MAR 28, 2017Shock Wave’s Modus Operandi
Kinematics, mechanics and the world of Physics…simple, yet so complex to observe phenomenon and express it in mathematical form. Arguably one of the best in the matter of mechanics, Sir Isaac Newton summarized as the third law of motion that for every action, there is an equal and opposite reaction. Forces always come in pairs - known as "action-reaction force pairs." Does this principle apply to shock waves? The answer is without exception, yes.
It is a fact that shock waves are capable to generate the “action” force via compressive pressure of its positive pressure signal, and high velocity jets (another “action” force) during the implosion of cavitational bubbles produced by tensile/negative pressure of the shock wave pressure signal (only when shock waves are traveling through liquids).
Typical Shockwave Pressure Pulse
However, it is even more complex when living organism are involved, and toned-down medical shock waves are acting at the cellular level or tissue level. The action-reaction principle is still applicable at the moment shock waves pass through tissue, which gives the instantaneous “action” of the shock waves and “reaction” of the tissue (macro level) and at cellular level (micro level). The less typical and interesting part is the “secondary reaction” or “delayed reaction”, with far more implications on the tissue and cells, as the medical professionals nicknamed “MOA” or mechanism of action.
When produced by explosion, the shock waves’ action-reaction effect is noticed immediately in close proximity to the point of origin, as seen in the one presented below, from archive photos of first nuclear explosion tests. The compressive force generated by acoustic pressure shock waves is the “action” that rolled/pushed the school bus for about 50 feet, and the “reaction” is the rolling motion of the bus that consumed completely the “action” force until the bus got to a complete rest. At the time when the bus stopped from its rolling motion, the shock wave front that started the “action” on the bus was further away, due to the fact that shock waves travel in air with 300 m/s (0.186 mile/s), thus shock wave “action” was then felt in other places.
What happens at large distances away from the explosion’s epicenter? It’s fast and furious.
When military tried to monitor one atomic bomb explosion, from the air and at a considered safe distance from explosion’s epicenter, the high energy-generated shock waves showed action farther than expected. To general surprise, the zeppelin used for observation turned into a “victim” of the shock wave action by crushing it and easily sending it down, as seen from picture below.
When they specifically travel through liquids and not atmosphere, the other possible “action” forces of shock waves are the cavitational jets produced by the collapse/implosion of the cavitation bubbles generated by the negative pressure of the shock waves in its tensile phase, as seen below.
Shock Wave Bubbles Implosion with Micro-jets
In many cases, cavitation action forces can generate undesirable consequences. In devices such as propellers and pumps, cavitation causes a great deal of noise, damage to components, vibrations, and a loss of efficiency. In domestic plumbing, when a pipe is suddenly closed at the outlet (downstream), the mass of water before the closure is still moving, thereby building up high pressure and a resulting shock wave that manifest as a loud banging resembling a hammering noise, known as “water hammer”, which can cause pipelines to break, if the pressure is high enough. The action forces produced by cavitation can produce “reaction forces” in materials surrounding the fluid, that can exceed the strength of the material, which can be devastating, as it shows in the below picture depicting the total destruction by cavitation of a headrace cement tunnel from a hydroelectric dam.
In medicine, the shock waves are used either to destroy kidney stones or to stimulate living tissue to repair and regenerate. The immediate “action” of the shock waves is practically to stretch the tissue and produce tissue strain, thus generating the immediate tissue “reaction” (macro level, immediate reaction). When cavitation bubbles produced in any of the body’s fluids (blood, interstitial fluid, urine, etc.) collapse, they produce micro-jets (the “action force”) that interact at micro-level with individual cells from the fabric of the tissue or the adjacent structures.
Regarding kidney stones destruction, the shock wave “action” forces exceed the kidney stone’s strength, thus producing stone fragmentation. For tissue regeneration medical application, the shock wave “action forces” are reduced in intensity in order to produce “reaction forces” at the macro and micro level and generate a cascade of “secondary body reactions”, as the reactive oxygen species (ROS) inside body fluids, expression of growth factors, angiogenic factors, inflammation modulation, improved microcirculation and oxygen supply that ultimately produce cell proliferation and differentiation.
The summary of all these reactions, demonstrated with numerous scientific publications results, are part of the shock waves mechanism of action or “MOA” inside the living tissue, as presented in the following movie.
In conclusion, shock waves definitely follow the nature principle of action and reaction, although shock waves have their own nuances when it comes to living tissue reaction: a “double reaction” (instantaneous and delayed) can be seen, can regenerate cells/tissues and constitute a non-invasive mean to add to our armamentarium of ways to keep one healthy, repair damaged tissue, which ultimately translates in a more productive life for both society and personal benefit.
FEB 23, 2017What Is A Shock Wave?
It is the theory that the Universe started with the “Big Bang”, which is the first cosmic scale shock wave that created the vast expanse of the stellar space. It was just the beginning, as planets, stars and galaxies still continue to form through collisions, explosions, implosions and other events which created other shock waves at cosmic scale.
When life appeared on Earth at cellular, multicellular level and complex organisms, there was a constant bombardment of meteors, intense volcanic activity, and sustained earthquakes, all sources of strong shock waves. As a reaction to the environmental generated shock waves, in time, living organisms adjusted to mechanical/pressure stimulus produced by shock waves similar to their reaction to other stimuli such as heat/cold, chemical, electrical, etc. This explains human body’s sustained reaction when subject to modulated shock waves, that translates in healing and regeneration due to cellular/tissue interaction.
Generally, an acoustic pressure shock waves is an audible and very strong pressure impulse in any elastic medium (air, water or solid), created by supersonic craft, lightning, explosions, earthquakes or other extreme phenomena that generate sudden and significant changes in pressure.
Explosions of any kind produce shock waves in air/water/solids, as can be seen from next videos:
Shock waves are very fast, invisible, powerful and propagate in any direction through all types of organic and inorganic matter. They travel with 300 m/s (0.186 mile/s) in air, 1500 m/s (0.932 mile/s) in liquids and up to 9000 m/s (5.592 mile/s) in solids, which makes them to reach almost instantaneous proximity targets and can travel large distances. Humans have used shock waves for their destructive power mainly in military purposes, but in the second half of the last century also for medical purposes (breaking of kidney stones and for tissue stimulation and regeneration).
The “beauty” of medical acoustic pressure shock waves is the harnessing and modulation of their power to be focused and pass through the human body without destroying soft tissue, when kidney stones are targeted, or for stimulating tissue regeneration (both hard tissues, as bone, and soft tissues, as skin and muscles). The focusing and propagation of shock waves is presented in the following picture captured using high speed photography.
The pressure profile of a shock wave is characterized by a sudden increase in compressive pressure (compressive phase) followed by an exponential decrease until the pressures get negative in the tensile phase of the shock waves. Medical shock waves are usually producing compressive pressures up to 100 MPa (1000 bar) that act on tissue macro level and negative/tensile pressures of up to -15 MPa (150 bar) that produce cavitation in fluids and act at cellular micro level.
In our divided world for any possible reasons, where the same event can be seen as “bad” or “good” depending on one’s opinion, it seems that acoustic pressure shock waves fit the same mold too. On one hand, shock waves can be used for their significant destructive power, whereas on the other hand they can heal the human body. The choice is always in front of us.