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Stute NL, Szeghy RE, Stickford JL, Province VP, Augenreich MA, Ratchford SM, Stickford ASL. Longitudinal observations of sympathetic neural activity and hemodynamics during 6 months recovery from SARS-CoV-2 infection. Physiol Rep 2022; 10:e15423. [PMID: 36151607 PMCID: PMC9508384 DOI: 10.14814/phy2.15423] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2022] [Revised: 07/14/2022] [Accepted: 07/23/2022] [Indexed: 06/16/2023] Open
Abstract
Cross-sectional data indicate that acute SARS-CoV-2 infection increases resting muscle sympathetic nerve activity (MSNA) and alters hemodynamic responses to orthostasis in young adults. However, the longitudinal impact of contracting SARS-CoV-2 on autonomic function remains unclear. The aim of this study was to longitudinally track MSNA, sympathetic transduction to blood pressure (BP), and hemodynamics over 6 months following SARS-CoV-2 infection. Young adults positive with SARS-CoV-2 reported to the laboratory three times over 6 months (V1:41 ± 17, V2:108 ± 21, V3:173 ± 16 days post-infection). MSNA, systolic (SBP) and diastolic (DBP) blood pressure, and heart rate (HR) were measured at rest, during a cold pressor test (CPT), and at 30° head-up tilt (HUT). Basal SBP (p = 0.019) and DBP (p < 0.001) decreased throughout the 6 months, whereas basal MSNA and HR were not different. Basal sympathetic transduction to BP and estimates of baroreflex sensitivity did not change over time. SBP and DBP were lower during CPT (SBP: p = 0.016, DBP: p = 0.007) and HUT at V3 compared with V1 (SBP: p = 0.041, DBP: p = 0.017), with largely no changes in MSNA. There was a trend toward a visit-by-time interaction for burst incidence (p = 0.055) during HUT, wherein at baseline immediately prior to tilting, burst incidence was lower at V3 compared with V1 (p = 0.014), but there were no differences between visits in the 30 HUT position. These results support impairments to cardiovascular health, and potentially autonomic function, which may improve over time. However, the improvements in BP over 6 months recovery from mild SARS-CoV-2 infection are likely not a direct result of changes in sympathetic activity.
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Affiliation(s)
- Nina L. Stute
- Department of Health and Exercise ScienceAppalachian State UniversityBooneNorth CarolinaUSA
| | - Rachel E. Szeghy
- Department of Health and Exercise ScienceAppalachian State UniversityBooneNorth CarolinaUSA
| | - Jonathon L. Stickford
- Department of Health and Exercise ScienceAppalachian State UniversityBooneNorth CarolinaUSA
| | - Valesha P. Province
- Department of Health and Exercise ScienceAppalachian State UniversityBooneNorth CarolinaUSA
| | - Marc A. Augenreich
- Department of Health and Exercise ScienceAppalachian State UniversityBooneNorth CarolinaUSA
| | - Stephen M. Ratchford
- Department of Health and Exercise ScienceAppalachian State UniversityBooneNorth CarolinaUSA
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2
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Nolde JM, Marisol Lugo‐Gavidia L, Carnagarin R, Azzam O, Galindo Kiuchi M, Mian A, Schlaich MP. Machine learning powered tools for automated analysis of muscle sympathetic nerve activity recordings. Physiol Rep 2021; 9:e14996. [PMID: 34427381 PMCID: PMC8383713 DOI: 10.14814/phy2.14996] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Revised: 07/07/2021] [Accepted: 07/10/2021] [Indexed: 01/04/2023] Open
Abstract
Automated analysis and quantification of physiological signals in clinical practice and medical research can reduce manual labor, increase efficiency, and provide more objective, reproducible results. To build a novel platform for the analysis of muscle sympathetic nerve activity (MSNA), we employed state-of-the-art data processing and machine learning applications. Data processing methods for integrated MSNA recordings were developed to evaluate signals regarding the overall quality of the signal, the validity of individual signal peaks regarding the potential to be MSNA bursts and the timing of their occurrence. An overall probability score was derived from this flexible platform to evaluate each individual signal peak automatically. Overall, three deep neural networks were designed and trained to validate individual signal peaks randomly sampled from recordings representing only electrical noise and valid microneurography recordings. A novel data processing method for the whole signal was developed to differentiate between periods of valid MSNA signal recordings and periods in which the signal was not available or lost due to involuntary movement of the recording electrode. A probabilistic model for timing of the signal bursts was implemented as part of the system. Machine Learning algorithms and data processing tools were implemented to replicate the complex decision-making process of manual MSNA analysis. Validation of manual MSNA analysis including intra- and inter-rater validity and a comparison with automated MSNA tools is required. The developed toolbox for automated MSNA analysis can be extended in a flexible way to include algorithms based on other datasets.
