General Description 

The Tracheal Pressure and Air Flow sensor (later named TP/AF sensor) consists of an integrated pneumotachometer with a differential pressure sensor, as well as a pressure sensor for the tracheal pressure. The sensor is connected to two TAM-A amplifiers, one for Air Flow, the second for the Tracheal Pressure. Airflow, Tracheal pressure are available as phasic signals on the respective analog BNC-outputs of the TAM-A
modules. By analyzing these signal using a dedicated software respiratory parameters such as peak inspiratory- (PIF), peak expiratory- (PEF) flow, Tidal Volume (TV), respiratory rate (RR) and peak tracheal pressure (TP) can be
evaluated.

Item 734106 Tracheal pressure and air flow sensor for rats.

Item 734011 Tracheal pressure and air flow sensor for Mice

Technical Description

The TP/AF sensor consists on a pneumotachometer. The air flow during respiration is measured with the pneumotachometer. This transducer is based on the principle of pressure drop along a pipe. Any pipe offers some resistance to fluid or gas flow owing to the internal resistance of the medium, i.e. the viscosity of the fluid or gas. The pressure drop along the pipe can be used as a measure of the flow. If the flow is sufficiently low so that the flow is laminar, then the pressure difference Δp between two points along the pipe is proportional to the
flow.

Fig.1: Principle of air flow measurement with a Fleisch tube (laminar flow principle). Near each end of the tube bundle there are different pressures p1 und p2. The flow F is directly proportional to the pressure difference p1 -
p2.
 

Physics has a formula for this relationship, the Hagen-Poiseuille Law:

Where: 

F = flow

p1, p2 = pressures at two points along the pipe

r = radius of the pipe

l = distance between the points where pressures p1 and p2 are measured

ŋ= viscosity of the fluid

This law states that at laminar flow in straight circular tubes the flow is proportional to the pressure drop Δp per
unit length. This means that a differential pressure transducer is required in addition to the flow tube. The differential pressure transducer is integrate in the AF/TP sensor. A pressure transducer for the tracheal pressure is also integrated.

Versions

There are two versions available

Item 734106 Tracheal pressure and air flow sensor for rats and guinea pigs.

Item 734011 Tracheal pressure and air flow sensor for Mice

As we can see from the formula, the differential pressure is depending on the respiratory flow. The flow of a rat is about 10 times the flow of a mouse. To allow to have a reasonable signal noise ration on the Airflow signal, the pneumotachometer for the mouse has a channel diameter of 0.9 mm, the rat guinea-pig pneumotachometer has
an ID of 1.2 mm.

As the resistance is proportional to the radius exponent four, a small change in diameter gives a large change in
resistance and therefore in differential pressure. The smaller diameter also allows to reduce dramatically the dead space of the pneumotachometer. The pressure transducer is the same in both versions as that pressure does not vary much with the species. The sensors are differentiated by the label on the side of the sensor (see below the label for a Rat/Guinea pig sensor).

Additional Equipment Required for use

You will also need:

• A PLUGSYS case
• Two TAM-A PLUGSYS transducer amplifiers
• A data acquisition system PULMODYN if vital parameters like respiratory rate, tidal volume are of interest.

Electrical Connection

The AF/TP Sensor has two connectors to be connected to the transducer input socket of the TAM-Amplifiers. As the excitation voltage for the two sensors is supplied via the plug for the tracheal pressure transducer, it is necessary to connect both if Airflow is to be measured.

Installation and Use

Installation

The sensor is connected via a cable and two connectors to the two TAM-A amplifiers. See labels on the connectors before connecting. 

A magnetic ball with bar allows easy mounting on a stand using an X-Block

Connecting the cannula

Different types of cannulae can be used. The standard HSE-Harvard Apparatus stainless steel tracheal cannula (Figure A) or stainless steel intubation cannula with luer connector (Figure B) which are available in several sizes or the commercially available VasoFix® or Introcan® (Figure C)

Stainless Steel Cannulae Reference Chart

The Vasofix® or Introcan® are available in diameters of diameter of 14, 16, 17, 18, 20, 22, 24G.

