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Cardiorespiratory > Lung Physiology > Flashcards

Lung Physiology Flashcards

1
Q

What is PaC02?

A

Arterial CO2

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2
Q

What is PACO2?

A

Alveolar CO2

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3
Q

What is PaO2?

A

Arterial O2

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4
Q

What is PAO2?

A

Alveolar O2

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5
Q

What is PiO2?

A

Pressure of inspired O2

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6
Q

What is VA?

A

Alveolar Ventilation

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7
Q

What are equations for CO2 elimination and oxygenation

A

PaCO2 = k v̇CO2 / v̇A

PAO2 = PiO2 – PaCO2/R (Alveolar Gas Equation)

R=Respiratory Quotient (approx 0.8)

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8
Q

What is the equation for carbonic acid equilibrium?

A

Carbonic acid equilibrium
CO2 + H2O  H2CO3  H+ + HCO3-

Carbonic anhydrase

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9
Q

What is the Henderson-Hasselbach equation?

A

pH=6.1 + log10[[HCO3-]/[0.03*PCO2]]

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10
Q

What is FEV1?

A

Forced expiratory volume in one second (litres)

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11
Q

What is FVC?

A

Forced Vital Capacity (litres)

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12
Q

How do you plot a graph for forced expiration?

A

Volume/Time plot

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13
Q

What is TLC?

A

Breathe in to total lung capacity

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14
Q

What is RV?

A

Exhale as fast as possible to residual volume

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15
Q

What is FVC?

A

Volume produced is the vital capacity

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16
Q

How to plot a forced expiration (flow/volume) graph?

A

Take the exact same procedure
Re plot the data showing flow as a function of volume
PEF; peak flow
FEF25; flow at point when 25% of total volume to be exhaled has been exhaled
FVC; forced vital capacity

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17
Q

What is PEF?

A

Peak expiratory flow (rate)

Single measure of highest flow during expiration
Peak Flow Meter, spirometer

Gives reading in L/min
Very effort dependent
May be measured over time, by giving a patient a PEF meter and chart

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18
Q

Give ways to measure RV and TLC?

A

Gas dilution
Body box (total body plethysmography; shown)

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19
Q

What is Gas Dilution?

A

Measurement of all air in the lungs that communicates with the airways

Does not measure air in non-communicating bullae

Gas dilution techniques use either closed-circuit helium dilution or open-circuit nitrogen washout.

Usually, the patient is connected at the end-tidal position of the spirometer, measuring FRC

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20
Q

What is the nitrogen-washout technique?

A

In the nitrogen-washout technique, the patient breathes 100% oxygen, and all the nitrogen in the lungs is
washed out.

The exhaled volume and the nitrogen concentration in that volume are measured.

The difference in nitrogen volume at the initial concentration and at the final exhaled concentration allows a calculation of intrathoracic volume, usually FRC.

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21
Q

What is total body plethysmography?

A

Alterative method of measuring lung volume, (Boyle’s law), including gas trapped in bullae.

From the FRC, patient “pants” with an open glottis against a closed shutter to produce changes in the box pressure proportionate to the volume of air in the chest.

The volume measured (TGV) represents the lung volume at which the shutter was closed

FRC, inspiratory capacity, expiratory reserve volume, vital capacity all measured

From these volumes and capacities, the residual volume and total lung capacity can be calculated.

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22
Q

What is the equation for Total Lung Capacity (TLC)?

A

TLC = VC+RV

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23
Q

Explain Transfer estimates?

A

Carbon monoxide used to estimate DLCO, as it has high affinity for binding to haemoglobin

DLCO is an overall measure of the interaction of;
- alveolar surface area
- alveolar capillary perfusion
- physical properties of the alveolar capillary interface
- capillary volume
- haemoglobin concentration, and the reaction rate of carbon - monoxide and hemoglobin.

Single 10 second breath-holding technique
10% helium, 0.3% carbon monoxide, 21% oxygen, remainder nitrogen.

Alveolar sample obtained;
DLCO is calculated from the total volume of the lung, breath-hold time, and the initial and final alveolar concentrations of carbon monoxide.

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24
Q

What is the compliance lung?

