PFT (Raf) Flashcards
Why is PEF not used in pediatrics?
- Effort dependent
- High variability
- Low sensitivity
● It is effort dependent -PEF is affected by the fullness of the preceding inspiration, caliber of the large airways, expiratory muscle strength, and voluntary effort. As might be expected, PEF can vary substantially with patient effort and coordination
● It has high variability -When PEF and FEV1 are measured in the same subjects, the SD for PEF readings is consistently higher than that of FEV1
● PEF is less sensitive than standard spirometry in detecting reversibility of airflow obstruction after bronchodilator administration as well as worsening of airflow limitation in response to inhalational challenge
- Because PEF is so bad, often symptoms are actually better to monitor, apart from specific scenarios where there is value in PEF for short or long-term monitoring
Formula for Rint
Rint = Pao/Flow
Pao at time of occlusion
Flow prior to occlusion
(Need to document if maneuver during inspiration or expiration)
Resistance is for both airway and parenchymal resistance
How many acceptable maneuvers for PFT?
3 acceptable FEV1 and 3 acceptable FVC for grade A recommendation
What is usability versus acceptability of a maneuver?
There are strict criteria for a maneuver to be acceptable. A maneuver may be clinical useful (useable), even if not acceptable
What is the purpose of back extrapolated volume?
To determine the time “0” for the start of forced expiration and all the measurements. On a volume versus time graph, the peak flow corresponds to the steepest slope. Draw a tangent down to x axis to figure out time 0. The volume prior to time 0 is the back extrapolated volume.
Why is it important that the back extrapolated volume is not too high?
It ensures that FEV1 and FVC are from a maximal effort
What should the back extrapolated volume be?
<5% of FVC or <100 mL, which is greater.
This is part of acceptability for both FEV1 and FVC
What is hesitation time?
on the volume time graph that is used to calculate back extrapolated volume, the hestitation time is from maximal inhalation to time 0, as defined based on back extrapolatd volume. It should 2 seconds or less
If there is a high BEV, which parameter will be abnormal?
“eroneously high FEV1”–I don’t understand why
What is the last maneuver on a spirometry test?
- The last maneuver is a maximal inspiration (to TLC). Therefore, we describe EOFE (end of forced exhalation) as opposed to end of test
If EOFE is not achieved, which spirometric parameter is abnormal?
FVC (since the test is not really finished)
What are the criteria for EOFE?
Need to achieve one of: (These are in order of ideal to less ideal, but all are acceptable)
- Plateau: <25 mL/second change in the last second and this is the MOST reliable indicator. (Having glottic closure would over ride meeting this criteria)
- Forced exhalation time of >=15 seconds
OR
- For patients who can’t blow out long enough to achieve plateau (eg. kids who will have elastic recoil), they just need to achieve a consistent FVC, which is: greater than or within repeatability tolerance of largest FVC prior. (If there are 2 different sets of tests done such as pre/post bronchilator, you compare to the FVC within that set)
If EOFE is not met, is there any value in the forced exhalation time maneuver.
Yes, you would be able to use the FEV1 or the FEV0.75. (There is no requirement for a specific forced exhalation time)
How should FIVC compared to FVC for acceptability?
FIVC - FVC <=100 mL or 5% of FVC, which is greater
Which parameter is affected by cough in the first second?
Just the FEV1
Which parameter is affected by glottic closure in the first second? After first second?
First second: FEV1
After first second: FVC
What happens if there is a faulty zero flow setting?
Can over or underestimate both FEV1 and FVC
What are the within test acceptability criteria?
Start of test:
- Back extrapolated volume <5% of FVC or 100 mL, which is greater
- FIVC-FVC <5% of FVC or 100 mL, which is greater
(Same numbers to memorize for these initial criteria)
During test:
- No faulty zero flow setting
- No cough in first second
- No glottic closure in first second or after first scecond
- No leak
- No obstruction of mouthpiece
End of forced exhalation, achieve 1 of the 3 criteria:
- Plateau: <25 mL/second change in the last second of the test
- Expiratory time >=15 seconds
- FVC is larger than or within repeatability tolerance of the largest FVC prior
For the within test criteria, which criteria are NOT required for usability, but ARE required for acceptability?
