scholarly journals Long Duration Bed Rest Modifies Cardiovagal Baroreflex Control but not Baroreflex Control of Muscle Sympathetic Action Potential Activity in Humans

2021 ◽  
Vol 35 (S1) ◽  
Author(s):  
Tyler Vermeulen ◽  
Stephen Klassen ◽  
Steven De Abreu ◽  
Danielle Greaves ◽  
Philippe Arbeille ◽  
...  
Keyword(s):  
Action Potential ◽  
Bed Rest ◽  
Baroreflex Control ◽  
Long Duration ◽  
Potential Activity

scholarly journals Long-duration bed rest modifies sympathetic neural recruitment strategies in male and female participants

2018 ◽  
Vol 124 (3) ◽  
pp. 769-779 ◽  
Author(s):  
Stephen A. Klassen ◽  
Steven De Abreu ◽  
Danielle K. Greaves ◽  
Derek S. Kimmerly ◽  
Philippe Arbeille ◽  
...  
Keyword(s):  
Action Potential ◽  
Retrospective Analysis ◽  
Physiological Stress ◽  
Muscle Sympathetic Nerve Activity ◽  
Bed Rest ◽  
Burst Frequency ◽  
Male And Female ◽  
Time Interaction ◽  
Long Duration ◽  
The Impact

To understand the impact of physical deconditioning with head-down tilt bed rest (HDBR) on the malleability of sympathetic discharge patterns, we studied 1) baseline integrated muscle sympathetic nerve activity (MSNA; microneurography) from 13 female participants in the WISE-2005 60-day HDBR study (retrospective analysis), 2) integrated MSNA and multiunit action potential (AP) analysis in 13 male participants performed on data collected at baseline and during physiological stress imposed by end-inspiratory apnea in a new 60-day HDBR study, and 3) a repeatability study (control; n = 6, retrospective analysis, 4 wk between tests). Neither baseline integrated burst frequency nor incidence were altered with HDBR (both P > 0.35). However, baseline integrated burst latency increased in both HDBR studies (male: 1.35 ± 0.02 to 1.39 ± 0.02 s, P < 0.01; female: 1.23 ± 0.02 to 1.29 ± 0.02 s, P < 0.01), whereas controls exhibited no change across two visits (1.25 ± 0.02 to 1.25 ± 0.02 s, group-by-time interaction, P = 0.02). With the exception of increased AP latency ( P = 0.03), male baseline AP data did not change with HDBR (all P > 0.19). The change in AP frequency on going from baseline to apnea (∆94 ± 25 to ∆317 ± 55 AP/min, P < 0.01) and the number of active sympathetic clusters per burst (∆0 ± 0.2 to ∆1 ± 0.2 clusters/burst, P = 0.02) were greater post- compared with pre-HDBR. The change in total clusters with apnea was ∆0 ± 0.5 clusters pre- and ∆2 ± 0.7 clusters post-HDBR ( P = 0.07). These data indicate that 60-day HDBR modified discharge characteristics in baseline burst latency and sympathetic neural recruitment during apneic stress. NEW & NOTEWORTHY Long-duration bed rest did not modify baseline sympathetic burst frequency in male and female participants, but examination of additional features of the multiunit signal provided novel evidence to suggest augmented synaptic delays or processing times at baseline for all sympathetic action potentials. Furthermore, long-duration bed rest increased reflex-sympathetic arousal to apneic stress in male participants primarily by mechanisms involving an augmented firing rate of action potential clusters active at baseline.

