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versão impressa ISSN 1806-0013
Rev. dor vol.13 no.1 São Paulo jan./mar. 2012
Effects of ΔF delivery ramp variation on the accommodation of the interferential current in healthy women*
Thais Eduarda Carvalho GuerraI; Gladson Ricardo Flor BertoliniII
IGraduated in Physical Therapy, State University of Western Paraná (UNIOESTE). Cascavel, PR, Brazil
IIProfessor of the Physical Therapy Course, State University of Western Paraná (UNIOESTE). Cascavel, PR, Brazil
BACKGROUND AND OBJECTIVES: Interferential current is a common electrotherapy modality in physical therapy, but the regulation of its parameters is still empirical, being necessary studies to establish adequate parameters for its application. This study aimed at evaluating onset time of the first accommodation and the number of times it occurs during 10 minutes of interferential current application, varying its presentation form of delta F (ΔF) delivery ramps.
METHOD: The sample consisted of 18 women divided in 3 groups: Group A 1:1 (variation every 1 second), in the 2nd day 1:5:1 (frequencies increase and decrease in 1 second and maintenance for 5 seconds), 3rd day 6:6 (frequency increase and decrease in 6 seconds); Group B 1:5:1 in the 1st day, in the 2nd day we used 6:6 and in the 3rd day 1:1; Group C 6:6 in the 1st day, 1:1 in the 2nd and 1:5:1 in the 3rd day. Stimulation was above the sensory threshold during 10 minutes and volunteers would indicate the moment of the first accommodation and how many times would accommodation occur.
RESULTS: During accommodation threshold evaluation, no ΔF delivery ramp presented significant difference. There has been significant difference in total number of accommodations when comparing ramp 1:5:1 to ramp 6:6 with the latter presenting the highest number of accommodations.
CONCLUSION: ΔF delivery ramp has not influenced accommodation threshold and ramp 1:5:1 had the lowest number of accommodations as compared to ramp 6:6.
Keywords: Analgesia, Electric stimulation therapy, Electricity.
Interferential current therapy is a type of electrical stimulation, since the device delivers medium frequency AC currents1. This therapy is described as the application of two phases of medium frequency currents (2 or 4 KHz) which are transmitted through the skin surface and the device produces a modulated amplitude current2. Resulting current has a frequency equal to the mean of the two currents and will have a new amplitude modulated frequency (AMF) equal to the difference between these currents (e.g., if a 4000 Hz and a 4100 Hz currents are mixed, resulting frequency will be 4050 Hz, with AMF of 100 Hz)3.
The literature describes interferential therapy as one of the most widely used electrotherapeutic modalities in the clinical practice4. It is indicated to increase muscle strength and resistance, to produce analgesia, to promote tissue recovery and to decrease spasticity5.
In the beginning, current intensity is gradually increased until patient reports a tingling sensation. As soon as this sensation decreases, that is, accommodates, intensity may be increased to maintain a constant stimulation6. The accommodation process occurs when a physiological response is continuously decreased with the repetitive application of a same stimulation. Initially, receptors respond with high frequency impulses, progressively decreasing as the stimulation becomes constant. Stimulation frequency maintenance is presented as a way of appearance of accommodation7.
There are different electric characteristics available in the interferential device, most of them allow the user to adjust such characteristics and there are few studies on optimal parameters for the use of the interferential device2,8,9.
ΔF is an AMF variation where there are frequency increases and decreases in patterns established in the equipment, which go from 1 to 100 Hz. So, if an AMF of 100 Hz is used with a ΔF of 50 Hz, modulation variation will happen between 100 and 150 Hz. This will prevent accommodation because, in addition to intensity, frequency change is another factor preventing accommodation10. In ΔF, ramp patterns are used with frequency changes over baseline AMF as a function of time, always aiming at preventing accommodations, and for equipment lacking such resource, such as low frequency transcutaneous electrical nerve stimulation (TENS), it is important to increase current intensity to prevent it11.
There are also beliefs about the use of ΔF delivery ramps, as ramp 1:1 for chronic cases, ramp 1:5:1 for sub acute cases and ramp 6:6 for acute cases. Therefore, there is the need for studies to establish whether there are ΔF delivery ramp variation effects on accommodation, whether there are adequate parameters for the use of this device and even to help professionals who use the interferential device as therapy.
This study aimed at evaluating onset time (seconds) of the first accommodation and the number of times it occurred during 10 minutes of interferential current application, by comparing current accommodation and varying the presentation of ΔF delivery ramps (1:1, 1:5:1, 6:6).
After the approval of the Ethics Committee for Research with Human Beings, State University of Western Paraná (UNIOESTE) under protocol 1043/2011, this quantitative crossover clinical trial with intentional and non-probabilistic sample was carried out. Participated in this study 18 healthy female volunteers with mean age of 20.60 ± 2.43 years, body mass of 58.33 ± 9.19 kg, height of 1.67 ± 0.06 m and body mass index (BMI) of 21.72 ± 1.36. Patients were randomly distributed into groups.
After being explained about study objectives and procedures, volunteers were submitted to evaluations to identify possible exclusion factors. After having accepted the invitation and being considered eligible for the study, volunteers signed the free and informed consent term.
Inclusion criteria were availability to participate in the evaluations and tests in predetermined days and times and patients should have used interferential current at least once in their lives. Exclusion criteria were absence in electrical stimulation days, presence of neurological or other diseases which could impair cognition, volunteers with clinical and surgical history on the spine and pregnancy.
