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Villar R, Hughson RL. Vascular conductance and muscle blood flow during exercise are altered by inspired oxygen fraction and arterial perfusion pressure. Physiol Rep 2017; 5:5/5/e13144. [PMID: 28292884 PMCID: PMC5350166 DOI: 10.14814/phy2.13144] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2017] [Accepted: 01/08/2017] [Indexed: 01/02/2023] Open
Abstract
We tested the hypothesis during the combined challenges of altered inspired O2 fraction (FIO2) and posture changes at lower power output regardless of body position that the vascular conductance (VC) recruitment to the exercising muscle would not limit muscle perfusion and estimated O2 delivery (DO2est). However, in head‐down tilt at the higher power output exercise in hypoxia, the recruitment of VC would have a functional limitation which would restrict muscle blood flow (MBF) leading to a limitation in DO2est with consequent increases in metabolic stress. Ten healthy volunteers repeated plantar flexion contractions at 20% (low power output = LPO) and 30% (higher power output = HPO) of their maximal voluntary contraction in horizontal (HOR), 35° head‐down‐tilt (HDT) and 45° head‐up‐tilt (HUT). Popliteal diameter and muscle blood flow velocity were measured by ultrasound determining MBF. VC was estimated by dividing MBF flow by MPP, and DO2est was estimated by MBF times saturation. LPOHUT in hypoxia was associated with no changes in VC and MBF leading to reduced DO2est. In LPOHDT under hypoxia, despite no apparent functional limitation in the VC recruitment, rise in MBF to maintain DO2est was associated with marked increase in muscle electromyographic activity, indicating greater metabolic stress. In HPOHDT under hypoxia, a functional limitation for the recruitment of VC constrained MBF and DO2est. Elevated muscle electromyographic signal in HPOHDT under hypoxia was consistent with challenged aerobic metabolisms which contributed to a greater increase in the relative stress of the exercise challenge and advance the onset of muscle fatigue.
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Affiliation(s)
- Rodrigo Villar
- Division of Natural Sciences, Faculty of Health Sciences, Franklin Pierce University, Rindge, New Hampshire .,Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada.,Coordenação de Aperfeiçoamento de Pessoal de Nivel Superior (CAPES), Brasilia DF, Brazil
| | - Richard L Hughson
- Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada.,Schlegel-University of Waterloo Research Institute for Aging, Waterloo, Ontario, Canada
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Villar R, Hughson RL. Effect of altered arterial perfusion pressure on vascular conductance and muscle blood flow dynamic response during exercise in humans. J Appl Physiol (1985) 2013; 114:620-7. [DOI: 10.1152/japplphysiol.01094.2012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Changes in vascular conductance (VC) are required to counter changes in muscle perfusion pressure (MPP) to maintain muscle blood flow (MBF) during exercise. We investigated the recruitment of VC as a function of peak VC measured in three body positions at two different work rates to test the hypothesis that adaptations in VC compensated changes in MPP at low-power output (LPO), but not at high-power output (HPO). Eleven healthy volunteers exercised at LPO and HPO (repeated plantar flexion contractions at 20–30% maximal voluntary contraction, respectively) in horizontal (HOR), 35° head-down tilt (HDT), and 45° head-up tilt (HUT). Muscle blood flow velocity and popliteal diameter were measured by ultrasound to determine MBF, and VC was estimated by dividing MBF flow by MPP. Peak VC was unaffected by body position. The rates of increase in MBF and VC were significantly faster in HUT and slower in HDT than HOR, and rates were faster in LPO than HPO. During LPO exercise, the increase in, and steady-state values of, MBF were less for HUT and HDT than HOR; the increase in VC was less in HUT than HOR and HDT. During HPO exercise, MBF in the HDT was reduced compared with HOR and HUT, even though VC reached 92% VC peak, which was greater than HOR, which was, in turn, greater than HUT. Reduced MBF during HPO HDT exercise had the functional consequence of a significant increase in muscle electromyographic index, revealing the effects of MPP on O2 delivery during exercise.
