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Stewart LC, Wainman L, Ahmadian M, Duffy J, Seethaler R, Mueller PJ, Eves ND, West CR. The left ventricle increases contractility in response to baroreceptor unloading, which is sympathetically mediated in the anesthetized rat. J Appl Physiol (1985) 2024; 137:136-144. [PMID: 38813608 DOI: 10.1152/japplphysiol.00722.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Revised: 05/16/2024] [Accepted: 05/24/2024] [Indexed: 05/31/2024] Open
Abstract
Contemporary discussion of the baroreflex includes the efferent vascular-sympathetic and cardiovagal arms. Since sympathetic postganglionic neurons also innervate the left ventricle (LV), it is often assumed that the LV produces a sympathetically mediated increase in contractility during baroreceptor unloading, but this has not been characterized using a load-independent index of contractility. We aimed to determine 1) whether LV contractility increases in response to baroreceptor unloading and 2) whether such increases are mediated via the sympathetic or parasympathetic arm of the autonomic nervous system. Ten male Wistar rats were anesthetized (urethane) and instrumented with arterial and LV pressure-volume catheters to measure mean arterial pressure (MAP) and load-independent LV contractility [maximal rate of increase in pressure adjusted to end-diastolic volume (PAdP/dtmax)], respectively. Rats were placed in a servo-controlled lower-body negative pressure (LBNP) chamber to reduce MAP by 10% for 60 s to mechanically unload baroreceptors under control conditions. LBNP was repeated in each animal following infusions of cardiac autonomic blockers using esmolol (sympathetic), atropine (parasympathetic), and esmolol + atropine. Under control conditions, PAdP/dtmax increased during baroreceptor unloading (26 ± 6 vs. 31 ± 9 mmHg·s-1·μL-1, P = 0.031). During esmolol, there was no increase in LV contractility during baroreceptor unloading (11 ± 2 vs. 12 ± 2, P = 0.125); however, during atropine, there was an increase in LV contractility during baroreceptor unloading (26 ± 6 vs. 31 ± 9, P = 0.019). During combined esmolol and atropine, there was a small increase in contractility versus control (13 ± 3 vs. 15 ± 4, P = 0.046). Our results demonstrate that, in anesthetized rats, LV contractility increases in response to baroreceptor unloading, which is largely sympathetically mediated.NEW & NOTEWORTHY This study empirically demonstrates a sympathetically mediated increase in LV contractility in response to baroreceptor unloading using a load-independent index of cardiac contractility in the anesthetized rat.
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Affiliation(s)
- Liam C Stewart
- Centre for Chronic Disease Prevention and Management, University of British Columbia, Kelowna, British Columbia, Canada
- Centre for Heart, Lung & Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
- Faculty of Medicine, Department of Cellular & Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
| | - Liisa Wainman
- Centre for Chronic Disease Prevention and Management, University of British Columbia, Kelowna, British Columbia, Canada
- Centre for Heart, Lung & Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
- Faculty of Medicine, Department of Cellular & Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
| | - Mehdi Ahmadian
- Centre for Chronic Disease Prevention and Management, University of British Columbia, Kelowna, British Columbia, Canada
- Centre for Heart, Lung & Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
- Faculty of Education, School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
| | - Jennifer Duffy
- Centre for Chronic Disease Prevention and Management, University of British Columbia, Kelowna, British Columbia, Canada
- Centre for Heart, Lung & Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
- Faculty of Medicine, Department of Cellular & Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
| | - Rudolph Seethaler
- School of Engineering, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Patrick J Mueller
- Department of Physiology, School of Medicine, Wayne State University, Detroit, Michigan, United States
| | - Neil D Eves
- Centre for Heart, Lung & Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
