Pulm Function Testing Flashcards
1
Q
6 Indications for PFTs
A
- Categorize
- Obstructive v. restrictive
- Asthma v. emphysema
- Objective Assessment
- Document an abnormality - “disability”
- Distinguish from psych problem –> SOB
- Document Progression
- COPD
- ALS
- Document Response to Therapy
- Asthma control
- Lung volume reduction surgery
- Preoperative
- Want to make sure you have enough lung reserve to undergo lung cancer resection
- Timing of lung transplant
- Screen for sub-clinical disease
- May screen for emphysema in smokers or in those w/ occupation risk
2
Q
What does spirometry measure?
A
1- Exp Volumes
- Forced vital capacity (FVC) if max effort
- Slow vital capacity (SVC) if slow and steady exhalation
2- Exp Rate
- FEV1 - volume expired in 1st sec
- FEF 25-75 -flow rate b/n 25-75% forced vital capacity
- FEV1/FVC
3
Q
What are the normal spirometry values? Which ones fluctuate and how?
A
- normal FEV1/FVC > or = .7 regardless of demographics
- Whereas FEV1 and FVC individually fluctuate by demographics (dec w/ age, lower in females, lower in asians/blacks, inc w/ height)
- Normal = w/in 20% of predicted values (80-120% range)
4
Q
Why are flow-volume curves superior to volume-time curves for spirometry results?
A
- Better for detecting patterns
- Better for detecting quality control
**Should be … 4 seconds long, 3 acceptable loops w/ less than 5% difference b/n them
5
Q
Fixed Upper Airway Obstruction Pattern
Variable Extra-Thoracic Airway Obstruction Pattern
Intra-Thoracic Upper Airway Obstruction Pattern
A
- Fixed Upper Airway Obstruction - inspiratory and expiratory plateaus
- Ex) fixed tracheal stenosis
- Variable Extra-thoracic Obstruction - normal expiratory loop but inspiratory plateau
- Ex) glottic tumor or redundant tissue in obesity/sleep apnea
- Intra-thoracic Upper Airway Obstruction - have expiratory plateau but normal inspiration curve
- Ex) tracheal tumor OR chondromalacia
6
Q
Bronchodilator Response
A
- Determine reversibility of airway obstruction by comparing spirometry b/f and after bronchodilator med (usually beta-agonist)
- Pos - if inc FEV1 by 12%+ OR if inc FVC by 200 mL+
- Pos response to bronchodilator can dx asthma
7
Q
Bronchial Challenge
A
- For episodic symptoms you can induce them in office (chemicals, particulates, methacholine, histamine-derivative which induces bronchospasm only in those w/ asthma) OR give portable device to use at home or work
- 20% reduction in any parameter (FVC, FEV1 or peak expiratory flow) is positive
8
Q
Obstructive v. Restrictive Disease on Spirometry
A
OBSTRUCTIVE
- Normal volume expired but takes longer to come out due to resistance
- FEV1/FVC < .7
- Maybe first noticed as normal FEVI/FVC but FEF25-75 <65% predicted value
- Can have dec FVC (air trapping)
RESTRICTIVE
- Lower volume expired but normal rate
- Dec FVC and dec TLC
- BUT normal FEV1/FVC b/c both decrease in proportion (normal rate)
9
Q
2 Tests to Meas Vol in Lung
A
(RV, TLC, FRC)
- 1- Helium Dilution
- Use a closed system w/ helium of known amount into spirometer
- Conc1 x V1 = Conc2 x V2
- If you can meas change in helium conc then you can calculate the change in total gas volume when pt breaths in
- Use helium because it is not soluble so does not move into blood like oxygen or carbon dioxide would
- 2- Body Plethysmography
- Access pressure shift at mouth against closed airway (tells you change in pressure)
- Access change in box pressure (tells you change in lung volume)
- P1V1=P2V2
- Larger lung volume will cause huge dec in pressure w/ expansion (volume inc) v. smaller lung volume will cause smaller dec in pressure w/ expansion (volume inc)
- Look at change in mouth pressure and use this to determine original lung volume
10
Q
How do you measure diffusion capacity?
A
- Meas gas exchange NOT ventilation
- Give mix of small quantity of CO, helium and oxygen
- Helium tells you how much dilution there is
- CO tells you how much diffusion by meas conc of CO b/f and after (use CO b/c binds Hb and has high P gradient)
- Abnormal if less than 80% predicted value
