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Flashcards in Pulmonary Circulation Deck (77):
1

Pulmonary Circulation

Largest vascular bed
Accommodates the entire cardiac output from the right heart
Rarely concerned with directing bloodflow

2

Bronchial Circulation

1-2% of cardiac output
Empties into pulmonary vein
Generates physiological shunt
With greater pathology --> greater amount is shunted (wasted volume)

3

Cardiac Output

Output of blood per minute
5L/min
R = to lungs
L = to body

4

In contrast to systemic circulation, in the lung....

1. Rarely concerned with directing blood flow
2. Much lower pressure
3. Better clot filter
4. Contains about 10% of total blood volume

5

Lower pressure in pulmonary circulation

Maintained by low resistance due to # of capillaries
Less smooth muscle than vessels in systemic circulation --> so changes diameter

6

Pulm. Circ. better clot filter

Can be bad with pulmonary embolism
Fibrinolytic substances are released from endothelium

7

Relationship btw. perfusion pressure and resistance unique in the lung

P = flow * resistance
Resistance is inversely related to diameter and pressure
As arterial pressure goes up, resistance goes down

8

As you increase cardiac output, what happens to flow, resistance and pressure

Increase flow
Increase pressure
Decrease resistance - alveoli are recruiting more capillaries and distend the ones that are already open

9

How does vascular resistance get so low?

1. Recruitment
2. Distension

10

Recruitment

As you recruit more capillaries, pressure will drop
Fewer open capillaries at lung apex at rest
With increased CO2, the capillaries will open
As inc press, alveoli will recruit more and open up and keep resistance down

11

Distention

Inc CO2 stretches capillaries so they open more, pulmonary capillaries are thin and compliant

12

Benefits to vascular resistance being low

capillary recruitment and distension increase surface area for gas exchange
Decreases risk of pulmonary edema
- if had high pressure, there would be an inc in fluid leakage and edema

13

Resistance is affected by lung volume - inhalation

Alveolar vessels (pul cap) are exposed to expanding alveoli and are compressed
Extraalveolar vessels are exposed to decreasing intrapleural pressure and expand
Inhale = inc resistance

14

Resistance is affected by lung volume - exhalation

apposite occurs
Decrease resistance

15

Lower resistance does what to work of the heart

lowers the work

16

Resistance is lowest when>

FRC

17

Resistance affected by chemical mediators

Unique response to oxygen
Hypoxic Pulmonary VC = dec in O2 tension, Inc in pulmonary vascular resistance

18

Regional Hypoxia

due to bronchial obstruction
Diverts blood away from poorly ventilated areas
Constrict area with bad gas exchange and distribute blood to areas where gas exchange can occur

19

Generalized Hypoxia

Altitude --> widespread inc in pulmonary vascular resistance and pressure --> might lead to pulmonary hypertension and right heart hypertrophy

20

NE

Vasoconstriction
Bronchodilation

21

Hypoxic Pulmonary Vasoconstriction

Controls pulmonary blood flow distribution to better ventilated areas --> main mechanism for explaining sustained pulmonary hypertension

22

Hypoxic Pulmonary Vasoconstriction triggered by,...

1. Airway obstruction
2. Acute lung damage (pneumonia)
3. Altitude
4. Diseases like COPD

23

Pulmonary Arterioles Dec O2 vs. Inc O2

Dec = Vasoconstriction
Inc = Vasodilation

24

Systemic Arterioles Dec O2 vs Inc O2

Dec = vasodilation
Inc = vasoconstriction

25

Blood flow and air distribution in lung
More flow where?

More flow at base

26

More ventilation where?

Base

27

Ventilation Perfusion Mismatch -

Ideal match when ratio is 1, typically is .8 throughout the lung though

28

At base there is more

Flow than ventilation
More flow and ventilation though compared to apex

29

At apex there is more

Ventilation than flow
But both still lower at apex compared to base

30

Arterial pressure inc from...

apex to base

31

Alveolar pressure inc from

equal at apex and base

32

Transmural pressure

Talking blood vessels now...
Inc from apex to base, inc capillary distension and dec resistance from apex to base

33

Burly Alveoli

Get more ventilation than flow (apex)

34

Weakling Alveoli

More flow than ventilation (base)

35

Ventilation Perfusion Ratio

Mismatching of ventilation and blood flow is responsible for most defective gas exchange in pulmonary diseases

36

Global, at rest, ratio is...

