Notes
Lung Volume and Capacity
Sections
Overview
Spirometer: Measures an individual's pulmonary function.
Record lung volume measurements & generates a graph (spirogram) to analyze the efficiency of an individual's lung function.
Here, we analyze the spirogram of an average adult male:
y-axis = volume (liters) → spirograms record air volume (between 0 - 6 liters)
x-axis = time (seconds) → spirograms record over time.
Key Values and Spirogram Analysis
Tidal volume (TV):
Volume of air inspired during quiet breathing → 0.5 liters
Inspiratory reserve volume (IRV):
Forced inhalation → 3.0 liters
Maximal (peak) inspiration
= 6.0 liters lung volume
Expiratory reserve volume (ERV):
The volume of forceful exhalation → 1.0 liter
Maximal expiration
= 1.5 liters lung volume
Residual volume (RV):
The volume of air still in the lungs after maximal expiration
Lung capacity = sum of two or more lung volumes:
Vital capacity (VC): The difference between maximal inspiration and maximal expiration.
VC = TV + IRV + ERV
Total lung capacity (TLC): the total volume of air that the lungs can hold.
TLC = VC + RV
Inspiratory capacity (IC): the maximum volume of air that the lungs can inspire.
IC = IRV +TV
Functional residual capacity (FRC): the volume that remains in the lungs after a single quiet breath.
FRC = ERV + RV
Pulmonary Ventilation and Alveolar Gas Exchange
Conducting portion:
Trachea → left, right bronchi → terminal bronchioles. Air conduits, do not participate in gas exchange. This is the anatomic dead space.
Gas exchange primarily occurs in the respiratory bronchioles and alveoli.
Healthy Lungs vs. Emphysema
Healthy lungs:
Physiologic dead space = anatomic dead space.
Emphysema:
Physiological dead space > anatomic dead space.
Emphysema: Lungs lose elasticity → insufficient recoil → air is trapped in lungs, unable to be exhaled.
Effects:
- Increase in RV (volume of air remaining in the lungs after maximal expiration)
- Decrease in vital capacity.
- Individuals have "barrel chest" → accommodates increased RV