Lung Mechanics and Pulmonary Function Vocabulary

Vocabulary flashcards covering key concepts from the lecture notes on lung mechanics, surfactant biology, gas flow physics, and pulmonary function testing.

Dynamic compliance

Compliance measured during breathing, especially forced breathing; reflects real-time elasticity of the lungs and chest wall during airflow.

Static compliance

Compliance measured with no airflow, reflecting the elastic properties of the lungs and chest wall when at rest.

Surface tension

Tension at the air-liquid interface (alveolar surface) due to cohesive forces between water molecules; tends to collapse small alveoli and is reduced by surfactant.

Alveolar surface tension

Surface tension at the alveolar liquid surface; contributes to alveolar collapse without surfactant and is modulated by surfactant to stabilize alveoli.

Surfactant

A complex mixture of lipids (mostly phospholipids) and proteins produced by alveolar type II cells; lowers alveolar surface tension, increases compliance, prevents atelectasis, and aids uniform inflation.

Type II pneumocyte

Alveolar cell that synthesizes and secretes surfactant; serves as progenitor for type I cells; active mainly from ~24 to 34 weeks gestation for fetal lung maturation.

Type I pneumocyte

Alveolar cell specialized for gas exchange; thin and covers most of the alveolar surface.

Neonatal respiratory distress syndrome (RDS)

Respiratory failure in premature infants due to surfactant deficiency; leads to alveolar collapse (atelectasis); treated with exogenous surfactant.

Exogenous surfactant

Surfactant administered from outside the body to surfactant-deficient lungs to reduce surface tension and improve breathing.

Laplace's law (alveoli)

ΔP = 2S/r for a sphere; smaller radius requires higher pressure to keep alveolus open; surfactant helps by reducing surface tension more at smaller radii.

Intrapleural pressure

Pressure within the pleural cavity; normally negative (e.g., around -5 cm H2O during inspiration) to keep the lung inflated; more negative when surfactant is deficient or during strong inspiration.

Dipalmitoyl phosphatidylcholine (DPPC)

Major phospholipid component of surfactant that significantly reduces surface tension in the alveoli.

Poiseuille's law

Laminar flow resistance in a cylindrical tube is proportional to length and viscosity and inversely proportional to the radius to the fourth power; flow ∝ r^4.

Radius-resistance relationship (R ∝ 1/r^4)

Small changes in airway radius cause large changes in resistance; particularly important in pediatric airways where radius changes greatly affect flow.

Reynolds number

Dimensionless quantity predicting laminar vs turbulent flow; Re < 2300 is laminar, 2300–4000 is transitional, >4000 is turbulent; depends on density, velocity, radius, and viscosity.

Laminar flow

Smooth, orderly fluid flow with low resistance, typical in small airways under normal conditions.

Turbulent flow

Disordered, chaotic flow with higher energy loss, often occurring at sites of constriction or obstruction and increasing resistance.

Heliox

Helium-oxygen gas mixture with lower density than air; used to decrease Reynolds number and promote laminar flow in obstructed airways.

Inspiration (active) / Expiration (passive)

Inspiration requires muscle work (diaphragm and accessory muscles); expiration at rest is largely passive due to elastic recoil of lungs.

FEV1

Forced expiratory volume in one second; volume forcefully exhaled in the first second of a spirometry maneuver; reduced in obstructive disease.

FVC (Forced Vital Capacity)

Total volume exhaled forcefully after a maximal inhalation; a key spirometry parameter.

FEV1/FVC ratio

Ratio of FEV1 to FVC; reduced in obstructive diseases; normal or increased in restrictive diseases.

FEF25–75 (Forced Expiratory Flow 25–75%)

Middle-expiratory flow rate; reflects small- to mid-airway function; decreased in obstruction.

DLCO (Diffusion Capacity of the Lung for Carbon Monoxide)

Measurement of gas transfer across the alveolar-capillary membrane; reduced with fibrosis or emphysema; typically normal in asthma.

Bohr equation

VD/VT = (PACO2 − PECO2)/PACO2; links dead space to CO2, used to estimate physiologic dead space.

Alveolar dead space

Ventilated but not perfused alveoli; contributes to wasted ventilation; part of physiologic dead space.

Residual Volume (RV)

Volume remaining in the lungs after a maximal exhalation; cannot be measured by standard spirometry.

Functional Residual Capacity (FRC)

Volume in the lungs after a normal exhalation; RV plus ERV; not directly measurable by spirometry.

Total Lung Capacity (TLC)

Total volume in the lungs after maximal inspiration; sum of all volumes (RV + ERV + VT + IRV).

Inspiratory Reserve Volume (IRV)

Additional air that can be inhaled after a normal inspiration.

Expiratory Reserve Volume (ERV)

Additional air that can be exhaled after a normal expiration.

Tidal Volume (VT)

Volume of air inhaled or exhaled during a normal breath.

Flow-volume loop

Graph showing airflow (flow) versus lung volume during maximal inspiration and expiration; distinguishes obstructive vs restrictive patterns.

Bronchodilator responsiveness

Increase in FEV1 or FVC by at least 12% after bronchodilator administration; suggests reversible obstructive disease (e.g., asthma).