scholarly journals Baroreflex control of muscle sympathetic nerve activity: a nonpharmacological measure of baroreflex sensitivity

2010 ◽  
Vol 298 (3) ◽  
pp. H816-H822 ◽  
Author(s):  
Emma C. Hart ◽  
Michael J. Joyner ◽  
B. Gunnar Wallin ◽  
Tomas Karlsson ◽  
Timothy B. Curry ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Sympathetic Nerve ◽  
Baroreflex Sensitivity ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Pharmacological Intervention ◽  
Threshold Analysis ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Spontaneous Baroreflex

The sensitivity of baroreflex control of sympathetic nerve activity (SNA) represents the responsiveness of SNA to changes in blood pressure. In a slightly different analysis, the baroreflex threshold measures the probability of whether a sympathetic burst will occur at a given diastolic blood pressure. We hypothesized that baroreflex threshold analysis could be used to estimate the sensitivity of the sympathetic baroreflex measured by the pharmacological modified Oxford test. We compared four measures of sympathetic baroreflex sensitivity in 25 young healthy participants: the “gold standard” modified Oxford analysis (nitroprusside and phenylephrine), nonbinned spontaneous baroreflex analysis, binned spontaneous baroreflex analysis, and threshold analysis. The latter three were performed during a quiet baseline period before pharmacological intervention. The modified Oxford baroreflex sensitivity was significantly related to the threshold slope ( r = 0.71, P < 0.05) but not to the binned (1 mmHg bins) and the nonbinned spontaneous baroreflex sensitivity ( r = 0.22 and 0.36, respectively, P > 0.05), which included burst area. The threshold analysis was also performed during the modified Oxford manipulation. Interestingly, we found that the threshold analysis results were not altered by the vasoactive drugs infused for the modified Oxford. We conclude that the noninvasive threshold analysis technique can be used as an indicator of muscle SNA baroreflex sensitivity as assessed by the modified Oxford technique. Furthermore, the modified Oxford method does not appear to alter the properties of the baroreflex.

scholarly journals Device-guided slow breathing reduces blood pressure and sympathetic activity in young normotensive individuals of both sexes

2019 ◽  
Vol 127 (4) ◽  
pp. 1042-1049 ◽  
Author(s):  
Tessa E. Adler ◽  
Yasmine Coovadia ◽  
Domenica Cirone ◽  
Maha L. Khemakhem ◽  
Charlotte W. Usselman
Keyword(s):  
Blood Pressure ◽  
Body Mass Index ◽  
Body Mass ◽  
Sympathetic Nerve ◽  
Baroreflex Sensitivity ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Nerve Activity ◽  
Main Effect ◽  
Slow Breathing

Slow breathing (SLOWB) is recommended for use as an adjuvant treatment for hypertension. However, the extent to which blood pressure (BP) responses to SLOWB differ between men and women are not well-established. Therefore, we tested the hypothesis that an acute bout of SLOWB would induce larger decreases in BP in males than in females, given that males typically have higher resting BP. We also examined autonomic contributors to reduced BP during SLOWB; that is, muscle sympathetic nerve activity and spontaneous cardiovagal (sequence method) and vascular sympathetic baroreflex sensitivity. We tested normotensive females ( n = 10, age: 22 ± 2 y, body mass index: 22 ± 2 kg/m2) and males ( n = 12, age: 23 ± 3 y, body mass index: 26 ± 4 kg/m2). Subjects were tested at baseline and during the last 5 min of a 15-min RESPeRATE-guided SLOWB session. Overall, SLOWB reduced systolic BP by 3.2 ± 0.8 mmHg (main effect, P < 0.01). Females had lower systolic BP (main effect, P = 0.02); we observed no interaction between sex and SLOWB. SLOWB also reduced muscle sympathetic nerve activity burst incidence by −5.0 ± 1.4 bursts/100 heartbeats (main effect, P < 0.01). Although females tended to have lower burst incidence (main effect, P = 0.1), there was no interaction between sex and SLOWB. Cardiovagal baroreflex sensitivity improved during SLOWB (21.0 vs. 36.0 ms/mmHg, P = 0.03) with no effect of sex. Despite lower overall BP in females, our data support a lack of basement effect on SLOWB-induced reductions in BP, as SLOWB was equally effective in reducing BP in males and females. Our findings support the efficacy of the RESPeRATE device for reducing BP in both sexes, even in young, normotensive individuals. NEW & NOTEWORTHY We provide support for the effectiveness of device-guided slow breathing for blood pressure reduction in young normotensive women and men. Despite having lower baseline blood pressure and sympathetic nerve activity, women experienced equivalent reductions in both measures in response to RESPeRATE-guided slow breathing as men. Thus, slow breathing appears to be effective in young healthy normotensive individuals of both sexes and may be an ideal preventative therapy against future hypertension.

