16.1 Pattern Recognition: Obstruction, Restriction, Mixed, Severity

Domain III.C: From Clean Data to Clinical Pattern Language

Domain III.B asked whether results are reliable. Domain III.C — Clinical implications asks what the clean numbers mean for the referring clinician and how the pulmonary function technologist frames them on the report. On the NBRC PFT Examination (high cut / RPFT), pattern items map to III.C.3.a/b (obstructive patterns and severity cues), III.C.4.a/b (restrictive and mixed patterns), III.C.12 (bronchodilator response implications), and III.C.17–18 (serial change and integrated interpretation literacy).

You are not writing a discharge diagnosis. You are expected to:

1. Recognize classic physiologic patterns (obstruction, restriction, mixed).
2. Apply severity framing using %predicted and/or z-scores at technologist reporting literacy.
3. Read flow-volume loop morphology after effort is established.
4. Integrate volumes with spirometry before calling restriction.
5. State bronchodilator and serial change findings clearly without over-claiming etiology.

Classic Patterns: Obstruction, Restriction, Mixed

Obstructive pattern (airflow limitation)

Primary spirometric signal: reduced FEV1/FVC (or FEV1/VC) below the lower limit of normal (LLN) or a sufficiently negative z-score, with acceptable, repeatable efforts.

Exam rule: Low FEV1 with a normal ratio is not classic obstruction. Look for restriction, effort issues (already filtered in III.B), or mixed/other patterns after volumes.

Hyperinflation vs obstruction: Elevated TLC/RV supports the physiologic story of air trapping but does not replace a reduced ratio as the obstructive gate.

Restrictive pattern

Primary volume signal: reduced TLC (after reliable FRC/TGV method and VC linkage).

Critical RPFT trap: Reporting “restriction” from low FVC + normal ratio without volumes is incomplete. Many labs phrase this as “possible restriction—volumes recommended” or wait for TLC. Domain III.C expects you to know that spirometry can only suggest restriction; TLC confirms it.

Mixed pattern

Definition for pattern literacy: airflow limitation (low FEV1/FVC vs LLN) plus reduced TLC.

Do not call mixed because FVC is low in pure obstruction (air trapping can reduce FVC without true restriction). Volumes decide.

Severity Framing (%predicted and z-scores)

Severity language on the exam is reporting literacy, not freestanding physician diagnosis. After a pattern is established on reliable data:

• %predicted remains widely used on reports and in many DCO-style stems (e.g., FEV1 %predicted bands for obstructive severity framing).
• z-scores / LLN are the modern ATS/ERS-aligned way to define abnormal vs normal relative to reference equations (e.g., GLI).
• Severity grades (mild/moderate/severe) are applied to indices (commonly FEV1 once obstruction is present; TLC or FVC framing in restriction contexts per lab protocol)—always subordinate to pattern definition.

Worked mini-example (framing, not diagnosis): Acceptable spirometry shows FEV1/FVC below LLN, FEV1 48% predicted, TLC 110% predicted, RV elevated. Pattern: obstruction with hyperinflation/air-trapping context. Severity framing: moderate-to-severe reduction in FEV1 by %predicted convention used in the stem—not a final clinical stage without the ordering clinician’s synthesis.

Flow-Volume Loop Shape Cues (High-Yield for RPFT)

Morphology is powerful after Domain II/III.B effort gates are clean.

Exam contrast stems love upper-airway vs ordinary obstruction:

• Variable extrathoracic: inspiratory plateau/flattening more than expiratory scoop.
• Variable intrathoracic: expiratory flattening/plateau pattern distinct from smooth concavity of small-airway obstruction.
• Fixed lesion: both limbs truncated.

Always couple shape language with numeric indices. A pretty scoop without a reduced ratio is not automatic obstruction; a reduced ratio without morphology still can be obstruction if efforts are maximal and repeatable.

Integrating Volumes with Spirometry Before Calling Restriction

Workflow for III.C.4 literacy:

1. Spirometry first: ratio low → obstruction pathway; ratio NL/high with low FVC → possible restriction.
2. Obtain reliable TLC (box preferred when air trapping suspected; dilution method limitations noted).
3. TLC reduced → restriction confirmed (or mixed if ratio also low).
4. TLC normal/high with low FVC and low ratio → obstruction with air trapping / incomplete emptying, not mixed restriction.
5. TLC normal with isolated low FVC and normal ratio → re-check effort, neuromuscular, or non-pulmonary causes; do not force interstitial disease on the report.

Case vignette A — False restriction. FVC 62% predicted, FEV1/FVC 0.82, no volumes. Junior staff labels “moderate restriction.” Later box TLC is 98% predicted. Correct pattern language: spirometry suggested restriction but TLC excludes it; investigate effort, early termination history, or extra-thoracic/process issues—do not finalize restriction on FVC alone.

Case vignette B — True mixed. FEV1/FVC below LLN, FEV1 55% predicted, TLC 68% predicted with reliable pant loops. Pattern: mixed obstructive and restrictive. Report both signals; severity framing applies to the reduced indices per lab convention.

Case vignette C — Obstruction with air trapping. Ratio reduced, FVC low, TLC 125% predicted, RV/TLC high. Not mixed. Hyperinflation/air trapping explains the low FVC in an obstructive framework.

Bronchodilator Response and Serial Change (III.C.12, III.C.17–18)

Bronchodilator (BD) response — clinical meaning for reports

After pre/post testing with acceptable efforts:

• A significant BD response (lab/ATS-aligned thresholds for FEV1 and/or FVC improvement) supports reversible airflow limitation for the referring clinician—often relevant to asthma/AFO management discussions.
• A negative BD study does not prove “not asthma” and does not prove irreversible COPD by itself; it means no significant acute response under test conditions.
• Always report pre and post absolute values, % change, and absolute change, plus which post-BD set was selected under lab rules.

Serial change — reporting literacy

Serial PFTs compare visits after each session is reliable:

• Meaningful change exceeds expected biologic + measurement variability (stems may give % or absolute thresholds).
• Improvement after therapy vs decline suggesting progression are clinical uses—the technologist’s job is accurate paired reporting, same reference set awareness, and flagging method differences (e.g., different volume techniques across years).
• Do not equate a single noisy visit-to-visit wobble with “rapid progression.”

Case vignette D — BD. Pre FEV1 1.80 L (55% pred), post 2.20 L after albuterol with repeatable efforts; ratio improves but remains below LLN. Report: significant BD response with residual obstruction—useful for the ordering clinician; still an obstructive pattern post-BD if ratio remains reduced.

Integrated Reporting Checklist (Pattern Section)

1. Confirm III.B reliability for the indices you will pattern-label.
2. Classify obstruction from ratio/LLN (spirometry).
3. Confirm restriction only with reduced TLC (or clearly state volumes pending).
4. Reserve mixed for low ratio and low TLC.
5. Add severity framing with %predicted/z-score language appropriate to the indices.
6. Describe flow-volume morphology when it adds upper-airway or classic scoop/peak cues.
7. Attach BD response and serial change as separate, numeric statements—not free-text diagnoses.

Domain III.C.3, III.C.4, III.C.12, and III.C.17–18 reward technologists who speak pattern language precisely, integrate volumes before restriction, and keep severity and BD/serial statements at the reporting level the exam expects—clear, physiologic, and never a substitute for the physician’s clinical diagnosis.