CV Important things Flashcards
Definition preload
the initial stretching of the cardiac myocytes (muscle cells) prior to contraction. It is the ventricular filling pressure.
Definition afterload
- The resistance the heart must overcome in order to force blood OUT
What is EDVV
The volume of blood in the ventricle after diastolic filling
What is ESVV
The residual volume of blood remaining after ventricle systole
What affects EDVV adn why
- Diastolic filling time - too little time, prevents adequate V filling, hence reduces SV
- Preload - inc, inc EDVV and in turn inc SV
- Compliance -more stretch/elasticity of heart wall to accommodate a larger volume of blood entering which will then be pumped out during systole
What affects ESVV adn why
- Increased contractility - the degree to which the cardiac muscles are able to contract. More contraction means that a higher pressure will be generated and more blood will be forced out of the ventricles into systemic circulation hence reducing ESVV.
- Decreased afterload - afterload = the amount of resistance that the heart must overcome to open its semilunar valves to pump blood to systemic circulation. The higher the afterload the more resitance to flow and the greater a pressure difference the heart must generate to open its semilunar valves.
What is Stroke volume? How is it measured?
The volume of blood pumped out of each ventricle in each cardiac cycle. It is the DIFFERENCE between EDVV and ESVV.
SV = EDVV - ESVV
What is ejection fraction and how is it calculated?
- The fraction of the end diastolic volume that constitutes the stroke volume.
Usually expresses as a percentage
EF = SV/ EDVV
How do we increase preload?
- Pressure in the atria and veins must increase
- achieved by increasing overall blood volume or by reducing the space the blood needs to occupy
- e.g. reducing blood flow to non essential tissues
What would a persistent increase in preload result in and why?
- Preload is the filling pressure of the ventricle. It is approximately equal to the atrial pressure, which is about the same as the venous pressure
- SO persistent increase in venous pressure leads to fluid leaking out of the capillaries in the tissues and forming oedema (e.g. pulmonary oedema forms in left sided heart failure).
What are factors that increase preload during exercise?
- Increased action of the respiratory and skeletal muscle pumps
- They compress veins and thereby increase venous return to the heart
- As skeletal muscle contracts and relaxes it pumps the contents of the veins towards the heart. Backflow of blood is prevented by the vein valves
- The respiratory pump- when the diaphragm compresses the cranial abdominal veins, and the distension of the thoracic veins which occurs during inspiration causes blood to be drawn from the abdominal veins into the central circulation.
How does an inc EDVV affect contractility?
- Increasing the EDVV = more blood for the ventricle to expel
- through stretching of the cardiac muscle cells (and hence increased calcium release from the sarcoplasmic reticulum) leads to increased contractility.
- This is finite however – the SV plateaus even if EDVV continues to increase.
What is the difference between pulmonary and systematic systems?
- Pulmonary circulation moves blood between the heart and the lungs. It transports deoxygenated blood to the lungs to absorb oxygen and release carbon dioxide. The oxygenated blood then flows back to the heart.
- Systemic circulation moves blood between the heart and the rest of the body
Definition of compliance and how to measure
- measure of how readily the ventricular walls stretch during diastolic filling
- Compliance = change in volume ÷ change in pressure
How does a high preload affect compliance?
What disease does this occur in
- small change in preload leads to large change in EDVV
- Connective tissue in ventricle reaches its elastic limit
- The ventricles become stiffer and won’t accept more volume.
- SO a high preload, decreases compliance = stiffer ventricles
- Occurs in dilated cardiomyopathy
- Means needs a higher preload to maintain stroke volume
