Femoral Artery Vascular Conductance Research Articles

Renal vascular conductance is unrelated to leg vascular conductance or muscle sympathetic nerve activity at rest and during stress in humans.

The sympathetic nervous system is important for cardiovascular regulation, particularly during acute stress. Efferent sympathetic outflow can be regulated in an organ-dependent manner, but whether renal and leg vasoconstriction are associated at rest or during sympathetic stressors is unknown. Therefore, we sought to determine the relationships between muscle sympathetic nerve activity (MSNA), leg vascular conductance (LVC), and renal vascular conductance (RVC) at rest and during common laboratory-based sympathoexcitatory stimuli in a cohort of young healthy adults. Beat-to-beat arterial pressure (photoplethysmography), MSNA (microneurography), superficial femoral artery blood flow, and renal artery blood velocity (Doppler ultrasound) were measured at rest and during static handgrip exercise (30% maximal voluntary contraction), postexercise circulatory occlusion (PECO), and cold stress (hand in 3.8 ± 1.3°C water) in 37 young healthy adults (16 females, 21 males). At rest, RVC was unrelated to LVC (r = -0.11, P = 0.55) or MSNA burst frequency (ρ = -0.22, P = 0.26). Static handgrip, PECO, and cold stress each induced an increase in mean arterial pressure and MSNA and a reduction in RVC (all P < 0.001). LVC was unaltered during stress (all P ≥ 0.16), with the exception of a reduction during the second minute of cold stress (P = 0.03). During stress, changes in RVC were not associated with changes in LVC (handgrip: r = -0.24, P = 0.21; PECO: ρ = -0.04, P = 0.82; cold stress: r = -0.17, P = 0.38) or MSNA (handgrip: ρ = -0.14, P = 0.48; PECO: r = 0.27, P = 0.15; cold stress: r = -0.27, P = 0.16). Furthermore, MSNA was not associated with LVC at rest or during stress (all P ≥ 0.12). The present findings highlight the differential control of regional sympathetic vasoconstriction at rest and during stress in young healthy humans.NEW & NOTEWORTHY The sympathetic nervous system plays a critical role in cardiovascular regulation at rest and during stress. We demonstrate that renal artery vascular conductance is unrelated to superficial femoral artery vascular conductance or muscle sympathetic nerve activity at rest or during laboratory-based sympathetic stressors in young healthy adults. These findings support the concept of differential control of peripheral sympathetic outflow at rest and during stress in humans.

Peripheral vasodilation is reduced during exercise in perimenopausal women with elevated cardiovascular risk.

The menopausal transition has a negative effect on peripheral dilation in response to various stimuli including shear stress and exercise. Whether the presence of elevated traditional cardiovascular disease (CVD) risk factors in women going through menopause exacerbates the adverse effect on peripheral vasodilation is unclear. Forty-four perimenopausal women with relatively low CVD risk were divided into tertiles based on atherosclerotic CVD (ASCVD) 10-year risk scores (lowest: 0.1%-0.5%, middle: 0.6%-0.9%, higher: >1%). Comparisons were made across tertile groups for the femoral artery vascular conductance (FVC) response to single-leg knee extension exercise (0, 5, 10, 15 W) as measured using Doppler ultrasound. At higher exercise intensities, FVC was lower in women in the tertile group with the highest ASCVD 10-year risk scores (10 W: 6 ± 2 mL/min/mm Hg, 15 W: 8 ± 3 mL/min/mm Hg) compared to women in the lowest tertile group (10 W: 9 ± 3 mL/min/mm Hg, P = 0.01; 15 W: 12 ± 3 mL/min/mm Hg, P < 0.01) and middle tertile group (10 W: 10 ± 4 mL/min/mm Hg, P < 0.01; 15 W: 12 ± 5 mL/min/mm Hg, P < 0.01). The overall increase in FVC during exercise from 0 to 15 W remained lower (P ≤ 0.01) in women with the highest ASCVD risk scores compared to the other two tertile groups even after adjustment for chronological age, arterial stiffness, and fat-free mass adjusted aerobic fitness level. Our results show that the presence of mild differences in ASCVD risk scores may be associated with a blunted active limb blood flow during leg exercise in mid-life women transitioning through menopause.