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Affiliation(s)
- Rodrigo Villar
- Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada; and
- Coordenação de Aperfeiçoamento de Pessoal de Nivel Superior (CAPES), Brasilia, Brazil
| | - Richard L. Hughson
- Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada; and
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Villar R, Hughson RL. Lower limb vascular conductance and resting popliteal blood flow during head-up and head-down postural challenges. Clin Physiol Funct Imaging 2012; 33:186-91. [PMID: 23522011 DOI: 10.1111/cpf.12008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 10/12/2012] [Indexed: 10/27/2022]
Affiliation(s)
| | - Richard L. Hughson
- Faculty of Applied Health Sciences; University of Waterloo; Waterloo; ON; Canada
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Bruno RM, Ghiadoni L, Seravalle G, Dell'oro R, Taddei S, Grassi G. Sympathetic regulation of vascular function in health and disease. Front Physiol 2012; 3:284. [PMID: 22934037 PMCID: PMC3429057 DOI: 10.3389/fphys.2012.00284] [Citation(s) in RCA: 152] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2012] [Accepted: 06/29/2012] [Indexed: 01/16/2023] Open
Abstract
The sympathetic nervous system (SNS) is known to play a pivotal role in short- and long-term regulation of different functions of the cardiovascular system. In the past decades increasing evidence demonstrated that sympathetic neural control is involved not only in the vasomotor control of small resistance arteries but also in modulation of large artery function. Sympathetic activity and vascular function, both of which are key factors in the development and prognosis of cardiovascular events and disease, are linked at several levels. Evidence from experimental studies indicates that the SNS is critically influenced, at the central and also at the peripheral level, by the most relevant factors regulating vascular function, such as nitric oxide (NO), reactive oxygen species (ROS), endothelin (ET), the renin-angiotensin system. Additionally, there is indirect evidence of a reciprocal relationship between endothelial function and activity of the SNS. A number of cardiovascular risk factors and diseases are characterized both by increased sympathetic outflow and decreased endothelial function. In healthy subjects, muscle sympathetic nerve activity (MSNA) appears to be related to surrogate markers of endothelial function, and an acute increase in sympathetic activity has been associated with a decrease in endothelial function in healthy subjects. However, direct evidence of a cause-effect relationship from human studies is scanty. In humans large artery stiffness has been associated with increased sympathetic discharge, both in healthy subjects and in renal transplant recipients. Peripheral sympathetic discharge is also able to modulate wave reflection. On the other hand, large artery stiffness can interfere with autonomic regulation by impairing carotid baroreflex sensitivity.
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Affiliation(s)
- Rosa M Bruno
- Department of Internal Medicine University of Pisa, Italy
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Salzer DA, Medeiros PJ, Craen R, Shoemaker JK. Neurogenic-nitric oxide interactions affecting brachial artery mechanics in humans: roles of vessel distensibility vs. diameter. Am J Physiol Regul Integr Comp Physiol 2008; 295:R1181-7. [PMID: 18685062 DOI: 10.1152/ajpregu.90333.2008] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The purpose of this investigation was to assess the interactive influence of sympathetic activation and supplemental nitric oxide (NO) on brachial artery distensibility vs. its diameter. It was hypothesized that 1) sympathetic activation and NO competitively impact muscular conduit artery (brachial artery) mechanics, and 2) neurogenic constrictor input affects conduit vessel stiffness independently of outright changes in conduit vessel diastolic diameter. Lower body negative pressure (LBNP) and a cold pressor stress (CPT) were used to study the changes in conduit vessel mechanics when the increased sympathetic outflow occurred with and without changes in heart rate (LBNP -40 vs. -15 mmHg) and blood pressure (CPT vs. LBNP). These maneuvers were performed in the absence and presence of nitroglycerin. Neither LBNP nor CPT altered brachial artery diastolic diameter; however, distensibility was reduced by 25 to 54% in each reflex (all P < 0.05). This impact of sympathetic activation on brachial artery distensibility was not altered by nitroglycerin supplementation (21-54%; P < 0.05), although baseline diameter was increased by the exogenous NO (P < 0.05). The results indicate that sympathetic excitation can reduce the distensibility of the brachial artery independently of concurrent changes in diastolic diameter, heart rate, and blood pressure. However, exogenous NO did not minimize or reverse brachial stiffening during sympathetic activation. Therefore, sympathetic outflow appears to impact the stiffness of this conduit vessel rather than its diastolic diameter or, by inference, its local resistance to flow.
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Affiliation(s)
- Deborah A Salzer
- Neurovascular Research Laboratory, School of Kinesiology, Rm. 3110 Thames Hall, The Univ. of Western Ontario, London, ON, Canada N6A 3K7
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Abstract
Hypertension is a major risk factor for cardiovascular disease, and reduction of elevated blood pressure significantly reduces the risk of cardiovascular events. Endothelial dysfunction, which is characterized by impairment of nitric oxide (NO) bioavailability, is an important risk factor for both hypertension and cardiovascular disease and may represent a major link between the conditions. Evidence suggests that NO plays a major role in regulating blood pressure and that impaired NO bioactivity is an important component of hypertension. Mice with disruption of the gene for endothelial NO synthase have elevated blood pressure levels compared with control animals, suggesting a genetic component to the link between impaired NO bioactivity and hypertension. Clinical studies have shown that patients with hypertension have a blunted arterial vasodilatory response to infusion of endothelium-dependent vasodilators and that inhibition of NO raises blood pressure. Impaired NO bioactivity is also implicated in arterial stiffness, a major mechanism of systolic hypertension. Clarification of the mechanisms of impaired NO bioactivity in hypertension could have important implications for the treatment of hypertension.
