Effect of acute sympathetic nervous system activation on flow-mediated dilation of brachial artery

Acute sympathetic activation blunts the hyperemic and vasodilatory response to passive leg movement

Heightened muscle sympathetic nerve activity (MSNA) contributes to impaired vasodilatory capacity and vascular dysfunction associated with aging and cardiovascular disease. The contribution of elevated MSNA to the vasodilatory response during passive leg movement (PLM) has not been adequately addressed. This study sought to test the hypothesis that elevated MSNA diminishes the vasodilatory response to PLM in healthy young males (n = 11, 25 ± 2 year). Post exercise circulatory occlusion (PECO) following 2 min of isometric handgrip (HG) exercise performed at 25% (ExPECO 25%) and 40% (ExPECO 40%) of maximum voluntary contraction was used to incrementally engage the metaboreceptors and augment MSNA. Control trials were performed without PECO (ExCON 25% and ExCON 40%) to account for changes due to HG exercise. PLM was performed 2 min after the cessation of exercise and central and peripheral hemodynamics were assessed. MSNA was directly recorded by microneurography in the peroneal nerve (n = 8). Measures of MSNA (i.e., burst incidences) increased during ExPECO 25% (+ 15 ± 5 burst/100 bpm) and ExPECO 40% (+ 22 ± 4 burst/100 bpm) and returned to pre-HG levels during ExCON trials. Vasodilation, assessed by the change in leg vascular conductance during PLM, was reduced by 16% and 44% during ExPECO 25% and ExPECO 40%, respectively. These findings indicate that elevated MSNA attenuates the vasodilatory response to PLM and that the magnitude of reduction in vasodilation during PLM is graded in relation to the degree of sympathoexcitation.

A century of exercise physiology: key concepts in neural control of the circulation

Early in the twentieth century, Walter B. Cannon (1871-1945) introduced his overarching hypothesis of "homeostasis" (Cannon 1932)-the ability to sustain physiological values within a narrow range necessary for life during periods of stress. Physical exercise represents a stress in which motor, respiratory and cardiovascular systems must be integrated across a range of metabolic stress to match oxygen delivery to oxygen need at the cellular level, together with appropriate thermoregulatory control, blood pressure adjustments and energy provision. Of these, blood pressure regulation is a complex but controlled variable, being the function of cardiac output and vascular resistance (or conductance). Key in understanding blood pressure control during exercise is the coordinating role of the autonomic nervous system. A long history outlines the development of these concepts and how they are integrated within the exercise context. This review focuses on the renaissance observations and thinking generated in the first three decades of the twentieth century that opened the doorway to new concepts of inquiry in cardiovascular regulation during exercise. The concepts addressed here include the following: (1) exercise and blood pressure, (2) central command, (3) neurovascular transduction with emphasis on the sympathetic nerve activity and the vascular end organ response, and (4) tonic neurovascular integration.

Median Nerves' Electrical Activation Reduces Ipsilateral Brachial Arteries' Blood Flow and Diameter

Purpose

Our main objective in this study was to determine whether there is a difference between ipsilateral and contralateral brachial arteries' flow parameters in response to median nerves' electrical activation.

Material and Methods

The study was conducted in healthy and active subjects. The arterial diameter and flow were measured using the probe from the brachial artery. Then, the median nerve was stimulated for 5 seconds via the bipolar stimulus electrode. Arterial diameter and flow were measured once more with the Doppler transducer, which kept going to monitor continuously just after the fifth stimulus. After a week, the same subjects are invited for the purpose of measuring the contralateral brachial arteries' vasomotor response to the same stimulus.

Results

Before electrical stimulation, the median flow rate was 72.15 ml/min; after stimulation, the median flow rate was 39.20 ml/min. The drop in flow after stimulation was statistically significant (P < 0.001). While the median value of brachial artery vessel diameter before median nerve stimulation in the entire study group was 3.50 mm, the median value of vessel diameter after stimulation was 2.90 mm. After stimulation, the median nerve diameter narrowed statistically significantly (P < 0.001). As for the contralateral brachial in response to the right median nerves' activation, no significant flow or diameter change was found (P = 0.600, P = 0.495, respectively).

Conclusion

We discovered that electrical stimulation of the median nerve caused significant changes in ipsilateral brachial artery blood flow and diameter in healthy volunteers. The same stimulation does not result in flow parameter changes in the contralateral brachial artery.

Carbohydrate ingestion attenuates the reduction in complex cognitive function and cerebral blood flow during prolonged passive heat stress in humans

PURPOSE

To determine whether carbohydrate ingestion would reduce cognitive dysfunction in humans following long duration passive heat stress (PHS) versus consuming electrolytes alone.

METHODS

Fifteen young (27 ± 4 y) healthy adults were exposed to 120 min of PHS through the use of a liquid perfused suit (50 °C) on two randomized visits. Subjects consumed fluids supplemented with electrolytes (E) or electrolytes + carbohydrates (E + C). Pre- and post-heat stress, body mass (BM) and plasma osmolality (pOsm) were measured. Heart rate (HR), blood pressure (BP), Physiological Strain Index (PSI), core temperature (Tc), plasma glucose, respiration rate (RR), end-tidal CO2 (PetCO2) and internal carotid artery (ICA) blood flow were recorded at baseline and every 15 min of heat stress. Cognitive function was assessed via the Automated Neuropsychological Assessment Metric at baseline and at 30- and 120 min during heat stress.

RESULTS

There were no significant differences between fluid conditions for BM, pOsm, PSI, Tc, RR or PetCO2. Plasma glucose was ∼75% greater in the E + C condition compared to the E condition after 90 min of PHS (P < 0.05). Cognitive function (120 min) was impaired following PHS only in E condition (P < 0.05) and performance on complex cognitive tasks were better by ∼22-340% in the E + C vs. E (P < 0.05). Compared to the E condition, HR and BP were lower and ICA blood flow, vascular conductance, and glucose delivery was ∼90% greater in the E + C after 90 min of PHS (P < 0.05).

CONCLUSIONS

These data are the first to demonstrate that carbohydrate ingestion may have a protective effect on cognitive function during long duration PHS. Furthermore, this protection was associated with preserved ICA blood flow and glucose delivery to the brain.

High-glycemic index meal acutely potentiates blood pressure response to static handgrip exercise in healthy humans

Blood glucose levels acutely increase postprandially depending on the type of meal consumed. However, it remains unclear whether postprandial hyperglycemia temporally affects cardiovascular responses to static handgrip exercise (SHG-ex). Thus, this study aimed to examine whether increased blood glucose induced by consumption of a high-glycemic index (HGI) meal affects pressor response to SHG-ex. A total of 14 healthy participants (7 women and 7 men) consumed an HGI meal, a low-glycemic index (LGI) meal, or no meal (control). Participants performed 30% maximal voluntary contraction SHG-ex followed by a postexercise muscle ischemia (PEMI) test before the meal and 60 min after consuming the meal. Blood glucose, plasma insulin, and plasma triglyceride levels were measured, and the area under the curve until 60 min (AUC0-60 min) after meal consumption was calculated. The HGI and LGI groups showed higher blood glucose and insulin AUC0-60 min than the control group (P < 0.001). At 60 min after the meal, the changes in blood pressure during SHG-ex were significantly greater in the HGI group, but not in the LGI group, than in the control group. The changes in blood pressure at the onset and end of SHG-ex 60 min after the meal were positively correlated with blood glucose AUC0-60 min (r = 0.321, P = 0.038; r = 0.402, P = 0.008, respectively) and plasma insulin AUC0-60 min (r = 0.339, P = 0.028; r = 0.302, P = 0.052, respectively). However, no association was observed during PEMI. These data suggest that postprandial hyperglycemia and hyperinsulinemia acutely exaggerate pressor response during SHG-ex in healthy young adults.NEW & NOTEWORTHY Postprandial hyperglycemia following consumption of a high-glycemic index (HGI) meal potentiated blood pressure response to static handgrip exercise (SHG-ex) in healthy young adults. These findings provide important insight into the role of the diet on acute circulatory response to exercise in healthy adults.

Pharmacological modulation of adrenergic tone alters the vasodilatory response to passive leg movement in young but not in old adults

The age-related increase in α-adrenergic tone may contribute to decreased leg vascular conductance (LVC) both at rest and during exercise in the old. However, the effect on passive leg movement (PLM)-induced LVC, a measure of vascular function, which is markedly attenuated in this population, is unknown. Thus, in eight young (25 ± 5 yr) and seven old (65 ± 7 yr) subjects, this investigation examined the impact of systemic β-adrenergic blockade (propanalol, PROP) alone, and PROP combined with either α1-adrenergic stimulation (phenylephrine, PE) or α-adrenergic inhibition (phentolamine, PHEN), on PLM-induced vasodilation. LVC, calculated from femoral artery blood flow and pressure, was determined and PLM-induced Δ peak (LVCΔpeak) and total vasodilation (LVCAUC, area under curve) were documented. PROP decreased LVCΔpeak (PROP: 4.8 ± 1.8, Saline: 7.7 ± 2.7 mL·mmHg-1, P < 0.001) and LVCAUC (PROP: 1.1 ± 0.7, Saline: 2.4 ± 1.6 mL·mmHg-1, P = 0.002) in the young, but not in the old (LVCΔpeak, P = 0.931; LVCAUC, P = 0.999). PE reduced baseline LVC (PE: 1.6 ± 0.4, PROP: 2.3 ± 0.4 mL·min-1·mmHg-1, P < 0.01), LVCΔpeak (PE: 3.2 ± 1.3, PROP: 4.8 ± 1.8 mL·min-1·mmHg-1, P = 0.004), and LVCAUC (PE: 0.5 ± 0.4, PROP: 1.1 ± 0.7 mL·mmHg-1, P = 0.011) in the young, but not in the old (baseline LVC, P = 0.199; LVCΔpeak, P = 0.904; LVCAUC, P = 0.823). PHEN increased LVC at rest and throughout PLM in both groups (drug effect: P < 0.05), however LVCΔpeak was only improved in the young (PHEN: 6.4 ± 3.1, PROP: 4.4 ± 1.5 mL·min-1·mmHg-1, P = 0.004), and not in the old (P = 0.904). Furthermore, the magnitude of α-adrenergic modulation (PHEN - PE) of LVCΔpeak was greater in the young compared with the old (Young: 3.35 ± 2.32, Old: 0.40 ± 1.59 mL·min-1·mmHg-1, P = 0.019). Therefore, elevated α-adrenergic tone does not appear to contribute to the attenuated vascular function with age identified by PLM.NEW & NOTEWORTHY Stimulation of α1-adrenergic receptors eliminated age-related differences in passive leg movement (PLM) by decreasing PLM-induced vasodilation in the young. Systemic β-blockade attenuated the central hemodynamic component of the PLM response in young individuals. Inhibition of α-adrenergic receptors did not improve the PLM response in older individuals, though withdrawal of α-adrenergic modulation augmented baseline and maximal vasodilation in both groups. Accordingly, α-adrenergic signaling plays a role in modulating the PLM vasodilatory response in young but not in old adults, and elevated α-adrenergic tone does not appear to contribute to the attenuated vascular function with age identified by PLM.

