Introduction to Pulmonary Function Measurements

Flashcards covering pulmonary function measurements, including lung volumes, capacities, PFT methods (Helium dilution, Nitrogen washout, Plethysmography), and diagnostic criteria for obstructive vs. restrictive lung diseases.

Predicted Values

Statistically expected results for a patient's lung function generated by a computer using demographic information and reference databases.

Measured/Actual Values

The performance variables recorded during a patient’s actual pulmonary function tests.

Normal PFT Range

Generally accepted as being between $80$ to $120\%$ of the predicted value for most variables.

TLC (Total Lung Capacity)

The volume of gas in the lungs after a maximal inspiration; the sum of all lung volumes.

FRC (Functional Residual Capacity)

The volume of air remaining in the lungs after a normal, quiet exhalation, consisting of $ERV + RV$.

IC (Inspiratory Capacity)

The volume of air that can be inhaled after a normal exhalation; the sum of $TV + IRV$.

TV (Tidal Volume)

The amount of air inhaled and exhaled with each breath during quiet breathing, normally about $500\,mL$ in adults.

IRV (Inspiratory Reserve Volume)

The amount of air that can be forcibly inhaled beyond the normal tidal volume.

ERV (Expiratory Reserve Volume)

The amount of air that can be forcibly exhaled after a normal tidal volume exhalation.

RV (Residual Volume)

The amount of air remaining in the lungs after a maximal forced expiration; it cannot be exhaled and prevents lung collapse.

VC (Vital Capacity)

The total volume of air that can be exhaled after a maximal inspiration, representing all the volumes a person can actively manipulate.

Slow Vital Capacity

A test that measures the vital capacity and its subparts during unforced breathing; it cannot measure $RV$, $FRC$, or $TLC$.

Obstructive Lung Disease Mnemonic (A through F)

A method to classify obstructive diseases: $A$sthma, $B$ronchiectasis, $C$ystic Fibrosis, $D$arn chronic bronchitis, $E$mphysema, and $F$oreign body.

Air Trapping

A condition often seen in obstructive diseases characterized by an increase in $RV$ and $FRC$.

Minute Ventilation Formula

$\text{Minute Ventilation} = \text{Tidal Volume} \times \text{Respiratory Rate}$.

Restrictive Lung Diseases

Diseases characterized by a decrease in all lung volumes and capacities, often due to issues with the lungs themselves or the chest bellows.

Phrenic Nerve

The nerve originating from $C3$ through $C5$ that is responsible for signaling the diaphragm to contract.

Helium Dilution

An indirect method to measure $FRC$ where a patient breathes from a closed system containing a $10\%$ concentration of helium until equilibrium is reached.

Nitrogen Washout

A method to determine $FRC$ where the patient inhales $100\%$ oxygen to wash out all nitrogen from the lungs, typically taking about $3\,minutes$ in a normal lung.

Body Plethysmography

A PFT method based on Boyle's Law that uses a sealed booth to measure total thoracic gas volume ($TGV$), including trapped gases.

FVC (Forced Vital Capacity)

The volume of air exhaled as forcefully and quickly as possible after a maximal inspiration, typically completed in $4$ to $6\,seconds$ in healthy individuals.

FEV1 (Forced Expiratory Volume in 1 second)

The volume of air forcibly expired during the first second of an FVC maneuver; it is used as an index of severity in COPD.

FEV1/FVC Ratio

The primary value used to diagnose obstruction; a ratio of less than $70\%$ indicates an obstructive process.

GOLD Criteria

The Global Initiative for Chronic Obstructive Lung Disease framework that categorizes COPD severity into four levels (mild, moderate, severe, very severe) based on $FEV1\%$ predicted.

FEF 25-75

The mean average flow during the middle $50\%$ of an FVC maneuver, used to evaluate small to medium airways.

PEF (Peak Expiratory Flow)

The highest instantaneous flow achieved during a forced expiration, used to evaluate large/upper airway patency.

Effort Dependent Portion

The initial phase of the FVC test ($PEF$ and $FEF\,200$-$1200$) where results change based on the patient's muscular effort.

Effort Independent Portion

The portion of the FVC test following the first $1200\,mL$ of exhaled volume where flow cannot be increased by additional muscular effort.

Asthma Action Plan Green Zone

A zone indicating the patient is doing well, with peak flow measurements at $80\%$ or more of their personal best.

Asthma Action Plan Yellow Zone

A zone indicating caution where peak flow is between $50\%$ and $80\%$ of personal best, signaling potential shortness of breath.

Asthma Action Plan Red Zone

A medical emergency zone where peak flow is less than $50\%$ of personal best; the patient should go to the emergency room.

MVV (Maximum Voluntary Ventilation)

A test where the patient breathes as deep and fast as possible for $10$ to $15\,seconds$ to evaluate the overall strength and endurance of the respiratory system.