M04.07.002 Ventilation

Total Ventilation (Minute Ventilation)

Definition: Total ventilation, also known as minute ventilation (V̇_E), is the total volume of air moved in or out of the lungs per minute. It can be calculated using the following formula:

V̇_E = V_T × f

Where:

• V_T is the tidal volume (the amount of air per breath)
• f is the respiratory rate (breaths per minute)

Normal Resting Values:

Calculation Example:

V̇_E = 500 mL × 15 breaths/min = 7,500 mL/min

Dead Space

Definition: Dead space refers to regions of the respiratory system that contain air but do not participate in gas exchange with the blood (i.e., they do not exchange O2 and CO2).

Types of Dead Space:

• Anatomic Dead Space (V_D):
  • Refers to airway regions that, due to their structure, cannot perform gas exchange. It includes the conducting zones, which end at the terminal bronchioles.
  • The volume of anatomic dead space (V_D) in milliliters is approximately equal to a person’s weight in pounds. For instance, a 150-lb individual would have an anatomic dead space of 150 mL.

Alveolar Ventilation

Definition: Alveolar ventilation (V̇_A) is the volume of fresh air that reaches the respiratory zone per minute, where gas exchange occurs. It is calculated using the formula:

V̇_A = (V_T - V_D) × f

Where:

• V_T is the tidal volume
• V_D is the dead space volume
• f is the respiratory rate

Example Calculation:

Given:

• V_T = 500 mL
• V_D = 150 mL
• f = 15 breaths/min

V̇_A = (500 mL - 150 mL) × 15 breaths/min = 5,250 mL/min

Points to Remember

• Functional Residual Capacity (FRC): Acts as a buffer for gas exchange during periods of apnea when there is no ventilation but continuous blood flow.
• Depth vs. Rate of Breathing: Increasing the breathing depth equally increases total and alveolar ventilation. However, increasing the rate of breathing increases total ventilation more than alveolar ventilation.

Bibliography Reference Links

1. “Lung Mechanics and Ventilation.” [Accessed from a medical physiology textbook]
2. “Dead Space and Alveolar Ventilation.” [Journal of Respiratory Physiology]