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PT663 > Cardiovascular Physiology I > Flashcards

Cardiovascular Physiology I Flashcards

1
Q

What is cardiac output?

A

Cardiac output is the amount of blood the heart pumps per minute, calculated as heart rate times stroke volume.

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2
Q

What is the average resting heart rate for an adult?

A

The average resting heart rate is around 70 beats per minute.

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3
Q

What is the average stroke volume for a 70-kilogram man?

A

The average stroke volume is about 70 milliliters per beat.

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4
Q

Calculate the resting cardiac output for an adult with a heart rate of 70 beats per minute and a stroke volume of 70 milliliters.

A

Resting cardiac output = Heart rate × Stroke volume = 70 bpm × 70 mL = 4900 mL or approximately 5 liters per minute.

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5
Q

How much can cardiac output increase during heavy activity?

A

Cardiac output can increase to about 25 liters per minute during heavy activity.

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6
Q

What percentage of cardiac output typically goes to skeletal muscle at rest?

A

At rest, about 15% to 20% of cardiac output goes to skeletal muscle.

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7
Q

What happens to blood flow distribution during heavy exercise?

A

During heavy exercise, 80% to 85% of cardiac output is redistributed to skeletal muscle, while less blood flows to the gut and kidneys.

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8
Q

What is the equation that describes blood flow?

A

Flow = Pressure gradient / Resistance.

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9
Q

What are the key components to understand regarding cardiac output?

A
  1. The signal that causes the heart to beat.
  2. What happens when that signal is generated.
  3. How the heart functions as a pump (mechanical actions and electrical activity).
  4. How cardiac output is regulated.
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10
Q

What role does the cardiovascular system play in meeting increased metabolic demand during exercise?

A

The cardiovascular system increases cardiac output and redistributes blood flow to skeletal muscles to meet the increased metabolic demand during exercise.

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11
Q

What establishes the electrochemical gradient in cardiac cells?

A

The electrochemical gradient is established by membrane pumps and channels that maintain high potassium inside the cell, high sodium outside the cell, and low calcium inside the cell.

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12
Q

What is the resting membrane potential of a cardiac myocyte?

A

The resting membrane potential of a cardiac myocyte is approximately -90 millivolts.

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13
Q

What happens when a cardiac cell depolarizes?

A

Sodium channels open rapidly, allowing sodium to rush into the cell, causing the membrane potential to become more positive.

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14
Q

What is the role of calcium channels during cardiac depolarization?

A

Calcium channels open more slowly than sodium channels and remain open longer, allowing calcium to enter the cell, contributing to the positive membrane potential.

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15
Q

How do potassium channels affect the cardiac action potential?

A

When potassium channels open, potassium leaves the cell, which contributes to the membrane potential becoming more negative after depolarization.

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16
Q

Describe the phases of the cardiac action potential.

A

The action potential includes an initial spike due to sodium influx, a plateau phase due to calcium influx and potassium efflux, and a return to resting potential as potassium continues to leave the cell.

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17
Q

What is automaticity in cardiac myocytes?

A

Automaticity is the ability of cardiac myocytes, particularly in the sinoatrial (SA) node, to generate electrical impulses spontaneously, causing the heart to beat independently.

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18
Q

What are the two types of myocytes in the heart?

A

There are typical myocytes (muscle cells that generate force) and specialized myocytes (conductive cells that serve as pacemakers).

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19
Q

What is the sinoatrial (SA) node’s role in the heart?

A

The SA node is the dominant pacemaker of the heart, generating electrical signals that trigger heartbeats at a rate of 60 to 100 beats per minute.

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20
Q

Explain the concept of overdrive suppression.

A

Overdrive suppression occurs when the SA node generates impulses at a faster rate than other pacemaker tissues, preventing those tissues from depolarizing on their own.

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21
Q

What does an electrocardiogram (ECG) measure?

A

An ECG measures the electrical activity of the heart, displaying the timing of atrial and ventricular depolarization and repolarization.

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22
Q

What does the P wave in an ECG represent?

A

The P wave represents atrial depolarization.

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23
Q

What does the QRS complex represent in an ECG?

A

The QRS complex represents ventricular depolarization.

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24
Q

What does the T wave indicate in an ECG?

A

The T wave indicates ventricular repolarization.

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25
Q

Where is atrial repolarization observed in an ECG?

A

Atrial repolarization occurs but is typically not visible because it is buried within the QRS complex.

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26
Q

What is the main difference between the cardiac action potential and that of skeletal muscle?

A

The cardiac action potential has a much longer duration and includes a plateau phase, allowing for sustained contraction, whereas skeletal muscle action potentials are shorter

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27
Q

What is the role of calcium in cardiac myocyte contraction?

