• View in gallery

    Photograph of a force-measuring device being applied to the skin between the heel bulbs of a forefoot of a horse to measure the MNT (skin sensation) at that location before and at predetermined times for 2 hours after administration of a PDNB.

  • View in gallery

    Median percentage decrease in the vector sum from baseline (0 minutes; A) and median peak MNT (B) for 6 adult American Quarter Horse geldings with naturally occurring lameness localized to a forefoot at predetermined times after administration of a PDNB with 2% lidocaine (solid line), 1% lidocaine (dashed line), and 1% lidocaine + epinephrine (dotted line). Each horse received each treatment with a 3-day interval between treatments. One horse would not tolerate measurement of the MNT; thus, only 5 horses contributed to the median MNT at all time points for all 3 treatments.

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Effect of the addition of epinephrine to a lidocaine solution on the efficacy and duration of palmar digital nerve blocks in horses with naturally occurring forefoot lameness

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  • 1 Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, AL 36849.
  • | 2 Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, AL 36849.
  • | 3 Department of Agriculture, Ogden College of Science and Engineering, Western Kentucky University, Bowling Green, KY 42101.

Abstract

OBJECTIVE To determine whether addition of epinephrine to a lidocaine solution would prolong and potentiate the efficacy of a palmar digital nerve block (PDNB) in horses.

ANIMALS 6 adult horses with naturally occurring forefoot lameness.

PROCEDURES Initially, a PDNB with a 2% lidocaine solution was performed on the affected foot of each horse. Three days later, the PDNB was repeated with a 1% lidocaine solution or a 1% lidocaine solution containing epinephrine (dilution, 1:200,000). After another 3-day washout period, the PDNB was repeated with the treatment opposite that administered for the second PDNB. Gait was analyzed with a computerized lameness analysis system and heart rate and extent of skin sensation between the heel bulbs of the blocked foot were evaluated at predetermined times for 2 hours after each PDNB.

RESULTS Efficacy and duration of the PDNB did not differ significantly between the 2% and 1% lidocaine treatments. The addition of epinephrine to the 1% lidocaine solution improved the efficacy and prolonged the duration of the PDNB. It also resulted in a positive correlation between skin desensitization and amelioration of lameness. Median heart rate remained unchanged throughout the observation period for all 3 treatments. No adverse effects associated with the PDNBs were observed.

CONCLUSIONS AND CLINICAL RELEVANCE Addition of epinephrine (dilution, 1:200,000) to a 1% lidocaine solution improved the efficacy and prolonged the duration of a PDNB in horses with naturally occurring lameness and might be clinically useful for lameness evaluations and standing surgery of the forefoot of horses.

Abstract

OBJECTIVE To determine whether addition of epinephrine to a lidocaine solution would prolong and potentiate the efficacy of a palmar digital nerve block (PDNB) in horses.

ANIMALS 6 adult horses with naturally occurring forefoot lameness.

PROCEDURES Initially, a PDNB with a 2% lidocaine solution was performed on the affected foot of each horse. Three days later, the PDNB was repeated with a 1% lidocaine solution or a 1% lidocaine solution containing epinephrine (dilution, 1:200,000). After another 3-day washout period, the PDNB was repeated with the treatment opposite that administered for the second PDNB. Gait was analyzed with a computerized lameness analysis system and heart rate and extent of skin sensation between the heel bulbs of the blocked foot were evaluated at predetermined times for 2 hours after each PDNB.

RESULTS Efficacy and duration of the PDNB did not differ significantly between the 2% and 1% lidocaine treatments. The addition of epinephrine to the 1% lidocaine solution improved the efficacy and prolonged the duration of the PDNB. It also resulted in a positive correlation between skin desensitization and amelioration of lameness. Median heart rate remained unchanged throughout the observation period for all 3 treatments. No adverse effects associated with the PDNBs were observed.

CONCLUSIONS AND CLINICAL RELEVANCE Addition of epinephrine (dilution, 1:200,000) to a 1% lidocaine solution improved the efficacy and prolonged the duration of a PDNB in horses with naturally occurring lameness and might be clinically useful for lameness evaluations and standing surgery of the forefoot of horses.

