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Supply & Demand > Respiratory mechanics > Flashcards

Respiratory mechanics Flashcards

1
Q

What is contained in the thoracic cavity?

A 
lungs
thoracic muscles
ribcage
sternum 
thoracic vertebrae
connective tissue
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2
Q

Where does the respiratory tract begin?

A

nose/mouth to the trachea then to the pharynx and larynx

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3
Q

Where does the trachea branch?

A

bifurcates at the sternal angle

- branches at the major carina into the left and right bronchi which connect their respective lungs

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4
Q

How many generations are there in the lungs?

A

24

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5
Q

What are the conducting airways known as?

A

dead space- poorly or not perfused

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6
Q

What provides the structural support in the larger airways?

A

cartilage
- as generations increase and airways become smaller, the cartilaginous support is progressively lost and is replaced by smooth muscle and elastic connective tissue

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7
Q

The lungs are elastic in nature. What does this mean?

A

They comprise of elastin and collagen fibres

  • have a tendency to collapse inwards
  • in contrast the chest wall has a tendency to spring outwards
  • these 2 opposing forces balance each other out at rest thereby maintaining the overall shape of the thoracic cage
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8
Q

What are the functional units of the lungs?

A

Acini - meaning “little cavity” in latin

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9
Q

What do the pneumocytes do?

A

Type 1: form the alveolar wall

Type 2: secrete surfactant - surface tension and are moist for gas exchange

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10
Q

What is surfactant?

A

Phospholipoprotein that reduces surface tension in the alveoli
- facilitates expansion and relaxation

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11
Q

How does ventilation differ at rest and during exercise?

A

Relaxed tidal breathing is relatively passive and under subconscious control by rhythmic stimulation of the diaphragm

During exercise or in disease ventilation becomes more active and accessory muscles for inspiration and expiration are recruited

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12
Q

What happens during inspiration?

A
  1. Pulmonary system relaxed. The forces of the chest wall and lungs are at equilibrium
  2. Diaphragmatic contaction induces lung expansion (external intercostals also contract) and this causes a negative pressure in the airways
  3. Due to the negative pressure air flows into the lungs
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13
Q

What happens during expiration?

A
  1. After tidal inspiration, the atmospheric and alveolar air pressures are equal
  2. Diaphragmatic relaxation causes an increase in airway pressure
  3. Positive air pressure within the airways causing air to flow out of the lungs
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14
Q

What are the differences between laminar and turbulent flow?

A

Laminar = linear flow in the smaller airways which is slow

Turbulent = air bounces around and occurs in the larger airways and is much faster

Airflow in the alveolar ducts occurs by diffusion

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15
Q

What does the Reynolds No. refer to?

A

the transition from laminar to turbulent flow
= pVD/n
p= gas density
V= linear velocity (inversely proportional to the cross-sectional area)
D= diameter
n= gas viscosity

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16
Q

What are the ranges of the Reynolds No.?

A 
<2300 = completely laminar
2300= onset of turbulent flow (transition)
>4000= completely turbulent
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17
Q

What is the flow of gas/liquid inversely proportional to in a hollow tube?

A

the resistance
= greater resistance = slower the flow
- pulmonary airways exert a resistance to airflow during inhalation and exhalation

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18
Q

What is Pouseuille’s law?

A

R=8nl/pie r(power of 4)

  • n= viscosity
  • l= length of the tube

Dominant factor in determining resistance is radius

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19
Q

How does pousueille’s law apply to the lungs?

A

Resistance in the small airways is relatively low due to the large number of small bronchioles (large cross-sectional area)
- majority of airway resistance occurs within the larger bronchioles W

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20
Q

What is the relationship between cross sectional are and resistance in the lungs?

A

Resistance- increases initially up to lung generation 5 and then decreases as the lung generations increase

Cross sectional area increases as the lungs generations increase- steady increase at the start and more substantial the further down the respiratory tract

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21
Q

What is used to test airway resistance?

A

Body plethysmography
- airway resistance (Raw)- the pressure change between the alveoli and the mouth divided by the flow

= Raw is the pressure that must be applied between the alveoli and lips to secure a rate of flow through the airways

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22
Q

What is the reciprocal to resistance?

A

conductance - Gaw = I/Raw

  • when conductance is measured during relaxed ventilation it is referred to as “specific airway conductance” or sGaw
  • sGaw is a constant (independent of lung volume) and can be easier to interpret -its linear
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23
Q

What is oscillometry?

A

it looks at the structure of the airways during normal breathing

  • forced oscillations (5-35Hz) generated by a loudspeaker are applied at the mouth during ordinary tidal breathing
  • differentiate between large and small airway resistance
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24
Q

What does reactance comprise of?

A

Inertia: resistance to change in state of motion
Capacitance: ability to store energy

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25
Q

How is neural regulation involved in ventilation ?

