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

Mindful breathing as an effective technique in the management of hypertension

Introduction: Hypertension is one of the most important, modifiable risk factors for cardiovascular disease. The popularity of wearable devices provides an opportunity to test whether device guided slow mindful breathing may serve as a non-pharmacological treatment in the management of hypertension. Methods: Fitbit Versa-3 and Sense devices were used for this study. In addition, participants were required to own an FDA or Health Canada approved blood pressure measuring device. Advertisements were shown to 655,910 Fitbit users, of which 7,365 individuals expressed interest and filled out the initial survey. A total of 1,918 participants entered their blood pressure readings on at least 1 day and were considered enrolled in the study. Participants were instructed to download a guided mindful breathing app on their smartwatch device, and to engage with the app once a day prior to sleep. Participants measured their systolic and diastolic blood pressure prior to starting each mindful breathing session, and again after completion. All measurements were self reported. Participants were located in the United States or Canada. Results: Values of systolic and diastolic blood pressure were reduced following mindful breathing. There was also a decrease in resting systolic and diastolic measurements when measured over several days. For participants with a systolic pressure ≥ 130 mmHg, there was a decrease of 9.7 mmHg following 15 min of mindful breathing at 6 breaths per minute. When measured over several days, the resting systolic pressure decreased by an average of 4.3 mmHg. Discussion: Mindful breathing for 15 min a day, at a rate of 6 breaths per minute is effective in lowering blood pressure, and has both an immediate, and a short term effect (over several days). This large scale study demonstrates that device guided mindful breathing with a consumer wearable for 15 min a day is effective in lowering blood pressure, and a helpful complement to the standard of care.

Acute nasal breathing lowers diastolic blood pressure and increases parasympathetic contributions to heart rate variability in young adults

There is growing interest in how breathing pace, pattern, and training (e.g., device-guided or -resisted breathing) affect cardiovascular health. It is unknown whether the route of breathing (nasal vs. oral) affects prognostic cardiovascular variables. Because nasal breathing can improve other physiological variables (e.g., airway dilation), we hypothesized that nasal compared with oral breathing would acutely lower blood pressure (BP) and improve heart rate variability (HRV) metrics. We tested 20 adults in this study [13 females/7 males; age: 18(1) years, median (IQR); body mass index: 23 ± 2 kg·m-2, means ± SD]. We compared variables between nasal- and oral-only breathing (random order, five min each) using paired, two-tailed t tests or Wilcoxon signed-rank paired tests with significance set to P < 0.05. We report the median (interquartile range) for diastolic BP and means ± SD for all other variables. We found that nasal breathing was associated with a lower mean BP (nasal: 84 ± 7 vs. oral: 86 ± 5 mmHg, P = 0.006, Cohen's d = 0.70) and diastolic BP [nasal: 68(8) vs. oral: 72(5) mmHg, P < 0.001, Rank-biserial correlation = 0.89] but not systolic BP (nasal: 116 ± 11 vs. oral: 117 ± 9 mmHg, P = 0.48, Cohen's d = 0.16) or heart rate (HR; nasal: 74 ± 10 vs. oral: 75 ± 8 beats·min-1, P = 0.90, Cohen's d = 0.03). We also found that nasal breathing was associated with a higher high-frequency (HF) contribution to HRV (nasal: 59 ± 19 vs. oral: 52 ± 21%, P = 0.04, Cohen's d = 0.50) and a lower low frequency-to-HF ratio at rest (nasal: 0.9 ± 0.8 vs. oral: 1.2 ± 0.9, P = 0.04, Cohen's d = 0.49). These data suggest that nasal compared with oral breathing acutely 1) lowers mean and diastolic BP, 2) does not affect systolic BP or heart rate, and 3) increases parasympathetic contributions to HRV.NEW & NOTEWORTHY There is growing interest in how breathing pace, pattern, and training (e.g., device-guided or -resisted breathing) affect prognostic cardiovascular variables. However, the potential effects of the breathing route on prognostic cardiovascular variables are unclear. These data suggest that nasal compared with oral breathing 1) lowers mean and diastolic blood pressure (BP), 2) does not affect systolic BP or heart rate (HR), and 3) increases parasympathetic contributions to heart rate variability (HRV). These data suggest that acute nasal breathing improves several prognostic cardiovascular variables.

