scholarly journals Case Studies in Physiology: Sympathetic neural discharge patterns in a healthy young male during end-expiratory breath hold-induced sinus pause

2020 ◽  
Vol 129 (2) ◽  
pp. 230-237
Author(s):  
Tyler D. Vermeulen ◽  
Brooke M. Shafer ◽  
Anthony V. Incognito ◽  
Massimo Nardone ◽  
André L. Teixeira ◽  
...  
Keyword(s):  
Sympathetic Nerve Activity ◽  
Cardiac Cycle ◽  
Muscle Sympathetic Nerve Activity ◽  
Young Male ◽  
Discharge Pattern ◽  
Breath Hold ◽  
Single Cardiac Cycle ◽  
Discharge Patterns ◽  
Neural Discharge ◽  
Wave Discharge

We characterize the occurrence of a square-wave discharge pattern of efferent muscle sympathetic nerve activity during a sinus pause in a young healthy male. This discharge pattern comprised large recruited action potential clusters undetected at baseline that continuously discharged during the sinus pause. Notably, this discharge pattern was still contained within a single cardiac cycle.

scholarly journals Ventilation inhibits sympathetic action potential recruitment even during severe chemoreflex stress

2017 ◽  
Vol 118 (5) ◽  
pp. 2914-2924 ◽  
Author(s):  
Mark B. Badrov ◽  
Otto F. Barak ◽  
Tanja Mijacika ◽  
Leena N. Shoemaker ◽  
Lindsay J. Borrell ◽  
...  
Keyword(s):  
Action Potential ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Breath Hold ◽  
Nerve Activity ◽  
Hemoglobin Saturation ◽  
Residual Capacity ◽  
Per Se ◽  
Discharge Patterns

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

The impact of 6 months of exercise-based cardiac rehabilitation on sympathetic neural recruitment during apneic stress

2021 ◽  
Author(s):  
Andrew D'Souza ◽  
Mark B. Badrov ◽  
Katelyn N. Wood ◽  
Sophie Lalande ◽  
Neville Gordon Suskin ◽  
...  
Keyword(s):  
Cardiac Rehabilitation ◽  
Sympathetic Activity ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Firing Frequency ◽  
Sympathetic Activation ◽  
Nerve Activity ◽  
Sympathetic Nervous ◽  
Discharge Patterns ◽  
The Impact

The current study evaluated the hypothesis that six months of exercise-based cardiac rehabilitation (CR) would improve sympathetic neural recruitment in patients with ischemic heart disease (IHD). Microneurography was used to evaluate action potential (AP) discharge patterns within bursts of muscle sympathetic nerve activity (MSNA), in eleven patients with IHD (1 female; 61±9 years) pre- (Pre-CR) and post- six months of aerobic and resistance training-based CR (Post-CR). Measures were made at baseline and during maximal voluntary end-inspiratory (EI-APN) and end-expiratory apneas (EE-APN). Data were analyzed during 1-minute of baseline and the second half of apneas. At baseline, overall sympathetic activity was less Post-CR (all P<0.01). During EI-APN, AP recruitment was not observed Pre-CR (all P>0.05) but increases in both within-burst AP firing frequency (∆Pre-CR: 2±3 AP spikes/burst vs. ∆Post-CR: 4±3 AP spikes/burst; P=0.02) and AP cluster recruitment (∆Pre-CR: -1±2 vs. ∆Post-CR: 2±2; P<0.01) were observed in Post-CR tests. In contrast, during EE-APN, AP firing frequency was not different Post-CR compared to Pre-CR tests (∆Pre-CR: 269±202 spikes/min vs. ∆Post-CR: 232±225 spikes/min; P=0.54), and CR did not modify the recruitment of new AP clusters (∆Pre-CR: -1±3 vs. ∆Post-CR: 0±1; P=0.39), or within-burst firing frequency (∆Pre-CR: 3±3 AP spikes/burst vs. ∆Post-CR: 2±2 AP spikes/burst; P=0.21). These data indicate that CR improves some of the sympathetic nervous system dysregulation associated with cardiovascular disease, primarily via a reduction in resting sympathetic activation. However, the benefits of CR on sympathetic neural recruitment may depend upon the magnitude of initial impairment.

scholarly journals Sympathetic neural recruitment strategies following acute intermittent hypoxia in humans