4 of them:
- Glottic closure after first second
- Leak of mouthpiece
- Obstruction of mouthpiece
- FIVC - FVC
- All of the end of forced exhalation criteria
What are the repeatability criteria for >6 years of age?
- Two largest (so the largest and next largest) FVC within 150 mL
- Two largest FEV1 within 150 mL
What are the repeatability criteria for <= 6 years of age?
- Two largest FVC are within 100 mL or 10% of largest value, whichever is greater
- Two largest FEV1 are within 100 mL or 10% of largest value, whichever is greater
What is the maximum number of maneuvers?
8 in adults, may do more in children, be mindful of fatigue
For the spirometry report, how are other values (besides FEV1 and FVC determined)?
- FEV1/FVC is from the chosen FEV1 and FVC values
From the maneuver with highest sum of FEV1 and FVC–>I am 99% sure that this is not the case, there’s specifics about how other values are chosen
Which FEV1 and FVC for the spirometry report?
- FIVC and PEF: largest values from maneuver with acceptable FEV1
- Forced exhalation time is from maneuver with largest FVC
Do we measure bronchodilator reversibility or responsiveness?
Better to use the word “responsiveness” than “reversibility”, as per ATS 2019
When should BD testing be done?
- Initial diagnostic spirometry and then as needed
What is the BD withholding time for SABA?
4-6 hours
What is the BD withhold time for SAMA (eg. ipratropium)
12 hours
What is the BD withhold time for LABA (eg. formoterol, salmeterol?
24 hours (36 hours for methacholine challenge as per ERS 2017)
What is the BD withhold time for LAMA (eg. tiotropium)
36-48 hours
Does ICS need to be withheld for BD testing?
NO
Does LTRA need to be witheld for BD testing?
No
How is BD testing done?
Ventolin 100 mcg/puff x 4 doses, then wait 15 minutes
How does ATS define positive BD response?
- Does not differentiate based on age
- Increase in FEV1 or FVC by >=12% AND >= 200 mL
(This is a pure PFT interpretation of BD response)
In contrast, CTS asthma guideline just looks at FEV1 for BD response.
<12 years: >=12%
>=12 years: >=12% and >=200 mL
PFT for pulmonary vascular disease?
No obstruction
No restriction
Low DLCO
PFT for restrictive disease?
No obstruction
Low FVC and TLC
DLCO is low for ILD, pneumonitis
DLCO is normal for neuromuscular or chest wall disease
Obstruction, low DLCO, no restriction?
Emphysema
What is a moderately severe decrease in FEV1?
50-59%
What is a severe decrease in FEV1?
35-49%
What is a very severe decreased FEV1?
<35%
What are indications for spirometry?
- Diagnosis (eg. asthma)
- Monitoring (eg. CF, asthma)
- Disability/impairment evaluation (eg. monitoring as part of rehab program)
- Other (eg. research and clinical trial)
What are relative contraindications to spirometry?
Cardiac:
- Acute MI in the last week
- Uncontrolled pulmonary hypertension
- Syncope from forced exhalation or cough
- Acute cor pulmonale
- Unstable pulmonary embolism
Increased intracranial/intraocular pressure:
- Eye surgery in the last week
- Brain surgery in the last month
- Recent Concussion with ongoing symptoms
- cerebral aneurysm
Sinus and middle ear pressure:
- sinus or middle ear surgery/infection within last week
Intrathoracic/intraabdominal:
- pneumothorax
- thoracic or abdominal surgery in last month
- late term pregnancy
Infection control issues:
- TB
- Significant oral secretions or hemoptysis
Memory tool:
1 month for “big” surgeries
1 week for small surgeries like eye or ear
What is the effect of pulmonary hemorrhage on DLCO ?
Acute versus non-acute phase?
What is the anaerobic threshold?
The point at which you are in intense exercise and switch from aerobic to anaerobic metabolism–>increased lactate production, which exceeds removal. Also lots of CO2 production–>increased ventilation
Anaerobic threshold is also called ventilatory threshold
Methods for anaerobic threshold measurement?
