Medical Applications User Guide (pdf) - Freescale Semiconductor

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12.5
Alarm System
An important part of this application is an
alarm that can indicate different patient
parameters such as exhaled volume or airway
pressure. The ventilation system must be able
to detect whether a breath has been taken.
The MCU measures changes in aspiratory
flow and pressure by using sensors. If no
inspiration is detected within a certain period
of time, the monitor sounds an alarm. The
conditions to be programmed depend on each
system. PWM cycles can be programmed to
sound the alarms. Sometimes, the ventilation
system uses different alarms for different
situations. For more information on the alarm
circuit, refer to Chapter 3, Telehealth Systems.
12.6
Air and Oxygen Blender
and Mix Control
The air and oxygen blender provides a precise
oxygen concentration by mixing air and
oxygen. The concentration may be adjusted
to any value from controlled air to 100 percent
oxygen. Internally, a proportioning valve mixes
the incoming air and oxygen as the oxygen
percentage dial is adjusted. Variation in line
pressure, flow or pressure requirements for
any attached device will not affect the oxygen
concentration.
Figure 11-5: 12-5: Normal Lung Lung Volume Volume
TLC
0
Diagnostic and Therapy Devices
freescale .com/medical 67
V T
ERV
IRV
FRC
Figure 12-6: Blender Configuration
Figure 11-8: Blender Configuration
PWR
Accumulator/
Compressor
IC
Time
AIR O2
PWR
Blender
MCU/MPU
VC
RV