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  • 1
    In: The Journal of Physiology, Wiley, Vol. 600, No. 6 ( 2022-03), p. 1385-1403
    Abstract: Cerebrovascular CO 2 reactivity (CVR) is often considered a bioassay of cerebrovascular endothelial function. We recently introduced a test of cerebral shear‐mediated dilatation (cSMD) that may better reflect endothelial function. We aimed to determine the nitric oxide (NO)‐dependency of CVR and cSMD. Eleven volunteers underwent a steady‐state CVR test and transient CO 2 test of cSMD during intravenous infusion of the NO synthase inhibitor N G ‐monomethyl‐ l ‐arginine ( l ‐NMMA) or volume‐matched saline (placebo; single‐blinded and counter‐balanced). We measured cerebral blood flow (CBF; duplex ultrasound), intra‐arterial blood pressure and . Paired arterial and jugular venous blood sampling allowed for the determination of trans‐cerebral NO 2 − exchange (ozone‐based chemiluminescence). l ‐NMMA reduced arterial NO 2 − by ∼25% versus saline (74.3 ± 39.9 vs . 98.1 ± 34.2 nM; P  = 0.03). The steady‐state CVR (20.1 ± 11.6 nM/min at baseline vs . 3.2 ± 16.7 nM/min at +9 mmHg ; P  = 0.017) and transient cSMD tests (3.4 ± 5.9 nM/min at baseline vs . −1.8 ± 8.2 nM/min at 120 s post‐CO 2 ; P  = 0.044) shifted trans‐cerebral NO 2 − exchange towards a greater net release (a negative value indicates release). Although this trans‐cerebral NO 2 − release was abolished by l ‐NMMA, CVR did not differ between the saline and l ‐NMMA trials (57.2 ± 14.6 vs . 54.1 ± 12.1 ml/min/mmHg; P  = 0.49), nor did l ‐NMMA impact peak internal carotid artery dilatation during the steady‐state CVR test (6.2 ± 4.5 vs . 6.2 ± 5.0% dilatation; P  = 0.960). However, l ‐NMMA reduced cSMD by ∼37% compared to saline (2.91 ± 1.38 vs . 4.65 ± 2.50%; P  = 0.009). Our findings indicate that NO is not an obligatory regulator of steady‐state CVR. Further, our novel transient CO 2 test of cSMD is largely NO‐dependent and provides an in vivo bioassay of NO‐mediated cerebrovascular function in humans. image Key points Emerging evidence indicates that a transient CO 2 stimulus elicits shear‐mediated dilatation of the internal carotid artery, termed cerebral shear‐mediated dilatation. Whether or not cerebrovascular reactivity to a steady‐state CO 2 stimulus is NO‐dependent remains unclear in humans. During both a steady‐state cerebrovascular reactivity test and a transient CO 2 test of cerebral shear‐mediated dilatation, trans‐cerebral nitrite exchange shifted towards a net release indicating cerebrovascular NO production; this response was not evident following intravenous infusion of the non‐selective NO synthase inhibitor N G ‐monomethyl‐ l ‐arginine. NO synthase blockade did not alter cerebrovascular reactivity in the steady‐state CO 2 test; however, cerebral shear‐mediated dilatation following a transient CO 2 stimulus was reduced by ∼37% following intravenous infusion of N G ‐monomethyl‐ l ‐arginine. NO is not obligatory for cerebrovascular reactivity to CO 2 , but is a key contributor to cerebral shear‐mediated dilatation.
