Sympathetic activity is influenced by task difficulty and stress perception during mental challenge in humans

Sympathetic and blood pressure reactivity in young adults with major depressive disorder

BACKGROUND

Sympathetic and blood pressure (BP) hyper-reactivity to stress may contribute to increased cardiovascular disease (CVD) risk in adults with major depressive disorder (MDD); however, whether this is evident in young adults with MDD without comorbid disease remains unclear. We hypothesized that acute stress-induced increases in muscle sympathetic nerve activity (MSNA) and BP would be exaggerated in young adults with MDD compared to healthy non-depressed young adults (HA) and that, in adults with MDD, greater symptom severity would be positively related to MSNA and BP reactivity.

METHODS

In 28 HA (17 female) and 39 young adults with MDD of mild-to-moderate severity (unmedicated; 31 female), MSNA (microneurography) and beat-to-beat BP (finger photoplethysmography) were measured at rest and during the cold pressor test (CPT) and Stroop color word test (SCWT).

RESULTS

There were no group differences in resting MSNA (p = 0.24). Neither MSNA nor BP reactivity to either the CPT [MSNA: ∆24 ± 10 HA vs. ∆21 ± 11 bursts/min MDD, p = 0.67; mean arterial pressure (MAP): ∆22 ± 7 HA vs. ∆21 ± 10 mmHg MDD, p = 0.46)] or the SCWT (MSNA: ∆-4 ± 6 HA vs. ∆-5 ± 8 bursts/min MDD, p = 0.99; MAP: ∆7 ± 8 HA vs ∆9 ± 5 mmHg MDD; p = 0.82) were different between groups. In adults with MDD, symptom severity predicted MAP reactivity to the CPT (β = 0.78, SE = 0.26, p = 0.006), but not MSNA (p = 0.42).

LIMITATIONS

The mild-to-moderate symptom severity reflects only part of the MDD spectrum.

CONCLUSIONS

Neither sympathetic nor BP stress reactivity are exaggerated in young adults with MDD; however, greater symptom severity may amplify BP reactivity to stress, thereby increasing CVD risk.

Cerebral sympatholysis: experiments on in vivo cerebrovascular regulation and ex vivo cerebral vasomotor control

Whether cerebral sympathetic-mediated vasomotor control can be modulated by local brain activity remains unknown. This study tested the hypothesis that the application or removal of a cognitive task during a cold pressor test (CPT) would attenuate and restore decreases in cerebrovascular conductance (CVC), respectively. Middle cerebral artery blood velocity (transcranial Doppler) and mean arterial pressure (finger photoplethysmography) were examined in healthy adults (n = 16; 8 females and 8 males) who completed a control CPT, followed by a CPT coupled with a cognitive task administered either 1) 30 s after the onset of the CPT and for the duration of the CPT or 2) at the onset of the CPT and terminated 30 s before the end of the CPT (condition order was counterbalanced). The major finding was that the CPT decreased the index of CVC, and such decreases were abolished when a cognitive task was completed concurrently and restored when the cognitive task was removed. As a secondary experiment, vasomotor interactions between sympathetic transduction pathways (α1-adrenergic and Y1-peptidergic) and compounds implicated in cerebral blood flow control [adenosine, and adenosine triphosphate (ATP)] were explored in isolated porcine cerebral arteries (wire myography). The data reveal α1-receptor agonism potentiated vasorelaxation modestly in response to adenosine, and preexposure to ATP attenuated contractile responses to α1-agonism. Overall, the data suggest a cognitive task attenuates decreases in CVC during sympathoexcitation, possibly related to an interaction between purinergic and α1-adrenergic signaling pathways.NEW & NOTEWORTHY The present study demonstrates that the cerebrovascular conductance index decreases during sympathoexcitation and this response can be positively and negatively modulated by the application or withdrawal of a nonexercise cognitive task. Furthermore, isolated vessel experiments reveal that cerebral α1-adrenergic agonism potentiates adenosine-mediated vasorelaxation and ATP attenuates α1-adrenergic-mediated vasocontraction.

Differential control of sympathetic outflow to muscle and skin during physical and cognitive stressors

PURPOSE

Sympathetic nerve activity towards muscle (MSNA) and skin (SSNA) regulates various physiological parameters. MSNA primarily functions in blood pressure and flow, while SSNA operates in thermoregulation. Physical and cognitive stressors have been shown to have effects on both types of sympathetic activity, but there are inconsistencies as to what these effects are. This article aims to address the discrepancies in the literature and compare MSNA and SSNA responses.

METHODS

Microelectrode recordings were taken from the common peroneal nerve in 29 participants: MSNA (n = 21), SSNA (n = 16) and both MSNA and SSNA (n = 8). Participants were subjected to four different 2-min stressors: two physical (isometric handgrip task, cold pressor test) and two cognitive (mental arithmetic task, Stroop colour-word conflict test), the latter of which saw participants separated into responders and non-responders to the stressors. It was hypothesised that the physical stressors would have a greater effect on MSNA than SSNA, while the cognitive stressors would operate conversely.

RESULTS

Peristimulus time histogram (PSTH) analysis showed the mental arithmetic task to significantly increase both MSNA and SSNA; the isometric handgrip task and cold pressor test to increase MSNA, but not SSNA; and Stroop test to have no significant effects on changing MSNA or SSNA from baseline. Additionally, stress responses did not differ between MSNA and SSNA in participants who had both sets of data recorded.

CONCLUSIONS

This study has provided evidence to support the literature which claims cognitive stressors increase sympathetic activity, and provides much needed SSNA data in response to stressors.

A single session of aerobic exercise reduces systolic blood pressure at rest and in response to stress in women with rheumatoid arthritis and hypertension

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease characterized by increased risk of cardiovascular disease and hypertension (HT). A single session of aerobic exercise may reduce blood pressure (BP) in different clinical groups; however, little is known about the acute effects of exercise on BP in RA patients. This is a randomized controlled crossover study that assessed the effects of a single session of aerobic exercise on resting BP, on BP responses to stressful stimuli, and on 24-h BP in women with RA and HT. Twenty women with RA and HT (53 ± 10 years) undertook sessions of 30-min treadmill exercise (50% VO2max) or control (no exercise) in a crossover fashion. Before and after the sessions, BP was measured at rest, and in response to the Stroop-Color Word Test (SCWT), the Cold Pressor Test (CPT), and an isometric handgrip test. After the sessions, participants were also fitted with an ambulatory BP monitor for the assessment of 24-h BP. A single session of exercise reduced resting systolic BP (SBP) (-5 ± 9 mmHg; p < 0.05), and reduced SBP response to the SCWT (-7 ± 14 mmHg; p < 0.05), and to the CPT (-5 ± 11 mmHg; p < 0.05). Exercise did not reduce resting diastolic BP (DBP), BP responses to the isometric handgrip test or 24-h BP. In conclusion, a single session of aerobic exercise reduced SBP at rest and in response to stressful stimuli in hypertensive women with RA. These results support the use of exercise as a strategy for controlling HT and, hence, reducing cardiovascular risk in women with RA.Clinical Trial Registration: This study registered at the Brazilian Clinical Trials ( https://ensaiosclinicos.gov.br/rg/RBR-867k9g ) at 12/13/2019.

Exploring EEG characteristics of multi-level mental stress based on human-machine system

Objective.The understanding of cognitive states is important for the development of human-machine systems (HMSs), and one of the fundamental but challenging issues is the understanding and assessment of the operator's mental stress state in real task scenarios.Approach.In this paper, a virtual unmanned vehicle (UAV) driving task with multi-challenge-level was created to explore the operator's mental stress, and the human brain activity during the task was tracked in real time via electroencephalography (EEG). A mental stress analysis dataset for the virtual UAV task was then developed and used to explore the neural activation patterns associated with mental stress activity. Finally, a multiple attention-based convolutional neural network (MACN) was constructed for automatic stress assessment using the extracted stress-sensitive neural activation features.Main Results.The statistical results of EEG power spectral density (PSD) showed that frontal theta-PSD decreased with increasing task difficulty, and central beta-PSD increased with increasing task difficulty, indicating that neural patterns showed different trends under different levels of mental stress. The performance of the proposed MACN was evaluated based on the dimensional model, and results showed that average three-class classification accuracies of 89.49%/89.88% were respectively achieved for arousal/valence.Significance.The results of this paper suggest that objective assessment of mental stress in a HMS based on a virtual UAV scenario is feasible, and the proposed method provides a promising solution for cognitive computing and applications in human-machine tasks.