A hypotensive protocol of inspiratory muscle strength training: Systematic review and meta-analysis with trial sequential analysis

The aim of this study was to evaluate the hypotensive effect and optimal protocol of inspiratory muscle resistance training (IMST). Randomized controlled trials using IMST to lower blood pressure (BP) were retrieved from 12 databases as of July 2022. A meta-analysis of BP and heart rate variability (HRV) was performed and a trial sequence analysis was performed using trial sequential analysis (TSA) software. Twelve articles (n = 386 participants) from five countries were included, with a mean quality score of 5.83. IMST achieved significant results in reducing systolic, diastolic, and mean arterial pressure (-7.93 [-12.08, -3.78]; -3.80 [-6.08, -1.53]; -4.90 [-13.76, 3.96]). Furthermore, TSA has shown that the findings for systolic and diastolic BP are conclusive. Finally, considerable variation remained between studies when analyzing HRV. The overall hypotensive effect of IMST was demonstrated by the TSA and was well tolerated in different populations. Of these, two interventions, high resistance or low resistance combined with slow breathing, showed the best efficacy under an 8-week exercise intervention. In addition, the process of lowering BP by modulating sympathetic vagal activity has not been further confirmed in this study. Future long-term interventions, especially those over 3 months, are needed to observe the prolonged antihypertensive effects and modulatory mechanisms; controlling for variables such as respiratory rate and executing more rigorous studies to further explore antihypertensive options.

Monitoring of the regulatory ability and regulatory state of the autonomic nervous system and its application to the management of hypertensive patients: a study protocol for randomised controlled trials

INTRODUCTION

Many causes lead to sympathetic-vagus imbalance, which promotes the development of hypertension and accelerates the process of target organ damage. Many studies have shown that exercise training and heart rate variability (HRV) biofeedback can improve diseases caused by autonomic nerve dysfunction, such as hypertension. Based on these theories and the Yin-Yang balance theory of traditional Chinese medicine and Cannon's homeostasis theory, we have developed an assessment system of autonomic nerve regulation system and a harmony instrument. In this study, we aimed to find a new way to control blood pressure of hypertensive patients via cardiopulmonary resonance indices-based respiratory feedback training.

METHODS AND ANALYSIS

This is a prospective, randomised, parallel-controlled clinical trial, which aims to evaluate the effectiveness and safety of biofeedback therapy and exercise rehabilitation combined intervention in hypertension management. 176 healthy individuals will be recruited to get their autonomic nerve function parameters as normal control, while 352 hypertensive patients will be enrolled and randomly divided into a conventional treatment group and an experiment group in a ratio of 1:1. All patients will continue to receive standard hypertension blood pressure treatment, except that patients in the experiment group will have to complete additional daily respiratory training for 6 months. The primary outcome is the difference of clinical systolic blood pressure (SBP) between the two groups after 6 months of intervention. The secondary outcomes include the changes in the mean SBP and diastolic blood pressure (DBP) by 24-hour blood pressure monitoring, home SBP, clinical and home DBP, clinical and home heart rate, the standard-reaching rate of clinic and home SBP and the incidence of composite endpoint events at 6 months.

ETHICS AND DISSEMINATION

This study has been approved by the clinical research ethics committee of China-Japan Friendship Hospital (No. 2018-132 K98-2), the results of this study will be disseminated via peer-reviewed publications or conference presentations.

TRIAL REGISTRATION NUMBER

Chinese Clinical Trial Registry, ChiCTR1800019457, registered on 12 August 2018.