V-slope method and ventilatory equivalence method are the best, ATS recommends using a combination of both
1) V-slope method: graph of VCO2 versus VO2. There is an abrupt increase in slope and VCO2 increases relative to VO2
2) Ventilatory equivalence: PETO2 relative to workload, PETCO2 relative to worklaod
3) VE/VCO2 relative to VO2 and VE/VCO2 relative to VO2
How does exercise increasing diffusing capacity?
Increased diffusing capacity due to recruitment and distension of vessels
Pulmonary limitation to exercise, CPET findings?
Ventilatory limitation like decreased breathing reserve, expiratory flow limitation, dynamic hyperinflation
Desaturation <88%
HR
What are signs of maximal CPET
5 things:
- RER>=1.1
- HR>90% maximum
- VO2 plateau
- Borg dyspnea>9/10
- ventilatory limitation
Indications for CPET
Categories: exercise intolerance, tolerance, pulmonary, cardiac, rehab
- evaluation of undiagnosed exercise intolerance and assessment of cardiac or pulmonary etiology
- evaluation patients with pulmonary disease to determine exercise limits and provide oxygen prescription (eg. COPD, ILD)
- pulmonary rehab for exercise prescription
- evaluation of exercise tolerance like Peak VO2
Contraindications for CPET
These are all very obvious
- Room air desaturation <85% (but >85% is not a contraindication)
- Acute MI in last 3-5 days
- Syncope
- Uncontrolled asthma
- Acute PE
- Uncontrolled arrythmia
Contraindications for methacholine challenge
It’s actually the same contraindictations for all bronchial challenge tests (as per ERS 2017 but FEV1 cut off is 75% for exercise challenge):
- FEV1<60%
- Inability for acceptable and repeatable flow volume loops
- Inability to cooperate with maneuvers, such as young children
- Cardiac:
- MI in last 3 months
- uncontrolled hypertension
- aortic aneurysm
- recent eye surgery or risk of increased ICP
Specifically for methacholine:
- pregnant and nursing: not known if methacholine is released in breast milk (Relative contraindication)
- current use of cholinesterase inhibitor, eg. myasthenia gravis (relative contraindication)
What is the outcome in methacholine challenge?
PD20 = dose of methacholine at which FEV1 drops by 20%
What is the utility methacholine challenge? Is it rule out asthma or rule in asthma?
- biggest value is to EXCLUDE a diagnosis of asthma. Methacholine is very sensitive, so if the result is negative, then that is very helpful
What is the difference between direct versus indirect bronchial challenge tests?
Direct: direct stimulation of the muscarinic receptors on airway smooth muscle, since methacholine mimics acetylcholine. Direct challenge: methacholine, histamine. Direct challenge is very sensitive, so more helpful for ruling out a diagnosis of asthma if negative.
Indirect –pretty much everything, which indirectly will cause airway narrowing. Eg. exercise (which causes airway drying and cooling), eucapneic hyperventilation, osmolar agent like 3%, allergen. Indirect challenge is less sensitive, but with a positive result–>more helpful to rule in a diagnosis of asthma
How do you interpret methacholine challenge?
PD20 >400 (PC20>16) - negative
PD20<25 (PC20<1) - moderate to severe hyper-responsiveness so suggestive of asthma
PD20 25-400–indeterminate, most values will fall in this range
What medications need to be stopped before allergy skin testing?
- Antihistamine x 1 week
- Anithistamines for nausea x 2 weeks
- H2 receptor antagonist x 48 hours
- Nasal antihistamine x 3 days
- Topical glucocortoids x 1 week, only if that skin will be used for testing
- Xolair x 6 months (so think about doing skin testing BEFORE starting xolair)
- TCA x 2 weeks
- LTRA and ICS do NOT need to be stopped before skin testing
Aerobic threshold
Steady low level intensity–“feel like you could go for hours”
Corresponds to 70% of maximum heart rate (220-age) or 80% of lactate threshold
What is forced oscillation technique?
