the blood starts to fill the
atrium.
• In Reduced Ventricular Ejection phase, ejection velocity
decreases (reduced ejection).
• At the end of this phase, aortic valve is finally closed.
• Once the aortic valve is closed, Isovolumic Ventricular
Relaxation period starts.
• In this period, LV volume is lowest.
www.studyblue.com
hypocaffeinic.pbworks.com
• Once intraventricular pressure drops below atrial pressure,
mitral valve opens.
• Blood in the atrium starts to move into the ventricle in Rapid
Ventricular Filling phase.
• In Reduced Ventricular Filling (diastasis) phase, atrium and
ventricle are both fully relaxed.
• Arterial pressure continues to fall as blood flows into capillary
beds.
• This phase typically disappears when HR increases.
www.studyblue.com
hypocaffeinic.pbworks.com
•
•
•
•
•
•
•
•
LV does not empty completely during systole.
ESV is around 50 ml.
EDV - ESV = SV (stroke volume).
SV is the amount of blood transferred from LV to the arterial
system during systole.
In healty person SV should be > 60 ml.
EF (ejection fraction) = SV \ EDV (normally about 55% - 75%.
EF is an important measurement of cardiac efficiency.
EF is used clinically to assess cardiac status in patients with heart
failure.
• CO (L/min) = HR x SV
• HR is established on the SA node and is controlled by ANS.
• SV is dependent on,
• LV preload
• LV afterload
• Contractility
•
•
•
•
•
•
Preload: Muscle length before contraction begins.
Preload is related with the volume of blood entering the chamber (EDV)
Afterload: The load against which a myocyte must shorten.
The principal component of afterload is arterial pressure.
Contractility: measure of a muscle’s ability to shorten against a afterload.
Contractility equates with the cytoplasmic free Ca concentration.
Ability of a muscle cell to develop force (contractility)
(+) inotropic agents
(-) inotropic agents
- Epinephrine
- Norepineprine
- Digoxin
- β- blockers
- Ca channel blockers
Contractility equates with intracellular free Ca concentration
SNS
norepinephrine
PKA activation
β-1 receptors
cAMP
PKA activation
L - type Ca channels, Ca release channels, SERCA
• Heart performs two kinds of work:
I.
II.
Internal work
External work
• Internal work:
• Expended in «isovolumic contraction»
• The force necessary to open the aortic and pulmonary valves
• Accounts for ˃ 90% of total cardiac workload.
• External work (pressure-volume work):
• Expended in transferring blood to the arterial system against a resistance.
• Accounts for ˂ 10% of total cardiac workload.