- Faculty of Health and Social Development, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Christopher R West
- Centre for Chronic Disease Prevention and Management, University of British Columbia, Kelowna, British Columbia, Canada
- Centre for Heart, Lung & Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
- Faculty of Medicine, Department of Cellular & Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
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Ahmadian M, Williams AM, Mannozzi J, Konecny F, Hoiland RL, Wainman L, Erskine E, Duffy J, Manouchehri N, So K, Tauh K, Sala-Mercado JA, Shortt K, Fisk S, Kim KT, Streijger F, Foster GE, Kwon BK, O’Leary DS, West CR. A cross-species validation of single-beat metrics of cardiac contractility. J Physiol 2022; 600:4779-4806. [PMID: 36121759 PMCID: PMC9669232 DOI: 10.1113/jp283319] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Accepted: 09/02/2022] [Indexed: 12/24/2022] Open
Abstract
The assessment of left ventricular (LV) contractility in animal models is useful in various experimental paradigms, yet obtaining such measures is inherently challenging and surgically invasive. In a cross-species study using small and large animals, we comprehensively tested the agreement and validity of multiple single-beat surrogate metrics of LV contractility against the field-standard metrics derived from inferior vena cava occlusion (IVCO). Fifty-six rats, 27 minipigs and 11 conscious dogs underwent LV and arterial catheterization and were assessed for a range of single-beat metrics of LV contractility. All single-beat metrics were tested for the various underlying assumptions required to be considered a valid metric of cardiac contractility, including load-independency, sensitivity to inotropic stimulation, and ability to diagnose contractile dysfunction in cardiac disease. Of all examined single-beat metrics, only LV maximal pressure normalized to end-diastolic volume (EDV), end-systolic pressure normalized to EDV, and the maximal rate of rise of the LV pressure normalized to EDV showed a moderate-to-excellent agreement with their IVCO-derived reference measure and met all the underlying assumptions required to be considered as a valid cardiac contractile metric in both rodents and large-animal models. Our findings demonstrate that single-beat metrics can be used as a valid, reliable method to quantify cardiac contractile function in basic/preclinical experiments utilizing small- and large-animal models KEY POINTS: Validating and comparing indices of cardiac contractility that avoid caval occlusion would offer considerable advantages for the field of cardiovascular physiology. We comprehensively test the underlying assumptions of multiple single-beat indices of cardiac contractility in rodents and translate these findings to pigs and conscious dogs. We show that when performing caval occlusion is unfeasible, single-beat metrics can be utilized to accurately quantify cardiac inotropic function in basic and preclinical research employing various small and large animal species. We report that maximal left-ventricular (LV)-pressure normalized to end-diastolic volume (EDV), LV end-systolic pressure normalized to EDV and the maximal rate of rise of the LV pressure waveform normalized to EDV are the best three single-beat metrics to measure cardiac inotropic function in both small- and large-animal models.
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Affiliation(s)
- Mehdi Ahmadian
- School of Kinesiology, Faculty of Education, University of British Columbia, Vancouver, BC, Canada
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
- Centre for Chronic Disease Prevention and Management, University of British Columbia, Kelowna, BC, Canada
| | - Alexandra M. Williams
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
| | - Joseph Mannozzi
- Department of Physiology, School of Medicine, Wayne State University, Detroit, MI 48009
| | - Filip Konecny
- Transonic Scisense Inc., London, ON, Canada
- MaRS Centre Toronto Medical Discovery Tower, 3rd Floor, 101 College Street, M5G 1L7, Toronto, Ontario, Canada
| | - Ryan L. Hoiland
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