Ad libidum exercise improves functional sympatholysis in rats with spontaneous hypertension via the nitric oxide signal pathway

Objective To explore the effect of exercise on functional sympatholysis in rats modeling spontaneous hypertension and the role of the nitric oxide signal pathway. Methods Thirty Wistar rats with spontaneous hypertension were randomly divided into a sedentary group and an exercise group, each of 15, while another fifteen healthy rats acted as controls. The exercise group performed eight weeks of voluntary wheel running exercise while the other two groups did not. The rats were instrumented to stimulate the lumbar sympathetic chain (at 1 Hz, 2.5 Hz or 5 Hz) to induce vasoconstriction and the triceps surae muscle group was forced to contract by stimulating the tibial nerve electrically. The change in the femoral artery vascular conductance (FAVC) in response to sympathetic stimulation was recorded at rest and during contraction. The functional sympatholysis was calculated as the percentage difference in FAVC (△%FAVC) in response to sympathetic stimulation during muscular contraction and at rest (△%FAVC=%FAVC during contraction-%FAVC at rest). After administration of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), changes in FAVC were repeatedly determined. Results The average △%FAVC of the sedentary group was significantly lower than that of the control group at all stimulation frequencies, while the average △%FAVC in the exercise group was significantly higher than in the sedentary group. There were no significant differences between the exercise and control groups. After the administration of L-NAME, significant decrease was observed in the average △%FAVCs of the control and exercise groups, but there was no significant change in the sedentary group. Conclusion Voluntary exercise may improve functional sympatholysis in rats with spontaneous hypertension through improving NO-dependent signalling. Key words: Exercise; Hypertension; Functional sympatholysis; Nitric oxide

Evidence for the emergence of leg sympathetic vasoconstrictor tone with age in healthy women.

While muscle sympathetic nerve activity (MSNA) is elevated with advancing age, correlational evidence suggests that, in contrast to men, basal MSNA is not related to resting lower limb hemodynamics in women. However, limited data exists in women that have attempted to directly assess the degree of limb sympathetic vasoconstrictor tone, and whether it is altered with age. To address this issue, we measured changes in femoral artery vascular conductance (FVC) during an acute sympatho‐inhibitory stimulus (−60 mm Hg neck suction, NS) in groups of healthy younger (n = 8, 23 ± 1 years) and older (n = 7, 66 ± 1 years) women. The percent change in FVC in response to NS was significantly augmented in the older (P = 0.006 vs. young) women. Although NS caused no significant change (3 ± 3%, P = 0.33) in FVC in the young women, there was a robust increase in FVC (21 ± 5%, P = 0.003) in the old women. Collectively, these findings provide evidence that in women, leg sympathetic vasoconstrictor tone emerges with age.

Diving and exercise: the interaction of trigeminal receptors and muscle metaboreceptors on muscle sympathetic nerve activity in humans.

Swimming involves muscular activity and submersion, creating a conflict of autonomic reflexes elicited by the trigeminal receptors and skeletal muscle afferents. We sought to determine the autonomic cardiovascular responses to separate and concurrent stimulation of the trigeminal cutaneous receptors and metabolically sensitive skeletal muscle afferents (muscle metaboreflex). In eight healthy men (30 ± 2 yr) muscle sympathetic nerve activity (MSNA; microneurography), mean arterial pressure (MAP; Finometer), femoral artery blood flow (duplex Doppler ultrasonography), and femoral vascular conductance (femoral artery blood flow/MAP) were assessed during the following three experimental conditions: 1) facial cooling (trigeminal nerve stimulation), 2) postexercise ischemia (PEI; muscle metaboreflex activation) following isometric handgrip, and 3) trigeminal nerve stimulation with concurrent PEI. Trigeminal nerve stimulation produced significant increases in MSNA total activity (Δ347 ± 167%) and MAP (Δ21 ± 5%) and a reduction in femoral artery vascular conductance (Δ-17 ± 9%). PEI also evoked significant increases in MSNA total activity (Δ234 ± 83%) and MAP (Δ36 ± 4%) and a slight nonsignificant reduction in femoral artery vascular conductance (Δ-9 ± 12%). Trigeminal nerve stimulation with concurrent PEI evoked changes in MSNA total activity (Δ341 ± 96%), MAP (Δ39 ± 4%), and femoral artery vascular conductance (Δ-20 ± 9%) that were similar to those evoked by either separate trigeminal nerve stimulation or separate PEI. Thus, excitatory inputs from the trigeminal nerve and metabolically sensitive skeletal muscle afferents do not summate algebraically in eliciting a MSNA and cardiovascular response but rather exhibit synaptic occlusion, suggesting a high degree of convergent inputs on output neurons.

