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Medicine block 2 > Mechanisms of Breathing > Flashcards

Mechanisms of Breathing Flashcards

1
Q

How does the lung expand?

A

Muscle work, chest wall expansion + changes in pleural pressure (+ve pressure - blows air in, -ve pressure - sucks air in)

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2
Q

How does air move into the lung?

A

Air moves by bulk flow down a pressure gradient from positive atmospheric to more negative airway pressure created by lung expansion

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3
Q

What provides resistance to air flow?

A
  1. Diameter

2. Contents

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4
Q

What is the difference in effort required for inhalation and exhalation in quiet breathing?

A 
Inhalation = active process, requires muscular work
Exhalation = passive force provided by stretched elastic lung tissue
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5
Q

Why do you need the pleural space?

A

Provides lubrication

Enables transfer of expansile force to lungs

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6
Q

What thoracic muscles are used for breathing?

A
  1. External intercostals - elevate ribs + increase both anteroposterior + L/R dimensions (up + out)
  2. Diaphragm - depressed during contraction
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7
Q

What is the diaphragm? How is it innervated?

A

Principal muscle of respiration.

Innervation = phrenic nerve C3,4,5

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8
Q

Define the term ‘Work of Breathing’.

A

Energy expended during respiration

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9
Q

What are the 3 components for Work of Breathing?

A
  1. Compliance/elastic work - energy required to expand lungs against lung + chest elastic forces
  2. Tissue resistance work - energy required to overcome viscosity of lung + chest wall structures
  3. Airway resistance work - energy require to overcome airway resistance to move air into lungs
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10
Q

What happens in quiet breathing?

A
  1. Inhalation is active - lungs pulled open by muscle action against elastic tissues promoting recoil + resistance of airways to airflow (main component of Work of Breathing)
  2. Exhalation is passive - lungs return due to elastic recoil to functional residual capacity where opposing elastic forces of lung + chest wall are balanced
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11
Q

What are the muscles involved in breathing?

A
  1. Internal intercostals (extra cartilaginous portion) - move ribs down
  2. External intercostals - move ribs up + enlarge ribcage volume
  3. Internal intercostals (intra cartilaginous portions) - move ribs up
  4. Abdominal muscles - rectus abdomens, internal + external oblique, transverses abdomens - contract + increase intraabdominal pressure, pushing diaphragm up
  5. Diaphragm
  6. Scalenes - elevates 1st 2 ribs
  7. Sternocleidomastoid - raise sternum
  8. Pectoral girdle muscles
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12
Q

Which muscles are involved in inhalation and forced exhalation?

A

Inhalation:

  • Scalenes = elevate 1st and 2nd rib
  • Sternocleidomastoid = raises sternum
  • External intercostals = move ribs up + enlarge ribcage volume
  • Intercartilaginous internal intercostals = move ribs up + enlarge ribcage volume
  • Diaphragm

Forced Exhalation:

  • Abdominal muscles
  • Extracartilaginous internal intercostals = move ribs down
  • Pectoral girdle muscles
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13
Q

What is Functional Residual Capacity?

A

Lung volume at which opposing forces of expansile skeletal structure of chest wall (muscles at rest) and contractile lung are balanced (equilibrium volume)

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14
Q

Lungs and chest wall have different recoil properties. What are they? Why does the pleural space help with this?

A

Lungs want to collapse in
Chest wall wants to expand out

Pleural space allows 2 joined structures to move together - acts as seal that allows lungs to expand with chest

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15
Q

What type of pleura is associated with the lungs? Where is it attached?

A

Visceral pleura = attached to lung surface

Parietal pleura = attached to chest wall

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16
Q

What is the pleural space?

A

Tiny space between visceral and parietal pleura filled with thin layer of pleural fluid.
Lubricates pleural interface + provides a seal

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17
Q

What is the pressure within the pleura space?

A

2 forces opposing each other there is negative pressure (-0.5kPa)

During inhalation, chest wall is expanded and as pleural space stretches the intrapleural pressure decreases further
Because of pleural seal, suction on visceral pleura + attached lung causes lung to expand with chest wall (force greater than lung’s elastic recoil)

18
Q

What lung volume is represented when the forces inflating and deflating the lungs are equal? At what phase of the respiratory cycle does this occur?

A

Functional residual capacity (FRC)

Exhalation of quiet breathing

19
Q

The lungs are not adherent to the inside of the thoracic cavity. What stops them from collapsing away from the chest wall?

