Functional magnetic resonance signal changes in neural structures to baroreceptor reflex activation

A conceptual framework for a neurophysiological basis of art therapy for PTSD

Post-traumatic stress disorder (PTSD) is a heterogeneous condition that affects many civilians and military service members. Lack of engagement, high dropout rate, and variable response to psychotherapy necessitates more compelling and accessible treatment options that are based on sound neuroscientific evidence-informed decision-making. Art therapy incorporates elements proven to be effective in psychotherapy, such as exposure, making it a potentially valuable treatment option. This conceptual paper aims to inform the neurophysiological rationale for the use of art therapy as a therapeutic approach for individuals with PTSD. A narrative synthesis was conducted using literature review of empirical research on the neurophysiological effects of art therapy, with supporting literature on neuroaesthetics and psychotherapies to identify art therapy factors most pertinent for PTSD. Findings were synthesized through a proposed framework based on the triple network model considering the network-based dysfunctions due to PTSD. Art therapy's active components, such as concretization and metaphor, active art engagement, emotion processing and regulation, perspective taking and reframing, and therapeutic alliance, may improve symptoms of PTSD and prompt adaptive brain functioning. Given the scarcity of rigorous studies on art therapy's effectiveness and mechanisms of alleviating PTSD symptoms, the suggested framework offers a neurophysiological rationale and a future research agenda to investigate the impact of art therapy as a therapeutic approach for individuals with PTSD.

The effect of a single-session heart rate variability biofeedback on attentional control: does stress matter?

Introduction

Vagally mediated heart rate variability is an index of autonomic nervous system activity that is associated with a large variety of outcome variables including psychopathology and self-regulation. While practicing heart rate variability biofeedback over several weeks has been reliably associated with a number of positive outcomes, its acute effects are not well known. As the strongest association with vagally mediated heart rate variability has been found particularly within the attention-related subdomain of self-regulation, we investigated the acute effect of heart rate variability biofeedback on attentional control using the revised Attention Network Test.

Methods

Fifty-six participants were tested in two sessions. In one session each participant received a heart rate variability biofeedback intervention, and in the other session a control intervention of paced breathing at a normal ventilation rate. After the biofeedback or control intervention, participants completed the Attention Network Test using the Orienting Score as a measure of attentional control.

Results

Mixed models revealed that higher resting baseline vagally mediated heart rate variability was associated with better performance in attentional control, which suggests more efficient direction of attention to target stimuli. There was no significant main effect of the intervention on attentional control. However, an interaction effect indicated better performance in attentional control after biofeedback in individuals who reported higher current stress levels.

Discussion

The results point to acute beneficial effects of heart rate variability biofeedback on cognitive performance in highly stressed individuals. Although promising, the results need to be replicated in larger or more targeted samples in order to reach stronger conclusions about the effects.

Effect of hydrotherapy, balneotherapy, and spa therapy on blood pressure: a mini-review

Hypertension (high blood pressure) is one of the most common health conditions. When your blood pressure is high for a long term, it can cause health problems, such as heart disease. In addition to the main methods of treatment, there are various methods of adjuvant therapy, one of the most common of which is hydrotherapy. In this review study, we examined the effects of hydrotherapy, balneotherapy, and spa therapy on blood pressure. We searched the PubMed/MEDLINE, Web of Science, Scopus, and Science Direct databases until April 2022 using related keywords. In summary, the current study shows that different hydrotherapy methods may improve blood pressure. Hydrotherapy as one of the adjunctive therapy methods can be effective in lowering blood pressure. Blood circulation is smoothed by the warmth of the water. This improvement may be achieved by regulating heart rate, releasing hormones that control blood pressure, or regulating the activity of baroreceptors or chemoreceptors. In addition to using medications, hypertension patients also use non-pharmacological approaches in their care, including hydrotherapy, balneotherapy, and warm water foot soaks performed at home. Although several lines of evidence show the potential effects of hydrotherapy, balneotherapy, and spa therapy on blood pressure, many clinical trials are needed.

Altered 5-HT2A/C receptor binding in the medulla oblongata in the sudden infant death syndrome (SIDS): Part I. Tissue-based evidence for serotonin receptor signaling abnormalities in cardiorespiratory- and arousal-related circuits

The sudden infant death syndrome (SIDS), the leading cause of postneonatal infant mortality in the United States, is typically associated with a sleep period. Previously, we showed evidence of serotonergic abnormalities in the medulla (e.g. altered serotonin (5-HT)1A receptor binding), in SIDS cases. In rodents, 5-HT2A/C receptor signaling contributes to arousal and autoresuscitation, protecting brain oxygen status during sleep. Nonetheless, the role of 5-HT2A/C receptors in the pathophysiology of SIDS is unclear. We hypothesize that in SIDS, 5-HT2A/C receptor binding is altered in medullary nuclei that are key for arousal and autoresuscitation. Here, we report altered 5-HT2A/C binding in several key medullary nuclei in SIDS cases (n = 58) compared to controls (n = 12). In some nuclei the reduced 5-HT2A/C and 5-HT1A binding overlapped, suggesting abnormal 5-HT receptor interactions. The data presented here (Part 1) suggest that a subset of SIDS is due in part to abnormal 5-HT2A/C and 5-HT1A signaling across multiple medullary nuclei vital for arousal and autoresuscitation. In Part II to follow, we highlight 8 medullary subnetworks with altered 5-HT receptor binding in SIDS. We propose the existence of an integrative brainstem network that fails to facilitate arousal and/or autoresuscitation in SIDS cases.

Exploring the brain with sleep-related injuries, and fixing it

The focus of my research efforts rests with determining dysfunctional neural systems underlying disorders of sleep, and identifying interventions to overcome those disorders. Aberrant central and physiological control during sleep exerts serious consequences, including disruptions in breathing, motor control, blood pressure, mood, and cognition, and plays a major role in sudden infant death syndrome, congenital central hypoventilation, and sudden unexpected death in epilepsy, among other concerns. The disruptions can be traced to brain structural injury, leading to inappropriate outcomes. Identification of failing systems arose from the assessment of single neuron discharge in intact, freely moving and state-changing human and animal preparations within multiple systems, including serotonergic action and motor control sites. Optical imaging of chemosensitive, blood pressure and other breathing regulatory areas, especially during development, were useful to show integration of regional cellular action in modifying neural output. Identification of damaged neural sites in control and afflicted humans through structural and functional magnetic resonance imaging procedures helped to identify the sources of injury, and the nature of interactions between brain sites that compromise physiological systems and lead to failure. Interventions to overcome flawed regulatory processes were developed, and incorporate noninvasive neuromodulatory means to recruit ancient reflexes or provide peripheral sensory stimulation to assist breathing drive to overcome apnea, reduce the frequency of seizures, and support blood pressure in conditions where a failure to perfuse can lead to death.

Breathing Exercises for Improving Cognitive Function in Patients with Stroke

Patients with stroke may experience a certain degree of cognitive decline during the period of recovery, and a considerable number of such patients have been reported to show permanent cognitive damage. Therefore, the period of recovery and rehabilitation following stroke is critical for rapid cognitive functional improvements. As dysfunctional breathing has been reported as one of the factors affecting the quality of life post stroke, a number of studies have focused on the need for improving the breathing function in these patients. Numerous breathing exercises have been reported to enhance the respiratory, pulmonary, cognitive, and psychological functions. However, scientific evidence on the underlying mechanisms by which these exercises improve cognitive function is scattered at best. Therefore, it has been difficult to establish a protocol of breathing exercises for patients with stroke. In this review, we summarize the psychological, vascular, sleep-related, and biochemical factors influencing cognition in patients and highlight the need for breathing exercises based on existing studies. Breathing exercises are expected to contribute to improvements in cognitive function in stroke based on a diverse array of supporting evidence. With relevant follow-up studies, a protocol of breathing exercises can be developed for improving the cognitive function in patients with stroke.