    Type of Medium: Online Resource
    ISSN: 0022-3751 , 1469-7793
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2022
    detail.hit.zdb_id: 1475290-6
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  • 2
    In: Experimental Physiology, Wiley, Vol. 103, No. 9 ( 2018-09), p. 1277-1286
    Abstract: What is the central question of this study ? Common carotid artery (CCA) two‐dimensional strain imaging detects intrinsic arterial wall properties beyond conventional measures of arterial stiffness, but the effect of cardiorespiratory fitness on two‐dimensional strain‐derived indices of CCA stiffness is unknown. What is the main finding and its importance ? Two‐dimensional strain imaging of the CCA revealed greater peak circumferential strain and systolic strain rate in highly fit men compared with their less fit counterparts. Altered CCA wall mechanics might reflect intrinsic training‐induced adaptations that help to buffer the increase in pulse pressure and stroke volume during exercise. Abstract The influence of cardiorespiratory fitness on arterial stiffness in young adults remains equivocal. Beyond conventional measures of arterial stiffness, two‐dimensional strain imaging of the common carotid artery (CCA) provides new information related to the intrinsic properties of the arterial wall. Therefore, the aim of this study was to assess the effect of cardiorespiratory fitness on both conventional indices of CCA stiffness and two‐dimensional strain parameters, at rest and after a bout of aerobic exercise in young, healthy men. Short‐axis ultrasound images of the CCA were recorded in 34 healthy men {22 years old [95% confidence interval (CI), 19, 22]} before and immediately after 5 min of aerobic exercise (40% of maximal oxygen consumption). Images were analysed for arterial diameter, peak circumferential strain (PCS) and peak systolic and diastolic strain rates (S‐SR and D‐SR). Heart rate, systolic and diastolic blood pressure were simultaneously assessed, and Peterson's elastic modulus ( E p ) and β‐stiffness (β 1 ) were calculated. Participants were separated post hoc into moderate‐ and high‐fitness groups [maximal oxygen consumption, 48.9 (95% CI, 44.7, 53.2) versus 65.6 ml kg −1  min −1 (95% CI, 63.1, 68.1), respectively; P   〈  0.001]. The E p and β 1 were similar between groups at baseline ( P   〉  0.13) but were elevated in the moderate‐fitness group postexercise ( P   〈  0.04). The PCS and S‐SR were elevated in the high‐fitness group at both time points [3.0% (95% CI, 1.2, 4.9), P  = 0.002, and 0.401 s −1 (95% CI, 0.085, 0.72), P  = 0.02, respectively]. No group differences were observed in CCA heart rate, systolic or diastolic blood pressure or D‐SR throughout the protocol ( P   〉  0.05). Highly fit individuals exhibit elevated CCA, PCS and S‐SR, which might reflect training‐induced adaptations that help to buffer the increase in pulse pressure and stroke volume during exercise.
    Type of Medium: Online Resource
    ISSN: 0958-0670 , 1469-445X
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2018
    detail.hit.zdb_id: 1493802-9
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  • 3
    Online Resource
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    American Physiological Society ; 2019
    In:  American Journal of Physiology-Heart and Circulatory Physiology Vol. 317, No. 1 ( 2019-07-01), p. H181-H189
    In: American Journal of Physiology-Heart and Circulatory Physiology, American Physiological Society, Vol. 317, No. 1 ( 2019-07-01), p. H181-H189
    Abstract: This study focused on the influence of habitual endurance exercise training (i.e., committed runner or nonrunner) on the regulation of muscle sympathetic nerve activity (MSNA) and arterial pressure in middle-aged (50 to 63 yr, n = 23) and younger (19 to 30 yr; n = 23) normotensive men. Hemodynamic and neurophysiological assessments were performed at rest. Indices of vascular sympathetic baroreflex function were determined from the relationship between spontaneous changes in diastolic blood pressure (DBP) and MSNA. Large vessel arterial stiffness and left ventricular stroke volume also were measured. Paired comparisons were performed within each age category. Mean arterial pressure and basal MSNA bursts/min were not different between age-matched runners and nonrunners. However, MSNA bursts/100 heartbeats, an index of baroreflex regulation of MSNA (vascular sympathetic baroreflex operating point), was higher for middle-aged runners ( P = 0.006), whereas this was not different between young runners and nonrunners. The slope of the DBP-MSNA relationship (vascular sympathetic baroreflex gain) was not different between groups in either age category. Aortic pulse wave velocity was lower for runners of both age categories ( P 〈 0.03), although carotid β-stiffness was lower only for middle-aged runners ( P = 0.04). For runners of both age categories, stroke volume was larger, whereas heart rate was lower (both P 〈 0.01). In conclusion, we suggest that neural remodeling and upward setting of the vascular sympathetic baroreflex compensates for cardiovascular adaptations after many years committed to endurance exercise training, presumably to maintain arterial blood pressure stability. NEW & NOTEWORTHY Exercise training reduces muscle sympathetic burst activity in disease; this is often extrapolated to infer a similar effect in health. We demonstrate that burst frequency of middle-aged and younger men committed to endurance training is not different compared with age-matched casual exercisers. Notably, well-trained, middle-aged runners display similar arterial pressure but higher sympathetic burst occurrence than untrained peers. We suggest that homeostatic plasticity and upward setting of the vascular sympathetic baroreflex maintains arterial pressure stability following years of training.