Device-guided slow breathing with direct biofeedback of pulse wave velocity - acute effects on pulse arrival time and self-measured blood pressure

BACKGROUND

There isevidence that device-guided slow breathing using biofeedback acutely reduces blood pressure (BP) and pulse wave velocity [i.e. increased pulse arrival time (PAT)].

OBJECTIVES

The objectives of the study presented here were to test whether the results of changes observed in PAT in earlier studies are reproducible over 1 week and how changes in pulse wave velocity/PAT translate into absolute self-measured BP changes.

METHODS

Patients with a systolic BP 130-160 mmHg or treated essential hypertension (21 females/23 males) were trained to perform unattended device-guided slow breathing exercises for 10 min daily over 5 days. Furthermore, they were skilled to perform self-measurement of BP before and after the breathing exercise using a validated upper-arm device.

RESULTS

Office BP at screening [median (1, 3. Q)] was 137 (132, 142)/83 (79, 87) mmHg. We observed a significant ( P  < 0.05) increase in PAT of 5 ms (SD 12.5 ms) on average after 10 min of guided breathing and an additional 1 ms ( P  < 0.05, SD 8 ms) during the following 5 min of spontaneous breathing compared to baseline. PAT before the exercise remained constant over 5 days paralleled by constant self-measured BP before the exercise. Device-guided breathing was associated with a significant reduction of self-measured SBP of 5 mmHg ( P  < 0.01, SD 8 mmHg). Data furthermore demonstrated that these changes were highly reproducible over 1 week.

CONCLUSIONS

Device-guided slow breathing and biofeedback lead to reproducible and favorable changes (increase) in PAT and SBP (decrease).

Exploring mechanisms of blood pressure regulation in response to device-guided and non-device-guided slow breathing: A mini review

BACKGROUND

Hypertension is a widespread disease that, if persistent, increases the risks of coronary heart disease mortality and morbidity. Slow breathing is a recommended blood pressure-lowering strategy though the mechanisms mediating its effects are unknown.

OBJECTIVE

This review aims to evaluate autonomic and vascular function as potential mediators driving BP adaptive responses with slow breathing.

METHODS

We searched EBSCO host, Web of Science, Cochrane Central Register of Controlled Trials, and PubMed using key words for optimized search results.

RESULTS

Nineteen studies were included in this review (11 device-guided; 8 non-device-guided breathing). Though some studies showed increased vagally mediated components of heart rate variability during slow breathing, results from acute and long-term studies were incongruent. Increases in baroreflex sensitivity (BRS) following a single device-guided slow breathing bout were noted in normotensive and hypertensive adults. Long-term (4 weeks to 3 months) effects of slow breathing on BRS were absent. Device-guided breathing resulted in immediate reductions in muscle sympathetic nerve activity (MSNA) in normo- and hyper-tensive adults though results from long-term studies yielded inconsistent findings. Non-device-guided slow breathing posed acute and chronic effects on vascular function with reductions in arterial stiffness in adults with type I diabetes and increases in microvascular endothelial function in adults with irritable bowel syndrome. Non-device guided breathing also reduced pro-inflammatory cytokines in healthy and hypertensive adults in acute and chronic studies. No adverse effects or non-adherence to treatment were noted in these trials.

CONCLUSION

Device-guided slow breathing is a feasible and effective modality in improving BRS, HRV, and arterial stiffness though its long-term effects are obscure. Though less evidence exists supporting the efficacy of non-device-guided slow breathing, acute and chronic studies demonstrate improvements in vascular function and inflammatory cytokines. More studies are needed to further explore the long-term effects of slow breathing in general and non-device-guided breathing in particular.

Device-guided slow breathing alters postprandial oxidative stress in young adult males: A randomized sham-controlled crossover trial

BACKGROUND AND AIMS

Slow, deep breathing (SDB) lowers blood pressure (BP) though the underlying mechanisms are unknown. Redox improvements could facilitate hemodynamic adjustments with SDB though this has not been investigated. The purpose of this randomized, sham-controlled trial was to examine the acute effects of SDB on oxidative stress and endothelial function during a physiological perturbation (high-fat meal) known to induce oxidative stress.