Association between the acceleration of access to visual awareness of grating orientation with higher heart rate at high-altitude

Many studies have indicated a strong relationship between cardiac and brain activities, both of which are sensitive to high-altitude exposure. This study combined a consciousness access task and electrocardiograms (ECG) to uncover conscious awareness in response to high-altitude exposure and its relation to cardiac activity. When compared with the low-altitude groups, the behavioral results showed that the high-altitude participants shortened the time of access to visual awareness of grating orientation, which was accompanied by a faster heart rate, excluding the influence of pre-stimulus heart rate, extent of cardiac deceleration after presenting the stimulus, and task difficulty. Although there were post-stimulation cardiac deceleration and post-response acceleration at both high and low altitudes, a slight increase in heart rate after stimulation at high altitudes may indicate that participants at high altitudes could quickly readjust their attention to the target stimulus. More importantly, the drift diffusion model (DDM) was used to fit the access time distribution of all participants. These results suggest that shorter time at high altitudes might be due to the lower threshold, suggesting that less evidence in high-altitude participants was required to access visual consciousness. The participants' heart rates also negatively predicted the threshold through a hierarchical drift diffusion modeling (HDDM) regression. These findings imply that individuals with higher heart rates at high altitudes have a greater cognitive burden.

Blood pressure and muscle sympathetic nerve activity are associated with trait anxiety in humans

Chronic anxiety is prevalent and associated with an increased risk of cardiovascular disease. Prior studies that have reported a relationship between muscle sympathetic nerve activity (MSNA) and anxiety have focused on participants with anxiety disorders and/or metabolic syndrome. The present study leverages a large cohort of healthy adults devoid of cardiometabolic disorders to examine the hypothesis that trait anxiety severity is positively associated with resting MSNA and blood pressure. Resting blood pressure (BP) (sphygmomanometer and finger plethysmography), MSNA (microneurography), and heart rate (HR; electrocardiogram) were collected in 88 healthy participants (52 males, 36 females, 25 ± 1 yr, 25 ± 1 kg/m2). Multiple linear regression was performed to assess the independent relationship between trait anxiety, MSNA, resting BP, and HR while controlling for age and sex. Trait anxiety was significantly correlated with systolic arterial pressure (SAP; r = 0.251, P = 0.018), diastolic arterial pressure (DAP; r = 0.291, P = 0.006), mean arterial pressure (MAP; r = 0.328, P = 0.002), MSNA burst frequency (BF; r = 0.237, P = 0.026), and MSNA burst incidence (BI; r = 0.225, P = 0.035). When controlling for the effects of age and sex, trait anxiety was independently associated with SAP (β = 0.206, P = 0.028), DAP (β = 0.317, P = 0.002), MAP (β = 0.325, P = 0.001), MSNA BF (β = 0.227, P = 0.030), and MSNA BI (β = 0.214, P = 0.038). Trait anxiety is associated with increased blood pressure and MSNA, demonstrating an important relationship between anxiety and autonomic blood pressure regulation.NEW & NOTEWORTHY Anxiety is associated with development of cardiovascular disease. Although the sympathetic nervous system is a likely mediator of this relationship, populations with chronic anxiety have shown little, if any, alteration in resting levels of directly recorded muscle sympathetic nerve activity (MSNA). The present study is the first to reveal an independent relationship between trait anxiety, resting blood pressure, and MSNA in a large cohort of healthy males and females devoid of cardiometabolic comorbidities.

Dynamic fluctuations in ascending heart-to-brain communication under mental stress

Dynamical information exchange between central and autonomic nervous systems, as referred to functional brain-heart interplay, occurs during emotional and physical arousal. It is well documented that physical and mental stress lead to sympathetic activation. Nevertheless, the role of autonomic inputs in nervous system-wise communication under mental stress is yet unknown. In this study, we estimated the causal and bidirectional neural modulations between electroencephalogram (EEG) oscillations and peripheral sympathetic and parasympathetic activities using a recently proposed computational framework for a functional brain-heart interplay assessment, namely the sympathovagal synthetic data generation model. Mental stress was elicited in 37 healthy volunteers by increasing their cognitive demands throughout three tasks associated with increased stress levels. Stress elicitation induced an increased variability in sympathovagal markers, as well as increased variability in the directional brain-heart interplay. The observed heart-to-brain interplay was primarily from sympathetic activity targeting a wide range of EEG oscillations, whereas variability in the efferent direction seemed mainly related to EEG oscillations in the γ band. These findings extend current knowledge on stress physiology, which mainly referred to top-down neural dynamics. Our results suggest that mental stress may not cause an increase in sympathetic activity exclusively as it initiates a dynamic fluctuation within brain-body networks including bidirectional interactions at a brain-heart level. We conclude that directional brain-heart interplay measurements may provide suitable biomarkers for a quantitative stress assessment and bodily feedback may modulate the perceived stress caused by increased cognitive demand.

Three-minute bench step exercise as a countermeasure for acute mental stress-induced arterial stiffening

Acute mental stress (MS) induces a transient increase in arterial stiffness. We verified whether a single bout of bench step (BS) exercise for 3 minutes counteracts acute MS-induced arterial stiffening. Fifteen healthy young men (mean age, 21.7 ± 0.3 years) underwent two experimental trials: rest (RE) and exercise (EX) trials. Following a 5-minute MS task, the participants in the RE trial rested on a chair for 3 minutes (from 10 to 13 minutes after task cessation), whereas those in the EX trial performed the BS exercise for the same duration. The heart-brachial pulse wave velocity (PWV) (hbPWV), brachial-ankle PWV (baPWV), heart-ankle PWV (haPWV), and the cardio-ankle vascular index (CAVI) were measured at baseline and at 5 and 30 minutes after the task. In both trials, significant increases in hbPWV, haPWV, and CAVI occurred at 5 minutes after the task; these elevations persisted until 30 minutes after the task in the RE trial, but significantly decreased to baseline levels in the EX trial. baPWV was significantly elevated at 30 minutes after the task in the RE trial, but not in the EX trial. This study reveals that a 3-minute BS exercise offsets acute MS-induced arterial stiffening.

An experiential learning course for cardiovascular and sleep technology

Undergraduate programs related to allied health are often pursued by students to prepare for entrance into professional programs, but many students also ask about what types of employment options they may have upon completion of the bachelor's degree. This experiential learning course in cardiovascular and sleep technology was designed to provide opportunities for students to gain hands-on clinical skills that could help them to enter professional programs or to find employment in an allied health field such as cardiopulmonary rehabilitation, cardiovascular technology, or sleep technology. The prerequisites for this course were the completion of two semesters of anatomy and physiology. This course was based on experiential learning and was structured into three modules: clinical exercise physiology, autonomic physiology, and sleep physiology. As part of the course students completed a 4-page scientific report for one designated topic within each of the modules. The two exams in the course were essay based. The design of this course required students to review key topics from anatomy and physiology, to comprehend peer-reviewed manuscripts, to gain hands-on experiences with sophisticated physiological equipment, to work as individuals and in groups, and to become better oral and written communicators. The sleep physiology module included an introduction to electroencephalography (EEG) and a student-led nap study, which may be an effective way to introduce students to sleep medicine. We are hopeful that the summary of this course will be useful to physiology educators as they work to provide the most meaningful experiences to their undergraduates in the health sciences.NEW & NOTEWORTHY Experiential learning in clinical exercise, autonomic regulation, and sleep physiology is an impactful way to train undergraduate biomedical students to enter a variety of careers in healthcare, graduate programs in the health professions, or traditional research graduate programs. A hands-on course such as Cardiovascular and Sleep Technology provides a way, in addition to or independent of original research, to provide clinically relevant training.

Sympathetic neural reactivity to the Trier social stress test

Sympathetic responsiveness to laboratory mental stress is highly variable, making interpretations of its role in stress reactivity challenging. The present study assessed muscle sympathetic nerve activity (MSNA, microneurography) responsiveness to the Trier social stress test (TSST), which employs an anticipatory stress phase, followed by a public speaking and mental arithmetic task. We hypothesized that sympathetic reactivity to the anticipatory phase would offer a more uniform response between individuals due to elimination of confounds (i.e. respiratory changes, muscle movement, etc.) observed during more common stress tasks. Participants included 26 healthy adults (11 men, 15 women, age: 25 ± 6 years, body mass index: 24 ± 3 kg/m² ). Continuous heart rate (electrocardiogram) and beat-to-beat blood pressure (finger plethysmography) were recorded from all participants, while MSNA recordings were obtained in 20 participants. MSNA burst frequency was significantly reduced during anticipatory stress. During the speech, although burst frequency was unchanged, total MSNA was significantly increased. Changes in diastolic arterial pressure were predictive of changes in MSNA during anticipatory (β = -0.680, P = 0.001), but not the speech (P = 0.318) or mental maths (P = 0.051) phases. Lastly, sympathetic reactivity to anticipatory stress was predictive of subsequent reactivity to both speech (β = 0.740, P = 0.0002) and maths (β = 0.663, P = 0.001). In conclusion, anticipatory social stress may offer a more versatile means of assessing sympathetic reactivity to mental stress in the absence of confounds and appears to predict reactivity to subsequent mental stress paradigms. KEY POINTS: Cardiovascular reactivity to laboratory mental stress is predictive of future health outcomes. However, reactivity of the sympathetic nervous system to mental stress is highly variable. The current study assessed peripheral muscle sympathetic nerve activity in response to the Trier social stress test, a psychosocial stressor that includes anticipatory stress, public speaking and mental arithmetic. Our findings demonstrate that sympathetic neural activity is consistently reduced during anticipatory stress. Conversely, the classically observed inter-individual variability of sympathetic responsiveness was observed during speech and maths tasks. Additionally, sympathetic reactivity to the anticipatory period accurately predicted how an individual would respond to both speech and maths tasks, outlining the utility of anticipatory stress in future research surrounding stress reactivity. Utilization of the Trier social stress test in autonomic physiology may offer an alternative assessment of sympathetic responsiveness to stress with more consistent inter-individual responsiveness and may be a useful tool for further investigation of stress reactivity.