    Type of Medium: Online Resource
    ISSN: 0363-6135 , 1522-1539
    RVK:
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2019
    detail.hit.zdb_id: 1477308-9
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  • 4
    In: Journal of Applied Physiology, American Physiological Society, Vol. 130, No. 1 ( 2021-01-01), p. 149-159
    Abstract: We measured acute vascular responses to heat stress to examine the hypothesis that macrovascular endothelial-dependent dilation is improved in a shear-dependent manner, which is further modified by skin temperature. Twelve healthy males performed whole body heating (+1.3°C esophageal temperature), bilateral forearm heating (∼38°C skin temperature), and a time-matched (∼60 min) control condition on separate days in a counterbalanced order. Bilateral assessments of blood flow and brachial artery flow-mediated dilation (FMD) were performed before and 10 min after each condition with duplex Doppler ultrasound. To isolate the influence of shear stress, a pneumatic cuff was inflated (∼90 mmHg) around the right forearm during each condition to attenuate heat-induced rises in blood flow and shear stress. After forearm heating, FMD increased [cuffed: 4.7 (2.9)% to 6.8 (1.5)% and noncuffed: 5.1 (2.8)% to 6.4 (2.6)%] in both arms (time P 〈 0.01). Whole body heating also increased FMD in the noncuffed arm from 3.6 (2.2)% to 9.2 (3.2)% and in the cuffed arm from to 5.6 (3.0)% to 8.6 (4.9)% (time P 〈 0.01). After the time control, FMD decreased [cuffed: 6.3 (2.4)% to 4.7 (2.2)% and noncuffed: 6.1 (3.0)% to 4.5 (2.6)%] in both arms (time P = 0.03). Multiple linear regression (adjusted R 2  = 0.421 P = 0.003) revealed that changes in esophageal temperature, skin temperatures, and heart rate explained the majority of the variance in this model (34%, 31%, and 21%, respectively). Our findings indicate that, in addition to shear stress, skin and core temperatures are likely important contributors to passive heating-induced vascular adaptations. NEW & NOTEWORTHY The primary determinant of vascular adaptations to lifestyle interventions, such as exercise and heat therapy, is repeated elevations in vascular shear stress. Whether skin or core temperatures also modulate the vascular adaptation to acute heat exposure is unknown, likely due to difficulty in dissociating the thermal and hemodynamic responses to heat. We found that skin and core temperatures modify the acute vascular responses to passive heating irrespective of the magnitude of increase in shear stress.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    RVK:
    RVK:
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2021
    detail.hit.zdb_id: 1404365-8
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    SSG: 31
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  • 5
    In: Experimental Physiology, Wiley, Vol. 105, No. 8 ( 2020-08), p. 1396-1407
    Abstract: What is the central question of this study? Carotid artery peak circumferential strain (PCS) and strain rate attenuate with age, but appear to be modulated by cardiorespiratory fitness status in young males. However, the relationship between habitual endurance exercise (running) and these parameters has not been studied in young and middle‐aged men. What is the main finding and its importance? Young and middle‐aged runners exhibited elevated PCS and systolic strain rate (S‐SR) compared with non‐runners, but habitual running did not influence diastolic strain rate (D‐SR). Habitual exercise is associated with comparable improvements in carotid strain parameters in young and middle‐aged men, but the age‐related decline in PCS and S‐SR might be more amenable to habitual endurance exercise than D‐SR. Abstract Central arterial stiffness is an independent predictor of cardiovascular risk that can be modified by exercise training. However, conventional