Pulmonary Ventilation
Pulmonary Ventilation
Pulmonary Ventilation
V P F (flow of gases)
Boyles Law
• Boyles law – the relationship between the pressure and volume of
gases
P1V1 = P2V2
• P = pressure of a gas in mm Hg
• V = volume in cubic millimeters
• Subscripts 1 and 2 represent the initial and resulting conditions,
respectively
Inspiration
• The diaphragm and external intercostal muscles (inspiratory
muscles) contract and the rib cage rises
• The lungs are stretched and intrapulmonary volume increases
• Intrapulmonary pressure drops below atmospheric pressure (1 mm
Hg)
• Air flows into the lungs, down its pressure gradient, until
intrapleural pressure = atmospheric pressure
Expiration
• Inspiratory muscles relax and the rib cage descends due to gravity
• Thoracic cavity volume decreases
• Elastic lungs recoil passively and intrapulmonary volume decreases
• Intrapulmonary pressure rises above atmospheric pressure (+1 mm
Hg)
• Gases flow out of the lungs down the pressure gradient until
intrapulmonary pressure is 0
Physical Factors Influencing Ventilation: Airway Resistance
• Friction is the major nonelastic source of resistance to airflow
• The relationship between flow (F), pressure (P), and resistance (R)
is:
F = P
R
Physical Factors Influencing Ventilation: Airway Resistance
• The amount of gas flowing into and out of the alveoli is directly
proportional to P, the pressure gradient between the atmosphere
and the alveoli
P = (Patm – Palv)