RS3

Today's Topics

• Ventilation

  • Resting lung volumes and capacities, exercise changes, forced vital capacity (FVC), minute ventilation, dead space, and alveolar ventilation.

• Gas Exchange

  • Dalton’s Law and external respiration.

Ventilation – Volumes and Capacities

• Key Volumes:

  • Tidal Volume (TV): Air inspired/expired in one breath.

  • Inspiratory Reserve Volume (IRV): Additional air inspired after tidal inspiration.

  • Expiratory Reserve Volume (ERV): Additional air expired after tidal expiration.

  • Residual Volume (RV): Air remaining after maximal expiration.

• Capacities (Combinations of Volumes):

  • Vital Capacity (VC): $VC = IRV + TV + ERV$ (maximal inspiration to maximal expiration).

  • Total Lung Capacity (TLC): $TLC = IRV + TV + ERV + RV$ (maximum air lungs can contain).

Ventilation Changes – Rest to Exercise

• During exercise, TV increases, while IRV and ERV decrease as reserves are actively used. RV, TLC, and VC remain unchanged.

Ventilation – Forced Vital Capacity (FVC)

• FVC: Air forcibly expelled from maximal inspiration to maximal expiration.

• Forced Expiratory Volume in 1 Second (FEV1): Volume forcibly expired in the first second of FVC.

• Percentage FEV1 (%): ext{%FEV1} = \frac{FEV1}{FVC} \times 100

• Clinical Implications:

  • Obstructive Lung Diseases: Decreased FEV1 more than FVC, leading to a lower percentage.

  • Restrictive Lung Diseases: FVC and FEV1 decrease similarly, so the percentage may be normal or increased.

Ventilation – Minute Ventilation (VE)

• Definition: Air volume flowing into or out of the lungs per minute.

• Formula: $VE = VT \times f$ (tidal volume \times breathing frequency).

• During Exercise: VE increases linearly then exponentially; TV increases linearly then plateaus; breathing frequency increases linearly.

Ventilation – Dead Space (VD)

• Definition: Portion of minute ventilation not involved in gas exchange.

• Types: Anatomical (conducting zone airways), Alveolar (damaged/blocked alveoli), Physiological (sum of anatomical and alveolar).

Ventilation – Alveolar Ventilation (VA)

• Definition: Air volume flowing into and out of the alveoli over time.

• Formula: $VA = (VT - VD) \times f$

• Effective Ventilation (EV): Proportion of minute ventilation involved in gas exchange. $EV = \frac{VA}{VE} \times 100$

• Breathing Patterns: Higher effective ventilation is achieved with a higher tidal volume and lower breathing frequency.

Gas Exchange – Dalton’s Law

• Definition: Total pressure of a gas mixture is the sum of the partial pressures of individual gases. ($P<em>G = P</em>{atm} \times F_G$).

• Example: At sea level ($P<em>{atm} = 760 \text{ mmHg}$), $P</em>{O<em>2} = 159 \text{ mmHg}$, $P</em>{CO_2} = 0.3 \text{ mmHg}$.

Gas Exchange – External Respiration

• Occurs between alveoli and pulmonary capillaries.

• Oxygen Gradient: Alveolar $P<em>{O</em>2}$ (105 mmHg) > capillary $P<em>{O</em>2}$ (40 mmHg), leading to O2 movement into blood.

• Carbon Dioxide Gradient: Capillary $P<em>{CO</em>2}$ (46 mmHg) > alveolar $P<em>{CO</em>2}$ (40 mmHg), leading to CO2 movement into alveoli for expiration.