local measures of carotid artery stiffness display conflicting responses to habitual endurance exercise in young and older adults. Two‐dimensional (2D)‐Strain imaging of the common carotid artery (CCA) quantifies circumferential deformation (strain) of the arterial wall across the cardiac cycle, which is more sensitive at detecting age‐related alterations in CCA stiffness than conventional methods. Therefore, the study was designed to examine the relationship between habitual endurance exercise (running) and CCA 2D‐Strain parameters in young and middle‐aged men. Short‐axis ultrasound images of the CCA were obtained from 13 young non‐runners [23 years of age (95% confidence interval: 21, 26 years of age)], 19 young runners [24 (22, 26) years of age] , 13 middle‐aged non‐runners [54 (52, 56) years of age] and 19 middle‐aged runners [56 (54, 58) years of age] . Images were analysed for peak circumferential strain (PCS; magnitude of deformation) and systolic and diastolic strain rates (S‐SR and D‐SR; deformation velocity), and group differences were examined via two‐way ANOVA. PCS, S‐SR and D‐SR were attenuated in middle‐aged men compared with young men (all P  ≤ 0.001). PCS and S‐SR were elevated in young and middle‐aged runners when compared with non‐runners ( P  = 0.002 and P  = 0.009, respectively), but no age × training status interaction was observed. In contrast, there was no influence of habitual running on D‐SR. Habitual exercise is associated with comparable improvements in CCA 2D‐Strain parameters in young and middle‐aged men, but the age‐related decline in PCS and S‐SR might be more amenable to habitual endurance exercise than D‐SR.
    Type of Medium: Online Resource
    ISSN: 0958-0670 , 1469-445X
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2020
    detail.hit.zdb_id: 1493802-9
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  • 6
    In: European Journal of Applied Physiology, Springer Science and Business Media LLC, Vol. 122, No. 3 ( 2022-03), p. 801-813
    Abstract: We determined the effect of habitual endurance exercise and age on aortic pulse wave velocity (aPWV), augmentation pressure (AP) and systolic blood pressure (aSBP), with statistical adjustments of aPWV and AP for heart rate and aortic mean arterial pressure, when appropriate. Furthermore, we assessed whether muscle sympathetic nerve activity (MSNA) correlates with AP in young and middle-aged men. Methods Aortic PWV, AP, aortic blood pressure (applanation tonometry; SphygmoCor) and MSNA (peroneal microneurography) were recorded in 46 normotensive men who were either young or middle-aged and endurance-trained runners or recreationally active nonrunners (10 nonrunners and 13 runners within each age-group). Between-group differences and relationships between variables were assessed via ANOVA/ANCOVA and Pearson product-moment correlation coefficients, respectively. Results Adjusted aPWV and adjusted AP were similar between runners and nonrunners in both age groups (all, P   〉  0.05), but higher with age (all, P   〈  0.001), with a greater effect size for the age-related difference in AP in runners (Hedges’ g , 3.6 vs 2.6). aSBP was lower in young ( P  = 0.009; g  = 2.6), but not middle-aged ( P  = 0.341; g  = 1.1), runners compared to nonrunners. MSNA burst frequency did not correlate with AP in either age group (young: r  = 0.00, P  = 0.994; middle-aged: r  = − 0.11, P  = 0.604). Conclusion There is an age-dependent effect of habitual exercise on aortic haemodynamics, with lower aSBP in young runners compared to nonrunners only. Statistical adjustment of aPWV and AP markedly influenced the outcomes of this study, highlighting the importance of performing these analyses. Further, peripheral sympathetic vasomotor outflow and AP were not correlated in young or middle-aged normotensive men.
