Coagulation of dilated blood vessels

The problem of the removal of dilated blood vessels is pertinent to many people not only for aesthetic reasons, but also for medical reasons.
There are several methods for dealing with dilated blood vessels: surgical removal, sclerotherapy, cryodestruction, and, of course, laser coagulation Each method has its deficiencies: surgical excision results in an unappealing cosmetic effect, and, moreover, this method is not always applicable; sclerotherapy does not enable the removal of smaller veins, entails a long recovery period, and results in a large necrotic zone; cryodestruction destroys not only the vascular component, but all of the surrounding tissue. Of the procedures noted above, the only one that can be said to work selectively is laser coagulation of dilated blood vessels. In short, only by using a laser can the dilated blood vessel be treated without trauma to the surrounding skin, thus producing positive aesthetic results.

A little background information

A basic assumption is that all that is needed to selectively treat dilated blood vessels is to use a particular wavelength that will be absorbed by the blood vessels, and not by the surrounding skin. And so, the practice of using selective vascular lasers was initiated with the advent of the gas argon lasers. Oxyhaemoglobin was selected as the chromophore, which at the wavelength of an argon laser,has a high absorption coefficient (for some reason almost all of the theorists of transcutanus method of laser coagulation allow for the absorption of radiation is oxyhemoglobin, while focusing on coagulation of the deoxygenated blood).

Theoretically, this type of laser could effectively treat variants of angiodysplasia without damaging the skin. In practice, the results of treatment were less than optimal, and the amount of scarring was unacceptably high. With each new decade medical specialists strove to fully understand the factors hindering a positive medical and aesthetic outcome using these laser systems. First, they tried to optimise technological processes a vascular defect was not irradiated in a scanning mode, rather discrete laser spot treatment was introduced. This reduced the amount of scarring, but did not completely eliminate the problem. And then it became clear that the solution lay not in the method of treatment, but in the way in which the laser was generated. Gas lasers can generate the required amount of power, but only in a continuous, or quasi-continuous mode. This means that the vessel is heated rather slowly, but since the TRT (thermal relaxation time – the time during which an object is able to store heat rather than send it to the surrounding tissue) of small vessels can vary from tens of microseconds to tens of milliseconds, then the prevention of excessive heat outflow from the vessel into the skin is simply impossible. Thus, the fact that the wavelength used is effectively absorbed by oxyhaemoglobin does not guarantee selectivity in results of treatment. It is not possible to avoid excessively overheating the skin
without taking into account heat transfer process. To implement selective laser treatment one must consider not only optical, but also thermal selectivity. That is, ensuring coagulation of the vessels without overheating the surrounding tissues is possible only if the duration of the laser action is equal to or less then the TRT of the dilated vessel. This condition corresponds to pulsed lasers. Now virtually everybody understands this, but yet many manufacturers still offer laser devices that operate in a continuous or quasi-continuous mode allegedly for the selective treatment of vascular diseases.

The principles of selectivity

Thus, for successful treatment what is required is the ability to provide both optical and thermal selectivity. It is a simple enough matter to provide the thermal selectivity. All that needs to be done is to select a pulse duration that is less than the TRT of the vessel. It is true that contemporary vascular lasers use a duration of significantly greater length. We shall examine the reasons for this below. Here, we shall further discuss optical selectivity.

In the coagulation of dilated blood vessels, it is compliance with optical selectivity that turns out to be the most difficult task. At first glance, it would seem that nothing could be simpler – make sure the selected wavelength is easily absorbed by haemoglobin, and the problem is solved. Unfortunately, there are spurious chromophores that readily absorb radiation, but, during this process, are not located inside the blood vessels. In this case it is melanin, which in the blue-green region has a high absorption coefficient, and the haemoglobin itself, distributed in natural, unexpanded capillaries. Not knowing how to contend with spurious haemoglobin, researchers simply do not factor it into any subsequent calculations and focus their attention on melanin. Since the efficiency of radiation absorption by melanin decreases as the wavelength increases, they decided to use more longwave radiation. Moreover, shortwave radiation is not effective in penetrating either the skin or the blood vessels, so it can coagulate only the smallest blood vessels, such as blood vessels of the “port wine stain” category, and the result of the shallow depth of skin penetration this entails is that the energy is dissipated in a small volume, causing overheating. Thus, by increasing the wavelength from 514 and 532 nm to 575, 585, 595 nm, one can penetrate deeper into the skin and into the vessel. As a result, scientists succeeded in coagulating larger vessels while diminishing the amount of scarring. A further increase in the wavelength of the radiation used enables the coagulation of blood vessels of a larger diameter. Thus, by selecting the optimal wavelength for each given size of vessel, one is able to achieve coagulation. In other words, effective treatment is achieved, but that is all. As before, the cosmetic effects of this treatment are lamentable. Unless one factors in the impact of the spurious chromophores to provide the coagulation of only the dilated blood vessels without coagulation of the skin, it is extremely difficult to make headway with laser irradiation. Therefore, the amount of scarring resulting from the use of so-called “selective” lasers is only 50%.

