Aortic stiffness contributes to greater pressor responses during static hand grip exercise in healthy young and middle-aged normotensive men.

Central arterial stiffness can influence exercise blood pressure (BP) by increasing the rise in arterial pressure per unit increase in aortic inflow. Whether central arterial stiffness influences the pressor response to isometric handgrip exercise (HG) and post-exercise muscle ischemia (PEMI), two common laboratory tests to study sympathetic control of BP, is unknown. We studied 46 healthy non-hypertensive males (23 young and 23 middle-aged) during HG (which increases in cardiac output [Q̇c]) and isolated metaboreflex activation PEMI (no change or decreases in Q̇c). Aortic stiffness (aortic pulse wave velocity [aPWV]; applanation tonometry via SphygmoCor) was measured during supine rest and was correlated to the pressor responses to HG and PEMI. BP (photoplethysmography) and muscle sympathetic nerve activity (MSNA) were continuously recorded at rest, during HG to fatigue (35 % maximal voluntary contraction) and 2-min of PEMI. aPWV was higher in middle-aged compared to young males (7.1 ± 0.9 vs 5.4 ± 0.7 m/s, P < 0.001). Middle-aged males also exhibited greater increases in systolic pressure (∆30 ± 11 vs 10 ± 8 mmHg) and MSNA (∆2313 ± 2006 vs 1387 ± 1482 %/min) compared to young males during HG (both, P < 0.03); with no difference in the Q̇c response (P = 0.090). Responses to PEMI were not different between groups. Sympathetic transduction during these stressors (MSNA-diastolic pressure slope) was not different between groups (P > 0.341). Middle-aged males displayed a greater increase in SBP per unit change of Q̇c during HG (∆SBP/∆Q̇c; 21 ± 18 vs 6 ± 10 mmHg/L/min, P = 0.004), with a strong and moderate relationship between the change in systolic (r = 0.53, P < 0.001) and diastolic pressure (r = 0.34, P = 0.023) and resting aPWV, respectively; with no correlation during PEMI. Central arterial stiffness can modulate pressor responses during stimuli associated with increases in cardiac output and sympathoexcitation in healthy males.

Aortic haemodynamics: the effects of habitual endurance exercise, age and muscle sympathetic vasomotor outflow in healthy men.

PURPOSE: 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.

Evidence of region-specific right ventricular functional adaptation in endurance-trained men in response to an acute volume infusion.

NEW FINDINGS: What is the central question of this study? Endurance athletes demonstrate altered regional right ventricular (RV) wall mechanics, characterized by lower basal deformation, in comparison to non-athletic control subjects at rest. We hypothesized that regional adaptations at the RV base reflect an enhanced functional reserve capacity in response to haemodynamic volume loading. What is the main finding and its importance? Free wall RV longitudinal strain is elevated in response to acute volume loading in both endurance athletes and control subjects. However, the RV basal segment longitudinal strain response to acute volume infusion is greater in endurance athletes. Our findings suggest that training-induced cardiac remodelling might involve region-specific adaptation in the RV functional response to volume manipulation. ABSTRACT: Eccentric remodelling of the right ventricle (RV) in response to increased blood volume and repetitive haemodynamic load during endurance exercise is well established. Structural remodelling is accompanied by decreased deformation at the base of the RV free wall, which might reflect an enhanced functional reserve capacity in response to haemodynamic perturbation. Therefore, in this study we examined the impact of acute blood volume expansion on RV wall mechanics in 16 young endurance-trained men (aged 24 ± 3 years) and 13 non-athletic male control subjects (aged 27 ± 5 years). Conventional echocardiographic parameters and the longitudinal strain and strain rate were quantified at the basal and apical levels of the RV free wall. Measurements were obtained at rest and after 7 ml/kg i.v. Gelofusine infusion, with and without a passive leg raise. After infusion, blood volume increased by 12 ± 4 and 14 ± 5% in endurance-trained individuals versus control subjects, respectively (P = 0.264). Both endurance-trained individuals (8 ± 10%) and control subjects (7 ± 9%) experienced an increase in free wall strain from baseline, which was also similar following leg raise (7 ± 10 and 6 ± 10%, respectively; P = 0.464). However, infusion evoked a greater increase in basal longitudinal strain in endurance-trained versus control subjects (16 ± 14 vs. 6 ± 11%; P = 0.048), which persisted after leg raise (16 ± 18 vs. 3 ± 11%; P = 0.032). Apical longitudinal strain and RV free wall strain rates were not different between groups and remained unchanged after infusion across all segments. Endurance training results in a greater contribution of longitudinal myocardial deformation at the base of the RV in response to a haemodynamic volume challenge, which might reflect a greater region-specific functional reserve capacity.

The influence of barosensory vessel mechanics on the vascular sympathetic baroreflex: insights into aging and blood pressure homeostasis.

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.

The influence of habitual endurance exercise on carotid artery strain and strain rate in young and middle-aged men.

NEW FINDINGS: 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.

Upward resetting of the vascular sympathetic baroreflex in middle-aged male runners.

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 ß-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.