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S1, R > Pulmonary blood flow, gas exchange and transport > Flashcards

Pulmonary blood flow, gas exchange and transport Flashcards

1
Q

What is the systemic arterial supply for lungs?

A

Bronchial circulation

It is nutritive for lungs, supplies oxygenated blood to airway smooth muscle, nerves and lung tissue

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2
Q

What are the flow and pressure characteristics of pulmonary circulation?

A
  • High flow

- Low pressure

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3
Q

Explain the flow of the pulmonary circulation

A
  • Entire cardiac output from RV
  • L and R pulmonary arteries take blood to lungs
  • Supplies dense capillary network surround the alveoli, gas exchange with capillaries and returns oxygenated blood to LA via pulmonary vein
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4
Q

Gas exchange in lungs

A
  • Gas will move across a membrane that is permeable to that gas, down it’s partial pressure gradient
  • Will continue until equilibrium is reached
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5
Q

Normal values of alveolar O2 and CO2 partial pressure

A

P_AO2: 100 mmHg, 13.3 kPa
P_ACO2: 40 mmHg, 5.3 kPa

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6
Q

Normal values for arterial O2 CO2 partial pressure

A

P_aO2: 100 mmHg, 13.3 kPa
P_aCO2: 40 mmHg, 5.3 kPa

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7
Q

Normal values for venous O2 and CO2 partial pressure

A

P_vO2: 40 mmHg, 5.3 kPa
P_vCO2: 46 mmHg, 6.2 kPa

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8
Q

Difference between partial pressure and gas content

A

Partial pressure: O2 in solution

Total gas content: oxygen wrapped in haemoglobin + oxygen in solution

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9
Q

Rate of diffusion across the membrane is

A
  • Directly proportional to the partial pressure gradient -> O2 has higher diffusion rate
  • Directly proportional to gas solubility -> CO2 is highly soluble
  • Directly proportional to the available surface area -> alveoli to red blood cell, have a large area
  • Inversely proportional to the thickness of the membrane -> thin membrane
  • Most rapid over short distances -> have a short diffusion distance, type II and elastic fibres
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10
Q

How gas exchange changes emphysema

A

Destruction of alveoli reduces surface area for gas exchange
PO_2 normal or low in alveolar cell
PO_2 low for arterial blood

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11
Q

How gas exchange changes in fibrotic lung disease

A
  • Thickened alveolar membrane slows gas exchange
  • Loss of lung compliance may decrease alveolar ventilation
  • PO_2 normal or low for alveoli
  • PO_2 low for arterial blood
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12
Q

How gas exchange changes in pulmonary oedema

A
  • Fluid in interstitial space increases diffusion distance
  • Impedes movement of gas, particular oxygen
  • Arterial PCO_2 may be normal due to higher CO2 solubility in water
  • Exchange surface normal
  • PO_2 normal in alveoli
  • Increased diffusion disance
  • PO_2 low in arterial blood
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13
Q

How gas exchange changes in asthma

A
  • Increase airway resistance decreases airway ventilation
  • Bronchioles constricted
  • PO_2 low in alveoli
  • PO_2 low in arterial blood
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14
Q

By how much does the oxygen carrying capacity increase due to haemoglobin

A

200ml/l (98% of oxygen)

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15
Q

How much oxygen dissolves per litre of plasma?

A

3ml

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16
Q

What is the structure of haemoglobin?

A

4 polypeptide chains, 2 alpha, 2 beta chains, each associated with an iron containing haem group

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17
Q

What are the different types of haemoglobin in red blood cells and what are the percentages?

A
  • 92% are HbA

- 8% are HbA2, HbF and glycosylated Hb (HbA1a, HbA1b, HbA1c)

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18
Q

What determines the degree of saturation of haemoglobin with oxygen?

A

Partial pressure of oxygen in arterial blood

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19
Q

What percentage of arterial oxygen is extracted by peripheral tissues at rest?

A

~25%

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20
Q

Oxyhaemoglobin disassociation curve, at what point does the saturation of haemoglobin start significantly dropping?

