Physiology 2130 Lecture Notes - Lecture 50: Pulmonary Compliance, Thoracic Cavity, Intrapleural Pressure
1 May 2018
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Lecture 050: Ventilation and Lung Compliance
Ventilation
● Process by which air moves in and out of the lung
○ Inhalation and exhalation
● By changing the pressure of the thoracic cavity by moving the diaphragm
○ Air flows in when pressure is more negative (expanded thoracic cavity)
○ Use muscles of the diaphragm and intercostals
Inhalation
● Active process (contraction of inspiration muscles)
○ The diaphragm
○ The external intercostals
● Increase pressure gradient between lung and intrapleural space (inhalation)
Exhalation
● Normally a passive process
○ Lungs and chest wall return to their equilibrium position
● Active process during exercise or spontaneous hyperventilation
○ Muscles of the abdominal wall
○ The internal intercostals
● It doesn't take much effort to inhale
○ Relatively small changes in pressure can inflate a large surface area of the lungs
○ Due to distensibility of the lung (lung/pulmonary compliance)
● Compliance = ΔV / ΔP
○ Change in volume per unit pressure in change
○ Large compliance: large change in volume due to a small change in pressure
● Can be determined by creating a Pressure-Volume Curve
○ Take out the lungs
○ Inflate and deflate the lungs while measuring the pressure (cm H2O)
● Start and end of inflation
○ Low compliance
● Middle of inhalation
○ Much higher compliance
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● Deflation
○ Slightly different from inhalation
○ End of deflation has higher compliance
Pressure-Volume (PV) Curve
● Non-linear curve
● At high and low volumes the lung is less compliant
● At the same pressure the lung has more volume during
deflation compared to inflation
○ Hysteresis
● Note:
○ This is an experiment done with the lungs removed so the pressure goes from 0-
20
○ In an actual person, pressure changes can being in the middle of the curve (5-
10)
■ So small changes in pressure can generate large changes in volume
Compliance in humans
● Not a complete PV curve
● Compliance is approximately 220 mL/cm H2O
○ HIGH
What forces are involved in lung compliance?
● Elasticity of the ling
find more resources at oneclass.com
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Document Summary
Process by which air moves in and out of the lung. By changing the pressure of the thoracic cavity by moving the diaphragm. Air flows in when pressure is more negative (expanded thoracic cavity) Use muscles of the diaphragm and intercostals. Increase pressure gradient between lung and intrapleural space (inhalation) Lungs and chest wall return to their equilibrium position. Active process during exercise or spontaneous hyperventilation. Relatively small changes in pressure can inflate a large surface area of the lungs. Due to distensibility of the lung (lung/pulmonary compliance) Change in volume per unit pressure in change. Large compliance: large change in volume due to a small change in pressure. Can be determined by creating a pressure-volume curve. Inflate and deflate the lungs while measuring the pressure (cm h2o) At high and low volumes the lung is less compliant. At the same pressure the lung has more volume during deflation compared to inflation.
