Respiratory Physiology: Equations and Gas Laws

Comprehensive vocabulary flashcards covering key formulas, pressure definitions, respiratory mechanics, gas laws, and normal physiological constants in respiratory physiology.

Lung Compliance ($C_L$)

$$C_L = \frac{\Delta V}{\Delta P}$$

Airway Resistance ($R_{aw}$)

Calculated as $R_{aw} = \frac{\Delta P}{\text{flow}}$

Time Constant ($\tau$)

Calculated as $\tau = R \times C$

Minute Ventilation ($\dot{V}_E$)

Calculated as $\dot{V}_E = V_T \times f$

Alveolar Ventilation ($\dot{V}_A$)

Calculated as $\dot{V}_A = (V_T - V_D) \times f$

Elasticity / Elastance ($E$)

Calculated as $E = \frac{\Delta P}{\Delta V}$

Transpulmonary Pressure ($P_{tp}$)

Calculated as $P_{tp} = P_{alv} - P_{pl}$

Transmural Pressure ($P_{tm}$)

Calculated as $P_{tm} = P_{inside} - P_{outside}$

Transairway Pressure ($P_{tr}$)

Calculated as $P_{tr} = P_{aw} - P_{atm}$

Transrespiratory Pressure ($P_{rs}$)

Calculated as $P_{rs} = P_{aw} - P_{bs}$

Trans-thoracic Pressure ($P_w$)

Calculated as $$P_w = P_{pl} - P_{

Laplace's Law

Formulated as $P = \frac{2T}{r}$

Anatomical Dead Space ($V_D$)

Approximated by the rule of thumb $V_D \approx 1\,\text{mL} \times \text{ideal body weight (kg)}$

Total Lung Capacity ($TLC$)

Expressed as $TLC = RV + ERV + TV + IRV$

Boyle's Law

P,V, = P2P2

Charles's Law

Stated as $\frac{V_1}{T_1} = \frac{V_2}{T_2}$

Ideal Gas Law

Expressed as $PV = nRT$

Fick's Law of Diffusion

Expressed as $\dot{V}_{gas} \propto \frac{A \times D \times \Delta P}{T}$

Graham's Law of Diffusion

Expressed as $\frac{V_1}{V_2} = \sqrt{\frac{D_1}{D_2}} = \sqrt{\frac{M_2}{M_1}}$

Dalton's Law

Expressed as $P_{total} = P_1 + P_2 + P_3 + \dots$

Normal Barometric Pressure ($P_B$)

The standard atmospheric pressure at sea level, equal to $760\,\text{mmHg}$.

Atmospheric Oxygen ($O_2$)

Makes up $21\%$ of dry atmospheric air at sea level, exerting a partial pressure of $159.6\,\text{mmHg}$.

Atmospheric Nitrogen ($N_2$)

Makes up $78.08\%$ of dry atmospheric air at sea level, exerting a partial pressure of $592.8\,\text{mmHg}$.

Atmospheric Carbon Dioxide ($CO_2$)

Makes up $0.03\%$ of dry atmospheric air at sea level, exerting a partial pressure of $0.2\,\text{mmHg}$.

Water Vapor Pressure ($P_{H_2O}$)

Equal to $47\,\text{mmHg}$ at standard body temperature ($37\,^\circ\text{C}$); varies with temperature and is subtracted when calculating partial pressures of fully humidified alveolar gases.

Normal Resting Blood Gas Pressures

Standard normal physiological values at rest: alveolar $P_{AO_2} = 100\,\text{mmHg}$, arterial $P_{aCO_2} = 40\,\text{mmHg}$, venous $P_{vO_2} = 40\,\text{mmHg}$, and venous $P_{vCO_2} = 46\,\text{mmHg}$.