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In an earlier blog, we talked about the term “shock wave” and how it can be frightening and misleading to anyone who doesn’t have a degree in physics: http://www.pulsevet.com/whats-in-a-name/ .  When it comes to treating your beloved horse or dog it’s important to understand that there is a lot of variety in this technology, and the effectiveness of the treatment is greatly influenced by what type of shock wave is being used.

This is particularly important in veterinary medicine, because the FDA has very little regulation over how companies market their products to veterinarians and consumers.  Veterinary medicine, unlike human medicine, has very little government oversite.  This can sometimes be good, because new and exciting technologies can be brought to market and offered relatively quickly, but this is a double-edged sword.  Some products are brought out quickly and marketed aggressively with very little clinical proof of efficacy or even safety, leaving pet owners at a disadvantage if they are not aware of the differences.

In the earlier blog we describe a shock wave as a blast of sound energy – like the bang from an explosion or gun, thunder from lightning hitting the ground, or a sonic boom from a jet going faster than the speed of sound.  Graphically it looks like figure 1.  A pressure front, or wave, increases very rapidly (in millions or even billions of a second) and then drops off.

shock wave pressure over time (2)

The faster the pressure rises, the steeper that initial line is.  Extensive scientific research has confirmed again and again that this steeper rise leads to maximum clinical efficacy.  The height of that energy, or peak pressure, is also very important in achieving good results.

Once that wave is released, it is then focused in a similar way to a flash-light focusing light energy.  A reflector takes the source light and directs the energy forward to illuminate whatever the flashlight is pointed at (see figure 2). With a flash light, the generated energy beam is parallel or even a little divergent – meaning the beam is directed out to illuminate a larger area.

flashlight reflector

With shock wave, the beam is convergent, which means that the energy is all pointed at the same spot

shock wave convergent reflector

When the energy is all focused to one point (f2), it sort of piles on top of itself to a really high peak energy.  Figure 4 shows how at the focus point (f2) the energy really peaks, and further from the center the energy drops off significantly.  The area around that peak where most of the energy is deposited is called the focal volume.  The size of that focal volume and the amount of energy in that focal volume also determines the efficacy of the treatment.

Shock wave focal volume

To summarize, the main variables that determine the clinical efficacy of a shock wave device include the device’s peak energy, the rise time (how fast the energy peaks), the focal volume, and the total energy in the focal volume.  Variable penetration depth is also important for different indications – from superficial wounds to deep back or hip healing.

Next week we will discuss the different types of shock wave generators and what you should be asking for when you speak to your vet about shock wave therapy for your horse or dog.