76 Questions
Which factor is NOT an important mechanism for changing the force of cardiac contraction?
The % of activated muscle cells
Which factor primarily regulates the contractility of the heart?
The sympathetic nervous system
Which factor determines the overlap of actin and myosin in cardiac muscle?
The resting muscle stretch
What is the molecular makeup of the muscle that can influence the mechanical properties of the heart?
The contractile protein isoform expression
Which factor can change the mechanical properties of the twitch contraction in the heart?
The duration of the active state
Which factor is an important determinant of ventricular force generation?
The synchrony of activation
What determines the size of the Ca transient in the heart?
The availability of Ca2+
Which type of muscle is easily stretched at short muscle lengths?
Cardiac muscle
What is the protective mechanism in the whole heart that prevents overfilling?
All of the above
What are isometric contractions in cardiac muscle?
Contractions where the muscle develops force but is prevented from shortening
What determines the force generating capabilities of striated muscle?
The number of actin-myosin crossbridges
What is the relationship between resting length and cardiac function called?
The Frank Starling relationship
What is the sarcomere length beyond which it is very difficult to stretch resting cardiac muscle?
2.2 microns
What is the primary factor that regulates force development in cardiac muscle?
The number of actin-myosin crossbridges
What is the characteristic of resting cardiac muscle compared to skeletal muscle at sarcomere lengths near the peak of the length-active force relationship?
Resting cardiac muscle is significantly stiffer
What are the factors that regulate force development in cardiac muscle?
Resting muscle length and the number of actin-myosin crossbridges
Which phase of the cardiac cycle is represented by the bottom side of the pressure-volume loop?
Ventricular filling
What does the width of the pressure-volume loop represent?
Stroke volume
Which event occurs at the time represented by the corner of the pressure-volume loop labeled 'AC'?
Aortic valve closure
What determines the rate and magnitude of shortening in cardiac muscle?
The afterload and contractility
What happens to the velocity and magnitude of shortening as the afterload increases?
They decrease
Which type of muscle only functions on the 'ascending limb' of the length-tension relationship?
Cardiac muscle
What is the name of the loop that can be used to plot the instantaneous pressures and volumes throughout the cardiac cycle?
Pressure-volume loop
When does the muscle shorten at a maximal rate?
When the afterload is zero
Which one of these is true about the relationship between afterload and the velocity of shortening in cardiac muscle?
As afterload increases, the velocity of shortening decreases
What is the diastolic pressure-volume relationship (DPVR) in cardiac muscle?
The relationship between ventricular pressure and volume during filling
A decrease in diastolic ventricular compliance is represented by what?
Upward shift in the diastolic PVR
What can cause a decrease in diastolic ventricular compliance in cardiac muscle?
All of the above
What does the end-systolic pressure-volume relationship (ESPVR) represent in cardiac muscle?
The maximum pressure that the ventricle can develop at any volume
How is the end-systolic pressure-volume relationship (ESPVR) derived in cardiac muscle?
By allowing the ventricle to contract but not eject blood at different end-diastolic volumes
What happens to the maximum capability of the ventricle to develop pressure as the volume of the ventricle decreases in cardiac muscle?
It decreases
What happens to the velocity and magnitude of shortening as the afterload increases in cardiac muscle?
They decrease
Which of the following is true about compliance in cardiac muscle?
Compliance is greatest at low volumes
What is the relationship between ventricular ejection and the end-systolic pressure-volume relationship (ESPVR)?
Ventricular ejection ends when the ventricular volume intersects the ESPVR
What is contractility in cardiac muscle?
The ventricle's ability to develop pressure independent of load
Which of the following is true about the regulation of contractility in cardiac muscle?
Contractility is regulated by the sympathetic nervous system
What are some indices used to estimate changes in contractility?
Emax and dP/dt
What happens to stroke volume when contractility increases with no change in preload or afterload?
Stroke volume increases
How can contractility be modified in cardiac muscle?
By humoral and pharmacologic agents
What happens to contractility in cardiac diseases?
Contractility decreases
What causes reduced myofilament Ca binding affinity in cardiac muscle?
Ischemia
What is associated with reduced levels of SERCa2 and 'depressed' Ca handling in cardiac muscle?
Pathological cardiac hypertrophy
Which of the following is true about failing hearts?
They have increased sympathetic reflexes
What is preload in the context of the heart?
The stretch on the myocardial wall at the end of diastole
How is preload best represented?
End-diastolic volume (EDV)
What happens when there is an increase in preload (EDV)?
The ventricle moves higher on the Starling curve
What physiological factors can alter preload?
All of the above
What is the problem with using end-diastolic pressure (EDP) as a measure of preload when diastolic compliance is changing?
EDP is not a reliable indicator of preload, IF THE DIASTOLIC COMPLIANCE IS CHANGING
What can happen when + inotropic drugs are used to correct abnormal contractility in human heart failure?
They can worsen arrhythmias
What is the effect of an increase in end-diastolic volume (EDV) on the PV loop?
It displaces the right side of the PV loop to the right
What is the term for the reduced contractility in failing hearts?
Contractility reserve
Why is correcting abnormal contractility in human heart failure not easily accomplished?
It can worsen arrhythmias
Which of the following is a measure of afterload in the heart?
Systolic ventricular wall stress
What is the formula for mean blood pressure (MBP)?
MBP = CO X TPR
In patients with hypertension, increased afterload is primarily due to what factor?
High blood pressure
What happens to stroke volume when afterload is increased, while preload and contractility are held constant?
Stroke volume decreases
What is the formula for cardiac output (CO)?
CO = stroke volume * heart rate
What controls heart rate in normal people?
Sympathetic and parasympathetic nervous systems
What effect does increased sympathetic nerve activity have on heart rate?
Increases heart rate
What is the formula for calculating systolic ventricular wall stress?
S = (P x r) / 2 Th
What happens to the velocity of muscle fiber shortening when afterload is increased?
Velocity of muscle fiber shortening decreases
Which of the following is true about congestive heart failure (CHF)?
CHF is characterized by the inability of the heart to pump sufficient blood
What is the result of decreased parasympathetic nerve activity near the SA node?
Increased frequency of action potentials
What happens to stroke volume, cardiac output, and blood pressure when the time available for ventricular filling is reduced?
They decrease
What is the primary cause of congestive heart failure (CHF)?
Ischemic heart disease
What is the effect of increased end-diastolic volume (EDV) on the pressure-volume loop?
Dilated ventricles
What is the characteristic of the failing cardiac myocytes in congestive heart failure (CHF)?
Reduced contractility
What is the relationship between heart rate and time for ventricular filling?
Inverse relationship
What happens to the pressure generating capability of the ventricle as it dilates?
It decreases
What is the result of increased end-diastolic pressure (EDP)?
Systemic edema
What is the effect of increased exercise intensity on cardiac output?
It increases
Which of the following is a cause of increased afterload in patients with hypertension?
A and B
What happens to stroke volume when afterload is increased?
It decreases
Why does decreased stroke volume occur when afterload is increased?
Stroke volume is reduced because increased afterload reduces the velocity of muscle fiber shortening and the velocity by which the blood is ejected.
Which of the following can be used to assess afterload in the heart?
All of the above
Which of the following represents the pressure which the ventricle must overcome to begin ejection in the heart?
The diastolic pressure
Test your knowledge on the factors that determine the strength and speed of the heart. Learn about the activation of muscle cells, the importance of electrical coupling, and the role of synchrony in cardiac contraction.
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