A

Compliance of the lung
Change in volume per unit change in pressure gradient between the pleura and the alveoli; (transpulmonary pressure)

Can be measured during breath-hold;
STATIC COMPLIANCE

Can be measured during regular breathing;
DYNAMIC COMPLIANCE

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25
Q

What is Static Compliance?

A

A measure of distensibility

A lung of high compliance expands more than one of low compliance when exposed to same trans-pulmonary pressure

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26
Q

What is Dynamic Compliance?

A

Measured during tidal breathing at end of inspiration and expiration when lung is apparently stationary

Similar to static compliance in normal lungs

Reduced compared to static compliance in airway obstruction

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27
Q

What is the requirement of respiration?

A

Requirement is to
- Ensure haemoglobin is as close to full saturation with oxygen as possible
- Efficient use of energy resource
- Regulate PaCO2 carefully
- variations in CO2 and small variations in pH can alter physiological function quite widely

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28
Q

What is Respiration?

A

Breathing is automatic
- No conscious effort for the basic rhythm
Rate and depth under additional influences
- Depends on cyclical excitation and control of many muscles
Upper airway, lower airway, diaphragm, chest wall
Near linear activity
Increase thoracic volume

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29
Q

Explain the basic breathing rhythm?

A

Pons
- Pneumotaxic and Apneustic Centres

Medulla Oblongata
- Phasic discharge of action potentials

Two main groups
- Dorsal respiratory group (DRG)
- Ventral respiratory group (VRG)

Each are bilateral, and project into the bulbo-spinal motor neuron pools and interconnect

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30
Q

What is DRG?

A

DRG; predominantly active during inspiration

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31
Q

What is VRG?

A

VRG; active in both inspiration and expiration

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32
Q

What is Central Pattern Generator?

A

Neural network (interneurons)

Located within DRG/VRG
- Precise functional locations not known
- Start, stop and resetting of an integrator of background ventilatory drive

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33
Q

Explain what happens in inspiration

A
  • Progressive increase in inspiratory muscle activation

Lungs fill at a constant rate until tidal volume achieved
End of inspiration, rapid decrease in excitation of the respiratory muscles

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34
Q

Explain what happens in expiration

A
  • Largely passive due to elastic recoil of thoracic wall

First part of expiration; active slowing with some inspiratory muscle activity

With increased demands, further muscle activity recruited

Expiration can be become active also; with additional abdominal wall muscle activity

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35
Q

What are chemoreceptors?

A
  • Central (60% influence from PaCO2) and peripheral (40% influence from PaCO2)
  • Stimulated by [H+] concentration and gas partial pressures in arterial blood
  • Brainstem [primary influence is PaCO2]
  • Carotids and aorta [PaCO2, PaO2 and pH]
  • Significant interaction
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36
Q

What is the general rule of minute ventilation?

A

Proportional to PaCO2 and 1 / PaO2

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37
Q

What are central chemoreceptors?

A
  • Central is located in brainstem
  • Pontomedullary junction
  • Not within the DRG/VRG complex
  • Sensitive to PaCO2 of blood perfusing brain
  • Blood brain barrier relatively impermeable to H+ and HCO3-
  • PaCO2 preferentially diffuses into CSF
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38
Q

Where are peripheral chemoreceptors found?

A

These are located in;
- Carotid bodies
Bifurcation of the common carotid
IX cranial nerve afferents
- Aortic bodies
Ascending aorta
Vagal nerve afferents

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39
Q

What are peripheral chemoreceptors?

A

Responsible for [all] ventilatory response to hypoxia (reduced PaO2)

Generally not sensitive across normal PaO2 ranges

When exposed to hypoxia, type I cells release stored neurotransmitters that stimulate the cuplike endings of the carotid sinus nerve

Linear response to PaCO2

Interactions between responses

[Poison (e.g. cyanide) and blood pressure responsive]

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40
Q

What are lung receptors?

A

Stretch, J and irritant
Afferents; vagus (X)
Combination of slow and fast adapting receptors
Assist with lung volumes and responses to noxious inhaled agents

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41
Q

What is a stretch lung receptor?

A

Stretch
- Smooth muscle of conducting airways
- Sense lung volume, slowly adapting

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42
Q

What is an irritant lung receptor?