- Department of Anesthesiology, Pharmacology and Therapeutics, Faculty of Medicine, Vancouver General Hospital, 899 West 12th Avenue, University of British Columbia, Vancouver, BC, Canada, V5Z 1M9
| | - Liisa Wainman
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
- Centre for Chronic Disease Prevention and Management, University of British Columbia, Kelowna, BC, Canada
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
| | - Erin Erskine
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
- Centre for Chronic Disease Prevention and Management, University of British Columbia, Kelowna, BC, Canada
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
| | - Jennifer Duffy
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
- Centre for Chronic Disease Prevention and Management, University of British Columbia, Kelowna, BC, Canada
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
| | - Neda Manouchehri
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
| | - Kitty So
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
| | - Keerit Tauh
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
| | | | - Katelyn Shortt
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
| | - Shera Fisk
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
| | - Kyoung-Tae Kim
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
- Department of Neurosurgery, School of Medicine, Kyungpook National University Hospital, Daegu, South Korea
| | - Femke Streijger
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
| | - Glen E. Foster
- Centre for Heart, Lung, & Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, 3333 University Way, Kelowna, BC, V1V1V7
| | - Brian K. Kwon
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
| | - Donal S. O’Leary
- Department of Physiology, School of Medicine, Wayne State University, Detroit, MI 48009
| | - Christopher R. West
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
- Centre for Chronic Disease Prevention and Management, University of British Columbia, Kelowna, BC, Canada
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
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Mannozzi J, Al-Hassan MH, Kaur J, Lessanework B, Alvarez A, Massoud L, Bhatti T, O’Leary DS. Ventricular-Vascular Uncoupling in Heart Failure: Effects of Arterial Baroreflex-Induced Sympathoexcitation at Rest and During Exercise. Front Physiol 2022; 13:835951. [PMID: 35450162 PMCID: PMC9016757 DOI: 10.3389/fphys.2022.835951] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Accepted: 03/18/2022] [Indexed: 01/19/2023] Open
Abstract
Autonomic alterations in blood pressure are primarily a result of arterial baroreflex modulation of systemic vascular resistance and cardiac output on a beat-by-beat basis. The combined central and peripheral control by the baroreflex likely acts to maintain efficient energy transfer from the heart to the systemic vasculature; termed ventricular-vascular coupling. This level of control is maintained whether at rest or during exercise in healthy subjects. During heart failure, the ventricular-vascular relationship is uncoupled and baroreflex dysfunction is apparent. We investigated if baroreflex dysfunction in heart failure exacerbated ventricular-vascular uncoupling at rest, and during exercise in response to baroreceptor unloading by performing bilateral carotid occlusions in chronically instrumented conscious canines. We observed in healthy subjects that baroreceptor unloading caused significant increases in effective arterial elastance (Ea) at rest (1.2 ± 0.3 mmHg/ml) and during exercise (1.3 ± 0.2 mmHg/ml) that coincided with significant increases in stroke work (SW) (1.5 ± 0.2 mmHg/ml) and (1.6 ± 0.2 mmHg/ml) suggesting maintained ventricular-vascular coupling. Heart Failure significantly increased the effect of baroreceptor unloading on Ea at rest (3.1 ± 0.7 mmHg/ml) and during exercise (2.3 ± 0.5 mmHg/ml) whereas no significant increases in stroke work occurred, thus signifying further ventricular-vascular uncoupling. We believe that the enhanced ventricular-vascular uncoupling observed during baroreceptor unloading only worsens the already challenged orthostatic and exercise tolerance and thereby contributes to poor exercise performance and quality of life for heart failure patients.
