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Hanson BE, Casey DP. Intermittent versus continuous handgrip exercise and peripheral endothelial function: impact of shear rate fluctuations. J Appl Physiol (1985) 2023; 135:892-901. [PMID: 37650140 DOI: 10.1152/japplphysiol.00362.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2023] [Revised: 08/08/2023] [Accepted: 08/26/2023] [Indexed: 09/01/2023] Open
Abstract
Sustained exercise-induced elevations in shear rate (SR) have been well established as beneficial for improving endothelial function. However, the impact of intermittent fluctuations in SR is not understood. We investigated the effect of intermittent SR elevations compared with sustained elevations on peripheral endothelial function. Brachial artery flow-mediated dilation (FMD) was assessed in 13 adults (9 M/4 F; 22 ± 4 yr) before and after 30 min of handgrip exercise. Three different rhythmic forearm exercise interventions were performed at a rate of 20 contractions/min. Intermittent exercises (6 × 3 min exercise interspersed by 2 min of rest) were performed at 25% (INT-25%) and 15% (INT-15%) maximum voluntary contraction (MVC), and continuous exercise was completed at 15% MVC. Brachial artery diameter and velocity were measured using Doppler ultrasound. The total increase in SR above baseline throughout exercise was greater during INT-25% (4,441 ± 516 s-1) and continuous (4,070 ± 407 s-1) compared with INT-15% (2,811 ± 342 s-1, P < 0.05). The %FMD increased following all exercises (INT-25%: 5.7 ± 1.2% to 8.1 ± 1.2%; INT-15%: 5.2 ± 1.2% to 7.0 ± 1.1%; continuous: 5.5 ± 1.3% to 6.8 ± 1.3%, P < 0.05 for all). The increase following INT-25% was significantly greater than INT-15% and continuous (P < 0.05 for both). Normalized FMD to shear rate area under the curve increased with intermittent exercise (INT-25%: 2.2 ± 0.2% to 3.4 ± 0.3%; INT-15%: 2.1 ± 0.2% to 3.2 ± 0.2%, P < 0.05 for both) but did not following continuous (2.1 ± 0.2% to 2.5 ± 0.1%, P = 0.06). The increase in normalized FMD with intermittent exercises were greater than continuous (P < 0.05 for both). These findings suggest intermittent fluctuations in SR during handgrip exercise may be more beneficial than sustained elevations on improving peripheral endothelial function.NEW & NOTEWORTHY Exercise-induced increases in shear rate is a well-established stimulus for improving peripheral endothelial function. This study presents novel findings that intermittent elevations in shear rate may be more effective at acutely improving endothelial function compared with continuous elevations. Despite similar increases in total shear rate during handgrip exercise intermittent elevations produced a significantly greater increase in endothelial function when compared with continuous elevations potentially indicating intermittent elevations as a more effective stimulus for acute improvements.
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Affiliation(s)
- Brady E Hanson
- Department of Physical Therapy and Rehabilitation Science, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States
| | - Darren P Casey
- Department of Physical Therapy and Rehabilitation Science, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States
- Abboud Cardiovascular Research Center, University of Iowa, Iowa City, Iowa, United States
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, Iowa, United States
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Decker KP, Chiu A, Weggen JB, Richardson JW, Hogwood AC, Darling AM, Garten RS. High sodium intake differentially impacts brachial artery dilation when evaluated with reactive versus active hyperemia in salt resistant individuals. J Appl Physiol (1985) 2023; 134:277-287. [PMID: 36548512 DOI: 10.1152/japplphysiol.00461.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
This study sought to determine if high sodium (HS) intake in salt resistant (SR) individuals attenuates upper limb arterial dilation in response to reactive (occlusion) and active (exercise) hyperemia, two stimuli with varying vasodilatory mechanisms, and the role of oxidative stress in this response. Ten young, SR participants (9 males, 1 female) consumed a 7-day HS (6,900 mg/day) and a 7-day recommended sodium intake (RI: 2,300 mg/day) diet in a randomized order. On the last day of each diet, brachial artery (BA) function was evaluated via reactive (RH-FMD: 5 min of cuff occlusion) and active [handgrip (HG) exercise] hyperemia after consumption of both placebo (PL) and antioxidants (AO). The HS diet significantly elevated sodium excretion (P < 0.05), but mean arterial blood pressure was unchanged. During the PL condition, the HS diet significantly reduced RH-FMD when compared with RI diet (P = 0.01), but this reduction was significantly