METHODS AND RESULTS

Seventeen males (ages 18-35 years) were enrolled, and anthropometric measurements and 7-day physical activity monitoring were completed. Testing sessions consisted of 24-h diet recalls (ASA24), blood sample collection for superoxide dismutase (SOD) and thiobarbituric acid reactive substances (TBARS) analysis, and flow-mediated dilation (FMD). High-fat meals were ingested and 2-min breathing exercises (SDB or sham control breathing) were completed every 15 min during the 4-h postprandial phase. Blood sample collection and FMD were repeated 1-, 2-, and 4-h post meal consumption. Mean body mass index and step counts were 25.6 ± 4.3 kg/m2 and 8165 ± 4405 steps per day, respectively. Systolic and diastolic BP and nutrient intake 24 h prior were similar between conditions. No time or time by condition interaction effects were observed for FMD. The total area under the curve (AUC) for SOD was significantly lower during SDB compared to the sham breathing condition (p < 0.01). No differences were observed in TBARS AUC (p = 0.538).

CONCLUSIONS

Findings from the current investigation suggest that SDB alters postprandial redox in the absence of changes in endothelial function in young, healthy males.

CLINICAL TRIAL REGISTRATION NUMBER

NCT04864184.

CLINICAL TRIALS IDENTIFIER

NCT04864184.

The effects of slow deep breathing on microvascular and autonomic function and symptoms in adults with irritable bowel syndrome: A pilot study

BACKGROUND

Irritable bowel syndrome (IBS) is linked to disruptions in sympathovagal balance, which could impair vascular homeostasis and cause IBS symptoms. Studies have shown reductions in sympathetic activity following a single slow, deep breathing (SDB) bout in healthy adults; however, no studies have investigated its chronic effects in IBS. The purpose of this study was to evaluate the feasibility and impact of a SDB intervention on microvascular and autonomic function and symptoms in adults with IBS.

METHODS

Fourteen participants (ages 18-65 years) with IBS were randomly assigned to 4-week SDB or control conditions. The SDB group completed a 20-min video 5 times weekly while the control group maintained their normal activities. Microvascular endothelial function was measured using laser Doppler in response to thermal provocation and expressed as cutaneous vascular conductance at 39°C relative to a maximum response at 43.5°C (%CVC_max ). Heart rate variability (HRV) and post-exercise heart rate recovery (HRR) were employed as surrogate measures of autonomic function. IBS symptoms were assessed using the IBS-Severity Scale (IBS-SS).

KEY RESULTS

Thirteen participants (6 controls and 7 SDB) completed the study. Age (p = 0.541) and body mass index (p = 0.157) were similar between groups. In the SDB group, %CVC_max increased from 45% to 59% (p < 0.00001) after the 4-week intervention. HRV, HRR, and IBS-SS scores were unaltered.

CONCLUSIONS

and Inferences. These results demonstrate the feasibility of a SDB intervention in adults with IBS and suggest improvements in microvascular function in the absence of changes in symptoms or autonomic function in this population.

The Feasibility of Baroreflex Sensitivity Measurements in Heart Failure Subjects: The Role of Slow-patterned Breathing

INTRODUCTION

Increased muscle sympathetic nerve activity (MSNA) indicates an adverse outcome in heart failure. Decreased baroreflex modulation of MSNA is well known feature of the disease. The determinability of cardiovagal baroreflex sensitivity (BRS) in heart failure is low, however, the determinability of sympathetic BRS is not known.

METHODS

We have assessed the spontaneous, MSNA burst incidence-based baroreflex index (BRSsymp) in 33 stable heart failure patients and in 10 healthy controls using the traditional r≥0.5 cut-off for acceptable individual diastolic pressure-burst incidence slopes, and also a more stringent r≥0.7 cut-off. We have also assessed the influence of 6/min breathing.