Impact of acute mental stress on ankle blood pressure in young healthy men: a pilot study

Objective

Acute mental stress (MS) increases arm blood pressure (BP); however, it remains unclear whether a stress-induced pressor response is also observed in other vessels. This study aimed to examine the impact of acute MS on ankle BP. Fifty-six young, healthy men aged 19–24 years were divided into the MS (n = 29) and control (CON) (n = 27) groups; each group performed 5-min MS (mental arithmetic) or CON tasks. Systolic and diastolic BPs (SBP and DBP, respectively) of both the brachial and posterior tibial arteries were simultaneously measured at the baseline and 5 and 30 min after the task.

Results

In the MS group, brachial BP measures significantly increased (P < 0.05) until 30 min after the task; ankle BP measures were also significantly (P < 0.05) elevated during this time. In the CON group, no significant changes were found in brachial BP measures or ankle SBP, whereas a significant increase (P < 0.05) in ankle DBP was observed 30 min after the task. Our findings indicate that both brachial and ankle BP exhibit a sustained elevation after acute MS, suggesting a systemic pressor response by stress exposure. The measurement of ankle BP in addition to arm BP may be important to assess the stress response.

Trial Registration

UMIN Clinical Trials Registry UMIN000047796 Registered on: 20th May 2022.

The effectiveness of bench step exercise for ameliorating acute mental stress-induced arterial stiffening

Purpose

This study aimed to evaluate the effectiveness of bench step (BS) exercise for ameliorating arterial stiffening caused by acute mental stress (MS).

Methods

Fifteen young healthy men participated in two randomized trials: rest (RE) and exercise (EX) trials. Following a 5-min MS task (first task), the RE trial participants rested on a chair for 10 min (from 10 to 20 min after task cessation); the EX trial participants performed BS exercise for the same duration. At 40 min after the first task, the participants performed the same task (second task) again. Heart–brachial pulse wave velocity (PWV) (hbPWV), brachial–ankle PWV (baPWV), heart–ankle PWV (haPWV), and the cardio-ankle vascular index (CAVI) were measured simultaneously at 5, 30, and 50 min after the first task.

Results

Both trials caused significant elevations in hbPWV, haPWV, and CAVI at 5 min after the first task; these changes persisted until 30 min after the task in the RE trial, while they were abolished in the EX trial. baPWV significantly increased at 30 min after the task in the RE trial, but not in the EX trial. After the second task (from 30 to 50 min after the first task), none of the parameters significantly increased in the RE trial, although the values remained above baseline levels. In the EX trial, hbPWV, haPWV, and CAVI showed significant elevations.

Conclusion

Our findings suggest that a 10-min BS exercise after acute MS can counteract stress-induced arterial stiffening, but has only a limited effect against subsequent acute MS.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-022-04962-y.

Subdividing Stress Groups into Eustress and Distress Groups Using Laterality Index Calculated from Brain Hemodynamic Response

A stress group should be subdivided into eustress (low-stress) and distress (high-stress) groups to better evaluate personal cognitive abilities and mental/physical health. However, it is challenging because of the inconsistent pattern in brain activation. We aimed to ascertain the necessity of subdividing the stress groups. The stress group was screened by salivary alpha-amylase (sAA) and then, the brain’s hemodynamic reactions were measured by functional near-infrared spectroscopy (fNIRS) based on the near-infrared biosensor. We compared the two stress subgroups categorized by sAA using a newly designed emotional stimulus-response paradigm with an international affective picture system (IAPS) to enhance hemodynamic signals induced by the target effect. We calculated the laterality index for stress (LIS) from the measured signals to identify the dominantly activated cortex in both the subgroups. Both the stress groups exhibited brain activity in the right frontal cortex. Specifically, the eustress group exhibited the largest brain activity, whereas the distress group exhibited recessive brain activity, regardless of positive or negative stimuli. LIS values were larger in the order of the eustress, control, and distress groups; this indicates that the stress group can be divided into eustress and distress groups. We built a foundation for subdividing stress groups into eustress and distress groups using fNIRS.

Sympathetic Neural Control in Humans with Anxiety-Related Disorders

Numerous conceptual models are used to describe the dynamic responsiveness of physiological systems to environmental pressures, originating with Claude Bernard's milieu intérieur and extending to more recent models such as allostasis. The impact of stress and anxiety upon these regulatory processes has both basic science and clinical relevance, extending from the pioneering work of Hans Selye who advanced the concept that stress can significantly impact physiological health and function. Of particular interest within the current article, anxiety is independently associated with cardiovascular risk, yet mechanisms underlying these associations remain equivocal. This link between anxiety and cardiovascular risk is relevant given the high prevalence of anxiety in the general population, as well as its early age of onset. Chronically anxious populations, such as those with anxiety disorders (i.e., generalized anxiety disorder, panic disorder, specific phobias, etc.) offer a human model that interrogates the deleterious effects that chronic stress and allostatic load can have on the nervous system and cardiovascular function. Further, while many of these disorders do not appear to exhibit baseline alterations in sympathetic neural activity, reactivity to mental stress offers insights into applicable, real-world scenarios in which heightened sympathetic reactivity may predispose those individuals to elevated cardiovascular risk. This article also assesses behavioral and lifestyle modifications that have been shown to concurrently improve anxiety symptoms, as well as sympathetic control. Lastly, future directions of research will be discussed, with a focus on better integration of psychological factors within physiological studies examining anxiety and neural cardiovascular health. © 2022 American Physiological Society. Compr Physiol 12:1-33, 2022.

Vasoconstriction Response to Mental Stress in Sickle Cell Disease: The Role of the Cardiac and Vascular Baroreflexes

Recent studies have shown that individuals with sickle cell disease (SCD) exhibit greater vasoconstriction responses to physical autonomic stressors, such as heat pain and cold pain than normal individuals, but this is not the case for mental stress (MTS). We sought to determine whether this anomalous finding for MTS is related to inter-group differences in baseline cardiac and vascular autonomic function. Fifteen subjects with SCD and 15 healthy volunteers participated in three MTS tasks: N-back, Stroop, and pain anticipation (PA). R-R interval (RRI), arterial blood pressure and finger photoplethysmogram (PPG) were continuously monitored before and during these MTS tasks. The magnitude of vasoconstriction was quantified using change in PPG amplitude (PPGa) from the baseline period. To represent basal autonomic function, we assessed both cardiac and vascular arms of the baroreflex during the baseline period. Cardiac baroreflex sensitivity (BRSc) was estimated by applying both the "sequence" and "spectral" techniques to beat-to-beat measurements of systolic blood pressure and RRIs. The vascular baroreflex sensitivity (BRSv) was quantified using the same approaches, modified for application to beat-to-beat diastolic blood pressure and PPGa measurements. Baseline BRSc was not different between SCD and non-SCD subjects, was not correlated with BRSv, and was not associated with the vasoconstriction responses to MTS tasks. BRSv in both groups was correlated with mean PPGa, and since both baseline PPGa and BRSv were lower in SCD, these results suggested that the SCD subjects were in a basal state of higher sympathetically mediated vascular tone. In both groups, baseline BRSv was positively correlated with the vasoconstriction responses to N-back, Stroop, and PA. After adjusting for differences in BRSv within and between groups, we found no difference in the vasoconstriction responses to all three mental tasks between SCD and non-SCD subjects. The implications of these findings are significant in subjects with SCD since vasoconstriction reduces microvascular flow and prolongs capillary transit time, increasing the likelihood for vaso-occlusive crisis (VOC) to be triggered by exposure to stressful events.

A physiological and dynamical systems model of stress

Stress responses vary drastically for a given set of stimuli, individuals, or points in time. A potential source of this variance that is not well characterized arises from the theory of stress as a dynamical system, which implies a complex, nonlinear relationship between environmental/situational inputs and the development/experience of stress. In this framework, stress vs. non-stress states exist as attractor basins in a physiologic phase space. Here, we develop a model of stress as a dynamical system by coupling closed loop physiologic control to a dynamic oscillator in an attractor landscape. By characterizing the evolution of this model through phase space, we demonstrate strong sensitivity to the parameters controlling the dynamics and demonstrate multiple features of stress responses found in current research, implying that these parameters may contribute to a significant source of variability observed in empiric stress research.

