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KLowe Anesthesia Physiology 1: Respiratory > Lecture 3: Pulmonary And Bronchial Circulations > Flashcards

Lecture 3: Pulmonary And Bronchial Circulations Flashcards

1
Q

Blood flow varies throughout the lung as a result of (3 things):

A
  • Low vascular pressures
  • Gravity
  • Distensible pulmonary vessels
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2
Q

Right ventricle ejection fraction of blood is distributed into ___ and equals ___

A

Lungs and equals LV cardiac output

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3
Q

Why is pulmonary blood pressure lower than systemic blood pressure?

A

Because the resistance to flow in the pulmonary system is one tenth of systemic circulation

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4
Q

Resistance to flow in the pulmonary system is ___ of systemic circulation

A

1/10th

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5
Q

Describe the wall of the pulmonary artery

A
  • Thin walled (1/3 thickness of aorta)

- Very compliant

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6
Q

Pulmonary vessels are divided into ___ and ___

A

Alveolar and extra-alveolar vessels

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7
Q

Alveolar vessels are closely related to ___

A

Acini

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8
Q

What is acini?

A

Alveolocapillary network involved in gas exchange

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9
Q

Alveolar vessels are directly affected by…

A

Alveolar pressure

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10
Q

What collapses alveolar vessels during lung expansion?

A

High positive pressure

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11
Q

Alveolar capillaries can be ___ so that they contain ___

A

Compressed, no blood

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12
Q

What are the extra-alveolar vessels?

A

Arteries and veins which convey blood to-and-from the respiratory units

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13
Q

How does the structure of extra-alveolar vessels differ from alveolar vessels?

A

Larger vessels with thicker walls and substructure connective tissue

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14
Q

Are extra-alveolar vessels directly affected by pressures in the lung?

A

No

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15
Q

Do extra-alveolar vessels become compressed during positive pressure?

A

No

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16
Q

What pulls extra-alveolar vessels open during lung volume increases?

A

Surrounding lung tissue

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17
Q

What are the bronchial vessels?

A
  • Vessels that contain oxygenated blood from systemic circulation
  • Comprise 1-2% of cardiac output
  • Empty into left atrium
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18
Q

Alveolar vessels provide ___ ___ to flow

A

Longitudinal resistance to flow

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19
Q

What resists pulmonary blood flow in the alveolar vessel network?

A

Alveolar vessel network dimensions and distensibility

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20
Q

Alveolar network dimensions are not regulated by ___ or ___

A

Autonomic or hormone control

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21
Q

Alveolar capillary walls contribute ___% of total resistance

A

40%

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22
Q

Alveolar arterioles contribute ___% of resistance

A

50%

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23
Q

In the body, arterioles are…

A

Major resistance vessels—75% of total systemic circulation resistance!

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24
Q

What does the resistance of capillary vessels depend on?

A

Lung conditions

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25
Q

Reduced resistance at ___ lung volumes

A

Low

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26
Q

Reduced resistance at ___ blood flow rates

A

High

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27
Q

Greater resistance at ___ blood pressures or ___ vascular distending pressures

A

Low, less

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28
Q

___ regulation of blood flow through capillaries occurs in response to changes in cardiac output

A

Passive

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29
Q

What accommodates increases in alveolar blood flow?

A

Recruitment and distention

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30
Q

What do recruitment and distention of alveoli prevent?

A

Prevents rise in pulmonary driving pressure with increase in blood flow

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31
Q

What does recruitment mean?

A

Opening of previously closed vessels

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32
Q

What does distention mean?

A

Increase in caliber of vessels

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33
Q

What are two mechanisms for decreasing pulmonary vascular resistance?

A
  • Recruitment

- Distention

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34
Q

What are the pulmonary capillaries?

A

Extensive network within alveolar walls

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35
Q

___% of alveolar surface area is covered by capillary bed

A

70-80%

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36
Q

Total capillary surface area almost equals…

A

Alveolar surface area

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37
Q

What increases capillary volume?

A

Opening closed segments (recruitment)

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38
Q

What is the normal functional capillary volume (FCV) at rest?

A

70 ml (1 ml/kg body weight)

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39
Q

What is the maximal functional capillary volume (FCV)?

A

200 ml

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40
Q

What is the alveolocapillary network?

A

Continuous network over several alveoli

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41
Q

What is the average distance RBC travels through the alveolocapillary network?

A

600 to 800 micrometers

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42
Q

Capillary network blood volume =

A

RV stroke volume

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43
Q

How long does the RBC remain in the alveolocapillary network?

