Goals/Purpose:
Lower face laxity is an early signs of aging, caused by the relaxation of the SMAS among others. Mendelson highlights that collagen and elastin fibers of the SMAS become degraded over time. Although collagen contraction with heat is not new, no modality of non-ablative skin resurfacing has been designed to address SMAS collagen.
It has been hypothesized, that NMRF delivers energy causing deep dermal volumetric heating and contraction of the collagen framework by the following mechanism: Heat is produced when the tissue's inherent resistance (impedance) converts the electrical current into thermal energy within an RF field (Ohm's law). Nevertheless, the algorithms for optimal treatment remain unknown.
Bio-physics textbooks say, "the resistance of 1cm2 of dry human epidermis in contact with a conductor can become 105Ω. The skin's resistance is variable according to thickness, humidity and temperature, as well as the magnitude of the potential difference, therefore, Ohm's law doesn't apply to skin."
The skin is the first layer of the facial 3-D structure, which is arranged in concentric layers whith different electrical behavior. ĄCan facial tissues be thought of as an Ohmic conductor and does NMRF really work according to Ohm's law?"
The objective was to analyze the electrical behavior of facial tissues when increasing energy were applied with a NMRF system to see if they can be considered as Ohmic conductors. An additional goal was to evaluate the clinical efficacy of this different algorithm to improve mandibular contour.
Methods/Technique: Eighty-one patients with mild to moderate facial laxity underwent one NMRF treatment. This device has a monitor which measures the impedance of tissue.The area of treatment was divided into 3 zones: Z1-between upper border of thyroid cartilage and posterior mandibular edge, Z2-from upper limit of Z1 to transversal line between oral commissure and tragus, and Z3-from upper limit of Z2 to horizontal line above zygomatic arch. The treatment began with 27J/cm2 and was gradually increased. For Z1 and Z2, the maximum limit of energy was defined by the patient, as for Z3, was 61J/cm2 to avoid atrophy to the soft tissues.
The impedance values were analyzed for 13 of 81 patient in 5 different topographic areas: fat-pad malar, mid-face tissue, jowl, chin, and the sub-mandibular region. The patients had at least 3 visits per year during clinical follow-up (4 to 24 months). Each set of standardized photos was evaluated by the author and the patient.
Results/Complications: The patients were divided into 3 groups . Excellent improvement was not observed in anyone.
IMPROVEMENT
AGE | GOOD (50-75%) | MODERATE (25-50%) |
30-39 | 66% | 17% |
40-49 | 60% | 27% |
50-60 | 38% | 35% |
Ten patients were reviewed after12 months and the lower face laxity began to reappear.
The impedance data was statistically processed. In all cases the impedance
fell between 11% and
16% when the energy levels were
increased. The highest amount of reduction in resistance was in the jowl
and the submandibular area. The initial
average value of resistance was 131.4 Ω and the final was 113.2 Ω.
Conclusion: : The limitation for these type of studies, is the inherent difficulties to scientifically quantify the improvement in cosmetic appearance. Digital images revealed high levels of efficacy with this algorithm of treatment (51% of patients) and the patient's age was an important factor in tissular reaction to thermal energy.
The thermal effect that RF has on the biological target depends on the electrical conductive properties of tissue. Dynamic modulation of the electrical conductivity as a function of temperature has been previously reported. Electrical conductivity increase by 2% for each degree Celsius.
The author focused this study on the idea that continuous application of RF treatment with increasing levels of energy will gradually "pre-heat" the deeper tissues allowing to reduce impedance and to increase conductivity. Therefore, RF current could reach the target to stimulate collagen contraction at deeper levels, such as the SMAS.
For the commercial impedance analyzer, the body simply consists of limbs and a trunk, and the head is ignored. In NMRF Systems, the probe measures the sum of two types of impedance. 1-Local from the heated tissue directly under the probe, 2-Bulk, due to passing current through the unheated tissue. The relative contribution of everyone to the total value is still unknown.
The concept about Ohmic conductors states that you have an increase in resistivity when you icrease temperature, therefore if all tissues behave as Ohmic conductors, total impedance values should always increase and never decrease when the temperature is raised. When the resistivity of the materials decreases with an increase in temperature, this behavior indicates that the material is not an Ohmic conductor.
The author concludes that this results support the hypothesis that lower and mid face possibly behaves as a non-Ohmic conductor, and the proposed algorithm of treatment is associated with better clinical outcome and could be an alternative to improve mandibular contour.
