Datex-Ohmeda S/5 monitors
Document No. 800 1009-1
12
D-lite
TM
Patient Spirometry uses a specific sensor called D-lite
TM
flow sensor. Different types of the D-lite
sensors are available: adult sensor for measuring adults and pediatric sensor for children. Both are
available as reusable versions and D-lite sensor also for single use.
D-lite adapter is designed to measure kinetic pressure by two-sided Pitot tube. Velocity is
calculated from pressure difference according to Bernoulli's equation. Flow is then determined
using the calculated velocity.
v =
2 dP
×
ρ
(from Bernoulli's equation)
Formula 4
F = v A
×
,
where:
F = flow (l/min), v = velocity (m/s), A = cross area (m
2
), dP = pressure difference (cmH
2
O),
ρ
= density (kg/m
3
)
Finally the volume information is obtained by integrating the flow signal.
2.1.4
Gas exchange measurement
The gas exchange measurement uses the D-lite
TM
flow sensor and the gas sampler.
The basic data which is needed to obtain O
2
consumption and CO
2
production are
volumes
and
concentrations
.
Concentrations have been corrected for delay and deformation during the transport of the gas
sample in a sidestream gas measurement sensor.
To obtain the amount of O
2
consumed in ml/min, the amount which is exhaled is subtracted from
the amount that is inhaled.
To obtain the amount of CO
2
producted in ml/min, the amount which is inhaled is subtracted from
the amount that is exhaled.
These amounts can be obtained by multiplying each measured volume piece (dv) by the
corresponding gas concentration:
dv
f
dv
f
O
O
ò
−
ò
exp
2
2
insp
=
2
VO
Formula 5
and
dv
f
dv
f
CO
CO
ò
−
ò
insp
exp
=
2
VCO
2
2
Formula 6
Using inspiratory and expiratory minute volumes MV
i
and MV
e
and volume-weighted inspiratory
concentrations fi and fe these equations can be rewritten as:
e
O
i
O
=
2
MV
fe
-
MV
fi
VO
2
2
×
×
[ml/min]
Formula 7