The Solitary Nucleus Connectivity to Key Autonomic Regions in Humans MRI and Literature based Considerations

The nucleus tractus solitarius (NTS), is a key brainstem structure relaying interoceptive peripheral information to the interrelated brain centers for eliciting rapid autonomic responses and for shaping longer-term neuroendocrine and motor patterns. Structural and functional NTS' connectivity has been extensively investigated in laboratory animals. But there is limited information about NTS' connectome in humans. Using MRI, we examined diffusion and resting state data from 20 healthy participants in the Human Connectome Project. The regions within the brainstem (n=8), subcortical (n=6), cerebellar (n=2) and cortical (n=5) parts of the brain were selected via a systematic review of the literature and their white matter NTS connections were evaluated via probabilistic tractography along with functional and directional (i.e., Granger-causality) analyses. The underlying study confirms previous results from animal models and provides novel aspects on NTS integration in humans. Two key findings can be summarized: (i) the NTS predominantly processes afferent input and (ii) a lateralization towards a predominantly left-sided NTS processing. Our results lay the foundations for future investigations into the NTS' tripartite role comprised of interoreceptors' input integration, the resultant neurochemical outflow and cognitive/affective processing. The implications of these data add to the understanding of NTS' role in specific aspects of autonomic functions.

A Method for More Accurate Determination of Resonance Frequency of the Cardiovascular System, and Evaluation of a Program to Perform It

This study validated a more exact automated method of determining cardiovascular resonance frequency (RF) against the "stepped" protocol described by Lehrer et al. (Appl Psychophysiol Biofeedback 25(3):177-191, https://doi.org/10.1023/a:1009554825745 , 2000; in Foundations of heart rate variability biofeedback: A book of readings, The Association for Applied Psychophysiology and Biofeedback, pp 9-19, 2016). Thirteen participants completed a 15-min RF determination session by each method. The "stepped" protocol assesses HRV in five 3-min stationary windows from 4.5 to 6.5 breaths per minute (bpm), decreasing in 0.5 bpm steps. Multiple criteria, subjectively weighted by the clinician, determines RF. For this study, the proposed method used a sliding window with a fixed rate of change (67.04 ms per breath) at each of 78 breath cycles ranging from 4.25 to 6.75 bpm. Its algorithm analyzes IBI to locate the midpoint of the 1-min region of stable maximum peak-trough variability. RF is quantified from breath duration at that point. The software generates a visual display of superimposed HR and breathing data. Thus, the new method fully automates RF determination. Eleven of the 13 matched pairs fell within the 0.5 bpm resolution of the stepped method. Comparisons of LF power generated by the autoregressive (AR) spectral method showed a strong correlation in LF power production by the stepped and sliding methods (R = 0.751, p = 0.000). The "sliding" pacing protocol was favored by 69% of participants (p < 0.02). The new, fully-automated, method may facilitate both in-person and remote HRV biofeedback training. Software is available open-source.

Heart Rate Variability Biofeedback Improves Emotional and Physical Health and Performance: A Systematic Review and Meta Analysis

We performed a systematic and meta analytic review of heart rate variability biofeedback (HRVB) for various symptoms and human functioning. We analyzed all problems addressed by HRVB and all outcome measures in all studies, whether or not relevant to the studied population, among randomly controlled studies. Targets included various biological and psychological problems and issues with athletic, cognitive, and artistic performance. Our initial review yielded 1868 papers, from which 58 met inclusion criteria. A significant small to moderate effect size was found favoring HRVB, which does not differ from that of other effective treatments. With a small number of studies for each, HRVB has the largest effect sizes for anxiety, depression, anger and athletic/artistic performance and the smallest effect sizes on PTSD, sleep and quality of life. We found no significant differences for number of treatment sessions or weeks between pretest and post-test, whether the outcome measure was targeted to the population, or year of publication. Effect sizes are larger in comparison to inactive than active control conditions although significant for both. HRVB improves symptoms and functioning in many areas, both in the normal and pathological ranges. It appears useful as a complementary treatment. Further research is needed to confirm its efficacy for particular applications.

Functional organization of the insula in men and women with obstructive sleep apnea during Valsalva

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) patients show impaired autonomic regulation, perhaps related to functional reorganization of the insula, which in healthy individuals shows sex-specific anterior and right dominance during sympathetic activation. We examined insular organization of responses to a Valsalva maneuver in OSA with functional magnetic resonance imaging (fMRI).

METHODS

We studied 43 newly diagnosed OSA (age mean ± SD: 46.8 ± 8.7 years; apnea-hypopnea index (AHI) ± SD: 32.1 ± 20.1 events/hour; 34 males) and 63 healthy (47.2 ± 8.8 years; 40 males) participants. Participants performed four 18-second Valsalva maneuvers (1-minute intervals, pressure ≥ 30 mmHg) during scanning. fMRI time trends from five insular gyri-anterior short (ASG); mid short (MSG); posterior short (PSG); anterior long (ALG); and posterior long (PLG)-were assessed for within-group responses and between-group differences with repeated measures ANOVA (p < 0.05); age and resting heart rate (HR) influences were also assessed.

RESULTS

Right and anterior fMRI signal dominance appeared in OSA and controls, with no between-group differences. Separation by sex revealed group differences. Left ASG anterior signal dominance was lower in OSA versus control males. Left ASG and ALG anterior dominance was higher in OSA versus control females. In all right gyri, only OSA females showed greater anterior dominance than controls. Right dominance was apparent in PSG and ALG in all groups; females showed right dominance in MSG and PLG. OSA males did not show PLG right dominance. Responses were influenced substantially by HR but modestly by age.

CONCLUSIONS

Anterior and right insular fMRI dominance appears similar in OSA versus control participants during the sympathetic phase of the Valsalva maneuver. OSA and control similarities were present in just males, but not necessarily females, which may reflect sex-specific neural injury.

Heart Rate Variability and Erectile Function in Younger Men: A Pilot Study

Erectile dysfunction (ED) in younger men is an increasing concern. In middle aged and older men, ED was related to lower resting heart rate variability (HRV), but research in younger men is lacking. The present study examined, in a nonclinical sample of 105 men between 18 and 39 years, the association of ED with several parameters of resting HRV. Scores of the 5-item version of the International Index of Erectile Function (IIEF-5) below 22 were considered as indicating ED. Eighteen men (17.1%) reported ED (mild in 16, mild to moderate in 2). Welch's tests revealed that ED was associated with lower low-frequency power (LF), lower high-frequency power (HF), lower standard deviation of interbeat intervals, and lower standard deviation of the heart rate, which is influenced by both sympathetic and parasympathetic activity. After removing outliers, ED was unrelated to HF. In younger men, erections might be facilitated by a combination of higher parasympathetic tone and relatively higher sympathetic tone in the heart, as indicated by LF and greater standard deviation of the heart rate, a largely overlooked parameter in HRV research.