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Affiliation(s)
- Joseph Mannozzi
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, United States
| | | | - Jasdeep Kaur
- Department of Kinesiology and Health Education, University of Texas at Austin, Austin, TX, United States
| | - Beruk Lessanework
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, United States
| | - Alberto Alvarez
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, United States
| | - Louis Massoud
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, United States
| | - Tauheed Bhatti
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, United States
| | - Donal S. O’Leary
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, United States,*Correspondence: Donal S. O’Leary,
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Mannozzi J, Kim JK, Sala-Mercado JA, Al-Hassan MH, Lessanework B, Alvarez A, Massoud L, Bhatti T, Aoun K, O’Leary DS. Arterial Baroreflex Inhibits Muscle Metaboreflex Induced Increases in Effective Arterial Elastance: Implications for Ventricular-Vascular Coupling. Front Physiol 2022; 13:841076. [PMID: 35399256 PMCID: PMC8990766 DOI: 10.3389/fphys.2022.841076] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Accepted: 02/18/2022] [Indexed: 01/19/2023] Open
Abstract
The ventricular-vascular relationship assesses the efficacy of energy transferred from the left ventricle to the systemic circulation and is quantified as the ratio of effective arterial elastance to maximal left ventricular elastance. This relationship is maintained during exercise via reflex increases in cardiovascular performance raising both arterial and ventricular elastance in parallel. These changes are, in part, due to reflexes engendered by activation of metabosensitive skeletal muscle afferents-termed the muscle metaboreflex. However, in heart failure, ventricular-vascular uncoupling is apparent and muscle metaboreflex activation worsens this relationship through enhanced systemic vasoconstriction markedly increasing effective arterial elastance which is unaccompanied by substantial increases in ventricular function. This enhanced arterial vasoconstriction is, in part, due to significant reductions in cardiac performance induced by heart failure causing over-stimulation of the metaboreflex due to under perfusion of active skeletal muscle, but also as a result of reduced baroreflex buffering of the muscle metaboreflex-induced peripheral sympatho-activation. To what extent the arterial baroreflex modifies the metaboreflex-induced changes in effective arterial elastance is unknown. We investigated in chronically instrumented conscious canines if removal of baroreflex input via sino-aortic baroreceptor denervation (SAD) would significantly enhance effective arterial elastance in normal animals and whether this would be amplified after induction of heart failure. We observed that effective arterial elastance (Ea), was significantly increased during muscle metaboreflex activation after SAD (0.4 ± 0.1 mmHg/mL to 1.4 ± 0.3 mmHg/mL). In heart failure, metaboreflex activation caused exaggerated increases in Ea and in this setting, SAD significantly increased the rise in Ea elicited by muscle metaboreflex activation (1.3 ± 0.3 mmHg/mL to 2.3 ± 0.3 mmHg/mL). Thus, we conclude that the arterial baroreflex does buffer muscle metaboreflex induced increases in Ea and this buffering likely has effects on the ventricular-vascular coupling.
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Mannozzi J, Massoud L, Kaur J, Coutsos M, O'Leary DS. Ventricular contraction and relaxation rates during muscle metaboreflex activation in heart failure: are they coupled? Exp Physiol 2020; 106:401-411. [PMID: 33226720 DOI: 10.1113/ep089053] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Accepted: 11/18/2020] [Indexed: 01/08/2023]
Abstract
NEW FINDINGS What is the central question of this study? Does the muscle metaboreflex affect the ratio of left ventricular contraction/relaxation rates and does heart failure impact this relationship. What is the main finding and its importance? The effect of muscle metaboreflex activation on the ventricular relaxation rate was significantly attenuated in heart failure. Heart failure attenuates the exercise and muscle metaboreflex-induced changes in the contraction/relaxation ratio. In heart failure, the reduced ability to raise cardiac output during muscle metaboreflex activation may not solely be due to attenuation of ventricular contraction but also alterations in ventricular relaxation and diastolic function. ABSTRACT The relationship between contraction and relaxation rates of the left ventricle varies with exercise. In in vitro models, this ratio was shown to be relatively unaltered by changes in sarcomere length, frequency of stimulation, and β-adrenergic stimulation. We investigated whether the ratio of contraction to relaxation rate is maintained in the whole heart during exercise and muscle metaboreflex activation and whether heart failure alters these relationships. We observed that in healthy subjects the ratio of contraction to relaxation increases from rest to exercise as a result of a higher increase in contraction relative to relaxation. During muscle metaboreflex activation the ratio of contraction to relaxation is significantly reduced towards 1.0 due to a large increase in relaxation rate matching contraction rate. In heart failure, contraction and relaxation rates are significantly reduced, and increases during exercise are attenuated. A significant increase in the ratio was observed from rest to exercise although baseline ratio values were significantly reduced close to 1.0 when compared to healthy subjects. There was no significant change observed between exercise and muscle metaboreflex activation nor was the ratio during muscle metaboreflex activation significantly different between heart failure and control. We conclude that heart failure reduces the muscle metaboreflex gain and contraction and relaxation rates. Furthermore, we observed that the ratio of the contraction and relaxation rates during muscle metaboreflex activation is not significantly different between control and heart failure, but significant changes in the ratio in healthy subjects due to increased relaxation rate were abolished in heart failure.
