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Case 5 > Pulmonary Circulation and Lung Disease- an Overview > Flashcards

Pulmonary Circulation and Lung Disease- an Overview Flashcards

1
Q

What is the primary function of the pulmonary circulation

A

To bring venous blood into contact with the alveoli to facilitate gas exchange

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2
Q

What are the secondary functions of the pulmonary circulation

A

protect the body from thrombi/ emboli; metabolism vasoactive substances- angiotensin I (via ACE) to angiotensin II blood reservoir (500ml/10%) mobilised in shocked states

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3
Q

How does deoxygenated blood travel to the right atrium

A

Via systemic system

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4
Q

Describe the pulmonary circulatory system

A

Carries the same volume of blood as the systemic system but at much lower pressure

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5
Q

Describe resistance in the pulmonary circulation

A

High flow low pressure circuit= low resistance

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6
Q

What is pressure in the pulmonary ertery

A

25/8 compared to blood pressure in the aorta which is 120/70

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7
Q

Describe pulmonary artery/ arterioles

A

Deoxygenated blood, thinner walls than the aorta and more compliant, shorter containing less elastin and smooth muscle thus less ability to constict than thick walled muscular systemic arterioles

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8
Q

Describe pulmonary capillaries

A

Unlike systemic cap’s frequently arranged as a network of tubular vessels with some interconnections. Mesh network together in the alveolar wall- blood flow as a ‘single sheet’. Cap walls are exceedingly thin. More of a dense cap bed than a network, whole cap bed can collapse if local alevolar pressure exceeds cap pressure

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9
Q

What does the fine meshwork of capillaries around each alveoli result in

A

An increase in surface area for gas exchange

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10
Q

What happens when you stand up

A

There is hydrostatic pressure resulting in regional perfusion, therefore there is higher blood flow at the base of the lungs

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11
Q

Why do hydrostatic pressure have much stronger influences on pulmonary blood flow

A

Pulmonary circulation is low pressure

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12
Q

Describe the pressures in an area with no flow

A

Alveolar pressure > pulmonary artery pressure > pulmonary venous pressure

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13
Q

What is PA

A

Alveolar pressure

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14
Q

What is Pa

A

Pulmonary artery pressure

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15
Q

What is Pv

A

Pulmonary venous pressure

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16
Q

Describe the pressures in an area with pulsatile flow

A

Pulmonary artery pressure > alveolar pressure > pulmonary venous pressure

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17
Q

Describe the pressures in an area with continuous flow

A

Pulmonary artery pressure > pulmonary venous pressure > alveolar pressure

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18
Q

Explain the pressures observed in the lung

A

Alveolar pressure (PA) at end expiration is equal to atmospheric pressure (0 cm H20 differential pressure, at zero flow), plus or minus 2 cm H2O (1.5 mmHg) throughout the lung. On the other hand gravity causes a gradient in blood pressure between the top and bottom of the lung of 20 mmHg in the erect position (roughly half of that in the supine position). Overall, mean pulmonary venous pressure is ~5 mmHg. Local venous pressure falls to -5 at the apexes and rises to +15 mmHg at the bases, again for the erect lung. Pulmonary blood pressure is typically in the range 25 - 10 mmHg with a mean pressure of 15 mmHg. Regional arterial blood pressure is typically in the range 5 mmHg near the apex of the lung to 25 mmHg at the base

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19
Q

When is no flow observed (Zone 1)

A

Not observed in a normal healthy human lung. In normal health pulmonary arterial pressure exceeds alveolar pressure in all parts of the lung. It is generally only observed when a person is ventilated with positive pressure. In these circumstances blood vessels can become completely collapsed by alveolar pressure and blood does not flow through these regions. They become alveolar dead space

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20
Q

When does pulsatile flow occur (Zone 2)

A

Part of the lungs about 3cm above the heart. In this region blood flows in pulses. At first there is no flow because of obstruction at the venous end of the capillary bed. Pressure from the arterial side builds up until it exceeds alveolar pressure and flow resumes. The dissipates the capillary pressure and returns to the start of the cycle

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21
Q

When does continuous flow (Zone 3) occur

A

Comprises the majority of the lungs in health. There is no external resistance to blood flow and blood flow is continuous throughout the cardiac cycle

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22
Q

In which zone is the ventilation perfusion ratio higher when a person is standing

A

Zone 1 than zone 3. If you increase pressure to the lungs too much you turn off blood flow to the lungs and therefore worsen hypoxia

