Bilateral comparison of forearm skin temperature during handgrip force exercise

Handgrip force (HGF) test has been used to provide important occupational health information about subject’s nutritional and physiological condition. Handgrip force (average and maximum) and exercise accumulated work can be measured using a dynamometer connected to a computer, other physiological energy spent in the HGF test can be obtained with infrared thermal (IRT) imaging at the anterior forearm region. A protocol has been developed combining both measurements, showing correlations between the measured values and the degrees of similarity between bilateral limbs was assessed, varying at maximum of 1.6 ºC in the considered thermal regions of interest of the forearm. The obtained results on 13 subjects at three different endurance HGF tests showed that the procedure is reproducible and can be applied in both limbs for physiological assessments in occupational, rehabilitation or geriatric contexts.info:eu-repo/semantics/publishedVersio

Representation of Somatosensory Afferents in the Cortical Autonomic Network

The relationship between somatosensory stimulation and the autonomic nervous system has been established with effects on heart rate (HR) and sympathetic tone. However, the involvement of the cortical autonomic network (CAN) during muscle sensory afferent stimulation has not been identified. The main objective of the research in this dissertation was to determine the representation of somatosensory afferents in the CAN and their physiologic impact on cardiovascular control. Somatosensory afferent activation was elicited by electrical stimulation of type I and II afferents (sub-motor threshold) and type III and IV afferents (motor threshold), and CAN patterns were assessed using blood-oxygenation level-dependent functional magnetic resonance imaging. Study 1 (Chapter 2) established CAN regions associated with sub-motor stimulation including the ventral medial prefrontal cortex (vMPFC), subgenual anterior cingulate cortex (sACC), and posterior insula, along with a trend towards increased heart rate variability (HRV). Motor threshold stimulation was associated with activation in the posterior insula. Having established the CAN regions affected by sensory afferent input, diffusion tensor imaging was used (Chapter 3) to establish structural connections between the cortical regions associated with functional cardiovascular control. We identified two discrete patterns of white matter connectivity between the anterior insula-sACC and posterior insula-posterior cingulate cortex, suggesting that a structural network may underlie functional roles in autonomic regulation and sensory processing. As somatosensory stimulation had modest impact on cardiovascular control under baseline conditions, Study 3 (Chapter 4) aimed to establish the effects of somatosensory stimulation during baroreceptor unloading (lower-body negative pressure, LBNP) on muscle sympathetic nerve activity (MSNA) and cortical activity. Sensory stimulation during LBNP led to an attenuated increase in MSNA burst frequency, as well as absent activity in the right insula and dorsal ACC, supporting the sympatho-excitatory role of these regions. No effect of somatosensory stimulation during chemoreflex-mediated sympatho-excitation was observed on MSNA, while right insular and dorsal ACC activities were maintained. Overall, the results of these studies provide evidence of somatosensory representation within the CAN regions that are anatomically linked, and highlight a role for type I and II sensory afferents in modulating autonomic outflow in a manner that depends upon baroreceptor loading

The Effect of Cognitive Limb Embodiment on Vascular Physiological Response

The rubber hand illusion (RHI) is a visual-tactile perceptual illusion commonly used to study body ownership. In this paradigm, a rubber hand is positioned in front of a participant, and the person’s real hand is hidden from sight behind a barrier. When the real hand and the rubber hand are stroked synchronously, individuals perceive the rubber hand as if it were their own; it becomes “embodied.” This illusory experience of body ownership is associated with multimodal integration of touch and vision. From these visual-tactile-cognitive mechanisms, we establish that our hands belong to us when what we see matches what we feel. Recently, studies have established a correlation between the induction of the RHI and temperature changes at the skin surface. Interestingly, when the brain perceives its real limb to be “disembodied” during the cognitive illusion, the temperature of that real limb drops. The central hypothesis for the proposed study is that cognitive limb embodiment directly affects blood flow patterns; blood flow in a specific limb can be disrupted by altering the sense of the limb’s embodiment. Our rationale is that understanding the mechanisms underlying thermal-vascular regulation in healthy and diseased populations is clinically significant because blood flow can be used as a physiological marker of cognitive limb embodiment and may also be particularly important in identifying and understanding disease states. Physiological correlates of embodiment, such as temperature and blood flow changes, may have significant potential for quantitatively assessing various diseases. The first aim was to develop a modified ultrasound method to measure blood flow under the conditions of the RHI. In addition, the Doppler waveform indices were examined as physiological markers for cognitive embodiment. The second aim was to investigate the link between temperature changes and blood flow during cognitive limb embodiment. Taken together, this work seeks to provide a comprehensive understanding of the effects of cognitive limb embodiment on vascular physiological response

