scholarly journals Baroreflex control of muscle sympathetic nerve activity after 120 days of 6° head-down bed rest

2000 ◽  
Vol 278 (2) ◽  
pp. R445-R452 ◽  
Author(s):  
Atsunori Kamiya ◽  
Satoshi Iwase ◽  
Hiroki Kitazawa ◽  
Tadaaki Mano ◽  
Olga L. Vinogradova ◽  
...  
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Valsalva Maneuver ◽  
Muscle Sympathetic Nerve Activity ◽  
Linear Regression Analysis ◽  
Bed Rest ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Before And After ◽  
Head Up Tilt

To examine how long-lasting microgravity simulated by 6° head-down bed rest (HDBR) induces changes in the baroreflex control of muscle sympathetic nerve activity (MSNA) at rest and changes in responses of MSNA to orthostasis, six healthy male volunteers (range 26–42 yr) participated in Valsalva maneuver and head-up tilt (HUT) tests before and after 120 days of HDBR. MSNA was measured directly using a microneurographic technique. After long-term HDBR, resting supine MSNA and heart rate were augmented. The baroreflex slopes for MSNA during Valsalva maneuver (in supine position) and during 60° HUT test, determined by least-squares linear regression analysis, were significantly steeper after than before HDBR, whereas the baroreflex slopes for R-R interval were significantly flatter after HDBR. The increase in MSNA from supine to 60° HUT was not different between before and after HDBR, but mean blood pressure decreased in 60° HUT after HDBR. In conclusion, the baroreflex control of MSNA was augmented, whereas the same reflex control of R-R interval was attenuated after 120 days of HDBR.

scholarly journals Attenuated sympathetic nerve responses after 24 hours of bed rest

2002 ◽  
Vol 282 (6) ◽  
pp. H2210-H2215 ◽  
Author(s):  
Mazhar H. Khan ◽  
Allen R. Kunselman ◽  
Urs A. Leuenberger ◽  
William R. Davidson ◽  
Chester A. Ray ◽  
...  
Keyword(s):  
Cardiac Output ◽  
Negative Pressure ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Lower Body Negative Pressure ◽  
Muscle Sympathetic Nerve Activity ◽  
Bed Rest ◽  
Nerve Activity ◽  
Before And After ◽  
Reduced Rate

Bed rest reduces orthostatic tolerance. Despite decades of study, the cause of this phenomenon remains unclear. In this report we examined hemodynamic and sympathetic nerve responses to graded lower body negative pressure (LBNP) before and after 24 h of bed rest. LBNP allows for baroreceptor disengagement in a graded fashion. We measured heart rate (HR), cardiac output (HR × stroke volume obtained by echo Doppler), and muscle sympathetic nerve activity (MSNA) during a progressive and graded LBNP paradigm. Negative pressure was increased by 10 mmHg every 3 min until presyncope or completion of −60 mmHg. After bed rest, LBNP tolerance was reduced in 11 of 13 subjects ( P < .023), HR was greater ( P< .002), cardiac output was unchanged, and the ability to augment MSNA at high levels of LBNP was reduced (rate of rise for 30- to 60-mmHg LBNP before bed rest 0.073 bursts · min−1 · mmHg−1; after bed rest 0.035 bursts · min−1 · mmHg−1; P < 0.016). These findings suggest that 24 h of bed rest reduces sympathetic nerve responses to LBNP.

Sympathetic Responses to Valsalva's Manoeuvre Following Bed Rest

2003 ◽  
Vol 28 (3) ◽  
pp. 342-355 ◽  
Author(s):  
J. Kevin Shoemaker ◽  
Cynthia S. Hogeman ◽  
Lawrence I. Sinoway
Keyword(s):  
Blood Pressure ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Bed Rest ◽  
Pressure Control ◽  
Burst Frequency ◽  
Nerve Activity ◽  
Head Up Tilt ◽  
Valsalva's Manoeuvre