A

One cardiac cycle (0.75 sec)

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44
Q

How long does the RBC require for gas exchange equilibrium?

A

Less than 0.25 seconds for gas exchange equilibrium

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45
Q

What is pulmonary circulation volume?

A

Total blood volume from the main pulmonary artery to the left atrium

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46
Q

How much is the pulmonary circulation volume?

A

500 ccs

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47
Q

Lung is ___% blood by weight

A

40-50%

This volume fraction is > than any other organ

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48
Q

What is the capacitance reservoir for the left atrium?

A

The idea that the pulmonary vasculature acts as a reservoir and can alter its volume from 50% to 200% of resting volume

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49
Q

What does the capacitance reservoir prevent?

A

Prevents changes in blood return to the right ventricle from affecting the left ventricular diastolic filling pressures over 2-3 cardiac cycles

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50
Q

What is pulmonary capillary volume?

A

Approximately equal to stroke volume of the right ventricle

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51
Q

How much blood does the capillary bed contain at rest?

A

70 ml

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52
Q

What is the maximum volume of blood in the capillary bed during exercise?

A

200 ml

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53
Q

What is recruitment?

A

Process of increasing capillary volume by opening closed vessels

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54
Q

Increased CO ___ pulmonary vascular pressures, BUT ___ pulmonary vascular resistance

A

Raises pulmonary vascular pressures, decreases pulmonary vascular resistance

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55
Q

When does recruitment occur?

A

Occurs during periods of stress and increased tissue oxygen demand

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56
Q

Recruitment ___ pulmonary vascular resistance

A

Decreases—chief mechanism for fall in PVR!

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57
Q

Recruitment ___ pulmonary vascular pressures

A

Raises

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58
Q

What is distention?

A

When internal vessel pressures raise and open capillary beds

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59
Q

What is the effect of elevated left atrial pressure on distention of pulmonary capillary beds?

A

It increases distention (i.e.: mitral regurgitation, LV failure)

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60
Q

What does elevated left atrial pressure lead to long term?

A

Lung congestion; ultimately heart failure

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61
Q

Distention is seen at ___ vascular pressures

A

High vascular pressures

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62
Q

How does strenuous exercise affect cardiac output?

A

Increases cardiac output significantly

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63
Q

Increased CO during exercises ___ pulmonary arterial pressure

A

Raises

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64
Q

How does increased CO during exercise affect recruitment of alveolar wall capillaries?

A

Increased CO = more recruitment of alveolar wall capillaries

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65
Q

What happens to capillary volume during exercise? Why?

A

Capillary volume doubles to give time for adequate gas exchange during increased blood flow

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66
Q

Inspiration pleural pressure

A

More negative than -5 mm H2O

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67
Q

Pressure gradient for blood flow into thorax during inspiration is ___

A

Increased

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68
Q

How does inspiration affect blood flow in RV/LV?

A
  • RV receives greater blood volume in diastole
  • Increase of venous blood return into thorax
  • LV ejects less blood secondary to increased pressure gradient between LV and systemic pressures
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69
Q

Expiration pleural pressure

A

Lower pleural pressure gradient—pleural pressure less negative than -5 mm H2O

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70
Q

How does thoracic pressure during expiration affect venous blood return?

A

More positive thoracic pressure decreases venous blood return

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71
Q

Decreased pressure gradient during expiration prevents…

A

Venous blood return to RV

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72
Q

What is the RV ejection pressure during expiration?

A

Less

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73
Q

The reduced gradient between LV and systemic arteries during expiration allows…

A

Increased stroke volumes

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74
Q

What alters pulmonary vascular resistance?

A

Changes in lung volumes during breathing

75
Q

PVR is minimal when…

A

Lung volume is close to FRC

76
Q

PVR is increased with…

A

Higher and lower lung volumes

77
Q

What dilates during inspiration?

A

Extra-alveolar vessels

78
Q

How does inspiration affect the diameter and flow resistance of extra-alveolar vessels?

A
  • Increases diameter

- Reduces flow resistance

79
Q

How much blood volume do the extra-alveolar vessels get during inspiration, and what is the effect on the alveolar vessels?

A

There is increased blood volume to the extra-alveolar vessels during inspiration; higher alveolar pressure compresses alveolar vessels

80
Q

What happens to the alveolar vessels during inspiration?

A

Alveolar vessels compress

81
Q

How do elevated alveolar pressures affect capillary resistance?

