P. Gopalkrishnan et Ka. Sluka, Effect of varying frequency, intensity, and pulse duration of transcutaneous electrical nerve stimulation on primary hyperalgesia in inflamed rats, ARCH PHYS M, 81(7), 2000, pp. 984-990
Objectives: To examine the effect of varying frequency, intensity, and puls
e duration of transcutaneous electrical nerve stimulation (TENS) on primary
hyperalgesia (increased response to a noxious stimuli) to heat and mechani
cal stimuli induced by carrageenan paw inflammation in rats.
Design: Inflammation was induced by injection of 3% carrageenan into the hi
ndpaw. Two frequencies (high, 100Hz; low, 4Hz), 2 intensities (high, motor;
low, sensory), and 2 pulse durations (100 mu sec, 250 mu sec) were applied
for 20 minutes to the inflamed paw. The paw withdrawal latency (PWL) to ra
diant heat, threshold to mechanical stimuli, and spontaneous pain-related b
ehaviors were measured before and 4 hours after induction of inflammation,
after TENS, and at 8, 12, and 24 hours after inflammation. A 3-factor (freq
uency, intensity, pulse duration) repeated-measures (time) design was used
to analyze the changes in PWL. Mechanical threshold and spontaneous pain-re
lated behaviors were compared for frequency, intensity, and pulse duration
with a Kruskal-Wallis analysis of variance.
Results: For changes in PWL to heat, there was an effect for time (p = .000
1) and frequency (p = .0001), but not for intensity (p = .45) or pulse dura
tion (p = .21). For changes in mechanical threshold, there was also an effe
ct for frequency (p = .007), but not for intensity (p = .055) or pulse dura
tion (p = .058), after treatment with TENS. High-frequency TENS significant
ly reduced the primary hyperalgesia to heat and mechanical stimuli when com
pared with controls receiving no TENS or treatment with low-frequency TENS.
High-frequency motor TENS also reduced spontaneous pain-related behaviors
for 1 day after treatment.
Conclusion: High-frequency TENS reduces primary hyperalgesia to heat and me
chanical stimuli for up to 1 day after treatment. In contrast, low-frequenc
y TENS is ineffective in reducing primary hyperalgesia. Varying intensity o
r pulse duration had no effect on the degree of antihyperalgesia produced b
y high-frequency TENS.