The purpose of this study was to examine whether 14 days of head-down tilt bed rest (HDBR) alters autonomic regulation during Valsalva's manoeuvre (VM) and if this would predict blood pressure control during a 60° head-up tilt (HUT) test. To examine autonomic control of blood pressure, we measured the changes in systolic (ΔSBP) and diastolic (ΔDBP) blood pressure between baseline and the early straining (Phase IIE) period of VM (20 sec straining to 40 mmHg; N = 7) in conjunction with changes in muscle sympathetic nerve activity (MSNA; microneurography) burst frequency (B/min) and total activity (%Δ) from baseline over the 20-sec straining period. MSNA data were successfully recorded from 6 of the 7 individuals. The averaged responses from three repeated VMs performed in the supine position were compared between the pre- and post-HDBR tests. Compared with the pre-HDBR test, a greater reduction in SBP, DBP, and MAP was observed during Phase IIE following HDBR, p < 0.05. The increase in MSNA burst frequency during straining was augmented in the post- compared with the pre-HDBR test, p < 0.0001, as was the Phase IV blood pressure overshoot, p < 0.05. Although all subjects completed the 20-min pre-HDBR tilt test without evidence of hypotension or orthostatic intolerance, the post-HDBR test was stopped early in 5 of the 7 subjects due to systolic hypotension. The responses during the VM suggest that acute autonomic adjustments to rapid blood pressure changes are preserved after bed rest. Furthermore, MSNA and blood pressure responses during VM did not predict blood pressure control during orthostasis following HDBR. Key words: muscle sympathetic nerve activity, blood pressure, orthostatic tolerance, head-up tilt

Baroreflex control of muscle sympathetic nerve activity in postural orthostatic tachycardia syndrome

2005 ◽  
Vol 289 (3) ◽  
pp. H1226-H1233 ◽  
Author(s):  
N. Muenter Swift ◽  
N. Charkoudian ◽  
R. M. Dotson ◽  
G. A. Suarez ◽  
P. A. Low
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Valsalva Maneuver ◽  
Muscle Sympathetic Nerve Activity ◽  
Vasoactive Drug ◽  
Postural Orthostatic Tachycardia Syndrome ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Control Subjects ◽  
Healthy Control

Postural orthostatic tachycardia syndrome (POTS) is characterized by excessive tachycardia during orthostasis. To test the hypothesis that patients with POTS have decreased sympathetic neural responses to baroreflex stimuli, we measured heart rate (HR) and muscle sympathetic nerve activity (MSNA) responses to three baroreflex stimuli including vasoactive drug boluses (modified Oxford technique), Valsalva maneuver, and head-up tilt (HUT) in POTS patients and healthy control subjects. The MSNA response to the Valsalva maneuver was significantly greater in the POTS group (controls, 26 ± 7 vs. POTS, 48 ± 6% of baseline MSNA/mmHg; P = 0.03). POTS patients also had an exaggerated MSNA response to 30° HUT (controls, 123 ± 24 vs. POTS, 208 ± 30% of baseline MSNA; P = 0.03) and tended to have an exaggerated response to 45° HUT (controls, 137 ± 27 vs. POTS, 248 ± 58% of baseline MSNA; P = 0.10). Sympathetic baroreflex sensitivity calculated during administration of the vasoactive drug boluses also tended to be greater in the POTS patients; however, this did not reach statistical significance ( P = 0.15). Baseline MSNA values during supine rest were not different between the groups (controls, 23 ± 4 vs. POTS, 16 ± 5 bursts/100 heartbeats; P = 0.30); however, resting HR was significantly higher in the POTS group (controls, 58 ± 3 vs. POTS, 82 ± 4 beats/min; P = 0.0001). Our results suggest that POTS patients have exaggerated MSNA responses to baroreflex challenges compared with healthy control subjects, although resting supine MSNA values did not differ between the groups.

