Relief of Chronic Pain May Be Accompanied by an Increase in a Measure of Heart Rate Variability

Wearable Devices: Current Status and Opportunities in Pain Assessment and Management

INTRODUCTION

We investigated the possibilities and opportunities for using wearable devices that measure physical activity and physiometric signals in conjunction with ecological momentary assessment (EMA) data to improve the assessment and treatment of pain.

METHODS

We considered studies with cross-sectional and longitudinal designs as well as interventional or observational studies correlating pain scores with measures derived from wearable devices. A search was also performed on studies that investigated physical activity and physiometric signals among patients with pain.

RESULTS

Few studies have assessed the possibility of incorporating wearable devices as objective tools for contextualizing pain and physical function in free-living environments. Of the studies that have been conducted, most focus solely on physical activity and functional outcomes as measured by a wearable accelerometer. Several studies report promising correlations between pain scores and signals derived from wearable devices, objectively measured physical activity, and physical function. In addition, there is a known association between physiologic signals that can be measured by wearable devices and pain, though studies using wearable devices to measure these signals and associate them with pain in free-living environments are limited.

CONCLUSION

There exists a great opportunity to study the complex interplay between physiometric signals, physical function, and pain in a real-time fashion in free-living environments. The literature supports the hypothesis that wearable devices can be used to develop reproducible biosignals that correlate with pain. The combination of wearable devices and EMA will likely lead to the development of clinically meaningful endpoints that will transform how we understand and treat pain patients.

Heartbeat-enhanced immersive virtual reality to treat complex regional pain syndrome

Objectives

To develop and test a new immersive digital technology for complex regional pain syndrome (CRPS) that combines principles from mirror therapy and immersive virtual reality and the latest research from multisensory body processing.

Methods

In this crossover double-blind study, 24 patients with CRPS and 24 age- and sex-matched healthy controls were immersed in a virtual environment and shown a virtual depiction of their affected limb that was flashing in synchrony (or in asynchrony in the control condition) with their own online detected heartbeat (heartbeat-enhanced virtual reality [HEVR]). The primary outcome measures for pain reduction were subjective pain ratings, force strength, and heart rate variability (HRV).

Results

HEVR reduced pain ratings, improved motor limb function, and modulated a physiologic pain marker (HRV). These significant improvements were reliable and highly selective, absent in control HEVR conditions, not observed in healthy controls, and obtained without the application of tactile stimulation (or movement) of the painful limb, using a readily available biological signal (the heartbeat) that is most often not consciously perceived (thus preventing placebo effects).

Conclusions

Next to these specific and well-controlled analgesic effects, immersive HEVR allows the application of prolonged and repeated doses of digital therapy, enables the automatized integration with existing pain treatments, and avoids application of painful bodily cues while minimizing the active involvement of the patient and therapist.

Classification of evidence

This study provides Class III evidence that HEVR reduces pain and increases force strength in patients with CRPS.

Heart Rate Variability: A Novel Modality for Diagnosing Neuropathic Pain after Spinal Cord Injury

Background: Heart rate variability (HRV), the physiological variance in the heart's R-R interval length, can be analyzed to produce various parameters reflective of one's autonomic balance. HRV analysis may be used to capture those autonomic aberrations associated with chronic neuropathic pain (NP) in spinal cord injury (SCI). This study assesses the capacity of HRV parameters to diagnose NP in an SCI cohort.

Methods: An electrocardiogram (ECG) was collected at rest from able bodied participants (AB, n = 15), participants with SCI only (SCI-NP, n = 11), and those with SCI and NP (SCI+NP, n = 20). HRV parameters were analyzed using conventional time and frequency analysis.

Results: At rest, there were no heart rate differences amongst groups. However, SCI+NP participants demonstrated lower overall HRV, as determined by the SDNN time domain parameter, compared to either AB (p < 0.01) or SCI-NP (p < 0.05) groups. Moreover, AB and SCI-NP participants were statistically comparable for all HRV time and frequency domain parameters. Additional analyses demonstrated no differences in HRV parameters between T4, above vs. T5, below SCI groups (for all parameters: p > 0.15) or between C8, above vs. T1, below SCI groups (p > 0.30).

