Unit 5.2 - Lung Volume and Surfactant

Pulmonary Volumes

Tidal Volume - volume of air inspired or expired during a normal and quiet respiratory cycle (≈ 500mL)

Inspiratory Reserve Volume - volume of air that can be inspired forcefully after a normal quiet inspiration (≈ 3000mL)

Expiratory Reserve Volume - volume of air that can be expired forcefully after a normal quiet inspiration (≈ 1100mL)

Residual Volume - volume of air that remains in the respiratory passages and lungs after forceful expiration (≈ 1200mL), can’t be measured.

Pulmonary Capacities

Total Lung Capacity - inspiratory + expiratory reserve volume + tidal + residual volume (≈ 5800mL)

Inspiratory Capacity - inspiratory reserve volume + tidal volume (≈ 3500mL)

Functional Residual Capacity - volume of air that remains in the lungs after quiet expiration (≈ 2300mL), can’t be measured

Vital Capacity - volume of air that can be forcefully expired after the maximum forceful inspiration (≈4600mL)

Ventilation Types

Ventilation Frequency (f) = respiratory rate = 12-15 breaths/minute

Minute Ventilation = tidal volume * f = 500mL * 12 breaths/minute = 6000ml/min

Dead Space

The area within the conducting zone where gas exchange does not take place.

Anatomical dead space - ≈ 150mL

Physiological dead space - anatomical dead space + any alveoli volume in which gas exchange is less than normal.

Surfactant

1. Reduces surface tension of the lungs

2. Promotes stability of the alveoli

3. Prevents excessive accumulation of fluid on the alveolar surface