Validation of Affect-tag Affective and Cognitive Indicators

The Affect-tag solution measures physiological signals to deliver indicators derived from cognitive science. To provide the most accurate and effective results, a database of electrodermal activity (EDA) signals acquired using the Affect-tag A1 band was created. An experimental paradigm was designed to measure action-taking, autonomic regulation, cognitive load (CL), emotions, and stress, affects, and social stress. The Affect-tag emotional power (EP), emotional density (ED), and CL affective and cognitive indicators were refined based on the physiological responses of 48 participants during these tasks. Statistical significance was obtained for all indicators in tasks they were designed to measure, resulting in a total accuracy score of 89% for the combined indicators. Data obtained during this study will be further analyzed to define emotional and affective states.

Preliminary Evidence of Orthostatic Intolerance and Altered Cerebral Vascular Control Following Sport-Related Concussion

Concussions have been shown to result in autonomic dysfunction and altered cerebral vascular function. We tested the hypothesis that concussed athletes (CA) would have altered cerebral vascular function during acute decreases and increases in blood pressure compared to healthy controls (HC). Ten CA (age: 20 ± 2 y, 7 females) and 10 HC (age: 21 ± 2 y, 6 females) completed 5 min of lower body negative pressure (LBNP; −40 mmHg) and 5 min of lower body positive pressure (LBPP; 20 mmHg). Protocols were randomized and separated by 10 min. Mean arterial pressure (MAP) and middle cerebral artery blood velocity (MCAv) were continuously recorded. Cerebral vascular resistance (CVR) was calculated as MAP/MCAv. Values are reported as change from baseline to the last minute achieved (LBNP) or 5 min (LBPP). There were no differences in baseline values between groups. During LBNP, there were no differences in the change for MAP (CA: −23 ± 18 vs. HC: −21 ± 17 cm/s; P = 0.80) or MCAv (CA: −13 ± 8 vs. HC: −18 ± 9 cm/s; P = 0.19). The change in CVR was different between groups (CA: −0.08 ± 0.26 vs. HC: 0.18 ± 0.24 mmHg/cm/s; P = 0.04). Total LBNP time was lower for CA (204 ± 92 s) vs. HC (297 ± 64 s; P = 0.04). During LBPP, the change in MAP was not different between groups (CA: 13 ± 6 vs. HC: 10 ± 7 mmHg; P = 0.32). The change in MCAv (CA: 7 ± 6 vs. HC: −4 ± 13 cm/s; P = 0.04) and CVR (CA: −0.06 ± 0.27 vs. HC: 0.38 ± 0.41 mmHg/cm/s; P = 0.03) were different between groups. CA exhibited impaired tolerance to LBNP and had a different cerebral vascular response to LBPP compared to HC.

Acute mental stress-caused arterial stiffening can be counteracted by brief aerobic exercise

PURPOSE

Acute mental stress (MS) causes an elevation in pulse wave velocity (PWV), an index of arterial stiffness. In contrast, aerobic exercise acutely decreases arterial stiffness, even in the short term. The present study aimed to examine whether acute MS-caused arterial stiffening can be counteracted by brief aerobic exercise.

METHODS

Thirteen young healthy men (mean age, 20 ± 1 years) participated in two randomized experimental visits where they were subjected to acute MS followed by seated rest (RE) or cycling exercise (EX) trials. Following a 5-min MS task, the participants in the RE trial rested on a chair for 10 min (from 10 to 20 min after the cessation of the task), whereas those in the EX trial cycled at 35% of heart rate reserve for the same duration. Heart-brachial PWV (hbPWV), brachial-ankle PWV (baPWV), heart-ankle PWV (haPWV), and the cardio-ankle vascular index (CAVI) were simultaneously measured at baseline and 5, 30, and 45 min after the task.

RESULTS

Both trials caused significant elevations (P < 0.05) in hbPWV, haPWV, and CAVI at 5 min after the task; subsequently, this persisted until 45 min after the task in the RE trial, whereas the elevations in the EX trial were eliminated. In the RE trial, baPWV significantly increased (P < 0.05) at 30 and 45 min after the task, whereas such an increase was not observed in the EX trial.

CONCLUSION

The findings of the present study reveal that brief aerobic exercise counteracts arterial stiffening caused by acute MS.

Shift working disorders among nurses of Tehran hospital and its related factors in 2016

INTRODUCTION

Many adverse effects occur among the nurses due to shift work Hence, the present study aimed to determine the prevalence of shift work-related disorders and its related factor among the nurses at Tehran University Subsidiary Hospital, Iran, and to find solutions for managing the relevant health problems.

METHODS

In this cross-sectional study, the Survey of Shift workers (SOS) questionnaire and the Personal Information Form were used to collect data related to demographics and working conditions of 1259 randomly selected nurses working at Tehran University Subsidiary Hospital as statistical population.

RESULTS

According to the results, psychological disorders (95%), digestive problems (85%) and social problems (80%) were the most frequent problems among the subjects. Additionally, the satisfaction rate was higher among the volunteer nurses compared to nurses who were forced to do shift work (P < 0.05).

CONCLUSION

The nurses volunteered for shift work had higher satisfaction rate compared to nurses forced to shift work system; moreover, they had more job satisfaction and less shift work-related complaints. Therefore, it is important to select the nurses who are volunteer for shift work system. In addition, the shift work schedule in hospitals should be set based on workload and requirements because the shift schedule can adversely influence the social and family issues of the nurses, as well as their sleep quality and body biological process.

The role of the dorsomedial and ventromedial hypothalamus in regulating behaviorally coupled and resting autonomic drive

Nearly a century ago it was reported that stimulation of the hypothalamus could evoke profound behavioral state changes coupled with altered autonomic function. Since these initial observations, further studies in animals have revealed that two hypothalamic regions-the dorsomedial and ventromedial hypothalamic nuclei-are critical for numerous behaviors, including those in response to psychological stressors. These behaviors are coupled with changes in autonomic functions, such as altered blood pressure, heart rate, sympathetic nerve activity, resetting of the baroreflex and changes in pituitary function. There is also growing evidence that these two hypothalamic regions play a critical role in thermogenesis, and suggestions they could also be responsible for the hypertension associated with obesity. The aim of this chapter is to review the anatomy, projection patterns, and function of the dorsomedial and ventromedial hypothalamus with a particular focus on their role in autonomic regulation. While most of what is known about these two hypothalamic regions is derived from laboratory animal experiments, recent human studies will also be explored. Finally, we will describe recent human brain imaging studies that provide evidence of a role for these hypothalamic regions in setting resting sympathetic drive and their potential role in conditions such as hypertension.

Impact of acute mental stress on segmental arterial stiffness

PURPOSE

It has been reported that acute brief episodes of mental stress (MS) result in a prolonged increase in carotid-femoral pulse wave velocity (cfPWV), an index of aortic stiffness. However, whether acute MS also impacts arterial stiffness in other segments is unclear. The present study aimed to examine the impact of acute MS on segmental arterial stiffness.

METHODS

In the main experiment, 17 young male subjects (mean age, 20.1 ± 0.7 years) performed a 5-min MS and control (CON) task in a random order. Pulse wave velocity (PWV) from the heart to the brachium (hbPWV) and the ankle (haPWV), PWV between the brachial artery and the ankle (baPWV), and the cardio-ankle vascular index (CAVI) were simultaneously measured at baseline and 5, 15, and 30 min after the task.

RESULTS

Compared to baseline values, hbPWV, baPWV, haPWV, and CAVI significantly increased until 30 min after the MS task, whereas these variables did not significantly change following the CON task. At 5 and 30 min after the MS task, percentage changes from baseline were significantly higher in hbPWV (+ 5.2 ± 4.4 and 6.6 ± 4.9%) than in baPWV (+ 2.2 ± 2.1 and 2.2 ± 2.0%) or haPWV (+ 3.6 ± 2.6 and 4.3 ± 2.9%) and were also significantly lower in baPWV than in haPWV.

CONCLUSION

These findings suggest that acute MS elicits an increase in arterial stiffness in various segments and this arterial stiffening is not uniform among the segments.

