Respiratory Physiology Flashcards
What are the contraindications for spirometry?
Haemoptysis of unknown cause
Pneumothorax
Unstable cardiovascular status
Recent MI or PE
Thoracic/abdo/ocular aneurysm
Recent thoracic/abdo/ocular surgery
Nausea/vomiting
What is the expected annual decline in FEV1 each year?
Approx 25ml/year
Nb. healthy pt expires 80% of lung volume in first second
What measurements would make spirometry reproducible?
3xFEV1 + FVC within 150ml
Max 8 tries
Difference of 5% between insp and exp volume allowed
What are spirometry criteria for obstructive airways disease?
FEV1/FVC <0.7
<0.65 if over 65
What does flow-volume loop look like in obstructive airways disease?
Scalloped expiration
What does flow-volume loop look like in coughing?
Sudden drops of flow rate to 0 before returning back to curve
What does flow-volume loop look like in exercise-induced asthma?
Gets smaller each time
What is the underlying cause of a flow volume loop where the fastest flow is reach after 0.1 seconds? E.g more even looking curve up and down in expiration?
Poor technique - expired too slow. Should get fastest rate (PEFR) within 0.1 seconds
What is the z-score on spirometry?
Number of standard deviations away from mean. Normal is within 1.64
What does flow-volume loop look like in restrictive lung disease?
Normal shape but don’t reach FVC
What is the diagnosis in a flow volume loop with a flattened inspiratory curve?
Variable extrathoracic obstruction
- vocal cord paralysis
- extrathoracic goitre
- laryngeal tumour
–> expiratory part normal as obstruction pushed outwards by force of expiration
What is the diagnosis in a flow volume loop with a flattened expiratory curve?
Variable intrathoracic obstruction?
- Tracheal tumour
–> inspiratory part normal as tumour sucked out during inspiration
What is the diagnosis in a flow volume loop with flattened inspiratory and expiratory curves?
Fixed large airway obstruction
- Tracheal stenosis
- Circular tracheal tumour
- Granulomatosis with polyangitis
A patient with COPD is going on holiday and asks re air travel. His SATS are 96% on air. He gets breathless when hurrying on the level. What assessment does he need?
None (nb. MRC 2)
If SATS ≥95% on RA and MRC ≤ 2, then no hypoxic challenge or oxygen required
MRC 1 - SOB on vigourous exercise
2 - hurrying level or walking up slight hill
3 - slower than ppl of same age or stop while walking on level
4 - stop after 100m
5- can’t leave house or SOB on dressing
A patient with COPD is going on holiday and asks re air travel. His SATS are 93% on air. He has to stop to catch his breath after 100m. He has a hx of T2RF but doesn’t use NIV. What assessment does he need?
Hypoxic challenge (unless already done and no recent hospital admissions, exacerbations or significant changes to treatment)
Results - if PaO2 ≥6.6 or SATS ≥85% (90 for CF) then nothing. Otherwise needs O2 to get above this.
Nb. MRC score irrelevant (4 in this case) as SATS <95% on air. If were above, then if MRC ≥3, would need 6MWT/shuttle walk.
A patient with COPD is going on holiday and asks re air travel. His SATS are 93% on air. He has no hx of T2RF. What assessment does he need?
None - can safely be given 2 litres O2 on plane.
- if at risk of T2RF, would need hypoxic challenge
- if already on LTOT, then would get 2 litres more than normal setting (would still need hypoxic challenge if T2RF)
A patient with COPD is going on holiday and asks re air travel. His SATS are 96% on air. He gets breathless when while walking on a level. What assessment does he need?
MRC 3 therefore needs 6MWT/shuttle walk - if SATS <84% + hx/risk of T2RF, then hypoxic challenge. Otherwise 2litres O2.
MRC 1 - SOB on vigourous exercise
2 - hurrying level or walking up slight hill
3 - slower than ppl of same age or stop while walking on level
4 - stop after 100m
5- can’t leave house or SOB on dressing
What SATS would you expect a healthy person to have on a plane?
> 90%
Does pt who has had previous significant intolerance to plane travel e.g. emergency O2/diversion need hypoxic challenge?
No - can give 2litres O2. Unless T2RF risk then needs.
Pt has severe asthma and symptoms not controlled. Want to travel on plane. Do they need tests?
Yes - need hypoxic challenge
Pt has lung disease and FEV1<50%. Do they need tests?
Yes. Hypoxic challenge
Pt has ILD. Wants to travel on plane. What do you need to know?