A
  • Larger conducting airways
  • Rapidly adapting [cough, gasp]
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43
Q

What is an J; juxtapulmonary capillary lung receptor?

A
  • Pulmonary and bronchial C fibres
44
Q

What are the different types of airway receptors?

A

Nose, nasopharynx and larynx
- Chemo and mechano receptors
- Some appear to sense and monitor flow
Stimulation of these receptors appears to inhibit the central controller

Pharynx
- Receptors that appear to be activated by swallowing
respiratory activity stops during swallowing protecting against the risk of aspiration of food or liquid

45
Q

What are muscle proprioceptors?

A

Joint, tendon and muscle spindle receptors
Intercostal muscles > > diaphragm
Important roles in perception of breathing effort

46
Q

What is a spirometry?

A

Functional test of the lungs.

The most important spirometry test is the FVC (Forced Vital Capacity).

Other tests include the CV (Vital Capacity or Slow Vital Capacity) and MVV (Maximum Voluntary Ventilation).

47
Q

What is Forced Vital Capacity?

A

The Forced Vital Capacity consists of a forced expiration in the spirometer.

The patient either sits or stands.
He inspires fully and expires all the air out of the lungs as fast as he can.

The results of the test are compared to the predicted values that are calculated from his age, size, weight, sex and ethnic group.

Two curves are shown after the test: the flow-volume loop and volume-time curve.

48
Q

How much does a healthy patient expire in the first second during the FVC manoeuvre?

A

Approximately 80% of all the air out of their lungs

49
Q

What is a Slow Vital Capacity?

A

This test resembles the FVC.
The difference is that the expiration in the spirometer is done slowly.

The patient inspires fully and than slowly expires all the air in his lungs (Inspiratory Vital Capacity) or the other way around: the patient expires fully and inspires slowly to a maximum (Expiratory Vital Capacity).

50
Q

How much of the lung capacity is residual volume?

A

About 20-25% of lung capacity

51
Q

What is Maximum Voluntary Ventilation?

A

For this test the patient inspires and expires in the spirometer over and over again as fast as he can, during at least 12 seconds.

This is no longer a very common test as it can be dangerous for some people.
Sometimes the MVV is still done in athletes.

52
Q

What is respiratory failure?

A

Failure of gas exchange
Inability to maintain normal blood gases
Low PaO2
With or without a rise in PaCO2

Respiratory failure can occur with normal or abnormal lungs

53
Q

What are the different types of respiratory failure?

A

Acute, rapidly
- For example; opiate overdose, trauma, pulmonary embolism

Chronic, over a period of time
- For example; COPD, fibrosing lung disease

54
Q

What is a respiratory quotient?

A

Ratio of the volume of carbon dioxide (CO2) produced to the volume of oxygen (O2) used

55
Q

What is Type 1 Respiratory Failure?

A
  • Most pulmonary and cardiac causes produce type I failure
  • Hypoxia
    Mismatching of ventilation and perfusion
    Shunt
    Diffusion impairment
    Alveolar hypoventilation

Similar effects on tissues seen with
Anaemia
CO poisoning
methaemoglobinaemia

56
Q

What are cases of Type 1 Respiratory Failure?

A
  • Infection
    Pneumonia
    Bronchiectasis
  • Congenital
    Cyanotic congenital heart disease
  • Neoplasm
    Lymphangitis carcinomatosis
  • Airway
    COPD
    Asthma
  • Vasculature
    Pulmonary embolism
    Fat embolism
  • Parenchyma
    Pulmonary fibrosis
    Pulmonary oedema
    Pneumoconiosis
    Sarcoidosis
57
Q

What are mechanisms of Type 2 Respiratory Failure?

A

Mechanisms
(i) Lack of respiratory drive
(ii) Excess workload
(iii) Bellows failure

58
Q

What are the causes of Type 2 Respiratory Failure?

