Pulmonary Function Tests Flashcards
When are PFTs indicated?
- Pretty much anytime someone presents with Cough or Dyspnea
- Pre-operative evaluations and response to drugs may also indicate the need for a PFT.
How should you instruct the impatient while performing Spirometry tests?
• what does each of these steps represent in terms of volumes and capacities?
- Breath quietly (Tidal breathing)
- Make maximal inpiratory effort (from FRC to TLC)
- Exhale maximally (TLC to RV) volume expelled is the FVC
What happens happens to Expiratory Reserve volume and Functional vital capacity in obestity?
Both Expiratory Reserve volume and Vital capacity are reduced in obestity.
What does spirometry measure?
• what kind of graph is created as a result of spirometry?
• how long should expiratory effort last in spirometry?
Spirometry measures vital capacity (either FORCE or SLOW) which is important in determining the quality of effort. Spirometry is graphed as Volume-time. Expiratory effors should last at least 6 seconds.
Why is it useful to measure vital capacity using spirometry?
• what are the predictors of FVC?
• Vital Capacity measurements over time are good for knowing if there is an obstruction in the airway. You look at FEV1/FVC. Age, sex, and height are all predictors of FVC
What change in FEV1/FVC after using a bronchodilator tells you that there is a positive change in response to the drug? What disease does this indicate?
200ml increase or 15% increase from basal FEV1 after using a bronchodilator indicates
What is MVV (maximum voluntary volume)?
• what does it tell you?
• what indicates an abnormality?
• what is a possible reason for this?
MVV tell you how much air the patient can exchange in 1 min. You do this by having the patient take deeper than normal breaths for 10-12 seconds. amount of air should be 40xFEV1 if its less it may indicate muscle problems/fatigue
After a pneumonectomy we hope that the MVV is still _________% of FEV1 and after a lobectomy we hope that MVV stays higher than ________% of FEV1.
After a pneumonectomy we hope that the MVV is still 55% of FEV1 and after a lobectomy we hope that MVV stays higher than 45% of FEV1.
Comment on the elastic recoil and flow of gas in this patient’s lungs.
This patient has normal lung function, you can see that FEV1/FVC is 80% indicating adequate lung function.
Comment on the elasticity and flow of this lung
This lung is very elastic (lots of recoil) and FEV1 is a huge percentage of FVC, notice that BOTH are still reduced. This is a restrictive lung disease.
Comment on the elasticity and flow in this lung
This lung has almost no elastic tissue. You can tell this by how long it takes to get all the air out. This person have a reduced FEV1 and FVC, but the FEV1 is reduced more so this is an obstructive disorder.
What are some special methods to measure TLC, because spirometry can’t measure residual volume?
- Body plethysmograph
- Nitrogen washout
- Helium dilution
- Chest Radiography
****WHAT CAUSES REDUCED TLC?****
****WHAT CAUSES REDUCED VC?****
you must know this…
REDUCED TLC:
• Diseases of the Thorax
• Inspiratory Muscles
• Pleural Diseases
• Loss of Functioning Alveoli
REDUCED VC:
• Chest Pain
• Fatigue
• Poor Effort
***What process is happening to a COPD patient at rest?
***what about when they excercise?
At rest COPD patients experience Air Trapping - with this they are cutting into what used to be inspiratory RESERVE volume and are now using it in regular tidal breaths => higher FRC
When excercising patients experience Dynamic Hyperinflation - with this they experience increased air trapping and exhalation is still blunted => FRC gets raised even higher than with just air trapping at rest.
What are the axes of a compliance curve?
• how is compliance measured?
Axes:
• Vol (y-axis) as a function of the amount of pressure needed to distend the lung (X-axis)
Compliance = ∆V/∆P
**Why would you do a slow vital capacity (SVC)?
• what does a normal SVC exlude?
• Laminar flow in an SVC EXCLUDES a RESTRICTIVE DISORDER. Remember laminar flow won’t be possible for people will always push air out at such a high velocity that flow cannot be lamiar
For a restrictive lung disease, patients will have __________ flow velocities for each instananeous volume.
For a restrictive lung disease, patients will have HIGHER flow velocities for each instananeous volume.
• this is easy to understand b/c the lungs have increase elastic recoil, this is what prevents laminar flow in a slow exhalation
What are some causes of upper-airway obstruction?
• what sound is characteristic in this?
INSPIRATORY STRIDOR = upper airway obstruction, note this is any obstruction above the sternal notch
Possible Causes:
• vocal cord paralysis
• Tracheal stenosis
• Goiter
If there is an Extrathoracic airway obstruction, do you expect patients to have more of a problem on inspiration or expiration?
• what will the flow volume loop look like?
Extrathoracic obstructions will cause difficulty in Inspiration. Bottom (inspiratory) portion of the flow-volume loop will be flattened.
What is indicated by flattening of the expiratory portion of the flow-volume loop?
Intrathoracic obstruction
Why can CO be used to measure the diffusion capacity of the lung?
It has high affinity for Hb and is found in low concentration in the blood prior to testing
What two things are required for the appropriate ventilation of O2?
1. Functioning Capillary bed that is IN CONTACT with
2. Ventilated Alveoli
In what patients might you worry about using the single breath method on?
**WHY?**
***Single Breath required an inhaled vital capacity of greater than 1L and 10 seconds of breath holding => this could be a problem in severly diseased patients
Why might DLCO be disproportionately high in a smoker?
• what is a normal DLCO?
CO from inhaled cigarettes may cause a slight increase in measured DLCO, however the single breath method is pretty insensitive to this
NORMAL = 81-140%
Explain why someone might have increased DLCO?
• general principle behind all of these?
Increased DLCO caused by anything that makes diffusion faster (unlikely) or that increased the amount of hemoglobin in the lungs at any given time.
3 Cases:
• Polycythemia
• Hemmorhage in lungs (goodpasture’s, wegner’s)
• Pulmonary HTN (would think this would be the most likely cause)
