Cardiac Performance I Flashcards
Stages to the cardiac cycle. What is the state of the valves at each stage?
- Isovolumic relaxation
- AV valves closed
- Semilunar valves closed
- Inflow: (Ventricular filling)
- AV valves open
- Semilunar valves closed
- Inflow: (Ventricular filling with Atrial systole)
- AV valves open
- Semilunar valves closed
- Isovolumic contraction
- AV valves closed
- Semilunar valves closed
- Ejection: Ventricular ejection
- AV valve closed
- Semilunar valves open
Which factors affect preload?
- Amount and rate of venous return
- Exercise
- Increase in blood volume
- Sympathetic activity
Preload is affected by which two cardiac pumps? How?
-
Respiratory Pump
- Intrapleural pressure decreases during inspiration and abdominal pressure increases, squeezing local abdominal veins, allowing thoracic veins to expand and increase blood flow towards the right atrium.
-
Skeletal muscle pump
- In the deep veins of the legs, surrounding muscles squeeze veins and pump blood back towards the heart. This occurs most notably in the legs. Once blood flows past valves it cannot flow backwards and therefore blood is “milked” towards the heart.
S1 heart sounds corrrespond to the closing of which valves?
Tricupsid and mitral
S2 heart sounds corrrespond to the closing of which valves?
Aortic and pulmonary
What does S3 correspond to and when is it heard?
S3 correspons to the passive filling of the ventricle, heard if the ventricle is full or if the circulation is hyperdynamic
What does S4 correspond to?
The atrial systole against a stiff ventricle
The delay of T1 (clsing of tricupsid valve) even more than normally causes the split S1 which is heard in a _____________.
right bundle branch blockage
REMEMBER: The mitral valve typically closes slightly before the tricupsid valve. But a significant difference can cause a split sound that is heard in right bundle branch blockage.
A split S2 has a _________ pitch.
High
*Split S2 is when the aortic valve closes substaintally before the pulmonary valve
S3 sound has a ________ pitch.
Low
Stroke work
The work done by the ventricle to eject a volume of blood (i.e., stroke volume). The force that is applied to the volume of blood is the intraventricular pressure. Therefore, ventricular stroke work can be estimated as the product of stroke volume and mean systolic pressure during ejection.
Frank- Starling Law
The stroke volume of the heart increases in response to an increase in the volume of blood in the ventricles, before contraction, when all other factors remain constant.
What is the diffence between the stroke volume on the right and left sides of the heart?
The only difference from left and right, the left is 8x higer than right in terms of pressure. You eject the same volume, but the left has to eject from higher pressure than the right. Your left is ejecting against a high peripheral restiance.
Indicators of cardiac performance
-
Load-dependent
- Indicators of performance change as you change the end diastolic volume
-
Load- independent
- End systolic volume, so contractility doesn’t deoend in the load at all
Examples of indicatiors of cardiac performance that are load-dependent.
Stroke volume
Cardiac output
Ejection fraction
Maximal rate of pressure
Examples of indicatiors of cardiac performance that are load-independent.
End-systolic elastance (measure of contractility)
Pre-load recruitable stroke work
Normal ejection fraction
55-65%
*Stroke volume/ end diastolic volume x100
Cardiac index
Cardiac output/ BSA
*BSA is body surface area in m2
Determinants of cardiac performance
- Loading conditions: Preload, afterload, Frank-Starling mechanism
- Heart Rate
- Contractile state
What is the relationship between pressure and EDV in patients with diastolic heart failure?
- In normal patients, filling their heart to 120 mL produces pressure of 8 mmHg
- In patients with diastolic heart failure, if the EDV increases filling heart to 120 mL produces a pressure of 30 mmHg, this is because there is stiffen in the heart but you still have the same volume. This causes an increase in the pressure.
As afterload increases, cardiac output __________ (increases/ decreases).
decreases
How does the heart reduce wall stress?
By thickening the wall
Force frequency relationship
Heart rate affects cardiac contractility through the ____________ relationship.
Force- frequency
How is the cardiac cycle affected by an increase in heart rate?
An increase in heart rate leads to a reducton in the duration of the cardiac cycle that mostly affects the duration of diastole. Ventricular filling is then affected by heart rate.
Although cardiac performance depends on loading, ____ does not.
Contractility
Shortening against a constant load is _________ contraction.
Isotonic
Lusitropy
rate of myocardial relaxation
*The increase in cytosolic calcium of cardiomyocytes via increased uptake leads to increased myocardial contractility (positive inotropiceffect), but the myocardial relaxation, or lusitropy, decreases.
Relaxion of the heart is negatively impacted by which factors?
- Calcium overload – too much intracellular calcium
-
Reduced rate of calcium removal from myocyte through pumps if calcium is not removed from the cell quickly enough.
- Plasma membrane Calcium ATPase
- Sodium-Calcium (Na/Ca) exchanger
- Impaired Sarco-Endoplasmic Reticulum Calcium ATPase (SERCA) this primary active transporter pumps calcium from the cytoplasm of the myocyte into its sarco-endoplasmic reticulum.
Relaxion of the heart is positively impacted by which factors?
- Increased catecholamine
dP/dt
Maximal rate of rise of left ventricular pressure (LVP), but it is determined by myocardial contractility and the loading conditions on the ventricle, thus it is an imperfect and sometimes incorrect predictor of the inotropic state (myocardial contractility).
Maximal dP/dt depends on ___ and ________.
Heart rate ; loading
% of it cardiac muscle metabolism uses _____ for 70% of its metabolic energy requirements.
Fatty acids
NOTE: Anaerobic glycolysis takes over under stress and ischemic conditions, because using glucose is mroe efficient
What parameters does diastolic function depend on?
Passive ventricular stiffness
Elastic recoil after end- systole
Relaxation (active process)
Heart rate (which mainly affects the duration of diastole)
Diastolic function depends on which extraventricular factors?
Reight ventricle interaction with left ventricle
Pericardium
Minimal dP/dt
A negative value during isovolumic relaxation. The more negative this value is, the better the relaxation is
Tau
Time constant of the relaxation process where the pressure decay over time is “curve-fitted”
*Echo is the best imaging method