Conclusions: Participants with SCI and NP exhibit a lower overall HRV, which can be determined by HRV time domain parameter SDNN. HRV analysis is an innovative modality with the capacity for objective quantification of chronic NP in participants with SCI.

Autonomic dysfunction in reversible cerebral vasoconstriction syndromes

Background

Autonomic imbalance may play an important role in the pathogenesis of reversible cerebral vasoconstriction syndromes (RCVS). This study aimed to assess the autonomic function by analyzing heart rate variability (HRV) in patients with RCVS.

Methods

Patients with RCVS and age- and gender-matched controls were consecutively recruited. All patients (both ictal and remission stage) and controls underwent 24-hour ambulatory electrocardiographic (ECG) recordings. HRV measures covering time and frequency domains were used to assess autonomic functioning.

Results

Thirty-nine patients with RCVS and 39 controls completed the study. Compared to the controls, RCVS patients during the ictal stage showed reductions in parasympathetic-related indices, including the root mean square of difference of consecutive interbeat intervals (RMSSD) (22.1 ± 7.0 vs. 35.2 ± 14.2, p < 0.001), the percentage of adjacent intervals that varied by more than 50 ms (pNN50) (3.7 ± 3.4 vs. 10.6 ± 8.1, p < 0.001), and high-frequency power (HF) (5.82 ± 0.73 vs. 6.77 ± 0.74; p < 0.001), and increased low-frequency/high-frequency (LF/HF) ratio (index of sympathovagal balance) (3.38 ± 1.32 vs. 2.48 ± 1.07; p =0.001). These HRV indices improved partially but remained significantly different from controls during remission.

Conclusions

Decreased parasympathetic modulations and accentuated sympathetic activity might be a biological trait in patients with RCVS.

Painful and painless diabetic neuropathy: one disease or two?

Painful diabetic polyneuropathy (PDPN) is generally considered a variant of diabetic polyneuropathy (DPN) but the identification of distinctive aspects that characterize painful compared with painless DPN has however been addressed in many studies, mainly with the purpose of better understanding the mechanisms of neuropathic pain in the scenario of peripheral nerve damage of DPN, of determining risk markers for pain development, and also of recognizing who might respond to treatments. This review is aimed at examining available literature dealing with the issue of similarities and differences between painful and painless DPN in an attempt to respond to the question of whether painful and painless DPN are the same disease or not and to address the conundrum of why some people develop the insensate variety of DPN whilst others experience distressing pain. Thus, from the perspective of comparing painful with painless forms of DPN, this review considers the clinical correlates of PDPN, its distinctive framework of symptoms, signs, and nerve functional and structural abnormalities, the question of large and small fiber involvement, the peripheral pain mechanisms, the central processing of pain and some new insights into the pathogenesis of pain in peripheral polyneuropathies and PDPN.

Personality differences affect brainstem autonomic responses to visceral pain

Brainstem autonomic nuclei integrate interoceptive inputs including pain, with descending modulation, to produce homeostatic and defence outputs. Cardiac Vagal Control is especially implicated in psychophysiological processes for both health and disease and is indexed non-invasively by heart rate variability. The study aim was to determine the nature of psychophysiological response profiles for visceral pain. Nineteen healthy subjects had electrocardiographic recordings at rest and during 10 painful oesophageal balloon distensions. Cardiac Vagal Control originating from nucleus ambiguus (CVC(NA)) was determined by polynomial filter application to the electrocardiogram inter-beat interval series. Heart rate and 'Cardiac Sympathetic Index (CSI)' were also determined. Psychological state and trait, including neuroticism and extroversion, were assessed. Subjects who increased CVC(NA) to pain were more neurotic, anxious and sensory sensitive than those who decreased CVC(NA.) Cluster analysis identified two psychophysiological groups: Group 1 (n = 11) demonstrated lower baseline CVC(NA) (P = 0.0001), higher heart rate (P = 0.02) and CSI (P = 0.015), pain tolerance at lower balloon volumes (P = 0.04), but attenuated heart rate response to pain (P = 0.01). Group 2 (n = 8) had the converse profile. Neuroticism scores were higher (P = 0.0004) and extroversion lower (P = 0.01) for group 1 than group 2. Two distinct psychophysiological response profiles to visceral pain exist that are influenced by personality. These may reflect different psychobiological bases for active and passive defence repertoires. Prevalence and clinical relevance of these endophenotypes as vulnerability factors for pain and emotion disorders warrant further exploration.

