An ultrasonic wave is created by applying electromagnetic energy from the Generator 300 to a piezoelectric transducer located between metal cylinders in the hand piece. In response to the electric field, the waves, traveling as sine waves from the hand piece to the blade, create mechanical vibrations. Silicon rings are located on the positions of the blade where the amplitude of the wave is zero in order to guide the blade.²

These mechanical vibrations then drive the active blade of the device. Vibrating 55,500 times per second, when the blade comes into contact with the tissue and pressure is applied, the blood vessels are coapted.

This coaptation breaks up positive hydrogen molecules, denaturing the protein in the cells. The denatured protein then forms a sticky coagulum, which forms a hemostatic seal, allowing the surgeon to simultaneously cut and coagulate.

Harmonic devices have four qualities of action: cutting, coagulation, coaptation, and cavitation. These actions can be achieved singularly or in combination with one another. In surgical procedures, all of these effects are typically applied consecutively.²

Cutting

Unlike electrosurgery, which uses extreme local heat to vaporize and disrupt tissue, Harmonic devices use a combination of tension and pressure to rapidly stretch tissue. When the tissue reaches its elastic limit, the blade or device tip is able to cut smoothly through it.²

Coaptation

Coaptation, or the adherence of tissue, is achieved by Harmonic devices disrupting hydrogen bonds, causing collagen molecules to collapse and adhere to one another at a low temperature. The tissue is then transformed into a sticky coaptate. For the preliminary control of vessels in preparing for surgery, coaptation and pressure are key.2

Coagulation

By applying ultrasound energy to tissue a few seconds longer than it takes to achieve coaptation, a rise in temperature leads to the release of water vapor and then to coagulation (maximum temperature of 150°C). Rather than defragmenting protein molecules as with coaptation, coagulation is achieved by denaturizing protein.

Cavitation

A side effect of the ultrasonic waves used to cut, coapt, and coagulate, cavitation occurs when the high-frequency vibration of a Harmonic device is transmitted to the surrounding tissue, causing rapid volume changes of the tissue and cell fluid. Vapor bubbles are then formulated at body temperature. ²

Cavitation effect aids in tissue plane dissection, and dissecting tissue planes enhances visibility in the operative field, which can be especially beneficial in anatomically remote regions or near vital structures.²