RESULTS

The determinability of BRSsymp in heart failure patients was 64% during spontaneous breathing with r≥0.5 cut-off, and 39% using the r≥0.7 cut-off. The determinability of these indices further decreased during 6/min breathing, dropping to 29% with the r≥0.7 cut-off. In contrast, the determinability of the cardiovagal BRS indices increased significantly with 6/min breathing (from 24% to 66%; p<0.001). Patients who still had determinable BRSsymp at the r≥0.7 cut-off had a significantly lower baseline burst incidence than those with an undeterminable index (70±14 vs.89±10 burst/100 cycles; p<0.002). Neither the 6/min breathing, nor the r≥0.7 cut-off limit influenced the high availability of BRSsymp in healthy subjects.

CONCLUSION

The determinability of BRSsymp in heart failure patients is limited, especially with the 0.7 limit for correlation. Undeterminable BRSsymp in patients is associated with higher sympathetic activity. 6/min breathing improves the determinability of cardiovagal BRS indices, but not that of BRSsymp. This article is protected by copyright. All rights reserved.

Sex differences in sympathetic neuro-vascular and neuro-hemodynamic relationships during the cold pressor test

Muscle sympathetic nerve activity (MSNA) affects vascular resistance differently in women and men. However, whether this sex difference persists during pronounced increases in MSNA remains unclear. Therefore, the purpose of this study was to examine sex differences in neurovascular transduction during cold pressor test (CPT)-mediated sympatho-excitation. Integrated peroneal MSNA (microneurography) was measured at rest and during a 3-minute CPT in young healthy women (n=11) and men (n=10). Mean arterial pressure (MAP) was measured beat-by-beat (Finometer) and superficial femoral artery blood flow was measured using duplex ultrasound. Femoral vascular resistance (FVR) was quantified as MAP/femoral blood flow (mmHg/mL/min). Baseline MSNA was similar between women and men (14±9 vs 15±9 bursts/100hb, respectively; P=0.83), whereas MAP was lower (86±7 vs 92±4 mmHg; P=0.047), and FVR was greater in women than men (0.54±0.16 vs 0.36±0.15 mmHg/mL/min; P=0.02). CPT-induced increases in MSNA were similar between the sexes (+19±11 vs +26±14 bursts/100hb; P=0.26) while increases in MAP (+7±3 vs +10±3mmHg; P=0.03) and FVR (+3.2±18.6 vs +26.8±12.8%; P<0.01) were smaller in women than men. Within men, CPT- induced increases in MSNA predicted increases in MAP (R²=0.51, P=0.02) and FVR (R²=0.49, P=0.02). However, MSNA did not predict MAP (R²=0.11, P=0.35) or FVR (R²=0.07, P=0.46) in women. Our findings demonstrate that men experience robust CPT-induced MAP responses that are driven by both neuro-vascular (MSNA-FVR) and neuro-hemodynamic (MSNA-MAP) coupling. These relationships were not observed in women, indicating that even during pronounced increases in sympathetic outflow, MSNA is not predictive of vascular nor blood pressure outcomes in young healthy women.

Sympathetic Neural Control in Humans with Anxiety-Related Disorders

Numerous conceptual models are used to describe the dynamic responsiveness of physiological systems to environmental pressures, originating with Claude Bernard's milieu intérieur and extending to more recent models such as allostasis. The impact of stress and anxiety upon these regulatory processes has both basic science and clinical relevance, extending from the pioneering work of Hans Selye who advanced the concept that stress can significantly impact physiological health and function. Of particular interest within the current article, anxiety is independently associated with cardiovascular risk, yet mechanisms underlying these associations remain equivocal. This link between anxiety and cardiovascular risk is relevant given the high prevalence of anxiety in the general population, as well as its early age of onset. Chronically anxious populations, such as those with anxiety disorders (i.e., generalized anxiety disorder, panic disorder, specific phobias, etc.) offer a human model that interrogates the deleterious effects that chronic stress and allostatic load can have on the nervous system and cardiovascular function. Further, while many of these disorders do not appear to exhibit baseline alterations in sympathetic neural activity, reactivity to mental stress offers insights into applicable, real-world scenarios in which heightened sympathetic reactivity may predispose those individuals to elevated cardiovascular risk. This article also assesses behavioral and lifestyle modifications that have been shown to concurrently improve anxiety symptoms, as well as sympathetic control. Lastly, future directions of research will be discussed, with a focus on better integration of psychological factors within physiological studies examining anxiety and neural cardiovascular health. © 2022 American Physiological Society. Compr Physiol 12:1-33, 2022.

