To date ultrasound has failed to displace diathermy devices as the most popular way to cut tissue haemostatically.

We believe the technological advancement in Lotus has at last provided the opportunity to optimize the use of mechanical vibration to energize tissue. Whereas electric current flows in any direction in which the conductivity of the tissue permits it, ultrasonic devices are set to vibrate and deliver energy in a particular direction. Until now all such scalpels have adopted the easiest vibration mode, a longitudinal one in which the tip (and equally spaced points along the waveguide) vibrates back and forth along the waveguide axis. It is generated by a transducer lying at the proximal end of the waveguide and along the same axis. This provides a high compressive force at the distal tip of the longitudinal waveguide, but the energy is needed along one edge. This is because in most cases the surgeon grasps target tissue between forcep-type pincers. If coagulation and cutting is required this must also be done via a pincer. Therefore power to coagulate and cut must be directed transversely into the tissue.

Lotus achieves exactly this. The first step was to use a different type of vibration mode, a torsional one in which the tip (and equally spaced points along the waveguide) vibrates back and forth in a short arc around the waveguide axis. It is generated by applying an harmonic torque about the proximal end of the waveguide axis. The two types of vibration mode can be shown diagrammatically as illustrated.

You are looking at two waveguides end-on, the compressional standing wave in the longitudinal waveguide (on the left) is shown by yellow dots in and out of the screen while the shear (torsional) standing wave in the torsional waveguide (centre and right) is shown by red arrows rotating in the plane of the screen.

The longitudinal waveguide exerts a transverse shear force, through friction, on any tissue contacting its sides, represented by red dots.

The unbroken torsional waveguide, in the centre, also exerts a similar transverse shear force, including at the distal face.

The second step was to devise a blade design that used the torsional mode of vibration to redirect the vibration energy. If a groove is cut into the side of the torsional waveguide, as shown on the right, we expose facets that exert a compressional force on tissue contacting them.

The distal face and the round sides of the torsional waveguide continue to exert the transverse shear force but we have now derived an additional compressional force acting normally to the waveguide axis. This is the central idea in Lotus.

In each system energy enters the tissue via two possible processes:

In both systems friction heat is very quickly generated at the metal/tissue interface and this diffuses through the tissue causing coagulation.

In the longitudinal waveguide vibration could be transmitted into tissue as a shear wave. However, the shear modulus is low in fluid-filled cells resulting in low transmission.

In the torsional waveguide vibration is transmitted through tissue as a compression wave. Young’s modulus is significantly higher than shear modulus in fluid-filled cells giving rapid transmission. We expect the full volume of tissue between the blade and the jaw to be energized almost instantaneously.

So, by transmitting a shear (ie torsional) wave down the waveguide and cutting grooves near the tip we develop a compression wave at the tip, turning the power through 90° and focusing it into the target.

In practice Lotus uses two grooves with a central ridge between them extending out to the full radius of the waveguide.

The central blade performs the cut once the side grooves have energised the tissue and welded it.

   

These diagrams illustrate an artery being cut with simultaneous welding of the free ends by Lotus. The jaw pushes tissue into the grooves (A) which coagulate the tissue (B, C) before the jaw closes along the central ridge (C) causing separation (D). In fact it all happens virtually simultaneously with a tissue weld each side of the cut.