Respiratory Diseases and the Fire Service - IAFF

14 Chapter 1-1 • Anatomy
Where:
Figure 1.1.1
Figure 1-1.1 Lung Volumes Measured in a Pulmonary Function Test
VT = Tidal Volume: volume of air normally inhaled or exhaled (0.4-1.0 L).
IRV = Inspiratory Reserve Volume: the additional volume of air inhaled
(after the tidal volume) by taking a full deep breath (2.5-3.5 L).
ERV = Expiratory Reserve Volume: the additional volume of air exhaled
(after the tidal volume) by forcing out a full deep breath (2.5-3.5 L).
RV = Residual Volume: the volume of air that remains in the lungs following
a maximal exhalation (0.9-1.4 L for men; 0.8-1.2 L for woman).
VC = Vital Capacity: maximal volume of air that can be forced out after
a maximal inspiration, down to the residual volume (4-5 L in men, 3-4
L in woman). This equals IRV + TV + ERV.
TLC = Total Lung Capacity: the amount of gas contained in the lungs
at maximal inspiration (4-6 L). This equals VC + RV.
FRC = Functional Residual Capacity: the amount of air in the lungs at
the end of a normal breath; i.e., after the tidal volume is exhaled. This
equals ERV + RV.
Ventilation is also dependent on airflow. Through the upper airways and
to the level of the terminal bronchioles, airflow occurs by bulk movement or
convection. Because of the vast increase in cross-sectional area after the terminal
bronchioles airflow slows and the gas molecules move by diffusion. The
velocity of airflow is dependent on both airway resistance related to the size of
the airway and lung compliance (stiffness) that results from the mechanical
constraints of the chest wall.
All areas of the lungs do not receive equal ventilation. The base of the lung
receives more ventilation per volume of lung than does the top or apex. This
distribution varies with position of the body. For example when lying on the