A
  • Airway
    COPD
    Asthma
    Laryngeal oedema
    Sleep apnoea syndrome
  • Drugs
    Suxamethonium
  • Metabolic
    Poisoning
    Overdose
  • Neurological
    Central
    Primary hypoventilation
    Head and Cervical spine injury
  • Muscle
    Myasthenia
    Polyneuropathy
    Poliomyelitis
    Primary muscle disorders
59
Q

Clinical Features of Hypoxia

A
  • Central Cyanosis
    Oral cavity
    May not be obvious in anaemic patients
  • Irritability
  • Reduced intellectual function
  • Reduced consciousness
  • Convulsions
  • Coma
  • Death
60
Q

Clinical Features of Hypercapnia

A
  • Variable patient to patient
  • Irritability
  • Headache
  • Papilloedema
  • Warm skin
  • Bounding pulse
  • Confusion
  • Somnolence
  • Coma
61
Q

What is treatment for Type 2 respiratory failure?

A

Assisted ventilation
Invasive
Non invasive

Inadequate PaO2 despite increasing FiO2
Increasing PaCO2
Patient tiring

62
Q

What are oxygen treatments?

A

Treatment for serious illnesses needing high levels of O2

5-10 litres/min face mask or 2-6 litres/min nasal cannulae
Aim for SpO2 of 94-98%
If saturation <85% and not at risk of hypercapnic respiratory failure
10-15 litres/ min reservoir mask
Patients with COPD and other risk factors for hypercapnia;
Aim for SpO2 of 88-92% pending blood gases
Adjust to SpO2 of 94-98% if CO2 normal unless previous history of high CO2 or ventilation

63
Q

What is the requirement of the respiratory pump?

A

Requirement to move 5 litres / minute of inspired gas [cardiac output 5 litres / min]

64
Q

What is the respiratory pump?*

A

Generation of negative intra-alveolar pressure
Inspiration active requirement to generate flow
Bones, muscles, pleura, peripheral nerves, airways all involved.

Bony structures support respiratory muscles and protect lungs.
Rib movements; pump handle and water handle

65
Q

What are the muscles used in respiration?

A

Muscles of respiration
- Inspiration
Largely quiet and due to diaphragm (C3/4/5) contraction
External intercostals (nerve roots at each level)

  • Expiration
    Passive during quiet breathing
66
Q

What is the pleura?

A

Pleura
- 2 layers, visceral and parietal
- Potential space only between these, few millilitres of fluid

67
Q

What nerves are used in the respiratory pump?

A

Nerves
- Sensory;
Sensory receptors assessing flow, stretch etc..
C fibres
Afferent via vagus nerve (10th cranial nerve)
- Autonomic sympathetic, parasympathetic balance

68
Q

What is meant by static lungs?

A

Both chest wall and lungs have elastic properties, and a resting (unstressed) volume

Changing this volume requires force
Release of this force leads to a return to the resting volume.
Pleural plays an important role linking chest wall and lungs.

69
Q

What is Ventilation?

A

VENTILATION; Bulk flow in the airways allows;
O2 and CO2 movement
Large surface area required, with minimal distance for gases to move across. Total combined surface area for gas exchange 50-100 m2
300,000,000 alveoli per lung

70
Q

What is perfusion?

A

PERFUSION; Adequate pulmonary blood supply also needed

71
Q

What is alveolar ventilation?

A

Dead space
Volume of air not contributing to ventilation

Anatomic; Approx 150mls
Alveolar; Approx 25mls

Physiological
(Anatomic+Alveolar) = 175mls

72
Q

What is bronchial circulation? *

A

Blood supply to the lung; branches of the bronchial arteries

Paired branches arising laterally to supply bronchial and peri-bronchial tissue and visceral pleura

Systemic pressures (i.e. LV/aortic pressures)

Venous drainage; bronchial veins draining ultimately into the superior vena cava

73
Q

What is pulmonary circulation?

A

Left and right pulmonary arteries run from right ventricle
Low(er) pressure system (i.e. RV / pulmonary artery pressures)

17 orders of branching
Elastic (>1mm ) and non elastic
Muscular (<1mm )
Arterioles (<0.1mm )
Capillaries

74
Q

What is the broncho-vascular bundle?

A

Pulmonary artery and bronchus run in parallel

75
Q

What is the normal pulmonary artery pressure?

A

24mm/10mm

76
Q

How many capillaries are there per alveolus?

A

1000

77
Q

What is alveolar perfusion?