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23
Q

What does regional ventilation mean

A

The lower parts of the lung (base) are better ventilated than the top part (apex)

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24
Q

What are the lungs supported by

A

Only the hilum

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25
Q

What intrapleural pressure exists at the apex of the lungs

A

Negative intrapleural pressure

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26
Q

Why are the alveolar at the apex larger

A

Because there is negative intrapleural pressure at the base of the lungs

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27
Q

What happens to the alveoli when you take a deep breath

A

The alveolar at the base get much bigger as more air goes to the base

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28
Q

Describe intrapleural pressure

A

It is always below atmospheric pressure during both inspiration and expiration

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29
Q

Describe intrapleural pressure gradients

A

Exist from the upper lung region to the lower lung region

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30
Q

What are the changes in intrapleural pressure due to

A

gravity, distribution of weight in the lungs, lungs are suspended at the hilum, lung base weighs more than the apex (increased blood flow), greater negative pressure in the upper regions causes the alveoli in those areas to be more expanded than alveoli in the lower regions, many alveoli are close to or at their total filling capacity

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31
Q

Compare the compliance of alveoli in the upper and lower regions

A

Compliance of alveoli in the upper regions is lower than compliance of the alveoli in the lower regions

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32
Q

Where is ventilation much greater and more effective

A

In the lower lung regions

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33
Q

What is a normal V/Q ratio

A

0.8-1.2 ventilation/ perfusion ratio

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34
Q

What is alveolar minute ventilation

A

4-6 L

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35
Q

What is normal cardiac output

A

5 L (500ml per tidal volume)

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36
Q

What does Va/Q determine

A

The gas exchange in a single unit

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37
Q

What do regional differences in Va/Q ratio cause

A

A pattern of regional gas uptake

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38
Q

What does Va/Q inequality impair

A

Uptake or elimination of gases

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39
Q

Where are blood flow and ventilation higher

A

At the base of the lung than the apex

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40
Q

What happens as blood flow increases

A

There is a decrease in resting lung therefore the mismatch is greater

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41
Q

What is hypoxaemia

A

An abnormally low concentration of oxygen in the blood

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42
Q

What are the 4 causes of hypoxaemia

A

Hypoventilation, diffusion limitation, shunt, Va/Q inequality

43
Q

What is a capillary shunt

A

There is an issue present with the alveolus itself e.g. pneumonia

44
Q

What does pulmonary fibrosis mean

A

There is a thickening of the alveolar membrane which presents as a shunt-like effect

45
Q

What happens in pulmonary embolism

A

Ventilation is not affected but there is hypoxia so the blood is blocked by the embolism resulting in hypoxia

46
Q

What happens in bronchospasm

A

There is a mismatch between ventilation and perfusion resulting in hypoxia

47
Q

What happens in bronchoconstriction

A

There is gas trapping resulting in dynamic hyperinflation resulting in a barrel chest as you can’t get air out. Gas trapping results in rapid accumulation of carbon dioxide as there is no gas exchange taking place

48
Q

Describe the pressure of the systemic system

A

High pressure system, mean systemic pressure 70-105 mmHg, easily measured

49
Q

Describe the pressure of the systemic system

A

Low pressure system, mean pulmonary pressure 10-22 mmHg, estimated via ECHO, directly measured with pulmonary artery pressure

50
Q

Why do we estimate rather than measure pulmonary pressure

A

Very invasive to directly measure pulmonary artery pressure, therefore we use ECHO to estimate it

51
Q

What is used to directly measure pulmonary artery pressure

A

Swan-Ganz catheter

52
Q

What is PCW

A

Pulmonary capillary wedge pressure. PCW is an estimate of pressure in the left atrium

53
Q

What does PCW pressure record changes in

A

Pulmonary venous pressure and left atrium pressure which has profound effects on gas exchange

54
Q

What happens if the left side of the heart is failing

A

There is an increase in pulmonary capillary wedge pressure resulting in fluid leaking out into the interstitial space which decreases the distance over which gas exchange occurs and decreases the area available for gas exchange as the alveoli are filled with fluid

55
Q

What do you do when a person has pulmonary oedema

A

You give them oxygen to help improve gas exchange and diuretic to get rid of excess fluid which decreases the amount of fluid around the lungs and reduces the issues of increased distance for gas exchange and reduced surface area

56
Q

What is Type I ventricular failure

A

An issue with oxygen but not carbon dioxide levels, carbon dioxide is 19x more soluble than oxygen, therefore in a hypoxic state you have normal carbon dioxide levels

