Unit 2 - Reference Equations + "Normal" Values Interpretation

Question 1

How are the patient’s values evaluated during a pulmonary function (PF) test?

Answer 1

They are compared to reference (expected) values, which are based on healthy population data.

Question 2

What is the role of ‘reference values’ in interpreting PFT results?

Answer 2

They act as a standard to determine what is considered normal vs abnormal, based on large sets of people without lung disease.

Question 3

Which organizations help determine what is considered ‘normal’ in PFT reference values?

Answer 3

The American Thoracic Society (ATS) and European Respiratory Society (ERS).

Question 4

If a patient’s result is 92% of predicted, is it automatically abnormal?

Answer 4

Not necessarily; context is needed for interpretation.

Question 5

What does a result of 102% of predicted indicate in pulmonary function testing?

Answer 5

It is not automatically abnormal; interpretation depends on context.

Question 6

What context is needed to interpret pulmonary function test results?

Answer 6

Cutoffs and interpretation strategies such as ±20% or LLN/ULN.

Question 7

Fill in the blank: Reference values are based on data from a _______.

Answer 7

[healthy population]

Question 8

True or False: Reference values are universal and do not vary between populations.

Answer 8

False

Question 9

How are reference equations for pulmonary function created?

Answer 9

By collecting large data sets from healthy individuals, identifying relationships (e.g. height ↔ lung size), and converting these into mathematical equations that predict upper and lower ranges.

Question 10

What is the purpose of using broad population data in reference equations?

Answer 10

It allows equations to represent a wide range of healthy individuals and improves accuracy of what’s considered “normal.”

Question 11

What are the 3 primary factors required in all predictive equations for PFT values?

Answer 11

Height, Age, and Biological Sex.

Question 12

What are some additional factors sometimes included in predictive equations?

Answer 12

Ethnicity, BMI/weight, and arm span (used only to estimate height if the patient cannot stand, e.g. spinal cord injury).

Question 13

Why might arm span be used instead of height when calculating predicted pulmonary values?

Answer 13

For patients who cannot stand (e.g. spinal cord injury). It’s a good estimate of height but may need correction factors.

Question 14

Give examples of patient data typically entered into PFT software to calculate predicted values.

Answer 14

Height, age, biological sex, ethnicity, weight, smoking history, and sometimes other factors.

Question 15

Within the same biological sex, what is the most important factor for predicting lung size/volume?

Answer 15

Standing height. Taller individuals usually have greater lung volumes.

Question 16

How can arm span be used in PFTs? What are its limitations?

Answer 16

Used if patient cannot stand (measured fingertip to fingertip).
- Correction factors may be needed, especially if <16 years old, since accuracy is lower.

Question 17

How should height be measured for PFT testing?

Answer 17

• Shoes off + back straight
• eyes forward
• back flush against wall/stadiometer, using a fixed measuring tool.

Question 18

At what age is peak lung function typically reached, and how does it change after that?

Answer 18

Peak at 20–25 years, minimal change to ~35, then gradual decline after.

Question 19

How does aging affect lung compliance and chest wall rigidity?

Answer 19

Lungs → more compliant (floppier, less elastic recoil). Chest wall → more rigid (greater opposing force to inspiration).

Question 20

Does total lung capacity (TLC) change with age?

Answer 20

No, TLC stays about the same, but the volumes making up TLC change.

Question 21

With aging, what happens to Residual Volume (RV), Functional Residual Capacity (FRC), Vital Capacity (VC), Peak Expiratory Flow (PEF), and Diffusion Capacity (DLCO)?

Answer 21

RV ↑, FRC ↑, VC ↓, PEF ↓, DLCO ↓.

Question 22

At the same height, how do lung values compare between males and females?

Answer 22

Males usually have greater lung volumes, flows, and diffusion capacity (mostly due to lung size).

Question 23

How should predicted values be determined for transgender individuals?

Answer 23

Based on childhood and adolescent development.

Question 24

Why is ethnicity considered in PFT reference values?

Answer 24

Different ethnicities may have different body proportions (e.g. chest size, trunk-to-height ratio) that affect lung size.

Question 25

What is the major global data set used for lung reference values?

Answer 25

The Global Lung Initiative (GLI) — >160,000 data points, >30 countries, ages 3.5–95.

Question 26

What is a limitation of ethnicity-based reference equations?

Answer 26

They cannot fully represent all populations. GLI only has limited categories (African American, NE Asian, SE Asian, White, Other/mixed). Results may be over- or underestimated.

Question 27

Should ethnicity-specific equations be used?

Answer 27

Not recommended, even though they exist.

Question 28

Is weight included in most reference equations?

Answer 28

No. But extreme weights (very high or low BMI) can still influence pulmonary values.

Question 29

How does being at the very low end of weight spectrum affect pulmonary function?

Answer 29

Reduced muscle mass and thoracic support → reduced volume and effort.

Question 30

How does being at the very high end of weight spectrum affect pulmonary function?

Answer 30

Larger abdomen restricts diaphragm movement → lower volumes and flows, especially when BMI >30–40 kg/m².

Question 31

What are the two main methods for classifying PFT results as normal or abnormal?

Answer 31

80–120% method (100 ± 20%) and Lower & Upper Limits of Normal (LLN/ULN, z-score method)

Question 32

How does the 80–120% method classify results?

Answer 32

<80% of predicted → abnormally low 120% of predicted → abnormally high

Question 33

What three numbers are typically displayed in PFT reports to support interpretation?

