3001002 Rev. T
Page 7
Section 3
Principles of operation
The Precision Flow
®
warms and humidifies breathing gas for delivery by nasal cannula at flows
from 1 to 40 lpm. The unit incorporates an electronic blender and flow sensors that allow the
oxygen percentage and total gas flow to be set independently.
The Precision Flow
®
consists of two parts:
Main unit
• The
main unit
which contains all the electrical and electronic components including the
electronic blender and flow controllers, and remote sensors to monitor the disposable water
path. The main unit has no water pathways and the gas pathway contains only dry gas at room
temperature, and consequently does not need internal cleaning or disinfection.
• The flow of oxygen and air are measured by
mass flow sensors
. The operating software
calculates the required flow of each needed to reach the target flow and oxygen percentage
set by the operator. The system controls gas flows accordingly by adjusting proportional
solenoid valves
on the gas lines. An
oxygen sensor
monitors the gas mixture and signals any
discrepancy between target and measured percentage. The oxygen sensor is automatically
calibrated with oxygen at power-up and every 24 hours.
•
Firmware
running in the main unit uses sensors to monitor gas pressure, water temperature, and
to detect air leaks into the disposable patient circuit (bubble detector). Alarms are displayed if any
parameters are outside the normal range. Other indicators show low charge in the backup battery, and
the type of cartridge installed. See Appendix for a description of the firmware states and transitions.
• After a two hour charging period, an internal
battery
backup will maintain the set flow and
oxygen blend for at least 15 minutes without AC power. The battery is not operator replaceable.
WARNING
: The back-up battery is designed for temporary use only, when AC power to the unit
has been interrupted. After the battery is fully discharged the device will not operate and patient
gas flow will cease. There are no alarms or display indicators after the battery has discharged.
The battery is not intended for patient transport.
Disposable patient circuit
• The
disposable patient circuit
(DPC) is comprised of the disposable water path (DWP), vapor
transfer cartridge (VTC) and delivery tube. Conditions in the circulating water and gas streams
are sensed remotely via the interface between the main unit and the disposable water path.
•
Vapor transfer cartridge
. In the cartridge, blended gas passes through the lumens of hundreds
of parallel hollow fibers made of a specially developed polymer. Warm water circulates around
the fibers and diffuses as vapor through the fiber material into the gas stream flowing through
each fiber. Unlike most humidifiers, there is no direct contact between the water and gas
streams. The gas stream leaves the cartridge saturated with vapor at the set temperature.
Note
: Use
only
approved cartridges from Vapotherm Inc.
•
Patient delivery tube.
The warmed humidified gas passes through the center of a triple-lumen
heated delivery tube. The center lumen is surrounded by two outer lumens circulating warmed
water to maintain the temperature of the inner lumen and to minimize rain-out. A proprietary
short nasal cannula is connected to the end of the delivery tube and passes the humidified
breathing gas to the patient’s nares. It is normal for non-DEHP PVC tubing to appear slightly
cloudy, or yellow, especially during longer use or when operated at higher temperatures.
•
Disposable water path.
The disposable water path houses a water reservoir, pump,connections
for the vapor transfer cartridge and delivery tube, and sensor interfaces to the main unit.
Water is pumped past a heater plate through the outer lumens of the delivery tube. Returning
water passes through the outer jacket of the specially designed vapor transfer cartridge where
some water is lost as vapor to the gas stream. There is no direct contact between water and gas
flows. The water then returns to the pump reservoir. Heater power automatically maintains the
set temperature. Water flows into the circuit from the sterile water supply to replace evaporative
losses in the vapor transfer cartridge. Air is purged to atmosphere from the circulation via a
hydrophobic filter membrane.
See Section 5 for a description of the modes of operation.