A

Elevated alveolar pressures increase capillary resistance

82
Q

Pulmonary capillaries are vessels of…

A

Major vascular resistance

83
Q

Alveolar pressure is ___ by mechanical positive pressure ventilation

A

Artificially increased

84
Q

Mechanical ventilation increases amount of zone ___ lung volume relative to pulmonary venous pressure

A

2

85
Q

The rise in alveolar pressure increases resistance to…

A

Blood flow in zone 2

86
Q

Positive-pressure ventilation can ___ cardiac output or ___ V/Q imbalance

A

Decrease cardiac output; increase V/Q imbalance

87
Q

What is the bronchial circulation?

A

Circulation of oxygenated blood from the aorta returning to nourish the lung

88
Q

What lung structures are perfused by the bronchial circulation?

A
  • Conducting airways to terminal bronchioles

- Parenchyma supporting structures: pleura, interlobar septal tissues, pulmonary arteries and veins

89
Q

Bronchial blood flows at ___ and is ___% cardiac output

A

Systemic pressures, 1-2% of cardiac output

90
Q

___% of bronchial blood circulation returns to right atrium via azygos vein

A

50%

91
Q

The rest of the bronchial blood exits lung by…

A

Small anastomoses with pulmonary veins contributing to normal venous admixture (right-to-left shunt)

92
Q

What does the pulmonary lymphatic system do?

A
  • Keeps alveoli free of fluid moving from capillaries
  • Hydrostatic starling forces tend to move fluid out at 20 ml/hr
  • Numerous lymphatics drain fluid from interstitium
93
Q

Alveolar edema interferes with…

A

Pulmonary gas exchange

94
Q

The pulmonary interstitium is kept at a slight ___ pressure

A

Negative

95
Q

Effect of gravity on systemic blood pressure—in upright position, arterial pressure is higher…

A

In the feet than the head (postural dependent relationship with gravity)

96
Q

Effects of gravity on pulmonary circulation—___ alterations in flow occur because pulmonary circulation pressures are ___

A

Greater alterations; pulmonary circulation pressures much lower

97
Q

Distribution of blood flow in the lung is affected by ___

A

Gravity

98
Q

What affects distribution of blood flow over the height of the lung?

A

Changes in pulmonary arterial pressure

99
Q

What is hydrostatic pressure?

A

The pressure effect gravity has on a column of fluid

100
Q

What are considered zero reference points?

A

The right atrium level and middle of the lung

101
Q

What positions minimize hydrostatic pressures?

A
  • Supine

- Prone

102
Q

___ affects the perfusion of blood in the different zones of the lungs

A

Gravity

103
Q

What part of the lungs receives a greater portion of the RV ejection fraction?

A

Lung base receives a greater portion than the apex of the lung

104
Q

Hydrostatic pressure causes ___ and ___ of pulmonary capillaries in base of lung

A

Distention and recruitment

105
Q

Blood flow distribution over the height of the lung is divided into ___ functional zones

A

3

106
Q

Blood flow depends on pressure in ___ vessels relative to ___ pressure

A

Pulmonary vessels, relative to alveolar pressure

107
Q

Pressures in pulmonary vessels/alveoli are dependent on (4 things):

A
  • Hydrostatic pressure
  • Gravity
  • Transmural compressive pressure
  • Lung volume
108
Q

The perfusion zones of the lung depend on the relationship between what two things?

A

The relationship between alveoli and blood pressure in pulmonary arteries and veins

109
Q

Zone 1

A
  • Region does not receive blood flow
  • Alveolar pressure > regional pulmonary blood pressure (PA > Pa)
  • Pulmonary capillaries are collapsed by higher PA
110
Q

Zone 2

A
  • Occurs where blood flow driving force is arterial-Alveolar pressure gradient
  • Pa > PA > PV
  • Intermittent blood flow
  • ‘Water fall’ effect—downstream venous pressure changes do not alter blood flow
111
Q

Zone 3

A
  • Conditions exist in lung base because of effect of gravity
  • Hydrostatic gravity pressures cause distention and recruitment of pulmonary capillaries
  • Pa > PV > PA
  • Distention and recruitment decrease resistance to blood flow (increased flow in zone 3)
112
Q

Zone 4

A
  • An abnormal condition of reduced blood flow
  • High pulmonary venous pressures (i.e.: LV failure or mitral stenosis)
  • Pulmonary edema creates fluid accumulation and vascular cuffing
  • Increased vascular resistance and reduced local blood flow
113
Q

___ affects the regional distribution of blood flow in the different lung zones

A

Gravity

114
Q

Transmural distending pressure of vessels at ___ of lung > apex

A

Bottom

115
Q

Describe blood flow in the base of the lung (3 things)

A
  • Blood vessels are more distended in base
  • Decreased resistance to flow in base
  • Greater blood flow in lower lung
116
Q

___ pressure affects blood flow

A

Alveolar

117
Q

What pressures are higher in the apex of the lung?

