Mairead - The Heart - values and forces Flashcards
What is the cardiac cycle
The period between the start of one heartbeat and the start of the next
Alternating cycles of contraction and relaxation
What is systole
The period of contraction (emptying)
What is diastole
The period of relaxation (and filling)
What is cardiodynamics
The movements and forces generated during cardiac contraction
What is EDV?
End diastolic volume
The volume of blood in the ventricles at the end of atrial contraction/systole
What is ESV
End systolic volume
The volume of blood in the ventricle at the end of ventricular systole
What is SV
Stroke volume
What is the equation for stroke volume?
Sv = EDV - ESV
What is ejection fraction?
The % of EDV that becomes the SV
What is cardiac output
The amount of blood flow in the circulation
What is the equation for CO?
Cardiac output = SV X HR
What is the equation for blood flow?
Pressure/resistance
How might SV be changed?
By increasing venous return
By altering the force of contraction of the heart
How can heart rate be changed?
It can be increased/decreased by changing the pacemaker excitability
How might heart rate by altered?
By autonomic innervation
By hormones
How can cardiac output by altered?
Changed in heart rate or stroke volume
What determines EDV?
Venous return
Filling time
What is filling time
The duration of ventricle diastole: this depends on heart rate
What is venous return
The rate of blood flow during ventricular diastole (filling)
What affects venous return
CO
Blood volume
Peripheral circulation (vasoconstriction/vasodilation)
Skeletal muscle activity
Respiratory pump
Hormones
What factors affect end systolic volume?
Preload
Contractility of the ventricles
Afterload
What is preload
(5)
The degree of stretching of the ventricle prior to contraction
This is produced by blood returning from the veins
This affects muscle tension
There is a physiological range of preload
Optimum preload is with a degree of stretch so that greater tension can develop when the ventricles contract
What two factors cause preload to vary?
Posture
Exercise
What is Frank starling Principle/ Starling’s Law of the heart
Within physiological limits the heart pumps out all the blood pumped into it
More in = more out
What is contractility?
The amount of force produced during a contraction at a given preload
What is contractility determined by?
ANS
Hormones
Extracellular ions
How is contractility affected by ANS and hormones?
They have an ionotrophic effect on Ca++
What is a positive ionotrophic effect?
(2)
Where there is an increase in Ca++ entry during contraction
This increases the force and duration of contraction
What is negative ionotrophic effect?
Where the Ca++ entry is blocked
What is afterload
The amount of tension the contracting ventricles must generate to open the semilunar valves
What affects afterload and how?
High aortic pressure will increase the time of isovolumetric contraction and decrease the time of emptying
What are two causes of high pressure?
Blood vessel constriction
Circulatory blockage
