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AVEA ventilator systems
Anatomic Dead Space (Vd ana)
Total volume of the conducting airways from the nose to the level of the terminal bronchioles
(areas that do not participate in gas exchange). Anatomic dead space also includes any
mechanical dead spaces added to the ventilator circuit between the CO
patient.
At end of each exhalation, calculation is carried out equivalent to the graphical method defined
by Fowler
exhaled.
Using Fowler's nomenclature, phase I is the initial exhaled volume with constant FCO
during phase I is calculated as FI. Phase III is the linear part of the capnogram associated with
exhalation of gas from the lung gas exchange units. This is calculated using linear regression
over that part of the capnogram representing 30 to 70% of exhaled CO
is calculated as m, with offset at the FCO
Shaded areas x and y are equal.
The volume above the capnogram and below the regression line through phase III is
calculated as A.
Anatomical dead space is defined as that point on the volume axis at which the volumes
shaded below and above the curve are equal. This is calculated using an algebraic method
This parameter is calculated for each breath and then averaged over the same period as
V
.
CO
2
If either phase I or phase III is ill-defined, based on variation of slope, then anatomical dead
space is not calculated and this parameter is displayed as '***'.
3. Fowler W S, Lung Function Studies II: The Respiratory Dead Space, Am J Physiol 1948; 154: 405-416
4
Heller H, Könen-Bergmann M, Schuster K D, An Algebraic Solution to Dead Space Determination According to Fowler's
Graphical Method, Comput Biomed Res 1999; 32: 161-167
L2786 Rev. M
Appendix I: Volumetric CO2 Calculations
3
. The fraction of CO
2
in the exhaled gas is considered as a function of volume
axis FO.
2
235
sensor and the
2
. FCO
2
. The slope of phase III
2
4
2
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