Mental stress augments central artery stiffness in young individuals of both sexes

Mental stress is a daily stimulus that can acutely activate the sympathetic nervous system. Whether sympathetic stimulation can augment central artery stiffness (CAS) has not yet been well documented. Moreover, sex differences in sympathetic neurovascular transduction have been reported. We assessed whether mental stress augments CAS in both sexes and whether any CAS increase is blunted in women compared with men. The hf-PWV (heart-femoral pulse wave velocity; index of CAS), MAP (mean arterial pressure), PP (pulse pressure), TPR (total peripheral resistance), and HR (heart rate) were measured in 26 young individuals (13 men, 13 women) at rest and throughout a 10-minute bout of stress induced by mental arithmetic. Data over the mental stress period were compared to the preceding baseline values and between sexes. Mental stress increased hf-PWV, MAP, PP, and HR from baseline throughout the entire stimulation period (p < .005). TPR diminished in the first minute of stimulation (p < .001) in both sexes and increased in the last minutes in women only (p < .005). Hf-PWV was lower in women than men (p < .001) at rest and during mental stress, but the changes from baseline were similar in both sexes. There were sex differences in the PP and TPR changes, which were evident at different times of stimulation. Mental stress increased CAS in both sexes throughout the stimulation period. Although values of CAS were lower in women both at rest and during mental stress, the CAS increase due to mental stress was similar in both sexes.

Circadian Variations in Sympathetic Vasoconstriction in Older Adults with and Without Type 2 Diabetes

INTRODUCTION

An impact of the sympathetic nervous system in the higher rate of cardiovascular events in the early morning compared to the evening has been claimed. Augmented sympathetic vasoconstriction increases cardiovascular risk by augmenting pulse pressure and cardiac afterload. Type 2 diabetes (T2DM) further increases sympathetic neurovascular transduction and cardiovascular risk.

AIM

We assessed whether peripheral vasoconstriction triggered by a standardized sympathetic stressor is augmented at 6am vs 9pm in adults between 50-80 years with type 2 diabetes (T2DM50-80) vs healthy ones (H50-80).

METHODS

Mean values of sympathetic vasoconstrictor responsiveness (SVR), vascular conductance (VC), brachial artery blood flow, and mean arterial pressure were measured on the contralateral forearm over two 5-minute bouts of rest and handgrip-mediated sympathetic stimulation, respectively.

RESULTS

Although baseline VC values were lower (p < 0.01) in the morning vs evening in both groups, SVR values in response to sympathoexcitation were similar in H50-80 (- 0.43 ± 12.44 vs - 2.57 ± 11.63 %, p = 0.73) and T2DM50-80 (+6.64 ± 10.67 vs +5.21 ± 7.64 %, p = 0.90), but higher (p < 0.01) in T2DM50-80 vs H50-80 at both day hours. Individuals with T2DM reported positive SVR values and VC change-scores, while healthy individuals reported statistically different (p < 0.02) negative SVR values and VC change-scores.

CONCLUSION

Peripheral vasoconstriction triggered by a standardized sympathetic stressor is similar between morning and evening, regardless of T2DM and different baseline VC values. However, peripheral vasoconstriction responsiveness is blunted in individuals with T2DM as handgrip-mediated sympathoexcitation induces vasodilation in the contralateral forearm in adults with T2DM and vasoconstriction in healthy age-matched controls, highlighting a neurovascular response altered by T2DM.

Sympathetic-mediated blunting of forearm vasodilation is similar between young men and women

BACKGROUND

The in-vivo regulation of vascular conductance (VC) is a continuous balance between endothelial vasodilation and sympathetic vasoconstriction. Although women may report blunted sympathetic vasoconstriction along with higher endothelial vasodilation than men, it is currently unknown whether the interaction between vasoconstriction and vasodilation leads to different regulation of VC between sexes. This study assessed sex differences in sympathetic-mediated blunting of endothelial vasodilation after a brief period of ischemia and whether any restriction of vasodilation blunts tissue blood flow (BF) and re-oxygenation.

METHODS

13 young women and 12 young men underwent two 5-min forearm circulatory occlusions followed by reperfusion, one in basal conditions and the other during cold pressor test-induced sympathetic activation (SYMP). Brachial artery diameter and BF, mean arterial pressure, total peripheral resistance (TPR), and thenar eminence oxygenation were collected. Percent changes normalized to baseline values of forearm VC, brachial artery BF and flow-mediated dilation (FMD), TPR, and hand oxygenation after circulatory reperfusion were calculated.

RESULTS

TPR increased during SYMP in men (p = 0.019) but not in women (p = 0.967). Women showed a greater brachial artery FMD than men (p = 0.004) at rest, but sex differences disappeared after normalization to shear rate and baseline diameter (p > 0.11). The percent increases from baseline of peak and average forearm VC after circulatory reperfusion did not differ between sexes in basal conditions (p > 0.98) or during SYMP (p > 0.97), and were restrained by SYMP similarly in both sexes (p < 0.003) without impairing the hand re-oxygenation (p > 0.08) or average hyperemic response (p > 0.09).

CONCLUSIONS

Although women may report blunted sympathetic vasoconstriction than men when assessed separately, the similar sympathetic-mediated restriction of vasodilation suggests a similar dynamic regulation of VC between sexes. SYMP-mediated restrictions of the normal forearm vasodilation do not impair the average hyperemic response and hand re-oxygenation in both sexes.

The acute effect of a laboratory shame induction protocol on endothelial function in young, healthy adults

NEW FINDINGS

What is the central question of this study? Shame is a form of social stress which involves internalizing social devaluations imposed by others. The aim of this study was to determine, for the first time, how acutely experiencing shame impacts endothelial function. What is the main finding and its importance? Brachial artery flow-mediated dilation, an index of endothelial function, was impaired following an intervention that acutely increased self reported shame. This occurred without increases in cortisol or tumor necrosis factor alpha receptor binding. Frequent or prolonged shame induced endothelial dysfunction could have important cardiovascular consequences.

ABSTRACT

Objective The objective of this study was to examine the impact of a shame induction protocol on endothelial function. Methods Fifteen participants (n = 7 men, n = 8 women) completed both a written shame induction and control protocol on two different experimental days. Pre- and post-protocol we assessed: 1) Endothelial function and arterial shear rate via a standard brachial artery reactive hyperemia flow-mediated dilation (FMD) test across two post-intervention time points (15 and 35-min post); 2) Perceived shame via the Experiential Shame Scale (ESS), and; 3) Cortisol and sTNFαRII (soluble tumor necrosis factor alpha receptor) through oral fluid analysis. Results Shame increased after the shame induction protocol (pre: 2.9±.6 vs. post: 3.7±.5, p<.001) but not the control protocol (pre: 3.0±.5 vs. post: 2.8±.5, p = .15) (protocol by time interaction: p<.001). When all three time points were included in the analysis, %FMD did not change over time. Considering only the lowest point, %FMD significantly decreased in response to the shame protocol (pre: 4.8±1.9 vs. post: 3.2±1.6, p<.001) but not the control protocol (4.2±1.8 vs. post: 3.8±1.5, p = .45) (protocol by time interaction: p = .035). Covariation of the shear rate stimulus for FMD did not alter the FMD results. When including both the control and shame protocol, but not the shame protocol alone, increased shame was significantly associated with decreased FMD (r = -.37, p<.046). There were no significant time by protocol interaction effects for cortisol or sTNFαRII. Conclusions Temporary increases in shame may cause transient endothelial dysfunction which, if chronically repeated, could manifest as reduced vasoprotection against atherosclerosis. This article is protected by copyright. All rights reserved.

Effects of acute sympathetic activation on the central artery stiffness after strenuous endurance exercise

Purpose

Augmented central arterial stiffness (CAS) increases cardiovascular risk. CAS can be augmented by physical exercise and sympathetic activation (SYMP) induced by stressful stimuli. Interestingly, sympathetic vasoconstriction triggered by a sympathetic stimulant is augmented immediately after a strenuous half-marathon compared to at rest. This study assessed whether CAS also augments more post- than pre-half-marathon in response to SYMP. Such assessment takes on relevance considering the growing popularity of strenuous, long-distance endurance exercises.

Methods

13 healthy recreational runners (age 46.1 ± 6.5 years; $$V^{\prime}{\text{O}}_{2} \max$$ V ′ O 2 max 54.23 ± 9.31 mlO2/min/kg) provided the following measurements prior to and within 10 min following a strenuous half-marathon: beat-by-beat aortic pulse wave velocity (aPWV; index of CAS), mean blood pressure, and heart rate assessment. Measures were performed at rest and during a 2 min handgrip-mediated SYMP. The effects of the half-marathon and SYMP were assessed by two-way repeated-measures ANOVA.

Results

Measurements of the aPWV pre- and post-race were not significantly different (7.5 ± 0.8 vs 7.8 ± 0.8 m/s, p = 0.34; pre- vs post-race). 2 min of SYMP increased the baseline aPWV post-race (7.8 ± 0.8 vs 8.4 ± 0.8, p = 0.003; rest vs SYMP) but not pre-race (7.5 ± 0.8 vs 7.9 ± 0.9, p = 0.21).

Conclusion

The baseline aPWV assessed 7 to 8 min after a strenuous half-marathon is similar to that pre-race in healthy runners. This agrees with previous studies suggesting CAS being at or below resting values > 5 min following completion of aerobic exercises. The same sympathetic stressor augments CAS to a greater extent 8–10 min post-race than pre-race, suggesting a greater post-exercise stiffening of central artery segments triggered by the same task.

