Effects of repeated electrocutaneous pain stimulation on facial blood flow

Video-based sympathetic arousal assessment via peripheral blood flow estimation

Electrodermal activity (EDA) is considered a standard marker of sympathetic activity. However, traditional EDA measurement requires electrodes in steady contact with the skin. Can sympathetic arousal be measured using only an optical sensor, such as an RGB camera? This paper presents a novel approach to infer sympathetic arousal by measuring the peripheral blood flow on the face or hand optically. We contribute a self-recorded dataset of 21 participants, comprising synchronized videos of participants' faces and palms and gold-standard EDA and photoplethysmography (PPG) signals. Our results show that we can measure peripheral sympathetic responses that closely correlate with the ground truth EDA. We obtain median correlations of 0.57 to 0.63 between our inferred signals and the ground truth EDA using only videos of the participants' palms or foreheads or PPG signals from the foreheads or fingers. We also show that sympathetic arousal is best inferred from the forehead, finger, or palm.

The Effect of Acute and Sustained Pain on Corticomotor Excitability: A Systematic Review and Meta-Analysis of Group and Individual Level Data

Pain alters motor function. This is supported by studies showing reduced corticomotor excitability in response to experimental pain lasting <90 minutes. Whether similar reductions in corticomotor excitability are present with pain of longer durations or whether alterations in corticomotor excitability are associated with pain severity is unknown. Here we evaluated the evidence for altered corticomotor excitability in response to experimental pain of differing durations in healthy individuals. Databases were systematically searched for eligible studies. Measures of corticomotor excitability and pain were extracted. Meta-analyses were performed to examine: (1) group-level effect of pain on corticomotor excitability, and (2) individual-level associations between corticomotor excitability and pain severity. 49 studies were included. Corticomotor excitability was reduced when pain lasted milliseconds-seconds (hedges g's = -1.26 to -1.55) and minutes-hours (g's = -0.55 to -0.9). When pain lasted minutes-hours, a greater reduction in corticomotor excitability was associated with lower pain severity (g = -0.24). For pain lasting days-weeks, there were no group level effects (g = -0.18 to 0.27). However, a greater reduction in corticomotor excitability was associated with higher pain severity (g = 0.229). In otherwise healthy individuals, suppression of corticomotor excitability may be a beneficial short-term strategy with long-term consequences. PERSPECTIVE: This systematic review synthesised the evidence for altered corticomotor excitability in response to experimentally induced pain. Reduced corticomotor excitability was associated with lower acute pain severity but higher sustained pain severity, suggesting suppression of corticomotor excitability may be a beneficial short-term adaptation with long-term consequences.

Touch-induced pupil size reflects stimulus intensity, not subjective pleasantness

Interpersonal touch is known to influence human communication and emotion. An important system for interpersonal touch is the C-tactile (CT) system, which is activated by a soft stroke on hairy skin with a velocity of 1–10 cms⁻¹. This system been proposed to play a unique role in hedonic valence and emotion of touch. For other sensory modalities, hedonic processing has been associated with pupil dilation. However, it is unclear whether pupil dilation can be modulated by hedonic touch. The current study investigated in two experiments how pupil size reacts to both affective and non-affective stroking. Pupil-size data were obtained to investigate differences between stroking conditions. In addition, an adjusted version of the Touch Perception Task (TPT) was used to assess subjective touch pleasantness ratings. In Experiment 1, affective (3 cms⁻¹) and non-affective (0.3 and 30 cms⁻¹) stroking was applied to the dorsal side of the right hand. Results revealed that stroking velocity had a significant effect on TPT-item scores, showing higher that affective touch was rated as more pleasant compared to non-affective touch, thereby replicating the previous studies. Results, however, revealed no specific pupil dilation for the 3 cms⁻¹ condition; instead, a logarithmic relation was found between pupil-size dilation and stroking velocity. This relation was confirmed in a second experiment. Furthermore, the palm of the hand was used as a control site for tactile stimulation, for which similar findings were obtained as for the dorsal side of the hand. In addition, skin conductance recordings showed a pattern of response to different stroking velocities similar to pupil dilation. These results suggest that pupil-size dilation does respond to tactile input, but that this response is related to arousal caused by changes in stimulus intensity (e.g., stroking velocity) rather than specific C-tactile stimulation.

Understanding Monitoring Technologies for Adults With Pain: Systematic Literature Review

BACKGROUND

Monitoring of patients may decrease treatment costs and improve quality of care. Pain is the most common health problem that people seek help for in hospitals. Therefore, monitoring patients with pain may have significant impact in improving treatment. Several studies have studied factors affecting pain; however, no previous study has reviewed the contextual information that a monitoring system may capture to characterize a patient's situation.