The Effect of Cognitive Limb Embodiment on Vascular Physiological Response

The rubber hand illusion (RHI) is a visual-tactile perceptual illusion commonly used to study body ownership. In this paradigm, a rubber hand is positioned in front of a participant, and the person’s real hand is hidden from sight behind a barrier. When the real hand and the rubber hand are stroked synchronously, individuals perceive the rubber hand as if it were their own; it becomes “embodied.” This illusory experience of body ownership is associated with multimodal integration of touch and vision. From these visual-tactile-cognitive mechanisms, we establish that our hands belong to us when what we see matches what we feel. Recently, studies have established a correlation between the induction of the RHI and temperature changes at the skin surface. Interestingly, when the brain perceives its real limb to be “disembodied” during the cognitive illusion, the temperature of that real limb drops. The central hypothesis for the proposed study is that cognitive limb embodiment directly affects blood flow patterns; blood flow in a specific limb can be disrupted by altering the sense of the limb’s embodiment. Our rationale is that understanding the mechanisms underlying thermal-vascular regulation in healthy and diseased populations is clinically significant because blood flow can be used as a physiological marker of cognitive limb embodiment and may also be particularly important in identifying and understanding disease states. Physiological correlates of embodiment, such as temperature and blood flow changes, may have significant potential for quantitatively assessing various diseases. The first aim was to develop a modified ultrasound method to measure blood flow under the conditions of the RHI. In addition, the Doppler waveform indices were examined as physiological markers for cognitive embodiment. The second aim was to investigate the link between temperature changes and blood flow during cognitive limb embodiment. Taken together, this work seeks to provide a comprehensive understanding of the effects of cognitive limb embodiment on vascular physiological response

Master of Science

thesisThe objective of this thesis was to determine the role of nonadrenergic vasoactive substances in the control of blood flow in the elderly. The first study aimed to determine the individual and potentiating effects of the renin-angiotensin-aldosterone (RAAS) and alpha-adrenergic systems on the regulation of blood flow in the young and old. We observed an enhanced maximal reduction in brachial artery blood flow in response to angiotensin-II (ANG-II) in the old compared to the young, which was abolished when the alpha-adrenergic component of the response was pharmacologically eliminated with phentolamine. These data suggest that with healthy aging, the increased ANG-IImediated vasoconstriction may be attributed, in part, to potentiation of alpha-adrenergic vasoconstriction, and indicates that the "cross-talk" between the RAAS and adrenergic systems could be an important therapeutic consideration for hypertension in the elderly. The second study of this project was focused on the role of endogenous endothelin-1 (ET-1) in the regulation of vascular tone at rest and during exercise, with a secondary emphasis on how this pathway is altered with advancing age. The first portion of the second study thus sought to characterize the role of ET-1 on blood flow, arterial blood pressure, and oxygen consumption (VO2) during knee extensor exercise in young, healthy adults. This study documented an increase in exercising limb blood flow following ET-1 receptor subtype A (ETA) antagonism (BQ-123), which was accompanied by a decrement in arterial blood pressure and an increase in VO2. Together, these findings have identified a significant role of the ET-1 pathway in the cardiovascular response to exercise, implicating vasoconstriction via the ETA receptor as an important mechanism for both restraint of blood flow in the exercising limb and support of arterial blood pressure in healthy, young adults. During the aging portion of the second study, at rest, blood flow was reduced by 30% in the elderly compared to the young. ETA antagonism did not change resting blood flow in the young, but restored blood flow in the old to a level similar to that of the young. During exercise, BQ-123 increased blood flow and VO2 to a similar degree in both the young and old. Likewise, the increase in arterial blood pressure during exercise was attenuated in a similar manner between groups after BQ-123 administration. Together these findings demonstrate differences in the regulatory role of the ET-1 pathway at rest and exercise with advancing age. Collectively, these studies have provided insight into the role of nonadrenergic vasoactive substances, specifically ANG-II and ET-1, in the regulation of vascular tone with age. Findings from these studies may provide new information concerning the prevention and treatment of ageassociated cardiovascular diseases

Short term sensory and vascular responses to physical agent modalities and exercise in healthy volunteers and patients with distal radius fracture.