Hyperventilation alters arterial baroreflex control of heart rate and muscle sympathetic nerve activity

2000 ◽  
Vol 279 (2) ◽  
pp. H536-H541 ◽  
Author(s):  
Philippe Van de Borne ◽  
Silvia Mezzetti ◽  
Nicola Montano ◽  
Krzysztof Narkiewicz ◽  
Jean Paul Degaute ◽  
...  
Keyword(s):  
Heart Rate ◽  
Sympathetic Nerve ◽  
Baroreflex Sensitivity ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Normal Subjects ◽  
Arterial Baroreflex ◽  
Baroreceptor Sensitivity ◽  
Nerve Activity ◽  
Baroreflex Control

Interactions between mechanisms governing ventilation and blood pressure (BP) are not well understood. We studied in 11 resting normal subjects the effects of sustained isocapnic hyperventilation on arterial baroreceptor sensitivity, determined as the α index between oscillations in systolic BP (SBP) generated by respiration and oscillations present in R-R intervals (RR) and in peripheral sympathetic nerve traffic [muscle sympathetic nerve activity (MSNA)]. Tidal volume increased from 478 ± 24 to 1,499 ± 84 ml and raised SBP from 118 ± 2 to 125 ± 3 mmHg, whereas RR decreased from 947 ± 18 to 855 ± 11 ms (all P < 0.0001); MSNA did not change. Hyperventilation reduced arterial baroreflex sensitivity to oscillations in SBP at both cardiac (from 13 ± 1 to 9 ± 1 ms/mmHg, P < 0.001) and MSNA levels (by −37 ± 5%, P < 0.0001). Thus increased BP during hyperventilation does not elicit any reduction in either heart rate or MSNA. Baroreflex modulation of RR and MSNA in response to hyperventilation-induced BP oscillations is attenuated. Blunted baroreflex gain during hyperventilation may be a mechanism that facilitates simultaneous increases in BP, heart rate, and sympathetic activity during dynamic exercise and chemoreceptor activation.

scholarly journals Influence of multiparity on sympathetic nerve activity during normal pregnancy

2020 ◽  
Vol 318 (4) ◽  
pp. H816-H819 ◽  
Author(s):  
Mark B. Badrov ◽  
Jeung-Ki Yoo ◽  
Craig D. Steinback ◽  
Margie H. Davenport ◽  
Qi Fu
Keyword(s):  
Blood Pressure ◽  
Cardiovascular Disease ◽  
Sympathetic Nerve ◽  
Baroreflex Sensitivity ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Disease Development ◽  
Neural Regulation ◽  
Nerve Activity

