Lecture 3 Flashcards
Exam 1 content
When the body needs to enhance CO for say running a marathon, what does it do?
It changes the systemic filling pressure by constricting arteries to organs it doesn’t need. Veins also constrict.
What obstacles does the blood coming back to the heart face?
thoracic pressure (positive pressure ventilation)
If you have decreased CO d/t increased thoracic pressure, what can you do to overcome the positive pressure ventilation?
- give more volume
- give phenylephrine
Where does phenylephrine primarily work?
on the veins
If you only increase the work of the heart and don’t change anything about the circulatory system (normal filling pressure) how much can you increase your CO?
from about 5L/min to 6L/min
In our class what is the average surface area of a 70 kg patient?
1.7 m^2
what is the average cardiac index (for our class) for a middle aged person?
3 L/min/m^2
When we inspire what happens to CO?
increases CO
With positive pressure ventilation what happens to CO?
intrapleural pressure is chronically high and this reduces CO
If you use a vasodilator that mainly impacts the arterioles like an ACE inhibitor, what happens to the filling pressure? CO?
filling pressure doesn’t change, but CO increases
If you use a vasodilator that preferentially works on the veins like nitroglycerin, what happens to the filling pressure? CO?
filling pressure decreases and CO decreases
What are two ways you can increase filling pressure?
vasoconstriction (decrease venous compliance)
increase volume
What are two ways you can decrease filling pressure?
vasodilation (increase venous compliance- nitroglycerin)
decrease volume (give diuretics)
CVP is tightly correlated but not the same as right atrial pressure why?
CVP is often higher depending on where you are measuring from as the result of distance from the right heart and due to some gravitational force
How does a failing heart try to overcome a lower CO?
it increases filling pressure
What would you expect to see with an AV fistula?
filling pressure would be about the same but CO would be higher because the resistance to venous return is lower as there are more pathways for the blood to travel
What is the biggest obstacle to venous return that we will come across?
thoracic pressure from positive pressure ventilation
-4 mmHg equals how many cm H2O
-5 cm H20
What does an increased SVR do to the venous return curve?
decreases CO, but filling pressure remains the same. So the slope is less steep
What does a decreased SVR do to the venous return curve?
it increased CO, but filling pressure remains the same causing a more steep slope
What does SVR mainly impact in regards to the circulatory system?
arterioles
Give an example of a vasodilator that primarily effects the arterioles?
ACE inhibitors
Give an example of a vasodilator that primarily effects the veins?
Nitroglycerin
What is the primary effect of nitroglycerin?
Reduces preload (not dilating coronaries)