On intubation cannulae, the main differences are the tips, the flexibility and the available sizes. The stainless steel cannulae have a rounded tip to ensure better sealing. The stainless steel is rigid and does not require a special tool for introduction. The rigidity allows to have less wall thickness and therefore a larger ID by the same OD and less flow resistance.

The Vasofix® or Introcan® have a conic tip. They are more flexible but but don’t seal as well and require a
special tool (wire) for the placement into the trachea. The tool is supplied with the cannula.

The cannula is connected to the port with the male luer connector.

Connecting a ventilator

If a ventilator is connected, the ports for inspiration and expirations are connected together using a Y-piece. The Y-piece is connected to the barbed connector opposite of the cannula. The tubing connecting the Y-piece to the sensor should be reduced to a minimum to maintain the dead volume as small as possible.
 

Troubleshooting

Cleaning

If mucus has entered the Flow/Pressure head or in case of an obstruction in the flow pathway inside the Flow/Pressure head the pathway must be cleaned before the mucus dries out. If the mucus is dried it is nearly impossible to remove it from the pneumotachometer. The sensor must then be sent back to the manufacturer to exchange the pneumotachometer. 

To clean the pathway we recommend to use a syringe about 2 ml, containing distilled water. Push the content of the syringe through the pathway without exceeding too much pressure, the water should flow easily through the pathway. Look at the display of the TAM amplifiers, the bar graph should not reach the upper or the lower display on both. 

If the water does not pass easily, use a dental thread to try to open the pathway. If it is not blocked use the protocol with the syringe to clean. 

Detergent such as mucasol can be added to the water.

To dry the lumen connect the sensor to a respirator and run it for about 30 minutes. The dry air of the ventilator should dry the lumen sensor. 

After cleaning it is suggested to perform a sensor calibration. The calibration should give about the same values as before the cleaning. If the values are not close we would recommend cleaning the sensor again. If the values continue to range far from expected values the flow/pressure transducer can be returned to HSE or Harvard Apparatus for service. 

NOTE: Organic solvents cannot be used for cleaning. Using organic solvents will result in damage to the internal components. 

Calibration

The following description assumes that the HSE software PULMODYN or any other HSE software like BDAS or
HAEMODYN with the respiratory option is used.

Flow Sensor Calibration

Adjusting the Transducer amplifier (TAM)

Be sure the internal GAIN jumper is set on x1000.

Adjust know the zero of the flow amplifier on the PLUGSYS module (mainly a TAM-A module). Follow the procedure described in the relevant instruction manual of the amplifier.

For the TAM-A:
Put the switch "CAL-OFF-MEASURE" in position "MEASURE"

Press for 3 seconds the "AUTO" button

The LED above the button should go on for a few seconds and automatically go off. The fix and the mobile LED's on the bar graph should now be overlapping on 0.

If the LED above the "AUTO" button is flashing, the range for the auto-compensation is too small. Use the delivered small screwdriver and turn the "COARSE" and "FINE" trimmers to have the fix and the mobile LED's on the bar graph overlapping. Restart the operation by pressing the "AUTO" button.

Enter the baseline value

Now select in the “Calibration & Scale” menu the “Start” button for “Lower Calibration Point”. This opens the small calibration window showed below, where the measured AD points and the corresponding voltage is displayed. For Baseline, the AD point value is around 2048 and the voltage should read near zero Volt. If the received value is stable quit this menu with “OK”. The zero value is now displayed. Take care that the assigned physical value is set to 0 ml/min.
 

By starting the lower calibration the software reads the actual zero signal, after a stable reading 2048 (±3 to 5 points) click the Ok button.

Volume Calibration

Select the “Start” button for “Upper Calibration Point." This opens the small window below, where the calibration volume must be entered. Enter use volume in this window. That calibration volume should be in the tidal volume range of the animal (e.g. 2 to 4ml for rats or guinea pigs and 500µl to 1ml for mice). Prepare a syringe, filled with the chosen volume of air (in our case 2 ml for rat, 1ml for mouse).

Connect the syringe to the flow pathway, opposite to the tracheal cannula

Enter in the intended volume of your calibration volume

After pressing okay the next window is:

• Click "START".
• You will hear a beep and the upper scale of this window you will see the measured baseline (zero) in green.
• Inject the content of your calibration syringe into the AF/TP sensor.

