Influence of high voltage pulsed direct current on edema formation following impact injury.

Edema results in pain and may lead to reduced functional mobility High voltage pulsed direct current (HVPC) has recently been advocated for edema control. The purpose of our study was to determine the effect of HVPC on edema formation in frogs Hind limbs of 20 anesthetized frogs were injured dropping a 450-g weight onto the plantar aspects of the feet. One bind limb of each frog was randomly selected to receive continuous 120-Hz HVPC at voltages 10% lower than those needed to evoke muscle contraction. Four 30-minute treatments were administered at l.5-hour intervals beginning 10 minutes after trauma. Limb volumes were measured water displacement. An analysis of variance for repeated measures and a Newman-Keuls post hoc test were used to determine the significance of treatment effects The HVPC significantly (p<.01) reduced edema formation. We hypotbesize that HVPC may also be effective in controlling edema formation after impact injuries in humans [Bettany JA Fish DR, Mendel FC: Influence of high voltage pulsed direct current on edema formation following impact injury. Phys Ther 70219-224, 1990] Key Words: Edema; Electrotherapy, electrical stimulation; Wounds and injuries. Edema results in pain and may also lead to prolonged immobilization of the injured body part. indeed, reduced functional mobility and fibrosis are recognized as secondary complications associated with unchecked edema.1,2 Therefore, minimization of edema is a common treatment goal in physical therapy. The application of high voltage pulsed direct current (HVPC) has recently been advocated as a means of controlling edema and as a means of controlling joint effusion,3,4 but the effectiveness of HVPC for achieving these clinical goals has not vet been established. Reed investigated the effect of HVPC on permeability of microvessels to plasma proteins by administering histamine, a substance known to increase capillary permeability, to hamster cheek pouches and treating some with HVPC at different voltages., Histamine increased the number of sites at which fluorescein-labeled dextran was seen to escape from the capillary bed, but the number of leaks was significantly lower in animals that also received HVPC at 30 and 50 V. Because increased permeability of capillary membranes is a primary mode of edema formation following trauma,6,7 Reed's demonstration that HVPC may reduce this permeability5 pointed to the need for a study that would directly test the effect of HVPC on posttraumatic edema formation. Impact injuries are common in humans, but naturally occurring injuries vary in severity and anatomical location. This variability makes it difficult or impossible to precisely determine treatment effects in clinical situations. Studies of the effects of HVPC on edema in humans require large sample sizes to reduce the confounding influences of variability in such factors as severity of injury, site of injury, and time elapsed from injury to initiation of treatment. To minimize or avoid such research design problems, rats have been used extensively to test the effectiveness of various treatments, especially those involving anti-inflammatory medications, on posttraumatic swelling.8 In most such studies, rat paws are injured after administration of anesthesia and limb volumes are determined repeatedly by plethysmography (ie, immersion of limb and measurement of displaced water).9 Mohr et al recognized the desirability of the rat paw model and used it to study the effect of HVPC on edema reduction.10 Unfortunately, however, their results are difficult to interpret because free movement of the animals between measurements probably influenced limb volume changes. To permit monitoring of edema formation uncomplicated by stress or movement, it is desirable to anesthetize animals for up to 24 hours. Unfortunately, however, rats and other small mammals do not tolerate prolonged anesthesia. Relatively high metabolic rates in small mammals preclude prolonged anesthesia without intravenous feeding; heat and water loss are also difficult to counteract without tampering directly with the vascular system. Such interference may well affect activities at the capillary level. We therefore selected bullfrogs (Rana catesbeiana) as the experimental model in this study. These animals can be anesthetized, and thus rendered immobile, for an entire day without interdicting their vascular system. The purpose of our study was to measure the effect of HVPC on edema formation following impact injuries. Our null hypothesis was that posttraumatic limb volume increases would not be influenced significantly by administration of HVPC. Method Subjects Twenty bullfrogs, weighing 250 to 650 g X- = 450 g), were used in this study. The method of anesthesia and handling procedures, including mode of traumatizing hind limbs, were approved by the Institutional Laboratory Animal Care Committee of the State University of New York at Buffalo. instrumentation Trauma was induced by a procedure patterned after the technique described by Suckert.11 This procedure consisted of dropping a steel rod weighing 450 g through a vertical tube from a height of 1.1 m. A rectangular piece of wood (4 x 2.5 x 0.3 cm) was placed between a hind