The behaviour of the flow-mediated brachial artery vasodilatation during orthostatic stress in normal man

Neurally mediated syncope: Is it really an endothelial dysfunction?

OBJECTIVE

Syncope is a common problem in children and adolescents. Neurally mediated syncope is the most frequent form of this disorder. Although several studies have evaluated the pathophysiology of neurally mediated syncope, it is still not completely understood.

METHODS

We performed a cross-sectional study that included 27 patients aged 5-20 years with unexplained syncope and 30 healthy subjects as a control group. All subjects in both groups were assessed for endothelial function by investigating the following physical and chemical factors: flow-mediated dilation (FMD), intima-media thickness (IMT), circulating vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM)], and endothelial leucocyte adhesion molecule (E-selectin), as well as epinephrine and norepinephrine. The data were statistically analyzed utilizing the SPSS 20.Significant differences between the groups in terms of mean scores were assessed using an independent sample t-test.

RESULTS

Mean FMD was significantly higher in the syncope case group than in the control group (p=0.028). There was no significant difference in IMT between the two groups; however, mean levels of ICAM (p=0.02) and VCAM (p=0.008) were significantly higher in the case group than in the control group. The levels of E-selectin also increased in the case group, but not to a statistically significant extent. The mean levels of epinephrine (p=0.01) were significantly lower in the case group than in the control group, and the level of norepinephrine serum decreased slightly, but not significantly, in the syncope patients.

CONCLUSION

Our results showed that an endothelial dysfunction or augmented endothelial function might exist in patients with neurally mediated syncope.

Effect of computerized cognitive training with virtual spatial navigation task during bed rest immobilization and recovery on vascular function: a pilot study

We investigated the effects of bed rest (BR) immobilization, with and without computerized cognitive training with virtual spatial navigation task (CCT), on vascular endothelium on older subjects. The effects of 14-day BR immobilization in healthy older males (n=16) of ages 53–65 years on endothelial function were studied using EndoPAT^®, a noninvasive and user-independent method. From the group of 16 older men, 8 randomly received CCT during the BR, using virtual navigation tasks in a virtual environment with joystick device. In all the cases, EndoPAT assessments were done at pre- and post-BR immobilization as well as following 28 days of ambulatory recovery. The EndoPAT index increased from 1.53±0.09 (mean ± standard error of the mean) at baseline to 1.61±0.16 following immobilization (P=0.62) in the group with CCT. The EndoPAT index decreased from 2.06±0.13 (mean ± standard error of the mean) at baseline to 1.70±0.09 at the last day of BR study, day 14 (BR14) (P=0.09) in the control group. Additionally, there were no statistically significant differences between BR14 and at 28 days of follow-up (rehabilitation program) (R28). Our results show a trend of immobilization in older persons affecting the vasoconstrictory endothelial response. As the control subjects had a greater increase in EndoPAT index after R28 (+0.018) compared to subjects who had cognitive training (+0.11) (calculated from the first day of BR study), it is possible that cognitive training during BR does not improve endothelial function but rather contributes to slowing down the impairment of endothelial function. Finally, our results also show that EndoPAT may be a useful noninvasive tool to assess the vascular reactivity.

Effect of orthostasis on endothelial function: a gender comparative study

As the vascular endothelium has multiple functions, including regulation of vascular tone, it may play a role in the pathophysiology of orthostatic intolerance. We investigated the effect of orthostasis on endothelial function using EndoPAT®, a non-invasive and user-independent method, and across gender. As sex steroid hormones are known to affect endothelial function, this study examined the potential effect of these hormones on the endothelial response to orthostasis by including females at different phases of the menstrual cycle (follicular and luteal—where the hormone balance differs), and females taking an oral contraceptive. A total of 31 subjects took part in this study (11 males, 11 females having normal menstrual cycles and 9 females taking oral contraceptive). Each subject made two visits for testing; in the case of females having normal menstrual cycles the first session was conducted either 1–7 (follicular) or 14–21 days (luteal) after the start of menstruation, and the second session two weeks later, i.e., during the other phase, respectively. Endothelial function was assessed at baseline and following a 20-min orthostatic challenge (active standing). The EndoPAT® index increased from 1.71 ± 0.09 (mean ± SEM) at baseline to 2.07 ± 0.09 following orthostasis in females (p<0.001). In males, the index increased from 1.60 ± 0.08 to 1.94 ± 0.13 following orthostasis (p<0.001). There were no significant differences, however, in the endothelial response to orthostasis between females and males, menstrual cycle phases and the usage of oral contraceptive. Our results suggest an increased vasodilatatory endothelial response following orthostasis in both females and males. The effect of gender and sex hormones on the endothelial response to orthostasis appears limited. Further studies are needed to determine the potential role of this post orthostasis endothelial response in the pathophysiology of orthostatic intolerance.

