Fluke VT Plus HF User manual

VT Plus HF
Gas Flow Analyzer
Operators Manual
PN 2137275
May 2005
© 2005 Fluke Corporation. All rights reserved. Printed in USA
All product names are trademarks of their respective companies

Gas Flow Analyzer
Notices
i
Notices
Fluke Biomedical
6920 Seaway Blvd.
Everett, WA 98203 USA
Customer Support and Sales:
USA and Canada: 800-648-7952
Outside USA: 775-883-3400 •
E-mail: [email protected]
Internet: http://www.flukebiomedical.com
Service:
USA and Canada: 888.993.5853
Outside USA: 425.446.5560
E-Mail servic[email protected]
References in this manual to Bio-Tek International, Inc. and DNI Nevada, refer to companies that
are now owned by Fluke Biomedical.
All Rights Reserved
Copyright 2005, Fluke Biomedical. No part of this publication may be reproduced, transmitted,
transcribed, stored in a retrieval system, or translated into any language without the written
permission of Fluke Biomedical.
Restrictions and Liabilities
Information in this document is subject to change and does not represent a commitment by Fluke
Biomedical. Changes made to the information in this document will be incorporated in new
editions of the publication. No responsibility is assumed by Fluke Biomedical for the use or
reliability of software or equipment that is not supplied by Fluke Biomedical, or its affiliated
dealers.
Claims
Our routine method of shipment is via common carrier, FOB origin. Upon delivery, if physical
damage is found, retain all packing materials in their original condition and contact the carrier
immediately to file a claim.
If the instrument is delivered in good physical condition but does not operate within specifications,
or if there are any other problems not caused by shipping damage, please contact Fluke
Biomedical or your local sales representative.
Certification
This instrument was thoroughly tested and inspected. It was found to meet Fluke Biomedical’s
manufacturing specifications when it was shipped from the factory. Calibration measurements are
traceable to the National Institute of Standards and Technology (NIST). Devices for which there are
no NIST calibration standards are measured against in-house performance standards using
accepted test procedures.
Obtaining Assistance
If you have trouble operating the VT Plus HF, or just need some clarification on its operation,
contact Fluke Biomedical’s Technical Assistance Center at 800-648-7952.
Manufacturing Location
Fluke Biomedical
6920 Seaway Blvd.
Everett, WA. USA.

VT Plus HF
Operators Manual
ii
Safety Considerations
Warnings and Cautions
Use of this instrument is restricted to qualified personnel who recognize shock hazards and are
familiar with safety precautions used when operating electrical equipment. Read the manual
carefully before operating the VT PLUS HF.
 The following warning and informational symbols may be found on the VT PLUS HF.
Symbol Description
Alternating current
Caution: refer to accompanying
documentation
Off (power: disconnection from mains)
On (power: connection to mains)
Caution: risk of electric shock
Direct / alternating current
Direct current
Protective earth (ground)
Inspect the lead ends for possible wear, cracks, or breaks before each use.
If operating the VT PLUS HF at 110 and 220 volts, turn the power switch to the OFF
position before changing the supply voltage.

Gas Flow Analyzer
Safety Considerations
iii
Hazard Warnings
Warning! Power Rating. The VT PLUS HF mains power input must be
connected to an external power supply that provides voltage and current within
the specified rating for the system.
Warning! Internal Voltage. Always turn off the power switch and unplug the
power cord before cleaning the outer surface of the VT PLUS HF.
Warning! Liquids. Avoid spilling liquids on the analyzer; fluid seepage into
internal components creates a potential shock hazard. Do not operate the
instrument if internal components are exposed to fluid.
Precautions
The following precautions are provided to help you avoid damaging the system:
 Caution: Service. Authorized service personnel should service the VT PLUS
HF. Only qualified technical personnel should perform troubleshooting and
service procedures on internal components.
Caution: Environmental Conditions. Do not expose the system to temperature
extremes. Ambient temperatures should remain between 18-40°C. System
performance may be adversely affected if temperatures fluctuate above or below
this range.
Caution: Do NOT Immerse. Clean only with a mild detergent, and gently wipe
down with a clean, lint-free cloth.

VT Plus HF
Operators Manual
iv
Applicable Testing Standards
The VT PLUS HF has been tested by an independent laboratory and meets the requirements
listed here.
Safety Requirements
USA UL 3101-1, Electrical Equipment for Laboratory Use;
Part 1: General Requirements.
Canada CAN/CSA C22.2 No. 1010.1 (1992), Safety Requirements for
Electrical Equipment for Measurement, Control and Laboratory
Use, Part 1: General Requirements.
EC Directive
73/23/EEC
EN 61010-1, Safety requirement for electrical equipment for
measurement, control and laboratory use, Part 1: General
Requirements.

