Alveolar Gas Exchange Gas Exchange Volumes - PowerPoint Presentation

Slide1

Alveolar Gas Exchange

Gas Exchange Volumes

and Minute Volumes

Determination of Alveolar and Dead Space Ventilation and Volumes

If we take

F

DCO2

to be zero (b/c room air is defined as zero):

One way to easily find CO

2

production:

Therefore:

Therefore:

And:

What Determines

P

ACO2(assuming inspired CO2 = 0)

What Determines

PAO2

Greater alveolar ventilation or higher inspired O

2

gives higher alveolar O2; Higher rate of oxygen consumption lowers alveolar O2.

Can We Combine These into One Overall Relationship to Describe Alveolar Gases?

c

is the same in both equations (=1 / (PB-P

H2O)):

AND

Since

c = c:

R

: The Respiratory Exchange Ratio

Unlike

RQ

, defined at the respiratory exchanger (alveoli) – otherwise, mathematically the same.

Over and Under Ventilation

Hyperventilation

-- where elimination of CO2 is greater than production at the tissue level.

Normally considered as a difference between input (from tissues) and elimination (at exchanger) of blood CO

2.

But, we can also consider a sort of hyperventilation that might occur if we over perfuse the tissues where we consider the effects on tissues (? What controls perfusion??)

Hypoventilation

-- the opposite

What are the acid base disturbances associated with hyper- and hypo-ventilation.

Steady and Non-Steady State Ventilation

Recall our multiple stage gas exchange model.

In

steady-state

ventilation:

In

non-steady state

, one or more of these will not be equal.

Let's Combine the Notions on the Last Two Slides:

AND

AND

CO

2 – O2

Diagram and Gas Exchange