Pulmonary Function Tests

Question 1

lung volumes

Answer 1

*VT = tidal volume
*IRV = inspiratory reserve volume
*ERV = expiratory reserve volume
*RV = residual volume

Question 2

lung capacities

Answer 2

*inspiratory capacity (IC)
*vital capacity (VC)
*functional residual capacity (FRC)
*total lung capacity (TLC)

note - a capacity is a sum of 2 or more volumes

Question 3

functional residual capacity (FRC) =

Answer 3

*FRC = expiratory reserve volume + residual volume
*respresents the volume of gas in lungs after a normal expiration

Question 4

total lung capacity (TLC) =

Answer 4

*TLC = inspiratory reserve volume + tidal volume + expiratory reserve volume + residual volume
*represents the volume of gas present in lungs after a maximal inspiration

Question 5

spirometry - overview

Answer 5

*measures AIRFLOW at the mouth
*a single maneuver: Forced Vital Capacity measured by a spirometer
*normal values are predicted based on patient age, sex, and height
*we use the 5th percentile as the lower limit of normal (LLN)
*unable to measure the entire lung volume
*unable to measure diffusing capacity (DLCO)

Question 6

spirometry: FEV1

Answer 6

*forced expiratory volume in the FIRST SECOND

Question 7

spirometry: FVC

Answer 7

*FVC = forced vital capacity
*how much volume is exhaled in the total maneuver (at least 6 seconds long)

Question 8

spirometry: FEV1/FVC

Answer 8

*a ratio showing how much of the total volume is exhaled in the first second
*a normal ratio is > 0.70 (most of your vital capacity is exhaled in the first second)

Question 9

obstructive lung diseases

Answer 9

*diseases where the FEV1/FVC ratio is abnormally low (<0.70)

Question 10

2 steps to interpreting spirometry values

Answer 10

1. is airflow obstruction present?
   -is the FEV1/FVC ratio <0.70?
   -a decreased FEV1/FVC ratio defines obstructive lung disease
2. is the vital capacity decreased?
   -a decreased vital capacity might indicate restrictive lung disease

Question 11

if an identified obstructive lung disease responds to a bronchodilator…

Answer 11

*spirometry can be performed before and after albuterol is given
*RESPONSE (partial or complete) is an INCREASE of 10 or more points in the % PREDICTED value of either FEV1 or FVC
-complete response makes asthma more likely
-partial response may indicate bronchial hyperreactivity in either asthma or COPD

Question 12

bronchoprovocation testing - overview & important measure

Answer 12

*a test designed to provoke the bronchi
*a controlled way to induce bronchospasm - causes diffuse airway narrowing and airflow obstruction
*spirometry is performed before and after the patient inhales increasing concentrations of an airway irritant (methacholine)
*the important measure is the PC20: concentration causing 20% reduction in FEV1
*normal patients’ FEV1 will not fall by 20% during the test

Question 13

bronchoprovocation testing - clinical uses

Answer 13

*a POSITIVE test makes hyperresponsive airways (asthma) more likely [useful when symptoms are infrequent]

*a NEGATIVE test is even better, and makes hyperresponsive airways much less likely
-it is a very sensitive test
-helps to RULE OUT diseases with hyperreactive bronchoconstriction (such as asthma)

Question 14

flow-volume loops

Answer 14

*the best PFT for diagnosing PROXIMAL airway obstruction (ex. obstruction of trachea or mainstem bronchus)

Question 15

effects of lung recoil & chest wall on lung volume

Answer 15

*lung recoil: at all lung volumes, the lungs tend to collapse; they pull away from the chest wall and make a positive force for Prs
*chest wall: at high volumes, the lung recoils inward, producing a positive contribution to Prs

Question 16

functional residual capacity

Answer 16

*the point where chest wall and lung forces are balanced (B)
*the person is “at rest”

Question 17

measuring functional residual capacity (FRC)

Answer 17

*easy for the patient (just sit “at rest”)
*3 methods to measure FRC:
-helium dilution
-nitrogen washout
-body plethysmography

Question 18

restrictive lung disease

Answer 18

*if a patient has a decreased FVC (forced vital capacity), decreased total lung capacity (TLC) confirms RESTRICTIVE lung disease

Question 19

determining the severity of an airflow abnormality (obstructive or restrictive)

Answer 19

*the severity is described based on the FEV1
*if FEV1 is <50% predicted, then this usually indicates SEVERE disease

Question 20

diffusing capacity

Answer 20

*sometimes called “transfer factor”
*examines how well gas diffuses across the alveolar-capillary membrane
*value is called DLCO

Question 21

examples of diseases that cause elevated DLCO

Answer 21

*asthma
*obesity
*early heart failure
*diffuse alveolar hemorrhage