Gas Flow Analyzer
Applicable Testing Standards
v
Electromagnetic Interference and Susceptibility
 USA FCC Class A
Warning: Changes or modifications to this unit not expressly approved by the manufacturer
could void the user's authority to operate the equipment.
This equipment has been tested and found to comply with the limits for a Class A digital device,
pursuant to Part 15 of the FCC Rules.
These limits are designed to provide reasonable protection against harmful interference when the
equipment is operated in a commercial environment. Like all similar equipment, this equipment
generates, uses, and can radiate radio frequency energy and, if not installed and used in
accordance with the instruction manual, may cause harmful interference to radio
communications. Operation of this equipment in a residential area is likely to cause interference,
in which case the user will be required to correct the interference at his/her own expense.
 Canadian Department of Communications Class A
This digital apparatus does not exceed Class A limits for radio emissions from digital apparatus
set out in the Radio Interference Regulations of the Canadian Department of Communications.
Le present appareil numerique n'met pas du bruits radioelectriques depassant les limites
applicables aux appareils numerique de la Class A prescrites dans le Reglement sur le brouillage
radioelectrique edicte par le ministere des Communications du Canada.

VT Plus HF
Operators Manual
vi
Based on the testing standards below,
this device bears the
mark.
EC Directive 89/336/EEC Electromagnetic Compatibility
 Emissions - Class A
The system has been type tested by an independent, accredited testing laboratory and found to
meet the requirements of EN 61326-1:1998 for Radiated Emissions and Line Conducted
Emissions. Verification of compliance was conducted to the limits and methods of the following:
CISPR 16-1:1993 and CISPR 16-2:1996
 Immunity
The system has been type tested by an independent, accredited testing laboratory and found to
meet the requirements of EN 61326-1:1998 for Immunity. Verification of compliance was
conducted to the limits and methods of the following:
EN 61000-4-2 (1991) Electrostatic Discharge
EN 61000-4-3 (1995) Radiated EM Fields
EN 61000-4-4 (1995) Electrical Fast Transient/Burst
EN 61000-4-5 (1995) Surge Immunity
EN 61000-4-6 (1996) Conducted Disturbances
EN 61000-4-11 (1994) Voltage Dips, Short Interruptions and Variations
EC Directive 73/23/EEC Low Voltage (User Safety)
The system has been type tested by an independent testing laboratory and found to meet the
requirements of EC Directive 73/23/EEC for Low Voltage. Verification of compliance was
conducted to the limits and methods of the following:
EN 61010-1 (1993) and IEC 1010-1
“Safety Requirements for Electrical Equipment for Measurement, Control and Laboratory
Use, Part 1: General requirements” (including amendments 1 and 2).

Gas Flow Analyzer
Warranty
vii
Warranty
Fluke Biomedical warrants this instrument against defects in materials and workmanship for one
full year from the date of original purchase. During the warranty period, we will repair or, at our
option, replace at no charge a product that proves to be defective, provided you return the
product, shipping prepaid, to Fluke Biomedical. This warranty does not apply if the product has
been damaged by accident or misuse or as the result of service or modification by other than
Fluke Biomedical. IN NO EVENT SHALL FLUKE BIOMEDICAL BE LIABLE FOR
CONSEQUENTIAL DAMAGES.
Only serialized products and their accessory items (those products and items bearing a distinct
serial number tag) are covered under this one–year warranty. PHYSICAL DAMAGE CAUSED BY
MISUSE OR PHYSICAL ABUSE IS NOT COVERED UNDER THE WARRANTY. Items such as
cables and nonserialized modules are not covered under this warranty.
Recalibration of instruments is not covered under the warranty.
This warranty gives you specific legal rights, and you may also have other rights which vary from
state to state, province to province, or country to country. This warranty is limited to repairing the
instrument to Fluke Biomedical’s specifications.
Warranty Disclaimer
Should you elect to have your instrument serviced and/or calibrated by someone other than Fluke
Biomedical, please be advised that the original warranty covering your product becomes void
when the tamper-resistant Quality Seal is removed or broken without proper factory authorization.
We strongly recommend, therefore, that you send your instrument to Fluke Biomedical for factory
service and calibration, especially during the original warranty period.
In all cases, breaking the tamper-resistant Quality Seal should be avoided at all cost, as this seal
is the key to your original instrument warranty. In the event that the seal must be broken to gain
internal access to the instrument, you must first contact Fluke Biomedical’s Technical Assistance
Department at 775-883-3400. You will be required to provide the serial number for your
instrument as well as a valid reason for breaking the Quality Seal. You should break this seal only
after you have received factory authorization. Do not break the Quality Seal before you have
contacted us. Following these steps will help ensure that you will retain the original warranty on
your instrument without interruption.