A
  • Partial pressure of oxygen can drop from PO2 100 mmHg to PO2 60 mmHg with very little effect
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21
Q

If the ventilation drops by less than 40%, how is the saturation of haemoglobin affected?

A
  • There is very little effect

- Haemoglobin has an extremely high affinity for oxygen

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22
Q

Why does the haemoglobin saturation go from having very little desaturation to a sudden drop?

A
  • Haemoglobin has a high affinity for oxygen

- However, once one oxygen starts to leave, then it is far more will start to leave

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23
Q

What’s the partial pressure of a resting cell?

A

40 mmHg

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24
Q

Factors that alter the oxyhaemoglobin disassociation curve

A
  • pH
  • pCO2
  • Temperature
  • BPG (chemical given off in hypoxic conditions, whether altitude or pathology)
  • Exercise
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25
Q

How is the oxygen disassociation curve affected by exercise?

A
  • pH decreases, acidosis
  • PCO2 increases
  • Temperature rises
  • Oxygen demand increases
  • Curve shift to right
  • Haemoglobin gives off more oxygen to accomodate demand and lower saturation
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26
Q

What factors decrease the affinity of haemoglobin for oxygen?

A
  • Decrease in pH
  • Increase in PCO2
  • Increase in temperature
  • Binding BPG
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27
Q

What is the role of BPG?

A

Helps maintain oxygen release of tissues with inadequate oxygen supply

28
Q

So what would happen in hypothermia to the affinity of haemoglobin for oxygen?

A

Haemoglobin’s affinity for oxygen would increase

29
Q

What has a higher affinity for O2, foetal haemoglobin and myoglobin or haemoglobin?

A

HbF and myoglobin as it is necessary for extracting O2 from maternal/arterial blood

30
Q

Where is myoglobin?

A

Mostly in oxidative muscle fibres, needs that oxygen affinity to work

31
Q

When does foetal haemoglobin leave during adult life?

A

Trick question, it remains in the blood during adult life

32
Q

What forms is CO2 carried in the blood and what quantities?

A
  • Dissolved in plasma and erythrocytes: 7%

- 93% moves into RBCs

33
Q

What does CO2 do once it moves into RBCs?

A
  • 23% binds with deoxyhaemoglobin to form carbamino compounds
  • 70% combine with water and forms carbonic acid -> dissociates to form bicarbonate and protons
34
Q

What happens to the CO2 when it forms carbonic acid?

A
  • Disassociated to form bicarbonate and protons
  • Most bicarb goes into the plasma, exchange for Cl- ions
  • Excess H+ bind to deoxyhaemoglobin
  • Lower pH, lower affinity of oxygen in haemoglobin
35
Q

What does carbonic annhdrase do in CO2 transport?

A
  • Speeds up the conversion of CO2 to bicarb and protons
36
Q

What is the ventilation-perfusion relationship?

A
  • Ideally ventilation (air getting into alveoli l/min) should match perfusion (local blood flow l/min)
37
Q

What is anaemia?

A
  • Any condition where the oxygen carrying capacity of the blood is compromised
  • Iron deficiency, haemorrhage, vitamin B12 deficiency
38
Q

What would happen to the P_aO2 in anaemia?

A
  • It would be normal, anaemia has no effect on ventilation or diffusion
  • The problem is total blood O2 content is low
39
Q

What determines the oxygen content of blood?

A
  • Amount of oxygen in haemoglobin, which is determined by the partial pressure
40
Q

What pressures is the distribution of blood flow influenced by?

A
  • Hydrostatic pressure (Pa)

- Alveolar pressure

41
Q

How does blood flow change over the lung?

A

It is indirectly proportional to vascular resistance and declines with height across the lung

42
Q

What is the flow of blood at the top of lung and why?

A
  • It lower at the apex
  • Arterial pressure is less than alveolar pressure and vascular resistance
  • The arterioles are compressed and vascular resistance is increased
43
Q

What is the flow of blood at the bottom of the lung and why?

A
  • It is higher at the bottom of the lung

- Arterial pressure exceeds alveolar pressure and vascular resistance

44
Q

What is the ventilation perfusion ratio at the apex?