Transcutaneous Auricular Vagus Nerve Stimulation Combined With Slow Breathing: Speculations on Potential Applications and Technical Considerations

OBJECTIVES

Transcutaneous auricular vagus nerve stimulation (taVNS) is a relatively novel noninvasive neurostimulation method that is believed to mimic the effects of invasive cervical VNS. It has recently been suggested that the effectiveness of taVNS can be enhanced by combining it with controlled slow breathing. Slow breathing modulates the activity of the vagus nerve and is used in behavioral medicine to decrease psychophysiological arousal. Based on studies that examine the effects of taVNS and slow breathing separately, this article speculates on some of the conditions in which this combination treatment may prove effective. Furthermore, based on findings from studies on the optimization of taVNS and slow breathing, this article provides guidance on how to combine taVNS with slow breathing.

MATERIALS AND METHODS

A nonsystematic review.

RESULTS

Both taVNS and slow breathing are considered promising add-on therapeutic approaches for anxiety and depressive disorders, chronic pain, cardiovascular diseases, and insomnia. Therefore, taVNS combined with slow breathing may produce additive or even synergistic beneficial effects in these conditions. Studies on respiratory-gated taVNS during spontaneous breathing suggest that taVNS should be delivered during expiration. Therefore, this article proposes to use taVNS as a breathing pacer to indicate when and for how long to exhale during slow breathing exercises.

CONCLUSIONS

Combining taVNS with slow breathing seems to be a promising hybrid neurostimulation and behavioral intervention.

Inspiratory muscle training improves breathing pattern and sympatho-vagal balance but not spontaneous baroreflex sensitivity in older women

Even though recent studies reported a positive inspiratory muscle training (IMT) effect on cardiovascular autonomic modulation, its underlying mechanisms as the breathing pattern remain unclear. The study aimed to investigate the IMT effects on resting heart rate variability (HRV), spontaneous baroreflex sensitivity (BRS), and spontaneous breathing pattern in older women. Fourteen healthy older women participated in this study, allocated in IMT (50 % MIP; n = 8) or Sham (5% MIP; n = 6) protocols for four weeks. Blood pressure, heart rate, and ventilatory data were continuously recorded before and after interventions. After four weeks, IMT-group increased maximal inspiratory pressure and vagal-mediated HRV, following by the reduction of sympatho-mediated HRV and the inspiratory time during the spontaneous breathing cycle compared to Sham-group, but did not change BRS. Therefore, the shorter inspiratory time suggests a putative mechanism behind improved vagal-mediated HRV post-IMT in older women.

Non-invasive quantification of the effect of device-guided slow breathing with direct feedback to the patient to reduce blood pressure

OBJECTIVE

Slow breathing is a relaxation exercise recommended for lowering blood pressure (BP). Biofeedback may improve patient adherence and enhance BP lowering effects. Since the pulse arrival time (PAT) is inversely proportional to BP, it can be used to estimate BP changes.

APPROACH

In this pilot study, 30 patients (age 62.9 (SD 7.7) years, 11 F/19 M, Sys. BP 133.0 (SD 17.1) mmHg, Dia. BP 83.8 (SD 10.6) mmHg) performed a device-guided slow breathing exercise. PAT was measured by ECG and plethysmography and immediately presented to the patient, and respiratory sinus arrhythmia (RSA) was calculated retrospectively to measure the adherence to the instructed respiratory rate.