2020 ◽  
Vol 318 (5) ◽  
pp. R961-R971 ◽  
Author(s):  
Elizabeth P. Ott ◽  
Dain W. Jacob ◽  
Sarah E. Baker ◽  
Walter W. Holbein ◽  
Zachariah M. Scruggs ◽  
...  
Keyword(s):  
Intermittent Hypoxia ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Burst Firing ◽  
Neural Firing ◽  
Carotid Chemoreceptors ◽  
Discharge Rates ◽  
Before And After ◽  
Discharge Patterns

We examined the effect of acute intermittent hypoxia (IH) on sympathetic neural firing patterns and the role of the carotid chemoreceptors. We hypothesized exposure to acute IH would increase muscle sympathetic nerve activity (MSNA) via an increase in action potential (AP) discharge rates and within-burst firing. We further hypothesized any change in discharge patterns would be attenuated during acute chemoreceptor deactivation (hyperoxia). MSNA (microneurography) was assessed in 17 healthy adults (11 male/6 female; 31 ± 1 yr) during normoxic rest before and after 30 min of experimental IH. Prior to and following IH, participants were exposed to 2 min of 100% oxygen (hyperoxia). AP patterns were studied from the filtered raw MSNA signal using wavelet-based methodology. Compared with baseline, multiunit MSNA burst incidence ( P < 0.01), AP incidence ( P = 0.01), and AP content per burst ( P = 0.01) were increased following IH. There was an increase in the probability of a particular AP cluster firing once ( P < 0.01) and more than once ( P = 0.03) per burst following IH. There was no effect of hyperoxia on multiunit MSNA at baseline or following IH ( P > 0.05); however, hyperoxia following IH attenuated the probability of particular AP clusters firing more than once per burst ( P < 0.01). Acute IH increases MSNA by increasing AP discharge rates and within-burst firing. A portion of the increase in within-burst firing following IH can be attributed to the carotid chemoreceptors. These data advance the mechanistic understanding of sympathetic activation following acute IH in humans.

scholarly journals Central vs. peripheral determinants of sympathetic neural recruitment: insights from static handgrip exercise and postexercise circulatory occlusion

2016 ◽  
Vol 311 (6) ◽  
pp. R1013-R1021 ◽  
Author(s):  
Mark B. Badrov ◽  
T. Dylan Olver ◽  
J. Kevin Shoemaker
Keyword(s):  
Neural Coding ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Voluntary Contraction ◽  
Synaptic Delay ◽  
Low Threshold ◽  
Discharge Patterns ◽  
Sympathetic Discharge ◽  
Perceptual Factors

Sympathetic outflow is modified during acute homeostatic stress through increased firing of low-threshold axons, recruitment of latent axons, and synaptic delay modifications. However, the role of central mechanisms versus peripheral reflex control over sympathetic recruitment remains unknown. Here, we examined sympathetic discharge patterns during fatiguing static handgrip (SHG) exercise and postexercise circulatory occlusion (PECO) to study the central vs. peripheral reflex elements of sympathetic neural coding. Muscle sympathetic nerve activity (MSNA; microneurography) was measured in six males (25 ± 3 yr) at baseline (3 min) and during 5 min of SHG exercise completed at 20% maximal voluntary contraction. Isolation of the peripheral metaboreflex component was achieved by PECO for 3 min. Action potential (AP) patterns were studied using wavelet-based methodology. Compared with baseline, total MSNA increased by minute 3 of SHG, remaining elevated throughout the duration of exercise and PECO (all P < 0.05). The AP content per burst increased above baseline by minute 4 of SHG (Δ4 ± 2), remaining elevated at minute 5 (Δ6 ± 4) and PECO (Δ4 ± 4; all P < 0.05). Similarly, total AP clusters increased by minute 4 of SHG (Δ5 ± 5) and remained elevated at minute 5 (Δ6 ± 3) and PECO (Δ7 ± 5; all P < 0.01), indicating recruitment of latent subpopulations. Finally, the AP cluster size-latency profile was shifted downward during minutes 4 (−32 ± 22 ms) and 5 (−49 ± 17 ms; both P < 0.05) of SHG but was not different than baseline during PECO ( P > 0.05). Our findings suggest that central perceptual factors play a specific role in the synaptic delay aspect of sympathetic discharge timing, whereas peripheral reflex mechanisms affect recruitment of latent axons.