A

> 1.0

  • More ventilation
  • This is where the majority of mismatch occurs
45
Q

What is the ventilation:perfusion ratio at the base and why?

A

< 1.0

- Blood flow has a greater influence on fluid exchange and flood flow is higher: perfusion dominates

46
Q

What percentage of the height of healthy lung performs well at matching blood and air?

47
Q

What unique property do pulmonary arterioles have in hypoxia?

A

They vasconstrict when in the systemic circulation, they dilate in hypoxia

48
Q

How does the body respond when ventilation < perfusion?

A
  • Hypoxia, pulmonary arterioles vasoconstrict
  • P_ACO2 increases and P_AO2 decreases
  • Blood flowing past doesn’t get oxygenated -> shunt
  • Underventilated arterolies constrict so blood is diverted to better ventilated alveoli
  • Increase in PCO2 causes mild bronchodilation
49
Q

How does the body respond when ventilation > perfusion?

A
  • Increased alveolar dead space
  • Increased P_AO2 -> pulmonary vasodilation
  • Decreased P_ACO2 -> bronchial constriction
  • Decrease in PaO2 in peripheries can lead to tachpnoea and dyspnoea if severe e.g. PE
50
Q

What is the definition of shunt?

A
  • Perfusion but no ventilation

- Blood flows from right side of heart to left side without being properly oxygenated

51
Q

What is the definition of alveolar dead space?

A
  • Ventilation but no perfusion

- Alveoli are ventilated but not perfused

52
Q

What is the definition of anatomical dead space?

A
  • Air in the conducting zone of the respiratory tract unable to participate in gas exchange
  • Walls of airways are too thick in these regions
53
Q

What is the definition of physiological dead space?

A

Alveolar dead space + anatomical dead space

54
Q

What are the five main types of hypoxia?

A
  1. Hypoxic hypoxia
  2. Anaemic hypoxia
  3. Ischaemic hypoxia
  4. Histotoxic hypoxia
  5. Metabolic hypoxia
55
Q

Hypoxic hypoxia

A
  • Most common

- Reduction in oxygen diffusion at lungs either due to decreased atmospheric oxygen or tissue pathology

56
Q

Anaemic hypoxia

A

Reduction of O2 carrying capacity of blood due to anaemia

57
Q

Ischaemic hypoxia

A
  • Heart disease, inefficient pumping of blood to lungs/around body
  • Cannot get O2 to tissues
58
Q

Histotoxic hypoxia

A
  • Poisoning prevents cells utilising oxygen delivered to them
  • E.g. carbon monoxide/cyanide
59
Q

Metabolic hypoxia

A
  • Oxygen delivery to the tissues does not meet increased oxygen demand by cells
  • e.g. someone unfit exercising beyond their fitness levels, tends to be quite transient
60
Q

What happens in carbon monoxide poisoning?

A
  • Binds to haemoglobin to become carboxyhaemoglobin
  • Has an affinity 250 times greater than O2
  • Binds readily and disassociates slowly
  • Only need 0.4 mmHg to cause progressive carboxyhaemoglobin formation
61
Q

What are the symptoms of carbon monoxide poisoning?

A
  • Hypoxia and anaemia, nausea and headaches
  • Cherry red skin and mucous membranes
  • RR is unaffected as normal PCO2
  • Potential brain damage and death
62
Q

What is the treatment for carbon monoxide poisoning/

A
  • 100% oxygen to increase PaO2

- Sometimes add CO2 to stimulate ventilation

63
Q

What is the acid-base balance equation?

A

CO2 + H2O H2CO3 HCO3 + H+

64
Q

What happens in the acid-base balance equation if CO2 increases?

A

H+ increases on the other side

65
Q

What happens in the acid-base balance in hypoventilation?

A
  • PCO2 will be retained and plasma H+ increases

- Results in respiratory acidosis

66
Q

What happens in the acid base balance in hyperventilation?

A
  • PCO2 falls and H+ falls

- Respiratory alkalosis occurs

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