Cardiac output - mechanical events and stroke volume Flashcards
What is the average heart rate?
6-72bpm.
What effect does a bigger heart have on stroke volume and heart beat?
Bigger stroke volume so slower heart beat.
Why do both ventricles have to have the same volume?
Otherwise blood would collect at a point in the body.
What are the two phases that the cardiac cycle can be divided into?
Systole and diastole. Systole is ventricular contraction and blood ejection whereas diastole is ventricular relaxation and blood filling.
What is the average blood pressure?
120mm/80mm.
What is the cardiac cycle mostly driven by?
Changes in pressure within the ventricles. There is a minor part played by atrial contraction.
What is isovolumetric contraction?
When the ventricles contract but there is no change in volume - the pressure is increasing but is not high enough yet.
What happens when the pressure in the ventricles continues to increase?
The aortic and pulmonary valves will open when the pressure is above 80mm on both sides.
What happens when the blood has left the heart and the pressure in the arteries starts to increase?
The valves will shut.
What draws blood into the heart?
There is a vacuum that is created as the heart relaxes which draws blood into the ventricles.
What happens when the vacuum has been created and the blood is drawn in?
The atria will contract to push the extra 10% of blood into ventricles.
What is the end diastolic volume?
The volume left in the heart when the heart as contracted - usually 65ml.
What is the maximal volume of blood the heart can hold?
130-140ml of blood.
What are the 4 stages of diastole and systole?
Ventricular filling, isovolumetric ventricular contraction, ventricular ejection, isovolumetric ventricular relaxation.
What is the first sound created when you listen with a stethoscope? (lub)
The closure of the atrioventricular valves.
What is the second sound created by the heart when you listen with a stethoscope? (dub)
The closure of the pulmonary and aortic valves.
What causes heart murmurs?
The change from laminar to turbulent flow.
What is the condition called with narrowed vessels?
Stenosis.
What is it called when blood flows backwards through leaky valves?
Insufficiency.
What is a septal defect?
A hole in the heart.
What is pre-load (end diastolic ventricular volume) determined by?
Central venous pressure.
What can affect the central venous pressure?
Breathing (respiratory pump) - the pressure difference between the abdomen and chest, changes in blood volume - reduced blood volume leads to reduced CVP, skeletal muscle pump - blood can be squeezed back towards the heart, and contraction of central and peripheral veins can increase CVP, gravity.
What is the Frank-Starling mechanism?
The idea that the ventricles contract with more force if it contains more blood. It is determined by the length-tension relationship in the muscle - the greater the strength the more tensioned developed in the cardiac muscle.
What is the purpose of the Frank-Starling mechanism?
It maintains the balance between right and left sides of the heart to stop accumulation of blood in the lungs.
What factors affect/regulate stroke volume?
The filling pressure (preload), the contractility and arterial pressure.
What is the equation for cardiac output?
Heart rate x stroke volume
What is congestive heart failure?
Reduced cardiac output.
What are some of the symptoms of congestive heart failure?
Tiredness and shortness of breath, fluid retention.
What is the most common type of congestive heart failure?
Chronic left ventricular failure - coronary artery disease leading to ischaemic heart disease and myocardial infarction (systolic dysfunction), hypertension (diastolic dysfunction) and cardiomyopathy (viral infection, heavy drinking).
What is systolic dysfunction?
Problems with ventricular ejection.
What is diastolic dysfunction?
Ventricular filling.