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Affiliation(s)
- Janis M. Nolde
- Dobney Hypertension CentreSchool of Medicine ‐ Royal Perth Hospital Research FoundationFaculty of MedicineDentistry & Health SciencesThe University of Western AustraliaPerthAustralia
| | - Leslie Marisol Lugo‐Gavidia
- Dobney Hypertension CentreSchool of Medicine ‐ Royal Perth Hospital Research FoundationFaculty of MedicineDentistry & Health SciencesThe University of Western AustraliaPerthAustralia
| | - Revathy Carnagarin
- Dobney Hypertension CentreSchool of Medicine ‐ Royal Perth Hospital Research FoundationFaculty of MedicineDentistry & Health SciencesThe University of Western AustraliaPerthAustralia
| | - Omar Azzam
- Dobney Hypertension CentreSchool of Medicine ‐ Royal Perth Hospital Research FoundationFaculty of MedicineDentistry & Health SciencesThe University of Western AustraliaPerthAustralia
| | - Márcio Galindo Kiuchi
- Dobney Hypertension CentreSchool of Medicine ‐ Royal Perth Hospital Research FoundationFaculty of MedicineDentistry & Health SciencesThe University of Western AustraliaPerthAustralia
| | - Ajmal Mian
- School of Computer Science and Software EngineeringThe University of Western AustraliaPerthAustralia
| | - Markus P. Schlaich
- Dobney Hypertension CentreSchool of Medicine ‐ Royal Perth Hospital Research FoundationFaculty of MedicineDentistry & Health SciencesThe University of Western AustraliaPerthAustralia
- Departments of Cardiology and NephrologyRoyal Perth HospitalPerthAustralia
- Neurovascular Hypertension & Kidney Disease LaboratoryBaker Heart and Diabetes InstituteMelbourneAustralia
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Holwerda SW, Carter JR, Yang H, Wang J, Pierce GL, Fadel PJ. CORP: Standardizing methodology for assessing spontaneous baroreflex control of muscle sympathetic nerve activity in humans. Am J Physiol Heart Circ Physiol 2021; 320:H762-H771. [PMID: 33275522 PMCID: PMC8082800 DOI: 10.1152/ajpheart.00704.2020] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/26/2020] [Revised: 11/24/2020] [Accepted: 11/24/2020] [Indexed: 12/28/2022]
Abstract
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 versus 1-mmHg and 2-mmHg diastolic blood pressure (BP) bin size, and 4) linear regression slopes were reduced when the acquired 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.