restored (P = 0.01) when supplemented with AO (HS + PL: 5.9 ± 3.4; HS + AO: 8.2 ± 2.7; RI + PL: 8.9 ± 4.7; RI + AO: 7.0 ± 2.1%). BA shear-to-dilation slopes, evaluated across all HG exercise workloads, were not significantly different across sodium intervention or AO supplementation. In SR individuals, HS intake impaired BA function when assessed via RH-FMD, but was restored with acute AO consumption suggesting oxidative stress as a contributor to this dysfunction. However, exercise-induced BA dilation was unaltered, potentially implicating an inability of HS intake to influence the mechanisms responsible for effectively maintaining skeletal muscle perfusion during exercise.NEW & NOTEWORTHY This study examined if high sodium (HS) intake in salt resistant (SR) individuals attenuates brachial artery (BA) flow-mediated dilation in response to reactive (occlusion) and active (exercise) hyperemia. In SR individuals, HS intake impaired reactive hyperemia-induced BA dilation, but not exercise-induced BA dilation. This finding suggests that although brachial artery nitric oxide bioavailability may be reduced following HS intake, the redundant mechanisms associated with adequate upper limb blood flow regulation during exercise are maintained.
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Affiliation(s)
- Kevin P Decker
- Department of Kinesiology and Applied Physiology, University of Delaware, Newark, Delaware
| | - Alex Chiu
- Department of Kinesiology and Health Sciences, Virginia Commonwealth University, Richmond, Virginia
| | - Jennifer B Weggen
- Department of Kinesiology and Health Sciences, Virginia Commonwealth University, Richmond, Virginia
| | - Jacob W Richardson
- Department of Kinesiology and Health Sciences, Virginia Commonwealth University, Richmond, Virginia
| | - Austin C Hogwood
- Department of Kinesiology, University of Virginia, Charlottesville, Virginia
| | - Ashley M Darling
- Department of Kinesiology, University of Texas at Arlington, Arlington, Texas
| | - Ryan S Garten
- Department of Kinesiology and Health Sciences, Virginia Commonwealth University, Richmond, Virginia
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Shields KL, Broxterman RM, Jarrett CL, Bisconti AV, Park SH, Richardson RS. The passive leg movement technique for assessing vascular function: the impact of baseline blood flow. Exp Physiol 2021; 106:2133-2147. [PMID: 34411365 DOI: 10.1113/ep089818] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Accepted: 08/18/2021] [Indexed: 12/30/2022]
Abstract
NEW FINDINGS What is the central question of this study? The passive leg movement (PLM) assessment of vascular function utilizes the blood flow response in the common femoral artery (CFA): what is the impact of baseline CFA blood flow on the PLM response? What is the main finding and its importance? Although an attenuated PLM response is not an obligatory consequence of increased baseline CFA blood flow, increased blood flow through the deep femoral artery will diminish the response. Care should be taken to ensure that a genuine baseline leg blood flow is obtained prior to performing a PLM vascular function assessment. ABSTRACT The passive leg movement (PLM) assessment of vascular function utilizes the blood flow response in the common femoral artery (CFA). This response is primarily driven by vasodilation of the microvasculature downstream from the deep (DFA) and, to a lesser extent, the superficial (SFA) femoral artery, which facilitate blood flow to the upper and lower leg, respectively. However, the impact of baseline CFA blood flow on the PLM response is unknown. Therefore, to manipulate baseline CFA blood flow, PLM was performed with and without upper and lower leg cutaneous heating in 10 healthy subjects, with blood flow (ultrasound Doppler) and blood pressure (finometer) assessed. Baseline blood flow was significantly increased in the CFA (∼97%), DFA (∼109%) and SFA (∼78%) by upper leg heating. This increase in baseline CFA blood flow significantly attenuated the PLM-induced total blood flow in the DFA (∼62%), which was reflected by a significant fall in blood flow in the CFA (∼49%), but not in the SFA. Conversely, lower leg heating increased blood flow in the CFA (∼68%) and SFA (∼160%), but not in the DFA. Interestingly, this increase in baseline CFA blood flow only significantly attenuated the PLM-induced total blood flow in the SFA (∼60%), and not in the CFA or DFA. Thus, although an attenuated PLM response is not an obligatory consequence of an increase in baseline CFA blood flow, an increase in baseline blood flow through the DFA will diminish the PLM response. Therefore, care should be taken to ensure that a genuine baseline leg blood flow is obtained prior to performance of a PLM vascular function assessment.