A

Alveolar pressures are higher than capillary pressures in the apex of the lung

118
Q

Pressure differences in the apex of the lung results in ___ perfusion in apex

A

Decreased perfusion

119
Q

What creates differences in lung zones? (3 things)

A

Pulmonary arterial, venous, and alveolar pressure

120
Q

What 3 factors expand zone 1 perfusion?

A
  • Decreased pulmonary artery pressure (i.e.: shock, hypovolemia)
  • Increased alveolar pressure (i.e.: PEEP)
  • Occlusion of blood vessels (i.e.: pulmonary embolism)
121
Q

What 2 factors reduce zone 1 perfusion?

A
  • Increased pulmonary artery pressure (i.e.: infusion of fluid or blood)
  • Reduced hydrostatic effect (i.e.: change patient position from standing to supine)
122
Q

___ PA pressures with increased CO (i.e.: during exercise)

A

Increased

123
Q

PVR =

A

The change in pressure over cardiac output

124
Q

Active regulation of blood flow in the pulmonary vasculature occurs by…

A

Altering vascular smooth muscle tone in pulmonary vessels (arterioles)

125
Q

Pulmonary capillary smooth muscle alters ___

A

PVR

126
Q

Most active regulation of pulmonary vessels is mediated by…

A

Local metabolic influences

127
Q

What two factors affect vasomotor tone/pulmonary vascular resistance?

A
  • Vasoconstrictors

- Vasodilators

128
Q

What are 5 vasoconstrictors that affect pulmonary vascular resistance?

A
  • Reduced PaO2
  • Increased PCO2
  • Thromboxane A2
  • Histamine
  • Prostaglandins
129
Q

What are 3 vasodilators that affect pulmonary vascular resistance?

A
  • Increased PaO2
  • Prostacyclin
  • Nitric oxide
130
Q

Thromboxane A2 is a ___

A

Potent vasoconstrictor—constrictor of pulmonary arterial and venous smooth muscle

131
Q

What is thromboxane A2 made of?

A

It is a product of cell membrane arachidonic acid metabolism

132
Q

When is thromboxane A2 produced?

A

Produced during acute lung tissue damage by macrophage, leukocytes, and endothelial cells

133
Q

Where does thromboxane A2 exert its effect?

A

Effect is localized to the injured region of the lung because the half-time of thromboxane inactivation is only seconds

134
Q

Prostacyclin (Prostaglandin I2) is a ___

A

Potent vasodilator

135
Q

Prostacyclin inhibits…

A

Platelet activation

136
Q

What produces prostacyclin?

A

Endothelial cells—product of arachidonic acid metabolism

137
Q

Nitric oxide (NO) is a ___

A

Epithelial vasodilator

138
Q

Where does NO work?

A

Strictly localized effect to the vascular site of production

139
Q

How does NO work?

A
  • NO activates guanylyl cyclase and increases cGMP
  • It causes smooth muscle relaxation through synthesis of cyclic GMP
  • How nitroglycerin and sodium nitroprusside work
140
Q

What is the clinical use of NO?

A

Selective pulmonary vasodilation delivered by inhalation technique

141
Q

NO at high concentrations is…

A

-Very toxic!

142
Q

NO binds irreversibly to…

A

Heme iron in hemoglobin

143
Q

NO binds to hemoglobin ___ times more than oxygen

A

200,000x

144
Q

Partial pressure of ___ in alveoli is a critical factor governing pulmonary circulation

A

Oxygen (PaO2)

145
Q

PaO2 in alveoli is more important than…

A

Oxygen tension in mixed venous blood

146
Q

Oxygen diffusing into pulmonary arteriole walls causes…

A

Smooth muscle dilation

147
Q

As alveolar oxygen tension decreases, surrounding arterioles ___

A

Constrict

148
Q

Low alveolar PaO2 causes increase in…

A

Local vascular resistance

149
Q

Low alveolar PaO2 causes blood flow to shift to areas of the lung with…

A

Higher PaO2

150
Q

Global reduction in alveolar oxygen tension ___ total PVR by…

A

Increases, by constriction of arterioles and small arteries

151
Q

Alveolar hypoxia produces…

A

Hypoxic pulmonary vasoconstriction (HPV)

152
Q

What is hypoxic pulmonary vasoconstriction (HPV)?