Perilymph Fistulas

1978 ◽  
Vol 87 (6) ◽  
pp. 797-803 ◽  
Author(s):  
George T. Singleton ◽  
Kathryn Nolan Post ◽  
Marc Simeon Karlan ◽  
Douglas G. Bock
Keyword(s):  
Discriminant Analysis ◽  
Effective Means ◽  
Bed Rest ◽  
Sudden Onset ◽  
Effective Control ◽  
Speech Discrimination ◽  
Mean Values ◽  
Long Duration ◽  
History Of ◽  
Physical Findings

Fifty-one patients suspected of having a perilymph fistula were evaluated. We postulated that many patients with predominantly vestibular complaints had unrecognized perilymph fistulas. An analysis was made of symptoms, physical findings, vestibular and audiometric test results in order to determine appropriate diagnostic criteria for the presence of perilymph fistulas. The patient population was divided into two groups, those with and without fistulas. Data from both groups were compared by mean values of variables, step-wise discriminant analysis, and factor analysis. A history of trauma with sudden onset of dizziness and/or hearing loss should alert the physician to a fistula. Findings of significance were positional nystagmus of short latency and long duration without import of nystagmus direction, canal paresis and reduced speech reception threshold with poor speech discrimination scores. Discriminant analysis correctly classified 19 fistula and 10 nonfistula cases explored operatively and identified two error judgments in 22 nonoperated cases. Bed rest for the first five days proved to be the most effective means of therapy. Surgical intervention with repair of the fistula by perichondrial graft provided effective control of vertigo more frequently than restoration of hearing.

scholarly journals Long-term bedrest study and astronaut training

2016 ◽  
Author(s):  
Edwin Mulder ◽  
Alexandra Noppe ◽  
Ulrich Limper
Keyword(s):  
Bed Rest ◽  
Dual Purpose ◽  
Planetary Environments ◽  
Exercise Regimen ◽  
Long Duration ◽  
Astronaut Training ◽  
Health Support ◽  
Art Research ◽  
Induced Changes

In the context of space physiology, research is being conducted to understand the physiological effects from radiation, hypogravity, spaceflight and planetary environments. The goal is to identify new methods to address the unique challenges in medical treatment, human factors, and behavioral health support on future exploration missions. As crew size is small and time is limited during actual missions, space agencies resort to addressing the effects of space travel in analog environments that have features similar to those of spaceflight. Head-down tilt bed rest (HDBR), for instance, is one of the established terrestrial models used to simulate some of the physiological changes experienced during spaceflight under weightless conditions and is therefore considered a valuable testbed to prepare for future long-duration exploration missions. HDBR studies are performed in extremely-well controlled laboratory settings, offering the possibility to test the effects of – what is in essence - physical inactivity and fluid shift. However, HDBR studies have a dual purpose, as they are also invaluable for the development, testing and validation of countermeasures aimed at mitigating microgravity-induced changes to the human body. With respect to the latter, the consensus is that short-term bed rest studies (< 14 days) serve foremost as a first screening of potential promising countermeasures, particularly for the cardiovascular system. Screening of preventative procedures and protocols for the muscular system requires at least mid-term (14 -28 days), whereas studies aiming to validate countermeasures for bone require long-term HDBR studies, in the order of 60-90 days. Hitherto the preferred countermeasure during spaceflight has been physical exercise. The presentation will therefore provide a short overview of the current onboard exercise regimen and will, in light of this, outline the scientific background and aims of the ongoing 60-day HDBR study at the :envihab (from the words ‘Environment’ and ‘Habitat’), the DLR Institute of Aerospace Medicine’s state-of-the-art research facility.

scholarly journals Epigenome Interactions with Patterned Neuronal Activity

2018 ◽  
Vol 24 (5) ◽  
pp. 471-485 ◽  
Author(s):  
Jillian Belgrad ◽  
R. Douglas Fields
Keyword(s):  
Gene Expression ◽  
Action Potential ◽  
Neural Development ◽  
Intracellular Signaling ◽  
Regulation Of Gene Expression ◽  
Temporal Coding ◽  
Dna Breaks ◽  
Action Potential Firing ◽  
Potential Activity ◽  
Activity Dependent

