Pulmonary Function Measurements and Diffusion of Pulmonary Gases

Comprehensive vocabulary flashcards covering pulmonary function testing, spirometric lung volumes and capacities, mechanical and dynamic flow parameters, obstructive and restrictive pathologies, alveolar diffusion mechanics, gas laws, and respiratory clinical calculations.

Tidal Volume ($V_T$)

The amount of air inhaled and exhaled with each breath during quiet, normal breathing; normally about $500\,mL$ in healthy adult males ($400\text{--}500\,mL$ in adult females) or approximately $5\text{ to }7\,mL/kg$ of ideal body weight.

Inspiratory Reserve Volume ($IRV$)

The maximum volume of air that can be forcibly inhaled beyond the normal resting tidal volume ($V_T$); averages approximately $3100\,mL$ in adult males and $1900\,mL$ in adult females.

Expiratory Reserve Volume ($ERV$)

The maximum volume of air that can be forcibly exhaled after a normal resting end-expiratory tidal exhalation; averages approximately $1200\,mL$ in adult males and $800\,mL$ in adult females.

Residual Volume ($RV$)

The volume of air remaining in the lungs after a maximal forced exhalation ($ERV$) that cannot be exhaled by voluntary effort; essential for keeping alveoli patent and preventing lung collapse, averaging $1200\,mL$ in adult males and $1000\,mL$ in adult females.

Vital Capacity ($VC$)

The maximum volume of air that can be exhaled after a maximal inspiration, calculated as the sum of $IRV + V_T + ERV$; averages approximately $4800\,mL$ in adult males and $3200\,mL$ in adult females.

Inspiratory Capacity ($IC$)

The maximal volume of air that can be inhaled from the resting end-expiratory level, calculated as the sum of tidal volume and inspiratory reserve volume ($V_T + IRV$); averages $3600\,mL$ in adult males and $2400\,mL$ in adult females.

Functional Residual Capacity ($FRC$)

The volume of air remaining in the lungs at the resting end-expiratory level where inward lung recoil and outward chest wall recoil are balanced, calculated as $ERV + RV$; averages $2400\,mL$ in adult males and $1800\,mL$ in adult females.

Total Lung Capacity ($TLC$)

The maximum volume of gas that the lungs can accommodate after a maximal inspiration, calculated as the sum of all four lung volumes ($V_T + IRV + ERV + RV$) or $VC + RV$; averages $6000\,mL$ in adult males and $4200\,mL$ in adult females.

Obstructive Lung Volume Pattern

A pattern of pulmonary volume alteration characterized by air trapping and hyperinflation, resulting in increased $RV$, $FRC$, and $TLC$, alongside decreased $VC$, $IC$, $IRV$, and $ERV$.

Restrictive Lung Volume Pattern

A pattern of pulmonary volume alteration caused by restriction of the lung parenchyma or chest wall, resulting in a global reduction across all lung volumes and capacities ($VC$, $IC$, $RV$, $FRC$, $V_T$, and $TLC$).

Closed-Circuit Helium Dilution

An indirect spirometric technique used to determine $FRC$ and $RV$ where the patient rebreathes a known volume ($V_1$) and concentration ($C_1$, usually $10\%$) of helium until equilibrium ($C_2$) is reached; solved using the rearrangement $V_2 = \frac{V_1 C_1}{C_2}$.

Open-Circuit Nitrogen Washout

An indirect spirometric test where the patient breathes $100\%\,O_2$ for up to $7\text{ minutes}$ to wash alveolar nitrogen ($N_2$) out from an initial $79\%$ down to $1.5\%$ or less, allowing calculation of $FRC$ using $V_1 = \frac{C_2 V_2}{C_1}$.

Body Plethysmography (Body Box)

An airtight testing chamber that determines thoracic gas volume ($V_{TG}$) at $FRC$ by applying Boyle's law while the patient pants against a closed shutter; considered the most accurate method for measuring trapped gas and residual volume.

Forced Vital Capacity ($FVC$)

The maximum volume of gas that can be exhaled as forcefully and rapidly as possible after a maximal inspiration; total expiratory time in healthy individuals is normally $4\text{ to }6\text{ seconds}$.