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Affiliation(s)
- Joseph Mannozzi
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, USA
| | - Louis Massoud
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, USA
| | - Jasdeep Kaur
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, USA
| | - Matthew Coutsos
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, USA
| | - Donal S O'Leary
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, USA
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Legg Ditterline BE, Aslan SC, Randall DC, Harkema SJ, Castillo C, Ovechkin AV. Effects of Respiratory Training on Heart Rate Variability and Baroreflex Sensitivity in Individuals With Chronic Spinal Cord Injury. Arch Phys Med Rehabil 2017; 99:423-432. [PMID: 28802811 DOI: 10.1016/j.apmr.2017.06.033] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 06/13/2017] [Accepted: 06/27/2017] [Indexed: 12/19/2022]
Abstract
OBJECTIVE To evaluate the effects of pressure threshold respiratory training (RT) on heart rate variability and baroreflex sensitivity in persons with chronic spinal cord injury (SCI). DESIGN Before-after intervention case-controlled clinical study. SETTING SCI research center and outpatient rehabilitation unit. PARTICIPANTS Participants (N=44) consisted of persons with chronic SCI ranging from C2 to T11 who participated in RT (n=24), and untrained control subjects with chronic SCI ranging from C2 to T9 (n=20). INTERVENTIONS A total of 21±2 RT sessions performed 5 days a week during a 4-week period using a combination of pressure threshold inspiratory and expiratory devices. MAIN OUTCOME MEASURES Forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), and beat-to-beat arterial blood pressure and heart rate changes during the 5-second-long maximum expiratory pressure maneuver (5s MEP) and the sit-up orthostatic stress test, acquired before and after the RT program. RESULTS In contrast to the untrained controls, individuals in the RT group experienced significantly increased FVC and FEV1 (both P<.01) in association with improved quality of sleep, cough, and speech. Sympathetically (phase II) and parasympathetically (phase IV) mediated baroreflex sensitivity both significantly (P<.05) increased during the 5s MEP. During the orthostatic stress test, improved autonomic control over heart rate was associated with significantly increased sympathetic and parasympathetic modulation (low- and high-frequency change: P<.01 and P<.05, respectively). CONCLUSIONS Inspiratory-expiratory pressure threshold RT is a promising technique to positively affect both respiratory and cardiovascular dysregulation observed in persons with chronic SCI.
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Affiliation(s)
- Bonnie E Legg Ditterline
- Department of Physiology, University of Louisville, Louisville, KY; Department of Neurological Surgery, University of Louisville, Louisville, KY
| | - Sevda C Aslan
- Department of Neurological Surgery, University of Louisville, Louisville, KY
| | - David C Randall
- Department of Physiology, University of Kentucky, Lexington, KY
| | - Susan J Harkema
- Department of Physiology, University of Louisville, Louisville, KY; Department of Neurological Surgery, University of Louisville, Louisville, KY
| | - Camilo Castillo
- Department of Neurological Surgery, University of Louisville, Louisville, KY
| | - Alexander V Ovechkin
- Department of Physiology, University of Louisville, Louisville, KY; Department of Neurological Surgery, University of Louisville, Louisville, KY.