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Affiliation(s)
- Matthias Hermann
- From the Department of Cardiology, the Cardiovascular Center, University Hospital Zurich, Switzerland
| | - Andreas Flammer
- From the Department of Cardiology, the Cardiovascular Center, University Hospital Zurich, Switzerland
| | - Thomas F. Lüscher
- From the Department of Cardiology, the Cardiovascular Center, University Hospital Zurich, Switzerland
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Charkoudian N, Joyner MJ, Barnes SA, Johnson CP, Eisenach JH, Dietz NM, Wallin BG. Relationship between muscle sympathetic nerve activity and systemic hemodynamics during nitric oxide synthase inhibition in humans. Am J Physiol Heart Circ Physiol 2006; 291:H1378-83. [PMID: 16648188 DOI: 10.1152/ajpheart.00234.2006] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Large interindividual differences exist in resting sympathetic nerve activity (SNA) among normotensive humans with similar arterial pressure (AP). We recently showed inverse relationships of resting SNA with cardiac output (CO) and vascular adrenergic responsiveness that appear to balance the influence of differences in SNA on blood pressure. In the present study, we tested whether nitric oxide (NO)-mediated vasodilation has a role in this balance by evaluating hemodynamic responses to systemic NO synthase (NOS) inhibition in individuals with low and high resting muscle SNA (MSNA). We measured MSNA via peroneal microneurography, CO via acetylene uptake and AP directly, at baseline and during increasing systemic doses of the NOS inhibitor NG-monomethyl-l-arginine (l-NMMA). Baseline MSNA ranged from 9 to 38 bursts/min (13 to 68 bursts/100 heartbeats). l-NMMA caused dose-dependent increases in AP and total peripheral resistance and reflex decreases in CO and MSNA. Increases in AP with l-NMMA were greater in individuals with high baseline MSNA ( PANOVA < 0.05). For example, after 8.5 mg/kg of l-NMMA, in the low MSNA subgroup ( n = 6, 28 ± 4 bursts/100 heartbeats), AP increased 9 ± 1 mmHg, whereas in the high-MSNA subgroup ( n = 6, 58 ± 3 bursts/100 heartbeats), AP increased 15 ± 2 mmHg ( P < 0.01). The high-MSNA subgroup had lower baseline CO and smaller decreases in CO with l-NMMA, but changes in total peripheral resistance were not different between groups. We conclude that differences in CO among individuals with varying sympathetic traffic have important hemodynamic implications during disruption of NO-mediated vasodilation.
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Affiliation(s)
- N Charkoudian
- Department of Physiology and Biomedical Engineering, JO 4-184W, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, MN 55905, USA.
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Cui J, Wilson TE, Crandall CG. Muscle sympathetic nerve activity during lower body negative pressure is accentuated in heat-stressed humans. J Appl Physiol (1985) 2004; 96:2103-8. [PMID: 14978004 DOI: 10.1152/japplphysiol.00717.2003] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The purpose of this project was to test the hypothesis that increases in muscle sympathetic nerve activity (MSNA) during an orthostatic challenge is attenuated in heat-stressed individuals. To accomplish this objective, MSNA was measured during graded lower body negative pressure (LBNP) in nine subjects under normothermic and heat-stressed conditions. Progressive LBNP was applied at -3, -6, -9, -12, -15, -18, -21, and -40 mmHg for 2 min per stage. Whole body heating caused significant increases in sublingual temperature, skin blood flow, sweat rate, heart rate, and MSNA (all P < 0.05) but not in mean arterial blood pressure (P > 0.05). Progressive LBNP induced significant increases in MSNA in both thermal conditions. However, during the heat stress trial, increases in MSNA at LBNP levels higher than -9 mmHg were greater compared with during the same LBNP levels in normothermia (all P < 0.05). These data suggest that the increase in MSNA to orthostatic stress is not attenuated but rather accentuated in heat-stressed humans.
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Affiliation(s)
- Jian Cui
- Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, 7232 Greenville Ave., Dallas, TX 75231, USA
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