High-dose ascorbic acid infusion abolishes chronic vasoconstriction and restores resting leg blood flow in healthy older men

Resting whole leg blood flow and vascular conductance decrease linearly with advancing age in healthy adult men. The potential role of age-related increases in oxidative stress in these changes is unknown. Resting leg blood flow during saline and ascorbic acid infusion was studied in 10 young (25 +/- 1 yr) and 11 older (63 +/- 2 yr) healthy normotensive men. Plasma oxidized LDL, a marker of oxidative stress, was greater in the older men (P < 0.05). Absolute resting femoral artery blood flow at baseline (iv saline control infusion) was 25% lower in the older men (238 +/- 25 vs. 316 +/- 38 ml/min; P < 0.05), and it was inversely related to plasma oxidized LDL (r = -0.56, P < 0.01) in all subjects. Infusion of supraphysiological concentrations of ascorbic acid increased femoral artery blood flow by 37% in the older men (to 327 +/- 52 ml/min; P < 0.05), but not in the young men (352 +/- 41 ml/min; P = 0.28), thus abolishing group differences (P = 0.72). Mean arterial blood pressure was greater in the older men at baseline (86 +/- 4 vs. 78 +/- 2 mmHg; P < 0.05), but it was unaffected by ascorbic acid infusion (P >/= 0.70). As a result, the lower baseline femoral artery blood flow in the older men was mediated solely by a 32% lower femoral artery vascular conductance (P < 0.05). Baseline femoral vascular conductance also was inversely related to plasma oxidized LDL (r = -0.65, P < 0.01). Ascorbic acid increased femoral vascular conductance by 36% in the older men (P < 0.05) but not in the young men (P = 0.31). In conclusion, ascorbic acid infused at concentrations known to scavenge reactive oxygen species restores resting femoral artery blood flow in healthy older adult men by increasing vascular conductance. These results support the hypothesis that oxidative stress plays a major role in the reduced resting whole leg blood flow and increased leg vasoconstriction observed with aging in men.

Cigarette smoking, regular exercise, and peripheral blood flow

Acute and chronic smoking reduces peripheral blood flow and shear stress, contributing to the increased incidence of peripheral arterial disease in smokers. Currently, it is not known whether physical activity status influences peripheral blood flow among chronic smokers. Blood flow was measured using Doppler ultrasound on the common femoral artery in nine young otherwise healthy sedentary smokers (eight males/one female) and nine physically-active smokers (six males/three females). Physically-active smokers performed strenuous exercise 4.4 times/week for 8 h/week. No significant differences in body fat, blood pressure, and total cholesterol were observed between groups. Basal femoral artery blood flow was ∼50% higher in physically-active smokers compared with sedentary smokers (259 ± 108 ml min −1 versus 173 ± 47 ml min −1, P < 0.05). The higher basal femoral artery blood flow in physically-active smokers compared with sedentary smokers was associated with a 47% higher femoral artery vascular conductance (2.99 ± 1.2 U versus 2.03 ± 0.5 U, P < 0.05) and a 39% lower vascular resistance (0.38 ± 0.13 U versus 0.53 ± 0.15 U, P < 0.05). Cardiac output, systemic vascular resistance, femoral intima-media thickness, and plasma norepinephrine concentration were not different between the groups. We concluded that smokers who habitually perform physical activity demonstrate greater levels of peripheral blood flow and peripheral vascular conductance. The findings from the present cross-sectional study suggest that chronic smokers may be able to negate, at least in part, the adverse effects of chronic smoking on the peripheral vasculature by performing regular physical activity.

Limb blood flow and vascular conductance are reduced with age in healthy humans: relation to elevations in sympathetic nerve activity and declines in oxygen demand.

