Phys: Cardiodynamics Flashcards
What is cardiodynamics?
The movement and forces generated during cardiac contractions
Why are physicians interested in cardiac output?
Because cardiac output is an indication of blood flow through the peripheral tissues
What is altered in the heart when adjusting the amount of blood being pumped? (3 things)
-heart rate (HR)
-stroke volume (SV)
-cardiac volume (CV)
What is frank sterling law?
The ability of the heart to stretch and increase the force of contraction
What is heart rate controlled by?
-Sympathetic and parasympathetic nervous system
-electrolytes (Na+, K+, Ca2+)
-chemicals
-hormones
What is stroke volume?
The amount of blood that is pumped out of the heart
What is stroke volume regulated by?
-preload
-afterload
-contractility
Preload:
Volume of blood in the ventricles at the end of diastole
Afterload:
Resistance that the heart has to overcome as it is pumping blood out of the aorta
If preload increases, how does it affect stroke volume?
It causes stroke volume to increase
How is stroke volume affected when there is an increase in afterload?
SV decreases
How does increased contractility affect stroke volume?
Stroke volume will increase
What 4 things increases venous return, and in turn, increases stroke volume?
-constriction of veins
-skeletal muscle pump
-thoracic pump
-nervous stimulation increasing heart rate
How much blood is in end-systolic volume?
50 mL
Approximate volume that represents stroke volume:
70 mL
What can cause stroke volume to decline during prolonged exercise?
-increase body temp
-redistribution of blood flow to the skin
-excessive fluids loss due to sweating
-decrease plasma volume
-dehydration
What is the best index for preload? why?
Left ventricular end diastolic volume because its the only one that can be measured clinically using echocardiography
Increase in contractility causes an increase in what?
Cross-bridge cycling and sensitivity of contractile machinery to calcium —->increase stroke volume
Cardiac output:
The amount of blood pumped by each ventricle in one minute
4 factors that determine cardiac output:
-heart rate
-myocardial contractility
-preload
-afterload
Coupling factors for cardiac output:
Preload and afterload
Cardiac factors for cardiac output:
-heart rate
-myocardia contractility
Cardiac output =
Stroke volume x heart rate
Stroke volume =
EDV-ESV
Increase in preload causing what to SV and EDV:
Increase SV, increase EDV
Increase in afterload causing what in SV and ESV:
Decrease SV and increase in ESV
Increase in inotrophy causes what in SV and ESV:
Increase SV and decreased ESV
Stretch of the sinus node causes increase in the heart rate as much as ___-___%
10-15%
Bainbridge reflex is initiated by:
Stretch of right atrium
How does right atrial pressure affect venous return?
Exerts a backward force on the veins to impede flow of blood from veins into right atrium
Mean systemic filling pressure affecting venous return:
Measurement of the degree of filling of the systemic circulation which forces the systemic blood toward the heart
Resistance to blood flow affects venous return by….
Increasing the resistance of blood flow into the right atrium from the peripheral vessels
Venous return is affected by which three things:
-systemic filling pressure
-right atrial pressure
-resistance to venous return
If you increase resistance there is…
Less blood return into the heart
If you decrease resistance there is…
More blood flow to the heart
What drugs have stimulatory effects on cardiac output?
Caffeine and nicotine
How does abnormal variations in ion concentrations or body temperature change heart rate?
The increase the SA nodal cells and increase contractility by affecting the cardiac muscle cells
How does hyperkalemia affect cardiac output?
muscle cells depolarize -> repolarization is inhibited -> cardiac contractions weaker and irregular -> will eventually stop in diastole
How does hypokalemia affect cardiac output?
The muscle cells become hyperpolarized -> less responsive to stimulation -> bradycardia -> heart will eventually stop in systole
How does hypercalcemia affect cardiac output?
Cardiac muscle is extremely excitable and contractions became more powerful and prolonged
How does hypocalcemia affect cardiac output?
Contractions become weaker
How does a decrease in body temperature affect cardiac output?
decreased metabolic processes -> decrease depolarization of the SA -> lowers the heart rate -> decreases force of contraction
Equation for venous return:
VR = Psf - PRA/RVR
Psf stands for
Mean systemic filling pressure
PRA stands for the…
Right atrial pressure
RVR stands for the…
Resistance to venous return
Two thirds of resistance to venous return is determined by _________ and one third is determined by the _____________
Venous resistance, arteriolar resistance
Forces generated during cardiac contractions depend on the:
-heart rate
-stroke volume
-cardiac output
-contractility
_______________is the most important factor when examining the cardiac cycle
Stroke volume
________________ is a good index for ventricular contractility and physicians use it to determine cardiac function
Ejection fraction
Ejection fraction =
EDV - ESV / EDV