Currently, there is weak evidence on the effectiveness of different rehabilitation regimens following distal radius fracture (DRF). This thesis evaluated sensory and vascular effects of exercise, thermal and ultrasound interventions that can be used in the mobilization phase (cast removal) after DRF. Methods This thesis includes 3 studies. The first study compared responses to Immersion in Cold water Evaluation (ICE) in the DRF and uninjured hands. Skin blood flow (Sbf), skin temperature (temp.) and sensory perception thresholds (sPT) at 2000Hz for A –beta fibres and at 5 Hz for C fibres were obtained before, immediately after ICE and 10 min later. The second study assessed Sbf, temp., and sPT before and after 3 conditions: control, 1 MHz continuous and 3 MHz pulsed US in healthy subjects. The third study assessed Sbf and sPT before and after 3 conditions: control, 5 min of high intensity and low intensity hand exercises in healthy subjects. Differences in these were analyzed using General Linear Models. Results In the DRF hand, Sbf increased (Mean Difference (MD) = -42.2 A.U.) immediately, at 1 min (MD= -35 A.U.), and 10 min after ICE (MD= -1 A.U.). There was a decrease in temp. for the index and little fingers immediately after ICE (MD=9. 9 & 9.1 o C) and these did not return to baseline by 10 min (MD= 4.4 & 4 o C). ICE had no effect on sPT at 5 Hz (p\u3e0.05). There was no difference between the DRF and uninjured hand on all measures(p\u3e0.05) except for the sPT at 2000Hz, which remained high on the DRF side for up to 10 min( MD= -1.8 m. A.). Both pulsed and continuous US caused small to moderate reductions in Sbf (MD= 2.8 A.U. & 3.9 A.U.), temp. (MD = 2.5 0 C & 1.1 0 C) and sPT at 5 Hz (MD=1.3 m. A. & 1 m. A.). US had no effect on sPT at 2000Hz (p\u3e0.05). Both type of exercises were insufficient to alter Sbf and sPT at 2000Hz and 5 Hz (p\u3e0.05). Conclusions Normal thermo-physiological responses were observed after ICE in both hands. A-beta fibres on the DRF side became less sensitive after ICE. Minor changes can occur in Sbf, temp., and sPT at 5 Hz following 3 to 5 min exposure to US in healthy subjects. Hand grip exercises had minimal impact on Sbf or sPT in healthy subjects. The changes seen with ICE and US are presumed to help with tissue healing and pain modulation which needs further investigation

Haemodynamic responses to heat stress and hypohydration in resting and exercising humans: Implications for the regulation of skeletal muscle blood flow

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Heat stress-induced hyperthermia and exercise-induced hypohydration are associated with marked alterations in limb and systemic haemodynamics in humans. However, the mechanisms underlying these alterations their effects on muscle blood flow are not well understood. The present thesis examined whether whole body and local heat stresses increased limb skin and muscle blood flow (Study 1) and whether hypohydration and hyperthermia compromised leg muscle, skin and systemic haemodynamics (Study 2). The effects of heat stress and combined hypohydration and hyperthermia were examined at rest and during mild small muscle mass exercise in humans. The results from Study 1 suggested that heat stress was accompanied by vasodilation in both skeletal muscle and skin vasculatures. Therefore in line with concomitant elevations in blood flow, skeletal muscle and skin vasodilation contribute to increases in leg blood flow and vascular conductance with whole body heat stress. Furthermore, increases in leg muscle and skin blood flow with isolated elevations in leg tissue temperature accounted for at least one half of the total increase in leg blood flow with whole body heat stress. Enhanced leg blood flow owed to a net vasodilation as explained by an elevation in vasodilator activity that exceeded increases in vasoconstrictor activity. This phenomenon was closely related to increases in muscle temperature and intravascular adenosine triphosphate (ATP). The results from Study 2 demonstrated that mild and moderate hypohydration and hyperthermia do not compromise leg muscle and skin blood flow or cardiac output at rest or during mild exercise in humans. Furthermore, acute rehydration did not alter leg muscle and skin blood flow or cardiac output compared to hypohydration and hyperthermia despite large alterations in blood volume and haematological variables and the restoration of core temperature. Taken together, the findings of this thesis indicate that: 1) heat stress induces vasodilation in both skeletal muscle and cutaneous vasculature, 2) elevations in muscle temperature and intravascular ATP play a role in heat stress- and exercise-induced hyperaemia, and 3) moderate hypohydrationinduced hypovolemia and haemoconcentration and rehydration-induced hypervolaemia and haemodilution do not alter leg blood flow or cardiac output at rest and during low intensity exercise in humans when a large cardiovascular reserve is available

