You no longer have to look up from your work to a monitor to know what the flow is. FlowSound communicates absolute volume flow audibly so that a musically attuned surgeon comfortable with FlowSound can save precious minutes in confirming functionality of a graft without taking her eyes from the surgical field. Even more time can be saved when examining grafts with technical error. Unlike Doppler’s “swoosh-swoosh” flow velocity sounds, the calibrated pitches of FlowSound provide direct audio feedback of bypass graft VOLUME FLOW!
Here’s How FlowSound Works
An increase in FlowSound’s pitch by one-half tone (E to F [Mi to Fa]) corresponds to a 12.5% increase in volume flow. One full tone increase in pitch (F to G [Fa to So]) corresponds to a 25% volume flow increase. An octave (C to C [Do to Do]) change in pitch equates to a fourfold volume flow increase. To perform an audiovisual graft patency assessment, listen to FlowSound and observe the heart beating.
- Temporarily Eliminate Competitive Flow: Competitive flow from the native coronary artery reduces and sometimes reverses graft flow. One should, therefore, measure the graft at its maximum flow capacity. Temporarily apply finger pressure to the native vessel proximal to the anastomosis. If competitive flow had been present, the FlowSound pitch would have increased, indicating its elimination.
- Diastolic Dominant Left Heart FlowSound: Contracted muscle resists inflow. Therefore, on a good graft to the left heart, one would expect low flow (a pitch within one’s vocal range) during systole, and a far higher-pitched FlowSound (above one’s vocal range) during diastole for a “Diastolic-dominant Flow Profile.”
- Systolic/Diastolic Balanced Right Heart FlowSound: The right side of the heart contracts less forcefully than the left heart. Therefore, bypass graft flow to a right heart coronary is less impeded during systole. Both systolic and diastolic FlowSound to a good right heart graft will be above one’s vocal range.
How Does FlowSound Relate to Graft Patency Assessment
- If mean graft flow is above 25 mL/min (above 20 mL/min for a smaller patient), graft flow is good. FlowSound’s pitch will be well above the normal vocal range. Mean flow is displayed on the AureFlo® display and front panel LED of the Flowmeter.
- When mean flow is suspect (<20 mL/min), technical error such as a misapplied stitch, thrombus formation and distal obstruction in the native coronary must be ruled out before one can conclude that the poor flow results from acceptable causes such as low blood pressure, diseased cardiac muscle or a limited flow delivering capacity of an arterial graft.
FlowSound is one more powerful tool in a CABG surgeon’s arsenal for knowing graft flow.