A
  • Localized response of pulmonary arterioles
  • Caused by hypoxia and enhanced by hypercapnia and acidosis
  • Contraction of smooth muscle in small arterioles in hypoxic region
  • Opposite reaction than systemic circulation to hypoxia
153
Q

HPV is an important mechanism of balancing what ratio?

A

-V/Q ratio—shift flow to better ventilated pulmonary regions

154
Q

What does HPV result from?

A

-Decreased formation and release of nitric oxide by pulmonary endothelium in hypoxic region

155
Q

What is pulmonary hypertension?

A

Increased resistance to blood flow in the lung

156
Q

Pulmonary vascular resistance and pulmonary artery pressures are both ___ in pulmonary HTN

A

Elevated

157
Q

What are effects of pulmonary HTN?

A
  • Generalized alveolar hypoxia increases total pulmonary resistance
  • Hypoventilation
  • Low inspired PO2
  • Increased PCO2
  • Pain
  • Histamine release
  • High altitudes
158
Q

Pulmonary hypertension causes increased work for the ___, leading to

A

Right ventricle, leading to:

  • right ventricular hypertrophy
  • tricuspid regurgitation
  • right heart failure (cor pulmonale)
159
Q

Pulmonary hypertension is a…

A

SERIOUS PULMONARY VASCULAR CONDITION

160
Q

In pulmonary HTN, small muscular pulmonary arteries ___

A

Narrow

161
Q

In pulmonary HTN, pulmonary arterial pressure ___

A

Increases

162
Q

In pulmonary HTN, right ventricle pressures ___

A

Rise to compensate until RV failure occurs

163
Q

What is the only effective treatment for pulmonary HTN?

A

Lung transplant

164
Q

What is the V/Q ratio?

A

Ventilation : perfusion ratio

165
Q

V/Q distribution is regulated to maintain systemic oxygen partial pressure range between ___ to ___ mm Hg

A

85-100

166
Q

Distribution of V/Q ratios among the terminal respiratory units are ___, even in a normal lung

A

Not uniform

167
Q

A diseased lung’s V/Q ratios may be very ___

A

Nonuniform

168
Q

Alveolar-arterial (A-a) PO2 differences express…

A

The unequal match of V/Q ratio

169
Q

Normal (A-a) PO2 differences are…

A

10 to 15 mm Hg

170
Q

Larger (A-a) PO2 gradients indicate…

A

Intrinsic pulmonary disease —> shunting

171
Q

Hypoxemia with normal (A-a) PO2 gradient indicates…

A

Hypoventilation

172
Q

What is the most common cause of inefficient O2 and CO2 exchange?

A

Mismatched V/Q ratio

173
Q

What are two causes of abnormal (A-a) PO2 differences?

A
  • Wasted ventilation

- Venous admixture

174
Q

Shunt =

A

Perfused but NOT ventilated

175
Q

A right-to-left heart shunt is AKA as…

A

Pulmonary venous admixture

176
Q

What happens in a right-to-left heart shunt?

A
  • A portion of cardiac output (CO) flowing through pulmonary circulation does not participate in gas exchange
  • A fraction of blood flow bypasses the lung to enter the systemic arteries without becoming oxygenated, leading to venous admixtures
  • Reduction of systemic arterial oxygen tension and concentration
  • Reduce efficiency of gas exchange
177
Q

Are small shunts normal?

A

Yes—because some venous blood bypasses the lung to enter the left heart

178
Q

Examples of true anatomical shunts (4)

A
  • bronchopulmonary venous anastomoses
  • intracardiac thebesian veins
  • mediastinal veins
  • pleural veins
179
Q

Venous admixture is the blood flow equivalent of…

A

Wasted ventilation

180
Q

A left-to-right heart shunt is AKA…

A

Pulmonary venous recirculation

181
Q

What happens in a left-to-right heart shunt?

A
  • A portion of CO returns to the right heart without flowing through the body
  • This type of shunt does not affect systemic arterial oxygen tension
  • The oxygen tension in the right heart is increased
182
Q

What indicates the site of a L-to-R shunt?

A
  • The location of increased oxygen concentration

- Amount of change in PO2 allows estimate of the shunt

183
Q

What are two types of heart shunts?

A
  • Right-to-left heart shunt (pulmonary venous admixture)

- Left-to-right heart shunt (pulmonary venous recirculation)

KLowe Anesthesia Physiology 1: Respiratory (13 decks)

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