Breathing-controlled Electrical Stimulation (BreEStim) for management of neuropathic pain and spasticity

Observations of Autonomic Variability Following Central Neuromodulation for Chronic Neuropathic Pain in Spinal Cord Injury

BACKGROUND

Spinal cord injury (SCI) persons with chronic neuropathic pain (NP) demonstrate maladaptive autonomic profiles compared to SCI counterparts without NP (SCI - NP) or able-bodied (AB) controls. These aberrations may be secondary to maladaptive neuroplasticity in the shared circuitry of the pain neuromatrix-central autonomic network interface (PNM-CAN). In this study, we explored the proposed PNM-CAN mechanism in SCI + NP and AB cohorts following centrally-directed neuromodulation to assess if the PNM and CAN are capable of being differentially modulated.

MATERIALS AND METHODS

Central neuromodulation was administered via breathing-controlled electrical stimulation (BreEStim), previously evidenced to operate at the PNM. To quantify CAN activity, conventional heart rate variability (HRV) recordings were used to gather time and frequency domain parameters of autonomic modulation. SCI + NP (n = 10) and AB (n = 13) cohorts received null and active BreEStim randomly in crossover fashion. HRV data were gathered pretest and 30 minutes posttest. Pain modulation was quantified at both time-points by visual analog scale (VAS) for SCI + NP persons and electrical detection and pain threshold levels (EDT, EPT) for AB persons.

RESULTS

Following active BreEStim only, SCI + NP persons demonstrated increased parasympathetic tone (increased NN50, p = 0.03, and pNN50, p = 0.02, HRV parameters). This parasympathetic restoration was associated with analgesia (VAS reduction, p < 0.01). Similarly, AB persons demonstrated increased noxious tolerance (increased EPT, p = 0.03, with preserved EDL, p = 0.78) only following active BreEStim. However, this increased pain threshold was not associated with autonomic changes.

CONCLUSIONS

Central modulation targeting the PNM produced autonomic changes in SCI + NP persons but not AB persons. These findings suggest that AB persons exhibit intact CAN mechanisms capable of compensating for PNM aberrations or simply that SCI + NP persons exhibit altered PNM-CAN machinery altogether. Our collective findings confirm the interconnectedness and maladaptive plasticity of PNM-CAN machinery in SCI + NP persons and suggest that the PNM and CAN circuitry can be differentially modulated.

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.

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

Voluntary breathing-controlled electrical stimulation (BreEStim), a novel non-invasive and non-pharmacological treatment protocol for neuropathic pain management, was reported to selectively reduce the affective component of pain possibly by increasing pain threshold. The underlying mechanisms involved in the analgesic effect of BreEStim were considered to result from combination of multiple internal pain coping mechanisms triggered during BreEStim. Findings from our recent studies have excluded possible roles of acupuncture and aversiveness and habituation of painful electrical stimulation in mediating the analgesia effect of BreEStim. To further investigate the possible role of voluntary breathing during BreEStim, the effectiveness of fast and deep voluntary breathing-only and BreEStim on experimentally induced pain was compared in healthy human subjects. Results showed no change in electrical pain threshold after Breathing-only, but a significant increase in electrical pain threshold after BreEStim. There was no statistically significant change in other thresholds after Breathing-only and BreEStim. The findings suggest that the analgesic effect of BreEStim is not likely attributed to fast and deep voluntary breathing. Possible mechanisms are discussed.

Habituation to experimentally induced electrical pain during voluntary-breathing controlled electrical stimulation (BreEStim)

Objective

Painful peripheral electrical stimulation to acupuncture points was found to cause sensitization if delivered randomly (EStim), but induced habituation if triggered by voluntary breathing (BreEStim). The objective was to systematically compare the effectiveness of BreEStim and EStim and to investigate the possible mechanisms mediating the habituation effect of BreEStim.

Methods

Eleven pain-free, healthy subjects (6 males, 5 females) participated in the study. Each subject received the BreEStim and EStim treatments in a random order at least three days apart. Both treatments consisted of 120 painful but tolerable stimuli to the ulnar nerve at the elbow on the dominant arm. BreEStim was triggered by voluntary breathing while EStim was delivered randomly. Electrical sensation threshold (EST) and electrical pain threshold (EPT) were measured from the thenar and hypothenar eminences on both hands at pre-intervention and 10-minutes post-intervention.

Results

There was no difference in the pre-intervention baseline measurement of EST and EPT between BreEStim and EStim. BreEStim increased EPT in all tested sites on both hands, while EStim increased EPT in the dominant hypothenar eminence distal to the stimulating site and had no effect on EPT in other sites. There was no difference in the intensity of electrical stimulation between EStim and BreEStim.

Conclusion

Our findings support the important role human voluntary breathing plays in the systemic habituation effect of BreEStim to peripheral painful electrical stimulation.

Modification of electrical pain threshold by voluntary breathing-controlled electrical stimulation (BreEStim) in healthy subjects

BACKGROUND

Pain has a distinct sensory and affective (i.e., unpleasantness) component. BreEStim, during which electrical stimulation is delivered during voluntary breathing, has been shown to selectively reduce the affective component of post-amputation phantom pain. The objective was to examine whether BreEStim increases pain threshold such that subjects could have improved tolerance of sensation of painful stimuli.

METHODS

Eleven pain-free healthy subjects (7 males, 4 females) participated in the study. All subjects received BreEStim (100 stimuli) and conventional electrical stimulation (EStim, 100 stimuli) to two acupuncture points (Neiguan and Weiguan) of the dominant hand in a random order. The two different treatments were provided at least three days apart. Painful, but tolerable electrical stimuli were delivered randomly during EStim, but were triggered by effortful inhalation during BreEStim. Measurements of tactile sensation threshold, electrical sensation and electrical pain thresholds, thermal (cold sensation, warm sensation, cold pain and heat pain) thresholds were recorded from the thenar eminence of both hands. These measurements were taken pre-intervention and 10-min post-intervention.

RESULTS

There was no difference in the pre-intervention baseline measurement of all thresholds between BreEStim and EStim. The electrical pain threshold significantly increased after BreEStim (27.5±6.7% for the dominant hand and 28.5±10.8% for the non-dominant hand, respectively). The electrical pain threshold significantly decreased after EStim (9.1±2.8% for the dominant hand and 10.2±4.6% for the non-dominant hand, respectively) (F[1, 10] = 30.992, p = .00024). There was no statistically significant change in other thresholds after BreEStim and EStim. The intensity of electrical stimuli was progressively increased, but no difference was found between BreEStim and EStim.

CONCLUSION

Voluntary breathing controlled electrical stimulation selectively increases electrical pain threshold, while conventional electrical stimulation selectively decreases electrical pain threshold. This may translate into improved pain control.