VT Plus HF
Operators Manual
viii
Contents
Notices................................................................................................................................. i
All Rights Reserved............................................................................................... i
Restrictions and Liabilities ..................................................................................... i
Claims ................................................................................................................... i
Certification............................................................................................................ i
Obtaining Assistance............................................................................................. i
Manufacturing Location ......................................................................................... i
Safety Considerations..........................................................................................................ii
Warnings and Cautions .........................................................................................ii
Applicable Testing Standards .............................................................................................iv
Safety Requirements ............................................................................................iv
Electromagnetic Interference and Susceptibility ................................................... v
EC Directive 89/336/EEC Electromagnetic Compatibility .....................................vi
EC Directive 73/23/EEC Low Voltage (User Safety).............................................vi
Warranty ............................................................................................................................vii
Warranty Disclaimer...........................................................................................................vii
Contents ........................................................................................................................... viii
1 Overview
Introducing the VT PLUS HF ........................................................................................... 1-1
Optional Accessories ....................................................................................................... 1-2
Theory of Operation......................................................................................................... 1-2
Pressure Measurements ................................................................................... 1-2
Oxygen Measurements ..................................................................................... 1-4
Flow Measurements .......................................................................................... 1-4
Breath Detection................................................................................................ 1-6
Calculated Parameters ...................................................................................... 1-8
About This Manual........................................................................................................... 1-9
2 Installation
Unpacking and Inspection................................................................................................ 2-1
Connecting the VT PLUS HF........................................................................................... 2-2
Pneumatic Connections..................................................................................... 2-2
Quick Installation/Operations Guide .................................................................. 2-3
Bi-directional Flow Mode ................................................................................... 2-3
Uni-directional Flow Mode ................................................................................. 2-4
Inspiratory Testing............................................................................................. 2-4
Expiratory Testing.............................................................................................. 2-4
Attaching the Printer Cable .............................................................................................. 2-6
3 Keypad Functions
VT PLUS HF Keypad Functions ...................................................................................... 3-1
4 System Setup
Using the Setup Screen................................................................................................... 4-1
Settings............................................................................................................................ 4-2
Gas Settings...................................................................................................... 4-2
Gas Temperature .............................................................................................. 4-4
Ambient Temperature........................................................................................ 4-4
Relative Humidity............................................................................................... 4-4
Correction Mode................................................................................................ 4-5
Barometric Pressure Units................................................................................. 4-5
Barometric Pressure.......................................................................................... 4-5
Breath Detection................................................................................................ 4-6
Breath Detect Threshold.................................................................................... 4-6
Inspiratory versus Expiratory Tidal Volumes...................................................... 4-7