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Affiliation(s)
- Katherine L Shields
- Department of Nutrition and Integrative Physiology, University of Utah, Salt Lake City, UT, USA
| | - Ryan M Broxterman
- Geriatric Research, Education, and Clinical Center, Veterans Affairs Medical Center, Salt Lake City, UT, USA.,Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA
| | - Catherine L Jarrett
- Geriatric Research, Education, and Clinical Center, Veterans Affairs Medical Center, Salt Lake City, UT, USA.,Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA
| | - Angela V Bisconti
- Geriatric Research, Education, and Clinical Center, Veterans Affairs Medical Center, Salt Lake City, UT, USA.,Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA
| | - Soung Hun Park
- Department of Nutrition and Integrative Physiology, University of Utah, Salt Lake City, UT, USA
| | - Russell S Richardson
- Department of Nutrition and Integrative Physiology, University of Utah, Salt Lake City, UT, USA.,Geriatric Research, Education, and Clinical Center, Veterans Affairs Medical Center, Salt Lake City, UT, USA.,Department of Internal Medicine, University of Utah, Salt Lake City, UT, USA
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Tremblay JC, Ainslie PN, Turner R, Gatterer H, Schlittler M, Woyke S, Regli IB, Strapazzon G, Rauch S, Siebenmann C. Endothelial function and shear stress in hypobaric hypoxia: time course and impact of plasma volume expansion in men. Am J Physiol Heart Circ Physiol 2020; 319:H980-H994. [PMID: 32886005 DOI: 10.1152/ajpheart.00597.2020] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
High-altitude exposure typically reduces endothelial function, and this is modulated by hemoconcentration resulting from plasma volume contraction. However, the specific impact of hypobaric hypoxia independent of external factors (e.g., cold, varying altitudes, exercise, diet, and dehydration) on endothelial function is unknown. We examined the temporal changes in blood viscosity, shear stress, and endothelial function and the impact of plasma volume expansion (PVX) during exposure to hypobaric hypoxia while controlling for external factors. Eleven healthy men (25 ± 4 yr, mean ± SD) completed two 4-day chamber visits [normoxia (NX) and hypobaric hypoxia (HH; equivalent altitude, 3,500 m)] in a crossover design. Endothelial function was assessed via flow-mediated dilation in response to transient (reactive hyperemia; RH-FMD) and sustained (progressive handgrip exercise; SS-FMD) increases in shear stress before entering and after 1, 6, 12, 48, and 96 h in the chamber. During HH, endothelial function was also measured on the last day after PVX to preexposure levels (1,140 ± 320 mL balanced crystalloid solution). Blood viscosity and arterial shear stress increased on the first day during HH compared with NX and remained elevated at 48 and 96 h (P < 0.005). RH-FMD did not differ during HH compared with NX and was unaffected by PVX despite reductions in blood viscosity (P < 0.05). The stimulus-response slope of increases in shear stress to vasodilation during SS-FMD was preserved in HH and increased by 44 ± 73% following PVX (P = 0.023). These findings suggest that endothelial function is maintained in HH when other stressors are absent and that PVX improves endothelial function in a shear-stress stimulus-specific manner.NEW & NOTEWORTHY Using a normoxic crossover study design, we examined the impact of hypobaric hypoxia (4 days; altitude equivalent, 3,500 m) and hemoconcentration on blood viscosity, shear stress, and endothelial function. Blood viscosity increased during the hypoxic exposure and was accompanied by elevated resting and exercising arterial shear stress. Flow-mediated dilation stimulated by reactive hyperemia and handgrip exercise was preserved throughout the hypoxic exposure. Plasma volume expansion reversed the hypoxia-associated hemoconcentration and selectively increased handgrip exercise flow-mediated dilation.