Recent evidence suggests an elevated risk of cardiovascular disease development in multiparous women. Therefore, we investigated the effects of multiparity on within-pregnancy sympathetic neural regulation in normotensive, pregnant women. We retrospectively analyzed heart rate (HR), blood pressure (BP), and muscle sympathetic nerve activity (MSNA; n = 8) data from 10 women whom participated in microneurographic research studies during two sequential pregnancies (i.e., PREG1 and PREG2). There was no difference in resting BP between pregnancies ( P > 0.05), whereas HR trended higher in PREG2 versus PREG1 ( P = 0.06). MSNA burst frequency was greater in PREG2 versus PREG1 after adjusting for age (32 ± 12 vs. 22 ± 12 bursts/min; P = 0.049), whereas burst incidence did not differ (40 ± 16 vs. 34 ± 17 bursts/100 heartbeats; P = 0.21). Sympathetic baroreflex sensitivity was not different between PREG1 and PREG2 ( P > 0.05). Our results may highlight a possible role of altered within-pregnancy sympathetic neural regulation in the observed relationship in women between parity and future cardiovascular disease risk. NEW & NOTEWORTHY To our knowledge, this is the first study to investigate the effects of multiparity on within-pregnancy sympathetic neural regulation. We observed augmented muscle sympathetic nerve activity in women’s second studied pregnancy versus their first. Conversely, blood pressure and sympathetic baroreflex sensitivity did not differ, whereas a trend for increased heart rate was observed. Our results highlight a possible role of altered within-pregnancy sympathetic neural regulation in the relationship between increased parity and cardiovascular disease development.

scholarly journals Standardizing methodology for assessing spontaneous baroreflex control of muscle sympathetic nerve activity in humans

2020 ◽  
Author(s):  
Seth W. Holwerda ◽  
Jason R. Carter ◽  
Huan Yang ◽  
Jing Wang ◽  
Gary L. Pierce ◽  
...  
Keyword(s):  
Linear Regression ◽  
Sympathetic Nerve ◽  
Baroreflex Sensitivity ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Correlation Coefficients ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Regression Slopes ◽  
Linear Regressions

The use of spontaneous bursts of muscle sympathetic nerve activity (MSNA) to assess arterial baroreflex control of sympathetic nerve activity has seen increased utility in studies of both health and disease. However, methods used for analyzing spontaneous MSNA baroreflex sensitivity are highly variable across published studies. Therefore, we sought to comprehensively examine methods of producing linear regression slopes to quantify spontaneous MSNA baroreflex sensitivity in a large cohort of subjects (n=150) to support a standardized procedure for analysis that would allow for consistent and comparable results across laboratories. The primary results demonstrated that 1) consistency of linear regression slopes was considerably improved when the correlation coefficient was above -0.70, which is more stringent compared with commonly reported criterion of -0.50, 2) longer recording durations increased the percentage of linear regressions producing correlation coefficients above -0.70 (1-min:15%, 2-min:28%, 5-min:53%, 10-min:67%, P<0.001) and reaching statistical significance (1-min:40%, 2-min:69%, 5-min:78%, 10-min:89%, P<0.001), 3) correlation coefficients were improved with 3-mmHg diastolic BP bin size vs. 1- and 2-mmHg, and 4) linear regression slopes were reduced when the acquired blood pressure (BP) signal was not properly aligned with the cardiac cycle triggering the burst of MSNA. In summary, these results support the use of baseline recording durations of 10 min, a correlation coefficient above -0.70 for reliable linear regressions, 3-mmHg bin size, and importance of properly time aligning MSNA and diastolic BP. Together, these findings provide best practices for determining spontaneous MSNA baroreflex sensitivity under resting conditions for improved rigor and reproducibility of results.

Baroreflex control of muscle sympathetic nerve activity as a mechanism for persistent sympathoexcitation following acute hypoxia in humans

2011 ◽  
Vol 301 (6) ◽  
pp. R1779-R1785 ◽  
Author(s):  
Jordan S. Querido ◽  
Erica A. Wehrwein ◽  
Emma C. Hart ◽  
Nisha Charkoudian ◽  
William R. Henderson ◽  
...  
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Acute Hypoxia ◽  
Error Signal ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Stimulus Response ◽  
Baroreflex Function ◽  
Spontaneous Baroreflex

