CVS Flashcards
What is the maximal ejection fraction in ventricles?
Maximal ejection is around 70%, so around 30% remains in the ventricles.
What is shown by the T-wave on an ECG?
Ventricular Repolarisation
What happen during the PR interval?
There is the delay at the AV node for electrical conduction to allow the ventricles to fill.
What is isovolumetric contraction?
When ventricles are contracting but the valve doesn’t open so pressure builds in the ventricle but volume stays the same. There is no ejection of blood yet.
What is preload?
(Pressure/Volume) Load present before ventricular contraction has started. Equivalent to the end diastolic (left ventricular) volume. Relates to the stretch in heart muscle sarcomeres before contraction.
What may cause increased preload?
Aortic stenosis, ventricular systolic failure
Define contractility
Inotropic state - The state if the heart which enables it to increase its contraction velocity to achieve higher pressure when contractility is increased. This is independent of load.
This is reflected in the end systolic pressure-volume relationship.
Define elasticity
The myocardial ability to recover its normal shape after removal of systolic stress.
Define Compliance
The relationship between the change in stress the resultant strain. This is reflected in the end diastolic pressure-volume relationship
Define Diastolic Distensibility
Pressure required to fill the ventricle to the same diastolic volume.
What is the Frank-Starling Law?
As stretch increases that contraction will increase. Stroke volume will increase in response to an increased end diastolic volume the other factors remain constant.
What is the equation of Stroke Volume
Stroke volume = End diastolic volume - End systolic volume
Mean arterial pressure equation
MAP =(Cardiac Output * Systemic vascular resistance) + Central venous pressure
MAP = Diastolic pressure + 1/3*pulse pressure
Pulse pressure equation
Pulse pressure=Systolic - Diastolic Pressure
Cardiac Output equation
CO= Stroke volume * Heart Rate