GE HEALTHCARE E-PRESTN, Technical Manual

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Compact Airway Modules, E-CAiOVX, E-CAiOV, E-CAiO, E-COVX, E-COV
9 - 5
2062973-004
The airway resistance, Raw, is calculated using an equation that describes the kinetics of the
gas flow between the lungs and the D-lite. The equation states that the pressure at the D-lite
can at any moment of the breath be approximated using the equation
Formula 3
where P(t), V’(t) and V(t) are the pressure, flow and volume measured at the D-lite at a time t,
Raw is the airway resistance, Compl is the compliance and PEEP
e
+PEEP
i
is the total positive end
expiratory pressure (PEEP
tot
).
D-lite
Patient Spirometry uses specific sensors called D-lite+/D-lite and Pedi-lite+/Pedi-lite flow
sensors. Different types of sensors are available: adult sensor for measuring adults and
pediatric sensor for children. Both are available as reusable and disposable versions.
D-lite and Pedi-lite adapters are designed to measure kinetic pressure by a two-sided Pitot
tube. Velocity is calculated from pressure difference according to Bernoulli's equation. Flow is
then determined using the calculated velocity.
(from Bernoulli's equation) Formula 4
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.
1.2.4 Gas exchange measurement
The gas exchange measurement uses the D-lite 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
produced 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:
Formula 5
and
Formula 6