Area postrema excites and inhibits sympathetic-related neurons in rostral ventrolateral medulla in rabbit

1994 ◽  
Vol 266 (3) ◽  
pp. H1075-H1086 ◽  
Author(s):  
C. G. Wilson ◽  
A. C. Bonham
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Cardiac Cycle ◽  
Area Postrema ◽  
Rostral Ventrolateral Medulla ◽  
Ventrolateral Medulla ◽  
Nerve Activity ◽  
Spike Triggered Averaging ◽  
Discharge Patterns ◽  
Alpha Chloralose

This study investigated the effects of area postrema stimulation on the activity of cardiovascular-related neurons in the rostral ventrolateral medulla and determined whether the effects were mediated by cell bodies. Results are based on recordings of extracellular spikes from 113 neurons in 37 alpha-chloralose- or pentobarbital sodium-anesthetized rabbits. Single sequential stimuli evoked an excitation (onset, 22 +/- 8 ms; duration, 20 +/- 14 ms) followed by an inhibition (onset, 53 +/- 21 ms; duration, 127 +/- 82 ms) in 1) 58 neurons with discharge patterns that were correlated with sympathetic nerve activity (determined by spike-triggered averaging) and with the cardiac cycle (determined by post-R wave-triggered histograms) and that were inhibited by increasing arterial pressure and 2) 27 neurons that exhibited a cardiac rhythm but not a sympathetic rhythm. Area postrema-evoked excitation and inhibition were markedly attenuated by kainic acid injections in area postrema, suggesting that both inputs were derived from cell bodies. The results suggest that area postrema neurons may modulate the activity of medullary neurons in the baroreflex-sympathetic arc as well as neurons in other networks that share baroreceptor input but may not be related to sympathetic nerve activity.

scholarly journals Calibrated variability of muscle sympathetic nerve activity during graded head-up tilt in humans and its link with noradrenaline data and cardiovascular rhythms

2016 ◽  
Vol 310 (11) ◽  
pp. R1134-R1143 ◽  
Author(s):  
Andrea Marchi ◽  
Vlasta Bari ◽  
Beatrice De Maria ◽  
Murray Esler ◽  
Elisabeth Lambert ◽  
...  
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Low Frequency ◽  
Nerve Activity ◽  
Low Pass ◽  
Head Up Tilt ◽  
Normalized Units ◽  
Neural Discharge ◽  
Relationship Of

Muscle sympathetic nerve activity (MSNA) variability is traditionally computed through a low-pass filtering procedure that requires normalization. We proposed a new beat-to-beat MSNA variability computation that preserves dimensionality typical of an integrated neural discharge (i.e., bursts per unit of time). The calibrated MSNA (cMSNA) variability technique is contrasted with the traditional uncalibrated MSNA (ucMSNA) version. The powers of cMSNA and ucMSNA variabilities in the low-frequency (LF, from 0.04 to 0.15 Hz) band were computed with those of the heart period (HP) of systolic and diastolic arterial pressure (SAP and DAP, respectively) in seven healthy subjects (age, 20–28 years; median, 22 years; 5 women) during a graded head-up tilt. Subjects were sequentially tilted at 0°, 20°, 30°, 40°, and 60° table inclinations. The LF powers of ucMSNA and HP variabilities were expressed in normalized units (LFnu), whereas all remaining spectral markers were expressed in absolute units. We found that 1) the LF power of cMSNA variability was positively correlated with tilt angle, whereas the LFnu power of the ucMSNA series was uncorrelated; 2) the LF power of cMSNA variability was correlated with LF powers of SAP and DAP, LFnu power of HP and noradrenaline concentration, whereas the relationship of the LFnu power of ucMSNA variability to LF powers of SAP and DAP was weaker and that to LFnu power of HP was absent; and 3) the stronger relationship of cMSNA variability to SAP and DAP spectral markers compared with the ucMSNA series was confirmed individually. The cMSNA variability appears to be more suitable in describing sympathetic control in humans than traditional ucMSNA variability.

