Term
| What are the available PFTs to test Ventilation, Diffusion and Circulation, respectively? |
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Definition
1) Ventilation
- Spirometry
- Lung volume
- Inspiratory (MIP) and Expiratory (MEP) pressures
- Lung compliance (rarely)
- Maximal voluntary ventilation
- Exercise ventilation (Ve-max, Vd/Vt)
2) Diffusion
- Diffusion capacity
- Exercise O2 sat
3) Circulation
- Diffusing capacity (DLco)
- Cardiopulmonary exercise (VO2-max) |
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Term
What is the most common PFT used to assess volume and flow rate?
How can it be used to detect airway obstruction? |
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Definition
Spirometry.
Normally, Forced VC and Slow VC are the same, but in the case of an obstruction, FVC will be lower because the extra effort leads to airway compression and early closure. |
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Term
| What does a FEV1/FVC ratio of 0.6 means in terms of pulmonary function? |
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Definition
FEV1 is forced expiratory air in 1s, but it depends upon starting volume, so it is normalized against the FVC for that individual.
Values <0.7 mean that there is significant airway obstruction (you can't expire much in a reasonable amount of time). Think of Chronic bronchitis, Emphysema and Asthma |
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Term
| What volume measurements can be obtained by spirometry alone? |
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Definition
Vital capacity (FVC and SVC)
NOT RV, FRC and TLC, because for these you must measure the air remaining in lungs. |
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Term
True or False:
Patient's of European decent tend to have spirometric values that are 10% lower than african americans |
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Definition
False.
AA and asians are 10% lower than whites
REMEMBER, +/- 20% is normal variation anyways |
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Term
A patient comes in for Spirometric testing and you find that their FVC is depressed. However, their FEV1/FVC ratio is slightly elevated. Which of the following could be their diagnosis?
1. Asthma
2. Emphysema
3. Pulmonary fibrosis
4. Chronic bronchitis |
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Definition
3. Pulmonary fibrosis
A depressed FVC with a normal/elevated FEV1/FVC ratio indicates RESTRICTIVE rather than obstructive pulmonary disease.
Asthma, Chronic bronchitis and Emphysema are all obstructive, while Pulmonary fibrosis represents a decrease in lung compliance.
Other good examples of restrictive disease are Pulmonary edema (lung compliance), Kyphoscoliosis (chest compliance), pleural disease and respiratory muscle disease. |
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Term
A patient comes in for Spirometric testing and you find that their FVC is depressed, with an FEV1/FVC of 0.5. Which of the following could be their diagnosis?
1. Pulmonary edema
2. Kyphoscoliosis
3. Pulmonary fibrosis
4. Chronic bronchitis
5. Pleural disease |
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Definition
FEV1/FVC ratio < 0.7 indicates obstructive disease. ONLY chronic bronchitis is an obstructive disease.
Pulmonary fibrosis, Kyphoscoliosis, Pleural disease and Pulmonary edema are all restrictive |
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Term
| Why give someone with a sprirometry FEV1:FVC ratio of 0.5 a beta-2 agonist and then retest them? |
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Definition
| To see if the obstruction is reversible. 12% improvement is considered positive |
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Term
| Why is Metacholine used clinically in PFT? |
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Definition
Bronchial challenge as part of spirometric testing for episodic diseases.
For example, you can induce vasospasm in occult asthmatics and look at FEV1, FVC and Peak expiratory flow.
A drop in PEF of >20% is positive! |
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Term
| Why is it useful to depict spirometric tracings as flow-volume loops rather then volume vs. time graphs? |
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Definition
1) assessment of effort on repetitive testing
2) presence of specific upper airway obstruction patterns |
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Term
| How can you tell between intrathoracic and extrathoracic variable upper airway obstructions with spirometry? |
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Definition
Intrathoracic obstructions will improve on inspiration, while Extrathoracic obstructions will worsen.
Look at the flow-volume loop to see if inspiration is blunted (extrathoracic) or whether expiratory peak is missing (intrathoracic) |
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Term
| Why might you use helium dilution? |
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Definition
Closed-circuit technique to measure RV
Fixed-amount of helium is inspired and expired with spirometer.
C1V1= C2 X (V1+ V2) |
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Term
| How can Body plethsymoography measure FRC? |
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Definition
Large glass box where patient sits in and breathes through mouth piece.
Uses boyle's law to see how much air is left in patients lungs at the time when the mouthpiece closes (if you have little left, you will suck in harder and create a higher intra-mouth piece pressure).
From FRC, other values can be calculated |
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Term
| Why is Body plethysmography preferred over Helium dilution testing in patients with bullous emphysema? |
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Definition
Helium dilution only measures gas that communicates with an equilibrates at the mouth, while BP measures total volume within the chest (including non-communicating bullae).
Helium dilution may underestimate RV and FRC |
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Term
| How is diffusing capacity of CO used clinically? |
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Definition
1) Single breath measurement assesses efficiency of gas exchange at pulmonary-capillary membrane. It represents the amount of functioning capillary bed in contact with ventilated alveoli.
- Since CO has such high binding affinity, limiting factor for diffusion becomes functional status of alveolar-capillary membrane.
2) Subject inhales mixture with CO and inert helium (adjusting for gas dilution) to TLC and holds for 10s, before exhaling. Initial and final concentrations are measured and a value <80% is abnormal. |
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Term
| When might you see elevated vs. depressed DCco? |
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Definition
1) Elevated (more capillary-alveolar contact)
- Polycythemia
- Mild CHF
- Asthma
- Pulmonary Hemorrhage
2) Depressed
- Emphysema
- Interstitial lung disease
- Pulmonary vascular disease |
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