Electrical Engineering Advice · Voltage Suppose that our power source is a 5- volt battery with a maximum current flow of 1 ampere. Clearly Ohms Law provides the relationship between voltage, current, and resistance. In a series circuit. A driving force (voltage); some material which will conduct the electricity Muscle depolarization is difficult to achieve with physical therapy modalities; Nerve Greater the cross-sectional area of a path the less resistance to current flow If you know the inter-relationship you can understand if one increased what happens. Electric power basic formulas calculator voltage current mathematical equation formula for power law watts resistance understanding.
We hypothesized that better analgesia would occur if electrodes were placed over sites with lower skin impedance. Optimal site selection OSS and sham site selection SSS electrode sites on the forearm were identified using a standard clinical technique.
Healthy volunteers were recruited ten for Experiment 1 [five male, five female] and 24 for Experiment 2 [12 male, 12 female]. Results Experiment 1 results demonstrate significantly higher impedance at SSS Conclusion Skin impedance is lower at sites characterized as optimal using the described technique of electrode site selection.
When TENS is applied at adequate intensities, skin impedance is not a factor in attainment of hypoalgesia of the forearm in healthy subjects. Further investigation should include testing in patients presenting with painful conditions.
However, there is conflicting literature on the effectiveness of TENS. Negative findings in TENS reviews may be explained by low fidelity, with bias in treatment outcome measures and suboptimal dosing.
Textbooks describe multiple methods of electrode placement and include segmental, peripheral, or contralateral site placement. Using this technique, the therapist detects points of decreased impedance — these points are associated with peripheral nerve anatomy and acupuncture points. Clinically, application of TENS at acupoint sites considered low resistance sites reduces pain and may be more effective than when applied over nonacupoint sites.
More importantly, TENS at acupoint sites has been shown to be associated with reduced opioid intake, nausea, and dizziness when compared to TENS at nonacupoint sites in postoperative hysterectomy patients. Acupoints are thought to be sites with lower skin impedance. The purpose of these experiments was to 1 determine if points of least resistance, determined with a common clinical technique, showed lower impedance and 2 determine if electrodes placed over points of least resistance OSS showed greater analgesia than electrodes placed over sham sites SSS, sham site selection.
We therefore performed two experiments. We further confirmed that selection sites had lower impedance and examined if active TENS produced its effects with lower intensity and more comfort when electrodes were placed over OSS. The first experiment evaluated skin impedance over eight sites in the forearm in healthy controls, characterized as either OSS or SSS during a single visit.
Subjects completed three visits, receiving a different allocation each visit. Outcome measurements were taken before and during a single TENS treatment.
Electrical impedance behavior of biological tissues during transcutaneous electrical stimulation
While comparing the impedance values obtained during LF and MF stimulation, at the same corporal segment, surface and inter-electrodes distance, the values were lower with MF for all variables, except at 30 cm of the LL-A. Correlation between the electrical impedance values and the inter-electrode distance was positive in the UL-A 0.
In Table 2it can be observed that the influence of the distance between the electrode over the impedance value was of Furthermore, the linear regression equation is presented, considering the segments and frequencies analyzed. The ratio between the impedance values during low and medium frequencies stimulation has lowered at 40 cm when compared to 10 cm in all regions, except T-P; at 30 cm in relation to the 10 cm in UL-A and LL-A and to the 40 cm compared to 20 cm in UL-A, as observed in Table 3.
For such, at the present study, no skin treatment with the objective to remove partially the corneous strata at the electrodes fixation locals was made If this layer were removed there would be an impedance decrease, facilitating the electrical current's passage Environmental temperature and air relative humidity were controlled during procedure, once temperature increase leads to a decrease of Keratin's hydration level, resulting in an increase of the cutaneous impedance Considering the behavior of the biological tissues' impedance during transcutaneous electrical stimulation, it can be observed a lack of publication on the subject.
Despite the assumption regarding the proportional relationship between the inter-electrodes distance and the biological tissues' impedance, no work, presenting quantitative data, was found. According to the results of this study, the relationship between the tissue's electrical impedance increase with the electrodes distancing, is true only for the upper and lower limbs. In some locations, next to the patella or at the shoulder there was no significant difference between the impedance values with the distance increase, and this behavior may be related to the positioning of the electrode over anatomical structures with differences in fluid quantity16, with corneous strata thickness10 or with electrical field distribution9.
In this context, it can be considered that the joint capsule and bursas under the electrodes have contributed for impedance reduction because of the presence of sinovial liquid.
In the trunk location, there was no correlation between electrical impedance and distance increase. The distinctive behavior of the trunk, when compared to the limbs, was reported by Zhu, Schditz and Levin8, that observed impedance decrease with the increase of distance between the electrode and current application point during analyses of bioelectrical impedance in this segment.