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Affiliation(s)
- Joshua C Tremblay
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan, Kelowna, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan, Kelowna, Canada
| | - Rachel Turner
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Hannes Gatterer
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Maja Schlittler
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Simon Woyke
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy.,Department of Anesthesiology and Intensive Care Medicine, Medical University of Innsbruck, Innsbruck, Austria
| | - Ivo B Regli
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy.,Department of Anesthesia and Intensive Care Medicine, "F. Tappeiner" Hospital, Merano, Italy
| | - Giacomo Strapazzon
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy.,Department of Anesthesiology and Intensive Care Medicine, Medical University of Innsbruck, Innsbruck, Austria
| | - Simon Rauch
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy.,Department of Anesthesia and Intensive Care Medicine, "F. Tappeiner" Hospital, Merano, Italy
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Li JP, Jiang WW, Bi WK, Jiang CH, Li ZK, Zou Y, Zhang SB, Bi MJ, Li Q. Feasibility analysis of external application of Xiao-Shuan-San in preventing PICC-related thrombosis. Complement Ther Med 2020; 52:102448. [PMID: 32951711 DOI: 10.1016/j.ctim.2020.102448] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Revised: 02/22/2020] [Accepted: 05/13/2020] [Indexed: 10/24/2022] Open
Abstract
PURPOSE We aim to analyze the feasibility of external application of Xiao-Shuan-Santo prevent peripherally inserted central catheter (PICC) -related thrombosis. METHODS A total of 218 patients with PICC catheterization were randomly divided into a control group (n = 103) and a treatment group (n = 115). Patients in the treatment group received additional external application of Xiao-Shuan-San. The changes of coagulation index, the incidence of PICC-related thrombosis and other complications, and the maximum blood flow rate (Vmax) of axillary vein were observed at 1 day before catheterization and 30 days after PICC. RESULTS At 30 days after PICC, the incidence of PICC-related thrombosis and other adverse events in the treatment group were obviously lower than that in the control group (P < 0.05), and the decreased Vmax value of axillary vein in the control group (11.75±1.91 cm/s) was more visible than that in the treatment group (14.63±3.03 cm/s), accompanied by a statistical significance (P < 0.05). CONCLUSIONS External application of Xiao-Shuan-San could reduce the incidence of PICC-related thrombosis and other complications.
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Affiliation(s)
- Jie-Ping Li
- Department of Integrated Chinese and Western Medicine, Yuhuangding Hospital Affiliated to Qingdao University, Yantai, 264000, China
| | - Wen-Wen Jiang
- Department of Integrated Chinese and Western Medicine, Yuhuangding Hospital Affiliated to Qingdao University, Yantai, 264000, China; Centre of Integrated Chinese and Western Medicine, School of Basic Medicine, Qingdao University, Qingdao, 266071, China
| | - Wei-Kang Bi
- Department of Clinical Medicine, Weifang Medical University, Weifang, 261000, China
| | - Cui-Hong Jiang
- Department of Integrated Chinese and Western Medicine, Yuhuangding Hospital Affiliated to Qingdao University, Yantai, 264000, China
| | - Ze-Kun Li
- Department of Integrated Chinese and Western Medicine, Yuhuangding Hospital Affiliated to Qingdao University, Yantai, 264000, China; Centre of Integrated Chinese and Western Medicine, School of Basic Medicine, Qingdao University, Qingdao, 266071, China
| | - Yong Zou
- Department of Integrated Chinese and Western Medicine, Yuhuangding Hospital Affiliated to Qingdao University, Yantai, 264000, China
| | - Shao-Bing Zhang
- Department of Clinical Medicine, Weifang Medical University, Weifang, 261000, China
| | - Ming-Jun Bi
- Emergency Center, The Affiliated Yantai Yuhuangding Hospital of Qingdao University, Yantai, Shandong, 264000, China.
| | - Qin Li
- Department of Integrated Chinese and Western Medicine, Yuhuangding Hospital Affiliated to Qingdao University, Yantai, 264000, China; Centre of Integrated Chinese and Western Medicine, School of Basic Medicine, Qingdao University, Qingdao, 266071, China.