Slow-Paced Breathing and Autonomic Function in People Post-stroke

Purpose: To determine if acute slow breathing at 6 breaths/min would improve baroreflex sensitivity (BRS) and heart rate variability (HRV), and lower blood pressure (BP) in adults after stroke. Methods: Twelve individuals completed two randomized study visits where they performed a 15-min bout of breathing exercises at 6 breaths/min (slow) and at 12 breaths/min (control). Continuous BP and heart rate (HR) were measured throughout, and BRS, BRS response to elevations in blood pressure (BRSup), BRS response to depressions in blood pressure (BRSdown), and HRV were calculated and analyzed before (pre), during, and after (post) breathing exercises. Results: BRS increased from pre to post slow breathing by 10% (p = 0.012), whereas BRSup increased from pre to during slow breathing by 30% (p = 0.04). BRSdown increased from pre to post breathing for both breathing conditions (p < 0.05). HR (control: Δ - 4 ± 4; slow: Δ - 3 ± 4 beats/min, time, p < 0.01) and systolic BP (control: Δ - 0.5 ± 5; slow: Δ - 6.3 ± 8 mmHg, time, p < 0.01) decreased after both breathing conditions. Total power, low frequency power, and standard deviation of normal inter-beat intervals (SDNN) increased during the 6-breaths/min condition (condition × time, p < 0.001), whereas high frequency increased during both breathing conditions (time effect, p = 0.009). Conclusions: This study demonstrated that in people post-stroke, slow breathing may increase BRS, particularly BRSup, more than a typical breathing space; however, paced breathing at either a slow or typical breathing rate appears to be beneficial for acutely decreasing systolic BP and HR and increasing HRV.

Disentangling sensorimotor and cognitive cardioafferent effects: A cardiac-cycle-time study on spatial stimulus-response compatibility

Cardiac-cycle-time effects are attributed to variations in baroreceptor (BR) activity and have been shown to impinge on subcortical as well as cortical processes. However, cognitive and sensorimotor processes mediating voluntary responses seem to be differentially affected. We sought to disentangle cardiac-cycle-time effects on subcortical and cortical levels as well as sensorimotor and cognitive processes within a spatial stimulus-response-compatibility paradigm employing startling stimuli of different modalities. Air-puffs and white noise-bursts were presented unilaterally during either cardiac systole or diastole while bilateral startle EMG responses were recorded. Modality, laterality and cardiac-cycle-time were randomly varied within-subjects. Cognitive and sensorimotor stimulus-response-compatibility was orthogonally varied between-subjects: Participants (N = 80) responded to the stimuli via left/right button-push made with either the contra- or ipsilateral hand (sensorimotor compatibility) on either the ipsi- or contralateral button (cognitive compatibility). We found that sensorimotor compatible reactions were speeded during systole whereas sensorimotor incompatible ones were prolonged. This effect was independent of cognitive compatibility and restricted to auditory stimuli. Startle was inhibited during systole irrespective of modality or compatibility. Our results demonstrate how differential cardiac-cycle-time effects influence performance in conflict tasks and further suggest that stimulus-response-compatibility paradigms offer a viable method to uncover the complex interactions underlying behavioral BR effects.

Resting regional brain activity and connectivity vary with resting blood pressure but not muscle sympathetic nerve activity in normotensive humans: An exploratory study

Blood pressure is tightly controlled by the central nervous system, particularly the brainstem. The aim of this study was to investigate the relationship between mean blood pressure (MBP), muscle sympathetic nerve activity (MSNA) and resting regional brain activity in healthy human subjects. Pseudocontinuous arterial spin labeling and functional magnetic resonance imaging of the brain were performed immediately following a laboratory microneurography recording of MSNA and BP measurement in 31 young, healthy normotensive subjects. Regional cerebral blood flow (CBF) correlated significantly with resting MBP levels in the region encompassing the rostroventrolateral medulla (RVLM), dorsolateral pons, and insular, prefrontal and cingulate cortices. Functional connectivity analysis revealed that the ventrolateral prefrontal cortex displayed greater resting connectivity strength within the RVLM in the lower compared with the higher MBP group. No significant differences in CBF were found when subjects were divided based on their MSNA levels. These results suggest that even subtle differences in resting MBP are associated with significant differences in resting activity in brain regions, which are well known to play a role in cardiovascular function. These data raise the question of the potential long-term consequences of differences in regional brain activity levels and their relationship with systemic blood pressure.

Blood pressure variability in the management of hypertensive emergency: A narrative review

Hypertensive emergencies (HTNe) primarily focus on decreasing the blood pressure to specific targets. However, there are emerging data surrounding the potential clinical effects of blood pressure variability (BPV) in patients with HTNe. This narrative review highlights the various definitions of BPV, the emerging role of BPV, and the clinical data surrounding BPV in the HTNe setting. Clinical studies were obtained from a PubMed search through October 2018 utilizing PICO methodology. Original research articles, systematic reviews, and meta-analyses were considered for inclusion. Articles were selected for inclusion based on the relevancy of the article investigating BPV in the HTNe setting. There is currently no accepted standard to express BPV in the acute care setting of HTNe, and various parameters have been reported. There are very limited data regarding BPV outside of the neurologic HTNe setting. In the acute treatment phase of neurologic HTNe, BPV is consistently associated with increased risk of unfavorable outcomes. In the HTNe setting, continuous infusion of calcium channel blockers may optimize BPV compared to other agents. Based on current data, BPV should be investigated in a prospective systemic fashion. Efforts should be taken to ensure that BPV is minimized in the acute phase of HTNe, especially for those patients with intracranial hemorrhage. This reduced BPV is associated with improved favorable outcomes, but further study investigating specific pharmacologic agents is needed.

Emotion regulation after acquired brain injury: a study of heart rate variability, attentional control, and psychophysiology

Primary objective: To examine the efficacy of heart rate variability biofeedback (HRV-BF) to treat emotional dysregulation in persons with acquired brain injury. Design: A secondary analysis of a quasi-experimental study which enrolled 13 individuals with severe chronic acquired brain injury participating in a community-based programme. Response-to-treatment was measured with two HRV resonance indices (low frequency activity [LF] and low frequency/high frequency ratio [LF/HF]). Main outcome: Behavior Rating Inventory of Executive Function-informant report (emotional control subscale [EC]). Results: Results show significant correlation between LF and EC with higher LF activity associated with greater emotional control; the association between LF/HF pre-post-change score and EC is not statistically significant. A moderation model, however, demonstrates a significant influence of attention on the relation between LF/HF change and EC when attention level is high, with an increase in LF/HF activity associated with greater emotional control. Conclusions: HRV-BF is associated with large increases in HRV, and it appears to be useful for the treatment of emotional dysregulation in individuals with severe acquired brain injury. Attention training may enhance an individual's emotional control.

Novel Approach to Elucidate Human Baroreflex Regulation at the Brainstem Level: Pharmacological Testing During fMRI

Introduction: Brainstem nuclei govern the arterial baroreflex, which is crucial for heart rate and blood pressure control. Yet, brainstem function is difficult to explore in living humans and is therefore mostly studied using animal models or postmortem human anatomy studies. We developed a methodology to identify brainstem nuclei involved in baroreflex cardiovascular control in humans by combining pharmacological baroreflex testing with functional magnetic resonance imaging. Materials and Methods: In 11 healthy men, we applied eight repeated intravenous phenylephrine bolus doses of 25 and 75 μg followed by a saline flush using a remote-controlled injector during multiband functional magnetic resonance imaging (fMRI) acquisition of the whole brain including the brainstem. Continuous finger arterial blood pressure, respiration, and electrocardiogram (ECG) were monitored. fMRI data were preprocessed with a brainstem-specific pipeline and analyzed with a general linear model (GLM) to identify brainstem nuclei involved in central integration of the baroreceptor input. Results: Phenylephrine elicited a pressor response followed by a baroreflex-mediated lengthening of the RR interval (25 μg: 197 ± 15 ms; 75 μg: 221 ± 33 ms). By combining fMRI responses during both phenylephrine doses, we identified significant signal changes in the nucleus tractus solitarii (t = 5.97), caudal ventrolateral medulla (t = 4.59), rostral ventrolateral medulla (t = 7.11), nucleus ambiguus (t = 5.6), nucleus raphe obscurus (t = 6.45), and several other brainstem nuclei [p < 0.0005 family-wise error (few)-corr.]. Conclusion: Pharmacological baroreflex testing during fMRI allows characterizing central baroreflex regulation at the level of the brainstem in humans. Baroreflex-mediated activation and deactivation patterns are consistent with previous investigations in animal models. The methodology has the potential to elucidate human physiology and mechanisms of autonomic cardiovascular disease.