Gas Flow Analyzer
Contents
ix
Zero Mode ......................................................................................................... 4-7
System............................................................................................................................. 4-8
Time .................................................................................................................. 4-8
Date................................................................................................................... 4-9
Date Format....................................................................................................... 4-9
Demo Data ...................................................................................................... 4-10
Filtering............................................................................................................ 4-10
Display Calibration Date on Startup Screen .................................................... 4-10
Serial Mode ..................................................................................................... 4-11
Printer Options................................................................................................. 4-11
Audio Levels.................................................................................................... 4-12
Restore Defaults.............................................................................................. 4-14
Utilities ........................................................................................................................... 4-15
Oxygen Calibration .......................................................................................... 4-15
System Diagnostics......................................................................................... 4-15
Linearization .................................................................................................... 4-16
Unlock Calibration ........................................................................................... 4-16
Information.....................................................................................................................4-16
5 Display Screens
Screen Objects ................................................................................................................ 5-1
Selecting Parameters....................................................................................................... 5-5
Flow Screens ................................................................................................................... 5-6
High-Flow Screen .............................................................................................. 5-6
Low-Flow Screen............................................................................................... 5-7
Pressure Screens ............................................................................................................ 5-8
High-Pressure Screen ....................................................................................... 5-8
Low Pressure Screen ........................................................................................ 5-9
Airway Pressure Screen .................................................................................. 5-10
Volume Screen .............................................................................................................. 5-11
Flow Zero ........................................................................................................ 5-11
Oxygen Screen .............................................................................................................. 5-12
Full Breath Parameters Test Screen.............................................................................. 5-13
Monitor Screen .............................................................................................................. 5-14
Units of Measure............................................................................................................ 5-15
6 Special Functions
Trend Test ....................................................................................................................... 6-1
Leak Test......................................................................................................................... 6-5
Stacked Volume Test....................................................................................................... 6-8
RT200 Emulation Mode ................................................................................................... 6-9
Assist Test .....................................................................................................................6-12
High Frequency Oscillator Mode.................................................................................... 6-13
7 Safety, Error Messages, Troubleshooting, and Support
Electrical Safety and System Maintenance...................................................................... 7-1
Replacing the Oxygen Sensor ......................................................................................... 7-2
Procedure for Calibrating the Oxygen.............................................................................. 7-2
Replacing the Fuses ........................................................................................................ 7-3
Error Messages ............................................................................................................... 7-4
Troubleshooting ............................................................................................................... 7-7
Returning the VT PLUS HF for Service.......................................................................... 7-12
8 VT Plus PC Software
Getting Started.................................................................................................................8-1
System Requirements ....................................................................................... 8-1
Connecting to the VT PLUS HF......................................................................... 8-1
Installing the Software ....................................................................................... 8-2

VT Plus HF
Operators Manual
x
Starting the Software ......................................................................................... 8-2
Overview of VT Plus for Windows  Software.................................................................. 8-3
Purpose and Intended Use................................................................................ 8-3
Using VT Plus for Windows® ............................................................................ 8-3
Menus and the Toolbar.................................................................................................... 8-5
Pull-down Menus............................................................................................... 8-5
Toolbar Description ........................................................................................... 8-7
Screens and Tests........................................................................................................... 8-8
Main Screens..................................................................................................... 8-8
Monitor Screen ............................................................................................ 8-8
Single Plot Screen ....................................................................................... 8-9
Loop Plots Screen ..................................................................................... 8-10
Full Test..................................................................................................... 8-11
Trend Test ................................................................................................... 8-12
Leak-Test Screen.......................................................................................... 8-15
Stacked Volume Test.................................................................................... 8-17
Serial Communications.................................................................................................. 8-19
Selecting COM Port......................................................................................... 8-19
Selecting the Serial Communications Mode .................................................... 8-19
Data and File Handling .................................................................................................. 8-20
File Structure - Background and Theory of Operation ..................................... 8-20
Events ............................................................................................................. 8-20
Opening and Closing Data Files ...................................................................... 8-22
File Control Interface ....................................................................................... 8-23
Generating Signal (.sig) Files .......................................................................... 8-26
Generating Parameter (.par) Files ................................................................... 8-26
Printing........................................................................................................................... 8-27
Loading Flash Memory .................................................................................................. 8-27
Plots............................................................................................................................... 8-28
Automatically Re-scaling Plots ........................................................................ 8-28
Manually Re-scaling Plots ............................................................................... 8-29
Signal Selection............................................................................................... 8-30
Zeroing........................................................................................................................... 8-31
Other Setup Functions................................................................................................... 8-32
Breath Detect................................................................................................... 8-32
Breath Detect Threshold.................................................................................. 8-32
Gas Settings.................................................................................................... 8-33
Gas Calculator................................................................................................. 8-35
Barometric Pressure........................................................................................ 8-36
Appendix A Specifications

1-1
Chapter 1
Overview
1. Introducing the VT PLUS HF
The VT PLUS HF is a general-purpose gas flow analyzer with special modes designed
specifically for testing mechanical patient ventilators. The VT PLUS HF measures bi-
directional flow in both high and low ranges as well as high- and low-pressure ranges.
Other features include:
Oxygen Concentration Measurement. An integrated sensor measures the oxygen
percent of the gas in the high flow channel of the VT PLUS HF.
Breath Parameters. The VT PLUS HF measures 17 parameters on each detected breath.
These parameters include tidal volume, minute volume, inspiratory and expiratory
pressures, lung compliance, etc.
Selectable Units. The VT PLUS HF allows the user to select the desired units for each of
the measured signals. For example, pressures can be displayed in mmHg, kPa, bar, mbar,
atm, inH2O, inHg, cmH2O or mmHg.
Leak Testing. The VT PLUS HF allows the user to test the leak rate of a sealed vessel or
test lung.
Trend Testing. The VT PLUS HF provides an automated test to see if a predetermined
parameter deviates from limits set by the user.
Evaluations/Troubleshooting. The VT PLUS HF can be used for pre-purchase
evaluations of ventilators, incoming and routine performance verification, and
troubleshooting clinical problems, as well as teaching principles of mechanical
ventilation.
1. Introducing the VT PLUS HF
2. Optional Accessories
3. Theory of Operation
4. About This Manual

