Shock Wave Physics: Why it Matters (part 2)
In last week’s blog, we introduced some parameters that define, in physics terms, how the body sees a shock wave:
Peak Energy, Rise Time, Focal Volume, Total Energy, and Penetration Depth
Before we talk about the different types of shock wave generators, we are going to add one additional parameter to that: Energy Flux Density (EFD). This sounds complicated, but it is really just a measure of the amount of energy deposited in a specific area. This would be similar to combining two parameters we already mentioned: Total Energy and Focal Volume.
There are two reasons that this parameter is important:
- The amount of energy in a specific area can define how effective the treatment is.
- If too much energy is put into a specific area, then potential harm could occur to the tissue.
We have established that shock wave generators are used to treat many types of indications in human and veterinary medicine. The most prolific use of shock wave is in treating kidney stones in a procedure called Lithotripsy. The energy literally breaks the stone into smaller pieces that can be passed naturally without surgical intervention. In veterinary medicine, we utilize shock wave therapy to accelerate healing of tendons, ligaments, muscle tissue, bone, skin, and other soft tissue. We also utilize it to treat muscle soreness and joint pain. Each of these indications can require different optimal parameters, but generally speaking, optimal settings are:
There are three types of shock wave devices used in veterinary medicine. There is a lot more detail on these types of devices here: http://www.pulsevet.com/shock-wave-physics/, but they are broken down into:
Electrohydraulic – highest energy waves with the most rapid rise time and the largest focal area to better treat large areas (tendons, joints, and backs). These are the most common used in equine therapy. Energy level and depth of penetration are variable to suit treatment site.
Electromagnetic – produces lower energy with a smaller focal area. This was designed to better focus on small targets like a kidney stone without affecting the surrounding tissue, but is also marketed for orthopedic indications in horses.
Pizeoelectric-produces a mechanical vibration of a crystal that has the smallest energy wave. This was designed to better focus on small targets like a kidney stone without affecting the surrounding tissue.
While technically not a shock wave, radial pressure devices have also been marketed as shock wave devices in veterinary medicine. These machines work like a small jack hammer to transmit mechanical energy to the body. These devices have much lower energy and extremely limited penetration relative to true shock wave devices.
It is clear that the ideal shock wave generator for any kind of indication other than lithotripsy is electro-hydraulic.
One last comment on Energy Flux Density (EFD): while it is an important parameter to ensure that total energy in a given area is an appropriate amount (high enough to be effective without being too high to cause damage), it can be misleading to use this parameter alone in determining which type of device to use. All of the true shock wave devices advertise EFD in similar ranges, but suggesting these devices are equivalent is misleading without knowing the focal volume and total energy. This number is just a fraction, so having a low energy and a low focal area could end up with a similar EFD as a device with a high energy and a large focal area….
It’s like saying a glass filled with water and a swimming pool filled with water are the same thing.
NOT ALL SHOCK WAVE DEVICES ARE CREATED EQUAL. GET YOURSELF A CHAMPION.