Neural sites involved in the sustained increase in muscle sympathetic nerve activity induced by inspiratory capacity apnea: a fMRI study

2006 ◽  
Vol 100 (1) ◽  
pp. 266-273 ◽  
Author(s):  
V. G. Macefield ◽  
S. C. Gandevia ◽  
L. A. Henderson
Keyword(s):  
Sympathetic Nerve ◽  
Signal Intensity ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Anterior Cingulate ◽  
Breath Hold ◽  
Inspiratory Capacity ◽  
Nerve Activity ◽  
Global Signal ◽  
Sustained Increase

A maximal inspiratory breath hold (inspiratory capacity apnea) against a closed glottis evokes a large and sustained increase in muscle sympathetic nerve activity (MSNA). Because of its dependence on a high intrathoracic pressure, it has been suggested that this maneuver causes unloading of the low-pressure baroreceptors, known to increase MSNA. To determine the central origins of this sympathoexcitation, we used functional magnetic resonance imaging to define the loci and time course of activation of different brain areas. We hypothesized that, as previously shown for the Valsalvsa maneuver, discrete but widespread regions of the brain would be involved. In 15 healthy human subjects, a series of 90 gradient echo echo-planar image sets was collected during three consecutive 40-s inspiratory capacity apneas using a 3-T scanner. Global signal intensity changes were calculated and subsequently removed by using a detrending technique, which eliminates the global signal component from each voxel's signal intensity change. Whole brain correlations between changes in signal intensity and the known pattern of MSNA during the maneuver were performed on a voxel-by-voxel basis, and significant changes were determined by using a random-effects analysis procedure ( P < 0.01, uncorrected). Significant signal increases emerged in multiple areas, including the rostral lateral medulla, cerebellar nuclei, anterior insula, dorsomedial hypothalamus, anterior cingulate, and lateral prefrontal cortexes. Decreases in signal intensity occurred in the dorsomedial and caudal lateral medulla, cerebellar cortex, hippocampus, and posterior cingulate cortex. Given that many of these sites have roles in cardiovascular control, the sustained increase in MSNA during an inspiratory capacity apnea is likely to originate from a distributed set of discrete areas.

scholarly journals Attenuation of sympathetic baroreflex sensitivity during the onset of acute mental stress in humans

2011 ◽  
Vol 300 (5) ◽  
pp. H1788-H1793 ◽  
Author(s):  
John J. Durocher ◽  
Jenna C. Klein ◽  
Jason R. Carter
Keyword(s):  
Arterial Pressure ◽  
Strong Correlation ◽  
Mental Stress ◽  
Baroreflex Sensitivity ◽  
Sympathetic Nerve Activity ◽  
Cardiac Cycle ◽  
Pressor Response ◽  
Muscle Sympathetic Nerve Activity ◽  
Nerve Activity ◽  
Spontaneous Fluctuations

Mental stress consistently induces a pressor response that is often accompanied by a paradoxical increase of muscle sympathetic nerve activity (MSNA). The purpose of the present study was to evaluate sympathetic baroreflex sensitivity (BRS) by examining the relations between spontaneous fluctuations of diastolic arterial pressure (DAP) and MSNA. We hypothesized that sympathetic BRS would be attenuated during mental stress. DAP and MSNA were recorded during 5 min of supine baseline, 5 min of mental stress, and 5 min of recovery in 32 young healthy adults. Burst incidence and area were determined for each cardiac cycle and placed into 3-mmHg DAP bins; the slopes between DAP and MSNA provided an index of sympathetic BRS. Correlations between DAP and MSNA were strong (>0.5) during baseline in 31 of 32 subjects, but we evaluated the change in slope only for those subjects maintaining a strong correlation during mental stress (16 subjects). During baseline, the relation between DAP and MSNA was negative when expressed as either burst incidence [slope = −1.95 ± 0.18 bursts·(100 beats)−1·mmHg−1; r = −0.86 ± 0.03] or total MSNA [slope = −438 ± 91 units·(beat)−1 mmHg−1; r = −0.76 ± 0.06]. During mental stress, the slope between burst incidence and DAP was significantly reduced [slope = −1.14 ± 0.12 bursts·(100 beats)−1·mmHg−1; r = −0.72 ± 0.03; P < 0.01], indicating attenuation of sympathetic BRS. A more detailed analysis revealed an attenuation of sympathetic BRS during the first 2 min of mental stress ( P < 0.01) but no change during the final 3 min of mental stress ( P = 0.25). The present study demonstrates that acute mental stress attenuates sympathetic BRS, which may partially contribute to sympathoexcitation during the mental stress-pressor response. However, this attenuation appears to be isolated to the onset of mental stress. Moreover, variable MSNA responses to mental stress do not appear to be directly related to sympathetic BRS.

