Pulmonary Function Tests Flashcards
What is the difference between capacities and volumes?
Volumes can be directly measured or at least estimated
Capacities are a sum of at least 2 volumes
What are the 3 patterns of disease you can see on PFT?
Obstructive
Restrictive
Mixed
How is residual volume measured?
It’s not, it has to be estimated based on previous measures of other dead people
What makes up functional residual capacity?
ERV and RV
What is the significance of the functional residual capacity!? TEST QUESTION
it is when the system is at equilibrium. It is the volume at which elastic recoil of the lung is balanced by desire of the chest wall
What comprises the functional residual capacity?
Sum of ERV and RV
this requires effort
What comprises the total lung capacity?
RV, ERV, TV, IRV
requires effort
requires estimation of RV
What is a normal airflow spirometry test?
6 second expiratory time
curved plateau for at least 1 second
you have to reproduce the test 3 times and do the maneuvers within 200 mL
What is a normal FEV1/FVC?
0.8
what is the hallmark of obstructive lung disease?
Reduced FEV1/FVC
How do you diagnose restrictive disease on spirometry?
You can’t diagnose restrictive diseases solely by spirometry. You must have lung volumes to accompany them. This is because FEV1/FVC can either be elevated or preserved
What portion of expiration is “effort independent” and how does this show up on a flow volume loop?
The latter 2/3rd of expiration are effort independent meaning that the rate of expiration will not increase with effort. This shows up as a linear decline in flow on the flow volume loop. This portion of the curve is solely determined by the elastic recoil of the lung and airway resistance
Which limb of the flow volume loop is typically symmetric?
inspiration side
How will obstructive disease show up on a flow volume loop?
Left shift with “caving”
how will restrictive disease show up on a flow volume loop?
supranormal airflow with right shift
What are the characteristics of a variable extrathoracic obstruction? What changes on the flow volume loop?
The obstruction is open during expiration and closed during inspiration.
Flow volume loop shows flattening of the inspiration curve
What are the characteristics of a variable intrathoracic obstruction? What changes on the flow volume loop?
The obstruction is closed during expiration and open during inspiration.
Flow volume loop shows flattening of expiration
What is a shortcut to figure out what type of variable obstruction is present from a flow volume loop?
draw a line from the flattest part to the pointiest part of the curve and which way the arrow points will point either up (extra thoracic) or down (intrathoracic)
what method of obtaining lung volumes is the most accurate and which formula does it use?
plethysomography (does not require diffusion of gas) and it uses Boyles Law (P1V1=P2V2)
What will be elevated in lung volumes if air trapping is present?
RV
What will be elevated in lung volumes with hyperinflation?
TLF or FRC >120% predicted and RV >140%
What are the characteristics of lung volumes that are restricted?
decreased TLC or FRC
What are the 4 things that determine DLCO?
Surface area
Membrane thickness
Diffusion gradient of gas
Presence of hemoglobin
how is DLCO measured?
CO breathhold for 10 seconds
you breathe in a known amount of CO and the amount of CO returned in INVERSELY PROPORTIONAL to alveolar function
What is the DLCO in emphysema and why?
decreased
because there is decreased surface area
What is the DLCO in interstitial lung disease and why?
decreased
because there is increased membrane thickness
What is the DLCO in pulmonary edema or pneumonia and why?
decreased
because there is alveolar filling
What is the DLCO in pulmonary vascular disease and why
decreased
because there is decreased pulmonary blood flow
what is the DLCO with alveolar hemorrhage?
increased
Why is it important to correct for lung volume in DLCO?
if the patient has a chest wall/pleural disease (obesity) or resection of the lung. You can still have normal alveolar function
Where is asthma on a PV curve?
at a higher volume but has the same slope as normal
where is emphysema on a PV curve?
increased volume and steeper slope
where is obesity on a PV curve?
decreased volume with same slope as normal
Where is pulmonary fibrosis on a PV curve?
lower volume with less steep curve
When is a bronchodilator challenge with albuterol positive?
> or equal to 12% change in FEV1 and/or FVC
AND 200 cc increase in volume
What are the 3 major factors that determine DLCO?
- surface area
- membrane thickness
- pulmonary blood flow