Effect of Upright Posture on Endothelial Function in Women and Men

Women are more prone to orthostatic intolerance compared to men and have a greater vasodilatory capacity. We investigated the hypothesis that women would have greater peripheral flow-mediated dilation (FMD) while in the upright posture compared to men, which could contribute to this phenomenon. In young healthy women (age: 20 ± 3, BMI: 27 ± 5 kg/m², n = 10) and men (age = 21 ± 2, BMI: 27 ± 8 kg/m², n = 8), we assessed FMD of the brachial artery and hemodynamics to determine endothelial function during the supine and 70° head-up tilt postures (randomized). The brachial artery was kept at heart level in both trials. We observed that FMD increased in both sexes during tilt (Women: 11.9 ± 5.3 to 15.7 ± 5.6%; Men: 8.4 ± 3.2 to 14.6 ± 3.4%, Main effect of tilt p = 0.005) which was not due to changes in blood pressure or shear stress. There were no interaction effects between sex and posture. In a second cohort of women (age: 22 ± 3, BMI: 23 ± 3 kg/m², n = 9) and men (age: 22 ± 2, BMI: 25 ± 8 kg/m², n = 8), we investigated reactive hyperemia by peripheral arterial tonometry (LnRHI) via EndoPAT. Interestingly, we found that the EndoPAT response was decreased in both sexes during tilt (LnRHI: Men: 0.70 ± 0.28 to 0.59 ± 0.40, Women: 0.52 ± 0.23 to 0.30 ± 0.32, Main effect of tilt p = 0.037). We previously found that FMD is related to coronary responses to acetylcholine and adenosine whereas EndoPAT is related to coronary responses to dobutamine. Therefore, we suggest that sympathetic mediated dilation is attenuated in the upright posture while the increased vasodilatory response as measured by FMD in the tilt posture could be attributed to increasing metabolite production from postural muscles.

Effect of acute sympathetic activation on leg vasodilation before and after endurance exercise

Vascular conductance (VC) regulation involves a continuous balance between metabolic vasodilation and sympathetic vasoconstriction. Endurance exercise challenges the sympathetic control on VC due to attenuated sympathetic receptor responsiveness and persistence of muscle vasodilation, especially in endurance athletes, predisposing them to blood pressure control dysfunctions. This study assessed whether acute handgrip-mediated sympathetic activation (SYMP) restrains sudden leg vasodilation before and after a half-marathon. Prior to, and within the 20 min following the race, 11 well-trained runners underwent two single passive leg movement (SPLM) tests to suddenly induce leg vasodilation, one without and the other during SYMP. Leg blood flow and mean arterial pressure were measured to assess changes in leg VC. Undertaking 60 sec of SYMP reduced the baseline leg VC both before (4.0 ± 1.0 vs. 3.3 ± 0.7 ml/min/mmHg; P=0.01; NO SYMP vs. SYMP, respectively) and after the race (4.6 ± 0.8 vs. 3.9 ± 0.8 ml/min/mmHg; P=0.01). However, SYMP did not reduce leg peak vasodilation immediately after the SPLM either before (11.5 ± 4.0 vs. 12.2 ± 3.8 ml/min/mmHg; P=0.35) or after the race (7.2 ± 2.0 vs. 7.3 ± 2.6 ml/min/mmHg; P=0.96). Furthermore, SYMP did not blunt the mean leg vasodilation over the 60 sec after the SPLM before (5.1 ± 1.7 vs. 5.9 ± 2.5 ml/min/mmHg; P=0.14) or after the race (4.8 ± 1.3 vs. 4.2 ± 1.5 ml/min/mmHg; P=0.26). This data suggest that the release of local vasoactive agents effectively opposes any preceding handgrip-mediated augmented vasoconstriction in endurance athletes before and after a half-marathon. Handgrip-mediated SYMP might improve normal vasoconstriction while athletes are still, but not necessarily while they move, as movements can induce a release of vasoactive molecules.

Effect of acute sympathetic activation on leg vasodilation before and after endurance exercise

Vascular conductance (VC) regulation involves a continuous balance between metabolic vasodilation and sympathetic vasoconstriction. Endurance exercise challenges the sympathetic control on VC due to attenuated sympathetic receptor responsiveness and persistence of muscle vasodilation, especially in endurance athletes, predisposing them to blood pressure control dysfunctions. This study assessed whether acute handgrip-mediated sympathetic activation (SYMP) restrains sudden leg vasodilation before and after a half-marathon. Prior to, and within the 20 min following the race, 11 well-trained runners underwent two single passive leg movement (SPLM) tests to suddenly induce leg vasodilation, one without and the other during SYMP. Leg blood flow and mean arterial pressure were measured to assess changes in leg VC. Undertaking 60 sec of SYMP reduced the baseline leg VC both before (4.0 ± 1.0 vs. 3.3 ± 0.7 ml/min/mmHg; P=0.01; NO SYMP vs. SYMP, respectively) and after the race (4.6 ± 0.8 vs. 3.9 ± 0.8 ml/min/mmHg; P=0.01). However, SYMP did not reduce leg peak vasodilation immediately after the SPLM either before (11.5 ± 4.0 vs. 12.2 ± 3.8 ml/min/mmHg; P=0.35) or after the race (7.2 ± 2.0 vs. 7.3 ± 2.6 ml/min/mmHg; P=0.96). Furthermore, SYMP did not blunt the mean leg vasodilation over the 60 sec after the SPLM before (5.1 ± 1.7 vs. 5.9 ± 2.5 ml/min/mmHg; P=0.14) or after the race (4.8 ± 1.3 vs. 4.2 ± 1.5 ml/min/mmHg; P=0.26). This data suggest that the release of local vasoactive agents effectively opposes any preceding handgrip-mediated augmented vasoconstriction in endurance athletes before and after a half-marathon. Handgrip-mediated SYMP might improve normal vasoconstriction while athletes are still, but not necessarily while they move, as movements can induce a release of vasoactive molecules.

The deleterious effects of acute hypoxia on microvascular and large vessel endothelial function

NEW FINDINGS

What is the central question of this study? The aim was primarily to determine the effect of hypoxia on microvascular function and secondarily whether superior cardiorespiratory fitness is protective against hypoxia-induced impairment in vascular function. What is the main finding and its importance? Hypoxia reduced endothelium-dependent but not endothelium-independent microvascular function. The extent of impairment was twofold higher in the microcirculation compared with the large blood vessels. This study suggests that individuals with superior cardiorespiratory fitness might preserve microvascular function in hypoxia. These findings highlight the sensitivity of the microvascular circulation to hypoxia.

ABSTRACT

Hypoxia is associated with diminished bioavailability of the endothelium-derived vasodilator, nitric oxide (NO). Diminished NO bioavailability can have deleterious effects on endothelial function. The endothelium is a heterogeneous tissue; therefore, a comprehensive assessment of endothelial function is crucial to understand the significance of hypoxia-induced endothelial dysfunction. We hypothesized that acute hypoxia would have a deleterious effect on microvascular and large vessel endothelial function. Twenty-nine healthy adults [24 (SD = 4 ) years of age] completed normoxic and hypoxic [inspired O₂  fraction = 0.209] trials in this double-blinded, counterbalanced crossover study. After 30 min, we assessed the laser Doppler imaging-determined perfusion response to iontophoresis of ACh as a measure of endothelium-dependent microvascular function and iontophoresis of sodium nitroprusside as a measure of endothelium-independent microvascular function. After 60 min, we assessed brachial flow-mediated dilatation as a measure of large vessel endothelial function. Thirty minutes of hypoxia reduced endothelium-dependent microvascular function determined by the perfusion response to ACh (median difference (x̃∆) = -109% {interquartile range: 542.7}, P < 0.05), but not endothelium-independent microvascular function determined by the perfusion response to sodium nitroprusside (x̃∆ = 69% {interquartile range: 453.7}, P = 0.6). In addition, 60 min of hypoxia reduced allometrically scaled flow-mediated dilatation compared with normoxia ( x ¯ Δ = - 1.19 [95% CI = -1.80, -0.58 (Confidence Intervals)]%, P < 0.001). The decrease in microvascular endothelial function was associated with cardiorespiratory fitness (r  = 0.45, P = 0.02). In conclusion, acute exposure to normobaric hypoxia significantly reduced endothelium-dependent vasodilatory capacity in small and large vessels. Collectively, these findings highlight the sensitivity of the microvascular circulation to hypoxic insult, particularly in those with poor cardiorespiratory fitness.

High-but not moderate-intensity exercise acutely attenuates hypercapnia-induced vasodilation of the internal carotid artery in young men

PURPOSE

Exercise-induced increases in shear rate (SR) across different exercise intensities may differentially affect hypercapnia-induced vasodilation of the internal carotid artery (ICA), a potential index of cerebrovascular function. We aimed to elucidate the effects of exercise intensity on ICA SR during exercise and post-exercise hypercapnia-induced vasodilation of the ICA in young men.

METHODS

Twelve healthy men completed 30 min of cycling at moderate [MIE; 65 ± 5% of age-predicted maximal heart rate (HR_max)] and high (HIE; 85 ± 5% HR_max) intensities. Hypercapnia-induced vasodilation was induced by 3 min of hypercapnia (target end-tidal partial pressure of CO₂ + 10 mmHg) and was assessed at pre-exercise, 5 min and 60 min after exercise. Doppler ultrasound was used to measure ICA diameter and blood velocity during exercise and hypercapnia tests.

RESULTS

SR was not altered during either exercise (interaction and main effects of time; both P > 0.05). ICA conductance decreased during HIE from resting values (5.1 ± 1.3 to 3.2 ± 1.0 mL·min^-1·mmHg^-1; P < 0.01) but not during MIE (5.0 ± 1.3 to 4.0 ± 0.8 mL·min^-1·mmHg^-1; P = 0.11). Consequently, hypercapnia-induced vasodilation declined immediately after HIE (6.9 ± 1.7% to 4.0 ± 1.4%; P < 0.01), but not after MIE (7.2 ± 2.1% to 7.3 ± 1.8%; P > 0.05). Sixty minutes after exercise, hypercapnia-induced vasodilation returned to baseline values in both trials (MIE 8.0 ± 3.1%; HIE 6.4 ± 2.9%; both P > 0.05).

CONCLUSION

The present study showed blunted hypercapnia-induced vasodilation of the ICA immediately after high-intensity exercise, but not a moderate-intensity exercise in young men. Given that the acute response is partly linked to the adaptive response in the peripheral endothelial function, the effects of aerobic training on cerebrovascular health may vary depending on exercise intensity.

Dependency of flow-mediated vasodilatation from basal nitric oxide activity

BACKGROUND

Flow-mediated vasodilatation (FMD) has become one of the most widely assessed parameters to analyse endothelial and vascular function in cardiovascular medicine. The degree of contribution of nitric oxide (NO) to FMD is inconclusive and varies widely depending on the device used. In this study, we used a semi-automatic ultrasound device to analyse to what extent basal NO activity contributes to FMD of the brachial artery.

METHODS

FMD was assessed with the UNEX EF device in a cross-over single blinded randomized study at baseline and then during infusion of either a NO-synthase-inhibitor (NG-monomethyl-L-arginine (L-NMMA)) or saline. The analysis was repeated after 1 week with the alternative infusion of L-NMMA or saline. All measurements were analysed both automatically and by a technician manually.