Effects of baroreceptor reflex on efferent pulmonary sympathetic nerve activity in anesthetized cat

1995 ◽  
Vol 268 (4) ◽  
pp. R1078-R1083 ◽  
Author(s):  
M. Shirai ◽  
K. Matsukawa ◽  
N. Nishiura ◽  
I. Ninomiya
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Cardiac Cycle ◽  
Maximum Level ◽  
Aortic Pressure ◽  
Baroreceptor Reflex ◽  
Renal Nerves ◽  
Nerve Activity ◽  
Renal Nerve ◽  
Discharge Patterns

We analyzed the baroceptor reflex effect on efferent pulmonary sympathetic nerve activity (PSNA) in anesthetized cats. PSNA was recorded from the central end of the cut nerve bundle, which was isolated from the lobar artery supplying the diaphragmatic lobe. Renal sympathetic nerve activity (RSNA) and aortic blood pressure (AP) were also simultaneously measured. There were grouped discharges synchronous with cardiac cycle and its respiratory modulation in PSNA. In a given cardiac cycle, the discharge patterns differed between the pulmonary and renal nerves. Average sympathetic nerve activity and AP obtained from 100 consecutive cardiac cycles showed that the baroreceptor reflex delay time on the pulmonary nerve (266 ms) was longer than that on the renal nerve (195 ms). The data indicate nonuniformity in the cardiac-related PSNA and RSNA. The grouped PSNA disappeared with hexamethonium bromide, indicating that PSNA originates from postganglionic efferent fibers. To examine the baroreflex response of PSNA, AP was increased by 70 mmHg with phenylephrine and decreased by 70 mmHg with nitroprusside. PSNA changed inversely to the changes in mean aortic pressure (MAP). In the delta MAP-delta PSNA curve, delta PSNA reached the maximum level (74%) and the noise level at -56 +/- 4 and 58 +/- 4 mmHg, respectively. The mean slope of the curve was 1.5 +/- 0.1%/mmHg. RSNA also responded inversely to the MAP change.(ABSTRACT TRUNCATED AT 250 WORDS)

Baroreflex mechanisms regulating the occurrence of neural spikes in human muscle sympathetic nerve activity

2012 ◽  
Vol 107 (12) ◽  
pp. 3409-3416 ◽  
Author(s):  
Aryan Salmanpour ◽  
J. Kevin Shoemaker
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Linear Regression Analysis ◽  
Threshold Probability ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Burst Strength ◽  
Discharge Patterns ◽  
Variable Impact

This study tested the hypothesis that the discharge patterns of action potentials (APs) within bursts of postganglionic muscle sympathetic nerve activity (MSNA) are subject to arterial baroreflex control but in a manner that varies inversely with AP size. MSNA data were collected over 5 min of supine rest in 15 young and healthy individuals (8 males; 24 ± 4 yr of age; means ± SD). The baroreflex threshold and sensitivity diagrams were constructed for both the integrated sympathetic bursts and for the AP clusters. For the integrated bursts, a strong linear relationship between burst probability and diastolic blood pressure (DBP) was observed ( P < 0.05). There was little relationship between integrated burst strength (amplitude) and DBP. On average, 12 AP clusters were observed across individuals. Larger APs tended to appear in the larger bursts. Linear regression analysis was used to study the baroreflex threshold (probability of AP cluster occurrence vs. DBP) as well as the baroreflex sensitivity (AP cluster size vs. DBP). A significant reflex threshold relationship was observed in 75–100% of AP clusters across all individuals. In contrast, significant reflex sensitivity relationships were observed in only 9 of 15 individuals and for limited APs. Overall, the slope of the AP baroreflex threshold relationship was greater for the small-medium sized AP clusters than that of the larger APs. Therefore, within each burst, the small-medium sized APs are governed by the baroreflex mechanism. However, the large APs, which tend to appear in the large integrated bursts, are weakly associated with a baroreflex control feature. The variable impact of baroreflex control over AP occurrence provides a plausible explanation for the overall weak baroreflex control over integrated burst strength, a feature that is determined by both the number and size of the AP complement.

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