After 5 seconds the window is updated. Scale 2 (red curve) shows the peak with another scaling. Begin and end of the peak are marked with green dotted lines. The peak flow is marked with a red dotted line. Please check your curve. It depends a little on the speed you use to empty the syringe. We recommend dispensing the volume at a steady rate and please do not stop during the injection. Important is that the software detects a maximum (red line appears) and the beginning and the end of the peak (green lines). The area under the red curve is the same as the area under corresponding square wave. Scale 3 (blue) shows a simulated signal with constant flow to reach the same volume over time. From this volume curve the software calculates by differentiation the corresponding airflow.

Check carefully this window for the localization of the lines Important are the two lines showing the beginning
and the end of injection. If these lines are not properly placed repeat the procedure by using the “Start” button. If they are well placed click on “OK." This will return you to the calibration window and the calibration is complete.

Note: Before starting the pressure calibration check the resolution and the maximal range for the signal is displayed. It is important to check these values. If the resolution is not as good as required (less than 0.1 ml/sec) the gain of the amplifier must be increased, so that higher values for the upper calibration point are received. If the calculated range seems too small, the gain of the amplifier must be reduced. If gain has been changed also redo the lower calibration.
 

Tracheal Pressure Sensor Calibration

Adjusting the Transducer Amplifier (TAM)

Be sure the internal GAIN jumper is set on 200.
Adjust know the zero of the tracheal pressure amplifier on the PLUGSYS module (mainly a TAM-A module). Follow the procedure described in the relevant instruction manual of the amplifier.

For the TAM-A:

Put the switch "CAL-OFF-MEASURE" in position "MEASURE"

Press for 3 seconds the "AUTO" button

The LED above the button should go on for a few seconds and automatically go off. The fix and the mobile LED's on the bar graph should now be overlapping on 0.

If the LED above the "AUTO" button is flashing, the range for the auto-compensation is too small. Use the delivered small screwdriver and turn the "COARSE" and "FINE" trimmers to have the fix and the mobile LED's on the bar graph overlapping. Restart the operation by pressing the "AUTO" button.

Enter the baseline value

Now select in the “Calibration & Scale” menu the “Start” button for “Lower Calibration Point”. This opens the small calibration window showed below, where the measured AD points and the corresponding voltage is displayed. For Baseline, the AD point value is around 2048 and the voltage should read near zero Volt. If the received value is stable quit this menu with “OK”. The zero value is now displayed. Take care that the assigned physical value is set to 0 cmH₂O.

By starting the lower calibration the software reads the actual zero signal. After a stable reading 2048 (±3 – 5 points) click the OK button.

Upper Calibration Value

Select the “Start” button for “Upper Calibration Point”. This opens the small calibration window showed below, where the measured AD points and the corresponding voltage is displayed. For Baseline, the AD point value is around 2048 and the voltage should read near zero Volt.

By starting the lower calibration the software reads the actual zero signal. After a stable reading 2048 (±3 – 5 points) click the OK button.

• Use a Standard Pressure cmH₂O Calibrator
• Keep one port closed using the supplied stopper.
• Apply a pressure of 10cmH₂O (100mmH₂O) to the other port.

NOTE: it does not matter which port is closed and which one receives the calibration pressure.

The voltage corresponding to the 10cmH₂O is now shown. It should be at least 1 volt. If it is not, the gain of the amplifier must be increased.

By applying the calibration pressure the actual signal should show at least 1 volt, if it is the case click on OK.

If the shown value is stable click "OK." The voltage for the upper calibration value is now displayed. Take care that the assigned physical value is set to 10cmH₂O.

Before starting the pressure calibration check the resolution and the max range for the signal is displayed. It is important to check these values. If the resolution is not as good as required (less than 0.1cmH₂O) the gain of the amplifier must be increased so that the higher values for the upper calibration are in range. If the calculated range seems too small, the gain of the amplifier must be reduced. If the gain has been changed also redo the lower calibration point. 

Technical Data

*Value in brackets = Sensor head, where other values are listed it is the sensor head with the tracheal cannula connector. 

User Manual Type 382