RESULTS

In total, 25 healthy men subjects completed the study. Diastolic blood pressure and heart rate significantly changed during infusion of L-NMMA. Infusion of L-NMMA reduced FMD significantly (-37%, p = 0.002). Saline solution had no effect on FMD (+14%, p = 0.392). Change in FMD was significantly different between the groups (ΔFMD_L-NMMA vs. ΔFMD_saline , p = 0.032). There was a statistically significant correlation between automatically analysed results and those obtained by an experienced technician (FMD_saline : r = 0.822, p < 0.001; FMD_L-NMMA : r = 0.645, p = 0.007).

CONCLUSION

The influence of NO on FMD is approximately 40% if assessed using the UNEX EF. Prior to use FMD as a marker of endothelial dysfunction, we should explore different methods including various duration of forearm ischaemia to increase NO dependency of FMD.

Vascular dysfunction and oxidative stress caused by acute formaldehyde exposure in female adults

Formaldehyde (FA) is a common, volatile organic compound used in organic preservation with known health effects of eye, nose, and throat irritation linked to oxidative stress and inflammation. Indeed, long-term FA exposure may provoke skin disorders, cancer, and cardiovascular disease. However, the effects of short-term FA exposure on the vasculature have yet to be investigated. We sought to investigate the impact of an acute FA exposure on 1) macrovascular function in the arm (brachial artery flow-mediated dilation, FMD), 2) microvascular function in the arm (brachial artery reactive hyperemia, RH) and leg (common femoral artery, supine passive limb movement, PLM), and 3) circulating markers of oxidative stress (xanthine oxidase, XO; protein carbonyl, PC; and malondialdehyde, MDA) and inflammation (C-reactive protein, CRP). Ten (n = 10) healthy females (23 ± 1 yr) were studied before and immediately after a 90-min FA exposure [(FA): 197 ± 79 ppb] in cadaver dissection laboratories. Brachial artery FMD% decreased following FA exposure (Pre-FA Exp: 9.41 ± 4.21%, Post-FA Exp: 6.74 ± 2.57%; P = 0.043), and FMD/shear decreased following FA exposure (Pre-FA Exp: 0.13 ± 0.07 AU, Post-FA Exp: 0.07 ± 0.03 AU; P = 0.016). The area under the curve for brachial artery RH (Pre-FA Exp: 481 ± 191 ml, Post-FA Exp: 499 ± 165 ml) and common femoral artery PLM (Pre-FA Exp: 139 ± 95 ml, Post-FA Exp: 129 ± 64 ml) were unchanged by FA exposure (P > 0.05). Circulating MDA increased (Pre-FA Exp: 4.8 ± 1.3 µM, Post-FA Exp: 6.3 ± 2.2 µM; P = 0.047) while XO, PC, and CRP were unchanged by FA exposure (P > 0.05). These initial data suggest a short FA exposure can adversely alter vascular function and oxidative stress, influencing cardiovascular health.NEW & NOTEWORTHY This study was the first to investigate the implications of acute formaldehyde (FA) exposure on adult female vascular function in the arms and legs. The main findings of this study were a decrease in conduit vessel function without any alteration to microvascular function following a 90-min FA exposure. Additionally, the oxidative stress marker malondialdehyde increased after FA exposure. Taken together, these results suggest acute FA exposure have deleterious implications for the vasculature and redox balance.Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/formaldehyde-exposure-decreases-vascular-function/.

Potential Implications of Blood Flow Restriction Exercise on Vascular Health: A Brief Review

Blood flow restriction (BFR) exercise (a.k.a. occlusion training) has emerged as a viable surrogate to traditional heavy-load strength rehabilitation training for a broad range of clinical populations including elderly subjects and rehabilitating athletes. A particular benefit of BFR exercise is the lower stress upon the joints as compared to traditional heavy resistance training, with similar gains in muscle strength and size. The application of an inflatable cuff to the proximal portion of the limbs increases the pressure required for venous return, leading to changes in venous compliance and wall tension. However, it is not known if long-term benefits of BFR exercise on muscle strength and size outweigh potential short and long-term complications on vascular health. BFR exercise could lead to clinical deterioration of the vasculature along with sympathetic overactivity and decreased vascular function associated with retrograde shear stress. This raises a fundamental question: Given the concern that excessive restriction could cause injury to endothelial cells and might cause detrimental effects on endothelial function, even in healthy individuals, should we critically re-evaluate the safety of this method for the general population? From this perspective, the purpose of this manuscript is to review the effects of BFR exercise on vascular function, and to provide relevant insights for training practice as well as future directions for research.

Chronic stress and endothelial dysfunction: mechanisms, experimental challenges, and the way ahead

Although chronic stress is an important risk factor for cardiovascular diseases (CVD) onset, the underlying mechanisms driving such pathophysiological complications remain relatively unknown. Here, dysregulation of innate stress response systems and the effects of downstream mediators are strongly implicated, with the vascular endothelium emerging as a primary target of excessive glucocorticoid and catecholamine action. Therefore, this review article explores the development of stress-related endothelial dysfunction by focusing on the following: 1) assessing the phenomenon of stress and complexities surrounding this notion, 2) discussing mechanistic links between chronic stress and endothelial dysfunction, and 3) evaluating the utility of various preclinical models currently employed to study mechanisms underlying the onset of stress-mediated complications such as endothelial dysfunction. The data reveal that preclinical models play an important role in our efforts to gain an increased understanding of mechanisms underlying stress-mediated endothelial dysfunction. It is our understanding that this provides a good foundation going forward, and we propose that further efforts should be made to 1) more clearly define the concept of stress and 2) standardize protocols of animal models with specific guidelines to better indicate the mental complications that are simulated.

Arterial structure and function during and after long-duration spaceflight

Spaceflight missions expose astronauts to increased risk of oxidative stress and inflammatory damage that might accelerate the development of asymptomatic cardiovascular disease. The purpose of this investigation was to determine whether long-duration spaceflight (>4 mo) results in structural and functional changes in the carotid and brachial arteries. Common carotid artery (CCA) intima-media thickness (cIMT), CCA distensibility and stiffness, and brachial artery endothelium-dependent and -independent vasodilation were measured in 13 astronauts (10 men, 3 women) ~180 and 60 days before launch, during the mission on ~15, 60, and 160 days of spaceflight, and within 1 wk after landing. Biomarkers of oxidative stress and inflammation were measured at corresponding times in fasting blood samples and urine samples from 24- or 48-h pools. Biomarkers of oxidative stress and inflammation increased during spaceflight, but most returned to preflight levels within 1 wk of landing. Mean cIMT, CCA stiffness, and distensibility were not significantly different from preflight at any time. As a group, neither mean endothelium-dependent nor -independent vasodilation changed from preflight to postflight, but changes within individuals in endothelial function related to some biomarkers of oxidative stress. Whereas biomarkers of oxidative stress and inflammation are elevated during spaceflight, CCA and brachial artery structure and function were not changed by spaceflight. It is unclear whether future exploration missions, with an extended duration in altered gravity fields and higher radiation exposure, may be problematic.NEW & NOTEWORTHY Carotid artery structure and stiffness did not change on average in astronauts during long-duration spaceflight (<12 mo), despite increased oxidative stress and inflammation. Most oxidative stress and inflammation biomarkers returned to preflight levels soon after landing. Brachial artery structure and function also were unchanged by spaceflight. In this group of healthy middle-aged male and female astronauts, spaceflight in low Earth orbit does not appear to increase long-term cardiovascular health risk.

Endothelial function in response to exercise in the cold in patients with coronary artery disease

BACKGROUND

Regular long-term physical exercise has favourable effects on endothelial function in patients with coronary artery disease (CAD). However, the effects of an acute exercise bout in the cold on endothelial function are not known.

METHODS

At first, the effects of moderate-intensity aerobic lower-body exercise were assessed in CAD patients (n = 16) in a neutral [+22°C] and cold [-15°C] environment. Secondly, responses to static and dynamic upper-body exercise in a neutral [+22°C] and cold [-15°C] environment were investigated in CAD patients (n = 15). All experiments were performed in a random order. Endothelial function was measured by flow-mediated dilation (FMD) of the brachial artery in response to reactive hyperaemia, before and after the exposures in a neutral environment.

RESULTS

No significant temperature*exercise*condition (pre-post) interaction was observed in FMD% when comparing rest versus aerobic exercise or static versus dynamic upper-body exercise. Relative reactive hyperaemia during FMD protocol, measured by changes in shear rate, was elevated after rest compared to aerobic exercise (p = .001) and after static compared to dynamic upper-body exercise (p < .001). However, no significant temperature*exercise*condition interaction was observed when FMD% was normalized for shear rate.

CONCLUSIONS

Endothelial function to an acute bout of exercise among CAD patients was not modified by the environmental temperature where the exercise was performed. The present findings argue against the hypothesis that exercise in cold environmental conditions impairs endothelial function in patients with CAD.

Self-Reported Everyday Psychosocial Stressors Are Associated With Greater Impairments in Endothelial Function in Young Adults With Major Depressive Disorder

Background

Despite the epidemiological associations between psychological stress, depression, and increased cardiovascular disease risk, no studies have examined the relation between naturally occurring psychosocial stressors and directly measured microvascular function in adults with major depressive disorder (MDD). We tested the hypothesis that young adults with MDD exposed to everyday psychosocial stressors would exhibit more severe impairments in endothelium‐dependent dilation (EDD) compared with: (1) healthy nondepressed adults (HCs); and (2) adults with MDD without acute psychosocial stress exposure.

Methods and Results

Twenty HCs (22±1 years) and 23 otherwise healthy adults with MDD (20±0.3 years) participated in the study. Participants completed a psychosocial experiences survey to document their exposure to any of 6 stressors over the preceding 24 hours (eg, arguments, work stressors). Red cell flux (laser Doppler flowmetry) was measured during graded intradermal microdialysis perfusion of acetylcholine (10⁻¹⁰ to 10⁻¹mol/L). EDD was expressed as a percentage of maximum vascular conductance (flux/mm Hg). Multiple linear regression was used to determine the associations between stress, EDD, and MDD. Adults with MDD reported a greater number and severity of psychosocial stressors compared with HCs (all P<0.05). EDD was blunted in adults with MDD (HCs: 91±2 versus MDD: 74±3%; P<0.001). Exposure to any stressor was related to more severe impairments in EDD in patients with MDD (no stressor: 81±3 versus 1+ stressors: 69±5%; P=0.04) but not in HCs (P=0.48).

Conclusions

These data indicate that exposure to everyday psychosocial stressors is associated with greater impairments in endothelial function in patients with MDD, suggesting a potential mechanistic link between daily stress and depression in increased cardiovascular risk.