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6
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Tryfonos A, Cocks M, Mills J, Green DJ, Dawson EA. Exercise-induced vasodilation is not impaired following radial artery catheterization in coronary artery disease patients. J Appl Physiol (1985) 2020; 128:422-428. [PMID: 31917624 DOI: 10.1152/japplphysiol.00695.2019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Diagnosis and treatment for coronary artery disease (CAD) often involves angiography and/or percutaneous coronary intervention. However, the radial artery catheterization required during both procedures may result in acute artery dysfunction/damage. While exercise-based rehabilitation is recommended for CAD patients following catheterization, it is not known if there is a period when exercise may be detrimental due to catheter-induced damage. Animal studies have demonstrated exercise-induced paradoxical vasoconstriction postcatheterization. This study aimed to examine arterial responses to acute exercise following catheterization. Thirty-three CAD patients (65.8 ± 7.3 yr, 31.5 ± 6.3 kg/m2, 82% men) undergoing transradial catheterization were assessed before and 1 wk postcatheterization. Radial artery (RA) diameter and shear rate were assessed during handgrip exercise (HE), in both the catheterized (CATH) and control (CON) arms. Endothelial function was also assessed via simultaneous bilateral radial flow-mediated dilation (FMD) at both time points. We found that the increase in RA diameter and shear stress in response to HE (P < 0.0001) was maintained postcatheterization in both the CATH and CON arms, whereas FMD following catheterization was impaired in the CATH [6.5 ± 3.3 to 4.7 ± 3.5% (P = 0.005)] but not in the CON [6.2 ± 2.6 to 6.4 ± 3.5% (P = 0.797)] limb. While endothelial dysfunction, assessed by FMD, was apparent 1 wk postcatheterization, the ability of the RA to dilate in response to exercise was not impaired. The impact of catheterization and consequent endothelial denudation on vascular dys/function in humans may therefore be stimulus specific, and a highly level of redundancy appears to exist that preserves exercise-mediated vasodilator responses.NEW & NOTEWORTHY Despite depressed flow-mediated endothelium-dependent dilation following catheterization-induced damage, radial artery responses to handgrip exercise were preserved. This suggests that arterial responses to catheterization may be stimulus specific and that redundant mechanisms may compensate for vasodilator impairment during exercise. This has implications for exercise-based rehabilitation after catheterization.
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Affiliation(s)
- Andrea Tryfonos
- Research Institute for Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom
| | - Matthew Cocks
- Research Institute for Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom
| | - Joseph Mills
- Liverpool Heart and Chest Hospital, Liverpool, United Kingdom
| | - Daniel J Green
- School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Crawley, Western Australia
| | - Ellen A Dawson
- Research Institute for Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom
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King TJ, Pyke KE. Evidence of a limb- and shear stress stimulus profile-dependent impact of high-intensity cycling training on flow-mediated dilation. Appl Physiol Nutr Metab 2019; 45:135-145. [PMID: 31251889 DOI: 10.1139/apnm-2019-0151] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Lower limb endurance training can improve conduit artery flow-mediated dilation (FMD) in response to transient increases in shear stress (reactive hyperemia; RH-FMD) in both the upper and lower limbs. Sustained increases in shear stress recruit a partially distinct transduction pathway and elicit a physiologically relevant FMD response (SS-FMD) that provides distinct information regarding endothelial function. However, the impact of training on SS-FMD is not well understood. The purpose of this study was to determine the impact of cycling training on handgrip exercise-induced brachial artery (BA) FMD (BA SS-FMD) and calf plantar-flexion-induced superficial femoral artery (SFA) FMD (SFA SS-FMD). RH-FMD was also assessed in both arteries. Twenty-eight young males were randomized to control (n = 12) or training (n = 16) groups. The training group cycled 30 min/day, 3 days/week for 4 weeks at 80% heart rate reserve. FMD was assessed in the BA and SFA before and after the intervention via Duplex ultrasound. Results are means ± SD. Training did not impact SS-FMD in either artery, and SFA RH-FMD was also unchanged (p > 0.05). When controlling for the shear rate stimulus via covariate analysis, BA RH-FMD improved in the training group (p = 0.05) (control - pre-intervention: 5.7% ± 2.4%, post-intervention: 5.3% ± 2.4%; training - pre-intervention: 5.4% ± 2.5%, post-intervention: 7.2% ± 2.4%). Thus, endurance training resulted in nonuniform adaptations to endothelial function, with an isolated impact on the BA's ability to transduce a transient increase in shear stress. Novelty Training did not alter SS-FMD in the arm or leg. RH-FMD was augmented in the arm only. Thus training adaptations were limb- and shear stress profile-specific.
