Resp Flashcards
Whats Dyspnoea?
Shortness of breath
What could the presenting complaint be in a respiratory examination?
Dyspnoea
Wheeze
Haemoptysis
Chest pain
Sputum
Cough
Whats used to grade breathlessness?
The MRC Dyspnoea Score
Grades of the MRC dyspnoea score:
- No breathlessness unless on strenuous exertion
- SoB when hurrying or walking up a slight hill
- Walks slower than others due to SoB on flat level, or has to stop for breath when walking at own pace
- Stops for breath after walking 100m or after a few minutes on level ground
- Too breathless to leave the house, or breathless when dressing or undressing
Whats Forced vital capacity (FVC)?
The volume of air that can be forcibly expelled from the lungs from a position of maximal inspiration.
Whats vital capacity?
Volume of air that can be expired from the lungs from a maximal inspiration using a relaxed/slow manoeuvre
Forced expired volume (FEV1)?
Following a maximal inspiration - The Volume of air forcibly expelled from the lungs in the first second.
FEV1/FVC
Volume of air forcibly expired in the first second as a percentage of the total volume exhaled.
What does a Restrictive volume time plot look like?
What does a Obstructive volume time plot look like?
What would the flow volume loop look like for:
- Normal
- Early small airways obstruction
- Chronic obstructive disease
- Fixed large airway obstruction
- Variable extrathoracic large airway obstruction
- Restrictive disease
Whats an obstructive lung disease briefly?
Difficulty with expiring air. FEV1 is reduced. (typically FVC is the same)
Examples of obstructive lung diseases?
COPD, asthma
Whats a restrictive lung disease briefly?
Cause problems by restricting a person’s ability to inhale (enough) air. FVC is decreased. (FEV1 can be reduced though proportionately).
Examples of restrictive lung disease:
Interstital lung disease, Myasthenia gravis
Pathophysiology of restrictive lung diseases
Occurs if lungs become too stiff or if inspiratory effort is compromised by muscle weakness/ injury/ deformity (or both)
Pathophysiology of obstructive lung conditions
Its all to do with resistance.
During expiration the small airways are compressed. This increases flow resistance, hence helping to reach a point where no more air can be driven out of the alveoli.
In COPD there is greater airway narrowing than normal, thus greater outflow resistance, thus expiratory outflow is compromised much earlier. Hence expiratory outflow is not satisfactory.
In asthma, the already narrowed airways (due to mucosal inflammation and smooth muscle hypertrophy) are further constricted due to increased smooth muscle tone. This causes resistance to airflow to become very high. This means the patient must work harder to overcome the increased resistance. This can lead to turbulent flow, causing the characteristic wheeze of an asthma attack.
COPD involves a balance between which two diseases?
Emphysema and chronic bronchitis.
Pathophysiology of emphysema
-Elastin breakdown and hence loss of alveolar integrity. Leading to destructive enlargement of airspaces distal to the terminal bronchioles.
-Also, the small bronchioles are narrowed due to the loss of elastic fibres in the surrounding alveoli. These fibres exert an outward pull on the small bronchioles and keep them open (radial traction). These airways can also therefore collapse when pressure increases e.g. during expiration (as they have no cartilage and reduced radial traction)
-Loss of elastic recoil, gain in compliance. Lungs are hyperinflated.
Pathology of Chronic Bronchitis
Excessive mucous secretions and impaired removal of the secretions (ciliary dysfunction)
How does Chronic Bronchitis lead to increased airway resistance
luminal obstruction of airways by secretions.
2 ways that airway resistance is increased by COPD
1) luminal obstruction of airways by secretions.
2) small bronchioles are narrowed due to the loss of elastic fibres exerting an outward pull (radial traction) on the small bronchioles.
In an Obstructive defect what happens to the FVC, FEV1, FEV1/FVC ratio?
- FEV1 is reduced
- FVC nearly normal (worsens as disease progresses, thus increasing residual volume at the cost of FVC)
- FEV1/FVC is <0.7
In a restrictive defect what happens to FVC, FEV1, FEV1/FVC ratio?
FVC is reduced
FEV1 is reduced proportionately
FEV1/FVC ratio is normal = greater than or equal to 0.7
Whats Hypoxia?
Deficiency of oxygen in the tissues
(correlates with low PaO2 I guess)
low PaO2 = hypoxemia
4 causes of low PaO2:
1) Hypoventilation
2) Diffusion impairment
3) Shunt
4) V/Q mismatch
pH ∝ ?
pH ∝ [HCO3-]/[(pCO2*0.23)]
CO2 + H2O ⇌ H+ + HCO3-
CO2 + H2O ⇌ H+ + HCO3-
Normal ratio of HCO3- to CO2? (this is to maintain normal blood pH!)
[HCO3-] : [CO2]
20:1
Normal ratio of HCO3- to CO2? (this is to maintain normal blood pH!)
[HCO3-] : [CO2]
20:1
Flow =
Flow = ΔP/R
Pathophysiology of COPD
(is an airflow limitation problem that is not fully reversible)
Lots… Main two:
1) Changes leading to increased airway resistance (especially on expiration, as pressure increases try to narrow the smaller airways). - luminal obstruction of airways by secretions. -Small bronchioles narrowing due to loss of radial traction.
Overall, meaning that expiratory flow is compromised much earlier in expiration. Hence expiratory outflow is not satisfactory
2) Decreased elastic recoil
This leads to:
-reduced expiratory force (flattens diaphragm)
-hyperinflation of the lungs
Overall both lead to expiratory flow limitation, therefore promoting air trapping in the lungs. This leads to “old” and “new” air mixing in the lungs.
https://pubmed.ncbi.nlm.nih.gov/15325838/
The poor airflow seen in COPD is due to emphysema or the small airways disease?
Both
https://en.wikipedia.org/wiki/Chronic_obstructive_pulmonary_disease#cite_note-Robbins1-87
My notes:
Obstructive is basically an airflow problem (airway obstruction)
Restrictive is basically a reduced volumes problem
My notes:
Obstructive is basically an airflow problem (airway obstruction)
Restrictive is basically a reduced volumes problem
What measure is useful when analysing the cause of a metabolic acidosis?
Anion Gap
Anion gap equation:
Anion gap = Na+ - (Cl- + HCO3-)
Normal anion gap is…
8-12