Chapter 37:
Pulmonary Ventilation
Guyton and Hall, Textbook of Medical Physiology, 12 edition
Respiration
• Four Major Functions of Respiration
1. Pulmonary ventilation
2. Diffusion of oxygen and carbon dioxide
between the alveoli and the blood
3. Transport of oxygen and carbon dioxide in
the blood and body fluids
4. Regulation of ventilation
Mechanics of Pulmonary Ventilation
• Muscles That Cause Lung Expansion and Contraction
Lungs can be expanded and contracted in two ways:
1. By downward and upward movement of the diaphragm
to lengthen and shorten the chest cavity
2. By elevation and depression of the ribs to increase and
decrease the anteroposterior diameter of the chest
cavity
Mechanics of Pulmonary Ventilation
Fig. 37.1 Contraction and expansion of the thoracic cage during expiration and
inspiration
Mechanics of Pulmonary Ventilation (cont.)
• Normal quiet breathing is accomplished almost
entirely by movement of the diaphragm
a. During inspiration, contraction of the diaphragm
pulls the lungs downward
b. During expiration, the diaphragm simply relaxes,
and the elastic recoil compresses the lungs and
expels the air
Mechanics of Pulmonary Ventilation (cont.)
• During heavy breathing the elastic forces are not
powerful enough, so extra force is generated by
the abdominal muscles
a. Muscles that raise the rib cage are the external
intercostals (most important), sternocleidomastoid,
anterior serratus, and scalenes
b. Muscles that pull the rib cage downward during
expiration are the abominal rectus, and the internal
intercostals
Mechanics of Pulmonary Ventilation (cont.)
• Pressures That Cause the Movement of Air In and
Out of the Lungs
a. Pleural pressure- pressure of the fluid in the thin
space between the lung pleura and the chest pleura;
there is a slight suction so the pressure is negative
b. Alveolar pressure- pressure of the air inside the lung
alveoli
c. Transpulmonary pressure- difference between the
pleural and alveolar pressures (recoil pressure)
Fig. 37.2 Changes in lung volume, alveolar pressure, pleural
pressure, and transpulmonary pressure during normal
breathing
Mechanics (cont.)
• Compliance of the Lungs- the extent to which the
lungs will expand for each unit increase in
transpulmonary pressure
• Compliance Diagram of the Lungs
a. Inspiratory compliance curve
b. Expiratory compliance curve
c. Characteristics of the diagrams are dependent on
1. Elastic forces of the lung tissue
2. Elastic forces caused by surface tension of the
fluid that lines the inside walls of the alveoli
Mechanics (cont.)
Fig. 37.3 Compliance diagram in a healthy person
Fig. 37.4 Comparison of the compliance of
saline and air-filled lungs when the
alveolar pressure is maintained at
atmospheric pressure and pleural
pressure is changed
Mechanics (cont.)
• Surfactant, Surface Tension, and Collapse of the Alveoli
a. Principle of Surface Tension-when water forms a surface
with air, the water molecules on the surface of the water
have an especially strong attraction for one another. As a
result, the water surface is always trying to contract.
b. Surfactant-surface active agent that reduces the surface
tension of water; secreted by Type II alveolar cells
Mechanics (cont.)
• Effect of the Thoracic Cage on Lung Expansibility
a. Compliance of the thorax and the lungs
b. Work of breathing (3 fractions)
1. Compliance or elastic work
2. Tissue resistance work
3. Airway resistance work
Pulmonary Volumes and Capacities
• Recording Changes in Pulmonary Volume-Spirometry
Fig. 37.5 Spirometer
Pulmonary Volumes and Capacities
• Pulmonary Volumes
a. Tidal Volume (TV)-amount of air inspired or expired
with each normal breath; usually about 500 ml
b. Inspiratory Reserve Volume (IRV)-extra volume that
can be inspired over and above the TV; usually about
3000 ml
c. Expiratory Reserve Volume (ERV)-max extra volume
that can be expired at the end of a normal TV; usually
about 1100 ml
Pulmonary Volumes and Capacities
• Pulmonary Volumes (cont.)
d. Residual Volume (RV)-amount of air remaining in the
lungs after the most forceful expiration; usually about
1200 ml
•
Pulmonary Capacities
a. Inspiratory Capacity- (TV + IRV); about 3500 ml
b. Functional Residual Capacity- (ERV + RV); about
2300 ml
Pulmonary Volumes and Capacities
• Pulmonary Capacities (cont.)
c. Vital Capacity (VC)- (IRV + TV + ERV); usually about
4600 ml
d. Total Lung Capacityi (VC + RV); usually about 5800 ml
Pulmonary Volumes and Capacities
Fig. 37.6 Diagram showing pulmonary volumes and pulmonary capacities
Minute Respiratory Volume
• Minute Respiratory Volume- total amount of new
air moved into the respiratory passages each
minute
1. Equal to the TV x Respiratory Rate
2. Usually 500ml x 12 bpm = 6 L/min
Alveolar Ventilation
• Effect of “Dead Space” – air that does not reach
the gas exchange areas but simply fill
respiratory passages where gas exchange does
not occur (dead air space)
• Rate of Alveolar Ventilation- alveolar ventilation per
minute is the total volume of new air entering the
alveoli each minute
Functions of the Respiratory Passages
Fig. 37.8 Respiratory passages