limb and the tube to distribute force of impact and prevent rupture of skin at the plantar aspect of the foot. A small-volume plethysmograph, modified after the device described by Singh and Mourya,9 was constructed. It consisted of an immersion vessel connected by a rubber tube to an overflow chamber Fig. 1). Water that spilled from the overflow chamber was collected in a small beaker. Glass components of the plethysmograph were silanized to minimize friction, thereby improving reliability of water-displacement measurements. Reliability was assessed by weighing water displaced following immersion of lead weights of two different sizes, singly and in combination. Ten repeated measurements were made for four different combinations of weights. The mean coefficient of variation was 0.0355% when data were expressed to the nearest milligram. Animals were suspended in a sling that was lowered by a pulley mechanism until the hind limb to be measured was submerged to the knee joint line. Immersion caused a volume of water equivalent to the limb volume to be displaced into the beaker. Displaced water was weighed on a micro-balance.* Each gram of water represented a volume of 1 mL. The HVPC treatments were administered by an immersion technique using an Intelect (registered trademark) 500S stimulator (trademark) that delivered a continuous train of twin negative pulses (75 usec duration) at 120 Hz. A seff-adhering carbon rubber electrode* (25 x 76 mm) was applied to the skin overlying the frog's hip (ie, as proximal as possible at the posterior aspect of the thigh); two similar electrodes were placed opposite one another on the inside walls of the beaker. Procedure Each animal was anesthetized by immersion in a solution of 3aminobenzoic acid ethyl ester (MS222), which was prepared by adding 3 g of anesthetic to 1 L of water. Anesthesia was maintained throughout the experimental procedure by placing the animals in towels moistened with the solution. joint lines of both knees were marked with quick-drying paint prior to plethysmography. Each hind limb was then traumatized by dropping a 450-g weight onto the plantar aspects of the feet immediately distal to the malleoli. Volume measurements were repeated immediately after injury. For each animal, one hind limb was randomly selected to receive HVPC treatments; the opposite limb served as a control. A series of four 30minute treatments was administered, with the first treatment beginning 10 minutes after trauma. Between each treatment, the frog was positioned prone for a one-hour rest period. During treatment periods, both hind limbs were immersed in tap water to premarked lines (in separate vessels), but only one limb was stimulated. Treatment intensity was established by slowly increasing voltage until a minimal muscle contraction (typically associated with minimal hip and knee flexion) was observed, then reducing the voltage level by 10%. Limb volumes were measured before and after trauma, before and after each of the four treatments, and at 8 and 17 hours posttrauma. Data were expressed as changes from pretrauma hind-limb volumes (in milliliters) per kilogram of body weight. All data were collected by a rater (JAB) ignorant of treatment assignment. Skin incisions at the ankle and foot were made just before sacrifice in a random sample (25%) of animals to confirm that volume changes were attributable to edema formation and not frank bleeding. Data Analysis The hypothesis that limb volumes would increase less in treated limbs than in untreated limbs was tested by a one-way analysis of variance (ANOVA) for repeated measures. Differences were accepted as significant at the .05 level. The sources of differences disclosed by the one-way ANOVA were probed by a NewmanKeuls multiple-comparison post hoch test for which a more stringent alpha level (p < .01) was required.12 To test the hypothesis that treatment effects would be achieved only during the administration of HVPC, we used Student's paired t tests to assess differences (p < .05) between treated and untreated limb volume changes during and between treatment periods. Finally, differences among mean voltages applied during the four treatments were assessed by one-way ANOVA and Scheffe post hoc tests. These differences were accepted as significant at the .05 level. Results High voltage pulsed direct current significantly reduced edema formation in treated limbs as compared with untreated limbs (Tab. 1, Fig. 2). The Scheffe post hoc analysis revealed that volumes of treated limbs were significantly less (p < .01) than volumes of untreated limbs from the end of the first treatment to the last volume measurement at 17 hours posttrauma. Table 2 shows that mean volumes of treated limbs did not increase significantly during HVPC administration, but did increase significantly- between treatments. Mean volumes of untreated limbs increased significantly during time intervals corresponding to treatment and rest periods (Tab. 2). We observed that the voltages necessary to evoke muscle contraction increased significantly throughout the treatment series Fig. 3). Discussion High voltage pulsed direct current reduced edema formation following impact injury in frogs. This finding is noteworthy in that, to our knowledge, it represents the first scientific