A

Each erythrocyte may come into contact with multiple alveoli

Erythrocyte thickness an important component of the distance across which gas has to be moved
At rest, 25% the way through capillary, haemoglobin is fully saturated

78
Q

What does perfusion of the capillaries depend on?

A

Pulmonary artery pressure
Pulmonary venous pressure
Alveolar pressure

79
Q

What is hypoxic pulmonary vasoconstriction?

A

A homeostatic mechanism that is intrinsic to the pulmonary vasculature

Intrapulmonary arteries constrict in response to alveolar hypoxia, diverting blood to better oxygenated lung segments, thereby optimizing ventilation/perfusion matching and systemic oxygen delivery

80
Q

What is meant by perfusion?

A

Blood Supply

81
Q

What is meant by little a in nomenclature?

A

Arterial

82
Q

What is meant by big A in nomenclature?

A

Alveolar

83
Q

Why is it important for the body to maintain pH?

A

Body maintains close control of pH to ensure optimal function (e.g. enzymatic cellular reactions)

Dissolved CO2/carbonic acid/respiratory system interface crucial to the maintenance of this control

84
Q

What is normal pH level in the body?

A

7.40

84
Q

What is normal H+ body concentration?

A

40nmol/l [34-44 nmol/l]

85
Q

Explain the sigmoid shape in the O2Hb dissociation curve?

A

As each O2 molecule binds, it alters the conformation of haemoglobin, making subsequent binding easier (cooperative binding)

86
Q

What are the varying influences of O2/Hb dissociation curve?

A

2,3 diphosphoglyceric acid
H+
Temperature
CO2

87
Q

What buffer is particular important?

A

Carbonic acid / bicarbonate buffer

88
Q

What is HCO3- under predominant control of?

A

Renal Control (less rapid)

89
Q

What is CO2 under predominant control of?

A

Respiratory Control (rapid)

90
Q

What are the 4 main acid-base disorders?

A

Respiratory acidosis
Respiratory alkalosis
Metabolic acidosis
Metabolic alkalosis

91
Q

What is respiratory acidosis?

A

Increased PaCO2
Decreased pH
Mild increased HCO3-

92
Q

What is respiratory alkalosis?

A

Decreased PaCO2
Increased pH
Mild decreased HCO3-

93
Q

What is metabolic acidosis?

A

Reduced bicarbonate
Decreased pH

94
Q

What is metabolic alkalosis?

A

Increased bicarbonate
Increased pH

95
Q

What do expiratory procedures measure?

A

Only measure VC not RV

96
Q

Where are central chemoreceptors located?

A

Brainstem
- Pontomedullary junction
- Not within the DRG/VRG complex

97
Q

What are central chemoreceptors sensitive to?

A
  • Sensitive to PaCO2 of blood perfusing brain
  • Blood brain barrier relatively impermeable to H+ and HCO3-
  • PaCO2 preferentially diffuses into CSF
98
Q

Where are peripheral chemoreceptors located?

A
  • Carotid bodies
    Bifurcation of the common carotid
    (IX) cranial nerve afferents
  • Aortic bodies
    Ascending aorta
    Vagal (X) nerve afferents
99
Q

What are peripheral chemoreceptors?

A

Responsible for [all] ventilatory response to hypoxia (reduced PaO2)

Generally not sensitive across normal PaO2 ranges

When exposed to hypoxia, type I cells release stored neurotransmitters that stimulate the cuplike endings of the carotid sinus nerve

100
Q

What type of response do peripheral chemoreceptors have to PaCO2?

A

Linear Response

Interactions between responses
[Poison (e.g. cyanide) and blood pressure responsive]

101
Q

What is respiratory failure?

A

Inability to maintain normal blood gases

102
Q

What is Hypoxemia?

A

Below normal level of O2 in blood
PaO2 less than 8kPa

103
Q

What is Hypercapnia?

A

Too much CO2 in the blood
More than 6.5kPa

104
Q

What is Type 1 respiratory failure?

A

Hypoxia
Low/Normal CO2

105
Q

What is Type 2 respiratory failure?

A

Hypoxia
Hypercapnia

106
Q

What are treatments for Type 1 resp failure?

A

Airway Patency
Oxygen Delivery

Cardiorespiratory (27 decks)

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