The temporal coding of action potential activity is fundamental to nervous system function. Here we consider how gene expression in neurons is regulated by specific patterns of action potential firing, with an emphasis on new information on epigenetic regulation of gene expression. Patterned action potential activity activates intracellular signaling networks selectively in accordance with the kinetics of activation and inactivation of second messengers, phosphorylation and dephosphorylation of protein kinases, and cytoplasmic and nuclear calcium dynamics, which differentially activate specific transcription factors. Increasing evidence also implicates activity-dependent regulation of epigenetic mechanisms to alter chromatin architecture. Changes in three-dimensional chromatin structure, including chromatin compaction, looping, double-stranded DNA breaks, histone and DNA modification, are altered by action potential activity to selectively inhibit or promote transcription of specific genes. These mechanisms of activity-dependent regulation of gene expression are important in neural development, plasticity, and in neurological and psychological disorders.

scholarly journals Head-down tilt bed rest with or without artificial gravity is not associated with motor unit remodeling

2020 ◽  
Vol 120 (11) ◽  
pp. 2407-2415 ◽  
Author(s):  
Julia Attias ◽  
Andrea Grassi ◽  
Alessandra Bosutti ◽  
Bergita Ganse ◽  
Hans Degens ◽  
...  
Keyword(s):  
Motor Unit ◽  
Compound Muscle Action Potential ◽  
Bed Rest ◽  
Artificial Gravity ◽  
Whole Body ◽  
Healthy Individuals ◽  
Long Duration ◽  
Muscle Action Potential ◽  
Abductor Digiti Minimi ◽  
Healthy Participants

Abstract Purpose The objective of this study was to assess whether artificial gravity attenuates any long-duration head-down 60 bed rest (HDBR)-induced alterations in motor unit (MU) properties. Methods Twenty-four healthy participants (16 men; 8 women; 26–54 years) underwent 60-day HDBR with (n = 16) or without (n = 8) 30 min artificial gravity daily induced by whole-body centrifugation. Compound muscle action potential (CMAP), MU number (MUNIX) and MU size (MUSIX) were estimated using the method of Motor Unit Number Index in the Abductor digiti minimi and tibialis anterior muscles 5 days before (BDC-5), and during day 4 (HDT4) and 59 (HDT59) of HDBR. Results The CMAP, MUNIX, and MUSIX at baseline did not change significantly in either muscle, irrespective of the intervention (p > 0.05). Across groups, there were no significant differences in any variable during HDBR, compared to BDC-5. Conclusion Sixty days of HDBR with or without artificial gravity does not induce alterations in motor unit number and size in the ADM or TA muscles in healthy individuals.

scholarly journals Change of cortical foot activation following 70 days of head-down bed rest

2018 ◽  
Vol 119 (6) ◽  
pp. 2145-2152 ◽  
Author(s):  
Peng Yuan ◽  
Vincent Koppelmans ◽  
Patricia Reuter-Lorenz ◽  
Yiri De Dios ◽  
Nichole Gadd ◽  
...  
Keyword(s):  
Neural Control ◽  
Balance Control ◽  
Brain Activity ◽  
Brain Activation ◽  
Bed Rest ◽  
Functional Mobility ◽  
Healthy Men ◽  
Control Subjects ◽  
Long Duration ◽  
Foot Tapping

Head-down tilt bed rest (HDBR) has been used as a spaceflight analog to study some of the effects of microgravity on human physiology, cognition, and sensorimotor functions. Previous studies have reported declines in balance control and functional mobility after spaceflight and HDBR. In this study we investigated how the brain activation for foot movement changed with HDBR. Eighteen healthy men participated in the current HDBR study. They were in a 6° head-down tilt position continuously for 70 days. Functional MRI scans were acquired to estimate brain activation for foot movement before, during, and after HDBR. Another 11 healthy men who did not undergo HDBR participated as control subjects and were scanned at four time points. In the HDBR subjects, the cerebellum, fusiform gyrus, hippocampus, and middle occipital gyrus exhibited HDBR-related increases in activation for foot tapping, whereas no HDBR-associated activation decreases were found. For the control subjects, activation for foot tapping decreased across sessions in a couple of cerebellar regions, whereas no activation increase with session was found. Furthermore, we observed that less HDBR-related decline in functional mobility and balance control was associated with greater pre-to-post HDBR increases in brain activation for foot movement in several cerebral and cerebellar regions. Our results suggest that more neural control is needed for foot movement as a result of HDBR. NEW & NOTEWORTHY Long-duration head-down bed rest serves as a spaceflight analog research environment. We show that brain activity in the cerebellum and visual areas during foot movement increases from pre- to post-bed rest and then shows subsequent recovery. Greater increases were seen for individuals who exhibited less decline in functional mobility and balance control, suggestive of adaptive changes in neural control with long-duration bed rest.