We tested the hypothesis that basal (resting) limb blood flow and vascular conductance are reduced with age in adult humans and that these changes are related to elevations in sympathetic vasoconstrictor nerve activity and reductions in limb oxygen demand. Sixteen young (28+/-1 years; mean+/-SEM) and 15 older (63+/-1 years) healthy normotensive adult men were studied. Diastolic blood pressure and body fat were higher (P<0.005) in the older men, but there were no other age-related differences in subject characteristics. Femoral artery blood flow (Doppler ultrasound) was 26% lower in the older men (P<0.005), despite similar levels of cardiac output (systemic arterial blood flow) in the 2 groups. Femoral artery vascular conductance was 32% lower and femoral vascular resistance was 45% higher in the older men (P<0. 005). Muscle sympathetic nerve activity (peroneal microneurography) was 74% higher in the older men (P<0.001) and correlated with femoral artery blood flow (r=-0.55, P<0.005), vascular conductance (r=-0.65, P<0.001), and vascular resistance (r=0.61, P<0.001). The age-related differences in femoral hemodynamics were no longer significant after correction for the influence of muscle sympathetic nerve activity. There were no significant age-group differences in leg tissue mass (by dual-energy x-ray absorptiometry), but estimated leg oxygen consumption was 15% lower in the older men (P<0.001). Femoral artery blood flow was directly related to estimated leg oxygen consumption (r=0.78, P<0.001). The age-group differences in femoral artery blood flow were no longer significant after correction for estimated leg oxygen consumption by ANCOVA. (1) Basal whole-leg arterial blood flow and vascular conductance are reduced with age in healthy adult men; (2) these changes are associated with elevations in sympathetic vasoconstrictor nerve activity; and (3) the lower whole-limb blood flow is related to a lower oxygen demand that is independent of tissue mass.

Faster femoral artery blood velocity kinetics at the onset of exercise following short-term training

Objective: The hypothesis that the adaptation to endurance exercise training included a faster increase in blood flow at the onset of exercise was tested in 12 healthy young men who endurance-trained (ET) 2 h/day, for 10 days at 65% V̇O2 peak on a cycl and in 11 non-training control (C) subjects. Methods: Blood flow was estimated from changes in femoral artery mean blood velocity (MBV) by pulsed Doppler. Beat-by-beat changes in cardiac output (CO) and mean arterial pressure (MAP) were obtained by impedance cardiography and a Finapres finger cuff, respectively. MBV, MAP and CO were measured at rest and during 5 min of dynamic knee extension exercise. Both legs worked alternately with 2 s raising and lowering a weight (15% maximal voluntary contraction) followed by 2 s rest while the other leg raised and lowered the weight. Results: In the ET group the time to 63% (T63%) of the approximately exponential increase in MBV following 10 days of training (8.6 ± 1.2 s, mean ± s.e.) was significantly faster than the Day 0 response (14.2 ± 2.1 s, P < 0.05). The T63% of femoral artery vascular conductance (VCfa) was also faster following 10 days of ET (9.4 ± 0.9 s) versus Day 0 (16.0 ± 2.5 s) (0.05). There was no change in the T63% of both MBV and VCfa for the C group. The kinetics of CO were not significantly affected by ET, but the amplitude of CO in the adaptive phase, and at steady state, were significantly greater (P < 0.05) at Day 10 compared to Day 0 for the ET group with no change in the C group. Conclusions: These data supported the hypothesis that endurance training resulted in faster adaptation of blood flow to exercising muscle, and further showed that this response occurred early in the training program.

Faster femoral artery blood velocity kinetics at the onset of exercise following short-term training

The hypothesis that the adaptation to endurance exercise training included a faster increase in blood flow at the onset of exercise was tested in 12 healthy young men who endurance-trained (ET) 2 h/day, for 10 days at 65% VO2 peak on a cycle ergometer, and in 11 non-training control (C) subjects. Blood flow was estimated from changes in femoral artery mean blood velocity (MBV) by pulsed Doppler. Beat-by-beat changes in cardiac output (CO) and mean arterial pressure (MAP) were obtained by impedance cardiography and a Finapres finger cuff, respectively. MBV, MAP and CO were measured at rest and during 5 min of dynamic knee extension exercise. Both legs worked alternately with 2 s raising and lowering a weight (15% maximal voluntary contraction) followed by 2 s rest while the other leg raised and lowered the weight. In the ET group the time to 63% (T63%) of the approximately exponential increase in MBV following 10 days of training (8.6 +/- 1.2 s, mean +/- s.e.) was significantly faster than the Day 0 response (14.2 +/- 2.1 s, P < 0.05). The T63% of femoral artery vascular conductance (VCfa) was also faster following 10 days of ET (9.4 +/- 0.9 s) versus Day 0 (16.0 +/- 2.5 s) (0.05). There was no change in the T63% of both MBV and VCfa for the C group. The kinetics of CO were not significantly affected by ET, but the amplitude of CO in the adaptive phase, and at steady state, were significantly greater (P < 0.05) at Day 10 compared to Day 0 for the ET group with no change in the C group. These data supported the hypothesis that endurance training resulted in faster adaptation of blood flow to exercising muscle, and further showed that this response occurred early in the training program.