====== Official PFT Guides ======
^Official Guides^
| [[https://www.thoracic.org/professionals/career-development/ats-virtual-network/resources/2021-rbc-pft-interpretation-card.pdf|ATS Rapid Interpretation Guide]]|
|[[https://goldcopd.org/wp-content/uploads/2016/04/GOLD_Spirometry_2010.pdf | 2010 GOLD Spirometry Guide]]|
|[[https://doi.org/10.1183/13993003.01499-2021 | 2022 ERS/ATS Interpretive Strategies for PFTs]]|

====== Interpretation Position ======
==== Why I use GOLD Criteria ====

At UMMC, PFTs do report LLN and reference value (pop mean?) but not percentiles or z scores.

One can back-calculate the SD using $\sigma = \frac{LLN - ref}{-1.65}$ (this assumed LLN on our reports corresponds to 5th percentile).

Once $\sigma$ is known for the each value (e.g., $\sigma_{FVC} \neq \sigma_{FEV1} \neq \sigma_{RV}$), you could then use $z = \frac{PT_{value} - ref}{\sigma}$ and refer to the tables below to grade severity.

Given the complexity of this, using ERS/ATS for diagnosing and grading abnormalities is not possible.

Therefore, I use GOLD criteria.


====== Step-by-Step to Interpreting PFTs ======


===== Assess Flow-Volume Loops =====
  - Are the loops similar between attempts?
    - YES: Skip to next
    - NO: See first page's comment if ATS reproducibility criteria was met
  - Roughly speaking, do the loops appear obstructive or restrictive?

===== Assess Spirometry =====

==== Spirometric Severity ====
=== ATS Criteria ===
[[https://erj.ersjournals.com/content/erj/60/1/2101499.full.pdf | Source]]
^ Grade  ^ FEV1 z score ^ Severity            ^
| NA     | −1.65 to −2.5 | Mild                |
| NA     | −2.51 to −4.0 | Moderate            |
| NA     | <−4.1 | Severe              |


=== GOLD Criteria ===
[[https://goldcopd.org/wp-content/uploads/2016/04/GOLD_Spirometry_2010.pdf | Source]]
^ Grade  ^ FEV1 Percent Predicted  ^ Severity     ^
| 1      | ≥80%                    | Mild         |
| 2      | 50% − 79%               | Moderate     |
| 3      | 30% − 49%               | Severe       |
| 4      | <30% or <50% with CHRF  | Very Severe  |

==== Bronchodilator Response ====
=== ERS/ATS Definition ===
  - Required:
    - BDR >10%

  - Calculation
    - $ BDR = \frac{FEV1_{postBD} - FEV1_{preBD}}{FEV1_{predicted}}$

**Important NOTE:**
  - Calculation is __not__
    - $ BDR = \frac{FEV1_{postBD} - FEV1_{preBD}}{FEV1_{preBD}}$
  - Does NOT require
    - $\Delta FEV1_{volume} >200 mL$

=== GOLD Definition ===
  - Required:
    - $BDR >12%$
    - $\Delta FEV1_{volume} \geq 200 mL$

  - Calculation 
    - $ BDR = \frac{FEV1_{postBD} - FEV1_{preBD}}{FEV1_{preBD}}$
    - **NOTE: this differs from ERS/ATS calculation**

==== Methacholine Challenge ====
[[https://doi.org/10.1183/13993003.01526-2016 | Source, ERS 2017]]

===Response Categorization ===
{{:resources:pulm:methacholine_response.png?900|}}

=== Testing Protocol ===
{{:resources:pulm:methacholine_challenge.png?600|}}
===== DLCO Severity=====
=== ERS / ATS Definition ===
{{:resources:pulm:ats_dlco.png?600|}}

[[https://erj.ersjournals.com/content/erj/60/1/2101499.full.pdf | Source]]
^ Grade  ^ FEV1 z score   ^ Severity  ^
| NA     | −1.65 to −2.5  | Mild      |
| NA     | −2.51 to −4.0  | Moderate  |
| NA     | <−4.1          | Severe    |

===Gold Definition===
^ DLCO Percent Predicted ^ Severity ^
|>140% | Abnormally High |
|76%-140% | Normal |
|61-75% | Mild |
|41-60% | Moderate |
|<40% | Severe |

===== Assessing Restriction =====
=== ATS Criteria ===
[[https://erj.ersjournals.com/content/erj/60/1/2101499.full.pdf | Source, pg 17]]
  - Check spiro
    - Is $FVC \cdot z_{score}  \leq -1.65$ (//e.g.// < 5th percentile)?
      - Yes: get lung volumes
      - No: no restriction
  - Check lung volumes
    - Is $TLC \cdot z_{score}  \leq -1.65$ (//e.g.// < 5th percentile)?

{{:resources:pulm:ats_restriction.png?600|}}

[[https://erj.ersjournals.com/content/erj/60/1/2101499.full.pdf | Source]]
^ Grade  ^ FEV1 z score ^ Severity            ^
| NA     | −1.65 to −2.5 | Mild                |
| NA     | −2.51 to −4.0 | Moderate            |
| NA     | <−4.1 | Severe           

=== GOLD Definition ===
  - Required:
    - FVC <80% predicted

^TLC Percent Predicted^Severity^
|>70% | Mild |
|50%-69% | Moderate |
|<50% | Severe |

===== Other Lung Volumes =====
VC: ↓ in restriction, ↓ in air trapping
RV & FRC: ↑ with air trapping
RV & FRC: ↓ with restriction
ERV: ↓ in obesity

==== Lung Volume ====
FRC is the primary thing calculated in lung volume calculations.

===== Other =====
=== Plethysmography ===
**Boyle’s Law**
  * $P_1V_1 = P_2V_2$
  * $\implies V_{tg} = 970\frac{\Delta V}{\Delta P}$

$ FRC = ERV + RV $

$TLC = VC + RV $

=== Helium ===
  * Helium is used because He doesn’t cross the alveolar-capillary membrane
      * $ C_1V_1 = C_2(V_1+V_2)$
      * $\implies V_2 = V1(\frac{C_1}{C_2}-1)$
      * **limitations** since inhalation done only for a few minutes, would get into poorly ventilated lungs, so will underestimate FRC

=== Nitrogen ===
Method for calculation is similar to [[#Helium]] method.