The effects of breathing at a frequency of 0.1 Hz on affective state, the cardiovascular system, and adequacy of ventilation

The present study aimed to investigate changes induced by breathing at 0.1 Hz in affective state, cardiovascular activity, and adequacy of ventilation as well as the relation between changes in peripheral physiological processes and alteration of affect. Eighty-three participants were randomly assigned to one of three groups: Two groups doing paced breathing at 0.1 Hz, one with and the other without a cover story hiding the goal of the experiment, and, as a control, paced breathing at 0.28 Hz. We measured the effects of breathing at 0.1 Hz on affective state (unpleasant and pleasant arousals), respiratory sinus arrhythmia (RSA), sympathetic control of the heart (preejection period, PEP), and adequacy of ventilation as measured by partial pressure of end-tidal CO₂ (PetCO₂ ). The use of a cover story did not influence the effects of paced breathing on the study outcomes. In the 0.1 Hz groups, unpleasant arousal decreased only among men. Changes in RSA were not related to changes in affect. Respiratory frequency did not influence PEP. However, changes in PEP were inversely related to changes in pleasant arousal. PetCO₂ decreased in all conditions, and a larger drop in PetCO₂ predicted a greater decrease in unpleasant arousal. The results obtained corroborate previous findings showing that slow paced breathing may lead to moderate hyperventilation among untrained participants and suggest that hyperventilation during breathing at 0.1 Hz is not deep enough to produce an increase in affective arousal.

Reducing Psychological Stress in Peripartum Women With Heart Rate Variability Biofeedback: A Systematic Review

Peripartum women are exposed to a variety of stressors that have adverse health consequences for the maternal-child dyad (e.g., impaired bonding). To combat these adverse health consequences, heart rate variability biofeedback (HRVBF) may be implemented by holistic nurses to aid peripartum women experiencing a high level of stress. A systematic review was completed using the guidelines established in the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement. To be included in the review, studies had to meet the following criteria: (a) published scientific articles, (b) studies published in English, (c) experimental, quasi-experimental, or case reports, (d) use of HRVBF as the main treatment, (e) use of psychological stress as a dependent variable, and (f) studies published until December 2017. The major findings of this review can be described as follows: (a) HRVBF and psychological stress in peripartum women are related concepts, (b) peripartum women who completed HRVBF report a reduction in stress compared with participants who did not receive HRVBF, and (c) there is currently no information on the effectiveness of HRVBF on psychological stress in the first and early second trimester of pregnancy. Overall, this systematic review of the literature provides objective evidence that HRVBF may be a potential beneficial adjuvant treatment for stress management in peripartum women.

Cardiac cycle time effects on selection efficiency in vision

The effect of cardiac cycle time on attentional selection was investigated in an experiment in which participants classified target letters in a visual selection task. Stimulus onsets were aligned to the R wave of the electrocardiogram and stimuli presented either during the ventricular systole or diastole. Selection efficiency was operationalized as difference in target selection performance under conditions of homogeneous and heterogeneous distractors. Differences in performance (i.e., the impact selection difficulty had on the ability to select the target) were attenuated for stimuli presented during the ventricular systole compared to the diastole. Increased baroafferent signal transmission during the systole appears to reduce interference of highly distracting stimuli on visual selection efficiency.

Lateralized Resting-State Functional Brain Network Organization Changes in Heart Failure

Heart failure (HF) patients show brain injury in autonomic, affective, and cognitive sites, which can change resting-state functional connectivity (FC), potentially altering overall functional brain network organization. However, the status of such connectivity or functional organization is unknown in HF. Determination of that status was the aim here, and we examined region-to-region FC and brain network topological properties across the whole-brain in 27 HF patients compared to 53 controls with resting-state functional MRI procedures. Decreased FC in HF appeared between the caudate and cerebellar regions, olfactory and cerebellar sites, vermis and medial frontal regions, and precentral gyri and cerebellar areas. However, increased FC emerged between the middle frontal gyrus and sensorimotor areas, superior parietal gyrus and orbito/medial frontal regions, inferior temporal gyrus and lingual gyrus/cerebellar lobe/pallidum, fusiform gyrus and superior orbitofrontal gyrus and cerebellar sites, and within vermis and cerebellar areas; these connections were largely in the right hemisphere (p<0.005; 10,000 permutations). The topology of functional integration and specialized characteristics in HF are significantly changed in regions showing altered FC, an outcome which would interfere with brain network organization (p<0.05; 10,000 permutations). Brain dysfunction in HF extends to resting conditions, and autonomic, cognitive, and affective deficits may stem from altered FC and brain network organization that may contribute to higher morbidity and mortality in the condition. Our findings likely result from the prominent axonal and nuclear structural changes reported earlier in HF; protecting neural tissue may improve FC integrity, and thus, increase quality of life and reduce morbidity and mortality.

Cerebellar fastigial nucleus: from anatomic construction to physiological functions

Fastigial nucleus (FN) is the phylogenetically oldest nucleus in the cerebellum, a classical subcortical motor coordinator. As one of the ultimate integration stations and outputs of the spinocerebellum, the FN holds a key position in the axial, proximal and ocular motor control by projecting to the medial descending systems and eye movement related nuclei. Furthermore, through topographic connections with extensive nonmotor systems, including visceral related nuclei in the brainstem, hypothalamus, as well as the limbic system, FN has also been implicated in regulation of various nonsomatic functions, such as feeding, cardiovascular and respiratory, defecation and micturition, immune, as well as emotional activities. In clinic, FN lesion or dysfunction results in motor deficits including spinocerebellar ataxias, and nonmotor symptoms. In this review, we summarize the cytoarchitecture, anatomic afferent and efferent connections, as well as the motor and nonmotor functions of the FN and the related diseases and disorders. We suggest that by bridging the motor and nonmotor systems, the cerebellar FN may help to integrate somatic motor and nonsomatic functions and consequently contribute to generate a coordinated response to internal and external environments.

Aberrant Insular Functional Network Integrity in Patients with Obstructive Sleep Apnea

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is accompanied by tissue injury to the insular cortices, areas that regulate autonomic pain, dyspnea, and mood, all of which are affected in the syndrome. Presumably, the dysregulation of insular-related functions are mediated by aberrant functional connections with other brain regions; however, the integrity of the functional connectivity (FC) to other sites is undescribed. Our aim was to examine resting-state FC of the insular cortices to other brain areas in OSA, relative to control subjects.

METHODS

We collected resting-state functional magnetic resonance imaging (MRI) data from 67 newly diagnosed, treatment-naïve OSA and 75 control subjects using a 3.0-Tesla MRI scanner. After standard processing, data were analyzed for the left and right insular FC.