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Affiliation(s)
- Trevor J King
- Cardiovascular Stress Response Lab, School of Kinesiology and Health Studies, Queen's University, Kingston, Ontario, Canada.,Cardiovascular Stress Response Lab, School of Kinesiology and Health Studies, Queen's University, Kingston, Ontario, Canada
| | - Kyra E Pyke
- Cardiovascular Stress Response Lab, School of Kinesiology and Health Studies, Queen's University, Kingston, Ontario, Canada
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Tremblay JC, Williams JS, Pyke KE. Ramp and step increases in shear stress result in a similar magnitude of brachial artery flow-mediated dilation. Eur J Appl Physiol 2019; 119:611-619. [PMID: 30603795 DOI: 10.1007/s00421-018-4049-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 11/28/2018] [Indexed: 02/07/2023]
Abstract
PURPOSE There is evidence that the endothelium is responsive to both the rate and magnitude of increases in shear stress. However, whether flow-mediated dilation stimulated by sustained increases in shear stress (SS-FMD) is rate sensitive in humans is unknown. The purpose of this investigation was to test whether ramp (gradual) and step (instantaneous) increases in shear stress elicit disparate SS-FMD. METHODS Young, healthy men (n = 18, age = 22 ± 2 years, body mass index = 25 ± 3 kg m-2) performed two 11-min bouts of rhythmic handgrip exercise; one with a 5.5-min ramp-increase in shear stress and one with an immediate step increase in shear stress. Ramp increases in shear stress were achieved through incremental increases in handgrip exercise intensity [increases of 4% maximum voluntary contraction (MVC) every 30 s for 5.5 min, ending at 44% MVC] and step increases in shear stress were achieved through a combination of arterial compression and commencing handgrip exercise at 44% MVC. RESULTS Shear rate was greater in the step versus ramp protocol in minutes 1-6, but not different thereafter. Similarly, SS-FMD was greater in the step versus ramp protocol during minutes 2-6, but similar in minutes 7-11 (minute 11: ramp 8.7 ± 4.6%; step 9.4 ± 3.6%; P = 0.343). SS-FMD continued to increase over time with maintenance of a steady shear stress stimulus (step minutes 2-11: 0.51 ± 0.36% min-1; ramp minutes 7-11: 0.64 ± 0.57% min-1; P = 0.259). CONCLUSIONS These findings indicate that in the brachial artery of humans, the magnitude of SS-FMD is determined by the magnitude and duration, but not the rate, of increases in shear stress.
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Affiliation(s)
- Joshua C Tremblay
- Cardiovascular Stress Response Laboratory, School of Kinesiology and Health Studies, Queen's University, 28 Division Street, Kingston, ON, K7L 3N6, Canada
| | - Jennifer S Williams
- Cardiovascular Stress Response Laboratory, School of Kinesiology and Health Studies, Queen's University, 28 Division Street, Kingston, ON, K7L 3N6, Canada
| | - Kyra E Pyke
- Cardiovascular Stress Response Laboratory, School of Kinesiology and Health Studies, Queen's University, 28 Division Street, Kingston, ON, K7L 3N6, Canada.
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