We now return to thermal selectivity, since it impacts the effectiveness of treatment and the ability to obtain a favorable aesthetic result just as profoundly as optical selectivity.
Nowadays, almost all vascular lasers use a pulse duration greatly exceeding the TRT of blood vessels. What is the reasoning behind this? After all, it is obvious that this will unavoidably result in overheating of the skin. But it turns out that in this case the effectiveness of the coagulation process is increased, and the process of removing the enlarged vessels looks very good. The vessels disappear right before your eyes during the procedure, and the patient is fully satisfied while bidding the doctor farewell. Of course, after some time, all, or almost all of the veins return, often with scarring, but once the patient sees this magic act, she will return, so that, once again, she can leave with unblemished skin. What’s the secret behind this “magic act”?
It turns out that laser irradiation causes the blood inside the vessel to boil, which, in turn causes the vessel to collapse and the walls to seal together. It true that there are some limits to this procedure. For example, the spot should be at least 3 mm in diameter, and, preferably, the duration of the pulse is longer. The argument for the increased pulse length is somehow understandable in the case of the coagulation of very large veins with TRTs in the tens of milliseconds, but in the case of small vessels, the effect is obviously not going to be selective. But we’ll talk more about this further on. For now, we will stay focused on the specifications relating to the diameter of the spots. What is the rationale for this? One could make reference to the reduction in the depth of penetration of radiation into the skin due to the small size of the spot. However, this restriction would be valid only for deep blood vessels, and this association was not found. In other words, of course the coagulation of deep blood vessels is more complicated, but even surface veins do not disappear with small laser spots.
Perhaps there is something amiss with the logic used to develop these procedures for removal of vessels? Maybe what we are observing has a different explanation? Let us try to get to the bottom of this. The first question to be answered is what exactly is chromophore? Is it haemoglobin or oxyhaemoglobin? Where is it located? Only in the dilated vessel? And what about the spurious haemoglobin from natural capillaries? Can we disregard the absorption of radiation in them? And if we consider the fact that the TRT of small vessels is much less than that of dilated vessels, it becomes clear why there is excessive overheating of the skin, and, as a result, scarring.
The second consideration is melanin. Its absorption coefficient is higher than that of haemoglobin in the visible and near infrared spectral range. In addition, the TRT for melanin is about one microsecond; that is, it effectively starts to heat the skin a mere microsecond after exposure.

Let’s try to imagine the dynamics of the procedure on dilated blood vessels with laser radiation exposures lasting tens of milliseconds.
A few microseconds after starting exposure, melanin begins to efficiently redistribute the heat, converted from absorbed radiation, to the skin. After a few tens of microseconds, this process is enhanced by tiny capillaries that are heated up, and transfer heat not to the epidermis, but directly to the dermis. In grade school everybody learns what happens to physical bodies when heated: they expand. So it stands to reason that skin cells exposed to heat from the melanin and haemoglobin in the natural capillaries will increase in size. If there are enough of these cells, they can exert enough of a physical impact on the dilated blood vessel to cause it to compress, in so doing, squeezing the blood out of it. Visually, this is manifested in the disappearance of the vein. However, we are simply not able to witness a change in the size of the cells, firstly, due to the very small nature of these changes, and secondly, because of the time span in which this impact occurs – in units of tens of milliseconds. If we accept this explanation, it becomes clear why the size of the spot is essential. After all, if the impact zone does not contain enough cells, their combined pressure is simply not enough to effect compression of the vessel. This also explains the large percentage of burns and scars. This method is simply not effective without the non-selective overheating of skin. And then the presence or absence of scarring will depend entirely on the skill and experience of the doctor performing the procedure.

For me, a physicist by training, this explanation of the mechanism of coagulation of vessels is, at the very least, puzzling. First, it has been affirmed that the blood inside the vessel evaporates, but the boiling point is significantly higher than that of the temperature for coagulation. It follows that we can significantly reduce the energy of the laser pulse to lower the risk of scarring and obtain effective coagulation of blood vessels. That is, we do not effect a spectacular manifestation of their disappearance; rather, it will take one or two weeks for the blood vessels to disappear. But something does not work out. Even when the blood vessels disappear—that is, the blood, as if, evaporates—we observe the return of the vessels already a day later. And if we reduce energy, then there is absolutely no effect. The result is a discrepancy. Let’s move forward. Blood is not distilled water, meaning it cannot transform into a gaseous state. That is, when boiled, some of the blood should evaporate, and the rest will solidify. But how, then, will the vessel disappear? I understand that it can shrink, but disappear? What, then, becomes of the solidified component? Again we have a discrepancy. Third, how can a vessel, when the blood in it is boiling, implode rather than expand? Try to imagine a boiling pressure cooker imploding. I understand that the collapse can be preceded by expansion, but where is the initial process of inflation of the vessel? Doubts are also raised by the notion that the vessel can maintain its integrity as the blood within it is boiling. I observed the process of boiling blood inside a vessel under the effects of a Q-Sw laser. In this case, the blood does not really have time to redistribute the heat, and some of the blood inside the vessel evaporates, in which event the vessel walls simply give way and tear.