One explanation for such event is the presence of a higher levels of hydration on the posterior trunk area when compared to the limbs, although there are no differences regarding the number of corneocyte layers According to the authors, the inversely proportional relationship between the number of corneous strata layers and water concentration is not valid for this surface of the trunk, since it was observed higher levels of hydration than in other less thick areas, such as cheeks, indicating the contribution of physical-chemical properties and factors such as sebaceous and sudoriparous secretion affecting the local humidity.
The lowest impedance values found at the posterior surface of the trunk in relation to the limbs, considering the same surface, distance and frequency, may be related to the electrical field formed due to geometrical differences between them.
Skin impedance is not a factor in transcutaneous electrical nerve stimulation effectiveness
Researchers17 analyzing body composition by segmented bioelectrical impedance, have verified that there is a lesser contribution of the trunk in comparison with the limbs in the body's total impedance. This could be explained by the fact that the impedance of a homogeneous conductive material is proportional to its length and inversely proportional to its transverse area4.
However, the presence of heterogeneous, anisotropic, and frequency-dependent features, in the skin and subcutaneous tissues, makes it difficult the employment of simplified physical models to determine its behavior19 and the current's real distribution13 via electrical stimulation. This difficulty is demonstrated by the linear regression equations, which are specific for the application location and the current frequency.
It is worth noting that for the posterior surface of the trunk, the equations are not representative and it was not possible to characterize linearity. Similar electrical impedance values in the anterior and posterior surfaces of the limbs may be related to the fact that there is no difference in the thickness and in water concentration of the corneous strata of ventral and dorsal surfaces Regarding stimulation with medium frequency current, lower electrical impedance was determined in all analyzed variables, except at 30 cm of the LL-A.
Since the skin acts as a capacitive barrier, it is considered that its impedance is inversely proportional to the frequency of the alternate current13, and its governed by the expression: Despite the fact that the electrical impedance behavior, during LF and MF stimulation, agrees with the literature16, the relationship between the obtained values is not equal to what has been postulated.
In addition, the lower influence of frequency with the increase of the inter-electrodes distance indicates a gradual reduction of the contribution of capacitive agents in the total impedance. This fact reinforces the model of skin and muscle impedance proposed by Reilly20, who proposed biological tissues as a complex circuit formed by resistors and capacitors disposed both in series and parallel.
The understanding created about the medium frequency currents behavior on the biological tissues may be consequence of a badly conducted interpretation of theoretical models. Alon12 contests the relation between skin impedance and the electrical current frequency, attributing its alterations to the phase's duration.
Thus, the author reports that any mono or biphasic wave will suffer the same impedance of the interferential current if the duration of their phases is the same. Contrary to such affirmative, the results from the present study demonstrate the influence of frequency on the electrical flux opposition, once distinct impedance values were obtained while applying currents with the same phase duration. These contrasting results reassert the necessity of more knowledge about the interaction of the currents produced by the equipments available on market with the biological tissues.
Studies about skin impedance, during utilization of therapeutic equipments, among them electrical current generators, are of interest for both manufacturers and users.
Stimulators should allow the use of an electric tension large enough to conduct a current that overcomes the conducting medium's impedance. On the other hand, the professional should consider the inter-electrodes impedance so that, by selecting the current's parameters, an efficient stimulation of the nerve and muscle might be done with less discomfort11 and no risk to the patient. In this context, results generalization should be limited, since the biological tissues' electrical impedance may vary with gender, due to the differences in variables not analyzed in the present study such as body composition, age, and specially cutaneous hydration.
In general, there was a positive correlation between the inter-electrodes distance and impedance both for low and medium frequency currents, when applied in both surfaces of the upper and lower limbs. This behavior was not observed in the posterior surface of the trunk. It was noticed a non-uniformity of the electrical impedance in the different segments and surfaces, characterizing tissue anisotropy. In addition, it was observed lower impedance for the medium frequency current because of the skin's capacitive components, despite the fact that this influence decreases with the distance between the electrodes.
Electrical stimulation in the treatment of pain. Safety of a combined strength and endurance training using neuromuscular electrical stimulation of thigh muscles in patients with heart failure and bipolar sensing cardiac pacemakers.
Functional electrical stimulation for a dropped foot. Bioelectrical impedance analysis - part I: Conductive differences in electrodes used with transcutaneous electrical nerve stimulation devices.
Three-dimensional current density distribuition under surface stimulation electrodes.
Med Biol Eng Comp. Estimation of trunk extracellular volume by bioimpedance. Skin appendageal macropores as a possible pathway for electrical current. J Investig Dermatol Symp Proc. A model for human skin impedance during surface functional neuromuscular stimulation.