Forced Expiratory Volume Timed ($FEV_T$)

The maximum volume of gas exhaled over specified time intervals during an $FVC$ maneuver; normal percentage standards for healthy young adults are $FEV_{0.5} = 60\%$, $FEV_{1.0} = 83\%$, $FEV_{2.0} = 94\%$, and $FEV_{3.0} = 97\%$.

$FEV_1/FVC$ Ratio ($FEV_1\%$)

The fraction of the forced vital capacity exhaled during the first second; the key pulmonary diagnostic index where a value below $70\%$ identifies an obstructive disorder, whereas in restrictive disorders it remains normal or increased.

Forced Expiratory Flow $25\%\text{--}75\%$ ($FEF_{25\%-75\%}$)

The average expiratory flow rate occurring during the middle $50\%$ of an $FVC$ maneuver, reflecting the integrity and patency of medium- to small-sized airways; averages $4.5\,L/sec$ ($270\,L/min$) in healthy males and $3.5\,L/sec$ ($210\,L/min$) in females.

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

The average expiratory flow rate occurring between the first $200\,mL$ and $1200\,mL$ of an $FVC$ maneuver, reflecting large airway function and patient muscular effort; averages $8\,L/sec$ ($480\,L/min$) in healthy males and $5.5\,L/sec$ ($330\,L/min$) in females.

Peak Expiratory Flow Rate ($PEFR$)

The maximum instantaneous flow rate achieved during an $FVC$ maneuver originating from large airways, typically measured with a handheld peak flow meter; averages $10\,L/sec$ ($600\,L/min$) in adult males and $7.5\,L/sec$ ($450\,L/min$) in females.

Maximum Voluntary Ventilation ($MVV$)

The largest volume of gas an individual can voluntarily breathe in and out of the lungs in $1\text{ minute}$, tested over a $12\text{ to }15\text{ second}$ interval to assess respiratory muscle endurance, compliance, and airway resistance; averages $170\,L/min$ in males and $110\,L/min$ in females.

Restrictive Flow-Volume Loop

A flow-volume graphic displaying a preserved, narrow, tall contour characterized by reduced overall lung volume ($FVC$) while expiratory flow rates remain normal or elevated relative to lung volume.

CBABE

A clinical mnemonic designating the five major obstructive lung disorders: Cystic fibrosis, Bronchitis (chronic), Asthma, Bronchiectasis, and Emphysema.

Effort-Dependent Portion of $FVC$

The initial $30\%$ of a forced expiratory maneuver originating from high lung volumes and large airways (measured by $FEF_{200-1200}$ and $PEFR$), wherein generated flow rates rise in direct proportion to patient muscular effort.

Effort-Independent Portion of $FVC$

The final $70\%$ of a forced expiratory maneuver during which flow rate cannot be increased by additional muscular effort because dynamic compression of the bronchial airways fixes maximum flow.

Equal Pressure Point ($EPP$)

The site along the tracheobronchial tree during forced expiration where intraluminal airway pressure equals surrounding intrapleural pressure ($P_{pl}$); downstream from this point toward the mouth, lateral airway pressure drops below pleural pressure, inducing dynamic compression.

Pursed-Lip Breathing

A ventilatory maneuver featuring a deep inhalation followed by prolonged exhalation through constricted lips, generating an internal positive back-pressure that stents airways open, off-sets dynamic compression, and prevents early bronchiolar collapse.

Maximum Inspiratory Pressure ($MIP$)

A clinical index of inspiratory muscle strength measured against an occluded airway at residual volume ($RV$); normal values average $-125\,cm\,H_2O$ in males and $-90\,cm\,H_2O$ in females, with values more negative than $-25\text{ to }-30\,cm\,H_2O$ indicating weaning potential.

Maximum Expiratory Pressure ($MEP$)

A clinical index of abdominal and expiratory muscle strength measured at total lung capacity ($TLC$); normal values average $+230\,cm\,H_2O$ in males and $+150\,cm\,H_2O$ in females, with values exceeding $+50\,cm\,H_2O$ required for an effective cough.

Rapid Shallow Breathing Index ($RSBI$)

A clinical weaning predictor calculating the ratio of spontaneous respiratory frequency to tidal volume in liters ($f / V_T$); an $RSBI < 105$ measured $1\text{ minute}$ after ventilator discontinuation indicates a high probability of successful extubation.

