Cavitation good or bad
DERMAforum – Nr.5 – May 2010
Publicity Gimmick or Innovation
The Great Cavitation Lie?
Lose fat without effort – that is what an increasing number of therapists promise by the help of a new generation of ultrasound devices, the so-called cavitation technology. The physician Klaus Hoffmann, MD, Bochum, says: better be careful.
Recently, the deployment of so-called ultrasound cavitation devices has been famed as the cutting-edge therapy method against body fat deposits. More and more of these devices work their way into the market. This tendency, focussing on the non-medical sector, particularly cosmetic and fitness establishments, can be observed in a special degree in Germany. At the occasion of the last Beauty trade fair in Duesseldorf, this technology for everbody's use has enjoyed outstanding advertising. So let us put the question what cavitation really is and can do.
The term "cavitation" can be found repeatedly in numerous forms as an effecting mechanism of the established ultrasound. Here, the term "cavitation" is frequently used as a catchphrase without knowledge of the underlying physical principles. This deficit, in combination as well with a lack of fundamental medical knowledge about the effects of ultrasound on the human body as an aggressive marketing strategy, increases the degree of possibly being endangered by deploying these devices.
The dermatological hospital of the Ruhr University Bochum with its experience of more than 20 years and numerous publications on ultrasound in dermatology has tried to catalogue and evaluate the devices present on the market.
However, it had to be stated that questions presented to producers and importers concerning the submission of approval documents, certifications and technical data have been in many cases remained unanswered or answered evasively and only in a few cases readiness has been met to provide devices for a testing in order to evaluate them in a relevant time period.
Validation? Never heard about it!
Producers and importers were unable to provide scientific investigations and studies based on evidence concerning cavitation devices; also our own research did essentially not yield any results – which were not expected in the first place. Considering the devastating status quo the advertized technology and the propagated effective method (1) have to be focussed scientifically: what do these devices really accomplish: cavitation, degasification, heat, or simply everything?
Physics defines cavitation as a local vaporisation of water molecules under great pressure changes. The dragging elements of these pressure changes, caused e.g. by ultrasound, tear the water molecules successively apart (vaporisation). From a certain relation of the statical partial pressure inside and outside the generated cavitation bubble onwards the cavities generated by this process cannot be sustained anymore. The result of this sudden imbalance is a spontaneous implosion of the cavitation bubble. Depending on the frequency and energy of the ultrasound signal the collapse is more or less energetic. In other words, our adipose cells, since they contain water, are "torn apart" – according to the insufficiently proven theory. Generally it can be assumed that authentic cavitation can be measured only with degasified and demineralized water. Concerning measuring attempts, gases and minerals contained in water would result in a superposition of degasification processes over real cavitation bubbles not letting the latter be visible. Interestingly, the water inside human adipose cells contains definitely dissolved gases: how then can anybody possibly prove the existence of the phenomenon?
The Market is Bursting
Bubble formation in an aqueous medium are in general sciences frequently referred to as non-authentic or stable cavitation but, speaking purely physically they have to be clearly differentiated from authentic cavitation through the fact that bubbles generated in this way cannot collapse spontaneously, that their energy level is low and that they decompose or dissolve slowly in the medium. This is not likely to work with an adipose cell! In order to be correct we would have to distinguish between vaporizing and degasifying cavitation, the physical properties of cell-destructive effect of which are blatantly different. We must bear the imposition of understanding these contexts because, as mentioned before, the subject is boiling hot and the market is bursting.
The extremely high pressures resulting from microjets (see illustration) out of the collapse of the authentic cavitation bubble cannot be observed with quasi-cavitations or stable cavitations. Cavitation following the vaporization of water molecules displays substantially higher pressures and is for this reason capable of causing microjets during the spontaneous collapse. By contrast, the bubbles of "stable" cavitation collapse with considerably lower speed and show therefore lower energies as well. Consequently, a tissue damage caused by stable cavitation is highly improbable. This becomes more clearly when put it in numbers:
Herbert et al. describe in 2006 minimal (!) pressures between -26 Mpa and -17 Mpa (-260 Bar and -170 Bar) and refer in addition to it in their meta-analysis to existing publications whose results differ between -16 Mpa (Berthelot method) and -140 Mpa (inclusion method). We have to keep in mind that high-energy cavitation bubbles whose collapse can result in highly energetic micro jets remain, as far as it concerns medical-technical applications, ultimately rather unwelcome and illicit both with respect to the standard regulations and the permission criteria and that they, according to the understanding of the author, should be excluded since they are capable of causing in the long term adverse effects by damaging tissue through secondary effects.