Diagnostic anesthesia is an essential part of most lameness examinations for horses, but interpretation of diagnostic anesthesia is often confusing when a nerve block results in only amelioration rather than resolution of lameness. When that happens, clinicians must decide whether the improvement in lameness was caused by incomplete resolution of signs of pain originating from 1 site in the blocked portion of the limb or the presence of painful lesions at other sites in the unblocked portion of the limb, which necessitates further investigation. Results of recent studies1,2 suggest that poor efficacy of the local anesthetic used for a nerve block should also be considered as a cause of incomplete resolution of lameness during diagnostic anesthesia. The use of a local anesthetic that is highly efficacious for pain desensitization in a nerve block should facilitate interpretation of diagnostic anesthesia results because it would eliminate poor anesthetic potency as a possible cause of incomplete resolution of lameness. The use of local anesthetics that produce an insufficient duration of analgesia can also interfere with interpretation of diagnostic anesthesia results, especially when multiple sites of pain contribute to the lameness and multiple nerve blocks have to be serially administered. In horses, use of a local anesthetic that has a sufficient duration of analgesia is also important for desensitization of a surgical site for standing surgery.

In human medicine, it is well established that the addition of epinephrine to a local anesthetic solution prolongs the analgesic effect by counteracting the vasodilatory effects that most local anesthetics have on neural vasculature, which slows the clearance of the local anesthetic from the injection site.3–6 A notable exception is ropivacaine, which is a local anesthetic with intrinsic vasoconstrictive properties.7 Epinephrine can also intensify the analgesic effect of a nerve block.3,5,6

The purpose of the study reported here was to determine whether the addition of epinephrine to a lidocaine solution would prolong and intensify the analgesic effect of lidocaine when the combination was administered as a PDNB in horses with signs of pain isolated to a foot. Our hypothesis was that the addition of epinephrine to a lidocaine solution would prolong and intensify the analgesic effect of lidocaine.

Materials and Methods

Animals

All study procedures were reviewed and approved by the Auburn University Animal Care and Use Committee, and all study horses were part of a teaching herd maintained by Auburn University. Six adult American Quarter Horse geldings with naturally occurring lameness that was localized to a forefoot were enrolled in the study. The horses ranged in age from 10 to 22 years (mean ± SD, 11.5 ± 4.6 years) and weight from 465 to 555 kg (mean ± SD, 473 ± 34.5 kg). All horses had a visually evident consistent forelimb lameness when at a trot. A potential sequela of SC perineural administration of epinephrine is the growth of white hair at the injection site,8,9 which can be an undesirable cosmetic outcome. None of the study horses had forelimb distal limb white hairs before starting the study‥

Experimental design

The study had a crossover design. All horses received each of 3 treatments with a 3-day washout period between treatments. Initially, each horse received a PDNB with a 2% lidocaine solution.a Gait was analyzed while the horse was trotting immediately before (baseline; 0 minutes) and at 5, 10, 15, 20, 25, 30, 45, 60, 75, 90, 105, and 120 minutes after administration of the PDNB. Heart rate and reaction to application of a stimulus to the skin between the heel bulbs of the hoof of the injected forelimb (heel bulb stimulus) were also evaluated at each of those times. For continued enrollment in the study, each horse had to have at least an 80% improvement in lameness after administration of the PDNB with the 2% lidocaine solution. The 6 horses that met that criterion were randomly assigned by means of a commercial software programb to 1 of 2 groups such that each group contained 3 horses. Three days after the initial PDNB (2% lidocaine treatment), one group received a second PDNB with a 1% lidocaine solution,c whereas the other group received a PDNB with a 1% lidocaine solutionc with epinephrine. To create the 1% lidocaine + epinephrine treatment, 0.1 mL of a 1:1,000 epinephrine solutiond was added to 20 mL of the 1% lidocaine solution to create a solution with a 1:200,000 dilution (5 μg/mL) of epinephrine immediately before the PDNB. Gait analysis and evaluation of heart rate and reaction to a heel bulb stimulus were performed as described for the 2% lidocaine treatment. Three days later, the process was repeated with each group receiving the treatment opposite that received during the second PDNB.