The impact of hypoxaemia on vascular function in lowlanders and high altitude indigenous populations

Exposure to hypoxia elicits widespread physiological responses that are critical for successful acclimatization; however, these responses may induce apparent maladaptive consequences. For example, recent studies conducted in both the laboratory and the field (e.g. at high altitude) have demonstrated that endothelial function is reduced in hypoxia. Herein, we review the several proposed mechanism(s) pertaining to the observed reduction in endothelial function in hypoxia including: (i) changes in blood flow patterns (i.e. shear stress), (ii) increased inflammation and production of reactive oxygen species (i.e. oxidative stress), (iii) heightened sympathetic nerve activity, and (iv) increased red blood cell concentration and mass leading to elevated nitric oxide scavenging. Although some of these mechanism(s) have been examined in lowlanders, less in known about endothelial function in indigenous populations that have chronically adapted to environmental hypoxia for millennia (e.g. the Peruvian, Tibetan and Ethiopian highlanders). There is some evidence indicating that healthy Tibetan and Peruvian (i.e. Andean) highlanders have preserved endothelial function at high altitude, but less is known about the Ethiopian highlanders. However, Andean highlanders suffering from chronic mountain sickness, which is characterized by an excessive production of red blood cells, have markedly reduced endothelial function. This review will provide a framework and mechanistic model for vascular endothelial adaptation to hypoxia in lowlanders and highlanders. Elucidating the pathways responsible for vascular adaption/maladaptation to hypoxia has potential clinical implications for disease featuring low oxygen delivery (e.g. heart failure, pulmonary disease). In addition, a greater understanding of vascular function at high altitude will clinically benefit the global estimated 85 million high altitude residents.

Acute hypotension attenuates brachial flow-mediated dilation in young healthy men

PURPOSE

This study aimed to test our hypothesis that acute hypotension attenuates brachial flow-mediated dilation (FMD) as an index of endothelial function in healthy humans.

METHODS

Twelve healthy men (21.8 ± 1.6 years, body mass index; 22.2 ± 1.6 kg/m²) participated in this study. Brachial FMD was measured in three trials: standardized FMD protocol (control trial), abrupt decrease in blood pressure (BP) via thigh cuff inflation-deflation (hypotension trial) and decrease in shear rate (SR) via a shortened forearm occlusion time (SR reduction trial). Brachial diameter and blood velocity were measured using Duplex ultrasound.

RESULTS

Mean arterial pressure during reactive hyperaemia showed a marked decrease in the hypotension trial (- 23.7 ± 6.0 mmHg), but not in the control and SR reduction trials. SR area under the curve was attenuated in the SR reduction trial (P < 0.001), but not in the control and hypotension trials (P = 0.316). Consequently, FMD was attenuated in the hypotension and SR reduction trials compared with that in the control trial (P = 0.003 and P = 0.043, respectively), and was attenuated to a greater extent in the hypotension trial compared with the SR reduction trial (P = 0.006; control, 6.9 ± 3.5%; hypotension, 3.5 ± 1.7%; SR reduction, 5.0 ± 2.2%). After adjusting FMD using SR, FMD remained attenuated in the hypotension trial (P = 0.014), but not in the SR reduction trial.

CONCLUSION

Our findings indicate that arterial pressure as well as sympathetic nervous system activation could be an important determinant of FMD. Blunted FMD of peripheral arteries may be a rational response to restore BP and/or prevent further reduction of BP following acute hypotension in healthy humans.

The effects of sympathetic activity induced by ice water on blood flow and brachial artery flow-mediated dilatation response in healthy volunteers

Objective

To investigate the association between sympathetic activity, reactive hyperemia and brachial artery flow-mediated dilation (FMD).

Background

It is claimed that major surgery has an impact on endothelial function, as observed by post-operative reduced brachial artery FMD response. However, another explanation for the observed reduced FMD response post-operatively may be sympathetic stress-induced reduction in blood flow.

Methods

Seventeen healthy volunteers with a median age (25^th-75^th percentiles) of 23.5 (23–24.8) years were recruited. Participants’ brachial blood flow and FMD response were measured (i) during normal non-stress conditions (Normal₁); (ii) during exposure to ice water; and (iii) afterwards, under normal non-stress conditions (Normal₂). We continuously measured arterial blood pressure (Finometer), heart rate (ECG), skin blood flow of the index finger (laser Doppler), and brachial artery blood flow and diameter (Ultrasound Doppler). Measurements were taken at baseline; before a 5-min suprasystolic forearm occlusion; and following a 3-min post-occlusion, to measure reactive hyperemia and FMD.

Results

Median (25^th-75^th percentiles) FMD response after exposure to ice water was reduced compared to non-stress conditions [4.9 (2.9–8.4) % during ice water vs. 9.7 (7.6–12.2) % Normal₁ and 9.7 (6.4–10.3) % Normal₂, P < 0.001]. Blood flow 60 s after cuff-deflation during ice water exposure was significantly reduced to 328 (289–421) mL compared to non-stress conditions (both P < 0.05). No differences were observed between Normal₁ [446 (359–506) mL] and Normal₂ [455 (365–515) mL] (both P > 0.05). Heart rate significantly increased during ice water exposure [67 (59–69) beats/min)] compared to 55 (49–60) beats/min during Normal₁ and 54 (47–60) beats/min during Normal₂ (both P < 0.05). MAP did not change during Normal₁ [72 (64–84)] or during Normal₂ [71 (65–81) mm Hg] (both P > 0.05), but increased to 86 (75–98) mm Hg during ice water exposure (P < 0.05).

Conclusions

Increased sympathetic activity resulted in decreased blood flow and brachial artery FMD response in healthy volunteers, independent of endothelial dysfunction. Future studies should adjust for blood flow when interpreting the FMD response.

Contribution of systemic vascular reactivity to variability in pulse volume amplitude response during reactive hyperemia

PURPOSE

The aim of the present study was to investigate why the magnitude of reactive hyperemia (RH) observed by pulse volume amplitude (PVA) after arm occlusion differs greatly among study subjects.

METHODS

Healthy subjects (n = 12) in the age range of 22-30 years participated in this study. Vascular reactivity was assessed by measuring the changes in finger PVA simultaneously in the test (occluded arm) and control arm (contralateral non-occluded arm) using two separate Photoplethysmographic sensors. Short-term HRV was computed from simultaneously acquired lead II ECG signal to monitor the changes in cardiac sympathetic nervous activity.

RESULTS

The observed coefficient of variation for inter-subject variability in PVA response in test arm during second minute of RH was 115.3%. In the control arm, significantly reduced PVA was observed during the period of occlusion as well as RH. This observation was corroborated by simultaneously acquired short-term HRV which showed a significant rise in total power (p value < 0.005) and low-frequency (LF) power (p value < 0.05) during release of occlusion when compared to the baseline. A significant positive correlation (Spearman r = 0.33; p = 0.02) was observed between % change in PVA in the control arm and in the test arm for first 3 min of RH.

CONCLUSIONS

Sympathetic activation possibly plays an important role in mediating the inter-subject variability of vascular responses during reactive hyperemia which warrants simultaneous recording of both the test and the control arm responses during RH to accurately assess endothelial function.

Unilateral application of an external pneumatic compression therapy improves skin blood flow and vascular reactivity bilaterally

Background

We sought to determine the effects of unilateral lower-limb external pneumatic compression (EPC) on bilateral lower-limb vascular reactivity and skin blood flow.

Methods

Thirty-two participants completed this two-aim study. In AIM1 (n = 18, age: 25.5 ± 4.7 years; BMI: 25.6 ± 3.5 kg/m²), bilateral femoral artery blood flow and reactivity (flow mediated dilation [FMD]) measurements were performed via ultrasonography at baseline (PRE) and immediately following 30-min of unilateral EPC treatment (POST). AIM2 (n = 14, age: 25.9 ± 4.5; BMI: 27.2 ± 2.7 kg/m²) involved 30-min unilateral EPC (n = 7) or sham (n = 7) treatment with thermographic bilateral lower-limb mean skin temperature (MST) measurements at baseline, 15-min of treatment (T15) and 0, 30 and 60-min (R0, R30, R60) following treatment.

Results

Comparative data herein are presented as mean ± 95% confidence interval. AIM1: No significant effects on total reactive hyperemia blood flow were observed for the treated (i.e., compressed) or untreated (i.e., non-compressed) leg. A significant effect of time, but no time*leg interaction, was observed for relative FMD indicating higher reactivity bilaterally with unilateral EPC treatment (FMD: +0.41 ± 0.09% across both legs; p < 0.05). AIM2: Unilateral EPC treatment was associated with significant increases in whole-leg MST from baseline during (T15: +0.63 ± 0.56 °C in the visible untreated/contralateral leg, p < 0.025) and immediately following treatment (i.e., R0) in both treated (+1.53 ± 0.59 °C) and untreated (+0.60 ± 0.45 °C) legs (p < 0.0125). Across both legs, MST remained elevated with EPC at 30-min post-treatment (+0.60 ± 0.45 °C; p < 0.0167) but not at 60-min post (+0.27 ± 0.46 °C; p = 0.165). Sham treatment was associated with a significant increase in the treated leg immediately post-treatment (+1.12 ± 0.31 °C; p < 0.0167), but not in the untreated leg (−0.27 ± 0.12 °C). MST in neither the treated or untreated leg were increased relative to baseline at R30 or R60 (p > 0.05). Finally, during treatment and at all post-treatment time points (i.e., R0, R30 and R60), independent of treatment group (EPC vs. sham), there was a significant effect of region. The maximum increase in MST was observed at the R0 time point and was significantly (p < 0.05) larger in the thigh region (+1.02 ± 0.31 °C) than the lower-leg (+0.47 ± 0.29 °C) region. However, similar rates of MST decline from R0 in the thigh and lower leg regions were observed at the R30 and R60 time points.

Discussion

Unilateral EPC may be an effective intervention for increasing skin blood flow and/or peripheral conduit vascular reactivity in the contralateral limb. While EPC was effective in increasing whole-leg MST bilaterally, there appeared to be a more robust response in the thigh compared to the lower-leg. Thus, proximity along the leg may be an important consideration in prospective treatment strategies.

