Physiology 4 - Control of Cardiac Output Flashcards
State the relationship between length of sarcomere and tension.
At the shortest and longest length of sarcomere, tension is 0, but reaches a peak in between the two
What is the primary mechanism by which stroke volume can be increased?
Increase end diastolic volume
How is the blood able to continue moving round the body, even when the ventricles are in diastole?
The aorta has excessive elastic tissue, meaning it can swell and almost pump blood itself round the body
What happens to the pressure in the aorta if the volume increases?
The pressure increases
What is meant by saying veins are very ‘compliant’?
You can put a large volume of blood through a vein, without a large change in pressure
How would you calculate the mean arterial blood pressure (MABP)?
Diastolic pressure + 1/3 Pulse pressure
How is pulse pressure calculated?
Systolic pressure - Diastolic pressure
Why can’t you just take the halfway point of systolic and diastolic pressure when calculating the MABP?
The ventricles are in a diastolic state for much longer than they are in a systolic state
List some factors that can affect flow of blood from the heart.
Viscosity
Radius of vessel
Length of vessel
How is arterial pressure calculated?
Cardiac Output x Total Peripheral Resistance (V = IR)
How is CO calculated?
HR x SV
How is the stroke volume calculated?
The difference between EDV and ESV
What effect does an increase in venous return have?
Increased EDV
Increased ejection fraction
What effect does increased EDV have on force of contraction?
Increase - Frank-Starling mechanism
What is the preload?
Venous pressure and venous return to the heart
What is the afterload?
The aortic/PA pressure
With regard to ‘force’, what does Frank-Starling’s Law of the Heart state?
Active force = total force - resting force
What does inotropic mean?
Modifying the force or speed of contraction of muscles
Increasing the sympathetic activity has an inotropic effect. What is this effect and how does it affect the appearance of a length-tension curve?
+‘ve inotropic effect
Make the length-tension curve steeper gradient and much greater tension
How does oscillation in BP decrease as blood nears capillaries from arteries and arterioles?
Vessels are less elastic
What two factors decrease compliance?
Age
Vasoconstriction
How is flow calculated?
Change in Pressure/Total peripheral Resistance (TPR)
How is arterial pressure calculated?
CO x TPR
What are normal systemic and pulmonary pressures?
120/75
26/8
What factor affects the magnitude of pulse pressure
Stroke Volume