PDNB technique

For each PDNB injection, each horse remained unsedated and was restrained in a standing position with a halter and lead rope. Following the application of a lip twitch, a PDNB was performed by the injection of 1.5 mL of the assigned treatment, SC, over the palmar digital nerve at the proximal border of the collateral cartilage of the lame forelimb with a 25-gauge, 5/8-inch (16-mm) needle. The same investigator (AVA) performed all PDNBs in all horses.

Gait analysis

Gait was analyzed with a computerized lameness analysis system.e During each gait evaluation, horses were trotted for at least 25 strides. The computerized system used inertial sensors to detect and quantify lameness by recording torso motion and calculating the mean ± SD for the MAXDIFFHEAD and MINDIFFHEAD between the left and right halves of the stride during forelimb evaluation (or the mean ± SD for the maximum and minimum differences in the height of the pelvis between the left and right halves of the stride during hind limb evaluation). Localization of the lameness to the right or left forelimb during a stride was determined by the association of head movement with the angular velocity of the right forelimb.10 The MAXDIFFHEAD and MINDIFFHEAD (in mm) between the left and right halves of each stride were generated by the device. Amplitude of the vector sum for MAXDIFFHEAD and MINDIFFHEAD correlated with the severity of lameness, with a value of approximately 6 mm generally used as the threshold to differentiate lame from nonlame limbs.11 Results of a validation study12 indicated that this inertial sensor system provided appropriate accuracy and sensitivity for clinical use.

For 5 of the 6 horses during each of the 3 treatments, the computerized system localized lameness to the limb contralateral to the one that received the PDNB. For those 5 horses, the vector sum for the PDNB-treated limb was added to the vector sum for the contralateral forelimb to determine the magnitude of lameness. For example, if the PDNB-treated limb had a vector sum of 15 mm at baseline and the contralateral limb had a vector sum of 10 mm at some time after the PDNB, the total vector sum (or magnitude of lameness) recorded was 25 mm at that time point. Fifteen minutes later, if the vector sum for the contralateral limb dropped to 5 mm, the total vector sum recorded for that time would be 20 mm, and the change from 25 to 20 mm would indicate that the effect of the PDNB was dissipating.f

Heel bulb stimulus

To assess the accuracy of each PDNB, skin sensation in the heel region of the foot of the treated limb was tested by use of a modification of a method described by Jordana et al.13 Briefly, the eye of the horse ipsilateral to the treated limb was covered to prevent a visual reaction to the investigator. Then, a 13-mm-diameter flat probe of a force-measuring deviceg was used to apply blunt pressure to the skin between the heel bulbs until the horse moved the limb (Figure 1). The pressure necessary to elicit movement of the limb (peak MNT) was recorded for each of 3 applications of the stimulus before the PDNB and before each gait analysis. For each time, the mean for the 3 applications was calculated and used for analysis. The same investigator (AVA) performed all the skin sensation measurements.

Figure 1—
Figure 1—

Photograph of a force-measuring device being applied to the skin between the heel bulbs of a forefoot of a horse to measure the MNT (skin sensation) at that location before and at predetermined times for 2 hours after administration of a PDNB.

Citation: American Journal of Veterinary Research 79, 10; 10.2460/ajvr.79.10.1028

Statistical analysis

Outcomes of interest were the percentage change in vector sum from baseline, MNT (skin sensation), and heart rate. Data were compared among the 3 treatments during 2 phases (the first 30 minutes after PDNB injection during which data were recorded every 5 minutes [phase 1] and the period from 30 to 120 minutes after PDNB injection during which data were recorded every 15 minutes [phase 2]). Data for each outcome variable were regressed over time, and residual plots were visually evaluated for normality. A logarithmic transformation was applied to the vector sum and skin sensation data to normalize those distributions for analysis. A linear mixed model was created for each outcome.14–16 Each model included fixed effects for treatment (2% lidocaine, 1% lidocaine, and 1% lidocaine + epinephrine) and time after PDNB (time) and a random effect for horse to account for repeated measures. To account for the nonindependence of observations within horses, data were modeled with 5 correlation structures (compound symmetry, first-order autoregressive, Toeplitz, unstructured, and unstructured with inhomogenous variance components), and the resulting models were compared on the basis of the Akaike information criterion.14–16 The correlation structure that yielded the lowest Akaike information criterion was used for all further modeling, and the Kenward-Roger correction was used for all models.14–16 The Tukey-Kramer method was used to prevent type I error inflation when multiple pairwise comparisons were necessary.17 Values of P ≤ 0.05 were considered significant. All analyses were performed with a commercial statistical software program.h