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Affiliation(s)
- Seth W Holwerda
- Department of Anesthesiology, University of Kansas Medical Center, Kansas City, Kansas
| | - Jason R Carter
- Department of Health and Human Development, Montana State University, Bozeman, Montana
| | - Huan Yang
- Department of Neurology, Beth Israel Deaconess Medical Center/Harvard Medical School, Boston, Massachusetts
| | - Jing Wang
- College of Nursing, University of Texas at Arlington, Arlington, Texas
| | - Gary L Pierce
- Department of Health and Human Physiology, University of Iowa, Iowa City, Iowa
| | - Paul J Fadel
- Department of Kinesiology, University of Texas at Arlington, Arlington, Texas
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El Sayed K, Macefield VG, Hissen SL, Joyner MJ, Taylor CE. Blood pressure reactivity at onset of mental stress determines sympathetic vascular response in young adults. Physiol Rep 2018; 6:e13944. [PMID: 30552755 PMCID: PMC6294720 DOI: 10.14814/phy2.13944] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Accepted: 11/22/2018] [Indexed: 11/24/2022] Open
Abstract
We have previously shown in young males that the rate of rise in blood pressure (BP) at the onset of mental stress determines whether or not muscle sympathetic nerve activity (MSNA) has a role in driving the pressor response. The aim of this study was to investigate these interactions in young females. BP and MSNA were recorded continuously in 19 females and 21 males during 2-min mental stressors (mental arithmetic and Stroop test). Physical stressor tasks (cold pressor, handgrip exercise, postexercise ischemia) were also performed. During the first minute of mental arithmetic, the rate of rise in mean arterial pressure (MAP) was significantly greater in negative responders (mean decrease in MSNA) compared with positive responders (mean increase in MSNA) in both males (1.9 ± 0.7 vs. 0.7 ± 0.3 mmHg/sec) and females (1.0 ± 0.3 vs. 0.5 ± 0.2 mmHg/sec). For the Stroop test, there was no significant difference in the rate of the rise in BP between positive and negative responders (P > 0.05). However, peak changes in MAP were significantly greater in negative responders compared with positive responders in both males (22 ± 6 vs. 13 ± 3 mmHg) and females (12 ± 2 vs. 6 ± 1 mmHg). Sympathetic baroreflex sensitivity was greater in negative responders and may contribute to the fall in MSNA experienced by these individuals during mental stress. During physical stressors there were consistent increases in BP and MSNA in males and females. The findings suggest that, in both males and females, BP reactivity at the onset of mental stress dictates whether or not there is an increase or decrease in MSNA.
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Affiliation(s)
- Khadigeh El Sayed
- School of MedicineWestern Sydney UniversitySydneyNew South WalesAustralia
| | - Vaughan G. Macefield
- School of MedicineWestern Sydney UniversitySydneyNew South WalesAustralia
- Neuroscience Research AustraliaSydneyNew South WalesAustralia
- Baker Heart and Diabetes InstituteMelbourneVictoriaAustralia
| | - Sarah L Hissen
- School of Science and HealthWestern Sydney UniversitySydneyNew South WalesAustralia
| | | | - Chloe E. Taylor
- School of MedicineWestern Sydney UniversitySydneyNew South WalesAustralia
- School of Science and HealthWestern Sydney UniversitySydneyNew South WalesAustralia
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5
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Hissen SL, Sayed KE, Macefield VG, Brown R, Taylor CE. The Stability and Repeatability of Spontaneous Sympathetic Baroreflex Sensitivity in Healthy Young Individuals. Front Neurosci 2018; 12:403. [PMID: 29962929 PMCID: PMC6010576 DOI: 10.3389/fnins.2018.00403] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2018] [Accepted: 05/25/2018] [Indexed: 01/18/2023] Open
Abstract
Spontaneous sympathetic baroreflex sensitivity (BRS) is a valuable tool for assessing how well the baroreflex buffers beat-to-beat changes in blood pressure. However, there has yet to be a study involving appropriate statistical tests to examine the stability of sympathetic BRS within an experimental session and the repeatability between separate sessions. The aim of this study was to use intra-class correlations, ordinary least products regression, and Bland–Altman analyses to examine the stability and repeatability of spontaneous sympathetic BRS assessment. In addition, the influence of recording duration on values of BRS was assessed. In eighty-four healthy young individuals (49 males, 35 