This study tested the hypothesis that acute isocapnic hypoxia results in persistent resetting of the baroreflex to higher levels of muscle sympathetic nerve activity (MSNA), which outlasts the hypoxic stimulus. Cardiorespiratory measures were recorded in humans (26 ± 1 yr; n = 14; 3 women) during baseline, exposure to 20 min of isocapnic hypoxia, and for 5 min following termination of hypoxia. The spontaneous baroreflex threshold technique was used to determine the change in baroreflex function during and following 20 min of isocapnic hypoxia (oxyhemoglobin saturation = 80%). From the spontaneous baroreflex analysis, the linear regression between diastolic blood pressure (DBP) and sympathetic burst occurrence, the T50 (DBP with a 50% likelihood of a burst occurring), and DBP error signal (DBP minus the T50) provide indexes of baroreflex function. MSNA and DBP increased in hypoxia and remained elevated during posthypoxia relative to baseline ( P < 0.05). The DBP error signal became progressively less negative (i.e., smaller difference between DBP and T50) in the hypoxia and posthypoxia periods (baseline: −3.9 ± 0.8 mmHg; hypoxia: −1.4 ± 0.6 mmHg; posthypoxia: 0.2 ± 0.6 mmHg; P < 0.05). Hypoxia caused no change in the slope of the baroreflex stimulus-response curve; however, there was a shift toward higher pressures that favored elevations in MSNA, which persisted posthypoxia. Our results indicate that there is a resetting of the baroreflex in hypoxia that outlasts the stimulus and provide further explanation for the complex control of MSNA following acute hypoxia.

scholarly journals Sympathetic baroreflex sensitivity is inversely related to vascular transduction in men but not women

2019 ◽  
Vol 317 (6) ◽  
pp. H1203-H1209 ◽  
Author(s):  
Sarah L. Hissen ◽  
Vaughan G. Macefield ◽  
Rachael Brown ◽  
Chloe E. Taylor
Keyword(s):  
Blood Pressure ◽  
Sympathetic Nerve ◽  
Inverse Relationship ◽  
Baroreflex Sensitivity ◽  
Sympathetic Nerve Activity ◽  
Diastolic Pressure ◽  
Muscle Sympathetic Nerve Activity ◽  
Nerve Activity ◽  
The Relationship ◽  
Compensatory Interactions

Sympathetic baroreflex sensitivity (BRS) is a measure of how effectively the baroreflex buffers beat-to-beat changes in blood pressure through the modulation of muscle sympathetic nerve activity (MSNA). However, current methods of assessment do not take into account the transduction of sympathetic nerve activity at the level of the vasculature, which is known to vary between individuals. In this study we tested the hypothesis that there is an inverse relationship between sympathetic BRS and vascular transduction. In 38 (18 men) healthy adults, continuous measurements of blood pressure, MSNA and superficial femoral artery diameter and blood flow (Doppler ultrasound) were recorded during 10 min of rest. Spontaneous sympathetic BRS was quantified as the relationship between diastolic pressure and MSNA burst incidence. Vascular transduction was quantified by plotting the changes in leg vascular conductance for 10 cardiac cycles following each burst of MSNA, and taking the nadir. In men, sympathetic BRS was inversely related to vascular transduction ( r = −0.49; P = 0.04). However, this relationship was not present in women ( r = −0.17; P = 0.47). To conclude, an interaction exists between sympathetic BRS and vascular transduction in healthy men, such that men with high sympathetic BRS have low vascular transduction and vice versa. This may be to ensure that blood pressure is regulated effectively, although further research is needed to explore what mechanisms are involved and examine why this relationship was not apparent in women. NEW & NOTEWORTHY Evidence suggests that compensatory interactions exist between factors involved in cardiovascular control. This study was the first to demonstrate an inverse relationship between sympathetic BRS and beat-to-beat vascular transduction. Those with low sympathetic BRS had high vascular transduction and vice versa. However, this interaction was present in young men but not women.

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