With other words: devices capable of all what is sold as cavitation would be bound to able to establish the extreme energies described above; this is unlikely to be permissible, and even if so, the operation of something like this would be restricted to physicians; and probably only to physicians with special qualification. There remains a need for clarification.
Advertisements for a combination of high- and low-frequency properties of devices may duly be called baffling. Combinations of main and supporting frequency are commonly confused with beats resulting from interferences. A beat like this in the physical sense is not an isolated additional frequency but a regular increase and decrease of the amplitudes of main and supporting frequency. (See Fig.) This is another case of artificial haze – meant to confuse the user?
Without going further into the relation of frequency, energy and size of cavitation bubbles we can assume that the pressures achieved in the so-called ultrasound lipolysis do not induce authentic cavitation effects in the physical sense and therefore a suspicion persists that these terms are used only for advertisement purposes for selling an ultrasound technology that has enjoyed no finite scientific investigation.
Likewise, an impression that is repeatedly conveyed that we only find a pseudo-scientific obfuscation by a sequence of scientifically painted phrases instead of concrete study results. No wonder if we consider the fact that the quest for a producer of medical devices standing behind a permitted device certificated according to ISO 13485 comes to nothing.
Nobody Capable of Cavitation
From the producers, we cannot exspect a profound answer for the question how and exactly on which structures the ultrasound deployed has effect – immediately (and permanently!?), as it is promised. Where are extensive histopathological studies, immune histologies, electronic-optical investigations, obligatory double-blind tests and, first of all: what about temperature changes in the treated area? Are minimal changes already enough?
There is reason to fear that maybe not a single one of the "cavitation devices" on the market is capable of effecting a cavitation in the proper physical sense described above.
The legislator has not been inactive and has comprised so-called cavitation devices within the law for protection from non-ionizing radiation to be used with humans (NiSG) which is due to taking effect by the 4.8.2009. According to the official rationale for the law (BT-DS 16/12276 dating from 17.3.2009, BR-DS 279/09 from 3.4.2009) " an exposition to ultrasound as a result of local generation of heat and cavitation can lead to tissue damages. Especially by cavitation local extremely high pressures and temperatures can be generated in the tissue … and by high-energy ultrasound the mentioned mechanism may induce thermic necrosis and tissue hemorrhage." Does this mean: it does work? But by this cavitation is explicitely called by name as a border effect, and by this devices advertising with such effects come within the rule – independent from the fact if this can indeed effect a cavitation in the physical sense. But is this not the case for a medical reservation concerning the use, are our professional associations not bound to storm against the development in the German market, on behalf of the protection of the population?
Interestingly, well-established serious producers of medical ultrasound supplies who abide by the security demands and certifications in every sense, the term "cavitation" is rather missing in the frame of permission and description of the effecting mechanisms.
Knowing the effect and the potential dangers of therapeutic ultrasound these producers of medical technique permit ultrasound devices for fat reduction in class IIb on which high security standards are imposed.
The Marketing Bubble Bursts
All things considered, the fuzz about cavitation could turn out to be a bubble with no content.
Contrary to this, it is foreseeable that after the burst of the marketing bubble "cavitation" the thermodynamic effecting mechanism of ultrasound devices will stay as an efficient method of treatment and will dain ground, and that the "advertisment community cavitation" will disappear from the scene again. In other words: I think that temperature changes in the fat effect something – but cavitation does not play any role in this. One question remains for us all: what temperature is needed? Is it really necessary to "cook" the fat painfully? Exactly this will be the scientific question for the next months since it is decisive for the question of who is treating fat with which method and technique in the most effective and protecting way. In this sense this contribution is the first attempt to initiate a discussion and to bring the companies in the market to become more precise and to start scientific studies which are far from existing in a sufficient extent.
Klaus Hoffmann, MD
Dermatological hospital of the Ruhr University Bochum
1) (graph with text inscribed)
Frequency B Interference with beat
Frequency A + B
2) (four small pictures)
Collapse of a cavitation bubble with formation of a microjet
3) (picture of the author)
Klaus Hoffmann, MD
"The cavitation devices are a marketing instrument and do not rest on scientific insight"
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