RESULTS

OSA subjects showed complex aberrant insular FC to several brain regions, including frontal, parietal, cingulate, temporal, limbic, basal ganglia, thalamus, occipital, cerebellar, and brainstem regions. Areas of altered FC in OSA showed linear relationships with magnitudes of sleep related and neuropsychologic-related variables, whereas control subjects showed no such relationships with those measures.

CONCLUSIONS

Brain functional connections from insular sites to other brain regions in OSA subjects represent abnormal autonomic, affective, sensorimotor, and cognitive control networks that may affect both impaired parasympathetic and sympathetic interactions, as well as abnormal sensorimotor integration, affected in the condition. The functional changes likely result from the previously reported structural changes in OSA subjects, as demonstrated by diverse neuroimaging studies.

Disrupted functional brain network organization in patients with obstructive sleep apnea

INTRODUCTION

Obstructive sleep apnea (OSA) subjects show impaired autonomic, affective, executive, sensorimotor, and cognitive functions. Brain injury in OSA subjects appears in multiple sites regulating these functions, but the integrity of functional networks within the regulatory sites remains unclear. Our aim was to examine the functional interactions and the complex network organization of these interactions across the whole brain in OSA, using regional functional connectivity (FC) and brain network topological properties.

METHODS

We collected resting-state functional magnetic resonance imaging (MRI) data, using a 3.0-Tesla MRI scanner, from 69 newly diagnosed, treatment-naïve, moderate-to-severe OSA (age, 48.3 ± 9.2 years; body mass index, 31 ± 6.2 kg/m(2); apnea-hypopnea index (AHI), 35.6 ± 23.3 events/h) and 82 control subjects (47.6 ± 9.1 years; body mass index, 25.1 ± 3.5 kg/m(2)). Data were analyzed to examine FC in OSA over controls as interregional correlations and brain network topological properties.

RESULTS

Obstructive sleep apnea subjects showed significantly altered FC in the cerebellar, frontal, parietal, temporal, occipital, limbic, and basal ganglia regions (FDR, P < 0.05). Entire functional brain networks in OSA subjects showed significantly less efficient integration, and their regional topological properties of functional integration and specialization characteristics also showed declined trends in areas showing altered FC, an outcome which would interfere with brain network organization (P < 0.05; 10,000 permutations). Brain sites with abnormal topological properties in OSA showed significant relationships with AHI scores.

CONCLUSIONS

Our findings suggest that the dysfunction extends to resting conditions, and the altered FC and impaired network organization may underlie the impaired responses in autonomic, cognitive, and sensorimotor functions. The outcomes likely result from the prominent structural changes in both axons and nuclear structures, which occur in the condition.

Functional Imaging of Autonomic Regulation: Methods and Key Findings

Central nervous system processing of autonomic function involves a network of regions throughout the brain which can be visualized and measured with neuroimaging techniques, notably functional magnetic resonance imaging (fMRI). The development of fMRI procedures has both confirmed and extended earlier findings from animal models, and human stroke and lesion studies. Assessments with fMRI can elucidate interactions between different central sites in regulating normal autonomic patterning, and demonstrate how disturbed systems can interact to produce aberrant regulation during autonomic challenges. Understanding autonomic dysfunction in various illnesses reveals mechanisms that potentially lead to interventions in the impairments. The objectives here are to: (1) describe the fMRI neuroimaging methodology for assessment of autonomic neural control, (2) outline the widespread, lateralized distribution of function in autonomic sites in the normal brain which includes structures from the neocortex through the medulla and cerebellum, (3) illustrate the importance of the time course of neural changes when coordinating responses, and how those patterns are impacted in conditions of sleep-disordered breathing, and (4) highlight opportunities for future research studies with emerging methodologies. Methodological considerations specific to autonomic testing include timing of challenges relative to the underlying fMRI signal, spatial resolution sufficient to identify autonomic brainstem nuclei, blood pressure, and blood oxygenation influences on the fMRI signal, and the sustained timing, often measured in minutes of challenge periods and recovery. Key findings include the lateralized nature of autonomic organization, which is reminiscent of asymmetric motor, sensory, and language pathways. Testing brain function during autonomic challenges demonstrate closely-integrated timing of responses in connected brain areas during autonomic challenges, and the involvement with brain regions mediating postural and motoric actions, including respiration, and cardiac output. The study of pathological processes associated with autonomic disruption shows susceptibilities of different brain structures to altered timing of neural function, notably in sleep disordered breathing, such as obstructive sleep apnea and congenital central hypoventilation syndrome. The cerebellum, in particular, serves coordination roles for vestibular stimuli and blood pressure changes, and shows both injury and substantially altered timing of responses to pressor challenges in sleep-disordered breathing conditions. The insights into central autonomic processing provided by neuroimaging have assisted understanding of such regulation, and may lead to new treatment options for conditions with disrupted autonomic function.

Sex, the brain and hypertension: brain oestrogen receptors and high blood pressure risk factors

Hypertension is a major contributor to worldwide morbidity and mortality rates related to cardiovascular disease. There are important sex differences in the onset and rate of hypertension in humans. Compared with age-matched men, premenopausal women are less likely to develop hypertension. However, after age 60, the incidence of hypertension increases in women and even surpasses that seen in older men. It is thought that changes in levels of circulating ovarian hormones as women age may be involved in the increase in hypertension in older women. One of the key mechanisms involved in the development of hypertension in both men and women is an increase in sympathetic nerve activity (SNA). Brain regions important for the regulation of SNA, such as the subfornical organ, the paraventricular nucleus and the rostral ventral lateral medulla, also express specific subtypes of oestrogen receptors. Each of these brain regions has also been implicated in mechanisms underlying risk factors for hypertension such as obesity, stress and inflammation. The present review brings together evidence that links actions of oestrogen at these receptors to modulate some of the common brain mechanisms involved in the ability of hypertensive risk factors to increase SNA and blood pressure. Understanding the mechanisms by which oestrogen acts at key sites in the brain for the regulation of SNA is important for the development of novel, sex-specific therapies for treating hypertension.

Baroreceptor activity impacts upon controlled but not automatic distractor processing

Changes within the cardiovascular system have been shown to alter sensorimotor and memory performance, pain perception as well as cortical arousal. This influence is assumed to be mediated by afferent feedback of baroreceptors that when stimulated exert inhibitory effects on cortical structures. Mainly responsible for short-term regulation of blood pressure, afferents of the baroreceptors are widely connected to subcortical and cortical structures like the insular cortex. A putative impact on cognitive control processes remains an open question, however. Using a sequential distractor priming task, the present study investigated whether inhibitory influences of baroreceptor activation apply to selective information processing in the presence of irrelevant information. In particular, we assessed distractor-response binding and Negative Priming as indices of automatic and controlled distractor processing, respectively. Baroreceptor activation was experimentally manipulated by the systematic variation of body position. The results showed that only Negative Priming but not distractor-response binding was modulated by body position suggesting that controlled but not automatic processing of distractors is affected by baroreceptor activity.