Elderly blacks have a blunted sympathetic neural responsiveness but greater pressor response to orthostasis than elderly whites

Neural control of blood pressure (BP) has been reported to differ between young blacks and whites. We hypothesized that elderly blacks have enhanced sympathetic neural responses during orthostasis compared with elderly whites. Muscle sympathetic nerve activity, arm-cuff BP, and heart rate were recorded continuously, and cardiac output, stroke volume, and total peripheral resistance were measured intermittently during supine and 5-minute 60° upright tilt in 10 blacks (65 [SD, 4] years; 4 women) and 20 whites (68 [6] years; 8 women). We found that muscle sympathetic nerve activity burst frequency was similar between blacks and whites in the supine position (44 [10] versus 42 [7] bursts per minute) and during upright tilt (59 [11] versus 60 [9] bursts per minute; P=0.846 for race, P<0.001 for posture, and P=0.622 for interaction). However, upright total muscle sympathetic nerve activity was smaller in blacks than in whites (162 [39] versus 243 [112]%; P=0.003). Systolic BP, heart rate, cardiac output, and stroke volume were not different between groups. Diastolic BP was similar in the supine position, increased in all of the subjects during tilting; upright diastolic BP was greater in blacks than in whites (80 [10] versus 71 [7] mmHg; P=0.008). Total peripheral resistance did not differ between blacks and whites in the supine position or during upright tilt (P=0.354 for race, P<0.001 for posture, P=0.825 for interaction). Thus, elderly blacks have a blunted sympathetic neural responsiveness but enhanced pressor response to orthostasis compared with elderly whites, which may be attributable to an augmented sympathetic vascular transduction and/or nonadrenergic vasoconstrictor mechanisms (ie, angiotensin II or the venoarteriolar response).

WISE 2005: responses of women to sublingual nitroglycerin before and after 56 days of 6° head-down bed rest

This study tested the hypothesis that cardiovascular effects of sublingual nitroglycerin (NG) would be exaggerated after 56 days of 6° head-down bed rest (HDBR) in women, and that an aerobic and resistive exercise countermeasure (EX, n = 8) would reduce the effect compared with HDBR without exercise (CON, n = 7). Middle cerebral artery maximal blood flow velocity (CBFV), cardiac stroke volume (SV), and superficial femoral artery blood flow (Doppler ultrasound) were recorded at baseline rest and for 5 min following 0.3 mg sublingual NG. Post-HDBR, NG caused greater increases in heart rate (HR) in CON compared with EX (+24.9 ± 7.7 and +18.8 ± 6.6 beats/min, respectively, P < 0.0001). The increase in HR combined with reductions in SV to maintain cardiac output. Systolic, mean, and pulse pressures were reduced 5-10 mmHg by NG, but total peripheral resistance was only slightly reduced at 3 min after NG. Reductions in CBFV of -12.5 ± 3.8 cm/s were seen after NG, but a reduction in the Doppler resistance index suggested dilation of the middle cerebral artery with no differences after HDBR. The femoral artery dilated with NG and blood flow was reduced ∼50% with the appearance of large negative waves suggesting a marked increase in downstream resistance, but there were no effects of HDBR. In general, responses of women to NG were not altered by HDBR; the greater increase in HR in CON but not EX was probably a consequence of cardiovascular deconditioning. These results contrast with the hypothesis and a previous investigation of men after HDBR by revealing no change in cardiovascular responses to exogenous nitric oxide.

Assessment of atherosclerosis: the role of flow-mediated dilatation

Evidence suggests that endothelial dysfunction is on the causal pathway for both atherogenesis and destabilization of established plaques. In this review, the role of flow-mediated dilatation (FMD) as a non-invasive method to assess endothelial function is discussed. Technical modifications and development of analysis software have significantly improved the variability of the method. Following a strict standardized protocol enables reproducible measurements to be achieved and export of the technique from specialized laboratories to population studies and multicentre settings. Endothelial function assessed by FMD has been shown to be affected by cardiovascular risk factors, to be related to structural arterial disease and to cardiovascular outcome, validating its use for studying the pathophysiology of arterial disease. Numerous studies have also demonstrated that it is responsive to physiological and pharmacological interventions. Flow-mediated dilatation provides unique opportunities in drug development programmes to assess an early rapidly responsive signal of risk or benefit, complementing endpoints of structural arterial disease and cardiovascular outcomes that take much longer and are more expensive.