Results

The mean percentage decrease in vector sum from baseline did not differ significantly (P = 0.672) among the 3 treatments during phase 1 (the first 30 minutes after PDNB administration). During phase 2 (30 to 120 minutes after PDNB administration), the mean percentage decrease in vector sum from baseline did not differ significantly (P = 0.623) between the 2% lidocaine and 1% lidocaine treatments but did differ significantly (P < 0.001) between the 1% lidocaine + epinephrine treatment and both the 2% lidocaine and 1% lidocaine treatments (Figure 2). When the 1% lidocaine + epinephrine treatment was administered, 3 of the 6 horses had a 100% improvement in lameness for the duration of the 2-hour observation period. For each of the 6 horses, the percentage decrease in the vector sum from baseline was greatest for the 1% lidocaine + epinephrine treatment at all time points.

Figure 2—
Figure 2—

Median percentage decrease in the vector sum from baseline (0 minutes; A) and median peak MNT (B) for 6 adult American Quarter Horse geldings with naturally occurring lameness localized to a forefoot at predetermined times after administration of a PDNB with 2% lidocaine (solid line), 1% lidocaine (dashed line), and 1% lidocaine + epinephrine (dotted line). Each horse received each treatment with a 3-day interval between treatments. One horse would not tolerate measurement of the MNT; thus, only 5 horses contributed to the median MNT at all time points for all 3 treatments.

Citation: American Journal of Veterinary Research 79, 10; 10.2460/ajvr.79.10.1028

Skin sensation could not be tested in 1 horse because it moved the treated limb every time it was approached with the force-measuring device despite its ipsilateral eye being covered. Therefore, skin sensation data were available for only 5 horses. The MNT (skin sensation) was not correlated with the percentage decrease in the vector sum from baseline (PDNB-induced improvement in lameness) for the 2% lidocaine and 1% lidocaine treatments. In fact, the MNT did not differ from baseline at any time for horses with 100% improvement in lameness following the 2% lidocaine and 1% lidocaine treatments. For the 1% lidocaine + epinephrine treatment, MNT was positively correlated with the percentage decrease in the vector sum from baseline. During phase 1, the median peak MNT did not differ significantly (P = 0.556) between the 2% lidocaine (97 N) and the 1% lidocaine (91 N) treatments; however, the median peak MNT for the 1% lidocaine + epinephrine treatment (205 N) was significantly greater (ie, the skin was less sensitive) than that for both the 2% lidocaine (P = 0.020) and 1% lidocaine (P = 0.002) treatments (Figure 2). Likewise, during phase 2, the median peak MNT did not differ significantly (P = 0.529) between the 2% lidocaine (79 N) and the 1% lidocaine (81 N) treatments, but the median peak MNT for the 1% lidocaine + epinephrine treatment (134 N) was significantly (P = 0.004) greater than that for the 1% lidocaine treatment and was numerically, if not significantly (P = 0.052), greater than that for the 2% lidocaine treatment.

The median HR remained at 44 beats/min for the duration of the observation period for all 3 treatments. All 6 horses were evaluated 3 months after administration of the third treatment, and no skin reactions, scars, or white hairs were observed at the PDNB injection site.

Discussion

For the adult horses with naturally occurring forefoot lameness evaluated in the present study, administration of a PDNB with a combined solution of 1% lidocaine and epinephrine (dilution, 1:200,000 [5 μg/mL]) in the affected limb resulted in improved regional anesthesia of longer duration than administration of a PDNB with either a 1% or 2% lidocaine solution without epinephrine. Lidocaine is available in solutions ranging from 0.5% to 4%. To our knowledge, prior to the present study, no studies had been conducted to compare the efficacy of PDNBs performed with lidocaine solutions of different concentrations. The onset, quality, and duration of a nerve block is dependent on the dose of local anesthetic administered,18 which is calculated as the anesthetic concentration multiplied by the volume injected. Therefore, because the volume of lidocaine solution was held constant for all PDNBs administered in the present study, we anticipated that the 1% solution would be less effective than the 2% solution for ameliorating lameness. However, the extent of analgesia induced by the 2% lidocaine treatment did not differ significantly from that induced by the 1% lidocaine treatment. We also expected that the addition of epinephrine to the 1% lidocaine treatment would increase the potency of the nerve block, and it did, although it took 30 minutes for that effect to become detectable. The potency of the 3 treatments evaluated during this study did not differ during the first 30 minutes after PDNB injection. That finding differed from what was observed in human patients, for whom regional anesthesia with a 1% lidocaine solution without epinephrine was completely ineffective, whereas regional anesthesia with 1% lidocaine plus 1:100,000 epinephrine was more effective than that induced by a 4% lidocaine solution.19