A

Calcium enters the cell during action potentials, triggering further calcium release from the sarcoplasmic reticulum, allowing actin and myosin to interact and generate force.

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28
Q

What are the key components of a cardiac myocyte?

A

Key components include the sarcolemma (cell membrane), sarcoplasmic reticulum (calcium storage), myofilaments (actin and myosin), and mitochondria.

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29
Q

Describe the process of excitation-contraction (EC) coupling.

A

EC coupling involves calcium influx during the action potential, calcium release from the sarcoplasmic reticulum, calcium binding to troponin, and the formation of cross-bridges between actin and myosin, leading to contraction.

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30
Q

What happens during the plateau phase of the cardiac action potential?

A

Calcium channels open, allowing calcium to enter the cell and interact with ryanodine receptors on the sarcoplasmic reticulum, leading to further calcium release.

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31
Q

What is the role of the SERCA pump during relaxation?

A

The SERCA pump actively transports calcium back into the sarcoplasmic reticulum, reducing intracellular calcium levels and allowing muscle relaxation.

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32
Q

How do sodium-calcium exchangers contribute to calcium regulation?

A

Sodium-calcium exchangers help remove calcium from the cell, contributing to the decrease in intracellular calcium levels during relaxation.

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33
Q

What is the effect of low calcium levels in cardiac myocytes?

A

Low calcium levels lead to the release of calcium from troponin, allowing tropomyosin to cover actin binding sites, which prevents actin-myosin interactions and causes relaxation.

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34
Q

What is the significance of automaticity in cardiac myocytes?

A

Automaticity allows specialized cardiac myocytes to generate spontaneous action potentials, causing the heart to beat independently of nervous system inp

35
Q

What is the difference between the sinoatrial node (SA node) and the atrioventricular node (AV node) regarding pacemaking?

A

The SA node has a faster intrinsic firing rate (60-100 bpm) and is the primary pacemaker, while the AV node has a slower rate (40-60 bpm) and serves as a backup.

36
Q

How does overdrive suppression maintain the SA node’s dominance as the heart’s pacemaker?

A

The SA node depolarizes more rapidly than other pacemaker tissues, sending signals before they can spontaneously depolarize, thus preventing them from taking over as pacemakers.

37
Q

What does an electrocardiogram (ECG) measure?

A

An ECG measures the electrical activity of the heart, displaying the timing of depolarization and repolarization of the atria and ventricles.

38
Q

What do the P wave, QRS complex, and T wave represent on an ECG?

A

The P wave represents atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave represents ventricular repolarization.

39
Q

How do you calculate stroke volume?

A

Stroke volume is calculated as the difference between end diastolic volume (EDV) and end systolic volume (ESV).

40
Q

What is ejection fraction, and what does it indicate?

A

Ejection fraction is the stroke volume divided by end diastolic volume; it indicates the heart’s pumping efficiency, with a normal value around 60-65%.

41
Q

Why is echocardiography an important tool in evaluating heart function?

A

Echocardiography provides images of the heart’s structure and function, allowing for the assessment of stroke volume and ejection fraction, crucial for diagnosing conditions like heart failure.

42
Q

What are the two main phases of the cardiac cycle?

A

Systole (contraction) and diastole (relaxation).

43
Q

What occurs during ventricular systole?

A

The ventricles contract, ejecting blood into the aorta and pulmonary artery.

44
Q

What occurs during ventricular diastole?

A

The ventricles relax and fill with blood from the atria.

45
Q

What is the Wiggers diagram?

A

A diagram that illustrates the cardiac cycle by showing the relationships between the ECG, ventricular volume, ventricular pressure, and aortic pressure over time.

46
Q

What does the ECG trace represent in the cardiac cycle?

A

The P wave represents atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave represents ventricular repolarization.

47
Q

What happens to ventricular volume during diastole?

A

Ventricular volume increases as blood flows in from the atria.

48
Q

What is isovolumetric contraction?

A

The period during ventricular systole when the mitral valve closes, and pressure builds in the ventricle without blood being ejected because the aortic valve is still closed.

49
Q

When does the aortic valve open?

A

The aortic valve opens when the pressure in the ventricle exceeds the pressure in the aorta, allowing blood to be ejected.

50
Q

What is isovolumetric relaxation?

A

The period during ventricular diastole when both the aortic and mitral valves are closed, and the ventricle relaxes but no blood is moving.

51
Q

What triggers the closure of the mitral valve?

A

The mitral valve closes when the ventricle begins to contract, and pressure increases above atrial pressure.

52
Q

What is the role of calcium in the cardiac cycle?

A

Calcium is essential for excitation-contraction coupling; it triggers muscle contraction and regulates the strength of the heartbeat.

53
Q

What does stroke volume represent?

A

Stroke volume is the amount of blood ejected by the heart in one contraction, calculated as the difference between end diastolic volume and end systolic volume.

