Treaton MV200, Руководство пользователя

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5.2 Volume capnometry
5-6
Method of calculation of the functional dead space that effectively allows to assess the volume
of gas lost in the respiratory tract, or gas that doesn’t take part in the gas exchange is modified
Bohr equation:
i
i
t
t
i
i
Vt
EtCO
dt t CO
t t
EtCO
Vd ⋅
⋅
−
−
=
∫
2
) ( 2
2 3
1
2
3
2
(3)
where: Vd
i
– functional dead space, ml,
Vt
i
– expiration volume,
dt t CO
t
t
⋅
∫
3
2
) ( 2
– average concentration of carbon dioxide in the exhalation
t3-t2 – expiratory time
Alveolar ventilation per minute is equal to the difference between the minute respiratory volume
and the amount of dead space ventilation.
VDi VTi MValv
n
i
m
− =
∑
= 1
(4)
Minute ventilation contains not only gas that participates in the gas exchange, but ventilation is
wasted in the airways. Thus the high minute ventilation does not always indicate the actual
achievement of the alveolar area. Some part of the tidal volume falls into non-perfused or poorly
perfused lung areas. MValv/Vd ratio characterizes the ratio of alveolar ventilation and dead
space ventilation, and allows to evaluate the severity of disease.
To display the volume capnometry parameters select “EtCO
2
/VCO
2
” and “MValv/Vd” in the
menu of settings of measuring parameter blocks (it.4.12.2) or by pressing of the touch button on
the corresponding measurement parameter field:
The device also displays the graph of the instantaneous amount of carbon dioxide CO
2
exhaled
by the patient
) ( 2 ) ( ) ( 2
pat
t CO t F t VCO ⋅ =
(5)