In human medicine, lidocaine solutions containing epinephrine fell out of favor for digital anesthesia in the middle of the 20th century because their use was associated with skin necrosis and gangrene.20 Many veterinary textbooks8,21,22 caution that use of local anesthetic solutions containing epinephrine for regional nerve blocks in horses could cause severe swelling, skin necrosis, and growth of white hair, and some authors advised against their use.21–24 Other authors claim that local anesthetic solutions containing epinephrine at a dilution of 1:100,000 or 1:200,000 are unlikely to cause necrosis when used for regional anesthesia in horses but might result in the subsequent growth of white hair.8 A review20 of the human medical literature indicates that local anesthetics containing epinephrine at a dilution of at least 1:200,000 do not cause necrosis and are safe to use for regional anesthesia. Furthermore, local anesthetics containing epinephrine at dilutions > 1:200,000 appear to offer no advantage in terms of prolonging regional anesthesia in human patients.25,26 None of the horses of the present study had an adverse reaction, such as edema or growth of white hairs at the injection site, to SC perineural administration of the 1% lidocaine + epinephrine treatment.

Multiple studies1,2,27,28 have evaluated the duration of efficacy of various local anesthetics used for regional anesthesia in horses with varying results. Effective regional anesthesia can be achieved for 30 minutes to 3 hours with a 2% lidocaine solution, 90 minutes to 3 hours with a 2% mepivacaine solution, and 3 to 8 hours with a 0.5% bupivacaine solution.29–31 In another study,32 the affected foot of horses with naturally occurring lameness was reliably desensitized for 3 hours following administration of a PDNB with 0.75% ropivacaine. In yet another study,28 administration of lateral and medial palmar nerve blocks to horses resulted in skin desensitization distal to the blocks for 60 minutes when a 2% lidocaine solution was used, compared with > 6 hours when a 2% lidocaine solution with epinephrine was used; however, the onset of skin desensitization was similar between blocks performed with lidocaine with and without epinephrine. Conflicting opinions regarding the duration of regional anesthesia induced by various local anesthetics likely reflect the fact that the duration of induced desensitization is partially dependent on the intensity of pain present.29 In horses with experimentally induced foot pain that were instrumented with the same computerized lameness analysis system used in the present study, a PDNB with a 0.5% bupivacaine solution was more effective for amelioration of lameness than a PDNB with a 2% lidocaine solution.2

Mepivacaine is a commonly used local anesthetic in horses because it causes less tissue reaction and has a longer duration of effect than other local anesthetics.9,33 We chose to use lidocaine in the present study because it causes greater perineural vasodilation than most other local anesthetics, including mepivacaine and bupivacaine; therefore, it seemed likely that the ability of a peripheral vasoconstrictor such as epinephrine to prolong and potentiate the effects of a local anesthetic would be more readily evident when used in conjunction with lidocaine than with other local anesthetics.3

The mechanism by which epinephrine potentiates a nerve block is poorly understood but 1 possible mechanism is its α1-adrenoceptor–mediated vasoconstrictive effects that antagonize the inherent vasodilatory effects of most local anesthetics, which in turn decreases the clearance rate of the local anesthetic, thereby increasing the amount of the drug available for neuronal blocking.3,34 Alternatively, epinephrine may alter the distribution of the local anesthetic within the nerve such that more of the anesthetic reaches deep perineural axon-containing compartments, the blockade of which might contribute to an increase in the analgesic intensity of the block.6 Additional epinephrine-induced analgesic effects may arise from systemic absorption of the drug and its interactions with α2-adrenoceptor in the brain and spinal cord.35