VT Plus HF
Operators Manual
1-2
2. Optional Accessories
The utility of the VT PLUS HF can be extended with the following optional accessories:
Graphics Printer. This instrument is designed to interface with a printer. With the
printer attached, flow and pressure values and breath parameters can be printed. See
Chapter 2, Installation for printer operation.
Computer Control and Data Logging. A standard bi-directional RS232 serial port
allows connection to a personal computer for external VT PLUS HF control and data
logging of test results. The instrument is compatible with VT Plus for Windows Software
program. See Chapter 8, VT Plus PC Software. For other interface needs, please call
Fluke Biomedical.
Lung Simulator. The VT PLUS HF will operate with or without a test lung attached. The
use of a test lung with integrated airway restrictors will assist the operator in evaluating
intermittent errors.
3. Theory of Operation
This section of the manual describes how the VT PLUS HF performs computations of the
information it displays.
The VT PLUS HF measures the basic signals of pressure, flow, and oxygen. From these
basic signals, other parameters are computed. Volume is obtained from the integration, or
summation, of the flow signal over a period of time.
Pressure Measurements
The VT PLUS HF provides several pressure measurement capabilities. There are two
external pressure measurements available to the user. There are also three more internal
pressure measurements.
External Pressure Measurements:These have been called "Low Pressure" and "High
Pressure". The low-pressure measurement has a range of ±500 mmHg (about 10 psi).
The high-pressure measurement has a range of ±100 psi (about 5200 mmHg).
Both the high and low pressures are "differential" measurements. As such, the measured
pressure is the pressure difference between the positive and negative ports. If only one of
the pressure connections is made, the measurement is equivalent to a "gauge"
measurement. For gauge pressures, the measurement is relative to the ambient pressure.
This is how a normal pressure gauge works.
If a positive gauge pressure is applied to the "+" measurement port, a positive pressure
reading will result. If a negative gauge pressure is applied to the "+" measurement port, a
negative pressure reading will result. Likewise, if a positive gauge pressure is applied to
the "-" measurement port, a negative pressure reading will result. If a negative gauge
pressure is applied to the "-" measurement port, a positive pressure reading will result.
Fluidic Pressure Measurements: The "+" connection for both the high and low pressure
are labeled as compatible with either fluids or gasses. When measuring fluidic pressures,
it is important to realize any fluid that enters the pressure measurement port or the
connecting tubing may cause a bias (error) in the measured pressure. For example, if a

Gas Flow Analyzer
Overview 1
1-3
fluidic pressure measurement is made and a 5 cmH2O column is in the connecting tubing,
an error of about 5 cmH2O may occur.
If fluid enters into the pressure measurements connections of the VT PLUS HF, it is
important to evacuate the fluid before storage and before any pressure measurements are
made. The fluid can be evacuated by connecting a 100 cc syringe directly to the pressure
measurement connection and then pulling back the syringe to create a vacuum.
Internal Pressure Measurements: The VT PLUS HF also has several internal pressure
measurements. These include barometric pressure, differential pressure for the flow
measurement, and airway pressure.
The airway pressure is measured internally in the tube for the flow sensors. This is done
for convenience for the user while measuring ventilator parameters. Having an additional
pressure measurement for airway pressure (i.e., besides the external low-pressure
measurement) ensures that the pressure is measured at a consistent location and
eliminates the need for cumbersome adapters for placing pressure taps in the airway
circuit.
When the VT PLUS HF is set to measure from the high-flow port, the airway pressure is
measured from the high-flow port. Likewise, when the low-flow range is selected, the
airway pressure is measured from the low-flow port. In both cases, the airway pressure
measurement is made on the "exhaust" side of the flow sensor.
Zeroing the Pressure Signals:The zero reading (offset) of the pressure measurements
may drift slightly with time and temperature. A zeroing function is provided for the user
to zero the offset drift. Typically, this is done when a non-zero reading occurs when there
is zero applied pressure. However, it is good practice to zero the respective signal before
any measurement is taken.
Although a five minute warm-up period is built into the VT PLUS HF power-up cycle, a
40 minute warm-up period is suggested for maximum measurement accuracy and
stability. The offset drift will be most significant while the sensors for the pressure
measurements are warming up. If the warm-up period is skipped, be aware that the offset
drift may be significant for the first 40 minutes of operation. If the VT PLUS HF has
been through an extreme temperature change, additional time may be required for the
warm-up. If the VT PLUS HF has only been turned off for, say a minute, the warm-up
period may be skipped.
The zeroing function for pressure acts as a "tare" function. As such, the applied pressure
when the signal is zeroed will be saved as the new "zero" reading. The applied pressure
during zero would then be read as zero. Measured pressures would have an offset error
equal to the applied pressure when the VT PLUS HF was zeroed.
Airway Zeroing, A Special Case: The airway pressure may be zeroed manually using the
ZERO key while the airway pressure screen is active. The airway pressure is also zeroed
automatically when the FLOW zero occurs. Note that the flow zero may either be
performed manually or in an "autozero" mode.
Barometric Pressure, Another Special Case: The offset drift can be adjusted on the
barometric pressure measurement by entering the correct barometric pressure on the
SETUP | SETTINGS menu. This is typically not needed. However, it provides a means
for the user to ensure that the barometric pressure measurement is as accurate as possible.

