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Moir ME, Klassen SA, Zamir M, Hamner JW, Tan CO, Shoemaker JK. Regulation of cerebrovascular compliance compared with forearm vascular compliance in humans: a pharmacological study. Am J Physiol Heart Circ Physiol 2023; 324:H100-H108. [PMID: 36459447 PMCID: PMC9799136 DOI: 10.1152/ajpheart.00377.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Increasing evidence indicates that cerebrovascular compliance contributes to the dynamic regulation of cerebral blood flow but the mechanisms regulating cerebrovascular compliance in humans are unknown. This retrospective study investigated the impact of neural, endothelial, and myogenic mechanisms on the regulation of vascular compliance in the cerebral vascular bed compared with the forearm vascular bed. An index of vascular compliance (Ci) was assessed using a Windkessel model applied to blood pressure waveforms (finger photoplethysmography) and corresponding middle cerebral artery blood velocity or brachial artery blood velocity waveforms (Doppler ultrasound). Data were analyzed during a 5-min baseline period (10 waveforms) under control conditions and during distinct sympathetic blockade (experiment 1, phentolamine; 10 adults), cholinergic blockade (experiment 2, glycopyrrolate; 9 adults), and myogenic blockade (experiment 3, nicardipine; 14 adults). In experiment 1, phentolamine increased Ci similarly in the cerebral vascular bed (131 ± 135%) and forearm vascular bed (93 ± 75%; P = 0.45). In experiment 2, glycopyrrolate increased cerebrovascular Ci (72 ± 61%) and forearm vascular Ci (74 ± 64%) to a similar extent (P = 0.88). In experiment 3, nicardipine increased Ci but to a greater extent in the cerebral vascular bed (88 ± 88%) than forearm vascular bed (20 ± 45%; P = 0.01). Therefore, adrenergic, cholinergic, and myogenic mechanisms contribute to the regulation of cerebrovascular and forearm vascular compliance. However, myogenic mechanisms appear to exert more specific control over vascular compliance in the brain relative to the forearm.NEW & NOTEWORTHY Vascular compliance represents an important determinant in the dynamics and regulation of blood flow through a vascular bed. However, the mechanisms that regulate vascular compliance remain poorly understood. This study examined the impact of neural, endothelial, and myogenic mechanisms on cerebrovascular compliance compared with forearm vascular compliance. Distinct pharmacological blockade of α-adrenergic, endothelial muscarinic, and myogenic inputs altered cerebrovascular and forearm vascular compliance. These results further our understanding of vascular control and blood flow regulation in the brain.
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Affiliation(s)
- M. Erin Moir
- 1School of Kinesiology, University of Western Ontario, London, Ontario, Canada
| | - Stephen A. Klassen
- 2Department of Kinesiology, Brock University, St. Catharines, Ontario, Canada
| | - Mair Zamir
- 3Department of Mathematics, University of Western Ontario, London, Ontario, Canada,4Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada
| | - J. W. Hamner
- 5Cerebrovascular Research Laboratory, Spaulding Hospital Cambridge, Cambridge, Massachusetts
| | - Can Ozan Tan
- 6RAM, Electrical Engineering, Mathematics, and Computer Science,
University of Twente, Enschede, The Netherlands
| | - J. Kevin Shoemaker
- 1School of Kinesiology, University of Western Ontario, London, Ontario, Canada,7Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
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2
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Olver TD, Badrov MB, Allen MD, Coverdale NS, Shoemaker JK. Acute changes in forearm vascular compliance during transient sympatho-excitation. Physiol Rep 2022; 10:e15256. [PMID: 35439367 PMCID: PMC9017978 DOI: 10.14814/phy2.15256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Revised: 04/07/2022] [Accepted: 03/20/2022] [Indexed: 06/14/2023] Open
Abstract
The study of vascular regulation often omits important information about the elastic properties of arteries under conditions of pulsatile flow. The purpose of this study was to examine the relationship between muscle sympathetic nerve activity (MSNA), vascular bed compliance, and peripheral blood flow responses in humans. We hypothesized that increases in MSNA would correlate with reductions in vascular compliance, and that changes in compliance would correspond with changes in peripheral blood flow during sympatho-excitation. MSNA (microneurography), blood pressure (Finopres), and brachial artery blood flow (Doppler ultrasound), were monitored in six healthy males at baseline and during the last 15 s of voluntary end-inspiratory, expiratory apneas and 5 min of static handgrip exercise (SHG; 20% maximum voluntary contraction) and 3 min of post-exercise circulatory occlusion (SHG + PECO; measured in the non-exercising arm). A lumped Windkessel model was employed to examine vascular bed compliance. During apnea, indices of MSNA were inversely related with vascular compliance, and reductions in compliance correlated with decreased brachial blood flow rate. During SHG, despite increased MSNA, compliance also increased, but was unrelated to increases in blood flow. Neither during SHG nor PECO did indices of MSNA correlate with forearm vascular compliance nor did vascular compliance correlate with brachial flow. However, during PECO, a linear combination of blood pressure and total MSNA was correlated with vascular compliance. These data indicate the elastic components of the forearm vasculature are regulated by adrenergic and myogenic mechanisms during sympatho-excitation, but in a reflex-dependent manner.