Volunteers received bipolar interferential current (Neurovector, Ibramed®) with electrodes longitudinally placed on an L1 vertebra and another on an S1 vertebra and care was taken to decrease skin resistance. Electrodes were of rubber-silicone with approximately 4 cm2. Equipment parameters: AMF 100 Hz, ΔF 50%, delta F delivery ramp depending on the day and on the group, intensity was increased until the sensory threshold was reached; then it was increased when the volunteer reported that it had decreased, that is, accommodated, during 10 minutes.
All volunteers received currents with delivery ramp and were divided in three groups (Figure 1):
Group A (GA) 1:1 (variation every second) in the 1st day, in the 2nd day 1:5:1 (frequencies increase and decrease in 1 second and maintenance for 5 seconds), and in the 3rd day 6:6 (frequency increase and decrease in 6 seconds);
Group B (GB) started with 1:5:1, in the 2nd day 6:6 and in the 3rd day 1:1;
- Group C (GC) 6:6 in the 1st day, 1:1 in the 2nd day and 1:5:1 in the 3rdday.
Volunteers were evaluated for a total of 10 minutes and were oriented to say "yes" as soon as the current tingling sensation decreased. The evaluator has recorded how long individuals took to say the first "yes" and how many times they repeated "yes" during the 10 minutes of evaluation. Time was evaluated with a stopwatch and recorded in a table for further statistical analysis.
Data normality was evaluated by Shapiro-Wilk test. Then, statistical analysis was performed with presentation of accommodation threshold data in mean and standard deviation with inferential analysis by ANOVA for repetitive measures and Bonferroni post-test. Data on number of accommodations in 10 minutes were presented as median and 1st and 3rd quartiles, using Friedman test for comparison and Dunn's post-test. Significance level for all cases was 5%.
There has been no significant difference in results of all ΔF delivery ramps for accommodation threshold. But for the total of observed accommodations there has been significant difference when comparing ramp 1:5:1 to ramp 6:6 with the latter with the highest number of accommodations (p < 0.05) (Table 1).
Electrical stimulation is widely used worldwide5 since decreased pain improves functionality and quality of life12. Interferential current is effective to treat painful conditions13 and may also be applied to other clinical conditions, such as edema reduction, tissue remodeling, bone healing, treatment or urinary incontinence2 and primary dysmenorrhea 14.
Our study aimed at analyzing ΔF delivery ramp in interferential currents since the literature is extremely poor in this regard, because even querying databases as Pubmed, Scielo and academic Google, no other studies addressing such subject were found. So, we tried to be based on indications of user manuals of electrotherapy equipment where it is mentioned that the ramp 6:6 is never "still", as it is the case with the others (1:1 and 1:5:1). It is continuously varying, that is, in the first six seconds it increases surpassing all frequencies within the chosen extension until it reaches the highest frequency, and immediately decreases in the next six seconds. This is automatically repeated. From the three types of ramps, this is the most agreeable, being a frequently used way to prevent accommodation.
However, one should take into consideration that ΔF delivery way may interfere little on accommodation because AMF may not be important for the stimulation effect, that is, baseline frequency variation may be very small as compared to AMF frequency15. In our study, baseline frequency variation was 4050 Hz to 4075 Hz and AMF variation was 100 to 150 Hz. So, regardless of the chosen delivery way, results have pointed to equal accommodation thresholds, and number of accommodations slightly worse for 6:6 as compared to 1:5:1. This may be occurred because its variation is that of the slowest delivery, however it is controversial whether AMF works or not, since some authors15,16 mention that AMF does not seem to influence mechanical pain sensitivity in healthy individuals, being unlikely that it would cause a hypoalgesic clinical or physiological effect. A study5 advocates that modulated current is more comfortable than the current without modulation. It also reports that bipolar current has better effects, with deeper action than the tetrapolar current, thus justifying the use of the bipolar current, as it was the case in this study. It is worth stressing that for low frequency stimulation modalities without devices such as ΔF delivery ramp, it is indicated that current intensity should always be high17 even if amplitude has to be increased for such11.
This study was carried out with healthy individuals because the objective was to evaluate the number of accommodations and not its therapeutic goals. For being a crossover study, there has been a plan with 3 sub-groups randomly chosen where all volunteers received the current for 3 consecutive days and the 3 types of ramps, thus working as their own control during comparisons.
In the clinical practice, interferential current therapy is a commonly used modality by physical therapists, even without many scientific evidences confirming the adequate parameters for the use of such modality. There are few studies on the subject showing that there is no scientific standardization about application ways and parameters of ΔF delivery ramps, about accommodation thresholds and numbers. So, such facts such foster new studies with further methodological rigor addressing this subject.
Analysis of results has shown that ΔF delivery ramp has not influenced accommodation threshold and that ramp 1:5:1 had the lowest number of accommodations as compared to ramp 6:6, thus with a slightly better result.
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Correspondence to: Submitted in November 17, 2011. * Received from the Laboratory of Injuries and Physical Therapy Resources, State University of Western Paraná (UNIOESTE). Cascavel, PR.
Gladson Ricardo Flor Bertolini
Rua Universitária, 2069 Jardim Universitário
Colegiado de Fisioterapia, CCBS, Campus Cascavel da UNIOESTE
85819-110 Cascavel, PR.
Accepted for publication in February 27, 2012.
Submitted in November 17, 2011.
* Received from the Laboratory of Injuries and Physical Therapy Resources, State University of Western Paraná (UNIOESTE). Cascavel, PR.