Respiratory Physiology: Lung Volumes & Capacities

Vocabulary flashcards covering lung volumes, capacities, ventilation parameters, dead space, spirometry metrics, and PFT findings in obstructive and restrictive lung diseases.

Pulmonary Function Tests (PFT)

Tests used to assess the functional status of the respiratory system, categorized into static PFTs (volume-based) and dynamic PFTs (rate/time-based).

Spirometry

The most common pulmonary function test, measuring the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled.

Static PFTs

Pulmonary function tests based on the volume of air that flows in or out of the lungs.

Dynamic PFTs

Pulmonary function tests based on the rate or time of air flowing in or out of the lungs.

Respiratory Rate (RR)

The number of breaths taken per minute, with a normal resting range of $12 - 20\,\text{breaths/min}$.

Bradypnea

A decreased respiratory rate defined as less than $12\,\text{breaths/min}$.

Tachypnea

An increased respiratory rate defined as greater than $20\,\text{breaths/min}$.

Tidal Volume ($V_T$)

The volume of air inhaled and exhaled in a single breath at rest, with a normal value of $\sim 500\,\text{mL}$, $7\,\text{mL/kg}$, or $0.5\,\text{L/breath}$.

Hypopnea

A condition characterized by a decreased tidal volume ($V_T$).

Hyperpnea

A condition characterized by an increased tidal volume ($V_T$).

Minute Ventilation ($V_E$)

The volume of air breathed in and out in $1\,\text{minute}$, calculated as $V_E = V_T \times RR$, with a normal range of $5 - 7.5\,\text{L/min}$ (averaging $\sim 6\,\text{L/min}$).

Hypoventilation

A condition characterized by a decrease in minute ventilation ($V_E$).

Hyperventilation

A condition characterized by an increase in minute ventilation ($V_E$).

Inspiratory Reserve Volume (IRV)

The maximum volume of air that can still be forcibly inhaled following the inhalation of a normal tidal volume ($V_T$), with a normal range of $3 - 3.5\,\text{L}$.

Expiratory Reserve Volume (ERV)

The maximum volume of air that can still be forcibly exhaled after the exhalation of a normal tidal volume ($V_T$), with a normal range of $1 - 1.5\,\text{L}$.

Residual Volume (RV)

The volume of air remaining in the lungs after a maximal exhalation, with a normal range of $1 - 1.5\,\text{L}$. It cannot be measured directly by spirometry.

Inspiratory Capacity (IC)

The maximum volume of air that can be inhaled after the exhalation of a normal tidal volume ($V_T$), calculated as $IC = IRV + V_T$, with a normal range of $3.5 - 4\,\text{L}$.

Vital Capacity (VC)

The maximum volume of air that can be exhaled after maximal inhalation, calculated as $VC = V_T + IRV + ERV$, with a normal range of $4.5 - 5\,\text{L}$.

Functional Residual Capacity (FRC)

The volume of air remaining in the lungs after the exhalation of a normal tidal volume ($V_T$), calculated as $FRC = RV + ERV$, with a normal range of $2.5 - 3\,\text{L}$.

Total Lung Capacity (TLC)

The volume of air in the lungs after maximal inhalation, calculated as $TLC = VC + RV$, with a normal range of $6 - 6.5\,\text{L}$.

Spirogram

A graphical representation generated during spirometry displaying lung volumes and capacities plotted over time.

Dead Space

The volume of air inspired during breathing that does not take part in gas exchange.

Anatomical Dead Space

The volume of inspired air that remains in the trachea and bronchi (conducting zone) and does not participate in gas exchange, normally about $150\,\text{mL}$.

Alveolar Dead Space

The volume of inspired air that reaches the alveoli but is unable to participate in gas exchange.

Physiologic Dead Space ($V_D$)

The total dead space of the lungs, defined as the sum of anatomical dead space and alveolar dead space.

Alveolar Ventilation

The total volume of new air entering the alveoli and adjacent gas exchange areas each minute, calculated as $(V_T - V_D) \times RR$, normally averaging $4200\,\text{mL/min}$.

Forced Vital Capacity (FVC)

The volume of air that can forcibly be blown out after maximal inspiration, measured in liters.

Forced Expiratory Volume in 1st Second (FEV1)

The maximum volume of air that can forcibly be blown out in the first second during the FVC maneuver, normally equal to $80\%$ of Vital Capacity ($VC$).

FEV1/FVC Ratio

The ratio of Forced Expiratory Volume in 1st Second to Forced Vital Capacity, which normally equals approximately $80\%$ in healthy adults.

Forced Expiratory Flow 25–75% (FEF 25–75%)

The average flow of air coming out of the lungs during the middle portion of expiration, also known as maximal mid-expiratory flow (MMEF).

Peak Expiratory Flow (PEF)

The maximal airflow speed achieved during a maximally forced expiration initiated at full inspiration, measured in liters per minute.

Maximum Voluntary Ventilation (MVV)

A measure of the maximum amount of air that can be inhaled and exhaled in one minute, measured in liters per minute.

Obstructive Lung Disease

Pathology (e.g., Asthma, COPD) marked by difficulty exhaling air due to airway narrowing, resulting in decreased $\text{FEV}_1$, decreased $\text{FEV}_1/\text{FVC}$ ratio, decreased $VC$, increased $RV$, and increased airway resistance.

Restrictive Lung Disease

Pathology (e.g., Pulmonary Fibrosis) marked by restricted lung expansion, resulting in normal or decreased $\text{FEV}_1$, normal or increased $\text{FEV}_1/\text{FVC}$ ratio, decreased $VC$, and decreased $TLC$.

Flow-Volume Curve

A graphical plot representing airflow speed versus lung volume during forced inspiration and expiration maneuvers.