OBJECTIVE

The objective of this study was to conduct a systematic review to (1) determine what types of technologies have been used to monitor adults with pain, and (2) construct a model of the context information that may be used to implement apps and devices aimed at monitoring adults with pain.

METHODS

A literature search (2005-2015) was conducted in electronic databases pertaining to medical and computer science literature (PubMed, Science Direct, ACM Digital Library, and IEEE Xplore) using a defined search string. Article selection was done through a process of removing duplicates, analyzing title and abstract, and then reviewing the full text of the article.

RESULTS

In the final analysis, 87 articles were included and 53 of them (61%) used technologies to collect contextual information. A total of 49 types of context information were found and a five-dimension (activity, identity, wellness, environment, physiological) model of context information to monitor adults with pain was proposed, expanding on a previous model. Most technological interfaces for pain monitoring were wearable, possibly because they can be used in more realistic contexts. Few studies focused on older adults, creating a relevant avenue of research on how to create devices for users that may have impaired cognitive skills or low digital literacy.

CONCLUSIONS

The design of monitoring devices and interfaces for adults with pain must deal with the challenge of selecting relevant contextual information to understand the user's situation, and not overburdening or inconveniencing users with information requests. A model of contextual information may be used by researchers to choose possible contextual information that may be monitored during studies on adults with pain.

Venipuncture procedure affects heart rate variability and chronotropic response

BACKGROUND

Heart rate variability (HRV) has been shown to be influenced by several factors such as noise, sleep status, light, and emotional arousal; however, little evidence is available concerning autonomic responses to a venipuncture. The purpose of this study was to investigate changes of HRV indexes and heart rate (HR) during and following a venipuncture procedure among healthy individuals.

METHODS

33 healthy individuals (22.8 ± 0.56 years, 167 ± 1.56 cm, 69.5 ± 2.61 kg) participated. Testing included 10-minute HRV analysis prior to the venipuncture, a 1-minute venipuncture procedure followed by a 10-minute analysis of HRV, and a total recording of 21 minutes. The first 5 minutes of the 21-minute recordings were discarded, and the remaining 5 minutes of the resting segment was analyzed (PRE), and the last 5 minutes of the 21-minute recording (POST). The log transformation of the time domain root mean squared of successive differences (lnRMSSD) and the frequency domains of high frequency (lnHF) and low frequency (lnLF) and LF/HF ratio (lnLF/HF) were used to quantify autonomic activity. HR was measured in 1-minute segments at 2 minutes prior (PRE), venipuncture (STICK), and post (P1-5).

RESULTS

HR significantly increased at STICK (P = 0.002), and fell below resting at P-5 (P < 0.001). lnRMSSD and lnHF increased significantly by POST (P < 0.001, P = 0.005). lnLF/HF ratio significantly decreased at POST (P = 0.047), while no significant changes occurred for lnLF (P = 0.590).

CONCLUSIONS

HRV and HR are influenced for 10 minutes following the venipuncture procedure. Practitioners and researchers who are interested in collecting blood and measuring HRV need to account for the influence of the venipuncture.

Autonomic arousal and experimentally induced pain: a critical review of the literature

BACKGROUND

Autonomic arousal frequently is assumed to be a component of the pain response, perhaps because physiological mechanisms connecting pain and autonomic reactivity can be easily conceptualized. The evidence clarifying autonomic responses specific to painful stimulation, however, has been rather sporadic and lacks coherence; thus, a summary and critical review is needed in this area.

OBJECTIVES

To summarize and integrate findings from 39 experimental investigations from 1970 to 2012 of pain-induced autonomic arousal in humans.

METHODS

Medline and PsycINFO databases were searched for relevant articles. References from these articles were also considered for review.

RESULTS

Painful stimuli increase respiration rate, induce muscle tension, intensify electrodermal activity and dilate the pupils. Cardiovascular activity also increases, but the pattern displayed in response to pain is complex; peripheral vasoconstriction and sympathetically mediated cardiac responses are most typical. Additionally, autonomic expression of pain shows inconsistent relations with verbal and overt motor responses.

CONCLUSIONS

Autonomic arousal can be legitimately measured and modified as one facet of the pain response. Future research should particularly focus on increasing sample size and broadening the diversity of participants. To improve the ability to compare and contrast findings across studies, as well as to increase the applicability of laboratory findings to naturalistic pain, investigators also must enhance experimental design by increasing uniformity or accounting for differences in methodology. Finally, further work remains to utilize more specific assessments of autonomic response and to assess relationships of autonomic reactivity with other cognitive (e.g., attention) and affective (e.g., anxiety) variables.