Blunted shear-mediated dilation of the internal but not common carotid artery in response to lower body negative pressure

Shear-mediated dilation in peripheral conduit arteries is blunted with sympathetic nervous system (SNS) activation; however, the effect of SNS activation on shear-mediated dilation in carotid arteries is unknown. We hypothesized that SNS activation reduces shear-mediated dilation in common and internal carotid arteries (CCA and ICA, respectively), and this attenuation is greater in the ICA compared with the CCA. Shear-mediated dilation in the CCA and ICA were measured in nine healthy men (24 ± 1 yr) with and without SNS activation. Shear-mediated dilation was induced by 3 min of hypercapnia (end‐tidal partial pressure of carbon dioxide +10 mmHg from individual baseline); SNS activity was increased with lower body negative pressure (LBNP; −20 mmHg). CCA and ICA measurements were made using Doppler ultrasound during hypercapnia with (LBNP) or without (Control) SNS activation. LBNP trials began with 5 min of LBNP with subjects breathing hypercapnic gas during the final 3 min. Shear-mediated dilation was calculated as the percent rise in peak diameter from baseline diameter. Sympathetic activation attenuated shear-mediated dilation in the ICA (Control vs. LBNP, 5.5 ± 0.7 vs. 1.8 ± 0.4%, P < 0.01), but not in the CCA (5.1 ± 1.2 vs. 4.2 ± 1.0%, P = 0.31). Moreover, absolute reduction in shear-mediated dilation via SNS activation was greater in the ICA than the CCA (−3.6 ± 0.7 vs. −0.9 ± 0.8%, P = 0.02). Our data indicate that shear-mediated dilation is attenuated during LBNP to a greater extent in the ICA compared with the CCA. These results potentially provide insight into the role of SNS activation on cerebral perfusion, as the ICA is a key supplier of blood to the brain.

NEW & NOTEWORTHY We explored the effect of acute sympathetic nervous system (SNS) activation on shear-mediated dilation in the common and internal carotid arteries (CCA and ICA, respectively) in young healthy men. Our data demonstrate that hypercapnia-induced vasodilation of the ICA is attenuated during lower body negative pressure to a greater extent than the CCA. These data may provide novel information related to the role of SNS activation on cerebral perfusion in humans.

Similarity between carotid and coronary artery responses to sympathetic stimulation and the role of α1-receptors in humans

Carotid artery (CCA) dilation occurs in healthy subjects during cold pressor test (CPT), while the magnitude of dilation relates to cardiovascular risk. To further explore this phenomenon and mechanism, we examined carotid artery responses to different sympathetic tests, with and without α₁-receptor blockade and assessed similarity to these responses between carotid and coronary arteries. In randomized order, 10 healthy participants (25 ± 3 yr) underwent sympathetic stimulation using the CPT (3-min left-hand immersion in ice-slush) and lower-body negative pressure (LBNP). Before and during sympathetic tests, CCA diameter and velocity (Doppler ultrasound) and left anterior descending (LAD) coronary artery velocity (echocardiography) were recorded across 3 min. Measures were repeated 90 min following selective α₁-receptor blockade via oral prazosin (0.05 mg/kg body wt). CPT significantly increased CCA diameter, LAD maximal velocity, and velocity-time integral area-under-the-curve (all P < 0.05). In contrast, LBNP resulted in a decrease in CCA diameter, LAD maximal velocity, and velocity time integral (VTI; all P < 0.05). Following α₁-receptor blockade, CCA and LAD velocity responses to CPT were diminished. In contrast, during LBNP (-30 mmHg), α₁-receptor blockade did not alter CCA or LAD responses. Finally, changes in CCA diameter and LAD VTI responses to sympathetic stimulation were positively correlated ( r = 0.66, P < 0.01). We found distinct carotid artery responses to different tests of sympathetic stimulation, where α₁ receptors partly contribute to CPT-induced responses. Finally, we found agreement between carotid and coronary artery responses. These data indicate similarity between carotid and coronary responses to sympathetic tests and the role of α₁ receptors that is dependent on the nature of the sympathetic challenge. NEW & NOTEWORTHY We showed distinct carotid artery responses to cold pressor test (CPT; i.e., dilation) and lower-body negative pressure (LBNP; i.e., constriction). Blockade of α₁-receptors significantly attenuated dilator responses in carotid and coronary arteries during CPT, while no changes were found during LBNP. Our findings indicate strong similarity between carotid and coronary artery responses to distinct sympathetic stimuli, and for the role of α-receptors.

Influence of physical inactivity on arterial compliance during a glucose challenge

NEW FINDINGS

What is the central question of this study? To understand better the effects of acute hyperglycaemia on arterial stiffness in healthy young individuals, we assessed arterial stiffness in physically active men before and after reduced ambulatory physical activity to decrease insulin sensitivity. What is the main finding and its importance? During an oral glucose tolerance test, we identified an increase in leg arterial stiffness (i.e. reduced femoral artery compliance) only when subjects were inactive for 5 days (<5000 steps day^-1 ) and not when they were engaging in regular physical activity (>10,000 steps day^-1 ). These results demonstrate the deleterious consequence of acute reductions in daily physical activity on the response of the peripheral vasculature to acute hyperglycaemia.

ABSTRACT

Acute hyperglycaemia has been shown to augment indices of arterial stiffness in patients with insulin resistance and other co-morbidities; however, conflicting results exist in healthy young individuals. We examined whether acute hyperglycaemia after an oral glucose tolerance test (OGTT) increases arterial stiffness in healthy active men before and after reduced ambulatory physical activity to decrease insulin sensitivity. High-resolution arterial diameter traces acquired from Doppler ultrasound allowed an arterial blood pressure (BP) waveform to be obtained from the diameter trace within a cardiac cycle. In 24 subjects, this method demonstrated sufficient agreement with the traditional approach for assessing arterial compliance using applanation tonometry. In 10 men, continuous recordings of femoral and brachial artery diameter and beat-to-beat BP (Finometer) were acquired at rest, 60 and 120 min of an OGTT before and after 5 days of reduced activity (from >10,000 to <5000 steps day^-1 ). Compliance and β-stiffness were quantified. Before the reduction in activity, the OGTT had no effect on arterial compliance or β-stiffness. However, after the reduction in activity, femoral compliance was decreased (rest, 0.10 ± 0.03 mm²  mmHg^-1 versus 120 min OGTT, 0.06 ± 0.02 mm²  mmHg^-1 ; P < 0.001) and femoral β-stiffness increased (rest, 8.7 ± 2.7 a.u. versus 120 min OGTT, 15.3 ± 6.5 a.u.; P < 0.001) during OGTT, whereas no changes occurred in brachial artery compliance (P = 0.182) or stiffness (P = 0.892). Insulin sensitivity (Matsuda index) was decreased after the reduction in activity (P = 0.002). In summary, in young healthy men the femoral artery becomes susceptible to acute hyperglycaemia after 5 days of reduced activity and the resultant decrease in insulin sensitivity, highlighting the strong influence of daily physical activity levels on vascular physiology.

Flow-mediated dilation stimulated by sustained increases in shear stress: a useful tool for assessing endothelial function in humans?

Investigations of human conduit artery endothelial function via flow-mediated vasodilation (FMD) have largely been restricted to the reactive hyperemia (RH) technique, wherein a transient increase in shear stress after the release of limb occlusion stimulates upstream conduit artery vasodilation (RH-FMD). FMD can also be assessed in response to sustained increases in shear stress [sustained stimulus (SS)-FMD], most often created with limb heating or exercise. Exercise in particular creates a physiologically relevant stimulus because shear stress increases, and FMD occurs, during typical day-to-day activity. Several studies have identified that various conditions and acute interventions have a disparate impact on RH-FMD versus SS-FMD, sometimes with only the latter demonstrating impairment. Indeed, evidence suggests that transient (RH) and sustained (SS) shear stress stimuli may be transduced via different signaling pathways, and, as such, SS-FMD and RH-FMD appear to offer unique insights regarding endothelial function. The present review describes the techniques used to assess SS-FMD and summarizes the evidence regarding 1) SS-FMD as an index of endothelial function in humans, highlighting comparisons with RH-FMD, and 2) potential differences in shear stress transduction and vasodilator production stimulated by transient versus sustained shear stress stimuli. The evidence suggests that SS-FMD is a useful tool to assess endothelial function and that further research is required to characterize the mechanisms involved and its association with long-term cardiovascular outcomes. NEW & NOTEWORTHY Sustained increases in peripheral conduit artery shear stress, created via distal skin heating or exercise, provide a physiologically relevant stimulus for flow-mediated dilation (FMD). Sustained stimulus FMD and FMD stimulated by transient, reactive hyperemia-induced increases in shear stress provide distinct assessments of conduit artery endothelial function.

UBC-Nepal Expedition: acute alterations in sympathetic nervous activity do not influence brachial artery endothelial function at sea level and high altitude

Evidence indicates that increases in sympathetic nervous activity (SNA), and acclimatization to high altitude (HA), may reduce endothelial function as assessed by brachial artery flow-mediated dilatation (FMD); however, it is unclear whether such changes in FMD are due to direct vascular constraint, or consequential altered hemodynamics (e.g., shear stress) associated with increased SNA as a consequence of exposure to HA. We hypothesized that 1) at rest, SNA would be elevated and FMD would be reduced at HA compared with sea-level (SL); and 2) at SL and HA, FMD would be reduced when SNA was acutely increased, and elevated when SNA was acutely decreased. Using a novel, randomized experimental design, brachial artery FMD was assessed at SL (344 m) and HA (5,050 m) in 14 participants during mild lower-body negative pressure (LBNP; -10 mmHg) and lower-body positive pressure (LBPP; +10 mmHg). Blood pressure (finger photoplethysmography), heart rate (electrocardiogram), oxygen saturation (pulse oximetry), and brachial artery blood flow and shear rate (Duplex ultrasound) were recorded during LBNP, control, and LBPP trials. Muscle SNA was recorded (via microneurography) in a subset of participants (n = 5). Our findings were 1) at rest, SNA was elevated (P < 0.01), and absolute FMD was reduced (P = 0.024), but relative FMD remained unaltered (P = 0.061), at HA compared with SL; and 2) despite significantly altering SNA with LBNP (+60.3 ± 25.5%) and LBPP (-37.2 ± 12.7%) (P < 0.01), FMD was unaltered at SL (P = 0.448) and HA (P = 0.537). These data indicate that acute and mild changes in SNA do not directly influence brachial artery FMD at SL or HA.NEW & NOTEWORTHY The role of the sympathetic nervous system on endothelial function remains unclear. We used lower-body negative and positive pressure to manipulate sympathetic nervous activity at sea level and high altitude and measured brachial endothelial function via flow-mediated dilation. We found that acutely altering sympathetic nervous activity had no effect on endothelial function.

Correlation of carotid artery reactivity with cardiovascular risk factors and coronary artery vasodilator responses in asymptomatic, healthy volunteers

OBJECTIVES

Carotid artery reactivity (CAR%), involving carotid artery diameter responses to a cold pressor test (CPT), is a noninvasive measure of conduit artery function in humans. This study examined the impact of age and cardiovascular risk factors on the CAR% and the relationship between CAR% and coronary artery vasodilator responses to the CPT.

METHODS

Ultrasound was used to measure resting and peak carotid artery diameters during the CPT, with CAR% being calculated as the relative change from baseline (%). We compared CAR% between young (n = 50, 24 ± 3 years) and older participants (n = 44, 61 ± 8 years), and subsequently assessed relationships between CAR% and traditional cardiovascular risk factors in 50 participants (44 ± 21 years). Subsequently, we compared left anterior descending (LAD) artery velocity (using transthoracic Doppler) with carotid artery diameter (i.e. CAR%) during the CPT (n = 33, 37 ± 17 years).