Although lidocaine solutions containing epinephrine are commercially available, for the present study, we chose to prepare the 1% lidocaine + epinephrine treatment immediately before use. Commercially prepared local anesthetic solutions that contain epinephrine also contain an antioxidant (sodium bisulfite) to maintain epinephrine stability. Sodium bisulfite decreases the pH of the solution.36 As the pH of a solution decreases, the percentage of nonionized (uncharged form) anesthetic available to diffuse through the nerve membrane and facilitate onset and quality of a regional block also decreases. In fact, local anesthetic solutions to which epinephrine is added immediately prior to use are reportedly more potent than commercially prepared local anesthetic solutions containing epinephrine and an antioxidant.5

For the horses of the present study, the vector sum decreased (ie, lameness improved) after each PDNB was administered, which indicated that the block was accurately placed. Skin sensitivity was a poor indicator of the accuracy of nerve block placement when the 1% and 2% lidocaine treatments were administered. However, skin sensitivity at the palmar portion of the coronary band was lost in all horses when the PDNB with 1% lidocaine + epinephrine was administered. A pointed probe (eg, a ball-point pen or hemostat) is often applied to skin to assess skin sensation. In the present study, we used a flat rather than a pointed probe to assess skin sensation because we were concerned that frequent serial assessments with a pointed probe might cause excessive damage to the skin. We are not aware of any studies that indicate that the application of pointed pressure is superior to blunt pressure for assessing skin sensation distal to a PDNB. In other studies in which 2% lidocaine was used to perform PDNBs in horses, skin sensation remained despite amelioration of lameness2 or skin was desensitized without concurrent amelioration of lameness.1 Similar to the investigators of those studies,1,2 we concluded that skin sensitivity was a poor indicator of the accuracy of a PDNB performed with lidocaine. The addition of epinephrine to lidocaine increases the likelihood of a positive correlation between skin desensitization and amelioration of lameness.

In the present study, the median heart rate remained constant throughout the observation period for all 3 treatments, which suggested that the small amount of epinephrine present in the 1% lidocaine + epinephrine treatment had no or only minimal effect on the cardiovascular system. Results of studies37,38 involving human patients likewise suggest that the use of epinephrine in combination with lidocaine for regional anesthesia has minimal effects on heart rate and blood pressure.

Results of the present study indicated that the addition of epinephrine (dilution, 1:200,000) to a 1% lidocaine solution immediately before use as a PDNB injection improved the efficacy and prolonged the duration of the block in horses with naturally occurring forefoot lameness, compared with the efficacy and duration of PDNBs with a 1% or 2% lidocaine solution without epinephrine. The efficacy and duration of the PDNB did not differ significantly between the 1% lidocaine and 2% lidocaine treatments. When the 1% lidocaine + epinephrine treatment was used for the PDNB, there was a positive correlation between skin desensitization and amelioration of lameness. Moreover, no adverse cardiovascular or skin reactions were observed in any of the horses following administration of the 1% lidocaine + epinephrine treatment. Thus, we concluded that PDNBs with a 1% lidocaine solution containing epinephrine at a 1:200,000 dilution might be clinically useful for lameness evaluations and standing surgery of the distal limb in horses.

Acknowledgments

No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.

The authors thank Britta Fischer for technical assistance.

ABBREVIATIONS

MAXDIFFHEAD

Maximum head height

MINDIFFHEAD

Minumum head height

MNT

Mechanical nociceptive threshold

PDNB

Palmar digital nerve block

Footnotes

a.

Lidocaine hydrochloride 2%, Hospira Inc, Lake Forest, Ill.

b.

STATA, version 8.1, Stata Corp, College Station, Tex.

c.

Lidocaine hydrochloride 1%, Hospira Inc, Lake Forest, Ill.

d.

Epinephrine (1:1,000), Hospira Inc, Lake Forest, Ill.

e.

Equinosis LLC, Columbia, Mo.

f.

Keegan KG, Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, Mo: Personal communication, 2017.

g.

Force Ten FDX Compact Digital Force Gage, Wagner Instruments, Greenwich, Conn.

h.

SAS, version 9.1, SAS Institute Inc, Cary, NC.

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Contributor Notes

Address correspondence to Dr. Velloso Alvarez (azv0023@auburn.edu).