54
Q

How is ejection fraction calculated?

A

Ejection fraction is calculated as stroke volume divided by end diastolic volume, expressed as a percentage.

55
Q

What produces the first heart sound (S1) in the cardiac cycle?

A

S1 is caused by the closure of the mitral and tricuspid valves at the beginning of ventricular systole.

56
Q

What produces the second heart sound (S2) in the cardiac cycle?

A

S2 is caused by the closure of the aortic and pulmonic valves at the end of ventricular systole.

57
Q

What is the fundamental equation for cardiac output?

A

Cardiac output = heart rate × stroke volume.

58
Q

What is the effect of increasing heart rate on cardiac output called?

A

A positive chronotropic effect.

59
Q

What happens to heart rate during a negative chronotropic effect?

A

The heart rate decreases.

60
Q

How does sympathetic nervous system activity affect heart rate?

A

It increases heart rate by releasing norepinephrine, which acts on beta-1 receptors in the heart.

61
Q

What is the role of the parasympathetic nervous system in heart rate regulation?

A

It decreases heart rate by releasing acetylcholine, which acts on muscarinic receptors.

62
Q

What effect does increased heart rate have on stroke volume if no other adjustments are made?

A

Stroke volume decreases due to reduced time for ventricular filling during diastole.

63
Q

What happens to cardiac output when heart rate increases above 100-150 beats per minute?

A

Cardiac output starts to decline due to a decrease in stroke volume.

64
Q

What is preload in the context of cardiac output?

A

Preload refers to the stretch on the myocardium, proportional to the volume of blood in the ventricles at the end of diastole.

65
Q

What is afterload?

A

Afterload is the resistance the ventricle must overcome to eject blood into the aorta, proportional to blood pressure.

66
Q

What is contractility?

A

Contractility refers to the strength of the myocardial contraction and is dependent on intracellular calcium levels.

67
Q

How does increasing preload affect stroke volume?

A

Increasing preload leads to increased stroke volume due to greater myocardial stretch.

68
Q

What effect does hypertension have on afterload?

A

Hypertension increases afterload, which can decrease stroke volume.

69
Q

How does sympathetic nervous system activation influence contractility?

A

It increases contractility through norepinephrine acting on beta-1 receptors, enhancing intracellular calcium levels.

70
Q

What is the effect of negative inotropic agents, such as calcium channel blockers?

A

They decrease the strength of the heart’s contraction by reducing intracellular calcium levels.

71
Q

What is the Frank-Starling curve used to illustrate?

A

It illustrates the relationship between end diastolic volume (preload) and stroke volume, showing that increased preload leads to increased stroke volume up to a point.

72
Q

What is oxygen consumption abbreviated as?

A

VO₂

73
Q

How is oxygen consumption (VO₂) calculated?

A

VO₂ = cardiac output × a-vO₂diff (arterial-venous oxygen difference).

74
Q

What happens to heart rate as oxygen consumption increases during exercise?

A

Heart rate increases linearly with oxygen consumption.

75
Q

What is the role of the sympathetic nervous system during exercise?

A

It increases heart rate by releasing norepinephrine, which acts on beta-1 receptors in the heart.

76
Q

What effect does the parasympathetic nervous system have on heart rate?

A

It decreases heart rate by releasing acetylcholine.

77
Q

Why does stroke volume initially increase with exercise but then plateau?

A

Stroke volume increases due to enhanced contractility and increased preload, but plateaus due to insufficient filling time at higher heart rates.

78
Q

What are two main mechanisms that augment venous return during exercise?

A

Constriction of veins by the sympathetic nervous system and the peripheral muscle pump.

79
Q

How does breathing assist in venous return?

A

Inhalation decreases thoracic pressure and increases abdominal pressure, facilitating blood flow back to the heart.

80
Q

What is the balance that determines myocardial oxygen supply and demand?

A

Oxygen supply is determined by coronary blood flow and arterial oxygen content, while oxygen demand is influenced by heart rate, preload, afterload, and contractility.

81
Q

What is ischemia, and why is it a concern in patients with cardiovascular disease?

A

Ischemia occurs when oxygen demand exceeds supply, potentially leading to tissue damage or infarction.

82
Q

What is the rate-pressure product, and how is it calculated?

A

Rate-pressure product is a clinical index of oxygen demand calculated as heart rate × systolic blood pressure.

83
Q

Why does coronary blood flow occur primarily during diastole?

A

During diastole, coronary vessels are not compressed, allowing for increased blood flow, while during systole, they can be compressed due to myocardial contraction.

84
Q

How does increasing heart rate affect diastolic filling time?

A

Increased heart rate reduces diastolic filling time, potentially compromising coronary blood flow.

PT663 (22 decks)

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