Background and objective.

External or percutaneous ultrasound (US) widely used, causes different histological effects depending on the frequency, intensity, wave amplitude, application time and the tissues through which it passes. It has been used for different purposes, among others, to facilitate liposuction and improve its results; however, as far as we have been able to review, there are no reports that relate the frequencies of the percutaneous US and the period of its application with the changes described in the adipose tissue.

Our aim is to establish frequency parameters and application times of the external US to standardize criteria, based on the histological analysis of the changes it causes to the adipose panniculus and to the adipocytes.

Methods.

A descriptive, comparative, open, experimental, prospective and longitudinal study was carried out in 59 fragments of adipose tissue taken from adult pigs. Fifty-four were subjected to US applied directly to each fragment, with different time parameters (5, 10 and 15 minutes) and different frequencies (low-1.1 Hz, medium-2.4 Hz and high-3.9 Hz). Five fragments were preserved as a control. Processed in 2 ways (paraffin and freezing) and stained with 2 techniques (hematoxylin/eosin and oil red). In each lamella 10 fields were observed.

Results.

Normal mature adipose tissue was observed in the control fragments. In those undergoing US, depending on the frequency and time applied, interstitial edema, disordered architecture, presence of inflammatory infiltrate and lysis of adipocyte membranes were observed, in various percentages that we qualified in degrees.

Thus, in the fragments exposed for 5 minutes at medium frequency, mild lysis was observed (10%), In those exposed for 10 minutes at medium frequency, lysis was mild to moderate ( 10-20%), similar to that observed with low frequency for 15 minutes. Applying US for 15 minutes with low frequency, the response was mild to moderate (10-20%) with medium frequency of moderate to severe (20-30%) and with high frequency it was frankly severe (30%).

Conclusions.

The application of external US causes lysis of the adipocytes and evident disorders in the adipose tissue architecture. Applying it with lower frequencies requires longer periods to achieve the same effects. With higher frequencies the same changes are achieved in less time. The use of frequencies from 2.4 to 3.9 Hz causes obvious changes, with a wide margin of safety.

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