Download Heart Anatomy and Function: Electrical Depolarization, Cardiac Output, and Wiggers Diagram and more Study Guides, Projects, Research Reasoning in PDF only on Docsity!
Chapter 18 (The Cardiovascular System: The Heart) is the second of 3 consecutive chapters about the cardiovascular system. (Chapter 17 covered blood; Chapter 19 covers blood vessels.) Your recollection of heart anatomy (chambers, valves, and blood vessels leading in and out) will come in handy here! We will focus especially on the following fascinating topics:
- Electrical depolarization and ECG
- Control of cardiac output
- The Wiggers diagram (slide 17)
- electrical activity
- mechanical activity
- blood volume
- blood pressure
- heart sounds Martini et al. (2015), Figure 20- (^161)
- Q1. Given a graph of left ventricular blood volume versus
time, or given similar information numerically, calculate
cardiac output.
- Example: calculate cardiac output from this. 2 Ch. 18: Test Question Templates Left ventricle blood volume (mL) Time (sec) 150 100 50 0 1 2
- Q2. Given one “line” of a Wiggers diagram, be able to fill
in the next “line,” according to the following order:
• A. ECG
- B. timing of atrial and ventricular systole and diastole
- C. atrial and ventricular volumes
- D. atrial, ventricular, and aortic pressures
- E. status of heart valves (open or closed)
- Example: Time Volume of blood Graph atrial AND ventricular volumes for the periods shown. Don’t worry about the exact shapes of the curves, just show whether volume is increasing or decreasing in each chamber during each period.
- Q3. Given a specific alteration in the electrical activity of the heart, explain and draw which ECG time interval(s) would be most affected, and in what way (increased, decreased, irregular).
- Example: Imagine a cardiac disorder in which, once the ventricular cells are depolarized, they stay depolarized longer than usual. How would the patient’s ECG be altered? Explain your reasoning.
- Q4. Given a change in HR, SV, EDV, and/or ESV, predict the direction of a change in cardiac output.
- Example: ESV increases. Everything else stays the same. Does CO go up or down?
- Q5. Given a specific malfunction (poor opening, or poor closing) of a specific heart valve, predict how end-diastolic volume and/or end- systolic volume would be affected by this malfunction.
- Example: A patient’s aortic valve does not open as readily as it should. How would this affect the patient’s EDV and/or ESV? Explain your reasoning.
- Q6. Given data on a patient’s ESV, EDV, and/or ejection fraction, determine whether the data are consistent with diastolic heart failure, systolic heart failure, both, or neither.
- Example: Echocardiography shows that when a patient’s pulmonary blood pressure is normal, her left ventricle has an EDV that is 70% of what is predicted for her age and size, and an ejection fraction of 60%. Is this patient likely to have diastolic heart failure, systolic heart failure, both, or neither? Explain your reasoning. 4
Pacemaker cells of the heart Q1. Where in the heart (chamber and specific structure) are the pacemaker cells located? Pacemaker cell action potentials (below) are somewhat different from action potentials in a typical neuron. Marieb & Hoehn (2019), Figure 18.12 7
- (1) Sloping baseline: slow influx of Na+^ through open channels.
- (2) When threshold (- 40 mV) is reached, voltage- gated Ca2+^ channels open.
- (3) Repolarization occurs via exit of K+^ through voltage-gated K+^ channels. “Well, Duh!” answer: Better answer: see figure. Q1. Label the components of the cardiac conduction system. Q2. Can the whole heart still be depolarized in the case of a bundle-branch block (BBB)? Q3. Does the cardiac conduction system tell the cells when to repolarize? Marieb & Hoehn (2019), Figure 18.13 8 How does depolarization spread through the heart?
9 Freeman et al. (2014), Figure 45. (like Marieb & Hoehn Figure 18.17)
... and its manifestation as an electrocardiogram (ECG)!
To get an ECG like the one above, you can put the electrodes in various places:
- Negative electrode on R wrist, positive electrode on L wrist
- Negative electrode on R wrist, positive electrode on L ankle Like an EMG signal, this signal represents a bunch of cells undergoing electrical changes. It is NOT the action potential of a single cell. Time (s) mV Reference chart: Cardiovascular Nursing Education Associates^10 A full clinical workup entails a “12-lead ECG.” Different electrode placements cause the ECG to look different and may reveal different abnormalities. For our purposes, we will stick to the standard ECG in the last slide.