RESULTS

A significantly larger CAR% was found in young versus older healthy participants (4.1 ± 3.7 versus 1.8 ± 2.6, P < 0.001). Participants without cardiovascular risk factors demonstrated a higher CAR% than those with at least two risk factors (2.9 ± 2.9 versus 0.5 ± 2.9, P = 0.019). Carotid artery diameter and LAD velocity increased during CPT (P < 0.001). Carotid diameter and change in velocity correlated with LAD velocity (r = 0.486 and 0.402, P < 0.004 and 0.02, respectively).

CONCLUSION

Older age and cardiovascular risk factors are related to lower CAR%, while CAR% shows good correlation with coronary artery responses to the CPT. Therefore, CAR% may represent a valuable technique to assess cardiovascular risk, while CAR% seems to reflect coronary artery vasodilator function.

The influence of prenatal exercise and pre-eclampsia on maternal vascular function

During healthy pregnancy, the cardiovascular system undergoes diverse adaptations to support adequate transfer of oxygen and nutrients from mother to fetus. In order to accommodate the large expansion of blood volume and associated cardiac output, the structure, mechanics, and function of the arteries are altered. Specifically, in healthy pregnancy there is a remodeling of arteries (increased angiogenesis and vasodilation), a generalized reduction in arterial stiffness (increased compliance), and an enhanced endothelial function. The development of pregnancy complications, specifically pre-eclampsia, is associated with poor placentation (decreased angiogenesis), increased arterial stiffness, and vascular dysfunction (reduced endothelial function). Many of the positive adaptations that occur in healthy pregnancy are enhanced in response to chronic exercise. Specifically, placental angiogenesis and endothelial function have been shown to improve to a greater extent in women who are active during their pregnancy compared with those who are not. Prenatal exercise may be important in helping to reduce the risk of vascular dysfunction in pregnancy. However, our knowledge of the vascular adaptations resulting from maternal exercise is limited. This review highlights maternal vascular adaptations occurring during healthy pregnancy, and contrasts the vascular maladaptation associated with pre-eclampsia. Finally, we discuss the role of prenatal exercise on vascular function in the potential prevention of vascular complications associated with pre-eclampsia.

Assessment of flow-mediated dilatation in the superficial femoral artery using a sustained shear stress stimulus via calf plantar-flexion exercise

NEW FINDINGS

What is the central question of this study? The aim was to establish the ability of a newly designed leg exercise technique to produce sustained elevations in shear rate that stimulate flow-mediated dilatation (FMD) in the superficial femoral artery and to determine the repeat trial stability of the FMD response. What is the main finding and its importance? Calf plantar-flexion exercise can be used to increase shear stress and stimulate FMD in the superficial femoral artery. However, the magnitude of FMD varied systematically when multiple trials were repeated in short succession. The superficial femoral artery (SFA) is susceptible to vascular disease, and a technique to assess flow-mediated dilatation (FMD) in this vessel in response to a sustained shear stress stimulus could provide important information about endothelial function. The aim of this study was to establish the ability of a newly designed SFA leg exercise-FMD (LEX-FMD) technique to produce sustained elevations in shear rate, which stimulate FMD, and to determine the repeat trial stability of the FMD response. The SFA FMD stimulated by reactive hyperaemia (RH) and calf plantar-flexion exercise (LEX) was assessed via ultrasound in 19 healthy men (n = 10) and women (n = 9). The two experimental visits included either four trials of LEX-FMD or four trials of RH-FMD. The shear stress stimulus was estimated as the shear rate (blood velocity/SFA diameter). Results are expressed as the means ± SD. The LEX steady-state shear rate was consistent between trials (P = 0.176), whereas the RH shear rate area under the curve was higher in trial 1 versus trials 2-4 (P < 0.05). The %RH-FMD (four-trial mean 4.9 ± 2.5%) and absolute RH-FMD were not significantly different between trials (P = 0.465 and P = 0.359, respectively). Both %LEX-FMD and absolute LEX-FMD were higher during trial 3 (4.8 ± 3.4%) than trial 1 (3.6 ± 2.7%; P = 0.026 and P = 0.026, respectively). The magnitude of RH-FMD and LEX-FMD did not differ (P = 0.241). These results indicate that calf plantar-flexion exercise can be used to increase shear stress and stimulate FMD in the SFA. However, although SFA RH-FMD was stable across four trials, LEX-FMD varied systematically when multiple trials were repeated in rapid succession.

A Novel Apparatus for the Multifaceted Evaluation of Arterial Function Through Transmural Pressure Manipulation

A novel apparatus for the multifaceted evaluation of artery function was developed. It measures endothelial and smooth muscle functions and the pressure-strain elastic modulus (E _p). A rigid airtight chamber with an ultrasound probe was attached to the upper arm to manipulate the transmural pressure of the brachial artery. Endothelial function was measured via a standard flow-mediated dilation (FMD) protocol. Smooth muscle function was evaluated via a myogenic contraction of the artery following the application of negative pressure to the chamber and was named pressure-mediated contraction (PMC). E _p was obtained by measuring the instantaneous increase in the artery diameter following the negative pressure application. The PMC and FMD values had a significant negative correlation with age, indicating that the age-related decrease in FMD is caused by the decay of endothelial and smooth muscle function. A consideration of PMC may help improve the accuracy of artery function measurement. E _p in subjects aged >40 years was found to be significantly higher in the supra-physiological pressure range than in the physiological one (p = 0.02); this did not occur in younger subjects. Artery stiffening may begin in the supra-physiological range, and this stiffness may also be used for the diagnosis of atherosclerosis.

The effect of α1 -adrenergic blockade on post-exercise brachial artery flow-mediated dilatation at sea level and high altitude

KEY POINTS

Our objective was to quantify endothelial function (via brachial artery flow-mediated dilatation) at sea level (344 m) and high altitude (3800 m) at rest and following both maximal exercise and 30 min of moderate-intensity cycling exercise with and without administration of an α₁ -adrenergic blockade. Brachial endothelial function did not differ between sea level and high altitude at rest, nor following maximal exercise. At sea level, endothelial function decreased following 30 min of moderate-intensity exercise, and this decrease was abolished with α₁ -adrenergic blockade. At high altitude, endothelial function did not decrease immediately after 30 min of moderate-intensity exercise, and administration of α₁ -adrenergic blockade resulted in an increase in flow-mediated dilatation. Our data indicate that post-exercise endothelial function is modified at high altitude (i.e. prolonged hypoxaemia). The current study helps to elucidate the physiological mechanisms associated with high-altitude acclimatization, and provides insight into the relationship between sympathetic nervous activity and vascular endothelial function.

ABSTRACT

We examined the hypotheses that (1) at rest, endothelial function would be impaired at high altitude compared to sea level, (2) endothelial function would be reduced to a greater extent at sea level compared to high altitude after maximal exercise, and (3) reductions in endothelial function following moderate-intensity exercise at both sea level and high altitude are mediated via an α₁ -adrenergic pathway. In a double-blinded, counterbalanced, randomized and placebo-controlled design, nine healthy participants performed a maximal-exercise test, and two 30 min sessions of semi-recumbent cycling exercise at 50% peak output following either placebo or α₁ -adrenergic blockade (prazosin; 0.05 mg kg ^-1 ). These experiments were completed at both sea-level (344 m) and high altitude (3800 m). Blood pressure (finger photoplethysmography), heart rate (electrocardiogram), oxygen saturation (pulse oximetry), and brachial artery blood flow and shear rate (ultrasound) were recorded before, during and following exercise. Endothelial function assessed by brachial artery flow-mediated dilatation (FMD) was measured before, immediately following and 60 min after exercise. Our findings were: (1) at rest, FMD remained unchanged between sea level and high altitude (placebo P = 0.287; prazosin: P = 0.110); (2) FMD remained unchanged after maximal exercise at sea level and high altitude (P = 0.244); and (3) the 2.9 ± 0.8% (P = 0.043) reduction in FMD immediately after moderate-intensity exercise at sea level was abolished via α₁ -adrenergic blockade. Conversely, at high altitude, FMD was unaltered following moderate-intensity exercise, and administration of α₁ -adrenergic blockade elevated FMD (P = 0.032). Our results suggest endothelial function is differentially affected by exercise when exposed to hypobaric hypoxia. These findings have implications for understanding the chronic impacts of hypoxaemia on exercise, and the interactions between the α₁ -adrenergic pathway and endothelial function.

Vascular function and endothelin-1: tipping the balance between vasodilation and vasoconstriction

Endothelin-1 (ET-1), a potent vasoconstrictor secreted by vascular endothelial cells, has been implicated in the pathophysiology of numerous cardiovascular diseases, yet the direct impact of ET-1 on vascular function remains unclear. Therefore, in seven young (23 ± 1 yr) healthy subjects, we investigated the effect of an intra-arterial infusion of ET-1 on reactive hyperemia (RH) and flow-mediated dilation (FMD) in the popliteal artery following 5 min of suprasystolic cuff occlusion. ET-1 infusion significantly attenuated basal leg blood flow (control: 62 ± 4 ml/min, ET-1: 47 ± 9 ml/min), RH [area-under-curve (AUC); control: 162 ± 15 ml, ET-1: 104 ± 16 ml], and peak RH (control: 572 ± 51 ml/min, ET-1: 412 ± 32 ml/min) (P < 0.05). Administration of ET-1 also reduced FMD (control: 2.4 ± 0.3%, ET-1: 0.5 ± 0.5%) and FMD normalized for shear rate (control: 10.5 × 10^-4 ± 2.0 × 10^-4%/s^-1, ET-1: 0.9 × 10^-4 ± 2.8 ×10^-4%/s^-1). These findings reveal that elevated levels of ET-1 have a significant impact on vascular function, indicating that studies employing RH and FMD as markers of microvascular function and nitric oxide bioavailability, respectively, should exercise caution, as ET-1 can impact these assessments by tipping the balance between vasodilation and vasoconstriction, in favor of the latter.NEW & NOTEWORTHY Endothelin-1 (ET-1) is recognized as the body's most potent endogenous vasoconstrictor, but the impact of this peptide on vascular function is not well understood. The present study revealed that the intra-arterial administration of ET-1 impaired both microvascular and conduit vessel function of the leg in young, healthy, humans. Studies employing vascular testing in patient cohorts that experience a disease-related increase in ET-1 should thus exercise caution, as ET-1 clearly impairs vascular function.