evidence supporting the use of HVPC for controlling limb volume increases following trauma. Reed showed that HVPC reduces capillary permeability to fluorescein-labeled dextran after topical application of histamine at hamster cheek pouches.5 His demonstration of that effect suggests that HVPC may modulate edema at the capillary membrane level. Furthermore, Reed's study suggests the utility of HVPC for controlling mammalian edema.5 Mohr et al attempted to measure the effect of HVPC on posttraumatic edema in rat paws.10 In that study, each rat was anesthetized before a 50-g mass was dropped from a height of 50 cm onto the dorsal aspect of the right hindpaw. Paw volume measurements were made before trauma, both before and after each of three HVPC treatments (applied at 24, 48, and 72 hours posttrauma), and at 96 hours posttrauma. Mean paw volumes of animals in the treatment and control groups increased significantly during the first 24 hours after trauma, then decreased over the remaining three days of data collection. No significant differences were observed between the HVPC and control groups. The authors concluded that their results suggest the "lack of effectiveness of electrical stimulation in the treatment of edema."10(p1706) We believe that such a conclusion may be unwarranted because there is another equally plausible explanation for their results. Animals were permitted to move freely at all times except while their paws were traumatized and treated. Thus, uncontrolled use of injured hind limbs, including voluntary muscle contractions that would presumably trigger lymphatic pressure changes (ie, the "muscle-pumping effect"), was possible at all times other than during the trauma procedure and the three 20-minute treatment periods. Such movements might superimpose considerable edema reduction effects on measured paw volumes, obscuring any treatment effects attributable to HVPC. That is, it is possible that three 20minute treatments may have been insufficient to result in measurable limb volume changes under those circumstances, even if HVPC were effective. Our results suggest that HVPC may be effective only during actual treatment; that is, the mechanism(s) of action seem to be short-lived. Analysis of limb volume changes that occurred during treatments as opposed to between treatments revealed the transient nature of HVPC effects. Treated limb volumes did not increase during HVPC administration but did increase during rest periods between HVPC applications. We believe this finding may have important clinical implications. If similar results are found in patient populations, then the length and number of treatments that are given may be directly related to desired treatment outcomes. Twenty-minute treatments applied once each day, however, may not be sufficient to produce measurable benefits.10 More aggressive application of HVPC may yield significant results. We anticipated that limb volumes would increase between treatments, but we could not predict the extent of the increase. Indeed, we were concerned that during rest periods, the rate of edema formation at treated limbs might be greater than that of control limbs, thereby reducing or eliminating overall treatment effects. That concern was not fully warranted. As shown in Figure 2, treated limb volumes remained significantly lower than untreated limb volumes throughout data collection, despite the influence of considerable rest times between treatments and after the treatment series. Table 2, however, shows that during rest intervals, mean volumes of treated limbs increased nearly twice as much as those of untreated limbs (1.67 mL kg-' vs 0.85 mL kg- 1). This observation suggests the desirability of aggressive application of HVPC or the use of alternative interventions such as ice, elevation, or compression during intervals between HVPC treatments. Our observation that voltages necessary to evoke muscle contractions increased during the course of data collection may also have clinical implications. As total edema increased, required voltages also increased. Clinicians should not infer from this finding that a cause-effect relationship exists between the amount of edema and the voltage needed to evoke muscle contraction because other factors such as depth of anesthesia might also have accounted for the increase in voltages that we applied over the course of the treatment series. Nevertheless, we believe that applying voltages based on physiologic responses to HVPC, such as observable muscle contraction, is advisable both in the research laboratory and in the clinic. The efficacy of this approach may especially be true in clinical settings in which electrode positions and skin preparation may vary from one treatment to another. The mechanism(s) by which treatment effects occur are unknown. Previous authors have suggested several possible mechanisms by which various forms of HVPC may influence edema. Such possibilities include reduction in capillary permeability to plasma proteins and reduction in capillary pressures within the traumatized area5 and the influence of polarity and activation of skeletal muscle.2,13 The mechanism(s) by which Reed achieved a reduction in capillary membrane leakiness by application of HVPC are unknown, but this effect can likely be explained by