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Cardiac Physiology and Hemodynamics
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Cardiac Physiology and Hemodynamics
Cardiac Physiology and Hemodynamics
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1
Question
What sequence of structures does the action potential follow through the conduction system of the heart?
Page 12
Answer
SA node, AV node, Bundle of His, bundle branches, Purkinje fibers, and finally the ventricular muscle
2
Question
Why is the left ventricular wall significantly thicker than the right ventricular wall?
Page 8
Answer
The left ventricle must generate high pressures to eject blood into the systemic circulation, whereas the right ventricle pumps blood into the lower-pressure pulmonary circuit
3
Question
How does blood flow from the left atrium to the left ventricle?
Page 8
Answer
Blood flows from the left atrium, across the mitral valve (left AV valve), and into the left ventricle
4
Question
Which valve regulates blood flow from the right atrium into the right ventricle?
Page 8
Answer
The tricuspid valve, also known as the right AV valve
5
Question
How does the resistance to blood flow differ between systemic and pulmonary circulations?
Page 10
Answer
Systemic circulation has high resistance, while pulmonary circulation has low resistance
6
Question
What is the primary difference in ventricular pump pressure between systemic and pulmonary circulations?
Page 10
Answer
Systemic circulation pumps at 120/0 mmHg, whereas pulmonary circulation pumps at 25/0 mmHg
7
Question
How does the distribution of total blood volume differ between systemic and pulmonary circulations?
Page 10
Answer
Systemic circulation contains 80-95% of total blood volume, while pulmonary circulation contains only 5-20%
8
Question
Why does the systemic circulation require thicker vessel walls compared to the pulmonary circulation?
Page 10
Answer
Systemic circulation must withstand much higher arterial pressures, requiring thicker vessel walls to maintain structural integrity
9
Question
What percentage of the body's total blood volume resides in the venous system?
Page 11
Answer
Approximately 60% of total blood volume is located in the veins
10
Question
How do veins function to maintain arterial blood pressure during physiological changes?
Page 11
Answer
Veins transfer stored blood into the arterial system to help maintain pressure when physiological conditions demand it
11
Question
Which organs serve as major blood reservoirs in the body?
Page 11
Answer
The spleen, liver, large abdominal veins, and venous plexus
12
Question
What unique reservoir function does the spleen perform?
Page 11
Answer
It serves as a special reservoir for red blood cells
13
Question
What role do gap junctions at the intercalated discs play in cardiac conduction?
Page 13
Answer
They provide low-resistance pathways that allow action potentials to spread rapidly between cells
14
Question
Why is the heart considered a functional syncytium?
Page 13
Answer
Because action potentials spread cell-to-cell throughout the atria, causing the tissue to contract as a single coordinated unit
15
Question
What is the resting membrane potential of the SA node?
Page 14
Answer
Approximately -60 mV
16
Question
What is the typical intrinsic resting heart rate in beats per minute?
Page 14
Answer
Approximately 70 beats/min (bpm)
17
Question
Why is the ef{Na+/K+-ATPase} pump essential for cardiac electrophysiology?
Page 14
Answer
It is an energy-dependent pump that maintains transmembrane ionic concentration gradients for sodium and potassium, which are necessary for normal action potentials
18
Question
What characterizes Phase 0 of the ventricular myocyte action potential?
Page 18
Answer
Rapid depolarization initiated by a transient increase in the conductance of voltage-gated fast sodium channels
19
Question
Which channels are responsible for the plateau phase (Phase 2) of the cardiac action potential?
Page 18
Answer
Long-lasting (L-type) calcium channels
20
Question
How does the Effective Refractory Period (ERP) protect the heart?
Page 19
Answer
By limiting the frequency of action potentials and subsequent contractions, preventing tetany
21
Question
What three mechanisms do autonomic nerves use to alter heart rate?
Page 20
Answer
Changing the slope of phase 4 depolarization, altering the threshold voltage for triggering phase 0, and altering the degree of hyperpolarization at the end of phase 3
22
Question
What cardiac event does the P wave represent on an ECG?
Page 21
Answer
Atrial depolarization
23
Question
Which cardiac event corresponds to the QRS complex on an ECG?
Page 21
Answer
Ventricular depolarization
24
Question
What does the T wave represent during a cardiac cycle?
Page 21
Answer
Ventricular repolarization
25
Question
What clinical information can clinicians derive from a 12-lead ECG?
Page 22
Answer
Abnormal cardiac rhythms, presence and location of ischemia or infarction, heart orientation, chamber size, and effects of electrolyte levels or drugs
26
Question
What is the fundamental hemodynamic equation relating flow, pressure, and resistance?
Page 24
Answer
Circulation (Q) = rac{ ext{Pressure gradient across the circulation } ( ext{\(\Delta P\)})}{ ext{Resistance of the circulation } ( ext{\(\textit{R}\)})}
27
Question
Where does the greatest resistance to blood flow occur in the circulation?
Page 24
Answer
In the smallest arteries and arterioles
28
Question
How is blood pressure force defined in millimeters of mercury?
Page 24
Answer
A pressure of 100 mmHg means the force of blood was sufficient to push a column of mercury 100 mm high
29
Question
How do you calculate Mean Arterial Pressure (MAP) using systolic and diastolic pressures?
Page 27
Answer
ext{MAP} = ext{Pdias} + rac{1}{3}( ext{Psys} - ext{Pdias})
30
Question
Why is Mean Arterial Pressure (MAP) not a simple arithmetic mean of systolic and diastolic pressures?
Page 26
Answer
Because of the irregular shape of the arterial pressure curve