Assessing the perceived quality of brachial artery Flow Mediated Dilation studies for inclusion in meta-analyses and systematic reviews: Description of data employed in the development of a scoring ;tool based on currently accepted guidelines

Brachial artery Flow Mediated Dilation (FMD) is widely used as a non-invasive measure of endothelial function. Adherence to expert consensus guidelines on FMD measurement has been found to be of vital importance to obtain reproducible data. This article lists the literature data which was considered in the development of a tool to aid in the objective judgement of the extent to which published studies adhered to expert guidelines for FMD measurement. Application of this tool in a systematic review of FMD studies (http://dx.doi.org/10.1016/j.atherosclerosis.2016.03.011) (Greyling et al., 2016 [1]) indicated that adherence to expert consensus guidelines is strongly correlated to the reproducibility of FMD data.

Sympathetic Neural and Hemodynamic Responses During Cold Pressor Test in Elderly Blacks and Whites

The sympathetic response during the cold pressor test (CPT) has been reported to be greater in young blacks than whites, especially in those with a family history of hypertension. Because blood pressure (BP) increases with age, we evaluated whether elderly blacks have greater sympathetic activation during CPT than age-matched whites. BP, heart rate, cardiac output, and muscle sympathetic nerve activity were measured during supine baseline, 2-minute CPT, and 3-minute recovery in 47 elderly (68 ± 7 [SD] years) volunteers (12 blacks and 35 whites). Baseline BP, heart rate, cardiac output, or muscle sympathetic nerve activity did not differ between races. Systolic and diastolic BP and heart rate increased during CPT (all P<0.001) with no racial differences (all P > 0.05). Cardiac output increased during CPT and ≤ 30 s of recovery in both groups, but was lower in blacks than whites. Muscle sympathetic nerve activity increased during CPT in both groups (both P<0.001); the increase in burst frequency was similar between groups, whereas the increase in total activity was smaller in blacks (P=0.030 for interaction). Peak change (Δ) in diastolic BP was correlated with Δ total activity at 1 minute into CPT in both blacks (r=0.78,P=0.003) and whites (r=0.43,P=0.009), whereas the slope was significantly greater in blacks (P=0.007). Thus, elderly blacks have smaller sympathetic and central hemodynamic (eg, cardiac output) responses, but a greater pressor response for a given sympathetic activation during CPT than elderly whites. This response may stem from augmented sympathetic vascular transduction, greater sympathetic activation to other vascular bed(s), or enhanced nonadrenergically mediated vasoconstriction in elderly blacks.

Correlations between endothelial function in the systemic and cerebral circulation and insulin resistance in type 2 diabetes mellitus

Insulin resistance is associated with endothelial dysfunction in type 2 diabetes mellitus, which can lead to impaired vascular reactivities of both systemic and cerebral circulations. Appropriate 'correction' of vascular reactivity results for non-endothelium-dependent systemic effects avoids misinterpretation of endothelial function. Therefore, we 'corrected' vascular reactivity results and explored the potential correlations between systemic vascular reactivity, cerebrovascular reactivity and insulin resistance. In 34 patients, 'systemic vascular reactivity' was assessed by quantifying reactive hyperaemia. Cerebrovascular reactivity was assessed by quantifying changes in cerebral blood flow velocity during hypercapnia. To minimize the influence of non-endothelium-dependent systemic effects on vascular reactivity results, 'corrected systemic vascular reactivity' was calculated by normalizing systemic vascular reactivity using the measurements from the contralateral side; and cerebrovascular reactivity results were corrected by calculating percentage and absolute changes in cerebrovascular conductance index ('percent cerebrovascular conductance index' and 'delta cerebrovascular conductance index', respectively). Insulin resistance was estimated by homeostatic model assessment. Correlation between conventional cerebrovascular reactivity and systemic vascular reactivity was not significant. But correlations between 'corrected systemic vascular reactivity' and 'percent cerebrovascular conductance index' (r = 0.51; p = 0.002) and 'corrected systemic vascular reactivity' and 'delta cerebrovascular conductance index' (r = 0.50; p = 0.003) were significant. Among all vascular reactivity parameters, only 'delta cerebrovascular conductance index' was significantly correlated with homeostatic model assessment of insulin resistance (r = -0.38; p = 0.029). In conclusion, endothelial function in the systemic and cerebral circulations is moderately correlated, provided that vascular reactivity estimates are corrected for non-endothelium-dependent influences.

Impact of sympathetic nervous system activity on post-exercise flow-mediated dilatation in humans

Transient reduction in vascular function following systemic large muscle group exercise has previously been reported in humans. The mechanisms responsible are currently unknown. We hypothesised that sympathetic nervous system activation, induced by cycle ergometer exercise, would contribute to post-exercise reductions in flow-mediated dilatation (FMD). Ten healthy male subjects (28 ± 5 years) undertook two 30 min sessions of cycle exercise at 75% HR(max). Prior to exercise, individuals ingested either a placebo or an α1-adrenoreceptor blocker (prazosin; 0.05 mg kg(-1)). Central haemodynamics, brachial artery shear rate (SR) and blood flow profiles were assessed throughout each exercise bout and in response to brachial artery FMD, measured prior to, immediately after and 60 min after exercise. Cycle exercise increased both mean and antegrade SR (P < 0.001) with retrograde SR also elevated under both conditions (P < 0.001). Pre-exercise FMD was similar on both occasions, and was significantly reduced (27%) immediately following exercise in the placebo condition (t-test, P = 0.03). In contrast, FMD increased (37%) immediately following exercise in the prazosin condition (t-test, P = 0.004, interaction effect P = 0.01). Post-exercise FMD remained different between conditions after correction for baseline diameters preceding cuff deflation and also post-deflation SR. No differences in FMD or other variables were evident 60 min following recovery. Our results indicate that sympathetic vasoconstriction competes with endothelium-dependent dilator activity to determine post-exercise arterial function. These findings have implications for understanding the chronic impacts of interventions, such as exercise training, which affect both sympathetic activity and arterial shear stress.

Opposing effects of shear-mediated dilation and myogenic constriction on artery diameter in response to handgrip exercise in humans

While the impact of changes in blood flow and shear stress on artery function are well documented, the acute effects of increases in arterial pressure are less well described in humans. The aim of this study was to assess the effect of 30 min of elevated blood pressure, in the absence of changes in shear stress or sympathetic nervous system (SNS) activation, on conduit artery diameter. Ten healthy male subjects undertook three sessions of 30 min unilateral handgrip exercise at 5, 10, and 15% of maximal voluntary contractile (MVC) strength. Brachial artery shear rate and blood flow profiles were measured simultaneously during exercise in the active and contralateral resting arms. Bilateral brachial artery diameter was simultaneously assessed before and immediately postexercise. In a second experiment, six subjects repeated the 15% MVC condition while continuous vascular measurements were collected during muscle sympathetic nerve activity (MSNA) assessment using peroneal microneurography. We found that unilateral handgrip exercise at 5, 10, and 15% MVC strength induced stepwise elevations in blood pressure (P < 0.01, Δmean arterial pressure: 7.06 ± 2.44, 8.50 ± 2.80, and 18.35 ± 3.52 mmHg, P < 0.01). Whereas stepwise increases were evident in shear rate in the exercising arm (P < 0.001), no changes were apparent in the nonexercising limb (P = 0.42). Brachial artery diameter increased in the exercising arm (P = 0.02), but significantly decreased in the nonexercising arm (P = 0.03). At 15% MVC, changes in diameter were significantly different between arms (interaction effect: P = 0.01), whereas this level of exertion produced no significant changes in MSNA. We conclude that acute increases in transmural pressure, independent of shear rate and changes in SNS activation, reduce arterial caliber in normotensive humans in vivo. These changes in diameter were mitigated by exercise-induced elevations in shear rate in the active limb.

Chronic stress impacts the cardiovascular system: animal models and clinical outcomes

Psychological stresses are associated with cardiovascular diseases to the extent that cardiovascular diseases are among the most important group of psychosomatic diseases. The longstanding association between stress and cardiovascular disease exists despite a large ambiguity about the underlying mechanisms. An array of possibilities have been proposed including overactivity of the autonomic nervous system and humoral changes, which then converge on endothelial dysfunction that initiates unwanted cardiovascular consequences. We review some of the features of the two most important stress-activated systems, i.e., the humoral and nervous systems, and focus on alterations in endothelial function that could ensue as a result of these changes. Cardiac and hematologic consequences of stress are also addressed briefly. It is likely that activation of the inflammatory cascade in association with oxidative imbalance represents key pathophysiological components of stress-induced cardiovascular changes. We also review some of the commonly used animal models of stress and discuss the cardiovascular outcomes reported in these models of stress. The unique ability of animals for adaptation under stressful conditions lessens the extrapolation of laboratory findings to conditions of human stress. An animal model of unpredictable chronic stress, which applies various stress modules in a random fashion, might be a useful solution to this predicament. The use of stress markers as indicators of stress intensity is also discussed in various models of animal stress and in clinical studies.

The effects of acute garlic supplementation on the fibrinolytic and vasoreactive response to exercise

Background

The purpose of this project was to examine the effects of acute garlic supplementation on fibrinolysis and vasoreactivity both at rest and following maximal exercise.

Methods

Eighteen healthy trained males (20.9 ± 2.2 years, 178 ± 7.7 cm, 75.5 ± 9.6 kg, VO₂max = 59.8 ± 6.7 ml • kg⁻¹ • min⁻¹) performed a graded treadmill test to volitional exhaustion. Blood samples were taken at rest, within two minutes post-exercise, and one hour post-exercise. Eleven of the subjects also had a brachial vasoreactivity test performed immediately after the blood sample to assess flow-mediated dilation (FMD) of the brachial artery. Participants were randomly assigned to ingest either 900 mg of powdered garlic or a placebo three hours before the exercise session. The supplement was distributed in a double-blind, crossover fashion. Participants repeated the protocol with the other treatment after a 14-day washout period. Paired t-tests were used to compare VO₂max between the two trials. A two-factor (treatment and time) repeated measures analysis of variance (ANOVA) was used to assess changes in FMD, tPA activity, tPA antigen, and PAI-1 activity. A priori statistical significance was set at P <0.05.

Results

VO₂max was greater for the garlic treatment trial vs. placebo (Placebo = 59.8 ± 6.7 ml • kg⁻¹ • min⁻¹; Garlic = 61.4 ± 6.6 ml • kg⁻¹ • min⁻¹). There was no main effect for treatment and no treatment x time interaction for FMD or any fibrinolytic variables examined.

Conclusion

Acute garlic supplementation does not alter vasoreactivity, fibrinolytic potential or the fibrinolytic response to exercise in young healthy trained males. Acute garlic supplementation does, however, cause a small but statistically significant increase in VO₂max. It remains unclear if this increase in VO₂max is of functional importance.