Pulmonary Function Measurements

Comprehensive vocabulary flashcards covering pulmonary function tests, lung volumes, capacities, mechanics, gas dilution techniques, flow-volume loops, and diagnostic parameters.

Alveolar Capillary Membrane (ACM)

The physiological barrier across which oxygen and carbon dioxide diffuse between the alveoli and pulmonary circulation during gas exchange.

Primary Function of the Lungs

To facilitate gas exchange by adding $O_2$ to the blood and removing $CO_2$.

Diagnostic Scope of PFTs

PFTs do not diagnose specific pulmonary diseases; they identify the presence of disease, quantify the degree of impairment (mild, moderate, or severe), and determine the type of disorder (obstructive or restrictive).

Significant Bronchodilator Response

An improvement of at least $15\%$ in pulmonary function testing parameters measured before and after bronchodilator administration.

Tidal Volume ($V_t$)

The volume of air that normally moves into and out of the lungs during a single quiet breath; normal value is approximately $500\,ml$.

Inspiratory Reserve Volume (IRV)

The maximum volume of air that can be inhaled following a normal tidal inhalation; normal value is approximately $3100\,ml$.

Expiratory Reserve Volume (ERV)

The maximum volume of air that can be forcefully exhaled following a normal tidal exhalation; normal value is approximately $1200\,ml$.

Residual Volume (RV)

The amount of air remaining in the lungs after a maximal exhalation; normal value is approximately $1200\,ml$. It is increased in obstructive disorders and decreased in restrictive disorders.

Vital Capacity (VC)

The maximal volume of air that can be exhaled following a maximal inspiration ($VC = IRV + V_t + ERV$); normal value is approximately $4800\,ml$.

Slow Vital Capacity (SVC)

A vital capacity maneuver performed slowly from maximal inhalation to maximal exhalation; preferred over FVC in patients with obstructive lung disease due to reduced dynamic airway collapse.

Inspiratory Capacity (IC)

The maximum volume of air that can be inhaled after a normal resting exhalation ($IC = IRV + V_t$); normal value is approximately $3600\,ml$.

Functional Residual Capacity (FRC)

The volume of air remaining in the lungs at the end of a normal tidal exhalation ($FRC = ERV + RV$); normal value is approximately $2400\,ml$. It must be measured indirectly.

Total Lung Capacity (TLC)

The maximum volume of air the lungs can accommodate following a maximal inhalation ($TLC = IC + FRC$ or $VC + RV$); normal value is approximately $6000\,ml$ ($6\,L$).

RV/TLC Ratio

The proportion of total lung capacity occupied by residual volume; normal is $<35\%$, while values $>35\%$ indicate air trapping seen in obstructive diseases.

Spirogram

A graphic record showing lung volume changes during breathing maneuvers, detailing the four lung volumes and four lung capacities.

Obstructive Lung Pattern

A pulmonary disorder pattern characterized by reduced expiratory flow rates, air trapping with increased $RV$, $FRC$, $V_t$, and $RV/TLC$ ratio, and normal or increased $TLC$.

Restrictive Lung Pattern

A pulmonary disorder pattern characterized by a generalized reduction in all lung volumes and capacities, including $TLC$, $VC$, $FRC$, and $RV$.

Five Classic Obstructive Disorders

Cystic fibrosis, asthma, emphysema, chronic bronchitis, and bronchiectasis.

Nitrogen Washout

An open-circuit indirect method where the patient breathes $100\%\,O_2$ for $7\,\text{minutes}$ to wash out alveolar nitrogen ($\approx 79\%$) until concentration falls below $1.5\%$ to measure FRC and RV.

Helium Dilution Method

A closed-circuit indirect technique in which a patient rebreathes a known volume and $10\%$ concentration of helium until equilibrium ($<0.2\%$ change over $7\,\text{minutes}$) is reached, calculated using $C_1 \times V_1 = C_2 \times (V_1 + V_2)$.

