Gas Laws & Respiratory Care – Key Vocabulary

These vocabulary flashcards cover essential terms, laws, and clinical applications of gas behavior relevant to respiratory care, enabling quick review for exams or practice.

Kinetic Molecular Theory

Explains macroscopic gas properties (pressure, temperature, viscosity, density, thermal conductivity, volume) based on molecular motion; assumes elastic collisions, negligible molecular volume, and no intermolecular attractions.

Gram Molecular Weight (gmw)

Mass (in grams) equal to one mole of a substance; numerically equals atomic or molecular weight.

Mole

The amount of substance containing 6.023 × 10²³ particles (Avogadro’s number).

Universal Molar Volume

Volume occupied by one mole of an ideal gas at STPD (0 °C, 1 atm): 22.4 L (22.3 L for CO₂).

Density (dw)

Mass per unit volume of a gas; for gases: gmw ÷ 22.4 L at STPD.

Pressure (P)

Force exerted by gas molecules per unit area; standard atmosphere (1 atm) equals 760 mm Hg or 101.3 kPa.

Partial Pressure

Pressure exerted by a single gas in a mixture; symbolized Pgas.

Atmospheric Pressure

Weight of the air column above a point; decreases with altitude, increases below sea level.

Dalton’s Law

Total pressure of a gas mixture equals the sum of the partial pressures of each component: Ptotal = ΣPgas.

Avogadro’s Law

Equal volumes of gases at the same temperature and pressure contain equal numbers of moles; formula V/n = k.

Heliox Therapy

Use of a helium–oxygen mix (low-density) to reduce upper-airway resistance and ease breathing through obstructions.

Hyperbaric Oxygen Therapy (HBO)

Breathing 100 % O₂ at 4–6 atm to increase blood PO₂, reduce bubbles (Boyle), and enhance healing.

Boyle’s Law

At constant temperature, gas volume varies inversely with pressure: P₁V₁ = P₂V₂.

Charles’ Law

At constant pressure, gas volume varies directly with absolute temperature: V₁/T₁ = V₂/T₂.

Gay-Lussac’s Law

At constant volume, gas pressure varies directly with absolute temperature: P₁/T₁ = P₂/T₂.

Combined Gas Law

Relationship combining Boyle’s, Charles’, and Gay-Lussac’s laws: (P₁V₁)/T₁ = (P₂V₂)/T₂.

Ideal Gas Law

Comprehensive gas equation: PV = nRT, where R = 0.08206 L·atm mol⁻¹ K⁻¹.

Gas Constant (R)

Proportionality constant in PV = nRT; value depends on pressure/volume units (0.08206 L·atm mol⁻¹ K⁻¹).

Diffusion

Net movement of molecules from high to low concentration due to random motion; basis of pulmonary gas exchange.

Graham’s Law

Rate of diffusion through gas inversely proportional to square root of gmw: D ∝ 1/√gmw; lighter gases diffuse faster.

Effusion

Passage of gas molecules through a tiny opening (e.g., balloon leak); rate follows Graham’s Law.

Fick’s Law of Diffusion

Gas flow across a membrane (Vgas) = (A × D × ΔP)/T; depends on surface area (A), diffusion coefficient (D), thickness (T), and partial-pressure gradient (ΔP).

Diffusing Capacity

Ability of lungs to transfer gas; determined by surface area, membrane thickness, diffusion constant, and pressure gradient (per Fick’s Law).

Henry’s Law

At constant temperature, the amount of gas dissolved in a liquid is directly proportional to its partial pressure: V = a × Pgas; solubility falls as temperature rises.

Solubility Coefficient (a)

Constant representing volume of gas dissolved per unit pressure in a specific liquid at a given temperature.

Isothermal Conditions

Process occurring at constant temperature; assumption for Boyle’s Law demonstrations.

Hyperoxygenation

Increasing dissolved O₂ in blood/tissue (e.g., via HBO) based on Henry’s Law.

Upper-Airway Obstruction

Blockage that elevates resistance; relieved partially by low-density Heliox per Avogadro’s and Graham’s principles.

Body Plethysmography

PFT technique using Boyle’s Law to measure lung volumes by relating pressure changes inside a sealed box to thoracic gas volume.

Nitric Oxide (INO)

Inhaled pulmonary vasodilator improving V/Q matching by decreasing pulmonary vascular resistance.

Effusive Decompression Sickness

Condition where dissolved gases form bubbles during rapid ascent from depth; prevention relies on Henry’s Law by ascending slowly.

Vasoconstriction (HBO effect)

Reduction in vessel diameter during HBO that helps decrease edema while maintaining oxygen delivery due to elevated PO₂.

Ideal vs. Real Gas

Ideal gases follow PV = nRT exactly; real gases deviate at high pressures or low temperatures due to intermolecular forces and finite molecular volume.