Aerospace Medicine and Biology: A continuing bibliography (supplement 229)

This bibliography lists 109 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1982

Fatigue at the Workplace: Measurement and Temporal Development

Fatigue at the workplace has been described as a multidimensional construct, affecting the overall state of the whole organism, which may be a consequence of prolonged work and various psychological, socioeconomic, and environmental factors. In the short term, fatigue may lead to discomfort, diminished motor control, reduced proprioception, increased force variability, and reduced strength capability, resulting in reduced performance, lowered productivity, deficits in work quality, and increased incidence of accidents and human errors. Fatigue may also lead to longer-term adverse health outcomes such as chronic fatigue syndrome, myalgia, and burnout syndromes, and may be a precursor to WMSDs – work-related musculoskeletal disorders. If indeed fatigue is a precursor to WMSDs and other long-term health outcomes, it may then be a relevant biomarker for cumulative exposure to repetitive and/or sustained work, and thus a useful risk indicator and/or a design and evaluation tool. However, little is known of the temporal pattern of fatigue development and its relationships with disorder risks and work performance. The objective of this thesis was to identify and evaluate a battery of fatigue measures for both laboratory and field-based research, and provide insight into fatigue development in work-relevant task conditions. Six studies were designed to address these objectives. In the first study, measures and analysis methods that detect fatigue-related changes were identified by a group of expert fatigue researchers. The second was an exploratory study focused on the responsiveness of a select number of measures during a workday and multiple workdays in realistic physically demanding residential plumbing work. In the third study, a selected number of conventional and novel measures were evaluated for their reliability and sensitivity in a controlled laboratory setting. This study also addressed the responsiveness of measures during a test battery or during the fatiguing activity (i.e., continuously), and the time between cessation of activity and test battery in which measures remain responsive. The fourth study reported on whether circadian effects were detectable by selected measures, providing insight towards the daylong reliability of these measures. In the fifth study, measures were evaluated in four fatiguing conditions, representing changes in type of contraction, intensity, and body segment. Furthermore, the pattern of fatigue development and the temporal responsiveness of measures were described. Finally, measures were assessed over an 8-hour light precision micropipetting task to investigate temporal responsiveness of measures and fatigue development. Errors were quantified and the effects of scheduled work breaks were reported. In study 1, fifty-seven measures were identified based on outcomes and/or effects of fatigue in the workplace. Based on the perceived validity, reliability, and practicality in laboratory and field investigations, four measures were recommended for both settings: maximum voluntary contractions, questionnaires and fatigue scales, Borg’s rating of perceived exercise or discomfort, and visual analog scales. On the other hand, twenty-five measures were not recommended for field studies, including methods traditionally recognized as “gold standard” in measuring cellular and metabolic changes. In study 2, fatigue was documented in realistic physically demanding work while employing a set of measures to provide a comprehensive picture of fatigue development. Not all measures revealed increasing fatigue over the workday or over the workweek, which may be a result of measures reflecting different fatigue processes. Thus, the study reinforced the need of a complementary set of measures, reflecting multiple domains, to measure and interpret the temporal development of fatigue. Two measures, rating of perceived discomfort and grip strength, indicated significant differences within a work day, notably an increase at the beginning and end of the shift (perceived discomfort) and a decrease between mid-shift and end of shift (grip strength). It was speculated that within-day trends were consistent with central fatigue mechanisms. Over multiple workdays, both central and peripheral components displayed a significant day effect. Fatigue accumulation over the workweek was observed with grip strength, physiological resting tremor, and postural tremor measures, particularly between day 1 (Tuesday) and day 4 (Friday). In study 3, test-retest reliability ranged between “poor agreement” and “almost perfect agreement”. In terms of sensitivity, action tremor, MMG RMS amplitude, postural tremor, and rating of perceived fatigue were highly responsive. Perceived fatigue remained elevated, relative to baseline, until 11 minutes post-exercise. Postural and physiological tremor persisted from baseline until the third minute of recovery. Action tremor, however, quickly recovered within