• Measures reactance and resistance during tidal breathing
• Reactance includes elasticity of respiratory tissues and inertness
• Technique:
• Non-Invasive
• small amplitude pressure oscillations are imposed on normal tidal breathing
• Measure: pressure and flow to obtain reactance and resistance
• Resistance (Rrs)—>includes resistance of airways and chest wall, so technically can’t differentiate between obstructive and restrictive. At the mid frequency range, airway resistance predominates (surrogate measure of airway resistance)
o At higher frequencies, the chest wall resistance dominates
o For clinical useful surrogate of airway resistance, you want to use a medium frequency range, which should include 4-8 Hz
o With increasing airway resistance, Rrs increases
• Limitations of this technique:
o Poor tolerance of the procedure by the child —refusal to use mouthpiece or face mask, inability to breathe without a leak, difficulty breathing against imposed oscillations
o Mouthpiece leak
o Wide range of reference values for a given height, which has limited the clinical potential of this test
Why does R increase with increase?
R = VCO2/VO2
- It initially increases because increased proportion of carbohydrate utilization
- when you reach anaerobic threshold, VCO2 increases relative to VO2. R is >=1.1, which is part of the interpretation of CPET as being maximal
What is O2 pulse?
VO2/heart rate (poor man’s version of stroke volume)
On CPET, which graph do you look at for breathing reserve?
VE on y axis
VCO2 on x axis
During exercise how does PaO2, PETO2 and A-a gradient change?
PaO2 is stable
PETO2 is initially stable, but then increases after anaerobic threshold due to increased ventilation (and decreased oxygen utilization)
A-a gradient increases after anaerobic threshold (which is why PaO2 is stabe)
What is the amino acid precursor of NO?
L-arginine
What enzyme produces NO?
Nitric oxide synthase
What is the role NO in asthma?
- Exact pathophys of NO in the airway unclear
- It may act as a proinflammatory mediator. Inflammationincreased NO synthaseincreased nitric oxideincrease airway hyperresponsiveness, formation of reactive nitrogen species
- OR: it may promote smooth muscle relaxationprotect against airway hyperresponsiveness and inhibits inflammation
What is the FEV1 cut off for contraindication to exercise challenge?
FEV1 <75% is a contraindication
What does a positive skin prick test or in vitro test of allergy?
It means that there is presence of allergen specific IgE and the patient may react on exposure
Is positive skin prick on vitro test enough to diagnose allergy?
No, since 3 criteria:
●Identification of the possible culprit allergen(s), usually through a careful clinical history.
●Demonstration of IgE specific to the allergen(s) by skin testing or in vitro testing.
●Determination that exposure to the allergen(s) results in symptoms, either by history or with a challenge procedure.
Advantages of skin prick test relative to in vitro (eg. Elisa or Rast)?
- MORE sensitive
- cost effective
- visual feedback
- can test unusual allergens
- rapid results in 15-20 min
Advantages of in vitro versus skin test for allergy?
- No risk of anaphylaxis
- Don’t need to withhold medication
- Not affected by skin reactivity–eg. lower reactivity in infants<12 months of age, dermatographia, extensive eczema, skin is less responsive for weeks post anaphylaxis
Aspects of quality control to establish PFT lab?
- daily calibration of spirometer at low, medium and high flow
- 3L daily calibration syringe: daily inspection for displacement of piston stop
- daily check for smooth movement of syringe, with no sticking or catching
- log book of quality control findings, repairs, adjustments, hardware and software updates
2005 statement:
- Manual of procedures containing calibration procedure, performance procedures, calculations, criteria, reference value source
- Documentation of daily instrument calibration, problems with the system, corrective measure, system hardware and software upgrades, recording of anomalous events and response to events
- Technician should keep a record of continuing education and results of education/evaluation/feedback from medical director
When speaking to an adult PFT tech, what are unique issues for pediatric versus adult PFT?
- Enthusiastic coaching
- Simple instructions
- Visual display
- Children may need to practice parts of a maneuver before doing a full maneuver
- May be ok to do more than 8 maneuvers since not all maneuvers may be maximal. (But be aware of enthusiasm and fatigue to avoid exhaustion or discouragement)
What is the FEV0.75
Used in children <6 years of age who a fast exhalation time as they have large airways (and I think higher elastic recoil). Can provide similar info as FEV1
Series of steps for PFT interpretation based on ATS interpretation algorithm from 2005?