Needs hypoxic challenge if rest PaO2 ≤9.42 or TLCO≤50% and SATS<95% with 6MWT or shuttle walk
If already on LTOT then can just increase by 2 litres
Pt has resp muscle weakness or chest wall deformity. What are indications for hypoxic challenge?
FVC <1litre (or risk/hx of T2RF)
Results - if PaO2 ≥6.6 or SATS ≥85% (90 for CF) then nothing. Otherwise needs O2 to get above this.
How long after thoracic surgery can pt travel on plane?
4 weeks (2 weeks if essential)
How do you manage asthma/copd exacerbation on board plane?
Normal inhalers
How long after PNX can pt travel on plane?
1 week after CXR resolution
How long after interventional bronch (transbronch biopsy, EBUS, valves etc) can pt travel on plane?
1 week
Pt smear +ve TB. How long before can travel on plane?
2xsmear negative.
If MDR/XDR then 2xculture negative + clinical improvement
Pt smear -ve TB (or unknown). How long before can travel on plane?
2 weeks after treatment (no restriction if extra-pulmonary TB)
MDR/XDR TB. How long before can travel on plane?
2xculture negative + clinical improvement
Extrapulmonary TB. How long before can travel on plane
No restriction
Pt has pneumonia. How long before travel on plane?
1 week if SATS <94%
Pt has OSA and uses CPAP. What are suggestions for plane travel?
Bring CPAP and use if overnight flight
Pt has DVT/PE. Should they travel on plane?
Should delay 2 weeks
Pt has pulmonary HTN. NY heart class 3/4. What do they need for plane travel?
2 litres O2 or hypoxic challenge if concerns of T2RF. Double rate if on LTOT
Nb. NYHA 3/4 = SOB on less than ordinary activity or at rest
Can pt with lung cancer/mesothelioma travel on plane?
Suggest not during chemo due to ifx risk but otherwise no rules outside of other conditions
What are contraindications for plane travel with respect to resp disease?
Untreated resp failure
Untreated PNX
Active infectious risk
Bronchogenic cyst
Nb. O2>4litres no longer a restriction
What is a normal RV/TLC ratio?
<0.35 - if over, suggests air trapping e.g. obstructive airways disease
What kind of spirometry is found in obesity?
Restrictive defect
- low functional residual capacity (volume left after normal tidal volume breath out)
- RV/TLC likely normal
What are the grades of severity of restrictive lung disease based on spirometry?
Mild: FVC≥70%
Moderate: ≥60% but <70%
Moderately severe: ≥50% but <60
Severe: ≥34% but <50
Very severe: <34%
What is pt exposed to in hypoxic challenge?
Gas mixture with 15% O2 for 20 mins or in equilibrium
What spirometry findings might you get in diaphragmatic weakness?
- FVC 75% unilateral, <50% bilateral.
- marked fall in supine position (healthy person drop only 5%) –> 30% drop considered severe
What are the criteria for reversibility on spirometry?
> 12% and 200ml
What is a methacholine challenge?
Test for bronchial hyperresponsiveness - test what concentration of methacholine required to get fall in FEV1 of 20% (PC20). >16mg/mL = excludes airway hyperresponsiveness
Nb. histamine challenge should also stimulate if hyperresponsive
What is best way to test for exercise-induced asthma?
Eucapnic voluntary ventilation (breath fast with gas mixture O2 21% and CO2 5% to mimic exercise, looks for drop in FEV1 of 10% within 20 mins)
Second best is exercise test, then nebuliser challenge
What is the Empey ratio?
FEV1 in ml/PEFR in L per min
Can be used to see if upper airways obstruction. Normal result is <10
E.g. 2500 / (600x60)
What is a normal A-a gradient?
FiO2 (e.g. 21) - (paCO2/0.8) - paO2
Normal in region of 1-3 (1-2 young/middle age, 2-3 elderly)
- normal gradient but hypoxic = alveolar hypoventilation. Will get elevated PaCO2 (CNS depression, OHS, COPD, high altitude)
- if V/Q mismatch, shunt or impaired diffusion then will be elevated
–> dead space ventilation (ventilation without perfusion) e.g. pneumonia, PE, asthma, COPD
–> shunt (perfusion without ventilation) e.g. pulmonary oedema, ARDS, pneumonia
–> diffusion limit e.g. ILD
What is a normal end-expiratory pressure?
-4kPa
Where are ventilation and perfusion highest in the lung?