A new method of effecting coagulation of dilated blood vessels

There is another means of bringing about coagulation of vessels, which in the process enables a high degree of selectivity. I developed this method over a period of several years, and now have demonstrated its effectiveness on tens of thousands of patients. Let’s take a look at the details.
For truly selective coagulation of dilated blood vessels, we need to get rid of unwanted chromophores: haemoglobin in natural capillaries and melanin. And we are more concerned with haemoglobin, as it, due to its location, can cause deep overheating, which cannot be compensated for by the surface cooling of the skin. This problem can be solved by employing the very mechanism of long-pulsed classical coagulation of vessels. After all, if we can squeeze blood out of dilated blood vessels, then the same can be done much more easily with small, natural capillaries because of their smaller diameter. That is, if the surface of the skin is first irradiated with a long pulse wavelength that effectively penetrates the skin and with a small energy pulse, we can create a swelling which will be enough to squeeze blood from the capillaries, but not enough to constrict the dilated blood vessels. In this case, after preliminary irradiation, haemoglobin remains only inside the enlarged vessels and further procedures can be implemented without fear of overheating the skin.
After this we can, using radiation, which is well absorbed by haemoglobin, cause coagulation of the dilated vessel. We could, but inevitably this would result in excessive exposure of the natural pigment that effectively absorbs the radiation of this wavelength. That is, this method is not applicable even for darker skinned patients (not to mention the darkest complexions), causing overheating of the skin, and as a result, the risk of scarring. Another approach is required. The best solution is to find another chromophore that can absorb radiation better than melanin and is located exclusively within the enlarged vessel. It’s understood that if such a chromophore existed, then we would be making use of it long before now. Unfortunately, chromophores like this are not naturally produced. However, what if one could be created? We know that coagulated blood differs from regular blood in colour. What is this difference in colour if not a difference in the absorption spectrum? This means that one can find the ranges where coagulated blood has a higher absorption coefficient and treat it in that range. Our studies have shown that in the near-infrared region, coagulated blood absorbs much better than otherwise, and even more effectively than melanin.
Now one need only create within the dilated vessel a region of coagulated blood and irradiate it.

In actuality, creating a micro-region of coagulated blood does not present special difficulties. You just need to take into account the difference in the mechanism of radiation effects on the chromophore of long and short (Q-Sw) pulses. In the case of absorption by the chromophore of a long pulse we get its gradual heating, connected to the fact that the absorption coefficient is certainly less than 100%. That is, part of the radiation passes through the chromophore and is absorbed in the underlying chromophores. If a blood vessel is exposed to radiation, this will lead to its entire volume becoming smooth and heated to approximately the same degree. If Q-Sw pulses are used (with a certain energy density) we increase the absorption rate of the chromophore to almost 100%. In other words, we limit the depth of penetration by radiation within the vessel. As a result, coagulation occurs only in the insignificant quantity of blood that lines the inner upper surface of the vessel wall. Thus, the coagulation of such small amounts of blood does not require high-energy pulses, which can significantly reduce the degree of exposure on melanin.

And so, within the vessel, a new chromophore is created, with high absorption in the near infrared zone, exceeding the level of absorption of melanin. This gives us the opportunity, using sequences (trains) of low energy nanosecond pulses to increase the absorption coefficient of coagulated blood, leaving the absorption coefficient of melanin at the same level. The coagulated vessel is subjected to a sequence of Q-Sw pulses with a duration not exceeding its TRT. Due to the increase in the absorption coefficient, each pulse in the sequence will effectively absorb the regions of coagulated blood, increasing their temperature and volume. As a result, all the blood in the lumen of the vessel will be gradually coagulated. Given that we have increased the absorption coefficient of the new chromophore to 100%, we can afford to significantly reduce the overall energy of laser irradiation. This reduces the overall thermal load on the skin, and since there is no coagulation of the natural capillaries, the entire blood stream can be reallocated to them almost immediately after the laser treatment, thereby reducing the risk of recanalization and reducing the period needed for recovery.

Of course, this method cannot be regarded as purely selective. Some of the laser action falls on natural capillaries and melanin, but the extent of this exposure is incomparably lower than with traditional methods. The results of treatment are self-evident.

Using this method, and with excellent cosmetic results, the following conditions can be treated:

  • progressive growing haemangiomas in infants;
  • various types of angiodysplasia;
  • telangiectasia;
  • veins in the legs;
  • cavernous haemangioma with cavity diameters of up to 6 – 8 mm.

  Treatment results Before-After

I have described in detail all the stages of laser treatment of the blood vessel in the process of coagulation. In practice, they are brought together and visually represent a single laser flash affected by pressing the pedal controlling the laser.
This procedure for coagulation of blood vessels was patented by myself in 2001 and implemented in the Multiline™ apparatus in the laser assembly Nd: YAP / Q-Sw / KTP.

Today, many manufacturers of laser technology offer two-wave lasers for the treatment of vascular lesions, but, as can be seen from the above – wavelength is not the definitive criterion for successful treatment.

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