Answer 33

Predicted values, actual (measured) values, and % predicted.

Question 34

What condition is often associated with values >120% of predicted TLC?

Answer 34

Hyperinflation, often seen in COPD.

Question 35

In the 80–120% method, what does FEV1 = 79% of predicted indicate? What about TLC = 121%?

Answer 35

FEV1 = abnormally low, TLC = abnormally high.

Question 36

What is a limitation of the 80–120% method?

Answer 36

It may misclassify patients → false negatives (young) or false positives (older).

Question 37

How does the LLN/ULN (z-score) method classify abnormal values?

Answer 37

Lowest 5% of population → abnormally low Highest 5% of population → abnormally high

Question 38

What does a z-score represent in PFT interpretation?

Answer 38

How many standard deviations a measured value is from predicted. ## Footnote 95% of healthy people: ±2 SD 90%: ±1.64 SD

Question 39

Example: If LLN for FVC is 2.09 L, what happens if patient’s FVC = 2.00 L?

Answer 39

It’s considered abnormally low.

Question 40

Why is LLN/ULN method considered superior to the 80–120% method?

Answer 40

It’s statistically based and reduces misdiagnosis.

Question 41

In the flow-volume loop with severe scooping and very low predicted flows, what disease is most likely?

Answer 41

Obstructive disease (e.g. COPD).

Question 42

If a flow-volume loop looks relatively normal in volumes but has an abnormal shape, what might this suggest?

Answer 42

Possible extrathoracic obstruction or inspiratory loop issue.

Question 43

In a case where pre-test values are normal but post-bronchodilation shows big changes, what condition is suspected?

Answer 43

Asthma (showing reversibility).

Question 44

How is the FEV₁/FVC ratio interpreted differently between the % method and LLN/ULN method?

Answer 44

% method → abnormal if <70% (fixed cutoff, regardless of age). LLN/ULN → uses specific cutoffs based on population data (accounts for age).

Question 45

Why is LLN/ULN preferred over the 80–120% method?

Answer 45

It’s statistically based and more accurate. The 80% method can cause: * False negatives in younger patients (abnormal but missed) * False positives in older patients (normal but flagged abnormal).

Question 46

A young patient’s FEV₁ is just below the LLN but above 80%. How would it be interpreted differently?

Answer 46

80% method → Normal. LLN method → Abnormal (more accurate).

Question 47

An older patient’s FEV₁ is above 80% but actually below the LLN. How would each method interpret it?

Answer 47

80% method → Abnormal (false positive). LLN method → Normal (correct).

Question 48

Why is the fixed 70% FEV₁/FVC cutoff problematic in older adults?

Answer 48

The ratio naturally declines with age. The fixed 70% method can wrongly classify normal aging lungs as abnormal. LLN/ULN adjusts for age, making it more accurate.

Question 49

What general disease categories can be identified by PFT?

Answer 49

Obstructive lung diseases Restrictive lung diseases Mixed lung diseases Cardiopulmonary vascular diseases (e.g. pulmonary hypertension)

Question 50

Examples of upper and lower airway obstructive diseases?

Answer 50

Upper: croup, extrathoracic obstruction (stridor, breathing in issues). Lower: asthma, COPD.

Question 51

How do obstructive diseases affect airflow?

Answer 51

Make it harder to get air out of the lungs. If obstruction worsens → ability to fully exhale decreases.

Question 52

What causes airway obstruction in asthma?

Answer 52

Inflammation, increased secretions, and bronchoconstriction (narrowing of smooth muscle).

Question 53

Examples of intra- vs extra-pulmonary restrictive diseases?

Answer 53

Intra: pulmonary fibrosis, silicosis, interstitial lung disease. Extra: circumferential burns, chest wall deformities, obesity.

Question 54

How do restrictive lung diseases affect airflow?

Answer 54

Make it harder to get air in. Inhalation volume/effort quickly limited → decreased compliance seen.

Question 55

What defines a mixed lung disease?

Answer 55

Combination of obstructive + restrictive patterns (rare, has features of both).

Question 56

How do cardiopulmonary vascular diseases appear on PFT?

Answer 56

Lung volumes and flows may look normal, but diffusion capacity (DLCO) is reduced.

Question 57

In what scenarios would PFT results be unreliable?

Answer 57

Testing during a cold/asthma flare → inconsistent. Cold-weather bronchospasm tested in spring. Patient takes bronchodilator before test. Poor coaching by tester. (All → unreliable results).

Question 58

What are the main factors used to predict PFT values?

Answer 58

Height, age, and sex ## Footnote These factors are essential for determining normal predicted values in pulmonary function tests.

Question 59

What is the ±20% method in PFT interpretation?

Answer 59

A common but less accurate method for interpreting results ## Footnote This method allows a variance of 20% around predicted values.

Question 60

What is the ULN/LLN method in PFT interpretation?

Answer 60

A more accurate but less commonly used method ## Footnote This method defines upper and lower limits of normal for specific populations.

Question 61

What caution should be taken when interpreting PFT results?

Answer 61

Patient effort and other factors can skew results ## Footnote Ensuring accurate effort is crucial for reliable test outcomes.

Question 62

What is more important in PFT results: isolated values or trends over time?

Answer 62

Trends over time ## Footnote Observing changes over time provides better insight into lung function.

Question 63

Does degree of obstruction in PFT results indicate a specific diagnosis?

Answer 63

No, obstruction does not automatically indicate COPD ## Footnote Other conditions can also present with obstructive patterns.