CO, Venous Return and their Regulation Flashcards
Define Venous return (VR)
quantity of blood flowing from vein to atrium each minute
Describe the relationship between CO and VR
CO = VR
How is cardiac output expressed?
As cardiac index (CO/square meter of body surface area)
What mechanism controls the CO by VR?
Frank-Starling Mechanism
The Frank-Starling mechanism states:
When there is an increase in blood quantity flowing into the heart, there is an increases stretch of walls of chambers, which increases muscle contraction force
Why does CO increase in relation to the Frank-Starling mechanism?
Increased stretch of the myocardial muscle fibers
How does the HR increase in the Bainbridge reflex?
By acting on the VMC in the brain
What directly affects the rhythmicity of the sinus node in the Bainbridge reflex?
The stretch of the RA wall (sinus node)
The sum of all the local blood flow through individual tissue segments of peripheral circulation?
Venous return
What is the law that the CO curve is derived from?
Ohm’s Law
CO = _____ / _________
CO = AP/TPR
T/F AP is a constant value in Ohm’s Law
True
If TPR decreases, what happens to CO?
it increases
What is the normal CO?
13L/min
What can enhance cardiac performance?
nervous stimulation and hypertrophy
List some factors that cause a hypoeffective heart
- nervous inhibition
- pathological factors
- hypertension
What causes intense dilatation of the peripheral blood vessels by increasing metabolism of tissues?
Dinitrophenol
What happens to AP during exercise?
AP increases to above normal
During exercise, the increased AP allows for CO to do what?
CO increases
Right AP, Mean systemic filling pressure, and resistance to blood flow are factors affecting what?
Venous return
T/F a negative Right AP has little effect on venous return
True
Mean circulatory filling pressure (psf) is measured by ?
Stopping heart’s pumping ability by shocking it
List the 2 determinants of psf
- degree of sympathetic stimulation
- amount of blood in circulation
T/F Blood volume is not proportional to the psf
False, the greater the BV the greater the psf
A strong sympathetic stimulation will in turn (increase/decrease) mean filling pressure
increase
What is the normal systemic filling pressure?
7 mmHg
T/F: The greater the system is filled the easier it is for blood to flow into the heart
True
If RAP = 7, then the pressure gradient is equal to what?
psf
What is the difference between psf and RAP pressure called?
pressure gradient for Venous Return
The mean pressure forcing the venous blood back to the right heart is?
Psf
RVR is defined as?
resistance to the venous flow of blood
Normal venous return is:
5 L/min
Describe the relationship between RVR and VR
It is an inverse relationship:
If RVR increases, then VR decreases and viceversa
When does the VR become zero?
When RAP=VR
Transfusion causes a (Increase/decrease) in psf and a (increase/decrease) in RVR
increase; decrease
Does sympathetic stimulation increase or decrease the psf and RVR?
Increase
How can you measure CO in animals?
Via electromagnetic or ultrasonic flowmeter
The O2 Fick method and the indicator dilution method are ways to do what?
Measure CO in HUMANS