Decreased physiologic variability as a generalized response to human endotoxemia*

OBJECTIVE

To test the effect in normal human volunteers of transient systemic inflammation on the variability in time-series behaviors of widely divergent physiologic measures of the human inflammatory response.

DESIGN

Prospective study of human volunteers who were tested on 2 consecutive days, a control day and a treatment day. Each participant served as his or her own control.

SETTING

Critical care facility of a university medical center.

SUBJECTS

Subjects were eight healthy human volunteers.

INTERVENTIONS

Participant subjects were tested on both a baseline day with no intervention and on a treatment day when they received 4 ng/kg intravenous Escherichia coli endotoxin.

MEASUREMENTS AND MAIN RESULTS

Continuous electrocardiographic recordings and serial blood sampling (performed every 5 mins) were used to create time-series of heart rate (R-R intervals), neutrophil function (phagocytosis), and plasma cortisol concentrations. For each primary measure, we recorded a significant increase in the regularity (decreased variability) of the functional measurement as assessed by the statistical entity, approximate entropy.

CONCLUSIONS

Increased regularity, or decreased variability, of organ functions is a generalized response to systemic inflammation that occurs in widely divergent systems during endotoxemia.

Thermal thresholds predict painfulness of diabetic neuropathies

OBJECTIVE

Pathophysiology explaining pain in diabetic neuropathy (DN) is still unknown.

RESEARCH DESIGN AND METHODS

Thirty patients with peripheral DN (17 men and 13 women; mean age 52.4 +/- 2.5 years) were investigated. Fifteen patients had neuropathic pain, and 15 patients were free of pain. Patients were followed over 2 years and examined at the beginning and thereafter every 6 months. Clinical severity and painfulness of the DN were assessed by the neuropathy impairment score and visual analog scales (VASs). Cold and warm perception thresholds as well as heat pain thresholds were obtained for evaluation of Adelta- and C-fibers. Nerve conduction velocities (NCVs) and vibratory thresholds were recorded for analysis of thickly myelinated fibers. Moreover, for assessment of cardiac vagal function, heart rate variability (HRV) was evaluated. In order to reduce day-to-day variability of pain, mean values of the five time points over 2 years were calculated and used for further analysis. Data were compared with an age- and sex-matched control group of healthy volunteers.

RESULTS

There were significant differences regarding electrophysiological studies, HRV and quantitative sensory testing (QST) between patients and healthy control subjects (P < 0.001). Generally, patients with neuropathic pain were indistinguishable from pain-free patients. In the pain group, however, VAS pain ratings were correlated to the impairment of small-fiber function (cold detection thresholds, P = 0.02; warm detection thresholds, P = 0.056).

CONCLUSIONS

Intensity of pain in painful DN seems to depend on small nerve fiber damage and deafferentation.

Interpreting heart rate variability sleep/wake patterns in cardiac patients

Heart rate variability (HRV) measurement is an important tool in cardiac care that can provide clinicians and researchers with a 24-hour noninvasive measure of autonomic nervous system activity. Sleep and wake have profoundly different effects on HRV patterns and therefore significant implications for HRV interpretation. This article provides a brief overview of the processes underlying HRV, the standard measures of HRV, a basic overview of wake and sleep, the HRV patterns associated with different sleep and wake states, and the patterns of HRV exhibited in common cardiac conditions. The article concludes with an overview of some general health history factors that are important to consider when interpreting HRV patterns in the clinical and research setting.