    Type of Medium: Online Resource
    ISSN: 1439-6319 , 1439-6327
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2022
    detail.hit.zdb_id: 1459054-2
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  • 7
    In: American Journal of Physiology-Heart and Circulatory Physiology, American Physiological Society, Vol. 319, No. 2 ( 2020-08-01), p. H370-H376
    Abstract: Changes in the arterial baroreflex arc contribute to elevated sympathetic outflow and altered reflex control of blood pressure with human aging. Using ultrasound and sympathetic microneurography (muscle sympathetic nerve activity, MSNA) we investigated the relationships between aortic and carotid artery wall tension (indices of baroreceptor activation) and the vascular sympathetic baroreflex operating point (OP; MSNA burst incidence) in healthy, normotensive young ( n = 27, 23 ± 3 yr) and middle-aged men ( n = 22, 55 ± 4 yr). In young men, the OP was positively related to the magnitude and rate of unloading and time spent unloaded in the aortic artery ( r = 0.56, 0.65, and 0.51, P = 0.02, 0.003, and 0.03), but not related to the magnitude or rate of unloading or time spent unloaded in the carotid artery ( r = −0.32, −0.07, and 0.06, P = 0.25, 0.81, and 0.85). In contrast, in middle-aged men, the OP was not related to either the magnitude or rate of unloading or time spent unloaded in the aortic ( r = 0.22, 0.21, and 0.27, P = 0.41, 0.43, and 0.31) or carotid artery ( r = 0.06, 0.28, and −0.01; P = 0.48, 0.25, and 0.98). In conclusion, in young men, aortic unloading mechanics may play a role in determining the vascular sympathetic baroreflex OP. In contrast, in middle-aged men, barosensory vessel unloading mechanics do not appear to determine the vascular sympathetic baroreflex OP and, therefore, do not contribute to age-related arterial baroreflex resetting and increased resting MSNA. NEW & NOTEWORTHY We assessed the influence of barosensory vessel mechanics (magnitude and rate of unloading and time spent unloaded) as a surrogate for baroreceptor unloading. In young men, aortic unloading mechanics are important in regulating the operating point of the vascular sympathetic baroreflex, whereas in middle-aged men, these arterial mechanics do not influence this operating point. The age-related increase in resting muscle sympathetic nerve activity does not appear to be driven by altered baroreceptor input from stiffer barosensory vessels.
    Type of Medium: Online Resource
    ISSN: 0363-6135 , 1522-1539
    RVK:
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2020
    detail.hit.zdb_id: 1477308-9
    SSG: 12
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  • 8
    In: The Journal of Physiology, Wiley, Vol. 598, No. 3 ( 2020-02), p. 473-487
    Abstract: Intermittent hypoxia leads to long‐lasting increases in muscle sympathetic nerve activity and blood pressure, contributing to increased risk for hypertension in obstructive sleep apnoea patients. We determined whether augmented vascular responses to increasing sympathetic vasomotor outflow, termed sympathetic neurovascular transduction (sNVT), accompanied changes in blood pressure following acute intermittent hypercapnic hypoxia in men. Lower body negative pressure was utilized to induce a range of sympathetic vasoconstrictor firing while measuring beat‐by‐beat blood pressure and forearm vascular conductance. IH reduced vascular shear stress and steepened the relationship between diastolic blood pressure and sympathetic discharge frequency, suggesting greater systemic sNVT. Our results indicate that recurring cycles of acute intermittent hypercapnic hypoxia characteristic of obstructive sleep apnoea could promote hypertension by increasing sNVT.
    Type of Medium: Online Resource
    ISSN: 0022-3751 , 1469-7793
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2020
    detail.hit.zdb_id: 1475290-6
    SSG: 12
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  • 9
    In: Clinical Autonomic Research, Springer Science and Business Media LLC
    Type of Medium: Online Resource
    ISSN: 0959-9851 , 1619-1560
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2024
    detail.hit.zdb_id: 2081578-5
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  • 10
    In: CHEST, Elsevier BV, Vol. 164, No. 3 ( 2023-09), p. 686-699
    Type of Medium: Online Resource
    ISSN: 0012-3692
    RVK:
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2023
    detail.hit.zdb_id: 2007244-2
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