females), continuous measurements of blood pressure, heart rate and muscle sympathetic nerve activity (MSNA) were recorded for 10 min. In a subgroup of 13 participants (11 male, 2 female) the measurements were repeated on a separate day. Sympathetic BRS was quantified using MSNA burst incidence (BRSinc) and total MSNA (BRStotal) for the first 5-min period, the second 5-min period, and a 2-min segment taken from the second 5-min period. Intra-class correlation coefficients indicated moderate stability in sympathetic BRSinc and BRStotal between the first and second 5-min periods in males (BRSincr = 0.63, BRStotalr = 0.78) and females (BRSincr = 0.61, BRStotalr = 0.47) with no proportional bias, but with fixed bias for BRSinc in females. When comparing the first 5-min with the 2-min period (n = 76), the intra-class correlation coefficient indicated poor to moderate repeatability in sympathetic BRSinc and BRStotal for males (BRSincr = -0.01, BRStotalr = 0.70) and females (BRSincr = 0.46, BRStotalr = 0.39). However, Bland–Altman analysis revealed a fixed bias for BRStotal in males and proportional bias for BRStotal in females, with lower BRS values for 5-min recordings. In the subgroup, intra-class correlations indicated moderate repeatability for measures of BRSinc (9 male, 2 female, r = 0.63) and BRStotal (6 male, 2 female, r = 0.68) assessed using 5-min periods recorded on separate days. However, Bland–Altman analysis indicated proportional bias for BRSinc and fixed bias for BRStotal. In conclusion, measures of spontaneous sympathetic BRS are moderately stable and repeatable within and between testing sessions in healthy young adults, provided that the same length of recording is used when making comparisons.
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Affiliation(s)
- Sarah L Hissen
- School of Science and Health, Western Sydney University, Sydney, NSW, Australia
| | - Khadigeh El Sayed
- School of Medicine, Western Sydney University, Sydney, NSW, Australia
| | - Vaughan G Macefield
- School of Medicine, Western Sydney University, Sydney, NSW, Australia.,Baker Heart and Diabetes Institute, Melbourne, VIC, Australia.,Neuroscience Research Australia, Sydney, NSW, Australia
| | - Rachael Brown
- School of Medicine, Western Sydney University, Sydney, NSW, Australia
| | - Chloe E Taylor
- School of Science and Health, Western Sydney University, Sydney, NSW, Australia.,School of Medicine, Western Sydney University, Sydney, NSW, Australia
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Chen DLT, Brown R, Liess C, Poljak A, Xu A, Zhang J, Trenell M, Jenkins A, Chisholm D, Samocha-Bonet D, Macefield VG, Greenfield JR. Muscle Sympathetic Nerve Activity Is Associated with Liver Insulin Sensitivity in Obese Non-Diabetic Men. Front Physiol 2017; 8:101. [PMID: 28293196 PMCID: PMC5328983 DOI: 10.3389/fphys.2017.00101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2016] [Accepted: 02/07/2017] [Indexed: 12/14/2022] Open
Abstract
Introduction: Muscle sympathetic nerve activity (MSNA) may play a role in insulin resistance in obesity. However, the direction and nature of the relationship between MSNA and insulin resistance in obesity remain unclear. We hypothesized that resting MSNA would correlate inversely with both muscle and liver insulin sensitivity and that it would be higher in insulin-resistant vs. insulin-sensitive subjects. Materials and methods: Forty-five non-diabetic obese subjects were studied. As no significant relationships were found in women, the data presented in on 22 men aged 48 ± 12 years. Two-step (15 and 80 mU/m2/min) hyperinsulinaemic-euglycaemic clamps were performed using deuterated glucose to determine liver and muscle insulin sensitivity. Clinical and metabolic parameters were assessed. MSNA was measured via a microelectrode inserted percutaneously into the common peroneal nerve. Results: MSNA burst frequency correlated inversely with liver insulin sensitivity (r = -0.53, P = 0.02) and positively with the hepatokines C-reactive protein (CRP) and fibroblast growth factor (FGF)-19 (r = 0.57, P = 0.006, and r = -0.47, P = 0.03, respectively). MSNA burst frequency was lower in Liversen compared to Liverres (27 ± 5 vs. 38 ± 2 bursts per minute; P = 0.03). Muscle insulin sensitivity was unrelated to MSNA. Discussion: Sympathetic neural activation is related to liver insulin sensitivity and circulating hepatokines CRP and FGF-19 in non-diabetic obese men. These results suggest a potential hepato-endocrine-autonomic axis. Future studies are needed to clarify the influence of MSNA on liver insulin sensitivity in men.