A

Negative pressure within pleural space

20
Q

What is the commonest mechanism allowing lung collapse away from the chest wall?

A

Pneumothorax - lung surface/chest wall is punctured

21
Q

What happens if integrity of pleural seal is broken?

A

Pressure in pleural space will rise (as air fills pleural space), suction effect between 2 pleurae is removed (lose expansile force of chest wall) and lungs collapse away from chest wall under its unopposed elastic recoil force

22
Q

Name 1 type of pneumothorax. What are the signs?

A

Tension Pneumothorax

May lead to cardiac arrest if unrecognised

Signs:

  • Left lung completely compressed
  • Trachea pushed to right (Xray)
  • Right heart border pushed to right
  • Left hemidiaphragm depressed
23
Q

Define the term Compliance

A

Compliance = volume of change of the lung per unit of force applied

24
Q

What is compliance used to measure?

A
  1. Stiffness in respiratory system

2. Disposition of lungs to expand under traction/pressure

25
Q

Define the term Elastance

A

Elastance = measure of the disposition of the lungs to return to resting position due to their intrinsic elasticity

26
Q

What are the effects of disease on compliance? Give examples.

A

Emphysema - increase compliance, tissue stretches more easily, requires less pressure to stretch

Fibrosis - decrease compliance, scarred lung tissue means more pressure needed to stretch lungs

27
Q

Describe simple tests of lung function used in clinical practice

A

Look at basic lung function (FRC)

Xray

28
Q

Define the term ‘Surface Tension’

A

Molecular interactions resulting from hydrogen bonds between water molecules in liquid but not between water + air

29
Q

Explain surface tension in terms of the lungs

A

Surface tension of water is high and lungs would be difficult to expand in absence of agent to lower this surface tension.
Surface tension = important factor in compliance

30
Q

What is Hooke’s Law?

A

Force needed to extend or compress a spring by some distance is proportional to that distance (but lung is not ideal spring as stiffer at high/low lung volumes)

31
Q

What is the hysteresis curve?

A

X axis = change in intrapleural pressure
Y axis = volume change from FRC

Inhalation + exhalation plotted separately (straight line is elasticity of lung/thorax if it was the only factor)

32
Q

What is Laplace’s Law?

A

Alveoli are like soap bubbles that are interconnected by airways.
Alveoli have only 1 fluid/air surface:
pressure = 2(surface tension)/radius

33
Q

What is surfactant? What is its role in the lungs?

A

Surfactant - secreted by Type II epithelial cells (pneumocytes) lining alveoli

Reduces surface tension in lungs dramatically - reduces work of respiration + stabilises lung structure

Enables lungs to be expandable in early stage of inhalation - also reduces tendency for fluid transudation

34
Q

What is surfactant composed of?

A

Mixture of compounds

  • Major ingredient = phospholipid (dipalmitoyl phosphatidylcholine) - hydrophobic + projects into gas phase of alveolus
  • Surfactant proteins (SP-A, B, C, D)
35
Q

What are the functions of surfactant?

A
  • Reduces surface tension - stabilises alveoli + increases compliance
  • Reduces likelihood of tissue fluid transudation
  • Lipid component has antioxidant activity
  • SP-A and D immune activity (bind wide range of pathogens + activate macrophages and neutrophils via specific receptors)
36
Q

Why is the packing of alveoli beneficial?

A

Interdependence - support each other and limits the tendency to collapse

37
Q

What is the relationship between resistance and radius?

A

Resistance rises with radius to power 4

38
Q

Which airways provide the greatest resistance within the lungs?

A

Greatest resistance = medium sized bronchi

smallest airways are many in number + collectively have lower resistance

39
Q

What is the test for airway resistance?

A

Peak Expiratory Flow Rate (PEFR)

  • resistance negligible in health, but disease e.g. asthma, flow is limited by resistance
40
Q

What factors determine airway resistance?

A
  1. Autonomic NS - contraction of bronchial smooth muscle narrows airways (vagus parasympathetic NS = motor to this muscle) + relaxation of muscle by Adrenaline acting on B2 receptors (beta agonists used to treat asthma)
  2. Lung volume - increase volume increases airway radius (radial traction)
  3. Turbulent vs laminar flow - larger airways more prone to turbulent

Medicine block 2 (9 decks)

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