Both at bases
- Perfusion decreases faster than ventilation towards apices, therefore V/Q highest in apices
- lower V/Q tends towards shunts, where as higher V/Q tend towards dead space
What causes low DLCO?
ILD
Emphysema
Severe anaemia
PEs
Increased carboxyhaemoglobin
Hypothyroid
CCF
NB. normal/high KCO = extrapulmonary restriction e.g. obesity, neuromuscular disease, pleural disease, kyphoscoliosis, post-pneumonectomy
What causes high DLCO?
Pulmonary haemorrhage
Polycythaemia
Obesity
High altitude
Hyperthyroidism
Pneumonectomy
AV malformation (or other L-R shunt)
What is the relationship between PaO2 and FiO2 in normal lungs?
PaO2 = FiO2 x 0.75
- Normal FiO2 = 21%
What increase in 6MWT is considered a good outcome for pulmonary rehab?
50m
CPET testing - what is the RER?
Respiratory Exchange ratio
- VCO2/VO2
- Would expect VCO2 to increase with exercies
- At rest, ratio 0.8
- Hard exercise 1.1
- May also go up in hyperventilation
CPET testing - what is VO2?
Oxygen consumption
- Would expect >80% to be considered normal
Nb. O2 pulse = oxygen concentration/HR (if low, suggestive of cardiac problem)
CPET testing - what is anaerobic threshold?
Point where VCO2 faster than VO2 (usually when RER = 1)
- 50% is normal
- <40% considered disease state
CPET testing - what is ventilatory equivalence/VCO2 slope?
How efficient ventilation is i.e. how hard you breathe to move the same amount of CO2
- if VE is close to predicted max (>80%) then is what has caused you stop exercising as you have reached your resp limit
What stages should you go through to interpret CPET?
1) Is it maximal test
- VO2 plateau reached
- RER >1.1
- HR reserve low (i.e. close to maximal HR)
- Lactate >4
- Anaerobic threshold passed (point at which CO2 rises faster than VO2)
- Exhaustion
If yes,
2) Is the capacity normal? Peak VO2 >80% or 20ml/kg (considered normal) –> ie. if see VO2 >80% then can basically say is normal test
If no,
3) Did they reach resp limit?
- VE >80% of predicted max = FEV1x40
- ‘Low breathing reserve’
Or did they reach cardio limit?
- HR>80% predicted max = 220-age
- ‘Low heart reserve’ –> nb. this is what would expect in normal tests
4) If yes, did SATS fall by >4%? or rapid rise in HRR? or abnormal BP response?
- Y probably cardiac disease
- N probably deconditioning
CPET test - what is O2 pulse?
oxygen consumption (VO2) / HR
- normal is 10ml/min
- proxy of cardiac output
What are contraindications to diving in respiratory disease?
- bullae or cysts
- spontaenous PNX unless treated with bilateral surgical pleurectomy and normal CT after surgery (nb traumatic okay as long as CT and lung function normal)
- Airways disease and FEV1 <80%
- Active sarcoid (quiescent needs normal CT and lung function)
- CF
- ILD
What causes a biphasic flow volume loops (tails at the end of the exp and insp phase)?
Unilateral bronchial stenosis
- bronchial cancer or mets
- unilateral emphysema
- single lung tx
- granulation tissue at anastomosis post-tx
- GPA
- Sarcoid, amyloid
- Bronchogenic cyst
What is the best test for assessing lung volumes prior to lung volume reduction surgery in bullous disease?
Body plethysmography
how much would you expect vital capacity to fall when pt lying down?
10%
10-20% suggestive of diaphragm paralysis
>20% usually bilateral diaphragm paralysis
What can cause a flow-volume loop that has ‘vibrations’?
OSA
How is airways resistance proportional to the radius of the bronchi?
Inversely proportional to radius^4 (Poiseuilles Law)
e.g. if radius becomes twice as large, resistance decreases by 2^4 = 16
What is the limit for the transverse diameter of the trachea beyond which it is considered tracheomegaly?
3cm
Normal: 1.5-2.5cm men, 1.0-2.1cm women
What shifts the oxygen dissociation curve to the right? i.e. lower affinity of Hb for oxygen = more available for tissues
Low pH
Increase 2-3 DBP (organic phosphate)
Increase temp
What shifts the oxygen dissociation curve to the left? i.e. higher affinity of Hb for oxygen = less available for tissues
Increase pH
Decrease 2-3 DPG
Decrease temp