Diffusion Capacity of Carbon Monoxide ($DL_{CO}$)

A single-breath test assessing the functional surface area and membrane thickness of the alveolar-capillary barrier using carbon monoxide (which has a $210\times$ greater affinity for hemoglobin than oxygen); normal resting value averages $25\,mL/min/mm\,Hg$.

GOLD Classification of COPD

A staging guideline defining airflow limitation severity in patients with $FEV_1/FVC < 0.70$: GOLD 1 (Mild, $FEV_1 \ge 80\%$ predicted), GOLD 2 (Moderate, $FEV_1\text{ 50--79\%}$), GOLD 3 (Severe, $FEV_1\text{ 30--49\%}$), and GOLD 4 (Very Severe, $FEV_1 < 30\%$).

Asthma Action Plan Zones

A clinical peak flow monitoring framework: Green Zone ($\ge 80\%$ of personal best; stable/doing well), Yellow Zone ($50\text{ to }79\%$; caution/worsening), and Red Zone ($<50\%$; medical emergency requiring immediate intervention).

Dalton's Law of Partial Pressures

A physical law stating that the total pressure of a gas mixture is equal to the sum of the partial pressures of each individual gas ($P_{total} = P_1 + P_2 + P_3 \dots$), where each gas exerts a pressure proportional to its fractional concentration.

Atmospheric Gas Composition at Sea Level

The standard dry atmospheric gas fractions at $760\,mm\,Hg$: Nitrogen ($78.08\%$, $592.8\,mm\,Hg$), Oxygen ($20.95\%$, $159.6\,mm\,Hg$), Carbon dioxide ($0.03\%$, $0.2\,mm\,Hg$), and trace gases ($0.93\%$, $7.0\,mm\,Hg$).

Alveolar Water Vapor Pressure ($PH_2O$)

The partial pressure exerted by fully saturated water vapor at normal body temperature ($37^\circ C$), constant at $47.0\,mm\,Hg$ with an absolute humidity of $44.0\,mg/L$.

Ideal Alveolar Gas Equation

The physiological equation used to determine alveolar oxygen tension: $PAO_2 = (PB - 47) \times FiO_2 - PaCO_2 \times 1.25$, where $1.25$ represents the factor $1 \div R$ ($R = 0.8$).

Fick's Law of Diffusion

The law stating that gas transfer across a membrane is directly proportional to surface area ($A$), diffusion constant ($D$), and partial pressure difference ($P_1 - P_2$), and inversely proportional to membrane thickness ($T$): $V_{gas} = \frac{A \times D \times (P_1 - P_2)}{T}$.

Graham's Law

The physical law stating that the rate of diffusion of a gas through a medium is inversely proportional to the square root of its gram molecular weight ($D \propto \frac{1}{\sqrt{GMW}}$).

Henry's Law

The physical law stating that the volume of gas dissolving in a given liquid is directly proportional to the partial pressure of that gas in equilibrium with the liquid.

Perfusion-Limited Gas Transfer

Gas exchange in which the rate of gas movement across the alveolar-capillary membrane is limited solely by pulmonary blood flow because the gas (e.g., $N_2O$) does not bind to hemoglobin and reaches partial pressure equilibrium with plasma within $0.1\text{ seconds}$.

Diffusion-Limited Gas Transfer

Gas exchange in which the rate of gas movement across the alveolar-capillary membrane is limited strictly by the membrane barrier itself because the gas (e.g., $CO$) binds avidly to hemoglobin, maintaining a plasma partial pressure near zero throughout transit.

Alveolar-Capillary Transit Time

The total duration of time red blood cells spend traversing pulmonary capillaries at rest ($0.75\text{ seconds}$), where normal alveolar-capillary equilibrium for $O_2$ and $CO_2$ is attained within the first $0.25\text{ seconds}$ (one-third of transit time).

Hyperbaric Oxygen Therapy ($HBOT$)

The therapeutic delivery of $100\%\,O_2$ at ambient pressures greater than $1\,atm$ (typically $3\,atm = 2280\,mm\,Hg$) to dramatically increase dissolved plasma oxygen and treat conditions such as air embolism, decompression sickness, and clostridial gangrene.