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Raj SR, Faris PD, Semeniuk L, Manns B, Krahn AD, Morillo CA, Benditt DG, Sheldon RS. Rationale for the Assessment of Metoprolol in the Prevention of Vasovagal Syncope in Aging Subjects Trial (POST5). Am Heart J 2016; 174:89-94. [PMID: 26995374 DOI: 10.1016/j.ahj.2016.01.017] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Accepted: 01/20/2016] [Indexed: 11/29/2022]
Abstract
BACKGROUND Vasovagal syncope (VVS) is a common problem associated with a poor quality of life, which improves when syncope frequency is reduced. Effective pharmacological therapies for VVS are lacking. Metoprolol is a β-adrenergic receptor antagonist that is ineffective in younger patients, but may benefit older (≥40 years) VVS patients. Given the limited therapeutic options, a placebo-controlled clinical trial of metoprolol for the prevention of VVS in older patients is needed. STRUCTURE OF STUDY The POST5 is a multicenter, international, randomized, placebo-controlled study of metoprolol in the prevention of VVS in patients ≥40 years old. The primary endpoint is the time to first recurrence of syncope. Patients will be randomized 1:1 to receive metoprolol 25 to 100 mg BID or matching placebo, and followed up for 1 year. Secondary end points include syncope frequency, presyncope, quality of life, and cost analysis. Primary analysis will be intention to treat, with a secondary on-treatment analysis. POWER CALCULATIONS A sample size of 222, split equally between the groups achieves 85% power to detect a hazard rate of 0.3561 when the event rates are 50% and 30% in the placebo and metoprolol arms. Allowing for 10% dropout, we propose to enroll 248 patients. IMPLICATIONS This study will be the first adequately powered trial to determine whether metoprolol is effective in preventing VVS in patients ≥40 years. If effective, metoprolol may become the first line pharmacological therapy for these patients.
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Affiliation(s)
- Satish R Raj
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada; Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University, Nashville, TN.
| | | | - Lisa Semeniuk
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
| | - Braden Manns
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
| | - Andrew D Krahn
- Heart Rhythm Services, Division of Cardiology, University of British Columbia, Vancouver, BC, Canada
| | | | - David G Benditt
- Cardiac Arrhythmia and Syncope Center, University of Minnesota, Minneapolis, MN
| | - Robert S Sheldon
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada
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Moslehpour M, Kawada T, Sunagawa K, Sugimachi M, Mukkamala R. Nonlinear identification of the total baroreflex arc: chronic hypertension model. Am J Physiol Regul Integr Comp Physiol 2016; 310:R819-27. [PMID: 26791831 DOI: 10.1152/ajpregu.00424.2015] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 01/18/2016] [Indexed: 11/22/2022]
Abstract
The total baroreflex arc is the open-loop system relating carotid sinus pressure (CSP) to arterial pressure (AP). Its linear dynamic functioning has been shown to be preserved in spontaneously hypertensive rats (SHR). However, the system is known to exhibit nonlinear dynamic behaviors. The aim of this study was to establish nonlinear dynamic models of the total arc (and its subsystems) in hypertensive rats and to compare these models with previously published models for normotensive rats. Hypertensive rats were studied under anesthesia. The vagal and aortic depressor nerves were sectioned. The carotid sinus regions were isolated and attached to a servo-controlled piston pump. AP and sympathetic nerve activity were measured while CSP was controlled via the pump using Gaussian white noise stimulation. Second-order, nonlinear dynamics models were developed by application of nonparametric system identification to a portion of the measurements. The models of the total arc predicted AP 21-43% better (P < 0.005) than conventional linear dynamic models in response to a new portion of the CSP measurement. The linear and nonlinear terms of these validated models were compared with the corresponding terms of an analogous model for normotensive rats. The nonlinear gains for the hypertensive rats were significantly larger than those for the normotensive rats [-0.38 ± 0.04 (unitless) vs. -0.22 ± 0.03, P < 0.01], whereas the linear gains were similar. Hence, nonlinear dynamic functioning of the sympathetically mediated total arc may enhance baroreflex buffering of AP increases more in SHR than normotensive rats.
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Affiliation(s)
- Mohsen Moslehpour
- Department of Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan
| | - Toru Kawada
- Department of Cardiovascular Dynamics, National Cerebral and Cardiovascular Center, Osaka, Japan; and
| | - Kenji Sunagawa
- Department of Cardiovascular Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | - Masaru Sugimachi
- Department of Cardiovascular Dynamics, National Cerebral and Cardiovascular Center, Osaka, Japan; and
| | - Ramakrishna Mukkamala
- Department of Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan;
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