Understanding Respiratory Cycle & Gas Exchange: Normal Air & Gas Flow in Lungs, Notas de estudo de Física

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Jim Pierce

Bi 145a

Lecture 17, 2009-



How do we describe the normal flow

in and out of the mouth, lung, and

alveoli during a respiratory cycle?



How do we get air in and out of the

alveoli?



Volumes that go through the mouth:

• (^) Tidal Volume
• (^) Vital Capacity 

Volumes that exist inside the mouth

• (^) Residual Volume
• (^) End Expiratory Volume (aka Functional Residual Capacity)
• (^) End Inspiratory Volume
• (^) Full Lung Capacity

 We can subdivide the space from the mouth inside:  Anatomically

• (^) Upper Airways
• (^) Lower Airways
• (^) Alveoli  Functionally
• (^) Alveolar (Gas Exchanging)
• (^) Physiologic Dead Space (Not)

Anatomic Dead Space



Anatomic Dead Space



Physiologic Dead Space



We can use O 2 and CO 2 to Understand

Volumes:



Fowler’s Method –

Anatomic Dead Space



If you inhale a pure

gas, you will exhale:

• (^) Pure Gas
• (^) Mixed Gas
• (^) Alveolar Gas

 Bohr Equation – Physiologic Dead Space  All CO2 comes from alveolar gas (not dead space)  Arterial CO2 is almost always equal to Alveolar CO  There is conservation of mass.

 Bohr Equation – Physiologic Dead Space  So:  PACO2 * VA = PECO2 * VT = number of mols of exhaled CO

 Bohr Equation – Physiologic Dead Space  VA = PECO VT PACO  VD = 1 - VA VT VT  VD = 1 - PECO VT PACO