scholarly journals Intramural optical mapping of Vm and Cai2+ during long-duration ventricular fibrillation in canine hearts

2012 ◽  
Vol 302 (6) ◽  
pp. H1294-H1305 ◽  
Author(s):  
Wei Kong ◽  
Raymond E. Ideker ◽  
Vladimir G. Fast
Keyword(s):  
Ventricular Fibrillation ◽  
Action Potential ◽  
Short Duration ◽  
Action Potential Duration ◽  
Cycle Length ◽  
The Other ◽  
Membrane Voltage ◽  
Long Duration ◽  
Intracellular Ca ◽  
Rapid Pacing

Intramural gradients of intracellular Ca2+ (Cai2+) Cai2+ handling, Cai2+ oscillations, and Cai2+ transient (CaT) alternans may be important in long-duration ventricular fibrillation (LDVF). However, previous studies of Cai2+ handling have been limited to recordings from the heart surface during short-duration ventricular fibrillation. To examine whether abnormalities of intramural Cai2+ handling contribute to LDVF, we measured membrane voltage ( Vm) and Cai2+ during pacing and LDVF in six perfused canine hearts using five eight-fiber optrodes. Measurements were grouped into epicardial, midwall, and endocardial layers. We found that during pacing at 350-ms cycle length, CaT duration was slightly longer (by ≃10%) in endocardial layers than in epicardial layers, whereas action potential duration (APD) exhibited no difference. Rapid pacing at 150-ms cycle length caused alternans in both APD (APD-ALT) and CaT amplitude (CaA-ALT) without significant transmural differences. For 93% of optrode recordings, CaA-ALT was transmurally concordant, whereas APD-ALT was either concordant (36%) or discordant (54%), suggesting that APD-ALT was not caused by CaA-ALT. During LDVF, Vm and Cai2+ progressively desynchronized when not every action potential was followed by a CaT. Such desynchronization developed faster in the epicardium than in the other layers. In addition, CaT duration strongly increased (by ∼240% at 5 min of LDVF), whereas APD shortened (by ∼17%). CaT rises always followed Vm upstrokes during pacing and LDVF. In conclusion, the fact that Vm upstrokes always preceded CaTs indicates that spontaneous Cai2+ oscillations in the working myocardium were not likely the reason for LDVF maintenance. Strong Vm-Cai2+ desynchronization and the occurrence of long CaTs during LDVF indicate severely impaired Cai2+ handling and may potentially contribute to LDVF maintenance.

Effect of head-down-tilt bed rest and hypovolemia on dynamic regulation of heart rate and blood pressure

2000 ◽  
Vol 279 (6) ◽  
pp. R2189-R2199 ◽  
Author(s):  
Ken-Ichi Iwasaki ◽  
Rong Zhang ◽  
Julie H. Zuckerman ◽  
James A. Pawelczyk ◽  
Benjamin D. Levine
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Transfer Function ◽  
Stroke Volume ◽  
Plasma Volume ◽  
High Frequency ◽  
Function Analysis ◽  
Bed Rest ◽  
Baroreflex Control ◽  
Transfer Function Analysis

