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Cardiac Cycle and PV Loops II: Analysis of Cardiac Function
Terms in this set (27)
What is Cardiac Output (CO), and how is it usually measured (units of measurement)?
Cardiac output (CO) is the volume of blood pumped from the heart through the circulation in a period of time
- Usually as L/min or mL/min
How is cardiac output "corrected?" What is the equation used to evaluate cardiac output?
Corrected for body size as Cardiac Index
- More useful to use cardiac index in clinical setting (tells us what is appropriate for a given patient)
CO = SV X HR
*Note: How much blood is ejected per beat, times the number of beats per minute
What is End Diastolic Volume (EDV)? What is End Systolic Volume (ESV)?
- EDV is the amount of volume present in a chamber of the heart prior to contraction (following filling)
- ESV is the total volume remaining in the heart following a contraction (residual volume)
What is Stroke Volume (SV)?
SV = EDV - ESV
What effect do the following have on SV, without any additional changes:
1. Increased EDV?
2. Decreased EDV?
3. Increased ESV?
4. Decreased ESV?
1. SV increases, which is an increase in preload
2. Decrease in preload, which will cause decreased stroke volume
3. The heart didn't squeeze as hard because it left more blood in the chamber, decreasing stroke volume
- often comes from decreased force of contraction, and decreased contractility
4. Stroke volume increased, because the volume left behind is smaller, so more went through the valve
- Usually related to increased contractility (+ inotropic event)
Which corresponds to...
1. Increased preload?
2. Decreased preload?
3. Increased contractility?
4. Decreased contractility?
5. Effect of norepinephrine (Beta-1 adrenergic effect) on ESV and SV?
6. Ach on ESV and SV?
1. EDV increased
2. EDV decreased
3. ESV decreased
4. ESV increased
5. Decreased ESV, and increased SV
6. Leads to decreased contractility (increased ESV), and SV would decrease
*Note: Ach has more effect on timing that it does on force, but it does have an effect
What is Ejection Fraction (EF)? What is the equation we would use to calculate the value?
- Ejection fraction is the ratio of stroke volume to EDV
- EF = SV/EDV or (EDV - ESV)/EDV
What does the EF tell us? What are typical normal and abnormal values?
EF = a measure of pumping and a measure of preload. This tells us (if the ejection fraction has gone up) that we have increased contractility (+ inotropic effect)
- Normal value ~ 0.67
- If you have <0.50, you have cardiac failure (really abnormal)
What would be the effect of increased sympathetic activity? Parasympathetic activity?
Parasympathetic activity: is going to help reduce heart rate.
Sympathetic activity: will help to increase heart rate
What is contractility?
The forcefulness of contraction by the heart at a given preload
Note: the increase in work that occurs if you increase preload is not an effect of contractility
If preload and afterload are the same, but SV increased, what has happened to contractility?
If preload and afterload are the same, but SV decreased, what has happened to contractility?
Negative inotropic effect (Decreased Contractility)
If preload decreased, but SV is normal, what has happened to contractility?
If preload increased, but SV is low or normal, what happened to contractility?
Decreased contractility (negative inotropic effect)
What is the primary direct effect that we expect to see with increased contractility?
Decreased End Systolic Volume (ESV)
*Note: even though we had a slightly smaller EDV, the large decrease in ESV compensated
What is the primary direct effect that we expect to see with decreased contractility?
Increased ESV, and a somewhat smaller increase in EDV.
*Note: the reason you get decreased contractility is because the increase in ESV is far more significant than the increase in EDV
In evaluating Ejection Fracture, do we have any measure of afterload?
- No. We don't know what the heart is working against. There could be a great struggle going on, but we don't know this.
- Increased afterload doesn't only slow you down, but it means that you can't move as far
What is an agent or condition that increases contractility, and what is an example of one?
- A positive inotropic agent
What is a condition or substance that causes decreased contractility and what is an example of one?
- A negative inotropic effect
What happened to EF in this patient (See image on other side)?
Going from the black loop to the red loop, you have a decreased SV, and no change in EDV. We know that EF=SV/EDV. Thus, we have negative inotropic, or decreased contractility.
What happened to EF in patient #2 (See image on other side)?
Stroke volume has increased. EDV is the same. EF has increased, or in other words, positive inotropic effect. Increased contractility.
What happened to EF in patient #3 (See image on other side)?
SV is decreased. Preload has also decreased. There is little change in EF, because the changes balance each other out. Although we had decreased stroke volume, you had decreased preload which compensated (due to a human problem)
What happened to EF in patient #4 (See image on other side)?
Increased preload, you find that the EF hasn't changed much again. SV is increased because of increased EDV, mainly an effect of preload. Volume expanded.
What is stroke work?
- Stroke work is a measure of cardiac work. With increased stroke work the heart is working harder per beat, by increasing preload or afterload (taller on the graph), or increased contractility.
- With decreased preload, you tend to get decreased area and stroke work
How do you measure the rate of change of pressure with respect to time?
- It's like a velocity (how quickly the heart is developing pressure)
- An increase or decrease in dP/dt is interpreted as an increase or decrease in contractility
- Increased dP/dt, is a positive inotropic effect
What is the typical normal value in humans for Ejection Fraction?
0.67 +- 0.08 (+-SD)
*Note (IMPORTANT PRICIPLE): Any single measure of cardiac performance can be deceptive if you fail to evaluate the conditions under which it was obtained
What is the end systolic pressure-volume relation, what does it correlate to, and how do you read it?
- Line between intercept and ESP/ESV point
- Slope correlates with contractility and is related to max elastance
An increased slope, produces an increased stroke volume and increased pressure, despite having smaller preload, meaning that contractility went up
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