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Physio III 💘 > 6 - Venous Return > Flashcards

6 - Venous Return Flashcards

1
Q

Conduit of blood that transport to periphery BACK to the <3

A

Veins

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2
Q

Difference of veins from arteries

A

Distribution of components!

Arteries - thicker
Veins - more compliant

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3
Q

Aka volume reservoir

A

Veins

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4
Q

T or F. Veins are major reservoir which is not controllable.

A

False! They are controllable. How? Because of pressure and sphincters which regulate blood flow from the arterial to the microcirculation to the venous system

Veins also have their own smooth muscles which maintains own tone. (Responsible for tone: ANS)

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5
Q

Compare the compliance and thickness of the veins in the Lower Ex from that of the Upper Ex

A

Lower Ex veins are less compliant and thicker

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6
Q

Venous compliance increases/decreases with age?

A

Decreases

-Elastin decreases while collagen increases

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7
Q

Unique feature of veins

A

Have valves!

Valves prevent backflow in your low pressure system.

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8
Q

T or F. Venous return is independent of your cardiac output.

A

FALSE!!! Venous return normally limits CO! Under steady state, CO should be equal to venous return.

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9
Q

Venous Pressure vs. Central Venous Pressure

A

Venous Pressure - average BP within the venous compartment

Central Venous Pressure - BP in the thoracic vena cava; filling pressure of RV -> reflects SV

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10
Q

Relationship of venous pressure to venous volume and venous compliance

A

Venous pressure is directly proportional to venous volume.

VP is inversely proportional to venous compliance.

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11
Q

Relationship of venous pressure and compliance

A

More compliant = lower P needed

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12
Q

Effect of gravity on venous pressure

A

Dependent areas = higher VP

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13
Q

Why do some people have varicose veins?

A

Incompetent valves = accumulation in dependent areas aka legs

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14
Q

Effect of skeletal muscle pump on venous return

A

Woman standing on tippy toes
-> Calf contracts -> distal valves close and proximal valves open -> venous blood pushed upward -> increased venous return

Woman no longer standing on tippy toes
-> Calf ms relaxes -> Proximal valve closes due to gravity pushing valve shut -> distal valves open -> decrease venous return

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15
Q

Effect of ankle pump to a bedridden patient with no possibility of DVD

A

> Help venous return and to maintain range of motion (inc venous return)

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16
Q

Effect of respiratory activity on venous return

A

Inspire:
Inc P in abdomen -> Inc vol of thoracic cavity -> dec P in thoracic cavity (Boyle’s Law) -> venous return increases bringing blood back to the <3

During inspiration
Diaphragm contracts -> Diaphragm goes down -> TC vol increases -> TC P dec (dec in P reflected in the structures inside the TC e.g. <3, VC (pulmo circ) -> VR inc in RA

In left side of <3, Venous return decreases
Why? Pulmonary vessels are more compliant (than systemic). If there’s (-) pressure inside thoracic cavity -> pressure in pulmo circ decreases so blood accumulates in more compliant pulmo vessels (not in LA) -> So VR during decreases

During expiration
Diaphragm goes back (relaxes) -> Vol dec -> P increases -> VR decreases

In the left side, VR increases because P would compress highly compliant pulmonary vessels in the thoracic cavity which would squeeze blood towards L side -> VR in L slide/LA increases
Thus, SV/CO/BP inc

17
Q

During hyperventilation, CO increases/decreases?

A

Increases

18
Q

Effect of blood volume on CVP

A

Inc BV -> Inc CVP -> Inc EDV -> Inc SV

  • > Inc CO -> Inc MAP
  • > Dec ESV
19
Q

If you increase fiber length, why would you have an increase in tension?

A

If you increase ms fiber length -> increase sensitivity of troponin C to Ca2+ -> more tension produced in cross bridge cycling; If you stretch a ms -> bringing closer the distance between actin and myosin (shorter distance) -> more optimal interaction between actin and myosin

20
Q

Effect of venomotor tone in CVP? VR? Venous capacity?