Cardiovascular responses to and modulation of pressure pain sensitivity in normotensive, pain-free women

Background and purpose The psychophysiological responses to and modulation of pressure pain stimulation are relatively new areas of investigation. The aims of the present study were to characterize subjective and cardiovascular (CV) responses to pressure pain stimulation, and to examine the relationship between CV responding and pain pressure pain sensitivity. Methods Thirty-nine pain-free, normotensive women were included in the study and tested during the follicular phase of their menstrual cycles. Pain threshold and tolerance were recorded at the right masseter muscle and the sternum, and visual analogue scales (VAS) were used to rate both pain intensity (the sensory dimension) and discomfort (the affective dimension). Mean arterial pressure (MAP), heart rate (HR), and facial and digital skin blood flux (SBF) were registered continuously. Results The pain threshold and tolerance were significantly higher at the sternum compared with the masseter, but the level of affective distress was higher at the masseter tolerance point. No associations emerged between pressure pain threshold and tolerance stimulation levels, and the corresponding VAS ratings. Pressure pain stimulation of the masseter induced significant increases in MAP, HR, and a decrease in digital SBF. During sternum pressure stimulation a significant change in HR and digital SBF was observed. There were no significant correlations between CV responding and pressure pain sensitivity. Conclusion Healthy women seem to display higher pressure pain sensitivity at the masseter region relative to the sternum. Pressure pain stimulation was associated with significant changes in MAP, HR, and SBF, but was not modulated by CV responses. The validity of these findings is strengthened by our control for menstrual cycle events, weekend-related changes in physiology, and CV changes during pain stimulation. Implications This study extends previous reports of SBF sensitivity to electrocutaneous pain into the field of pressure stimulation. Moreover, this study suggests that the often demonstrated association between high BP and low pain sensitivity may not apply to pressure pain specifically. Alternatively, this finding adds to the literature of gender differences in the relationship between CV responding and acute pain sensitivity in general.

Psychophysiological responses to pain stimulation and cognitive tasks in female temporomandibular disorder patients

Background and purpose Psychophysiological factors may contribute to the development of temporomandibular disorders (TMD). Both local orofacial and systemic responses have been investigated. However, most studies have concentrated on physiological responding during cognitive challenges, while responses during painful tasks may be highly relevant for the development of chronic pain conditions. Moreover, the relationship between experimental challenges and physiological responding may be influenced by affective responses during the experimental tasks, an issue not often considered in the literature. Methods This study compared electromyography (EMG) of the left masseter and left trapezius muscles, orofacial and digital skin blood-flow (SBF), mean arterial pressure (MAP), and heart rate (HR) at rest, during orofacial isometric contraction, electrocutaneous pain stimulation of the left hand, pressure pain stimulation of the masseter muscle and the sternum, and three cognitive tasks (reading aloud, a simulated job interview, and visuomotoric tracking). The participants were 25 TMD patients and 25 matched pain-free controls, all females. Affective responses were assessed with the State part of the State-Trait Personality Inventory and with Visual Analogue Scales. Results Masseter EMG levels were significantly lower in the TMD group relative to the control group during jaw contraction, pressure pain stimulation, the relaxation periods, and cognitive tasks. SBF, MAP, and HR responses were largely similar in the two groups, with SBF responses to pain stimulation evident at lower levels of stimulation than previously found. The TMD patients reported significantly higher levels of negative affect during the experiment. Conclusions and implications The low EMG responses in the TMD group may be taken in support of the Pain Adaptation Model of musculoskeletal pain, in which reduced muscular activity serves to protect a painful area. However, it may also be supportive of the Integrated Pain Adaptation Model, where higher central nervous structures influence local muscular output. The group similarities in systemic physiological responding in combination with the elevated levels of negative state affect in the TMD patients confirm previous reports of psychosocial differences being more reliable indicators of TMD than generalized physiological responding.

Vasoconstriction and blood flow responses in visceral arteries to mental task in humans

The vascular responses to mental task in visceral arteries in humans have not been elucidated. We observed the responses in the renal (RA) and superior mesenteric (SMA) arteries to mental stress, using simultaneous pulsed and echo Doppler ultrasound flowmetry. Nine healthy females performed a computerized colour word conflict test (CWT) for 3 min. The mean blood velocity (MBV) in the right RA and SMA, heart rate (HR) and blood pressure were measured. The mean arterial pressure (MAP) was divided by the flow velocity to assess the vascular resistance (VR). The CWT significantly increased the MAP, HR and VR in both arteries from the first minute. During the CWT, flow in the RA decreased significantly at the third minute relative to baseline, while flow in the SMA showed no significant change from the first to the third minute. The degree of vasoconstriction in the RA bed was greater than that in the SMA bed. These results suggest that the mental task causes vasoconstriction in visceral arteries, and imply that it induces differential blood flow and vascular responses in visceral arteries.