VT Plus HF
Operators Manual
1-4
Oxygen Measurements
The oxygen measurement is performed using a galvanic oxygen cell on the high-flow
port near the exhaust. The VT PLUS HF interprets the measurement from the oxygen
sensor as a partial pressure of the total pressure in the high-flow circuit. The total
pressure is the airway pressure plus the barometric pressure.
The oxygen percentage is calculated as the fraction of the partial pressure of oxygen
relative to the total pressure. It should be noted that changes in the total pressure (i.e.
airway pressure) will result in a change in the partial pressure of the measured oxygen
even though the percentage of oxygen is the same. Since the pressure can change much
faster than the response time of the oxygen sensor, a small transient (1 to 2% of full-
scale) error can occur in the oxygen measurement when there is a fast change in the
pressure at the oxygen sensor.
Whenever an oxygen measurement is made, or when the oxygen sensor is calibrated or
zeroed, there should be sufficient gas flow pass the oxygen sensor. Only a small flow of
gas (say, 10 LPM) is needed to ensure that the oxygen concentration at the oxygen sensor
is as expected. For example, just opening the high-flow exhaust to room air does not
ensure that the oxygen sensor will "see" 20.9% oxygen. The oxygen concentration at the
sensor will not equilibrate with the room air unless a small amount of flow is present to
ensure gas mixing.
The oxygen sensor should last for more than one year, and is replaced during an annual
calibration of the unit. Sensor life is shortened, the longer the sensor is exposed to
oxygen. This includes oxygen in room air as well as higher flow rates of oxygen-
containing gases past the sensor. The VT PLUS HF will check to detect if the oxygen
sensor is depleted every time an oxygen zero is performed.
The oxygen sensor should be recalibrated by the user with 100% oxygen and dry air at
the beginning of any testing day in which oxygen concentrations will be measured. Refer
to Chapter 7, Safety, Error Messages, Troubleshooting, and Support for more details.
Flow Measurements
The flow measurements in the VT PLUS HF are made by measuring the differential
pressure across a resistive screen mesh. The resulting differential pressure is nearly linear
with respect to the volumetric flow. Simple corrections are applied to correct for any non-
linearities. A table of correction factors is applied for each the low- and high-flow
sensors. The information regarding these tables can be seen using the SETUP | UTILITES
| LINEARIZATION screen on the VT PLUS HF.
Gas Settings: The flow measurement sensors in the VT PLUS HF are linearly dependent
on the viscosity of the applied gas. The VT PLUS HF setup options allow the user to
specify what type of gas is being used. Additional choices are available using the USER
DEFINE MODE. The USER DEFINED gas settings are set using the PC software. The
gas calculator on the PC software can determine the effective viscosity for a combination
of various gases. Refer to Chapter 8, VT Plus PC Software for more details on the gas
calculator and on setting user defined gas types.
The VT PLUS HF calculates the temperature dependent viscosity for the gas type selected
(except for user-defined gases). Therefore, when a new flowing gas temperature is