Reversal of functional changes in the brain associated with obstructive sleep apnoea following 6 months of CPAP

Obstructive sleep apnoea (OSA) is associated with an increase in the number of bursts of muscle sympathetic nerve activity (MSNA), leading to neurogenic hypertension. Continuous positive airway pressure (CPAP) is the most effective and widely used treatment for preventing collapse of the upper airway in OSA. In addition to improving sleep, CPAP decreases daytime MSNA towards control levels. It remains unknown how this restoration of MSNA occurs, in particular whether CPAP treatment results in a simple readjustment in activity of those brain regions responsible for the initial increase in MSNA or whether other brain regions are recruited to over-ride aberrant brain activity. By recording MSNA concurrently with functional Magnetic Resonance Imaging (fMRI), we aimed to assess brain activity associated with each individual subject's patterns of MSNA prior to and following 6 months of CPAP treatment. Spontaneous fluctuations in MSNA were recorded via tungsten microelectrodes inserted into the common peroneal nerve in 13 newly diagnosed patients with OSA before and after 6 months of treatment with CPAP and in 15 healthy control subjects while lying in a 3 T MRI scanner. Blood Oxygen Level Dependent (BOLD) contrast gradient echo, echo-planar images were continuously collected in a 4 s ON, 4 s OFF (200 volumes) sampling protocol. MSNA was significantly elevated in newly diagnosed OSA patients compared to control subjects (55 ± 4 vs 26 ± 2 bursts/min). Fluctuations in BOLD signal intensity in multiple regions covaried with the intensity of the concurrently recorded bursts of MSNA. There was a significant fall in MSNA after 6 months of CPAP (39 ± 2 bursts/min). The reduction in resting MSNA was coupled with significant falls in signal intensity in precuneus bilaterally, the left and right insula, right medial prefrontal cortex, right anterior cingulate cortex, right parahippocampus and the left and right retrosplenial cortices. These data support our contention that functional changes in these suprabulbar sites are, via projections to the brainstem, driving the augmented sympathetic outflow to the muscle vascular bed in untreated OSA.

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Obstructive sleep apnoea increases muscle sympathetic nerve activity (MSNA).

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fMRI was used to identify brain sites temporally coupled to the increase in MSNA.

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Augmented BOLD signal intensity occurred in several cortical and subcortical sites.

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These changes were reversed following 6 months of CPAP, which reduced the MSNA.

Heart rate variability biofeedback: how and why does it work?

In recent years there has been substantial support for heart rate variability biofeedback (HRVB) as a treatment for a variety of disorders and for performance enhancement (Gevirtz, 2013). Since conditions as widely varied as asthma and depression seem to respond to this form of cardiorespiratory feedback training, the issue of possible mechanisms becomes more salient. The most supported possible mechanism is the strengthening of homeostasis in the baroreceptor (Vaschillo et al., 2002; Lehrer et al., 2003). Recently, the effect on the vagal afferent pathway to the frontal cortical areas has been proposed. In this article, we review these and other possible mechanisms that might explain the positive effects of HRVB.

Baroreceptor afferents modulate brain excitation and influence susceptibility to toxic effects of hyperbaric oxygen

Unexplained adjustments in baroreflex sensitivity occur in conjunction with exposures to potentially toxic levels of hyperbaric oxygen. To investigate this, we monitored central nervous system, autonomic and cardiovascular responses in conscious and anesthetized rats exposed to hyperbaric oxygen at 5 and 6 atmospheres absolute, respectively. We observed two contrasting phases associated with time-dependent alterations in the functional state of the arterial baroreflex. The first phase, which conferred protection against potentially neurotoxic doses of oxygen, was concurrent with an increase in baroreflex sensitivity and included decreases in cerebral blood flow, heart rate, cardiac output, and sympathetic drive. The second phase was characterized by baroreflex impairment, cerebral hyperemia, spiking on the electroencephalogram, increased sympathetic drive, parasympatholysis, and pulmonary injury. Complete arterial baroreceptor deafferentation abolished the initial protective response, whereas electrical stimulation of intact arterial baroreceptor afferents prolonged it. We concluded that increased afferent traffic attributable to arterial baroreflex activation delays the development of excessive central excitation and seizures. Baroreflex inactivation or impairment removes this protection, and seizures may follow. Finally, electrical stimulation of intact baroreceptor afferents extends the normal delay in seizure development. These findings reveal that the autonomic nervous system is a powerful determinant of susceptibility to sympathetic hyperactivation and seizures in hyperbaric oxygen and the ensuing neurogenic pulmonary injury.

Brain putamen volume changes in newly-diagnosed patients with obstructive sleep apnea

Obstructive sleep apnea (OSA) is accompanied by cognitive, motor, autonomic, learning, and affective abnormalities. The putamen serves several of these functions, especially motor and autonomic behaviors, but whether global and specific sub-regions of that structure are damaged is unclear. We assessed global and regional putamen volumes in 43 recently-diagnosed, treatment-naïve OSA (age, 46.4 ± 8.8 years; 31 male) and 61 control subjects (47.6 ± 8.8 years; 39 male) using high-resolution T1-weighted images collected with a 3.0-Tesla MRI scanner. Global putamen volumes were calculated, and group differences evaluated with independent samples t-tests, as well as with analysis of covariance (covariates; age, gender, and total intracranial volume). Regional differences between groups were visualized with 3D surface morphometry-based group ratio maps. OSA subjects showed significantly higher global putamen volumes, relative to controls. Regional analyses showed putamen areas with increased and decreased tissue volumes in OSA relative to control subjects, including increases in caudal, mid-dorsal, mid-ventral portions, and ventral regions, while areas with decreased volumes appeared in rostral, mid-dorsal, medial-caudal, and mid-ventral sites. Global putamen volumes were significantly higher in the OSA subjects, but local sites showed both higher and lower volumes. The appearance of localized volume alterations points to differential hypoxic or perfusion action on glia and other tissues within the structure, and may reflect a stage in progression of injury in these newly-diagnosed patients toward the overall volume loss found in patients with chronic OSA. The regional changes may underlie some of the specific deficits in motor, autonomic, and neuropsychologic functions in OSA.

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Global and regional putamen volumes were examined in newly-diagnosed OSA.

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Global volumes are higher, but subareas showed increases and decreases.

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The volume increases suggest transient tissue swelling from hypoxic action.

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Altered sites likely contribute to motor and other functional deficits in OSA.

Baroreflex-mediated cardiovascular responses to hyperbaric oxygen

The cardiovascular system responds to hyperbaric hyperoxia (HBO2) with vasoconstriction, hypertension, bradycardia, and reduced cardiac output (CO). We tested the hypothesis that these responses are linked by a common mechanism-activation of the arterial baroreflex. Baroreflex function in HBO2 was assessed in anesthetized and conscious rats after deafferentation of aortic or carotid baroreceptors or both. Cardiovascular and autonomic responses to HBO2 in these animals were compared with those in intact animals at 2.5 ATA for conscious rats and at 3 ATA for anesthetized rats. During O2 compression, hypertension was greater after aortic or carotid baroreceptor deafferentation and was significantly more severe if these procedures were combined. Similarly, the hyperoxic bradycardia observed in intact animals was diminished after aortic or carotid baroreceptor deafferentation and replaced by a slight tachycardia after complete baroreceptor deafferentation. We found that hypertension, bradycardia, and reduced CO--the initial cardiovascular responses to moderate levels of HBO2--are coordinated through a baroreflex-mediated mechanism initiated by HBO2-induced vasoconstriction. Furthermore, we have shown that baroreceptor activation in HBO2 inhibits sympathetic outflow and can partially reverse an O2-dependent increase in arterial pressure.

Aerobic exercise in subacute stroke improves cardiovascular health and physical performance

BACKGROUND AND PURPOSE

Cardiovascular health is often impaired after stroke. Reduced exercise capacity ((Equation is included in full-text article.)VO(2peak)) and changes in the vascular system in the stroke-affected limb may impact performance of physical activities such as walking. There is little information regarding the role of prescribed moderate- to high-intensity exercise in subacute stroke. The purpose of this study was to examine whether an 8-week aerobic exercise intervention would improve cardiovascular health and physical performance in participants with subacute stroke.

