Flashcards in Control of Cardiac Output Deck (67)
What happens to arterial and venous pressure if total peripheral resistance falls and cardiac output remains constant?
Arterial pressure will fall, Venous pressure will rise
Why will arterial pressure fall if total peripheral resistance falls?
Because the same volume into lower resistance allows pressure to fall
Why will venous pressure rise if total peripheral reistance falls?
Because there is more blood in the venous system than before, as we are not taking any more blood out of the system form the venous side, so in a snapshot of time, the rate that blood is going into the venous system increases
What happens to arterial and venous pressure if cardiac output rises and total peripheral resistance remains constant?
Arterial pressure will rise
Venous pressure will fall
Why does arterial pressure fall if cardiac output falls?
Not as much volume is pumped around
Why does venous pressure rise if cardiac output falls?
Because the blood stays in the venous system for longer, as less is pumped from the heart, and so the pressure rises
How are total peripheral resistance and the body’s need for blood related?
TPR is inversely proportional to need
What can cause a change in total peripheral resistance?
Changes in metabolism
Why does metabolism change total peripheral resistance?
It generates ‘signals’ in the form of changes in arterial and venous pressure. The pressure change is noticed by the body so it can change to respond
What is meant by demand led pumping?
If the body needs more blood, the heart needs to pump more to meet demand
How is demand expressed?
As changes in arterial and venous pressure
To what does the heart respond to by pumping more blood?
Falls in arterial pressure and rises in venous pressure
What is cardiac output the produce of?
How is cardiac output calculated?
CO = SV x HR
What affects stroke volume and heart rate?
Arterial and venous pressures
How is stroke volume calculated?
It is the difference between end diastolic volume and end systolic volume
What is end diastolic volume?
The volume in ventricles after relaxed
What is the end systolic volume?
The volume in ventricles after contraction
Is end systolic volume minimum systolic volume?
Not under normal conditions
Is end diastolic volume maximum diastolic volume?
Not under normal conditions
Why are end systolic and diastolic volumes not at their maximum?
Otherwise the heart would have nowhere to go when responding to demands
What is the ventricle connected to during filling?
It is isolated from the arteries, and connected to the veins
When do the ventricles fill until?
Until the walls stretch enough to produce an intraventricular pressure equal to venous pressure
What does a higher venous pressure result in?
The heart fills more during diastole
What is the relationship between venous pressure and ventricular volume known as?
The ventricular compliance curve
What happens if ventricular muscle is stretched before contracting?
It contracts harder
What is the ventricle contracting harder when stretched known as?
Starlings Law of the Heart
What does Starlings Law of the Heart state?
The more the heart fills, the harder it contracts, up to a limit
What limits the filling of the heart?
The pericardial sac