Lecture 6 - Cardiac Output Flashcards
define End-systolic volume
The volume of blood in a ventricle at the end of contraction
Define End-diastolic volume
The amount of blood in the ventricles just before systole
Define pre-load
The amount of blood that enters the ventricles before the ventricles contract
Define After-load
The amount of resistance that the heart must overcome to open aortic valve and push blood volume out into systemic circulation
Define stroke volume
The amount of blood pumped by the left ventricle of the heart in one contraction
What are factors that affect preload
Decrease in heart rate Increase in aortic pressure Increase in central venous pressure Increase ventricular compliance Increase atrial contractility
Decrease in heart rate
Slower heart rate means there is more time for blood to flow in and ventricles to fill
Increase ventricular filling time
Increase in aortic pressure
Reduce stroke volume by increasing end systolic volume
Increase in central venous pressure
Result from decreased venous compliance or thoracic blood volume
Increase total blood volume/ venous return
Increase ventricular compliance
Greater expansion of chamber
Inverse of stiffness
Ventricles will have certain stiffness
Increase atrial contractility
Sympathetic stimulation of atria
Increase in blood as atrium squeeze harder
What does the Frank-Starling mechanism represent
Relationship between stroke volume and end diastole volume
Frank-Starling Mechanism
The ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return
What does Frank-Starling mechanism show?
Changes in pre-load lead to changes in stroke volume
What does law state (Frank-Starling mechanism)?
Stroke volume of the heart increases in response to increase in volume of blood in ventricles, before contraction
What happens when a larger volume of blood flows into ventricles?
The blood stretches the cardiac muscle fibres
Increase in force of contraction
Increase preload = increase stroke volume
What is the Frank-Starling law of heart?
The greater be diastolic filling - the larger the EDV
The more the heart is stretched
The longer the cardiac fibres before contraction
Increased length > greater force in cardiac contraction > greater stroke volume
The heart normally pumps out during systole, the volume of blood returned during diastole
Increased venous return = increased SV
Preload = the extent of filling
What is inotropy?
The force of muscle contraction
Increase inotropy, increase velocity of the muscle fibres shortening preload/afterload
When a muscle fibre contracts, it shortens
What happens if inotropy is increased?
There will be little volume left in the vent files and the ESV will shift to the left
What happens when inotropy is decreased?
There will be more volumes in the left ventricles
ESV shift to right
Inotropy: what happens when the heart has increased contractility ?
The end systolic volume is lower because heart squeezes faster, there is almost no blood left in the ventricle
What does afterload do?
Increase arterial (aortic) pressure