0.8

37

Regional Differences - Apex

Too much ventilation for given blood flow (3)
Lots of O2 in alveolus (favorable for bacteria)
CO2 low in alveolus

38

Regional Differences - Base

Too much perfusion for the level of ventilation (0.6)
Some blood is not adequately oxygenated
Lower PO2 and higher PCO2 of blood leaving alveolar capillaries from here

39

When perfusion (blood flow) is greater than airflow - too much CO2

Base
Too much CO2 = Dilation of airway, decreases airway resistance, inc airflow

40

When perfusion (flow) is greater than airflow - too little O2

Constriction of blood vessels, Inc vascular resistance, dec blood flow

41

When ventilation is greater then flow - Too little CO2

Bronchoconstriction --> Inc airway resistance, Dec airflow

42

When ventilation is greater than flow - too much O2

Vasodilation --> dec vascular resis --> inc blood flow

43

Zone 1

More ventilation than flow
Alveolar presure is higher than arterial or venous press
No blood flow through here - dead space
nonexistent in healthy

44

Zone 2

alveolar is higher than venous but lower than arterial
Alveolar press is determining how much flow is going through

45

Zone 3

More blood flow than ventilation
Arterial and venous are higher than alveolar
Amount of flow depends on diff btw art and venous

46

Anatomical Dead Space

wasted air
150mL
happens normally

47

Alveolar Dead Space

Ventilation to alveolus but no flow to meet it
wasted air

48

Venous admixture

Wasted blood
Have blood coming in, but no air to diffuse into, getting less oxygen in

49

More likely to get dead space

Apex

50

More likely to get venous admixture

Base

51

Dead Space

Anatomic + Alveolar
Anatomic = air remaining in conducting zone
Alveolar = alveoli that don't participate in gas exchange

52

Embolism

Air coming into alveoli but no flow to meet it so now you have inc. alveolar dead space

53

Embolism Compensation

Vessels go through hypoxic vasoconstriction to redirect blood to areas of good ventilation so arterial press will inc and work load will inc too
Can lead to heart failure

54

What happens to CO2 with embolist

CO2 gets mroe diluted, end title CO2 dec.

55

Causes of alveolar dead space

1. Hydrostatic Pressure Failure (gravity effect)
2. Normal
3. Emobolus
4. Emphysema - destruction of walls and elastic tissue, more air going in that wont participate in gas exchange, destroys surface area
5. Pre-capillary constriction

56

Causes of venous admixture

1. Anatomical shunts
2. Low regional ventilation perfusion ratio

57

Anatomical Shunts

blood that doesn't get to ventilated areas of the lung
Atrial of ventricular septal defect
Direct connection of pulmonary artery to vein
Some bronchial venous blood dumps directly into pulmonary veins (normal)

58

Low regional ventilation perfusion ratio

Insufficient alveolar ventilation to adequately oxygenate blood in a region of the lung
Occurs at base of lung under normal conditions (weakling alveoli)
Partially restricted airway --> regional hypoventilation

59

Physiological Shunt

Total amount of wasted blood = venous admixture = anatomic shunt + low perfusion ratio
Normally 1-2% of cardiac output (higher with COPD)

60

Bronchial Circulation

Suplies blood to conducting airways and supportin tissues
Capable of angiogenesis (new vessel formation)

61

Routes for bronchial circulation

Bronchial Veins - Carry about 50% of bronchial blood flow directly to atrium
Bronchopulmonary Anastomoses - Connect bronchial blood flow to pulmonary veins, Contributes to Venous Admixture

62

Pulmonary Embolus

Dead Space
Wasted Air

63

Normal Apex Ratio

High V/Q
Burly Alveoli

64

Normal Base Ratio

Low V/Q
Weakling Alveoli
Limiting factor is ventilation

65

Airway Obstruction

Shunt
Ratio = 0
Wasted Blood/Venous Admixture - flow but no air to meet it

66

Pulmonary Embolism - what is it

Inc in alveolar dead space
Most commonly caused by thrombi from a leg or pelvic vein

67

Pulmonary Embolism - Clinical Picture

Severe respiratory distress - chest pain
Right ventricular failure
Hypoxemia
Hypotension

68

What is hypoxemia in pulmonary embolism caused by

Right to left shunting in areas of partial or complete atelectasis

69

What is the low BP in pulmonary embolidm caused by

You are inc press upstream of your embolist so this will make your right heart work a lot
downstream from the clot though there is not as much flow so not as much going into the left side so the pressure goes down

70

Interalveolar Connection

Pores of Kohn

71

Pores of Kohn

Pores btw. adjacent alveoli
Functions as means of collateral ventilation
If lung is partially deflated, ventilation can occur to some extent through the pores

72

Hydrostatic Pressure

Promotes fluid loss from capillaries
Fluid moves from capillaries into the interstitial space (edema)

73

Alveolar Surface Tension

Inward pressure on alveoli favors fluid loss from capillaries
Fluid moves from capillaries into interstitial space

74

Colloid Osmotic Pressure

Created by plasma proteins - inhibits fluid leakage from capillaries
From space into capillaries

75

Alveolar Pressure

Compresses interstiium and increases interstital pressure
From space into capillaries

76

Pulmonary Edema

Small net fluid efflux from pulmonary capillaries to interstitium
- lymphatics picks up the excess fluid
Excess fluid accumulation in interstitium is pulm edema

77

Causes of pulmonary edema

Increased capillary hydrostatic pressure
Increased capillary permeability
Loss of surfactant --> inc surface tension --> dec interstitial press
Starvation --> Loss of plasma proteins --> dec in osmotic press