Impaired brachial artery endothelial flow-mediated dilation and orthostatic stress in hemodialysis patients

PURPOSE

Chronic kidney disease (CKD) is associated with an impaired endothelial function, which may contribute to cardiovascular events. Whether impairment in endothelial function is involved in the circulatory response to orthostatic stress is unknown. We assessed endothelial function via brachial artery flow-mediated dilation (BAFMD), an index of endothelial-dependent vasodilation.

METHODS

We measured changes in brachial artery diameter (BAD) and blood flow by Doppler ultrasound in 35 CKD patients on hemodialysis, 37 young healthy controls (HC) and 50 non-uremic matched controls (MC), in the supine position and after 60 degrees head-up tilting (HUT).

RESULTS

In the supine position, endothelial flow-mediated BAD was significantly increased in HC (p<0.001) and MC (p<0.01) while no significant changes were detected in CKD. Mean percent blood flow changes were HC+323.5%, MC+195.1% and CKD+158.8% (HC vs. CKD p<0.001; HC vs. MC p<0.001; MC vs. CKD p=0.04). Similarly, during HUT mean BAD and blood flow increases were significantly impaired in CKD patients.

CONCLUSION

In CKD patients, an impaired response in the physiologic vascular reactivity, suggesting endothelial dysfunction, was found in the supine position and after orthostasis by BAFMD. Our results are in favor of a possible adjunctive role of uremia in the abnormal brachial artery response.

Neurovascular responses to mental stress in the supine and upright postures

The purpose of this study was to determine neurovascular responses to mental stress (MS) in the supine and upright postures. MS was elicited in 23 subjects (26 +/- 1 yr) by 5 min of mental arithmetic. In study 1 (n = 9), Doppler ultrasound was used to measure mean blood flow velocity in the renal (RBFV) and superior mesenteric arteries (SMBFV), and venous occlusion plethysmography was used to measure forearm blood flow (FBF). In study 2 (n = 14), leg blood flow (LBF; n = 9) was measured by Doppler ultrasound, and muscle sympathetic nerve activity (MSNA; n = 5) was measured by microneurography. At rest, upright posture increased heart rate and MSNA and decreased LBF, FBF, RBFV, and SMBFV and their respective conductances. MS elicited similar increases in mean arterial blood pressure ( approximately 12 mmHg) and heart rate ( approximately 17 beats/min), regardless of posture. MS in both postures elicited a decrease in RBFV, SMBFV, and their conductances and an increase in LBF, FBF, and their conductances. Changes in blood flow were blunted in the upright posture in all vascular beds examined, but the pattern of the vascular response was the same as the supine posture. MS did not change MSNA in either posture (change: approximately 1 +/- 3 and approximately 3 +/- 3 bursts/min, respectively). In conclusion, the augmented sympathetic activity of the upright posture does not alter heart rate, mean arterial blood pressure, or MSNA responses to MS. MS elicits divergent vascular responses in the visceral and peripheral vasculature. These results indicate that, although the upright posture attenuates vascular responses to MS, the pattern of neurovascular responses does not differ between postures.

Long-term use of sildenafil in the therapeutic management of heart failure

OBJECTIVES

This study sought to test the functional exercise capacity and endothelial function in a cohort of chronic heart failure (CHF) patients treated with chronic type 5 phosphodiesterase (PDE5) inhibitor.

BACKGROUND

In CHF, endothelial dysfunction is involved in muscle underperfusion, ergoreflex oversignaling, and exercise ventilation inefficiency. Inhibition of PDE5 by improving endothelial dysfunction might be beneficial.

METHODS

Stable CHF patients were randomly assigned to placebo (23 patients) or sildenafil at the dose of 50 mg twice per day (23 patients) in addition to their current drug treatment for 6 months, with assessments (at 3 and 6 months) of endothelial function by brachial artery flow-mediated dilatation (FMD), cardiopulmonary exercise testing, and ergoreflex response.