MAIN RESULTS

Respiratory rate was 13.6 (SD 1.9) bpm at baseline and 5.4 (SD 1.0) bpm during guided breathing. PAT continuously and progressively increased from 231.5 (SD 20.3) to 237.3 (SD 18.5) ms (p [Formula: see text] 0.001). The median deviation of RSA from the guided respiratory rate was 0.06 (IQR 0.19) bpm. In three patients, a deviation of > 0.20 bpm was detected, and two of them showed no increase in PAT. In total, 25 patients responded with increase in PAT.

SIGNIFICANCE

In this pilot study we have shown that biofeedback of PAT and RSA are feasible and can further improve motivation and adherence. Furthermore, we have shown that the exercise increased PAT, which indicates a reduction in BP. Due to its ease of use, this method is ideal for home use and self-monitoring.

The acute effects of vinyasa flow yoga on vascular function, lipid and glucose concentrations, and mood

While the chronic effects of certain styles of yoga on cardiometabolic factors have been investigated, little is known about the acute effects of a single yoga session on these outcomes. Moreover, vinyasa yoga's potential to modulate cardiometabolic outcomes has not been established. The purpose of this study is to determine the acute effects of a vinyasa yoga session on arterial stiffness, wave reflection, lipid and glucose concentrations, and mood in adults with prior yoga experience. Thirty yoga practitioners with a minimum of 3 months of practice experience were enrolled into the study. Carotid-femoral pulse wave velocity (cf-PWV), augmentation index (AIx), lipid profile, glucose concentrations, and mood (Positive and Negative Affect Scale) were assessed at baseline and immediately following a 1 -h vinyasa yoga session. After the yoga session, participants had significantly lower AIx (p < 0.001), non-HDL cholesterol (p < 0.05), and negative affect (p < 0.01) compared to baseline. These results highlight the efficacy of a single bout of yoga in altering wave reflection while improving mood and lipid concentrations in healthy adults with a history of yoga practice.

Sex differences in dynamic blood pressure regulation: beat-by-beat responses to muscle sympathetic nerve activity

It has been suggested that sex differences in acute blood pressure fluctuations occur during the periods of time between bursts of muscle sympathetic nerve activity. Therefore, we tested the hypothesis that men experience more dynamic changes in mean arterial pressure (Finometer MIDI) than women during acute sympathoinhibition (i.e., slow breathing) in which bursts of sympathetic activity occur more infrequently than at rest. We tested healthy women (n = 9) and men (n = 9) of similar age (22 ± 2 vs. 23 ± 3 yr, P = 0.6). Custom software was used to calculate beat-by-beat changes in blood pressure following sympathetic burst and nonburst sequences (recorded using microneurography) during 10 min of supine rest and a 15-min bout of slow breathing. During slow breathing following nonburst sequences, women demonstrated smaller overall reductions in mean arterial pressure compared with men over the subsequent 15 cardiac cycles (P < 0.01). In addition, following a burst of sympathetic activity, women experienced greater overall increases in mean arterial pressure compared with men over the following 15 cardiac cycles (P < 0.01). Despite these differences, the peak and nadir changes in arterial pressure following burst and nonburst sequences were not different between the sexes (P = 0.45 and P = 0.48, burst and nonburst sequences, respectively). As such, these data suggest that women respond to a burst of sympathetic activity with more sustained increases in blood pressure than men, coupled with improved maintenance of blood pressure during acute periods of sympathetic quiescence. In other words, these findings suggest that men rely more on frequent bursts of sympathetic activity to acutely regulate arterial pressure than women.NEW & NOTEWORTHY We demonstrate that during acute sympathoinhibition, women demonstrate more sustained increases in blood pressure following sympathetic bursts of activity than men. Likewise, during prolonged sympathetic quiescence, blood pressure is less labile in women than men. This suggests that lower overall blood pressure in young women may not be mediated by smaller beat-by-beat changes in blood pressure in response to sympathetic outflow but may instead be mediated by a lower frequency of sympathetic bursts.