charge repulsion, lymphatic activity, or alterations in blood flow.5 Reed suggested that decreased microvessel pore size may account for the decreased leakiness of capillary membranes to fluorescein-labeled dextran.5 Whether HVPC affects blood flow when applied at voltages lower than those needed to evoke muscle contractions remains to be determined. High voltage pulsed direct current may influence blood flow, but its effects are dependent on intensity, frequency, and site of stimulation. Mohr et al reported significant increases in femoral artery blood flow during and after HVPC stimulation of anesthetized rats.14 Stimuli were applied to hind limbs at intensities ranging from 20 to 200 V. As intensity of HVPC increased to a level sufficient to evoke muscle contraction, hind-limb blood flow increased significantly. Such results are in keeping with the fact that muscle contractions, whether voluntary or electrically induced, increase intramuscular metabolic demand and local blood flow. Hecker et al applied HVPC to upper limbs of humans at frequencies of 2, 8, 32, 64, and 128 Hz with both cathodal and anodal stimulation.15 They found no significant changes in blood flow at ipsilateral fingertips, perhaps because intensities of stimulation were lower than those needed to elicit muscle contractions. Reed noted no alterations in microvessel blood flow when applying HVPC to hamster cheek pouches., However, he viewed blood vessels at low power (25 X) and did not quantitatively measure blood flow. We did not measure blood flow either, but because voltages were set at 10% less than those needed to evoke muscle contraction, it seems unlikely that HVPC increased muscle blood flow in the frogs in our study. The influence of polarity on the effectiveness of HVPC in reducing edema formation is not yet known. Numerous authors, however, have advocated the use of negative polarity when HVPC is applied for that purpose.13,16-11, Depolarization of nerve and muscle membranes is typically accomplished more readily by cathodal than anodal stimulation.19 Therefore, at any given voltage, greater neurophysiologic responses are expected with cathodal stimulation. Use of negative polarity has also been suggested for the purpose of driving negative proteins from interstitial spaces into lymphatic channels.2,13 Only cathodal stimulation was applied in our study, so no conclusion relative to polarity effects can be made at this time. Studies that test the influence of polarity of HVPC on edema formation are needed. Electrical stimulation of skeletal muscle may induce contractions that result in compression of venous and lymphatic vessels. Repetitive contractions presumably induce increased venous and lymphatic return, which may reduce edema. Crisler reported edema reduction following application of surged electrical stimulation that induced repetitive muscle contractions.20 Such results are in accord with empirical evidence that muscle contractions, either voluntary or electrically induced, help to reduce edema. The method of stimulation that we used (ie, a 120-Hz continuous pulse train at voltages 10% below those needed to evoke visible muscle contraction), however, probably would not result in substantial muscle-pumping action. The clinical implications of our study must be tempered by the recognition that responses to trauma and HVPC treatment may differ between frogs and humans. In our study, an amphibian model was selected because anesthesia and immobilization could readily be achieved throughout the period of acute edema formation. Frogs differ from mammals, including humans, however, in several potentially important ways. Frogs are poikilothermic (ie, "cold-blooded") and also possess considerably more range of motion at the ankle-joint complex than do humans. Nevertheless, we believe that the results of this study are reflective of responses that might be found in a wide range of vertebrates. The fact that frogs are poikilothermic should not have played a substantial part in the responses that we measured because the animals were maintained at room temperature throughout data collection and the research design permitted statistical comparisons to contralateral control limbs, which were handled in precisely the same manner as treated limbs except for application of electrical stimuli. The great range of plantar flexion that is typically available at the ankles of frogs should not have been a factor in this study because the mode of injury involved impact at the plantar aspects of the feet (ie, distal to the ankle joint). Thus, we believe that it is reasonable to formulate hypotheses regarding human responses to HVPC based on our findings. We hypothesize that HVPC may be effective in minimizing edema formation after impact injury in humans. We further hypothesize that the mechanism(s) of action of HVPC may be short-lived. If subsequent studies support these hypotheses, then aggressive application of HVPC will be documented as effective in minimizing edema formation. Such edema control would presumably be beneficial to patients by reducing pain and enhancing function. Our future research will address responses to HVPC in mammals, including humans, and explore the influences of various treatment variables. Conclusions 1. High voltage pulsed direct current

