Flashcards in CVS 6.1 - Control of Cardiac Output Deck (17):
What happens if there is a decrease in total peripheral resistance, at a given cardiac output?
- Arterial pressure DECREASES as less pressure is needed to overcome a lower resistance (increases heart rate)
- Venous pressure INCREASES due to an increase in the rate of entry which increases the volume (increases heart rate)
What happens if there is an increase in total peripheral resistance, at a given cardiac output?
- Arterial pressure INCREASES due to needing to overcome more pressure
- Venous pressure DECREASES due to a decreased rate of entry which decreases volume
What happens if there is an increase in cardiac output, at a given TPR?
- Arterial pressure INCREASES - increased volume = increased pressure to overcome resistance
- Venous pressure DECREASES as the volume in the veins decreases to account for increased cardiac output
What happens if there is an decrease in cardiac output, at a given TPR?
- Arterial pressure DECREASES - decreased volume etc.
- Venous pressure INCREASES - blood retained in veins for longer = increased volume
What is end diastolic volume?
The volume of blood left in the ventricles at the end of diastole
What is end systolic volume?
The volume of blood left in the ventricles at the end of systole
What is stroke volume?
The difference between end diastolic volume and end systolic volume
What determines how much the ventricles fill during diastole?
- Venous pressure
- Ventricle fills until walls stretch and have enough blood to equal venous pressure
- Higher vp = more ventricles fill during diastole
What is pre-load?
The end diastolic stretch of the myocardium, determined by venous pressure
What is after-load?
The force necessary to expel blood in the arteries
What is the effect of an increased venous pressure on stroke volume?
Increases stroke volume
What is the effect of a decrease in arterial pressure on stroke volume?
Increases stroke volume
What is contractility?
- The potential of the muscle fibres of shortening and therefore contracting (more stretch = increased force of contraction)
- Shows the relationship between end diastolic volume and stroke volume
What increases contractility?
So makes heart more susceptible to venous pressure
What controls autonomic outflow to the heart?
- Signals sent by baroreceptors in the aortic arch and carotid sinus
- Sense arterial pressure and send messages to the medulla
What are the effects of changes in venous pressure on cardiac output?
- Increased VP = Increased CO (increases pre-load)
- Decreased VP = Decreased CO (decreases pre-load)