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Affiliation(s)
- T. Dylan Olver
- Biomedical SciencesWestern College of Veterinary MedicineUniversity of SaskatchewanSaskatoonSaskatchewanCanada
| | - Mark B. Badrov
- Division of CardiologyDepartment of MedicineUniversity Health Network and Sinai HealthUniversity of TorontoTorontoOntarioCanada
| | - Matti D. Allen
- Department of Physical Medicine and RehabilitationSchool of MedicineQueen's UniversityKingstonOntarioCanada
| | - Nicole S. Coverdale
- School of Kinesiology and Health StudiesQueen’s UniversityKingstonOntarioCanada
| | - J. Kevin Shoemaker
- Neurovascular Research LaboratorySchool of KinesiologyThe University of Western OntarioLondonOntarioCanada
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3
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Moir ME, Klassen SA, Zamir M, Shoemaker JK. Rapid changes in vascular compliance contribute to cerebrovascular adjustments during transient reductions in blood pressure in young, healthy adults. J Appl Physiol (1985) 2020; 129:27-35. [PMID: 32463732 DOI: 10.1152/japplphysiol.00272.2020] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Characterization of dynamic cerebral autoregulation has focused primarily on adjustments in cerebrovascular resistance in response to blood pressure (BP) alterations. However, the role of vascular compliance in dynamic autoregulatory processes remains elusive. The present study examined changes in cerebrovascular compliance and resistance during standing-induced transient BP reductions in nine young, healthy adults (3 women). Brachial artery BP (Finometer) and middle cerebral artery blood velocity (BV; Multigon) waveforms were collected. Beginning 20 beats before standing and continuing 40 beats after standing, individual BP and BV waveforms of every second heartbeat were extracted and input into a four-element modified Windkessel model to calculate indexes of cerebrovascular resistance (Ri) and compliance (Ci). Standing elicited a transient reduction in mean BP of 20 ± 9 mmHg. In all participants, a large increase in Ci (165 ± 84%; P < 0.001 vs. seated baseline) occurred 2 ± 2 beats following standing. Reductions in Ri occurred 11 ± 3 beats after standing (Ci vs. Ri delay: P < 0.001). The increase in Ci contributed to maintained systolic BV before the decrease in Ri. The present results demonstrate rapid, large but transient increases in Ci that precede reductions in Ri, in response to standing-induced reductions in BP. Therefore, Ci represents a discreet component of cerebrovascular responses during acute decreases in BP and, consequently, dynamic autoregulation.NEW & NOTEWORTHY Historically, dynamic cerebral autoregulation has been characterized by adjustments in cerebrovascular resistance following systematic changes in blood pressure. However, with the use of Windkessel modeling approaches, this study revealed rapid and large increases in cerebrovascular compliance that preceded reductions in cerebrovascular resistance following standing-induced blood pressure reductions. Importantly, the rapid cerebrovascular compliance response contributed to preservation of systolic blood velocity during the transient hypotensive phase. These results broaden our understanding of dynamic cerebral autoregulation.