Body Plethysmography

An airtight chamber method that measures thoracic gas volume (FRC) using Boyle's Law ($P_1V_1 = P_2V_2$) by assessing mouth and box pressure changes during panting against a closed shutter; considered the most accurate method because it measures trapped gas.

Forced Vital Capacity (FVC)

The maximal volume of gas that can be exhaled as forcefully and rapidly as possible after a maximal inspiration; normally completed in less than $6\,\text{seconds}$.

Forced Expiratory Volume Timed ($FEV_t$)

The volume of gas exhaled over specific intervals during an FVC maneuver; normal milestones are $FEV_{0.5} = 60\%$, $FEV_1 = 75\text{--}85\%$, $FEV_2 = 94\%$, and $FEV_3 = 97\%$ of FVC.

$FEV_1/FVC$ Ratio

The fraction of the forced vital capacity exhaled during the first second; normal is $>75\%$. Values $<75\%$ define an obstructive defect, whereas restrictive disorders show a normal or elevated ratio.

Forced Expiratory Flow 25–75 ($FEF_{25-75}$)

The average expiratory flow rate during the middle $50\%$ of an FVC maneuver; normal is $4\text{--}5\,L/s$ ($240\text{--}300\,L/min$), functioning as a sensitive indicator of early small airway disease.

Forced Expiratory Flow 200–1200 ($FEF_{200-1200}$)

The average expiratory flow rate occurring during an FVC maneuver after the first $200\,ml$ has been exhaled; normal is $6\text{--}8\,L/s$ ($360\text{--}480\,L/min$), measuring flow in the large, effort-dependent airways.

Peak Expiratory Flow Rate (PEFR)

The maximum flow rate achieved during a forced expiratory maneuver; normal is $6.5\text{--}10\,L/s$ ($400\text{--}600\,L/min$), routinely evaluated at the bedside to monitor asthmatic patients.

Maximum Voluntary Ventilation (MVV)

The largest volume of gas that can be breathed per minute with maximal rapid, deep breathing for at least $12\text{--}15\,\text{seconds}$; normal value is approximately $170\,L/min$, assessing respiratory muscle strength and endurance.

Flow-Volume Loop

A continuous graphic display plotting airflow on the vertical axis against lung volume on the horizontal axis during a maximal forced expiration (FVC) followed by a maximal forced inspiration (FIV).

Obstructive Flow-Volume Loop Pattern

A flow-volume tracing characterized by a scooped-out or concave expiratory curve and reduced peak expiratory flow caused by decreased airflow from diseased airways.

Restrictive Flow-Volume Loop Pattern

A flow-volume tracing characterized by a narrow, tall, convex appearance with normal flow rates relative to the severely diminished vital capacity volume.

Pathological Flow-Volume Loop Configurations

Distinctive loop morphologies reflecting specific respiratory pathologies, including early small airway obstruction, chronic obstructive disease, fixed large airway obstruction, variable extrathoracic large airway obstruction, and restrictive disease.

Dynamic Compression of the Airways

Flow limitation occurring during the final $70\%$ of an FVC maneuver where high intrathoracic pressure compresses non-cartilaginous bronchial walls, reducing lumen caliber and increasing airway resistance.

Maximum Inspiratory Pressure (MIP)

The maximum negative pressure generated against an occluded airway during inspiration; normal value is greater than $-20\,\text{cmH}_2\text{O}$, serving as a marker for inspiratory muscle strength and ventilator weaning readiness.

Maximum Expiratory Pressure (MEP)

The maximum positive pressure generated against an occluded airway during expiration; normal value is greater than $50\,\text{cmH}_2\text{O}$, reflecting expiratory and abdominal muscle strength.

Diffusing Capacity of the Lung for Carbon Monoxide (DLCO)

A test measuring the diffusion of carbon monoxide across the alveolar-capillary membrane using a single-breath technique ($11\,\text{second}$ hold); normal is $25\,ml/min/mmHg$. Emphysema is the only obstructive lung disease presenting with a decreased DLCO.