A

controlled by respiratory centers= series of interconnected brain cells within the lower and middle brain stem that coordinate respiratory movements
- respiratory centres send out impulses to the diaphragm and external intercostal muscles inducing contraction and subsequent inspiration -this ceases after about 2 seconds and the intercostal muscles and diaphragm relax = expiration

26
Q

What are the different regions of the respiratory centre and what are their functions?

A

Pneumotaxic centre: regulates the volume inspired with each breath

Caudal pons: Controls the facial muscles - important in talking and during exercising

Retrotrapezoid Nucleus: regulates the drive to breathe

Pre-Botzinger complex: Controls respiratory rate

27
Q

What regulates ventilation?

A

Central and peripheral chemoreceptors

  • actually driven by blood pH(related to CO2) and not by O2 - the CO2 response is much quicker than the O2 response
  • normally an increased concentration of CO2 is the strongest stimulus to breathe more deeply and more frequently
28
Q

Where are the central chemoreceptors located and what do they do?

A

Located in the ventrolateral medulla in the vicinity of exit of the 9th(glossopharyngeal) and 10th (vagal) nerves

  • detect changes in pH in the CSF
  • however a change in plasma pH alone will not stimulate them because H+ can’t cross the BBB, therefore they are only responsive to CO2
  • the CO2 diffuses across the BBB and reacts with H20 forming carbonic acid which decreases pH
29
Q

Where are the peripheral chemoreceptors located and what do they do?

A

Carotid and aortic bodies= sensory extensions of the PNS into blood vessels

  • detect changes in CO2 and O2
  • Afferent nerves carry signals back from the carotid (glossopharyngeal) and aortic (vagus) to the respiratory centre
30
Q

What is the Hering-Breuer reflex?

A

More important in babies than in adults

  • Pulmonary stretch receptors are present in smooth muscle throughout the lungs
  • during large inspirations, they feedback to the pneumotaxic centre via the vagus nerve to prevent over inflation
  • doesn’t seem to have a role in relaxed tidal volume in adults
31
Q

What are the juxtacapillary (J)-receptors?

A

Sensory nerve endings within alveolar walls in juxtaposition to the pulmonary capillaries

  • respond to pulmonary congestion (oedema, emboli, pneumonia)
  • stimulation induces rapid shallow breathing and a cough
32
Q

What are irritant (cough) receptors?

A

in the epithelium respiratory tract

  • sensitive to both mechanical and chemical stimuli
  • stimulation produces a cough which is necessary to remove the foreign material from the upper respiratory tract
33
Q

What are the two different types of sleep and what occurs in both?

A

Non-REM sleep

  • regular breathing
  • minute ventilation decreases by 13% in stage 2 and 15% in stages 3/4
  • contribution of the external intercostals increases
  • 4 stages - go deeper into sleep

REM sleep

  • breathing becomes less regular
  • fluctuations in frequency and amplitude, central apnoeas - hyperventilation can occur
  • contribution of the external intercostal muscles decreases
34
Q

In respiratory disorders wha are the most important effects that happen to the airways?

A

Airway calibre= resistance
compliance
- these altered lung mechanics can lead to impairment of function which initially presents symptomatically as breathlessness

35
Q

What are the four factors that need to be taken into account when predicating normal values for lung function ?

A
  • size of an individual’s lungs is determined by HEIGHT and SIZE
  • proportion of lung size to height also varies with RACR
  • lung function gradually deteriorates as healthy adults AGE = lose elastic support as we age
  • clinical interpretation involves comparison of obtained results to an individuals predicted normal range (based on 4 factors)
36
Q

What are the two values use to represent normal values?

A 
% of predicted values 
Standard residuals ("z-scores")- including Lower limit of normal

Neither are ideal, they both have pros and cons, but the standard residuals more accurately reflect what is likely to be normal (based on height, size, age and race)

37
Q

What are the 3 basic lung function tests?

A

1) spirometry
2) lung volumes
3) gas transfer

  • collectively these tests provide a good overview of general lung function
38
Q

What does spirometry assess?

A

Assesses ventilation
- measuring = VC, FVC, FEV1, PEF and FEV1/FVC ration

FEV1= forced expired volume in 1 second
FVC= forced vital capacity
PEF=peak expiratory flow (L/s)

39
Q

What happens in obstructive ventilatory defects?

A 
decrease in airway calibre leading to reduced airflow on exhalation and/or inhalation 
Example conditions:
- COPD
- Asthma
- Bronchiectasis 
- Cystic fibrosis 
- upper airway obstruction
40
Q

What happens in restrictive ventilatory defects?

A 
impaired ability of the lungs to expand due to extra pulmonary, pleural or parenchymal abnormality 
Example conditions 
- fibrosis 
- sarcoidosis
- systemic lupus erythematosus 
- muscle weakness 
- chest wall deformity
41
Q

What happens to the flow-volume loop in obstructive pulmonary disease?