Greater Daily Psychosocial Stress Exposure is Associated With Increased Norepinephrine-Induced Vasoconstriction in Young Adults

Background Epidemiological data suggest a link between psychological stress and increased cardiovascular disease risk; however, the underlying mechanisms remain incompletely understood. The purpose of this investigation was to directly examine the influence of daily psychosocial stress on microvascular adrenergic vasoconstrictor responsiveness in healthy adults. We hypothesized increased daily psychosocial stress would be positively related to increased norepinephrine-induced vasoconstriction. Methods and Results Eighteen healthy adults (19-36 years; 10 women) completed a daily psychosocial experiences telephone interview for 8 consecutive evenings in order to document their exposure and emotional responsiveness to common stressors (eg, arguments, work stress) over the preceding 24 hrs. On the last interview day, red cell flux (laser Doppler flowmetry) was measured during graded intradermal microdialysis perfusion of norepinephrine (10^-12 to 10^-2 mol/L) and expressed as a percentage of baseline vascular conductance. Exogenous norepinephrine elicited progressive and robust vasoconstriction in all individuals (maximal vasoconstriction: 71±4%_base; cumulative vasoconstriction [area under the curve]: 118±102 arbitrary units). Participants experienced a stressor on 51±5% of days and a total of 5.2±0.9 stressors over the 8-day time frame. Increased daily frequency of stressor exposure was positively related to both maximal (R²=0.26; P=0.03) and cumulative (R²=0.31; P=0.02) vasoconstrictor responsiveness. Likewise, the total number of stressors was associated with increased maximal (R²=0.40; P<0.01) and cumulative (R²=0.27; P=0.03) norepinephrine-induced vasoconstriction. Neither stressor severity nor stress-related emotions were related to vasoconstrictor responsiveness. Conclusions Collectively, these data suggest that daily psychosocial stressor exposure by itself is sufficient to adversely influence microvascular vasoconstrictor function, regardless of the perceived severity or emotional consequences of the stressor exposure.

Central Sympathetic Nervous System Effects on Cognitive-Motor Performance

Abstract. The intriguing interplay between acute stress physiology and cognitive processes has long been noted. However, while stress-induced release of glucocorticoids has repeatedly been shown to impact brain mechanisms underlying cognition and memory, less experimental research addressed the effects of stress-induced central sympathetic nervous system (SNS) activation on cognitive performance. Moreover, despite the long-standing notion that the way performance is modulated by arousal may crucially depend on task complexity, mechanistic research demonstrating a direct, causal influence of altered SNS activity is scarce. Twelve healthy men participated in a placebo-controlled, pharmacologic dose–response study involving three within-subject assessments (1-week intervals). Subjective and objective indices of SNS activity as well as reaction time (RT) in three different tasks varying in cognitive demand (simple RT, choice RT, and verbal RT in complex mental arithmetic) were assessed during modulation of central SNS tone by intravenous infusions of dexmedetomidine (alpha2-agonist), yohimbine (alpha2-antagonist), and placebo. Cognitive performance was negatively affected by alpha2-agonism in all task conditions. By contrast, administration of yohimbine improved simple RT, while diminishing complex RT, supporting the assumption of a nonlinear way of action depending on task characteristics. Our results highlight the consequences of central (noradrenergic) SNS activation for cognitive-motor performance in RT tasks of varying complexity.

Is Dementia in Parkinson' Disease Related to Chronic Stress, Anxiety, and Depression?

OBJECTIVES

Stress, anxiety, and depression are known to be associated with the development of neurodegenerative disorders through interactions with the underlying pathophysiology. We hypothesized that the presence of these symptoms contributes to cognitive disturbances and dementia in Parkinson's disease (PD). The present study aimed to investigate the levels of stress, anxiety, and depression in PD patients relative to healthy individuals.

MATERIALS AND METHODS

Anxiety, stress, and depression levels were assessed using standardized questionnaires in PD without dementia (PDND, n = 30), PD with dementia (PDD, n = 28), and healthy controls (HC, n = 26). Arithmetic subtraction task was used as a stressor. Galvanic skin response, heart rate and salivary cortisol, and alpha-amylase were measured during baseline and after induced stress (arithmetic task).

RESULTS

Acute anxiety, acute stress, and depression levels were significantly higher in PDND compared to HC, whereas both acute and chronic anxiety, stress, and depression levels were significantly higher in PDD compared to PDND and HC. Cortisol and alpha-amylase levels were significantly higher in PDND compared to HC during both baseline and postarithmetic task. Posttask levels of cortisol were lower in PDD compared to PDND.

CONCLUSION

This study concludes that higher levels of salivary cortisol and alpha-amylase at baseline and poststress task with normal levels of chronic stress and anxiety were associated with no dementia in PD. Presence of higher levels of acute, chronic anxiety, and stress along with depression with lower cortisol reactivity to stressor suggests onset of dementia in Parkinson's patients.

Surgeon Energy Expenditure and Substrate Utilization During Simulated Spine Surgery

INTRODUCTION

Orthopaedic surgery can be a physically demanding occupation with high rates of fatigue and burnout. Fatigue has been shown to affect surgeon performance with higher rates of errors in fatigued surgeons. The metabolic cost of performing surgery has yet to be quantified. A better understanding of these costs may provide insights into surgeon fatigue and its effect on patient safety.

METHODS

Eight subjects performed a one-level lumbar laminectomy and fusion on cadavers. Oxygen consumption (VO2) was measured via indirect calorimetry and used to calculate energy expenditure (EE). Substrate utilization was estimated from measurements of inspired and expired gases (ie, O2 and CO2, respectively). EE was also measured with the use of triaxial accelerometers.

RESULTS

The peak VO2 was 11.3 ± 0.4 mL/kg/min. The EEtotal was 132 ± 6 kcal corresponding to the EEtotal/hr of 142 ± 7 kcal/hr. Upper arm accelerometers (154.8 ± 9.8 kcal; r = 0.54) accurately estimated total EE. Subjects used, on average, 53% ± 4% CHO versus 47% ± 7% fat, with peak utilization of 65% ± 5% CHO versus 35% ± 15% fat.

DISCUSSION

Simulated orthopaedic spine surgery elicited modest but significant increases in EE over resting. Surgeons used a higher percentage of carbohydrate than would be expected for the intensity of the activity.

Mental stress causes vasoconstriction in subjects with sickle cell disease and in normal controls

Vaso-occlusive crisis (VOC) is a hallmark of sickle cell disease (SCD) and occurs when deoxygenated sickled red blood cells occlude the microvasculature. Any stimulus, such as mental stress, which decreases microvascular blood flow will increase the likelihood of red cell entrapment resulting in local vaso-occlusion and progression to VOC. Neurally mediated vasoconstriction might be the physiological link between crisis triggers and vaso-occlusion. In this study, we determined the effect of mental stress on microvascular blood flow and autonomic nervous system reactivity. Sickle cell patients and controls performed mentally stressful tasks, including a memory task, conflict test and pain anticipation test. Blood flow was measured using photoplethysmography, autonomic reactivity was derived from electrocardiography and perceived stress was measured by the State-Trait Anxiety Inventory questionnaire. Stress tasks induced a significant decrease in microvascular blood flow, parasympathetic withdrawal and sympathetic activation in all subjects. Of the various tests, pain anticipation caused the highest degree of vasoconstriction. The magnitude of vasoconstriction, sympathetic activation and perceived stress was greater during the Stroop conflict test than during the N-back memory test, indicating the relationship between magnitude of experimental stress and degree of regional vasoconstriction. Baseline anxiety had a significant effect on the vasoconstrictive response in sickle cell subjects but not in controls. In conclusion, mental stress caused vasoconstriction and autonomic nervous system reactivity in all subjects. Although the pattern of responses was not significantly different between the two groups, the consequences of vasoconstriction can be quite significant in SCD because of the resultant entrapment of sickle cells in the microvasculature. This suggests that mental stress can precipitate a VOC in SCD by causing neural-mediated vasoconstriction.

Unaltered neurocardiovascular reactions to mental stress after renal sympathetic denervation

Background: The impact of renal denervation (RDN) on muscle sympathetic nerve activity (MSNA) at rest remains controversial. Mental stress (MS) induces transient changes in sympathetic nerve activity, heart rate (HR) and blood pressure (BP). It is not known whether RDN modifies these changes.Purpose: The main objective was to assess the effect of RDN on MSNA and BP alterations during MS.Methods: In 14 patients (11 included in analysis) with resistant hypertension multi-unit MSNA, BP (Finometer ®) and HR were assessed at rest and during forced arithmetics at baseline and 6 months after RDN.Results: Systolic office BP decreased significantly 6 months after RDN (185 ± 29 vs.175 ± 33 mmHG; p = 0.04). No significant changes in MSNA at rest (68 ± 5 vs 73 ± 5 bursts/100hb; p = 0.43) were noted and no significant stress-induced change in group averaged sympathetic activity was found pre- (101 ± 24%; p = 0.9) or post-intervention (108 ± 26%; p = 0.37). Stress was associated with significant increases in mean arterial BP (p < 0.01) and HR (p < 0.01) at baseline, reactions which remained unaltered after intervention. We did not note any correlation between sympathetic nerve activity and BP changes after RDN.Conclusion: Thus, in our group of resistant hypertensives we find no support for the hypothesis that the BP-lowering effect of RDN depends on altered neurovascular responses to stress.