57
Q

What does pulmonary hypertension result in

A

Overloading the right ventricle which can result in sudden cardiac death

58
Q

Describe vascular remodelling in pulmonary arterial hypertension

A

Smooth muscle proliferation/ fibroid necrosis and narrowing of the lumen ultimately leads to right heart failure and death

59
Q

What does pulmonary vascular resistance equal

A 
PVR= mPAP-PCWP/ cardiac output
mPAP= mean pulmonary arterial pressure
PCWP= pulmonary capilliary wedge pressure
60
Q

How do you work out mPAP

A

(cardiac output x pulmonary vascular resistance) x PCWP

61
Q

What changes happen to the right ventricle in pulmonary arteriole hypertension

A

Thickening of the membrane, breakdown of elastin, decrease in radius therefore increase in resistance and in situ microthrombi which creates resistance to blood flow

62
Q

What does the thickened right ventricular wall in pulmonary hypertension result in

A

You get a thickened right ventricular wall and the intraventricular septum bows into the left ventricle meaning that the blood pressure in the pulmonary system is higher than in the systemic system

63
Q

What happens when the pressure in the pulmonary system becomes greater than the pressure in the systemic system

A

Poses a significant risk of heart failure and death

64
Q

Define PAH

A

mPAP >25 mmHg at rest (or > 30 mmHg with exercise) with normal PCWP (240 fynes/s/cm5)

65
Q

How can the diagnosis of PAH be made

A

With right heart catheterisation

66
Q

Describe the management of pulmonary hypertension

A

‘Targeted therapies’: prostanoid analogues, enothelin receptor antagonists (ERAs), phosphdiesterase-5 (PDE-5) inhibitors. Manage via inhibition. Viagra was used for management as it was designed as a blood pressure tablet. Use warfarin to prevent in situ microthrombi

67
Q

What can you do if you treat PAH early

A

You can stop vascular remodelling and vasoconstriction

68
Q

What is the diagnosis of PAH

A

Now 8 years, used to be 2. Class also correlates to survival: triple theraphy has increased LE

69
Q

Describe cor pulmonale

A

Enlargement and failure of the right ventricle as a response to increased vascular resistance or high lung blood pressure. In cor pulmonale there is an issue with the pulmonary circulatory system meaning that the right ventricle can’t keep up with the work and you get right side heart failure

70
Q

In order to be classed as cor pulmonale where must the cause originate

A

In the pulmonary circulation system

71
Q

What are the two major causes of cor pulmonale

A

a) tissue damage leading to vascular changes e.g. disease, chemical agents etc. b) hypoxic pulmonary vasoconstriction

72
Q

Describe the pathophysiology of cor pulmonale

A

Pulmonary vasoconstriction, anatomical changes in vasculature, increased blood viscocity, idiopathic or primary pulmonary hypertension

73
Q

Compare left and right side heart failure

A

Left side heart failure results in pulmonary oedema. Right side heart failure results in peripheral oedema and raised JVP

74
Q

What are the signs and symptoms of cor pulmonale

A

SOB which occurs on exertion but when severe can occur at rest, cyanosis, ascites, swelling of the ankles and feet (peripheral oedema), enlargement or prominent neck and facial veins, raised JVP. You get fluid overload of the systemic circulatory system

75
Q

What is the treatment of cor pulmonale

A

Elimination of irritant e.g. smoking, correct hypoxia, diuretics

76
Q

Describe pulmonary vascular resistance

A

RV pumps mixed venous blood through pulmonary arterial tree. All cardiac output (5L/min) pumped through at a much lower pressure. 10mmHg gradient pulmonary, 100mmHg gradient systemically. Low pulmonary pressure allows blood to flow through the lungs. Pulmonary vascular resistance (PVR) is low- 1/10 of systemic vascular resistance (SVR)

77
Q

Why is PVR normally so low

A

R= 8ηl/ πr4 where η= viscosity, l= vessel length, r= vessel radius. Therefore, small changes in radius result in a large change in resistance. An increase in radius by 1 would result in an increase in resistance by 16

78
Q

What happens to capillaries when you breath in

A

They become more circular as there is an increase in radius and a decrease in resistance

79
Q

What happens to capillaries when you breathe out

A

They become less circular as there is a decrease in radius and an increase in resistance

80
Q

What happens as you increase pressure in the lungs

A

Decrease in pulmonary vascular resistance. These changes are able to occur due to a redundancy in the lung capillary bed