Gas Flow Analyzer
Overview 1
1-5
entered by the user, the VT PLUS HF calculates the new viscosity. For air, the sensitivity
to temperature is about 0.25% of reading per degrees Celsius.
The VT PLUS HF viscosity calculation for the gas settings assumes dry gas is being used.
Increased water vapor content can slightly affect the flow accuracy. At room temperature,
a flow measurement error of -0.5% of reading can occur if the relative humidity of the
flowing gas is 50%.
Note: Never apply humidified gases to the VT PLUS HF flow sensors.
Condensation on the flow sensors will cause errors in the flow readings
until condensation is dried from flow sensors.
Balance Gas Settings: The gas settings allow for gas combinations with oxygen. For
example, the VT PLUS HF can be set to use Helium balance Oxygen. In this mode, the
VT PLUS HF uses the oxygen measurement to determine the oxygen concentration and
then assumes the balance of the gas concentration is helium. The VT PLUS HF calculates
the effective viscosity for the combination gas at the specified temperature. The oxygen
concentration used in the gas setting for the balance gases is automatically updated every
second.
Note: For air / oxygen mixtures use the nitrogen balance oxygen (N2 bal O2) gas
setting. The flowing gas is assumed to be dry and therefore the relative
humidity used in the viscosity calculation is assumed to be zero percent.
BTPS and STPD Corrections: The VT PLUS HF corrects all flow measurements to
conditions of ambient temperature and pressure without adjusting for the volume of water
vapor. The ambient pressure is obtained from the measured barometric pressure. The user
sets the ambient temperature by using the setup menu.
It should be noted that the relative humidity setting on the VT PLUS HF is only used for
the BTPS and STPD correction.
BTPS stands for "Body Temperature and Pressure Saturated with water vapor". In this
compensation mode, the flow rate (and therefore, volumes) are corrected such that the
reported flow is equal to the flow if the gas temperature and pressure was changed to
body conditions (37 °C and ambient pressure). Further, the flow is compensated to add
the amount of water vapor as if to make the gas fully saturated (i.e. 100% relative
humidity). In this correction, the relative humidity setting is used to determine the
amount of water vapor that would need to be added.
STPD0stands for "Standard Temperature and Pressure Dry". In this compensation mode,
the flow rate (and therefore, volumes) are corrected such that the reported flow is equal to
the flow if the gas temperature and pressure was changed to standard conditions (0 °C
and 760 mmHg). Further, the flow is compensated to subtract the amount of water vapor
as if the gas was dry (i.e. 0% relative humidity). In this correction, the relative humidity
setting is used to determine the amount of water vapor that would need to be subtracted.
STPD21 stands for "Standard Temperature and Pressure Dry". In this compensation mode,
the flow rate (and therefore, volumes) are corrected such that the reported flow is equal to
the flow if the gas temperature and pressure was changed to standard conditions (21°C
and 760 mmHg). Further, the flow is compensated to subtract the amount of water vapor
as if the gas was dry (i.e. 0% relative humidity). In this correction, the relative humidity
setting is used to determine the amount of water vapor that would need to be subtracted.

VT Plus HF
Operators Manual
1-6
Flow Zeroing: The differential pressure transducer used to measure the flow rate is
subject to baseline (offset) drift. This is most pronounced during the VT PLUS HF warm-
up period. The VT PLUS HF provides both a manual and an automatic zero function for
zeroing the flow.
In measuring flow, the same pressure transducer is used for both the high- and low-flow
ports. A set of valves is used to select between high- and low-flow ranges. Since one
pressure transducer is used for both, zeroing one flow range also zeros the other.
In the manual zero mode, if the user presses the ZERO key when the VT PLUS HF is at
the FLOW screen, a message will appear indicating that the flow must be removed from
the currently selected flow port. The user must remove the flow so that a correct zero
reading can occur.
In the autozero mode, the VT PLUS HF uses the valves that switch between the high- and
low-flow ports to obtain a zero reading. It is assumed that there is no flow in the
unselected port. The purpose of this is to provide a means to zero the flow without having
to disconnect from the ventilator circuit (or other flow source being measured).
Note: When autozeroing is selected, it is important that there is no flow on the
unselected flow port. For example, if the high flow range is selected, there
should not be any flow in the low flow port if autozeroing is selected.
When autozero is selected, the user may still push the ZERO key to initiate a flow zero.
The valves will still automatically switch to obtain the zero reading. Therefore, it is not
necessary for the user to disconnect the flow to zero. No message will appear indicating
that the flow source should be removed.
With the autozero setting enabled, the flow will automatically zero every 20 minutes. If
more frequent zeroing is desired, manually zero the flow using the number 7/Zero key on
the VT PLUS HF keypad. Since some data is lost during a zero, ventilator parameter data
for breaths affected by an autozero are discarded.
Airway pressure is also zeroed whenever flow is zeroed. Airway pressure can also be
independently zeroed from the airway pressure screen.
Breath Detection
To monitor ventilator parameters, the VT PLUS HF must first determine when a "breath"
occurred and delineate the various phases of the breath. For example, the breath detection
algorithm determines the beginning and ending of the integration periods for calculating
tidal volumes.
The breath detection algorithm is implemented as a state machine. The flow waveform is
the input to the state machine. The state changes are based on flow waveform crossing of
predefined thresholds. A threshold is applied to both positive (inspiratory) and negative
(expiratory) flows. The breath detection threshold can be set to a high flow rate to reject
noise near zero flow.
Bi-directional, Inspiratory, Expiratory Breath Detect Modes:Figure 1-1 shows the circuit
connection for setting up the VT PLUS HF in a "bi-directional" mode. The gas flows in
both directions through the VT PLUS HF.This is the preferred setup for using the VT
PLUS HF with a ventilator.