A
  • the FEV1 is substantially reduced and the FVC is also reduced, this causes a reduced ration
  • concavity = the more sever the obstruction the more severe the concavity
  • PEF reduced
  • inspiratory tends to be relatively normal
42
Q

What are the FEV1 % predicted values/FEV1.FEV1 ratio of diagnosis for obstructive pulmonary disease?

A

% predicted values

  • > 80%: mild
  • 50-79%: moderate
  • 30-49%: severe
  • <30%: very severe

FEV1/FVC ratio
- <70% for all

43
Q

What happens to the flow-volume loop in restrictive pulmonary disease?

A

PEF is reduced
FEV1 reduced
FVC is reduced proportional to FVC therefore ratio is normal or raise
there is a kink in the loop if the lungs are stiffer

44
Q

What are some additional uses of spirometry?

A

Test physiological response to pharmacological agents

  • bronchodilators - first line treatment
  • antibiotics - check if patient is allergic to antibiotics
  • Airway challenge agents - mannitol - inhibits release of histamine
  • drugs - methotrexate / chemo
Pre-operative assessment 
Home monitoring (post-transplant)= monitor spirometry daily
45
Q

What is spirometry useful in detecting?

A 
a reversal (partial or total) of airflow obstruction by bronchodilators 
- can be a good differentiator of COPD and asthma
46
Q

What are the different guidelines for reversibility criteria?

A

ARTP/BTS: 160ml FEV1 and/or 330ml FVC= based on absolute changes in volume therefore this the worse measures

ERS: >12% predicated FEV1 and 200ml = normally the one used in clinical practice

ATS: 12% and 200ml FEV1 or FVC

47
Q

What are some of the technical errors in spirometry?

A
  • slow start
  • poor effort
  • straining throat which causes a cough
  • glottic closure- normally towards the end of expiration
  • some patients simply can’t do spirometry- dementia, muscular weakness
48
Q

What are the diagnostic values of spirometry?

A
  • robust and simple assessment of ventilation
  • relates well to pathology and mortality
  • useful for monitoring
49
Q

What are the limitations of spirometry?

A
  • insensitive to early disease (esp. COPD)

- May not detect a clinically useful BD response

50
Q

What are the different lung volume indices?

A 
VC (L)
FRC (L)- functional residual capacity 
ERV (L) - expiratory reserve volume 
RV (L) - residual volume 
TLC (L) - total lung capacity
51
Q

What happens to lung volumes in obstructive respiratory disease (severe)?

A 
VC- reduced 
FRC- increased
ERV- reduced
RV- increased (air trapping) 
TLC - increased (less so than FRC) due to increased compliance
52
Q

What happens to lung volumes in restrictive respiratory disease (severe)?

A 
VC- reduced 
FRC- reduced (less than TLC)
ERV- reduced 
RV- redcued 
TLC - reduced
53
Q

What is the diagnostic value of lung volume tests?

A
  • provides information about the functional status of the lungs
  • useful in assessing degree of air trapping
  • useful for pre-transplant
54
Q

What are the limitations of lung volume tests?

A
  • not particularly informative

- plethysmography technically difficult - pant in and out against closed blockages

55
Q

What are the gas transfer test indices?

A

TLco= transfer factor of the lungs for CO

  • an estimate of overall efficiency of O2 uptake
  • also dependent upon Hb

VAeff= effective alveolar volume

  • the surface area over which gas transfer occurs
  • > 85% of TLC in absence of airflow obstruction - healthy lung

Kco= transfer coefficient (TLco/VAeff)
- estimate of efficiency of O2 uptake at alveolar level

56
Q

How do you interpret the gas transfer values?

A

Least well understood of all routine lung function tests
consider all parameters and interpret in conjunction with other tests and clinical information
understand non-pulmonary factors can affect gas transfer- cardiac shunt, anaemia, drugs

57
Q

What happens to the TLco and Kco in obstructive COPD and obstructive asthma?

A

COPD

  • TLco= reduced
  • Kco= reduced

Asthma

  • TLco= normal/increased
  • Kco= normal/increased
58
Q

What happens to the TLco and Kco in restrictive intrapulmonary and restrictive extrapulmonary?

A

Restrictive intrapulmonary

  • TLco= reduced
  • Kco= reduced

Restrictive extra pulmonary

  • TLco= reduced
  • Kco = normal
59
Q

What is the diagnostic value of gas transfer tests?

A
  • provides information about oxygen uptake
  • clinically very useful in aiding diagnosis - can differentiate between ventilatory and interstitial impairment
  • more sensitive to early disease than spirometry
60
Q

What is the limitations of gas transfer tests?

A
  • unable to perform with very small VC = patients simply don’t have the volume to do this if they have severe restrictive disease
  • not entirely representative of gas exchange during tidal ventilation
  • results do not correlate to arterial blood gases

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