RESULTS

In the sildenafil group only, at 3 and 6 months we observed reduction of systolic pulmonary artery pressure (from 33.7 to 25.2 mm Hg and 23.9 mm Hg), ergoreflex effect on ventilation (from 6.9 to 2.3 l x min(-1) and 1.9 l x min(-1)), ventilation to CO2 production slope (V(E)/VCO2, from 35.5 to 32.1 and 29.8), and breathlessness (score) (from 23.6 to 16.6 and 17.2), and an increase of FMD (from 8.5% to 13.4% and 14.2%), peak VO2 (from 14.8 to 18.5 ml x min(-1) x kg(-1) and 18.7 ml x min(-1) x kg(-1)), and ratio of VO2 to work rate changes (from 7.7 to 9.3 and 10.1). All changes were significant at p < 0.01. In the sildenafil group, a significant correlation was found at 3 and 6 months between changes in FMD and those in ergoreflex. Changes in ergoreflex correlated with those in peak VO2 and V(E)/VCO2 slope. No adverse effects were noted except for flushing in 3 patients.

CONCLUSIONS

In CHF, improvement in exercise ventilation and aerobic efficiency with sildenafil is sustained and is significantly related with an endothelium-mediated attenuation of exercising muscle oversignaling. Chronic sildenafil seems to be a remedy based on CHF pathophysiology and devoid of remarkable adverse effects.

Effects of cardioversion of atrial fibrillation on endothelial function in hypertension or diabetes

BACKGROUND

Cardioversion (CV) to sinus rhythm corrects endothelial dysfunction secondary to atrial fibrillation (AF). As AF often complicates hypertension and diabetes (disorders associated with impaired endothelial function) the study probed whether these comorbidities to AF produced an additive effect and to what extent CV might be advantageous.

MATERIALS AND METHODS

Brachial artery flow-mediated dilatation (FMD) was evaluated before and after CV in 17 lone AF patients (group 1), 16 patients with AF + hypertension (group 2) and 17 patients with AF + diabetes type II (group 3), while in supine and head-up tilting (HUT) positions, as this is when endothelial vasodilation is emphasized as a counterbalance to neurogenic vasoconstriction.

RESULTS

After 2 weeks, CV in group 1 increased (P < 0.01) supine FMD (from 7.22-->9.50%) and restored its HUT potentiation (from 9.31-->17.22%). In group 2, FMD also improved significantly with CV (supine from 4.92-->7.11% and HUT from 5.29-->11.83%; P < 0.01). In group 3, CV did not promote significant FMD changes (supine from 5.12-->4.92% and HUT from 4.98-->4.73%). After 3 months, FMD improvement persisted in groups 1 and 2 with enduring sinus rhythm, but not in those with AF relapse. In group 3, FMD remained unchanged regardless of cardiac rhythm.

CONCLUSIONS

Cardioversion persistently increases supine shear stress endothelial responsiveness and restores the orthostatic modulation in AF alone or in association with hypertension, but not with diabetes. Differences in background endothelial impairment may explain the presence (hypertension) or the absence (diabetes) of an additive AF effect in comorbidities, as well as CV results.

Supplementation with omega-3 polyunsaturated fatty acids augments brachial artery dilation and blood flow during forearm contraction

Omega-3 polyunsaturated fatty acids such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) have beneficial effects on the heart and vasculature. We tested the hypothesis that 6 weeks of dietary supplementation with DHA (2.0 g/day) and EPA (3.0 g/day) enhances exercise-induced increases in brachial artery diameter and blood flow during rhythmic exercise. In seven healthy subjects, blood pressure, heart rate and brachial artery diameter, blood flow, and conductance were assessed before and during the last 30 s of 90 s of rhythmic handgrip exercise (30% of maximal handgrip tension). Blood pressure (MAP), heart rate (HR), and brachial artery vascular conductance were also determined. This paradigm was also performed in six other healthy subjects who received 6 weeks of placebo (safflower oil). Placebo treatment had no effect on any variable. DHA and EPA supplementation enhanced contraction-induced increases in brachial artery diameter (0.28+/-0.04 vs. 0.14+/-0.03 mm), blood flow (367+/-65 vs. 293+/-55 ml min-1) and conductance (3.86+/-0.71 vs. 2.89+/-0.61 ml min-1 mmHg-1) (P<0.05). MAP and HR were unchanged. Results indicate that treatment with DHA and EPA enhances brachial artery blood flow and conductance during exercise. These findings may have implications for individuals with cardiovascular disease and exercise intolerance (e.g., heart failure).