Adaptation to head-down-tilt bed rest leads to an apparent abnormality of baroreflex regulation of cardiac period. We hypothesized that this “deconditioning response” could primarily be a result of hypovolemia, rather than a unique adaptation of the autonomic nervous system to bed rest. To test this hypothesis, nine healthy subjects underwent 2 wk of −6° head-down bed rest. One year later, five of these same subjects underwent acute hypovolemia with furosemide to produce the same reductions in plasma volume observed after bed rest. We took advantage of power spectral and transfer function analysis to examine the dynamic relationship between blood pressure (BP) and R-R interval. We found that 1) there were no significant differences between these two interventions with respect to changes in numerous cardiovascular indices, including cardiac filling pressures, arterial pressure, cardiac output, or stroke volume; 2) normalized high-frequency (0.15–0.25 Hz) power of R-R interval variability decreased significantly after both conditions, consistent with similar degrees of vagal withdrawal; 3) transfer function gain (BP to R-R interval), used as an index of arterial-cardiac baroreflex sensitivity, decreased significantly to a similar extent after both conditions in the high-frequency range; the gain also decreased similarly when expressed as BP to heart rate × stroke volume, which provides an index of the ability of the baroreflex to alter BP by modifying systemic flow; and 4) however, the low-frequency (0.05–0.15 Hz) power of systolic BP variability decreased after bed rest (−22%) compared with an increase (+155%) after acute hypovolemia, suggesting a differential response for the regulation of vascular resistance (interaction, P < 0.05). The similarity of changes in the reflex control of the circulation under both conditions is consistent with the hypothesis that reductions in plasma volume may be largely responsible for the observed changes in cardiac baroreflex control after bed rest. However, changes in vasomotor function associated with these two conditions may be different and may suggest a cardiovascular remodeling after bed rest.

scholarly journals Action-potential broadening and endogenously sustained bursting are substrates of command ability in a feeding neuron of Pleurobranchaea

1980 ◽  
Vol 43 (3) ◽  
pp. 669-685 ◽  
Author(s):  
R. Gillette ◽  
M. U. Gillette ◽  
W. J. Davis
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Motor Output ◽  
Buccal Ganglion ◽  
Short Pulses ◽  
Motor Network ◽  
Single Axon ◽  
Network Output ◽  
Bilateral Pair ◽  
Potential Activity

1. The ventral white cells (VWC's) of the buccal ganglion of Pleurobranchaea, so named for their position and color, are a bilateral pair of neuron somata. Each sends a single axon out its contralateral stomatogastric nerve and has a dendritic field originating close to the soma. 2. The vwcs exhibit spontaneous episodes of prolonged depolarization (duration 1--4 min) accompanied by repetitive action-potential activity and separated by regular intervals of 3--30 min. Such prolonged burst episodes can be triggered by short pulses of depolarizing current. During the repetitive activity of the spontaneous bursts or that driven by imposed depolarization, the action potentials progressively broaden to 5--16 times their initial duration. 3. During spontaneous bursting or activity driven by imposed depolarization, the cyclic motor output of the feeding network is initiated or accelerated with a latency corresponding with the development of appreciable VWC spike broadening. When broadening of antidromic VWC spikes is suppressed by imposed hyperpolarization of the soma, the frequency of feeding cycles is significantly lower than when broadened spikes are allowed to develop. When trains of spikes are driven by depolarizing current, the motor output of the feeding network is not initiated until the VWC spikes have broadened to a repeatable "threshold" duration, regardless of the intensity of the depolarizing current. 4. The endogenous production of prolonged burst episodes, triggered by depolarizing current pulses, and progressive spike broadening can be demonstrated in the surgically isolated VWC soma. 5. The paired VWCs are strongly electrically coupled and display highly synchronous activity. They receive synaptic inputs from many previously identified interneurons of the feeding network and are thus reciprocally coupled within the network. 6. These results demonstrate that the capacity of this neuron to generate broadened action potentials during repetitive activity confers the ability to command coordinated motor-network output. The appropriate repetitive activity can be produced endogenously in the form of prolonged bursts of spikes.

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