the first minute of recovery. This current study found that for most of the measures, there were no statistical differences between test battery and continuous measurement, but a few measures were approaching statistical significance. Action tremor and mechanomyography collected during a test contraction, and perceived fatigue assessed by a visual analog scale, were found to be most reliable, most responsive, comparable to continuous measures, and sensitive after the fatiguing activity, and should be considered with other measures of interest, as part of a test battery. In study 4, only two measures revealed a statistically significant time-of-day effect: mechanomyography of a flexor forearm muscle and action tremor at 30% MVC. These two measures exhibited rhythmicity based on cosinor analysis. Therefore a degree of caution might be required when interpreting daylong fatigue with these two measures, whereas the other measures may not be susceptible to, or detect, significant diurnal effects. Although the remaining measures did not reveal statistically significant time effects, most measures were characterized with similar patterns to those found in previous literature. In study 5, there was no one universal measure that was common, in terms of responsiveness, in all exercise conditions. Although no single measure was found to be most responsive in all conditions, there were measures responsive in most exercise conditions as either a continuous or test battery measure. This was the case with action tremor. A maximum voluntary contraction, which is dependent on processes in both central and peripheral domains, was similarly responsive. Rating of perceived fatigue, which has been cited as a centrally mediated indicator, was also found to increase with exercise progression in hand conditions. Therefore fatigue measures, reflecting changes to both central and peripheral processes, may be useful in measuring tasks and exercises of varying parameters. In this study, we support earlier investigations on the pattern of fatigue development in isometric and time-varying (e.g., intermittent isometric, concentric) contractions. The temporal responsiveness of central and peripheral measures, on the other hand, may be a better reflection of the intensity of the task. The shoulder intermittent condition was not consistent with the expected pattern for an intermittent isometric contraction. However, the study protocol may have inadvertently generated lower muscle activity, and therefore the extent of fatigue may have been minimal. There remains a need to understand complex combinations of task-dependent factors in both fatigue development and temporal responsiveness. In study 6, nine measurement parameters revealed significant increases in fatigue over the work period. Traditional field measures (i.e., MVC and EMG) did not lead to extraordinary time effects. Error rates followed similar trends to the 9 significant measurements: an increase from baseline towards mid-morning, a slight decrease prior to the lunch break, a nadir after lunch, and increasing fatigue effects over the course of the afternoon. Error rates, however, might not be a sole consequence of fatigue – cognitive and physical; but might also reflect changes in arousal level. Over the pipetting task, there was interplay between peripheral and central fatigue mechanisms in three body segments: thumb, hand, and shoulder. Fatigue developed at a “local” level (i.e., at the three body segments) and was consistent with expected patterns observed in study 5, particularly if thumb and shoulder actions were considered concentric actions and the grip force was a sustained isometric contraction. Overall, the collective assessments suggested that rating of perceived fatigue and action tremor, on average, were highly repeatable and responsive in multiple task conditions. Postural tremor or steadiness and maximum voluntary contractions were moderately reliable and responsive. Different forms of tremor may be responsive to different task conditions. Postural tremor amplitude was found to increase over the course of an 8-hour workday in a light precision work task, and over multiple days in physically demanding work. Action tremor, on the other hand, appeared to be responsive at higher work intensities performed at a shorter duration of time. Possibly, action tremor may be more indicative of changes in the periphery, whereas postural tremor reflects changes more central in nature. Consequently, these measures should be considered for inclusion into a test battery for field use. For the ergonomist or health and safety practitioner, this body of work provides some insight into the utility of a test battery of fatigue measures to complement current task analysis techniques. For workplace researchers, this dissertation provides insight into the temporal development of fatigue in various task conditions and the reliability and responsiveness of select measures in both short and longer-term work-studies. This research might subsequently elicit future investigations in the relationship between work exposure, fatigue development, and performance and longer-term health outcomes