81
Q

What does an increase in cardiac output result in

A

Recruitment of capillaries not being used and therefore distention. As radius of blood vessels increases there is a decrease in pulmonary resistance which promotes blood flow. A decrease in pulmonary vascular resistance means that gas exchange is maintained (such as during exercise). Pressure changes that occur are unique to pulmonary circulation

82
Q

What does an increase in perfusion pressure cause in systemic circulation

A

An increase in SVR

83
Q

Why is PVR normally so low

A

Resting conditions some capillaries are partially or completely closed (especially at top of lungs) because of low perfusion pressure. Primary cause for decrease in PVR as CO increases. As blood flow increases pressure rises and closed vessels open lowering PVR
Secondary cause is distension due to the fact that capillaries are thin walled and highly compliant

84
Q

Why is a low PVR useful

A

A fall in PVR as CO increases opposes the tendency of blood velocity speeding up with increased flow rate maintaining adequate time for gas exchange. Increased surface area for gas exchange. Protective effect against pulmonary oedema (pulmonary oedema is an abnormal collection of fluid in alveolar space impairing gas exchange)

85
Q

Describe what happens during exercise

A

CO 5L/min to 25L/min. Without recruitment/ distension rise in CAP pressure which leads to fluid shifts out of the CAP into the alveolar space which minimises the load on the RV. As a result there is a decrease in pulmonary vascular resistance so gas exchange can be maintained during exercise

86
Q

What does the fact that the left ventricle is cylindrical in shape mean

A

It is better at pumping out blood at a high pressure

87
Q

What is regulatory mechanism of hypoxia in the systemic circulation

A

Local vasodilation

88
Q

What is regulatory mechanism of hypoxia in the pulmonary circulation

A

Local vasoconstriction (alveolar hypoxia/ blood hypoxemia)

89
Q

What is regulatory mechanism of raised CO2 in the systemic circulation

A

Local vasodilation

90
Q

What is regulatory mechanism of raised CO2 in the pulmonary circulation

A

Local vasoconstriction

91
Q

What is regulatory mechanism of low pH in the systemic circulation

A

Local vasodilation

92
Q

What is regulatory mechanism of low pH in the pulmonary circulation

A

Local vasoconstriction

93
Q

What does an increase in PO2 resultin

A

A dramatic increase in blood flow

94
Q

What does the pulmonary circulation have to allow regional adaptation of blood flow to reduced ventilation

A

Small precaps and post caps of lungs

95
Q

Which PO2 determines blood flow

A

Alveolar PO2 not arterial PO2

96
Q

What are the beneficial effects systemically of alveolar PO2 determining blood flow

A

diversion of blood to hypoxic, hypercarbic acidic tissue, high risk of tissue death

97
Q

What are the beneficial effects pulmonary of alveolar PO2 determining blood flow

A

Diversion of blood flow away from poorly ventilated areas (hypoxic) to areas well ventilated, improves gas exchange

98
Q

Describe generalised hypoxa

A

(severe COPD, severe pulmonary fibrosis, high altitude) results in vasoconstriction throughout the lungs which results in worse gas exchange and is detrimental

99
Q

Describe regional hypoxic pulmonary vasoconstriction

A

One-lung ventilation is a common clinical example of regional HPV. HPV in the hypoxic atelectatic lung causes a redistribution of blood flow away from the hypoxic lung to the normoxic lung, thereby diminishing the amount of shunt flow (QS/QT) that can occur through the hypoxic lung. Inhibition of hypoxic lung HPV causes an increase in the amount of shunt flow through the hypoxic lung, thereby decreasing PaO2. Vasoconstriction throughout leading to rise PVR leads to PH and pathophysiological changes in pulmonary blood vessel

100
Q

What happens if ventricles fail

A

The heart fails and there is a decrease in PAP

101
Q

Describe WHO Class I PAH

A

Symptoms do not limit physical activity. Ordinary physical activity does not cause undue discomfort

102
Q

Describe WHO Class II PAH

A

Slight limitation of physical activity. The patient is comfortable at rest, yet experiences symptoms with ordinary physical activity

103
Q

Describe WHO Class III PAH

A

Marked limitation of physical activity. The patient is comfortable at rest, yet experiences symptoms with minimal physical activity

104
Q

Describe WHO Class IV PAH

A

Inability to carry out any physical activity. The patient may experience symptoms even at rest. Discomfort is increased by any physical activity. These patients manifest signs of right heart failure

Case 5 (8 decks)

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