Lecture 2 Flashcards
Exam 1
If Reynold’s number is greater than 2000…
You have turbulent flow.
Which three variables have a direct correlation with turbulent flow?
- velocity
- diameter
- density
The blood vessels most prone to turbulent flow are the______ and the _____.
large arteries and the aorta
What variable has an inverse relationship with turbulent flow?
viscosity
What is phase I of the pressure volume loop
passive filling
How much blood is leftover in the left ventricle (end systolic volume/ ESV)
50mL
How much blood can the atrial kick contribute in an unhealthy heart?
about 25% more blood to the left ventricle. Atrial kick doesn’t have much effect on a healthy heart.
What is the volume of blood in the left ventricle in a healthy heart at the end of phase I, or at the end of diastole?
120 mL (end diastolic volume)
What marks the start of phase II in the pressure volume loop?
left ventricle pressure > left atrial pressure this closes the mitral valve
What is happening in phase II?
isovolumetric contraction. No change in volume, but pressure increases in the left ventricle.
What marks the end of phase II/ beginning of phase III?
the pressure in the left ventricle > the pressure in the aorta which opens the aortic valve
How do you calculate stroke volume?
EDV - ESV = SV
What is phase III? How much blood is ejected each beat?
the period of ejection. In a healthy heart about 70mL of blood is ejected per beat.
What closes the aortic valve? What part of the pressure loop curve does this mark the beginning of?
the pressure in the left ventricle is lower than the pressure in the aorta. Phase IV.
How do you calculate CO?
SV x HR or 70mL x 72 bpm which is roughly 5L/min
What happens in phase IV?
The walls of the ventricle are relaxing and the pressure decreases, this phase ends when the mitral valve opens.
Which occurs first… the QRS (electrical event) or the pressure change in the ventricle (force generation)?
The electrical event occurs first. There is a slight delay after the QRS to allow Ca2+ in to initiate ventricular contraction which generates force.
When does systole start?
At the end of phase I and it continues until the end of phase III
When does diastole start?
When the aortic valve closes. At the end of phase III and continues until the start of phase II.
When are ventricular pressures lowest?
during filling
when are ventricular pressures highest?
just before ejection
Right atrial pressure is usually___ in a healthy heart. If RAP is higher than normal, what happens to venous return?
0mmHg. Venous return would decrease
What causes venous return to plateau around 6L/min?
We can augment venous return a little by decreasing RAP, but if pressure becomes too negative, the vena cava can collapse.
What is the average filling pressure of the heart (aka the systemic filling pressure)?
7 mmHg
What is the most effective way to increase systemic filling pressure?
increased resistance in the large veins. This is often impaired by anesthetics (need synthetic cathecholamines)
What is resistance to venous return (RVR)?
How easy is it to get blood back to the heart.
Increased RVR does what to CO? Decreased RVR does what to CO?
increased RVR decreases CO
decreased RVR increases CO
What are the two things that effect systemic filling pressure?
- volume retention
- venous tone
With a normal amount of sympathetic and parasympathetic stimulation, what is the maximum CO?
13 L/min
With maximum sympathetic stimulation what does that do to CO?
It increases CO, up to 23 L/min and even up to 40L/min in athletes
What are the three things the heart does in response to increased filling pressures?
- Frank Starling mechanism
- Direct atrial stretch
- Bainbridge reflex
How does the Frank Starling mechanism work?
cross-bridges are optimally aligned (at rest slightly under-stretched) which leads to better contractility.
How does direct atrial stretch work?
Increases HR 10-15% above BL. This is built into the cardiac conduction system in response to increased filling pressure.
How does the Bainbridge reflex work?
Increases HR 40-50% above BL. Output from the brainstem in response to increased atrial stretch increases sympathetic outflow and decreases parasympathetic output transmitted by the Vagas nerve. Both of these increase HR.
What are some examples discussed in class that would increase RVR?
Positive pressure ventilation, opening the chest during aurgery
Give an example of something that would decrease RVR…
AV fistula (more pathways for the blood to go therefore there’s less resistance to flow)