α-Adrenergic vascular responsiveness to sympathetic nerve activity is intact after head-down bed rest in humans

2004 ◽  
Vol 286 (1) ◽  
pp. R151-R157 ◽  
Author(s):  
Atsunori Kamiya ◽  
Daisaku Michikami ◽  
Satoshi Iwase ◽  
Junichiro Hayano ◽  
Toru Kawada ◽  
...  
Keyword(s):  
Vascular Resistance ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Bed Rest ◽  
Venous Occlusion ◽  
Vascular Conductance ◽  
Nerve Activity ◽  
Before And After ◽  
Vascular Responsiveness

Space-flight and its ground-based simulation model, 6° head-down bed rest (HDBR), cause cardiovascular deconditioning in humans. Because sympathetic vasoconstriction plays a very important role in circulation, we examined whether HDBR impairs α-adrenergic vascular responsiveness to sympathetic nerve activity. We subjected eight healthy volunteers to 14 days of HDBR and before and after HDBR measured calf muscle sympathetic nerve activity (MSNA; microneurography) and calf blood flow (venous occlusion plethysmography) during sympathoexcitatory stimulation (rhythmic handgrip exercise). HDBR did not change the increase in total MSNA ( P = 0.97) or the decrease in calf vascular conductance ( P = 0.32) during exercise, but it did augment the increase in calf vascular resistance ( P = 0.0011). HDBR augmented the transduction gain from total MSNA into calf vascular resistance, assessed as the least squares linear regression slope of vascular resistance on total MSNA (0.05 ± 0.02 before HDBR, 0.20 ± 0.06 U·min-1·burst-1after HDBR, P = 0.0075), but did not change the transduction gain into calf vascular conductance ( P = 0.41). Our data indicate that α-adrenergic vascular responsiveness to sympathetic nerve activity is preserved in the supine position after HDBR in humans.

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.

Relation between QT interval variability and muscle sympathetic nerve activity in normal subjects

2015 ◽  
Vol 309 (7) ◽  
pp. H1218-H1224 ◽  
Author(s):  
Fatima El-Hamad ◽  
Elisabeth Lambert ◽  
Derek Abbott ◽  
Mathias Baumert
Keyword(s):  
Supine Position ◽  
Sympathetic Nerve ◽  
Qt Interval ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Low Frequency ◽  
Normal Subjects ◽  
Nerve Activity ◽  
Head Up Tilt ◽  
Low Frequency Power

Beat-to-beat variability of the QT interval (QTV) is sought to provide an indirect noninvasive measure of sympathetic nerve activity, but a formal quantification of this relationship has not been provided. In this study we used power contribution analysis to study the relationship between QTV and muscle sympathetic nerve activity (MSNA). ECG and MSNA were recorded in 10 healthy subjects in the supine position and after 40° head-up tilt. Power spectrum analysis was performed using a linear autoregressive model with two external inputs: heart period (RR interval) variability (RRV) and MSNA. Total and low-frequency power of QTV was decomposed into contributions by RRV, MSNA, and sources independent of RRV and MSNA. Results show that the percentage of MSNA power contribution to QT is very small and does not change with tilt. RRV power contribution to QT power is notable and decreases with tilt, while the greatest percentage of QTV is independent of RRV and MSNA in the supine position and after 40° head-up tilt. In conclusion, beat-to-beat QTV in normal subjects does not appear to be significantly affected by the rhythmic modulations in MSNA following low to moderate orthostatic stimulation. Therefore, MSNA oscillations may not represent a useful surrogate for cardiac sympathetic nerve activity at moderate levels of activation, or, alternatively, sympathetic influences on QTV are complex and not quantifiable with linear shift-invariant autoregressive models.

scholarly journals Water drinking enhances the gain of arterial baroreflex control of muscle sympathetic nerve activity in healthy young humans

2018 ◽  
Vol 103 (10) ◽  
pp. 1318-1325 ◽  
Author(s):  
Lauro C. Vianna ◽  
Igor A. Fernandes ◽  
Daniel G. Martinez ◽  
André L. Teixeira ◽  
Bruno M. Silva ◽  
...  
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Arterial Baroreflex ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Water Drinking
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