applied by the immersion method

using continuous cathodal stimulation

at 120 Hz reduces the formation

of edema following impact

injuries in frogs. 2. High voltage pulsed direct current,

as applied in this study, reduces

edema formation only during the

administration of treatment. Acknowledgments We thank Dr Harold Burton for review and critical comments; Terry Whieldon, MS, PT, for technical advice; Linda Yerke, PT, and Laurence Bettany for technical assistance; john Nyquist for illustration; and Chattanooga Corporation for the complimentary loan of stimulators. References 1 Zarro VJ: Mechanisms of inflammation and repair. In Michlovitz SL (ed): Thermal Agents in Rehabilitation. Philadelphia, PA, F A Davis Co, 1986, pp 3-17 2 Newton RA: High voltage pulsed galvanic stimulation: Theoretical bases and clinical applications. In Nelson RM, Currier DP (eds): Clinical Electrotherapy. East Norwalk, CT, Appleton & Lange, 1987, pp 165-182 3 Voight ML: Reduction of posttraumatic ankle edema with high voltage pulsed galvanic stimulation. Athletic Training, Winter 1984, pp 278, 279, 311 4 Smith W: The application of cold arid heat in the treatment of athletic injuries. In Michlovitz SL (ed): Thermal Agents in Rehabilitation. Philadelphia, PA, F A Davis Co, 1986, pp 264 265 5 Reed BV: Effect of high voltage pulsed electrical stimulation on microvascular permeability to plasma proteins: A possible mechanism in minimizing edema. Phys Ther 68:491-495, 1988 6 Majno G: Mechanisms of abnormal permeability in inflammation. in Lewis T (ed): injury, Inflammation and Immunity. New York, NY, Pergamon Press Inc, 1964 7 Cotran RS, Majno G: A light and electron microscopic analysis of vascular injury. Ann NY Acad Sci 116:750-764, 1964 8 Riesterer L, Jacques R: The influence of anti-inflammatorv drugs on the development of an experimental traumatic paw oedema in the rat. Pharmacology 3:243-251, 1970 9 Singh RH, Mourya SP: Development and standardization of a new apparatus for accurate measurement of swelling in paw of small laboratory animals. Indian J Med Res 60:488490, 1972 10 Mohr TM, Akers TK, Landry RG: Effect of high voltage stimulation on edema reduction in the rat hind limb. Phys Ther 67:1703-1707, 1987 11 Suckert VR: Experimental models for traumatic edema in rat paws. Medicina et Pharmacologia Experimentalis 17:43-50, 1967 12 Kirk R: Experimental Design: Procedures for the Behavioral Sciences. Belmont, CA, Brooks/Cole Publishing Co, 1968, pp 91-93, 531 13 Alon G: High Voltage Stimulation. Chattanooga, TN, Chattanooga Corp, 1984 14 Mohr TM, Akers TK, Wessman HC: Effect of high voltage stimulation on blood flow in the rat hind limb. Phys Ther 67:526-533, 1987 15 Hecker B, Carron H, Schwartz DP: Effects of current frequency and polarity, on blood flow in healthy subjects. Arch Phys Med Rehabil 66:369-371, 1985 16 Newton RA: Electrotherapeutic Treatment: Selecting Appropriate Waveform Characteristics. Clifton, NJ, J A Preston Corp, 1984 17 Sawyer PN, Pate JW: Bioelectrical phenomena as etiological factors in intravascular thrombosis. Surgery 34:491 500, 1953 18 Burr HS, Taffel M, Harvey SC: An electrometric study of the healing wound in man. Yale J Biol Med 12:483-485, 1940 19 Cook TM: Principles of electrical stimulation. In Nelson RM, Currier DP (eds): Clinical Electrotherapy. East Norwalk, CT, Appleton & Lange, 1987, p 21 20 Crisler GR: Sprains and strains treated with the Ultrafaradic M-4 impulse generator. J Fla Med Assoc 40(l):32-34, 1953