- Start with FEV1/FVC
- Then look at FVC. If FVC is low, then look at TLC
- If FVC is normal, then look at DLCO
What causes variable intrathoracic obstruction? Draw the appearance.
- Tracheobronchomalacia
- Bronchogenic cysts
- Some types of tracheal cancer
Causes of variable extrathoracic airway obstruction? Draw the appearance
- Vocal cord paralysis
- Tracheomalacia
- Mobile tumors
Causes of fixed airway obstruction?
Draw the appearance
Tracheal stenosis
Tracheostomy
Subglottic stenosis
Goiter
Talk through the series of steps for CPET interpretation
CPET interpretation evernote
Findings on CPET for CV limitation
- Rapid increase in HR
- Low O2 pulse
- Low VO2 max
- Low anaerobic threshold
- VE increases rapidly since early anaerobic threshold and increased H+
Findings on CPET for athelete
- Flatter HR response
- High O2 pulse
- High VO2 max
- Higher anaerobic threshold
- Higher VE
- Athlete is cardiac and ventilatory limited
Which test is used to obtain LCI?
Multiple breath washout test
How is the LCI obtained?
- measuring washout of an inert tracer gas (either N2 or SF6) during relaxed tidal breathing. LCI is the number of lung turnovers for the end tidal tracer gas concentration to decrease to 1/40 of it’s initial concentration
LCI = cumulative expired volume/FRC
It’s more sensitive than spirometry for early lung disease in CF where is more distal small airway involvement
Unique features of PFT for preschool child?
- Combination of ATS 2019 and Preschool statement from 2006
- Volume-time and flow-time curve should be inspected for rapid rise to peak, smooth descent with no glottic closure or cough
- minimum of 3 maneuvers, no maximum
- (back-extrapolated volume is helpful to figure out time point for FEV1 starting), but a maneuver does not need to be rejected if it does not meet the back extrapolated volume criteria. (That being said, back extrapolated volume tends to be lower in children than in adults)
- Repeatability critieria is the same as 2019 statement: 2 largest FEV1 and FVC should be within 100 mL or 10% of largest value
- even if there is premature termination, the FEVt could be used, even if FVC and ratios cannot be used
Is skin testing better for positive or negative predictive value?
Role of histamine and saline controls?
- Skin tests are better for negative predictive value. They are sensitive, but not specific. As a whole, the positive predictive value is 50%. Higher sensitivity for inhalant allergens compared to food allergens.
- Histmamine: positive control. A positive skin test is wheel + erythema >= histamine response, which is usually 3 mm.
- Saline or other negative control–this should be the same diluent that is used for the allergen extracts
Staining for langerhan’s cell histiocytosis?
- CD1A
- S-100
- Langerin stain
What is the difference in lung volume obtained by gas dilution method versus body plethysmography?
- Gas dilution: this only measured ventilated lung volume, not lung that is not ventilated due to atelectasis or mucous plugging
- Body box: measures total volume in lungs, including gas that is trapped behind a closed airway
How do lung volumes change in obstructive disease?
- Obstructive airway disease–>can’t get air out, so lung volumes will increase as there is worsening disease severity
- Increased TLC, Increased RV, Increased FRC
- RV will increase more than TLC and this is why there is air trapping
- TLC can’t increase initially since there has not been an increase in chest wall size
- Earliest change: increased FRC, increased residual volume, increased RV/TLC
- With progression: increased TLC
- With severe obstruction, there is a decrease in the vital capacity
What are the lung volume abnormalities for a restrictive lung disease (extra thoracic or intrathoracic)?
- There are decreased lung volumes for all of them
- Decreased TLC, RV, VC, FRC but there is increased air trapping (RV/TLC)
Does air trapping (increased RV/TLC) differentiate obstructive versus restrictive disease?
- No, there can actually be air trapping in both
What are the general categories of restrictive lung disease?
- Extrathoracic: obesity, chest wall (eg. scoliosis), neuromuscular
- Intrathoracic: pulmonary (Eg. ILD)
- Pleural disease is on the list, though I’m not entirely sure how
From a purist perspective, if you are calculating FEV1/VC, then which VC measurement should use?
