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Anaesthetic FRCA Primary - eLFH Physiology > eLFH - Respiratory Physiology Part 2 > Flashcards

eLFH - Respiratory Physiology Part 2 Flashcards

1
Q

Compliance definition

A

Volume change per unit change in pressure

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2
Q

Compliance equation

A

C = V / P

Compliance = Volume / Pressure

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3
Q

Units of compliance

A

ml/cmH2O

or

L/kPa

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4
Q

Measurement of compliance

A

Measured on pressure-volume (PV) graph

Gradient of line represents degree of compliance
Steeper gradient = greater compliance and easier for lungs to expand

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5
Q

Values for lung compliance

A

1.5 - 2 L/kPa

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6
Q

Values for chest wall compliance

A

1.5 - 2 L/kPa

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7
Q

Values for total thoracic compliance

A

0.75 - 1 L/kPa

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8
Q

How to add compliances together

A
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9
Q

Static compliance definition

A

Lung compliance when gas flow has ceased

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10
Q

Dynamic compliance definition

A

Lung compliance during the respiratory cycle while gas flow is ongoing

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11
Q

Which is higher, static compliance or dynamic compliance

A

Static compliance usually higher

There is time for pressure and volume to equilibrate

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12
Q

Why doesn’t Pressure-Volume (PV) curve start at zero

A

Lungs are never completely collapsed so always some volume present

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13
Q

Why are PV curves different for inspiration and expiration

A

Hysteresis

Lung volume during expiration always greater for a given pressure than during inspiration

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14
Q

On which part of PV curve does tidal breathing usually occur

A

The steepest pert of PV curve as this is where compliance is greatest so minimises work of breathing

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15
Q

Changes in compliance at different parts of the lung

A

Compliance at base of lung is better than apex of lung

Volume at base is lower due to gravitational effects but ventilates better

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16
Q

Factors which decrease lung compliance

A

Extremes of lung volumes
Atelectasis
Kyphoscoliosis
Vascular engorgement
Lung fibrosis
Pulmonary oedema

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17
Q

Factors which increase lung compliance

A

Surfactant
Old age
Emphysema

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18
Q

What causes surface tension

A

Forces of attraction between molecules at the gas / fluid interface

19
Q

Action of surface tension

A

Collapse down the alveoli

Smaller radius of alveolus, the greater the pressure collapsing the sphere

20
Q

Laplace’s Law

A

P = 2T / R

P = Pressure
T = Tension
R = Radius

Refers to collapsing pressure of alveoli

21
Q

Why does saline filled lung have greater compliance than air filled lung

A

Gas/fluid interface is removed and therefore surface tension is removed

22
Q

Composition of surfactant

A

Phospholipid dipalmitoylphosphatidylcholine (DPPC), protein and carbohydrate

23
Q

Production of surfactant

A

Produced by Type II pneumocytes
From free fatty acids extracted from blood

24
Q

Factor which can impact surfactant production

A

Lack of blood flow can affect surfactant production as it uses free fatty acids extracted from blood

25
Q

Functions of surfactant

A

Increases compliance

Preventing transudation of fluid into alveoli (pulmonary oedema)

Stabilising alveoli - preventing collapse

26
Q

How does surfactant increase compliance of alveoli

A

Profoundly reduces surface tension by disrupting attractive forces

DPPC have hydrophilic heads and hydrophobic tails
Hydrophilic ends line up in alveoli and repel each other

27
Q

When is surfactant most effective at reducing surface tension and why

A

At lower volume / smaller radius of alveoli as repulsive forces between DPPC molecules is greater

28
Q

Action of surfactant to stabilise alveoli - diagrams

A
29
Q

How does surfactant reduce transudation of fluid into the alveoli

A

By reducing surface tension

Surface tension tends to draw fluid into the alveolus from the capillary

30
Q

Work of breathing definition

A

Effort required to overcome:
- elastic forces in the lung
- resistance force from air flow and viscous resistance of tissue moving over tissue

31
Q

Elastic forces of lung in terms of energy

A

Energy stored as potential energy during inspiration and utilised during expiration

32
Q

Resistance force of air flow and viscous resistance of tissue on tissue in terms of energy

A

Extra energy is dissipated as heat during quiet breathing where expiration is passive from elastic recoil portion of energy stored

33
Q

How to measure work of breathing

A

Area under a pressure-volume curve

34
Q

Work done equation (used for work of breathing) and derivation

A

Work done = Change in pressure x Change in volume

Derivation in picture shown

35
Q

Proportion of work done during inspiration for spontaneous breathing

A

65% total work done during inspiration to overcome elastic forces

Stored as potential energy

36
Q

Proportion of work done during expiration for spontaneous breathing

A

35% total work done during expiration to overcome resistance forces
(28% airway resistance, 7% viscous tissue resistance)

Extra energy dissipated as heat

37
Q

Effect of RR on work done

A

As RR increases, work against resistance forces increases

38
Q

Effect of tidal volume on work done

A

As VT increases, work against elastic tissues increases

39
Q

Optimal RR for a given minute ventilation to minimise total work done

A

RR 14 - 16

40
Q

Effect of obstructive lung defects on optimal RR and VT to minimise work done

A

Obstructive lung disease increases work of resistance

Therefore lower RR and higher VT minimise work

41
Q

Effect of restrictive lung defects on optimal RR and VT to minimise work done

A

Restrictive lung disease increases elastic work

Therefore higher RR and lower VT minimise work

42
Q

Factors which increase work of breathing

A

Anything that increases the area under the pressure-volume curve:

Larger tidal volumes
Reduced compliance
Obstructive defects
Exercise - increases VT and RR

43
Q

How does GA increase work of breathing in spontaneously breathing patients

A

Reduced FRC - lung compliance decreased

Narrow ETT and circuits - increased airway resistance

Anaesthetic FRCA Primary - eLFH Physiology (13 decks)

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