MAINTENANCE
Cuff Volume Verification / Calibration Procedures for Sonova
AFFECTED MODEL: Flo-Lab 2100

Calibrate every 1000 hours or once a year.

The PARKS Flo-Lab is totally automated and requires no additional action by the technologist above and beyond what is normally required to acquire good pulse volume waveforms.  Your Flo-Lab has been calibrated at the factory to accurately determine the cuff volume.  However, since the goal of calibrated pulse volume waveforms is to provide accurate and repeatable results, the technologist or Biomed person should initially and occasionally verify that the system is performing properly and should also be aware of several factors which can affect the results.  The following information is provided to help you obtain the most accurate and meaningful pulse volume amplitude information.

  1. On the Flo-Lab front panel, press the MENU button and advance to menu # -8-.  If needed, press the UP button to turn the VPR CAL sequence ON.  Connect the 1000 ml air chamber that was furnished with the Flo-Lab to the RED hose that is connected to the channel A VPR input.  Be sure you are connecting the air chamber directly to the Flo-Lab; do not connect through the Multi-Port Inflator for this sequence.
  2. On the computer keyboard, press [ESC] to return to the first Sonova menu.  Select New Patient Study, then Lower Arterial.  A screen comes up asking for the patient's Last and First names.  For this procedure, we want to create a dummy patient; use any name you want.  After you type in first and last names, hit the ENTER key, then hit ESC.  Now, select Test Select, then VPR.
  3. On the Flo-Lab front panel, press B to turn B off (if it's on), then press INFLATE.  The Flo-Lab will inflate, deflate, then reinflate the 1000 ml chamber.  As the second inflation starts, the calculated volume of the chamber will appear under the top graph on the computer monitor, on the left side, near the middle.  Repeat this procedure three times and average the measurements.  The calculated volume should be within 3% of the value marked on the chamber.  If not, press the MENU button to advance to menu # -9-, which will display the A Cal Factor.  If the calculated volume was high, press the UP button to increase the constant.  If the volume was low, press DOWN to decrease the constant.  Press DEFLATE, then INFLATE to repeat the test.  Note that an exact match will usually not occur, since the calculated volume changes by about 10 ml for each digit that the CAL factor is changed.  Record the A CAL factor for future reference.
  4. Connect the YELLOW hose to the 1000 ml volume chamber, press the A button to turn A off (button light will go out), and press B, to turn B on (light on).  B CAL factor is verified in the same way that A was, except that menu # -10- will display the B CAL factor, and the B volume numbers will be under the lower graph on the computer monitor.
  5. Press the [ESC] key until you reach the first Sonova screen, then press [Q] and [Y] to exit Sonova.  The cuff volume calibration tests are now complete.

NOTE: For optimum performance of your Flo-Lab, use only the hoses furnished with the system.  The calibration of cuff volume and volume change is based on using the nine foot hoses and adapters as furnished.  Any other length or size of tubing or the addition of an in-line air chamber will cause the reported cuff volume to be increased or decreased by the increase/decrease in volume.

If you do not have the correct hoses with your system, you can look up the part number and price for a replacement at http://www.parksmed.com/support/partnos.php.

These instructions are also listed in Section V, on page 74 of the Parks Vascular Flo-Lab Operating Manual.

 

DISCUSSION
VERIFYING CALIBRATED PULSE VOLUME RECORDINGS

Segmental pulse volume waveforms are acquired by placing pneumatic cuffs at various levels around an extremity, inflating the cuffs to a preset pressure and displaying the change in cuff pressure resulting from volume changes of the extremity under the cuff.  The amplitude and the shape (morphology) of the resulting waveform can then be used in evaluating the level of disease present in the proximal artery.

Waveform shapes are consistent over a variety of cuff pressures, cuff sizes, patient physiological differences, etc.  Consistent waveform aplitudes are much more difficult to obtain.  The following figure presents a range of waveform amplitudes acquired utilizing an uncalibrated VPR system versus a calibrated VPR system.  Three waveforms were acquired on the right ankle of the patient first with a loosely wrapped off, then a snugly wrapped cuff, and finally a very tightly wrapped cuff.  The results indicate that you could have up to 33% difference in the waveform amplitudes not using calibration, but with calibration, the maximum difference obtained was 7%.

These results indicate that if you are interested in obtaining accurate VPR amplitude measurements, the cuff volumes are very significant and should be monitored to ensure the accuracy of the results.  The calibration system in your FLO-LAB gives you the ability to monitor the cuff volume.  A numerical value is acquired which is based on the actual cuff volume, eliminating the need to rewrap cuffs to achieve a consistent volume measurement.

   
CUFF VOLUME (ML'S)
WAVE AMPLITUDE UNCALIBRATED (MM'S)
WAVE AMPLITUDE CALIBRATED (ML'S)
         
 

LOOSE

625
20
.28
 

SNUG

460
30
.30
 

TIGHT

300
40
.32
         
 

RANGE

 
30 (+/- 33%)
.30 (+/- 7%)

 

MM - MILLIMETERS OF DEFLECTION
ML - MILLILITERS OF VOLUME OR VOLUME CHANGE

Calibrated Pulse Volume Recordings