- Use the largest VC value, whether it’s the FVC or SVC
- If there is airway obstruction, then SVC may be larger then FVC
- By using the largest value, the ratio is more sensitive for detecting obstruction
What is mild obstruction?
- FEV1>70% (there is no upper limit), there doesn’t seem to even be a normal for FEV1
What is the definition of normal DLCO, based upon percent predicted?
75-125% is normal, unless there is a range for LLN and ULN provided
How does DLCO compare for chest wall disease, obesity, muscle weakness and pulmonary fibrosis?
- They all have a decreased total DLCO
- For non-pulmonary causes of restriction, there is less diffusion because the lung is smaller in volume
- Therefore, when DLCO is corrected for VA, it should normalize
- But for ILD, the main reason for poor diffusion is increased diffusion barrier thickness and so correcting for VA will not normalize DLCO
What disease causes obstruction + decreased DLCO?
Emphysema
What is the DLCO in asthma?
- Either normal or increased
my simplified explanation for why it’s increased: hyperinflation–>increased area for diffusion
What is the difference between SpO2 versus SaO2?
SpO2 is the saturation as measured using a pulse oximeter. This is an estimate of the SaO2, which is measured using a blood gas.
Why is a percent saturation <70% not accurate?
- The pulse oximeter will calculate a number called “R”, based on the absorption of the two wavelengths of light that it shot though tissue
- R will correspond to a particular percent saturation value
- The problem: the calibation was done based on healthy volunteers, so no one had a saturation <70%
How do abnormal hemoglobins affect percent saturation, as measured on oximeter?
- MethHb (chocolate colour): absorbs at both the red and infrared spectrum, so you get a persistent saturation of 85%
- CoHb: decreased absorbance at infrared, but same absorbance as oxyhemoglobin at red end of the spectrum, can get a falsely elevated saturation
- Fetal hemoglobin will not affect the percent saturation
- Saturation may not be accurate for abnormal hemoglobin, like sickle cell
What are the withhold times for various medications for methacholine challenge, including SABA, atrovent, LTRA, LABA, smoking, ICS?
From ERS 2017:
- SABA: 6 hours
- LABA: 36 hours
- Atrovent: 12 hours
- ERS 2017 specifically says that LTRA does NOT need to be with-held, caffeine does not need to be with-held
From a generic table in ATS 1999:
- LTRA: 24 hours
- Reactine: 3 days
- Food like coffee, cola: the day of
- Smoking: uncertin duration
- ICS does not need to be held
What is the normal range for FeNO? How is a significant change in FeNO defined?
- Adults: 25-50 intermediate, <25 is low, >50 is high
- Children: 20-35 intermediate, <20 is low, >35 is high
- Significant change:
- > 50: 20% change
- <50: 10 point change
- FeNO can be used in a complementary manner to diagnose and treat asthma, but can’t be used on it’s own
Advantages and disadvantages of FeNO?
- Easy test
- quantiative
- non-invasive
- identifies eosinophilic inflammation and patients who are likely to be steroid responsive
Disadvantage:
Non-specific to asthma (eg. can be elevated with EGPA, eosinophilic pneumonia, Cannot identify non-eosinophilic inflammation
Can lead to use of higher ICS doses with no clinical correlation
Methods of testing for allergen sensitization and their sensitivity?
- You can test for allergen specific IgE by:
- In vitro testing - such as ELISA, RAST
- Skin testing: prick puncture method or intradermal method
- Intradermal method > prick puncture > in vitro testing
What medications need to be with-held prior to allergen skin testing?
- Antihistamine x 1 week
- Nasal antihistamine x 3 days
- H2 receptor antagonist like ranitidine for 48 hours
- TCA antidepressant can decrease skin reactivity x 2 weeks
- Xolair can decrease skin reactivity x 6 months
- don’t need to stop ICS, inhaled steroid or LTRA
Anxiety on CPET, clues?
- hyperinflation with no airflow limitation
Clue for pulmonary hypertension on CPET?
- low CO2 due to hyperventilation
Why is CPET less sensitive for EIB?
because there is a warm up phase. With EIB testing, there is no warm up phase
What is normal breathing reserve on a CPET?
> 15%
Why is exercise a sensitive time to identify problems with lung diffusion?