Effects of breathing movement on the reduction of postural sway during postural-cognitive dual tasking

An execution of cognitive processing interferes with postural sway during quiet standing. It reduces sway variability in young adults, but the mechanism is not clear. To elucidate the mechanisms, we focused on breathing in the present study. The purpose of this study was to clarify whether a decrease in postural sway amplitude during a postural-cognitive task is related to the change in breathing movement. The center of pressure (COP) was recorded via a force plate and the motion of leg joints (ankle, knee, and hip), and breathing movements were measured with a 3D motion capture system in quiet standing and standing with cognitive (mental arithmetic) task conditions. The change ratios of each variable from the quiet standing condition to the cognitive task were also calculated. It was shown that the MASt condition produced a significantly smaller RMS of COP displacement as compared to the QSt condition (p < 0.01). The results revealed that the breathing rate was faster and the amplitude of breathing movement smaller when subjects performed the cognitive task. A significant positive correlation (r = 0.75, p < 0.01) was found between the change ratio of breathing amplitude and the COP amplitude. The present results suggest that reduced standing postural sway during a cognitive task is related, at least in part, to a decrease in breathing amplitude.

Forearm vasodilator responses to environmental stress and reactive hyperaemia are impaired in young South Asian men

Purpose

Prevalence of cardiovascular disease (CVD) is greater in South Asians (SAs) than White Europeans (WEs). Endothelial dysfunction and blunted forearm vasodilatation to environmental stressors have been implicated in CVD. We investigated whether these features are present in young SA men.

Methods

In 15 SA and 16 WE men (19–23 years), we compared changes in forearm blood flow, arterial blood pressure (ABP), forearm vascular conductance (FVC), heart rate, and electrodermal resistance (EDR; sweating) following release of arterial occlusion (reactive hyperaemia endothelium-dependent) and 5 single sounds at 5–10 min intervals (stressors).

Results

All were normotensive. Peak reactive hyperaemia was smaller in SAs than WEs (FVC increase: 0.36 ± 0.038 vs 0.44 ± 0.038 units; P < 0.05). Furthermore, in WEs, mean FVC increased at 5, 15, and 20 s of each sound (vasodilatation), but increased at 5 s only in SAs, decreasing by 20 s (vasoconstriction). This reflected a smaller proportion of SAs showing forearm vasodilatation at 15 s (5/15 SAs vs 11/16 WEs: P < 0.01), the remainder showing vasoconstriction. Concomitantly, WEs showed greater bradycardia and EDR changes. Intra-class correlation analyses showed that all responses were highly reproducible over five sounds in both WEs and SAs. Moreover, sound-evoked changes in ABP and FVC were negatively correlated in each ethnicity (P < 0.01). However, WEs showed preponderance of forearm vasodilatation and depressor responses; SAs showed preponderance of vasoconstriction and pressor responses.

Conclusions

Endothelium-dependent vasodilatation is blunted in young SA men. This could explain their impaired forearm vasodilatation and greater pressor responses to repeated environmental stressors, so predisposing SAs to hypertension and CVD.

Mechanisms underpinning sympathetic nervous activity and its modulation using transcutaneous vagus nerve stimulation

NEW FINDINGS

What is the topic of this review? This review briefly considers what modulates sympathetic nerve activity and how it may change as we age or in pathological conditions. It then focuses on transcutaneous vagus nerve stimulation, a method of neuromodulation in autonomic cardiovascular control. What advances does it highlight? The review considers the pathways involved in eliciting the changes in autonomic balance seen with transcutaneous vagus nerve stimulation in relationship to other neuromodulatory techniques. The autonomic nervous system, consisting of the sympathetic and parasympathetic branches, is a major contributor to the maintenance of cardiovascular variables within homeostatic limits. As we age or in certain pathological conditions, the balance between the two branches changes such that sympathetic activity is more dominant, and this change in dominance is negatively correlated with prognosis in conditions such as heart failure. We have shown that non-invasive stimulation of the tragus of the ear increases parasympathetic activity and reduces sympathetic activity and that the extent of this effect is correlated with the baseline cardiovascular parameters of different subjects. The effects could be attributable to activation of the afferent branch of the vagus and, potentially, other sensory nerves in that region. This indicates that tragus stimulation may be a viable treatment in disorders where autonomic activity to the heart is compromised.

Deciphering the Neural Control of Sympathetic Nerve Activity: Status Report and Directions for Future Research

Sympathetic nerve activity (SNA) contributes appreciably to the control of physiological function, such that pathological alterations in SNA can lead to a variety of diseases. The goal of this review is to discuss the characteristics of SNA, briefly review the methodology that has been used to assess SNA and its control, and to describe the essential role of neurophysiological studies in conscious animals to provide additional insights into the regulation of SNA. Studies in both humans and animals have shown that SNA is rhythmic or organized into bursts whose frequency varies depending on experimental conditions and the species. These rhythms are generated by brainstem neurons, and conveyed to sympathetic preganglionic neurons through several pathways, including those emanating from the rostral ventrolateral medulla. Although rhythmic SNA is present in decerebrate animals (indicating that neurons in the brainstem and spinal cord are adequate to generate this activity), there is considerable evidence that a variety of supratentorial structures including the insular and prefrontal cortices, amygdala, and hypothalamic subnuclei provide inputs to the brainstem regions that regulate SNA. It is also known that the characteristics of SNA are altered during stress and particular behaviors such as the defense response and exercise. While it is a certainty that supratentorial structures contribute to changes in SNA during these behaviors, the neural underpinnings of the responses are yet to be established. Understanding how SNA is modified during affective responses and particular behaviors will require neurophysiological studies in awake, behaving animals, including those that entail recording activity from neurons that generate SNA. Recent studies have shown that responses of neurons in the central nervous system to most sensory inputs are context-specific. Future neurophysiological studies in conscious animals should also ascertain whether this general rule also applies to sensory signals that modify SNA.

Orthostatic Intolerance in Older Persons: Etiology and Countermeasures

Orthostatic challenge produced by upright posture may lead to syncope if the cardiovascular system is unable to maintain adequate brain perfusion. This review outlines orthostatic intolerance related to the aging process, long-term bedrest confinement, drugs, and disease. Aging-associated illness or injury due to falls often leads to hospitalization. Older patients spend up to 83% of hospital admission lying in bed and thus the consequences of bedrest confinement such as physiological deconditioning, functional decline, and orthostatic intolerance represent a central challenge in the care of the vulnerable older population. This review examines current scientific knowledge regarding orthostatic intolerance and how it comes about and provides a framework for understanding of (patho-) physiological concepts of cardiovascular (in-) stability in ambulatory and bedrest confined senior citizens as well as in individuals with disease conditions [e.g., orthostatic intolerance in patients with diabetes mellitus, multiple sclerosis, Parkinson's, spinal cord injury (SCI)] or those on multiple medications (polypharmacy). Understanding these aspects, along with cardio-postural interactions, is particularly important as blood pressure destabilization leading to orthostatic intolerance affects 3-4% of the general population, and in 4 out of 10 cases the exact cause remains elusive. Reviewed also are countermeasures to orthostatic intolerance such as exercise, water drinking, mental arithmetic, cognitive training, and respiration training in SCI patients. We speculate that optimally applied countermeasures such as mental challenge maintain sympathetic activity, and improve venous return, stroke volume, and consequently, blood pressure during upright standing. Finally, this paper emphasizes the importance of an active life style in old age and why early re-mobilization following bedrest confinement or bedrest is crucial in preventing orthostatic intolerance, falls and falls-related injuries in older persons.

Ventilation inhibits sympathetic action potential recruitment even during severe chemoreflex stress

This study investigated the influence of ventilation on sympathetic action potential (AP) discharge patterns during varying levels of high chemoreflex stress. In seven trained breath-hold divers (age 33 ± 12 yr), we measured muscle sympathetic nerve activity (MSNA) at baseline, during preparatory rebreathing (RBR), and during 1) functional residual capacity apnea (FRC_Apnea) and 2) continued RBR. Data from RBR were analyzed at matched (i.e., to FRC_Apnea) hemoglobin saturation (HbSat) levels (RBR_Matched) or more severe levels (RBR_End). A third protocol compared alternating periods (30 s) of FRC and RBR (FRC-RBR_ALT). Subjects continued each protocol until 85% volitional tolerance. AP patterns in MSNA (i.e., providing the true neural content of each sympathetic burst) were studied using wavelet-based methodology. First, for similar levels of chemoreflex stress (both HbSat: 71 ± 6%; P = NS), RBR_Matched was associated with reduced AP frequency and APs per burst compared with FRC_Apnea (both P < 0.001). When APs were binned according to peak-to-peak amplitude (i.e., into clusters), total AP clusters increased during FRC_Apnea (+10 ± 2; P < 0.001) but not during RBR_Matched (+1 ± 2; P = NS). Second, despite more severe chemoreflex stress during RBR_End (HbSat: 56 ± 13 vs. 71 ± 6%; P < 0.001), RBR_End was associated with a restrained increase in the APs per burst (FRC_Apnea: +18 ± 7; RBR_End: +11 ± 5) and total AP clusters (FRC_Apnea: +10 ± 2; RBR_End: +6 ± 4) (both P < 0.01). During FRC-RBR_ALT, all periods of FRC elicited sympathetic AP recruitment (all P < 0.001), whereas all periods of RBR were associated with complete withdrawal of AP recruitment (all P = NS). Presently, we demonstrate that ventilation per se restrains and/or inhibits sympathetic axonal recruitment during high, and even extreme, chemoreflex stress.NEW & NOTEWORTHY The current study demonstrates that the sympathetic neural recruitment patterns observed during chemoreflex activation induced by rebreathing or apnea are restrained and/or inhibited by the act of ventilation per se, despite similar, or even greater, levels of severe chemoreflex stress. Therefore, ventilation modulates not only the timing of sympathetic bursts but also the within-burst axonal recruitment normally observed during progressive chemoreflex stress.