Gas Flow Analyzer
Overview 1
1-7
OutletInlet
Ventilator
Inspiratory Hose
Expiratory Hose
VT PLUS HF
TEST
LUNG
fig1-1.eps
Figure 1-1. Circuit Connection for the VT PLUS HF in bi-directional mode
Note: When using the VT PLUS HF with a ventilator and a test lung, the bi-
directional breath detect mode is preferred. Only use the inspiratory and
expiratory breath detect modes if measurements cannot be made in the
bi-directional mode.
Additional breath detect modes were implemented for users that are accustomed to
performing measurements with flow devices that can only measure flow in one direction.
Base Flow: In the inspiratory and expiratory limb of the breathing circuit, some
ventilators may have a bias flow when no flow is going to or from the patient (test lung).
This is implemented differently on different ventilators. This is also called by different
names by the various ventilator manufactures. It may be called base flow, bias flow,
flow-by, blow-by, or many other names.
In the inspiratory- or expiratory-only breath detection modes, the VT PLUS HF can
measure the base flow present. Refer to Chapter 2, Installation for circuit configurations
for the different modes. The detection and calculation of base flow may take 30 to 60
seconds. In expiratory-only mode, detection of base flow requires a sufficient end-
expiratory period and sufficient change in pressure. The use of lower-lung compliance
settings improves performance in expiratory mode.
During expiratory-only mode, the base flow is subtracted from the flow signal for
obtaining the ventilator parameters, such as tidal volume and peak flow. During
inspiratory-only mode, the base flow is not subtracted since the base flow is typically
turned of during the inspiratory phase on most ventilators.

VT Plus HF
Operators Manual
1-8
Calculated Parameters
The following is a list of parameters calculated by the VT PLUS HF.A breath detection
algorithm determines the various phases of a ventilator breath and then the following
parameters are calculated.
Parameter Abbreviation How Calculated
Inspiratory Time In Time The time of the inspiratory period
including the inspiratory hold time.
Expiratory Time Ex Time The time of the expiratory period
including the expiratory hold time.
Inspiratory Hold
Time
In Hold The time of the End Inspiratory State.
Expiratory Hold
Time
Ex Hold The time of the End Expiratory State.
Inspiratory to
Expiratory Time
Ratio
I:E The ratio of the inspiratory time to the
Expiratory Time.
Inspiratory Hold
Pressure
IPP The average pressure during the End
Inspiratory State.
Positive End-
Expiratory Pressure
PEEP The average pressure during the End
Expiratory State.
Mean Airway
Pressure
MAP The mean pressure over the entire
breath.
Peak Inspiratory
Pressure
PIP The maximum pressure during the
Inspiratory Time.
Tidal Volume Tidal Vol Total volume accumulated over the
Inspiratory Time.
Minute Volume Minute Vol The Expiratory Tidal Volume times the
respiratory rate in breaths per minute.
Reported as an eight-breath average.
Peak Inspiratory
Flow Rate
PIF The maximum of the absolute value of
the Flow Rate measured during the
Inspiratory Time.
Peak Expiratory
Flow Rate
PEF The maximum of the absolute value of
the Flow Rate measured during the
Expiratory Time.
Compliance N/A The Expiratory Tidal Volume divided by
the difference of the Inspiratory Hold
Pressure and PEEP.