- The A-a gradient increases with exercise, so normally the lung can increased diffusion through recruitment and distension (this ability to compensate will limited if there is a pre-existing diffusion problem)
- Less time for diffusion with exercise since increased HR
What are general features of the exercise challenge protocol?
- Rapid increase in intensity to peak exercise level over 2-4 minutes
- want to achieve high ventilation of 20x FEV1
- maintain high intensity for only a short period of time - about 6 minutes
- breathing dry air
What are some non-pharmacologic strategies for minimizing EIB?
- Warm up period–>this can induce a refractory period for EIB for about 2 hours
- Conditioning–with better cardiovascular conditioning, there is less respiratory demand during exercise
- Warming and humidfiying air - eg. wearing a mask, breathing through nose
Is there a FEV1 cut off for safety of doing exercise challenge test?
- FEV1>75% to proceed with testing
What is the difference between PD20 and PC20 and which one is preferable?
- PD20 = dose of methacholine (absolute dose)
- PC20 = concentration of methacholine from post diluent baseline)
- PD20 is better since it is easier to compare methacholine response across different protocols
What are the cutoffs for interpretation of methacholine challenge?
PC20:
- > 16: negative
- <4: mild positive
- <1: moderate positive
- <0.25 : very positive
PD20:
- > 400: negative
- <100: mild positive
- <25: moderately positive
- <6: very positive
(based on table in ERS 2017)
Normal values for MIP and MEP?
MEP: 90-230 cm H20 normal
MIP: 70-120 cm H2O
SNIP: 75-110 cm H20
PFT abnormalities with neuromuscular disease?
- decreased FVC
- normal or high RV
- normal or high RV
- TLC is decreased less than FVC
- high RV/TLC (air trapping in absence of obstruction)
- low MIP,MEP, SNIP
What spirometry values should be reported for preschool spirometry?
- FEV1, FEV0.5, FEV0.75
- FVC
- best curve is the one with the highest sum of FEV0.5 + FVC
What are the acceptability and repeatability criteria for spirometry in preschool children?
Acceptable:
- visual inspection of curve: rapid rise to peak, smooth descending limp
- may not reject a curve based on back extrapolated volume. (preschoolers tend to have lower back extrapolated volume)
- only need to have 2 acceptable maneuvers
Between test/repeatability:
- largest FEV1 and FVC need to be within 100 mL or 10%
Which preschool/infant PFT tests may be most useful in CF?
- MBW –>more useful for preschool children than infants
- RV-RTC
What is the potential clinical value of specific airway resistance (sRaw)?
- may be helpful in differentiating preschool children with asthma
- in CF, it is more sensitive than spirometry, but less sensitive than MBW
What is the clinical value of R interrupter?
- Unclear
- Doesn’t seem to be helpful for CF or kids with recurrent wheeze
What is the clinical utility of forced oscillation technique?
Iimited, doesn’t seem to be great for CF or asthma
Slow versus forced vital capacity and benefit?
When an FVC maneuver is performed, there is higher dynamic compression and airway collapse, reducing the ability to mobilize the volume of air during exhalation and therefore causing air trapping. Consequently, FVC values can be lower than SVC values; because SVC is measured through an unforced maneuver, there is less intrathoracic pressure, and, consequently, a larger volume of air can be mobilized
Using SVC instead of FVC in the FEV1/VC ratio enhances the yield of spirometry in detecting mild airflow obstruction in younger and obese subjects. The FEV1/SVC ratio, however, should be used with caution in elderly subjects with preserved FEV1/FVC because a low value may represent a false-positive finding for airflow limitation
(For health people without airflow obstruction, the FVC and SVC should be quite similar)
How is EIB defined?
> =10% decrease in FEV1 on spirometry completed within 30 minutes after end of exercise (difference between pre-exercise FEV1 and lowest FEV1 post exercise, within 30 minutes)
What is normal MIP/MEP?
80-120
<60: you are thinking about cough assist
what are some technical parameters that are required for the DLCO maneuver?
- IVC must >90% of vital capacity during same testing session
- Ideally want to have 2 repeatable maneuvers (within 2 mL/min/mmHg) and want to report the mean of these maneuvers