A

Venomotor tone
-tension created in a blood vessel

Veins can undergo constriction when the sympathetic NS dominates causing the smooth ms lining the veins to contract -> vasoconstriction -> inc tension -> inc venomotor tone
Remember: Role of vein - takes blood back to the heart

Vasoconstriction will inc CVP -> venous return will push the blood in front of constriction to the heart (like kinking a hose)

Inc venomotor tone -> Inc VR -> Decreases venous capacity

21
Q

Effect of valsalva maneuver on venous return

A

When u poop (forceful expiration with a closed glottis) -> initially VR would increase bc of contraction of diaphragm and abdomen which increases abdominal P

Remember: Vessels in your abdomen are splanchnic = highly compliant so compress initially -> inc venous return but if prolonged expiration -> followed by prolonged decrease venous return

So effect: initially increase but eventually prolonged decreased venous return

22
Q

Effect of venous filling pressure/VR on CO?

Effect of CO on VP?

A

Increase VR -> Inc CO because preload higher

Inc CO -> decreases VP
Why?
You increase amt of blood going out but right side connected to the venous side so you’re slowly drying up the well
(More blood being translocated to the arterial side)
*but eventually body will adjust to achieve homeostasis

23
Q

Relationship of CVP and CO

A

Increase VR -> Increase CVP, Preload, SV -> Inc CO

But inc CO -> dec VP and Volume in the venous circ

Decreased VP -> Decreases CO

24
Q

Venous Return formula

A

VR = (MAP - RAP)/SVR

*If high MAP (Pressure inside veins as compared to pressure inside atria) -> Flow proceeds from veins to RA

Venous return = CO (under steady conditions)

25
Q

Under steady conditions, relate CO and VR. What happens if you have a congestive <3 failure?

A

Under steady conditions, VR = CO.

If you have a congestive <3 failure

If incompetent L side/failing L side of <3 that CO is so low -> there’s pooling of blood in the pulmonary area = PULMONARY CONGESTION

If incompetent R heart (RV) -> blood remains in periphery so patient will be edematous (liver congestion)

26
Q

If patient is undergoing MRM bc of breast cancer (70 y.o.) -> tachycardia to 140 bpm 2’ to inadequate anesthesia and by ECG nagka ST elevations, T wave inversion, patient presented with pulmo congestion (may crackles)

What could have happened

A

Patient is undergoing MI (usually in MI, LV is affected) -> Won’t maintain CO (can’t pump blood back to <3 as efficiently as before so blood remains at the pulmo circ) -> *Give TropI!!!

27
Q

Effect of CO on MAP and RAP

A

Increased CO = INC MAP AND DEC RAP

28
Q

What is MCP? Depends on what factors?

A

Mean Circulatory Pressure
-Pressure throughout the vascular system when CO is 0/not pumping
-Pressure which keeps vessels open
~ 7 mmHg
-Depends on vascular compliance and blood volume

29
Q

MCP curve:

Shift to the right implies? Left?

A

MCP curve: CO vs. P

Shift to the right
= increased MCP and blood vol -> Decreased venous compliance

Shift to the left: opposite

Increase vol and dec compliance -> inc RAP (& CVP) -> Inc CO -> shifts curve to the right

30
Q

Systemic Vascular function curves

SVR vs. RAP

A

CO vs VP

Increased CO -> VP decreases
VP increases -> CO increases -> blood in R side of <3 decreases

Dec SVR -> inc RAP
Inc SVR -> dec RAP

Why?
Inc resistance in arterial system -> CVP & RAP decreases because…
You have highly constricted vessel -> harder to translocate blood from L to R side -> less blood translocating to arterial side which could have been translocated to the venous side which could have returned to RA

31
Q

When CO = 0, VP = ?

A

MCP

32
Q

Effect of RAP on CO?

A

Inc RAP -> Inc CO

Inc <3 performance -> Inc CO -> RAP decreases (shifts the curve up and to the left)

Dec CO -> shifts curve down to the right

Magnitude by which CO changes when cardiac performance is altered is determined by the state of systemic vascular fxn

33
Q

Effect of hypervolemia and hypovolemia

A

Hypervolemia (increased venous tone) fill the CV system -> raises MCP (by squeezing blood contained in the veins and, in turn, raising their internal pressure)

Hypovolemia
Dec venous tone -> dec VP

34
Q

Septic shock

A
  • Albumin no effect
  • Diuretics: SV affect which is not good; BP falls
  • Give constrictors (but if too constricted, give inotropes tom improve SV and CO)

Physio III 💘 (6 decks)

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