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Affiliation(s)
- M Erin Moir
- School of Kinesiology, University of Western Ontario, London, Ontario, Canada
| | - Stephen A Klassen
- School of Kinesiology, University of Western Ontario, London, Ontario, Canada
| | - Mair Zamir
- Department of Applied Mathematics, University of Western Ontario, London, Ontario, Canada.,Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada
| | - J Kevin Shoemaker
- School of Kinesiology, University of Western Ontario, London, Ontario, Canada.,Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
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Shoemaker JK, Badrov MB, Al-Khazraji BK, Jackson DN. Neural Control of Vascular Function in Skeletal Muscle. Compr Physiol 2015; 6:303-29. [PMID: 26756634 DOI: 10.1002/cphy.c150004] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The sympathetic nervous system represents a fundamental homeostatic system that exerts considerable control over blood pressure and the distribution of blood flow. This process has been referred to as neurovascular control. Overall, the concept of neurovascular control includes the following elements: efferent postganglionic sympathetic nerve activity, neurotransmitter release, and the end organ response. Each of these elements reflects multiple levels of control that, in turn, affect complex patterns of change in vascular contractile state. Primarily, this review discusses several of these control layers that combine to produce the integrative physiology of reflex vascular control observed in skeletal muscle. Beginning with three reflexes that provide somewhat dissimilar vascular patterns of response despite similar changes in efferent sympathetic nerve activity, namely, the baroreflex, chemoreflex, and muscle metaboreflex, the article discusses the anatomical and physiological bases of postganglionic sympathetic discharge patterns and recruitment, neurotransmitter release and management, and details of regional variations of receptor density and responses within the microvascular bed. Challenges are addressed regarding the fundamentals of measurement and how conclusions from one response or vascular segment should not be used as an indication of neurovascular control as a generalized physiological dogma. Whereas the bulk of the article focuses on the vasoconstrictor function of sympathetic neurovascular integration, attention is also given to the issues of sympathetic vasodilation as well as the impact of chronic changes in sympathetic activation and innervation on vascular health. © 2016 American Physiological Society.
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Affiliation(s)
- J K Shoemaker
- School of Kinesiology, Western University, London, Ontario, Canada.,Department of Physiology and Pharmacology, Western University, London, Ontario, Canada
| | - M B Badrov
- School of Kinesiology, Western University, London, Ontario, Canada
| | - B K Al-Khazraji
- Department of Medical Biophysics, Western University, London, Ontario, Canada
| | - D N Jackson
- Department of Medical Biophysics, Western University, London, Ontario, Canada
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Park J, Liao P, Sher S, Lyles RH, Deveaux DD, Quyyumi AA. Tetrahydrobiopterin lowers muscle sympathetic nerve activity and improves augmentation index in patients with chronic kidney disease. Am J Physiol Regul Integr Comp Physiol 2015; 308:R208-18. [PMID: 25477424 PMCID: PMC4313073 DOI: 10.1152/ajpregu.00409.2014] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Accepted: 12/01/2014] [Indexed: 11/22/2022]
Abstract
Chronic kidney disease (CKD) is characterized by overactivation of the sympathetic nervous system (SNS) that contributes to cardiovascular risk. Decreased nitric oxide (NO) bioavailability is a major factor contributing to SNS overactivity in CKD, since reduced neuronal NO leads to increased central SNS activity. Tetrahydrobiopterin (BH4) is an essential cofactor for nitric oxide synthase that increases NO bioavailability in experimental models of CKD. We conducted a randomized, double-blinded, placebo-controlled trial testing the benefits of oral sapropterin dihydrochloride (6R-BH4, a synthetic form of BH4) in CKD. 36 patients with CKD and hypertension were randomized to 12 wk of 1) 200 mg 6R-BH4 twice daily + 1 mg folic acid once daily; vs. 2) placebo + folic acid. The primary endpoint was a change in resting muscle sympathetic nerve activity (MSNA). Secondary endpoints included arterial stiffness using pulse wave velocity (PWV) and augmentation index (AIx), endothelial function using brachial artery flow-mediated dilation and endothelial progenitor cells, endothelium-independent vasodilatation (EID), microalbuminuria, and blood pressure. We observed a significant reduction in MSNA after 12 wk of 6R-BH4 (-7.5 ± 2.1 bursts/min vs. +3.2 ± 1.3 bursts/min; P = 0.003). We also observed a significant improvement in AIx (by -5.8 ± 2.0% vs. +1.8 ± 1.7 in the placebo group, P = 0.007). EID increased significantly (by +2.0 ± 0.59%; P = 0.004) in the 6R-BH4 group, but there was no change in endothelial function. There was a trend toward a reduction in diastolic blood pressure by -4 ± 3 mmHg at 12 wk with 6R-BH4 (P = 0.055). 6R-BH4 treatment may have beneficial effects on SNS activity and central pulse wave reflections in hypertensive patients with CKD.