METHODS

Ten subjects were enrolled in the study and 9 of them completed the intervention. Participants were aged 61.2 ± 4.7 years old, were 66.7 ± 41.5 days poststroke, and had minor motor performance deficits (Fugl-Meyer score, 100.3 ± 29.3). Outcome measures were taken at baseline, postintervention, and at 1-month follow-up. Brachial artery vasomotor reactivity (flow-mediated dilation [FMD]) of both arms was used to assess vascular health, and a peak exercise test was used to assess exercise capacity. The 6-minute walk test (6MWT) was used to assess physical performance. Participants exercised on a recumbent stepper 3 times per week for 8 weeks at a prescribed heart rate intensity.

RESULTS

At baseline, we identified between-limb differences in brachial artery FMD and low (Equation is included in full-text article.)VO(2peak) values. After the intervention, significant improvements were observed in the FMD in both arms, resting systolic blood pressure, and the 6MWT. Although we also observed improvements in the resting diastolic blood pressure, heart rate, and (Equation is included in full-text article.)VO(2peak) values, these changes were not significantly different.

DISCUSSION AND CONCLUSION

Aerobic exercise in participants with subacute stroke was beneficial for improving cardiovascular health, reducing cardiac risk, and improving physical performance (6MWT).

Different brain activation under left and right ventricular stimulation: an fMRI study in anesthetized rats

BACKGROUND

Myocardial ischemia in the anterior wall of the left ventricule (LV) and in the inferior wall and/or right ventricle (RV) shows different manifestations that can be explained by the different innervations of cardiac afferent nerves. However, it remains unclear whether information from different areas of the heart, such as the LV and RV, are differently processed in the brain. In this study, we investigated the brain regions that process information from the LV or RV using cardiac electrical stimulation and functional magnetic resonance imaging (fMRI) in anesthetized rats because the combination of these two approaches cannot be used in humans.

METHODOLOGY/PRINCIPAL FINDINGS

An electrical stimulation catheter was inserted into the LV or RV (n = 12 each). Brain fMRI scans were recorded during LV or RV stimulation (9 Hz and 0.3 ms width) over 10 blocks consisting of alternating periods of 2 mA for 30 sec followed by 0.2 mA for 60 sec. The validity of fMRI signals was confirmed by first and second-level analyses and temporal profiles. Increases in fMRI signals were observed in the anterior cingulate cortex and the right somatosensory cortex under LV stimulation. In contrast, RV stimulation activated the right somatosensory cortex, which was identified more anteriorly compared with LV stimulation but did not activate the anterior cingulate cortex.

CONCLUSION/SIGNIFICANCE

This study provides the first evidence for differences in brain activation under LV and RV stimulation. These different brain processes may be associated with different clinical manifestations between anterior wall and inferoposterior wall and/or RV myocardial ischemia.

Identification of sites of sympathetic outflow during concurrent recordings of sympathetic nerve activity and fMRI

The sympathetic division of the nervous system is critical for maintaining both resting arterial pressure and for producing changes in regional perfusion required by behavioral state changes. A primary determinant of arterial pressure is the level of vasoconstriction within skeletal muscle. It is well established that there is a tight relationship between dynamic changes in arterial pressure and muscle sympathetic nerve activity (MSNA) through the workings of the baroreflex. While the central circuitry underlying the baroreflex has been extensively investigated in anesthetized experimental animals, few studies have investigated the central circuitry responsible for the baroreflex in awake human subjects. Recently we were the first to record concurrently MSNA (using microneurography) and brain activity (using functional magnetic resonance imaging) in awake humans in a series of experiments designed to determine the central circuitry underlying the baroreflex in humans. We confirmed that the baroreflex involves activity changes within the nucleus tractus solitarius, caudal ventrolateral, and rostral ventrolateral medulla. Because conditions such as essential hypertension, obesity, and obstructive sleep apnea are all characterized by significant increases in resting MSNA, it is important to understand both brainstem and cortical sites involved in regulating resting levels of MSNA. Future investigations which define cortical sites involved in generating and modulating MSNA are important if we are to understand the underlying mechanisms of many conditions characterized by hypertension.

[Cardiac complications of acute brain injury]

The clinical importance of cardiovascular consequences resulting from cerebral injury has long been recognized. However, interactions between the brain and the cardiovascular system remain poorly defined and their importance for the management of patients suffering from acute brain injury is largely underestimated. This should have profound consequences on treatment strategies during anaesthesia and intensive cares of these patients, taking into account not only brain perfusion, but also cardiovascular optimisation. This report summarizes the main data available regarding the cardiovascular consequences of brain death, traumatic brain injury, stroke and epilepsy.

Forebrain organization representing baroreceptor gating of somatosensory afferents within the cortical autonomic network

Somatosensory afferents are represented within the cortical autonomic network (CAN). However, the representation of somatosensory afferents, and the consequent cardiovascular effects, may be modified by levels of baroreceptor input. Thus, we examined the cortical regions involved with processing somatosensory inputs during baroreceptor unloading. Neuroimaging sessions (functional magnetic resonance imaging [fMRI]) recorded brain activity during 30 mmHg lower-body negative pressure (LBNP) alone and combined with somatosensory stimulation (LBNP+SS) of the forearm (n = 14). Somatosensory processing was also assessed during increased sympathetic outflow via end-expiratory apnea. Heart rate (HR), blood pressure (BP), cardiac output (Q), and muscle sympathetic nerve activity (MSNA) were recorded during the same protocols in a separate laboratory session. SS alone had no effect on any cardiovascular or MSNA variable at rest. Measures of HR, BP, and Q during LBNP were not different compared with LBNP+SS. The rise in MSNA burst frequency was attenuated during LBNP+SS versus LBNP alone (8 vs. 12 bursts/min, respectively, P < 0.05). SS did not affect the change in MSNA during apnea. Activations within the insula and dorsal anterior cingulate cortex (ACC) observed during LBNP were not seen during LBNP+SS. Anterior insula and ACC activations occurring during apnea were not modified by SS. Thus, the absence of insular and dorsal ACC activity during LBNP+SS along with an attenuation of MSNA burst frequency suggest sympathoinhibitory effects of sensory stimulation during decreased baroreceptor input by a mechanism that includes conjoint insula-dorsal ACC regulation. These findings reveal that the level of baroreceptor input influences the forebrain organization of somatosensory afferents.

Pharmacological MRI of the choroid and retina: blood flow and BOLD responses during nitroprusside infusion

Nitroprusside, a vasodilatory nitric oxide donor, is clinically used during vascular surgery and to lower blood pressure in acute hypertension. This article reports a novel application of blood flow (BF) and blood oxygenation level dependent (BOLD) MRI on an 11.7T scanner to image the rat chorioretinal BF and BOLD changes associated with graded nitroprusside infusion. At low doses (1 or 2 μg/kg/min), nitroprusside increased BF as expected but decreased BOLD signals, showing an intriguing BF-BOLD uncoupling. At high doses (3-5 μg/kg/min), nitroprusside decreased BF and markedly decreased BOLD signals. To our knowledge, this is the first pharmacological MRI application of the retina. This approach has potential to open up new avenues to study the drug-related hemodynamic functions and to evaluate the effects of novel therapeutic interventions on BOLD and BF in the normal and diseased retinas.

