Pain modulation effect of breathing-controlled electrical stimulation (BreEStim) is not likely to be mediated by deep and fast voluntary breathing

Neuropathic pain modulation after spinal cord injury by breathing-controlled electrical stimulation (BreEStim) is associated with restoration of autonomic dysfunction

BACKGROUND

Recent findings have implicated supraspinal origins from the pain neuromatrix- central autonomic network (PNM-CAN) in the generation of neuropathic pain (NP) after spinal cord injury (SCI). The aim of this study was to further investigate the theorized PNM-CAN mechanisms in persons with SCI by using a centrally directed pain intervention, provided by breathing-controlled electrical stimulation (BreEStim), to measure resultant autonomic changes measured by time and frequency domain heart rate variability (HRV) analysis.

METHODS

Null and active BreEStim interventions were administered to SCI+NP subjects (n=10) in a random order. HRV data and VAS pain scores were collected at resting pre-test and 30 minutes post-test time points. Resting HRV data were also collected from SCI-NP subjects (n=11).

RESULTS

SCI+NP subjects demonstrated a lower baseline HRV and parasympathetic tone, via SD of the normal-to-normal intervals (SDNN) and low frequency (LF) parameters, compared with SCI-NP subjects. However, following active BreEStim, SCI+NP subjects exhibited an increase in HRV and parasympathetic tone, most notably via pairs of successive R-R beat lengths varying by greater than 50 ms (NN50) and proportion of NN50 for total number of beats (pNN50) parameters along with lower VAS scores. Additionally, the post-test SCI+NP group was found to have a statistically comparable autonomic profile to the SCI-NP group across all HRV variables, including SDNN and LF parameters.

CONCLUSION

The analgesic effects of active BreEStim in SCI+NP subjects were associated with restoration of autonomic dysfunction in this population.

Automated classification of pain perception using high-density electroencephalography data

The translation of brief, millisecond-long pain-eliciting stimuli to the subjective perception of pain is associated with changes in theta, alpha, beta, and gamma oscillations over sensorimotor cortex. However, when a pain-eliciting stimulus continues for minutes, regions beyond the sensorimotor cortex, such as the prefrontal cortex, are also engaged. Abnormalities in prefrontal cortex have been associated with chronic pain states, but conventional, millisecond-long EEG paradigms do not engage prefrontal regions. In the current study, we collected high-density EEG data during an experimental paradigm in which subjects experienced a 4-s, low- or high-intensity pain-eliciting stimulus. EEG data were analyzed using independent component analyses, EEG source localization analyses, and measure projection analyses. We report three novel findings. First, an increase in pain perception was associated with an increase in gamma and theta power in a cortical region that included medial prefrontal cortex. Second, a decrease in lower beta power was associated with an increase in pain perception in a cortical region that included the contralateral sensorimotor cortex. Third, we used machine learning for automated classification of EEG data into low- and high-pain classes. Theta and gamma power in the medial prefrontal region and lower beta power in the contralateral sensorimotor region served as features for classification. We found a leave-one-out cross-validation accuracy of 89.58%. The development of biological markers for pain states continues to gain traction in the literature, and our findings provide new information that advances this body of work.NEW & NOTEWORTHY The development of a biological marker for pain continues to gain traction in literature. Our findings show that high- and low-pain perception in human subjects can be classified with 89% accuracy using high-density EEG data from prefrontal cortex and contralateral sensorimotor cortex. Our approach represents a novel neurophysiological paradigm that advances the literature on biological markers for pain.

A novel nonpharmacological intervention - breathing-controlled electrical stimulation for neuropathic pain management after spinal cord injury - a preliminary study

Objective

The objective of this study was to examine the effectiveness of a novel nonpharmacological intervention – breathing-controlled electrical stimulation (BreEStim) – for neuropathic pain management in spinal cord injury (SCI) patients.

Subjects and methods

There were two experiments: 1) to compare the effectiveness between BreEStim and conventional electrical stimulation (EStim) in Experiment (Exp) 1 and 2) to examine the dose–response effect of BreEStim in Exp 2. In Exp 1, 13 SCI subjects (6 males and 7 females, history of SCI: 58.2 months, from 7 to 150 months, impairments ranging from C4 AIS B to L1 AIS B) received both BreEStim and EStim in a randomized order with at least 3 days apart. A total of 120 electrical stimuli to the median nerve transcutaneously were triggered by voluntary inhalation during BreEStim or were randomly delivered during EStim. In Exp 2, a subset of 7 subjects received BreEStim120 and 240 stimuli randomly on two different days with 7 days apart (BreEStim120 vs BreEStim240). The primary outcome variable was the visual analog scale (VAS) score.

Results

In Exp 1, both BreEStim and EStim showed significant analgesic effects. Reduction in VAS score was significantly greater after BreEStim (2.6±0.3) than after EStim (0.8±0.3) (P<0.001). The duration of analgesic effect was significantly longer after BreEStim (14.2±6 hours) than after EStim (1.9±1 hours) (P=0.04). In Exp 2, BreEStim120 and BreEStim240 had similar degree and duration of analgesic effects.

Conclusion

The findings from this preliminary study suggest that BreEStim is an effective alternative nonpharmacological treatment for chronic neuropathic pain in patients suffering from SCI.