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Affiliation(s)
- Daniel L. T. Chen
- Diabetes and Metabolism Division, Garvan Institute of Medical ResearchSydney, NSW, Australia
| | - Rachael Brown
- School of Medicine, University of Western SydneySydney, NSW, Australia
- Neuroscience Research AustraliaSydney, NSW, Australia
| | - Carsten Liess
- Philips HealthcareLuebeckertordamm, Hamburg, Germany
| | - Anne Poljak
- Bioanalytical Mass Spectrometry Facility, UNSW SydneySydney, NSW, Australia
- School of Medical Sciences, UNSW SydneySydney, NSW, Australia
| | - Aimin Xu
- State Key Laboratory of Pharmaceutical Biotechnology, University of Hong KongHong Kong, Hong Kong
| | - Jialiang Zhang
- State Key Laboratory of Pharmaceutical Biotechnology, University of Hong KongHong Kong, Hong Kong
| | | | - Arthur Jenkins
- Diabetes and Metabolism Division, Garvan Institute of Medical ResearchSydney, NSW, Australia
- School of Health Science, University of WollongongWollongong, NSW, Australia
| | - Donald Chisholm
- Diabetes and Metabolism Division, Garvan Institute of Medical ResearchSydney, NSW, Australia
| | - Dorit Samocha-Bonet
- Diabetes and Metabolism Division, Garvan Institute of Medical ResearchSydney, NSW, Australia
- School of Medical Sciences, UNSW SydneySydney, NSW, Australia
| | - Vaughan G. Macefield
- School of Medicine, University of Western SydneySydney, NSW, Australia
- Neuroscience Research AustraliaSydney, NSW, Australia
| | - Jerry R. Greenfield
- Diabetes and Metabolism Division, Garvan Institute of Medical ResearchSydney, NSW, Australia
- Department of Endocrinology and Diabetes Center, St. Vincent's HospitalSydney, NSW, Australia
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El Sayed K, Macefield VG, Hissen SL, Joyner MJ, Taylor CE. Rate of rise in diastolic blood pressure influences vascular sympathetic response to mental stress. J Physiol 2016; 594:7465-7482. [PMID: 27690366 DOI: 10.1113/jp272963] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Accepted: 09/26/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Research indicates that individuals may experience a rise (positive responders) or fall (negative responders) in muscle sympathetic nerve activity (MSNA) during mental stress. In this study, we examined the early blood pressure responses (including the peak, time of peak and rate of rise in blood pressure) to mental stress in positive and negative responders. Negative MSNA responders to mental stress exhibit a more rapid rise in diastolic pressure at the onset of the stressor, suggesting a baroreflex-mediated suppression of MSNA. In positive responders there is a more sluggish rise in blood pressure during mental stress, which appears to be MSNA-driven. This study suggests that whether MSNA has a role in the pressor response is dependent upon the reactivity of blood pressure early in the task. ABSTRACT Research indicates that individuals may experience a rise (positive responders) or fall (negative responders) in muscle sympathetic nerve activity (MSNA) during mental stress. The aim was to examine the early blood pressure response to stress in positive and negative responders and thus its influence on the direction of change in MSNA. Blood pressure and MSNA were recorded continuously in 21 healthy young males during 2 min mental stressors (mental arithmetic, Stroop test) and physical stressors (cold pressor, handgrip exercise, post-exercise ischaemia). Participants were classified as negative or positive responders according to the direction of the mean change in MSNA during the stressor tasks. The peak changes, time of peak and rate of changes in blood pressure were compared between groups. During mental arithmetic negative responders experienced a significantly greater rate of rise in diastolic blood pressure in the first minute of the task (1.3 ± 0.5 mmHg s-1 ) compared with positive responders (0.4 ± 0.1 mmHg s-1 ; P = 0.03). Similar results were found for the Stroop test. Physical tasks elicited robust parallel increases in blood pressure and MSNA across participants. It is concluded that negative MSNA responders to mental stress exhibit a more rapid rise in diastolic pressure at the onset of the stressor, suggesting a baroreflex-mediated suppression of MSNA. In positive responders there is a more sluggish rise in blood pressure during mental stress, which appears to be MSNA-driven. This study suggests that whether MSNA has a role in the pressor response is dependent upon the reactivity of blood pressure early in the task.