Reduced cardiorespiratory fitness after stroke: biological consequences and exercise-induced adaptations

Evidence from several studies consistently shows decline in cardiorespiratory (CR) fitness and physical function after disabling stroke. The broader implications of such a decline to general health may be partially understood through negative poststroke physiologic adaptations such as unilateral muscle fiber type shifts, impaired hemodynamic function, and decrements in systemic metabolic status. These physiologic changes also interrelate with reductions in activities of daily living (ADLs), community ambulation, and exercise tolerance, causing a perpetual cycle of worsening disability and deteriorating health. Fortunately, initial evidence suggests that stroke participants retain the capacity to adapt physiologically to an exercise training stimulus. However, despite this evidence, exercise as a therapeutic intervention continues to be clinically underutilized in the general stroke population. Far more research is needed to fully comprehend the consequences of and remedies for CR fitness impairments after stroke. The purpose of this brief review is to describe some of what is currently known about the physiological consequences of CR fitness decline after stroke. Additionally, there is an overview of the evidence supporting exercise interventions for improving CR fitness, and associated aspects of general health in this population.

Down-regulation of V1a vasopressin receptors in the cerebellum after myocardial infarction

Vasopressin V1a receptors (V1aR) were found in the cerebellum but their functional role has not been determined. As V1aR are engaged in the central regulation of the cardiovascular system and anxiogenic behavior and their role increases in the heart failure and stress, we decided to find out whether expression of V1aR is altered after myocardial infarction and chronic stressing. RT-PCR and Western blot analysis were performed to determine V1aR mRNA and protein expression in the cerebellum of four groups of rats (control sham-operated, infarcted, chronically stressed and infarcted chronically stressed). The myocardial infarct was produced by left coronary artery ligation, and chronic stressing by exposing the rat for four weeks to different types of mild stressors. The rats were sacrificed four weeks after the myocardial surgery or sham operation. Expressions of V1aR mRNA and protein were significantly lower in the infarcted and infarcted chronically stressed rats than in the sham-operated controls and chronically stressed not infarcted rats. No significant differences were found between the sham-operated controls and chronically stressed rats and between the infarcted rats and infarcted rats exposed to chronic stressing. It is concluded that V1aR mRNA and protein expressions are significantly down-regulated in the rats with the post-infarct heart failure but they are not affected by mild chronic stressing.

Protective effect of the daming capsule on impaired baroreflexes in STZ-induced diabetic rats with hyperlipoidemia

Background

The Daming capsule (DMC) is a traditional Chinese medicine used to treat hyperlipoidemia. Both clinic trials and studies on animal models have demonstrated that DMC is beneficial against diabetic symptoms. Impairment of the baroreflex can cause life-threatening arrhythmias and sudden cardiac death in patients with diabetes mellitus (DM). This study was designed to elucidate the effects of DMC on baroreflexes in streptozocin (STZ)-induced diabetic rats with hyperlipoidemia.

Methods

Wistar rats were randomly divided into three groups: untreated controls, rats pretreated STZ and high lipids (a diabetes model or DM rats), and DM rats treated with DMC. The baroreflex sensitivity was examined during intravenous injection of phenylephrine (PE) or sodium nitroprusside (SNP) and quantified by the change in heart rate over the change in mean arterial blood pressure (ΔHR/ΔMABP). Morphological remodeling of baroreceptors was analyzed by transmission electron microscopy (TEM). The mRNA levels and expression of GluR2 and a GABA_A receptor subunit were measured by quantitative RT-PCR and Western blotting.

Results

Compared to untreated DM rats, DMC significantly elevated the ratio of ΔHR/ΔMABP by enhancing the compensatory reduction in HR (-ΔHR) in response to PE-induced hypertension (+ΔMABP) (P < 0.05). In the presence of SNP, DMC increased the ΔMABP (P < 0.05). In addition, DMC markedly shortened the duration of blood pressure changes elicited by PE or SNP in DM rats compared to the untreated DM group (P < 0.05). Electron microscopy revealed disrupted myelin sheaths, swollen ER, and lysed mitochondria in the nucleus ambiguous (NAm) DM rats. These signs of neuropathology were largely prevented by treatment with DMC for 30 days. Treatment with DMC elevated both mRNA and protein level of GluR2 in the NAm of DM rats, but had no effect on GABA_A receptor expression.

Conclusion

The Daming capsule partially reversed the parasympathetic baroreflex impairment observed in STZ-induced diabetic rats with hyperlipoidemia. Treatment with DMC also prevented the degeneration of neurons and myelinated axons in the brain stem NAm and reversed the down-regulation of GluR2 mRNA. Rescue of NAm function may contribute to the medicinal properties of DMC in diabetic rats.

Real-time imaging of the medullary circuitry involved in the generation of spontaneous muscle sympathetic nerve activity in awake subjects

To understand the central neural processes involved in blood pressure regulation we recorded muscle sympathetic nerve activity (MSNA) via a tungsten microelectrode in the common peroneal nerve while performing functional magnetic resonance imaging (fMRI) of the brainstem at 3T. Blood oxygen level dependent (BOLD) changes in signal intensity were measured over 4 s every 8 s (200) volumes; MSNA was recorded during the previous 4 s epoch, which takes into account peripheral conduction delays along unmyelinated axons and neurovascular coupling delays. Analysis of temporal coupling between BOLD signal intensity and nerve signal intensity revealed sites in which the two signals covaried, but only in the medulla. Because scans were conducted in a caudorostral direction, we could constrain the analysis to the medulla by only examining the first 1 s of the fMRI and nerve signals. Increases in MSNA were associated with robust bilateral increases in signal intensity in the dorsolateral region of the medulla that corresponds to the human equivalent of the rostal ventrolateral medulla (RVLM). Reciprocal decreases in signal intensity occurred in the regions of the nucleus tractus solitarius (NTS) and caudal ventrolateral medulla (CVLM). Group analysis also revealed increases in signal intensity in the caudal pressor area (CPA), medullary raphé (MR), and dorsal motor nucleus of the vagus (DMX). We have shown for the first time that this combined approach of recording sympathetic neural activity and fMRI provides real-time imaging of the neural processes responsible for the generation of sympathetic nerve activity in awake human subjects.

Cortical and brain stem changes in neural activity during static handgrip and postexercise ischemia in humans

Static isometric exercise increases muscle sympathetic nerve activity (MSNA) and mean arterial pressure, both of which can be maintained at the conclusion of the exercise by occlusion of the arterial supply [postexercise ischemia (PEI)]. To identify the cortical and subcortical sites involved, and to differentiate between central command and reflex inputs, we used blood oxygen level-dependent (BOLD) functional MRI (fMRI) of the whole brain (3 T). Subjects performed submaximal static handgrip exercise for 2 min followed by 6 min of PEI; MSNA was recorded on a separate day. During the contraction phase, parallel increases in BOLD signal intensity occurred in the contralateral primary motor cortex and cerebellar nuclei and cortex; these matched the effort profile and ceased at the conclusion of the contraction. Progressive increases in the contralateral insula and primary and secondary somatosensory cortices, with progressive decreases in the perigenual anterior cingulate and midcingulate cortices, were sustained during the period of PEI and thus did not depend on central command. Discrete bilateral activation of the medial and lateral dorsal medulla was also observed during the contraction and PEI; we believe that these represent the nucleus tracts solitarius (NTS) and rostral ventrolateral medulla (RVLM), respectively. Given that metaboreceptor afferents are known to project to the NTS and that the RVLM is the primary output nucleus for MSNA, our data support that the metaboreflex is mediated by the medulla, whereas the somatosensory, insular, and anterior cingulate cortices are involved in the sensory and affective components of the maneuver.