13 Martini et al. (2015), Figure 20- 20 (like Marieb & Hoehn Figure 18.20) Cardiac output and its control Q1. SV is defined mathematically above. What is its definition in words? Q2. What units do HR, SV, and CO have? A very brief, very crude look at heart disease…
- Two basic categories for left heart failure: “diastolic heart failure” and “systolic heart failure.” - Diastolic heart failure: ventricles do not fill up with blood
well.
- Scar tissue => less flexible => can’t expand as well.
- EDV is much lower than predicted.
- Generally in the range of 60 - 150 mL, but depends on age, sex, size, etc.
- Systolic heart failure: ventricles do not expel blood well.
- Heart is weak => can’t force blood out.
- Ejection Fraction (EF) is below normal.
- Definition: SV/EDV x 100%
- Normal resting value: 50 - 70%.
- Either way, pumping of blood is inadequate.
- Analogous to obstructive and restrictive lung disease (Ch.
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Understanding cardiac valves, blood pressure, and blood flow
Heart valves prevent the backflow of blood and thus keep blood flowing in one direction. Heart valves open and close, somewhat like swinging double doors, because of the pressure on the two sides. When pressure on the “upstream side” is greater, the doors are open. When pressure on the “downstream side” is greater, the doors are closed. M. Jensen et al. (2014) 15 Note: a “chamber” in this diagram could be a heart chamber OR a blood vessel. Q1. When the pressure in Chamber A is greater than the pressure in Chamber B (PA > PB), is valve 1 open or closed? Q2. When the pressure in Chamber C is less than the pressure in Chamber B (PC < PA), is valve 2 open or closed? Q3. What relationship between pressures in Chambers A, B, and C results in valves 1 and 2 both being closed? Q4. If Chamber A represents the left atrium and Chamber B represents the left ventricle, name the part of the heart represented by the following elements of the diagram above.
- a. Valve 1 =
- b. Valve 2 =
- c. Chamber C = Q5. Using your answer to Q4, what do you predict would happen to the net cardiac output (CO) if Valve 2 did not close completely? 16
19 Patrick J.P. Brown (2016) (^) – (^) similar to (^) Marieb (^) & Hoehn Focus Figure 18. Next, let’s connect the heart’s electrical events (depolarization and repolarization/ECG) to its mechanical behavior (contraction and relaxation). When a chamber of the heart depolarizes, it will contract, decreasing the volume of that chamber. Find the part of the Wiggers diagram that indicates the contraction of the ventricles. Another word for “contraction” is “systole.” Q1. The times during which the atria and ventricles contract are already labeled. Where on the diagram are these labels? Q2. What does “diastole” mean? Q3. Compare the timing of a chamber’s electrical depolarization and its mechanical contraction. a. Which must begin first, depolarization or contraction? b. Once the muscle cells are fully depolarized, does contraction stop? 20
Q4. Now let’s connect the mechanical events (contraction and relaxation) to the volume of blood in the chambers.
- a. When the ventricle contracts, what happens to its volume of blood?
- b. When does most of the change in volume occur, according to the diagram?
- c. What do you think happens to the atrial volume during atrial contraction? Q5. Now let’s connect the changes in chamber volumes to changes in the blood pressure within those chambers.
- a. When a contracting chamber reduces its volume, what (if anything) will happen to the pressure on the blood in that chamber?
- b. When a relaxing chamber increases its volume, what (if anything) will happen to the pressure on the blood in that chamber? Q6. Find the atrial and ventricular pressures in the Wiggers diagram. Do the pressure increases and decreases occur about where you would expect, based on Q5? 21
Q7. Finally, let’s connect blood pressures to the heart valves,
remembering the earlier slides about valves.
- a. Under what conditions should the aortic semilunar (SL)
valve be open?
- when the ________________ pressure is higher than the ________________ pressure_
- b. Under what conditions should the left atrioventricular (AV)
valve be open?
- when the ________________ pressure is higher than the ________________ pressure_
- c. Look on the Wiggers diagram for indications of when these
valves open and close. Do they match your predictions in (a)
and (b)?
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Answer key for Suggested Lecture Outline file
• You should already have access to answers to some of the
questions (Check Your Understanding, online Practice
Quiz, online Practice Test)
• Answers to pre-lecture questions and end-of-chapter
Review Questions will be in the Presenter Notes that
accompany this slide.
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