FAQ: How to confirm your flow meter is working properly

Whether you’re getting unexpected results or new to the system and want to confirm you’re calibrating the flow measurement in ViViTest correctly, there is a quick, easy check to verify the operation of the flow measuring system used with the ViVitro Labs pulse duplicator.

This step can be done after calibration or in place of performing a calibration. Set-up the pulse duplicator as it would be for flow calibration (section 6.3 of the pulse duplicator user manual). Remember to remove all air from the VIA and bubbles from ventricle chamber. There needs to be a direct connection between the SuperPump pulsatile pump and the test fluid, with no compliant elements in the flow path.

Figure 1. Pulse duplicator setup for flow calibration in aortic (left) or mitral (right) configuration.

Set the waveform in ViViTest to Sine50. With the system static and ViViTest in Acquire mode, re-zero the sensors. Dial up the stroke volume to your intended test conditions (typically we do this at 75 mL/stroke for 70 BPM). Confirm that the stroke volume on the SuperPump controller matches the stroke volume displayed in ViViTest within ± 0.3 mL. If these values do not match, perform the ViViTest pump calibration as per Appendix E of the Pulse Duplicator User Manual. If these values do match, acquire 10 cycles and save an acq. file. Stop the pump and check that the flow zero hasn’t drifted.

Open this acq. file in the Analyze tab. Display all waveforms and click off the other traces so only the 10 cycles of the flow waveform are displayed. Move the flow markers to isolate the positive and negative portions of the waveform. This can be done several ways, but we do this by marking the positive portion as the closing volume and the negative portion as the leakage volume – this way, the values are displayed right on the user interface, without having to open the data table to see forward flow volume.

For an aortic collection, closing volume is captured between the f2 and f3 markers and leakage volume, between f3 and f4. Ensure the f1 marker stays to the left of f2. See figure 2 below for an example. For a mitral collection, closing volume is between f1 and f2 and leakage volume is between f2 and f3. Ensure the f4 marker stays to the right of f3.

Figure 2. Flow markers and results for an aortic flow verification check.

The volume captured by the absolute values of the positive and negative flow portions should match the controller stroke volume within ± 1.0 mL. If they do not, perform the flow calibration again. If these values still don’t match, contact us at techsupport@vivitrolabs.com if you need assistance with troubleshooting.