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Affiliation(s)
| | - Vaughan G Macefield
- School of Medicine, Western Sydney University, Sydney, Australia.,Neuroscience Research Australia, Sydney, Australia
| | - Sarah L Hissen
- School of Science and Health, Western Sydney University, Sydney, Australia
| | | | - Chloe E Taylor
- School of Science and Health, Western Sydney University, Sydney, Australia
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Johnson AW, Hissen SL, Macefield VG, Brown R, Taylor CE. Magnitude of Morning Surge in Blood Pressure Is Associated with Sympathetic but Not Cardiac Baroreflex Sensitivity. Front Neurosci 2016; 10:412. [PMID: 27660603 PMCID: PMC5014858 DOI: 10.3389/fnins.2016.00412] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Accepted: 08/25/2016] [Indexed: 11/13/2022] Open
Abstract
The ability of the arterial baroreflex to regulate blood pressure may influence the magnitude of the morning surge in blood pressure (MSBP). The aim was to investigate the relationships between sympathetic and cardiac baroreflex sensitivity (BRS) and the morning surge. Twenty-four hour ambulatory blood pressure was recorded in 14 young individuals. The morning surge was defined via the pre-awakening method, which is calculated as the difference between mean blood pressure values 2 h before and 2 h after rising from sleep. The mean systolic morning surge, diastolic morning surge, and morning surge in mean arterial pressures were 15 ± 2, 13 ± 1, and 11 ± 1 mmHg, respectively. During the laboratory protocol, continuous measurements of blood pressure, heart rate, and muscle sympathetic nerve activity (MSNA) were made over a 10-min period of rest. Sympathetic BRS was quantified by plotting MSNA burst incidence against diastolic pressure (sympathetic BRSinc), and by plotting total MSNA against diastolic pressure (sympathetic BRStotal). Cardiac BRS was quantified using the sequence method. The mean values for sympathetic BRSinc, sympathetic BRStotal and cardiac BRS were −1.26 ± 0.26 bursts/100 hb/mmHg, −1.60 ± 0.37 AU/beat/mmHg, and 13.1 ± 1.5 ms/mmHg respectively. Significant relationships were identified between sympathetic BRSinc and the diastolic morning surge (r = 0.62, p = 0.02) and the morning surge in mean arterial pressure (r = 0.57, p = 0.03). Low sympathetic BRS was associated with a larger morning surge in mean arterial and diastolic blood pressure. Trends for relationships were identified between sympathetic BRStotal and the diastolic morning surge (r = 0.52, p = 0.066) and the morning surge in mean arterial pressure (r = 0.48, p = 0.095) but these did not reach significance. There were no significant relationships between cardiac BRS and the morning surge. These findings indicate that the ability of the baroreflex to buffer increases in blood pressure via reflexive changes in MSNA may play a role in determining the magnitude of the MSBP.
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Affiliation(s)
- Aaron W Johnson
- School of Medicine, Western Sydney University Sydney, NSW, Australia
| | - Sarah L Hissen
- School of Science and Health, Western Sydney University Sydney, NSW, Australia
| | - Vaughan G Macefield
- School of Medicine, Western Sydney UniversitySydney, NSW, Australia; Neuroscience Research AustraliaSydney, NSW, Australia
| | - Rachael Brown
- School of Medicine, Western Sydney University Sydney, NSW, Australia
| | - Chloe E Taylor
- School of Science and Health, Western Sydney University Sydney, NSW, Australia
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