Voluntary reduction of force variability via modulation of low-frequency oscillations

Visual feedback can influence the force output by changing the power in frequencies below 1 Hz. However, it remains unknown whether visual guidance can help an individual reduce force variability voluntarily. The purpose of this study, therefore, was to determine whether an individual can voluntarily reduce force variability during constant contractions with visual guidance, and whether this reduction is associated with a decrease in the power of low-frequency oscillations (0-1 Hz) in force and muscle activity. Twenty young adults (27.6 ± 3.4 years) matched a force target of 15% MVC (maximal voluntary contraction) with ankle dorsiflexion. Participants performed six visually unrestricted contractions, from which we selected the trial with the least variability. Following, participants performed six visually guided contractions and were encouraged to reduce their force variability within two guidelines (±1 SD of the least variable unrestricted trial). Participants decreased the SD of force by 45% (P < 0.001) during the guided condition, without changing mean force (P > 0.2). The decrease in force variability was associated with decreased low-frequency oscillations (0-1 Hz) in force (R ² = 0.59), which was associated with decreased low-frequency oscillations in EMG bursts (R ² = 0.35). The reduction in low-frequency oscillations in EMG burst was positively associated with power in the interference EMG from 35 to 60 Hz (R ² = 0.47). In conclusion, voluntary reduction of force variability is associated with decreased low-frequency oscillations in EMG bursts and consequently force output. We provide novel evidence that visual guidance allows healthy young adults to reduce force variability voluntarily likely by adjusting the low-frequency oscillations in the neural drive.

Folic acid supplementation increases cutaneous vasodilator sensitivity to sympathetic nerve activity in older adults

During heat stress, blunted increases in skin sympathetic nervous system activity (SSNA) and reductions in end-organ vascular responsiveness contribute to the age-related reduction in reflex cutaneous vasodilation. In older adults, folic acid supplementation improves the cutaneous vascular conductance (CVC) response to passive heating; however, the influence of folic acid supplementation on SSNA:CVC transduction is unknown. Fourteen older adults (66 ± 1 yr, 8 male/6 female) ingested folic acid (5 mg/day) or placebo for 6 wk in a randomized, double-blind, crossover design. In protocol 1, esophageal temperature (T_es) was increased by 1.0°C (water-perfused suit) while SSNA (peroneal microneurography) and red cell flux in the innervated dermatome (laser Doppler flowmetry; dorsum of the foot) were continuously measured. In protocol 2, two intradermal microdialysis fibers were placed in the skin of the lateral calf for graded infusions of acetylcholine (ACh; 10^-10 to 10^-1 M) with and without nitric oxide synthase (NOS) blockade (20 mM nitro-l-arginine methyl ester). Folic acid improved reflex vasodilation (46 ± 4% vs. 31 ± 3% CVC_max for placebo; P < 0.001) without affecting the increase in SSNA (Δ506 ± 104% vs. Δ415 ± 73% for placebo; NS). Folic acid increased the slope of the SSNA-to-CVC relation (0.08 ± 0.02 vs. 0.05 ± 0.01 for placebo; P < 0.05) and extended the response range. Folic acid augmented ACh-induced vasodilation (83 ± 3% vs. 66 ± 4% CVC_max for placebo; P = 0.002); however, there was no difference between treatments at the NOS-inhibited site (53 ± 4% vs. 52 ± 4% CVC_max for placebo; NS). These data demonstrate that folic acid supplementation enhances reflex vasodilation by increasing the sensitivity of skin arterioles to central sympathetic nerve outflow during hyperthermia in aged human subjects.

Sensory trigeminal ULF-TENS stimulation reduces HRV response to experimentally induced arithmetic stress: A randomized clinical trial

Ultra Low Frequency Transcutaneous Electric Nervous Stimulation (ULF-TENS) is extensively used for pain relief and for the diagnosis and treatment of temporomandibular disorders (TMD). In addition to its local effects, ULF-TENS acts on the autonomic nervous system (ANS), with particular reference to the periaqueductal gray (PAG), promoting the release of endogenous opioids and modulating descending pain systems. It has been suggested that the PAG participates in the coupling between the emotional stimulus and the appropriate behavioral autonomic response. This function is successfully investigated by HRV. Therefore, our goal is to investigate the effects of trigeminal ULF-TENS stimulation on autonomic behavior in terms of HRV and respiratory parameters during an experimentally-induced arithmetic stress test in healthy subjects. Thirty healthy women between 25 and 35years of age were enrolled and randomly assigned to either the control (TENS stimulation off) or test group (TENS stimulation on). Heart (HR, LF, HF, LF/HF ratio, DET, RMSSD, PNN50, RR) and respiratory (BR) rate were evaluated under basal, T1 (TENS off/on), and stress (mathematical task) conditions. Results showed that HRV parameters and BR significantly changed during the arithmetic stress paradigm (p<0.01). Independently of stress conditions, TENS and control group could be discriminated only by non-linear HRV data, namely RR and DET (p=0.038 and p=0.027, respectively). During the arithmetic task, LF/HF ratio was the most sensitive parameter to discriminate between groups (p=0.019). Our data suggest that trigeminal sensory ULF-TENS reduces the autonomic response in terms of HRV and BR during acute mental stress in healthy subjects. Future directions of our work aim at applying the HRV and BR analysis, with and without TENS stimulation, to individuals with dysfunctional ANS among those with TMD.

Low-Frequency Oscillations and Control of the Motor Output

A less precise force output impairs our ability to perform movements, learn new motor tasks, and use tools. Here we show that low-frequency oscillations in force are detrimental to force precision. We summarize the recent evidence that low-frequency oscillations in force output represent oscillations of the spinal motor neuron pool from the voluntary drive, and can be modulated by shifting power to higher frequencies. Further, force oscillations below 0.5 Hz impair force precision with increased voluntary drive, aging, and neurological disease. We argue that the low-frequency oscillations are (1) embedded in the descending drive as shown by the activation of multiple spinal motor neurons, (2) are altered with force intensity and brain pathology, and (3) can be modulated by visual feedback and motor training to enhance force precision. Thus, low-frequency oscillations in force provide insight into how the human brain regulates force precision.

Neurovascular mechanisms underlying augmented cold-induced reflex cutaneous vasoconstriction in human hypertension

KEY POINTS

In hypertensive adults (HTN), cardiovascular risk increases disproportionately during environmental cold exposure. Despite ample evidence of dysregulated sympathetic control of the peripheral vasculature in hypertension, no studies have examined integrated neurovascular function during cold stress in HTN. The findings of the present study show that whole-body cold stress elicits greater increases in sympathetic outflow directed to the cutaneous vasculature and, correspondingly, greater reductions in skin blood flow in HTN. We further demonstrate an important role for non-adrenergic sympathetic co-transmitters in mediating the vasoconstrictor response to cold stress in hypertension. In the context of thermoregulation and the maintenance of core temperature, sympathetically-mediated control of the cutaneous vasculature is not only preserved, but also exaggerated in hypertension. Given the increasing prevalence of hypertension, clarifying the mechanistic underpinnings of hypertension-induced alterations in neurovascular function during cold exposure is clinically relevant.