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Affiliation(s)
- Jeanie Park
- Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; Research Service Line, Department of Veterans Affairs Medical Center, Decatur, Georgia;
| | - Peizhou Liao
- Department of Biostatistics and Bioinformatics, Rollins School of Public Health, Emory University, Atlanta, Georgia; and
| | - Salman Sher
- Cardiology Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia
| | - Robert H Lyles
- Department of Biostatistics and Bioinformatics, Rollins School of Public Health, Emory University, Atlanta, Georgia; and
| | - Don D Deveaux
- Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; Research Service Line, Department of Veterans Affairs Medical Center, Decatur, Georgia
| | - Arshed A Quyyumi
- Cardiology Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia
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Nielson CA, Frances MF, Fitzgeorge L, Prapavessis H, Zamir M, Shoemaker JK. Impact of a smoking cessation lifestyle intervention on vascular mechanics in young women. Appl Physiol Nutr Metab 2014; 39:572-80. [DOI: 10.1139/apnm-2013-0272] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We tested the hypotheses that smoking-induced changes in vascular mechanics would be detected earlier in the lumped properties of peripheral vascular beds, which include the properties of microvasculature, than in the local properties of central conduits, and that such changes are reversible with lifestyle changes that include smoking cessation and exercise. Vascular measures were made in 53 young (18–40 years) female smokers and 25 age-matched non-smokers. Twenty-two of the smokers were tested before and after a 14-week smoking cessation program and, of these, 13 were tested again after 52 weeks of smoking cessation. Compared with non-smokers, lumped forearm vascular bed compliance (C: mL/mm Hg) was lower, while lumped viscoelasticity (K: mm Hg/(mL·min)) and resistance (R: mm Hg/(mL·min)) were higher in the smoker group. Neither the carotid-to-toe pulse wave velocity nor local carotid artery elasticity indices were different between groups. Compared with non-smokers, brachial artery distensibility was less, and other markers of stiffness higher, in the smoker group. At 14 and 52 weeks of smoking cessation, forearm vascular R was reduced and C was increased while K was unchanged. The changes in C and R occurred while maintaining a constant R×C value, which represents a dynamic time constant. Thus, early changes in K were observed in the forearm vascular bed of smokers, which were not reflected in the local properties of central conduit vessels. Forearm C, but not K, was reversed following smoking cessation, a finding that may represent a persistent effect of smoking on the intercellular matrix of the vessel wall.
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Affiliation(s)
- Chantelle A. Nielson
- Neurovascular Research Laboratory, School of Kinesiology, Western University, London, ON N6A 3K7, Canada
| | - Maria F. Frances
- Neurovascular Research Laboratory, School of Kinesiology, Western University, London, ON N6A 3K7, Canada
| | - Lyndsay Fitzgeorge
- Exercise and Health Psychology Laboratory, School of Kinesiology, Western University, London, ON N6A 3K7, Canada
| | - Harry Prapavessis
- Exercise and Health Psychology Laboratory, School of Kinesiology, Western University, London, ON N6A 3K7, Canada
| | - Mair Zamir
- Departments of Applied Mathematics and of Medical Biophysics, Western University, London, ON N6A 3K7, Canada
| | - J. Kevin Shoemaker
- Neurovascular Research Laboratory, School of Kinesiology, Western University, London, ON N6A 3K7, Canada
- Department of Physiology and Pharmacology, Western University, London, ON N6A 3K7, Canada
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Noble E, Melling J, Shoemaker K, Tikkanen H, Peltonen J, Stuckey M, Petrella RJ. Innovation to Reduce Cardiovascular Complications of Diabetes at the Intersection of Discovery, Prevention and Knowledge Exchange. Can J Diabetes 2013; 37:282-93. [DOI: 10.1016/j.jcjd.2013.07.061] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Revised: 07/27/2013] [Accepted: 07/29/2013] [Indexed: 01/20/2023]
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