ABSTRACT

Despite ample evidence of dysregulated sympathetic control of the peripheral vasculature in hypertension, no studies have examined integrated neurovascular function during cold stress in hypertensive adults (HTN). We hypothesized that (i) whole-body cooling would elicit greater cutaneous vasoconstriction and greater increases in skin sympathetic nervous system activity (SSNA) in HTN (n = 14; 56 ± 2 years) compared to age-matched normotensive adults (NTN; n = 14; 55 ± 2 years) and (ii) augmented reflex vasoconstriction in HTN would be mediated by an increase in cutaneous vascular adrenergic sensitivity and a greater contribution of non-adrenergic sympathetic co-transmitters. SSNA (peroneal microneurography) and red cell flux (laser Doppler flowmetry; dorsum of foot) were measured during whole-body cooling (water-perfused suit). Sympathetic adrenergic- and non-adrenergic-dependent contributions to reflex cutaneous vasoconstriction and vascular adrenergic sensitivity were assessed pharmacologically using intradermal microdialysis. Cooling elicited greater increases in SSNA (NTN: +64 ± 13%_baseline  vs. HTN: +194 ± 26%_baseline ; P < 0.01) and greater reductions in skin blood flow (NTN: -16 ± 2%_baseline  vs. HTN: -28 ± 3%_baseline ; P < 0.01) in HTN compared to NTN, reflecting an increased response range for sympathetic reflex control of cutaneous vasoconstriction in HTN. Norepinephrine dose-response curves showed no HTN-related difference in cutaneous adrenergic sensitivity (logEC₅₀ ; NTN: -7.4 ± 0.3 log M vs. HTN: -7.5 ± 0.3 log M; P = 0.84); however, non-adrenergic sympathetic co-transmitters mediated a significant portion of the vasoconstrictor response to cold stress in HTN. Collectively, these findings indicate that hypertension increases the peripheral cutaneous vasoconstrictor response to cold via greater increases in skin sympathetic outflow coupled with an increased reliance on non-adrenergic neurotransmitters.

Cognitive Stress Reduces the Effect of Levodopa on Parkinson's Resting Tremor

Aims

Resting tremor in Parkinson′s disease (PD) increases markedly during cognitive stress. Dopamine depletion in the basal ganglia is involved in the pathophysiology of resting tremor, but it is unclear whether this contribution is altered under cognitive stress. We test the hypothesis that cognitive stress modulates the levodopa effect on resting tremor.

Methods

Tremulous PD patients (n = 69) were measured in two treatment conditions (OFF vs. ON levodopa) and in two behavioral contexts (rest vs. cognitive co‐activation). Using accelerometry, we tested the effect of both interventions on tremor intensity and tremor variability.

Results

Levodopa significantly reduced tremor intensity (across behavioral contexts), while cognitive co‐activation increased it (across treatment conditions). Crucially, the levodopa effect was significantly smaller during cognitive co‐activation than during rest. Resting tremor variability increased after levodopa and decreased during cognitive co‐activation.

Conclusion

Cognitive stress reduces the levodopa effect on Parkinson's tremor. This effect may be explained by a stress‐related depletion of dopamine in the basal ganglia motor circuit, by stress‐related involvement of nondopaminergic mechanisms in tremor (e.g., noradrenaline), or both. Targeting these mechanisms may open new windows for treatment. Clinical tremor assessments under evoked cognitive stress (e.g., counting tasks) may avoid overestimation of treatment effects in real life.

Cerebral and neural regulation of cardiovascular activity during mental stress

Background

Mental arithmetic has been verified inducing cerebral and cardiovascular responses. However, the mechanism and sequential responses are still ambiguous. This study aims to reveal the mechanism of cardiovascular and autonomic responses and the related scalp positions that regulate the autonomic nerves system (ANS) during MA task.

Methods

34 healthy male subjects aged between 19 and 27 years old (mean age 23.6 ± 2.3 years) were recruited in. Electrocardiogram, impedance cardiography, beat-to-beat blood pressure and electroencephalography were measured simultaneously and continuously during the experiments. And the analysis of time–frequency, approximate entropy and Pearson correlation coefficient were adopted. For statistical comparison, paired t test is utilized in the study.

Results

The results showed that mental arithmetic task increased heart rate (from 72.35 ± 1.88 to 80.38 ± 2.34), blood pressure (systolic blood pressure: from 112.09 ± 3.23 to 126.79 ± 3.44; diastolic blood pressure: from 74.15 ± 1.93 to 81.20 ± 1.97), and cardiac output (from 8.71 ± 0.30 to 9.68 ± 0.35), and the mental arithmetic induced physiological responses could be divided into two stages, the first stage (10–110 s) and late stage (150–250 s). The high frequency power component (HF) of HRV decreased during MA, but the normalized low frequency power component (nLF) and LF/HF ratio of HRV increased only at the late stage. Moreover, during first stage, the correlations between approximate entropy of electroencephalography at Fp2, Fz, F4, F7 and the corresponding time–frequency results of HF were significant. During the late stage, the correlations between approximate entropy of electroencephalography at Fp2, Fz, C3, C4 and the corresponding nLF was significant.

Conclusions

Our results demonstrated that (1) mental stress induces time-dependent ANS activity and cardiovascular response. (2) Parasympathetic activity is lower during mental arithmetic task, but sympathetic nerve is activated only during late stage of mental arithmetic task. (3) Brain influences the cardiac activity through prefrontal and temporal cortex with the activation of ANS during mental arithmetic.

Rate of rise in diastolic blood pressure influences vascular sympathetic response to mental stress

KEY POINTS

Research indicates that individuals may experience a rise (positive responders) or fall (negative responders) in muscle sympathetic nerve activity (MSNA) during mental stress. In this study, we examined the early blood pressure responses (including the peak, time of peak and rate of rise in blood pressure) to mental stress in positive and negative responders. Negative MSNA responders to mental stress exhibit a more rapid rise in diastolic pressure at the onset of the stressor, suggesting a baroreflex-mediated suppression of MSNA. In positive responders there is a more sluggish rise in blood pressure during mental stress, which appears to be MSNA-driven. This study suggests that whether MSNA has a role in the pressor response is dependent upon the reactivity of blood pressure early in the task.

ABSTRACT

Research indicates that individuals may experience a rise (positive responders) or fall (negative responders) in muscle sympathetic nerve activity (MSNA) during mental stress. The aim was to examine the early blood pressure response to stress in positive and negative responders and thus its influence on the direction of change in MSNA. Blood pressure and MSNA were recorded continuously in 21 healthy young males during 2 min mental stressors (mental arithmetic, Stroop test) and physical stressors (cold pressor, handgrip exercise, post-exercise ischaemia). Participants were classified as negative or positive responders according to the direction of the mean change in MSNA during the stressor tasks. The peak changes, time of peak and rate of changes in blood pressure were compared between groups. During mental arithmetic negative responders experienced a significantly greater rate of rise in diastolic blood pressure in the first minute of the task (1.3 ± 0.5 mmHg s^-1 ) compared with positive responders (0.4 ± 0.1 mmHg s^-1 ; P = 0.03). Similar results were found for the Stroop test. Physical tasks elicited robust parallel increases in blood pressure and MSNA across participants. It is concluded that negative MSNA responders to mental stress exhibit a more rapid rise in diastolic pressure at the onset of the stressor, suggesting a baroreflex-mediated suppression of MSNA. In positive responders there is a more sluggish rise in blood pressure during mental stress, which appears to be MSNA-driven. This study suggests that whether MSNA has a role in the pressor response is dependent upon the reactivity of blood pressure early in the task.

The patient's perspective: The effect of levodopa on Parkinson symptoms

BACKGROUND

Dopaminergic medication adjustments in Parkinson's disease are often solely based on patient reports. However, it is unclear how well patient-based ratings of the levodopa response correlate with clinician-based ratings, and whether this correlation differs between motor symptoms. Here we compare patient-clinician agreement for the effect of levodopa on resting tremor and bradykinesia/rigidity. Furthermore, given patients' reports that tremor is most troublesome during stress, we test for differences in patient-clinician agreement between tremor at rest and stress-induced tremor.

METHODS

We included 42 tremulous Parkinson patients, who were clinically rated (using the MDS-UPDRS) in a practically defined OFF-state and after levodopa-benserazide 200/50 mg. Using accelerometry, we quantified the effect of dopaminergic medication and behavioral context (rest vs. cognitive stress) on tremor intensity. Patients rated medication effects on tremor and bradykinesia/rigidity using visual analogue scales.

RESULTS

There was only moderate patient-clinician agreement for the effect of levodopa on bradykinesia/rigidity (R² = 0.18; p < 0.01), and a tendency towards larger agreement for tremor (R² = 0.44; p < 0.001; difference between correlation coefficients: z = 1.64; p = 0.051). Patient ratings of tremor changes correlated significantly better with accelerometry for tremor during cognitive stress (R² = 0.35; p < 0.001) vs. tremor at rest (R² = 0.12; p < 0.05; difference: z = -2.35, p < 0.01).

CONCLUSION

The moderate correlations between patient ratings and clinical/accelerometry changes indicate the need for methods to better monitor symptom severity and impairments in daily life, for example wearable sensors. Our findings also suggest that context matters: Parkinson patients' subjective experience of levodopa effectiveness on tremor was largely based on the ability of levodopa to reduce tremor during cognitive stress.