Central, peripheral and resistance arterial reactivity: fluctuates during the phases of the menstrual cycle

Impact of passive vibration on pressure pulse wave characteristics

The augmentation index (AIx), a marker of wave reflection, decreases following acute leg exercise. Passive vibration (PV) causes local vasodilation that may reduce AIx. This study investigated the effects of acute PV on wave reflection and aortic hemodynamics. In a crossover fashion 20 (M=9, F=11) healthy young (22±3 year) participants were randomized to 10 min PV or no vibration control (CON) trials. Subjects rested in the supine position with their legs over a vibration platform for the entire session. Radial waveforms were obtained by applanation tonometry before and after 3 min (Post-3) and 30 min (Post-30) of PV (∼5.37 G) or CON. No change in parameters was found at Post-3. We found significant time-by-trial interactions (P<0.01) at Post-30 for augmented pressure, AIx and second systolic peak pressure (P2), such that these parameters significantly (P<0.05) decreased (-2.3±3.0 mm Hg, -7.2±6.9% and -1.5±3.5 mm Hg, respectively) after PV but not after CON. These findings suggest that acute PV applied to the legs decreases AIx owing to a decrease in wave reflection magnitude (P2). Further research is warranted to evaluate the potential clinical application of PV in populations at an increased cardiovascular risk who are unable to perform conventional exercise.

Cutaneous constitutive nitric oxide synthase activation in postural tachycardia syndrome with splanchnic hyperemia

Models of microgravity are linked to excessive constitutive nitric oxide (NO) synthase (NOS), splanchnic vasodilation, and orthostatic intolerance. Normal-flow postural tachycardia syndrome (POTS) is a form of chronic orthostatic intolerance associated with splanchnic hyperemia. To test the hypothesis that there is excessive constitutive NOS in POTS, we determined whether cutaneous microvascular neuronal NO and endothelial NO are increased. We performed two sets of experiments in POTS and control subjects aged 21.4 ± 2 yr. We used laser-Doppler flowmetry to measure the cutaneous response to local heating as an indicator of bioavailable neuronal NO. To test for bioavailable endothelial NO, we infused intradermal acetylcholine through intradermal microdialysis catheters and used the selective neuronal NOS inhibitor l-N(ω)-nitroarginine-2,4-L-diamino-butyric amide (N(ω), 10 mM), the selective inducible NOS inhibitor aminoguanidine (10 mM), the nonspecific NOS inhibitor nitro-l-arginine (NLA, 10 mM), or Ringer solution. The acetylcholine dose response and the NO-dependent plateau of the local heating response were increased in POTS compared with those in control subjects. The local heating plateau was significantly higher, 98 ± 1%maximum cutaneous vascular conductance (%CVC(max)) in POTS compared with 88 ± 2%CVC(max) in control subjects but decreased to the same level with N(ω) (46 ± 5%CVC(max) in POTS compared with 49 ± 4%CVC(max) in control) or with NLA (45 ± 3%CVC(max) in POTS compared with 47 ± 4%CVC(max) in control). Only NLA blunted the acetylcholine dose response, indicating that NO produced by endothelial NOS was released by acetylcholine. Aminoguanidine was without effect. This is consistent with increased endothelial and neuronal NOS activity in normal-flow POTS.

Relationship between muscle sympathetic nerve activity and aortic wave reflection characteristics in young men and women

Increased arterial stiffness is associated with higher levels of aortic wave reflection and aortic blood pressure. Recent evidence suggests a link between muscle sympathetic nerve activity and indices of arterial stiffness. Therefore, the aims of this study were to examine the relationship between resting muscle sympathetic nerve activity and characteristics of aortic pressure wave reflection and the influence of sex on these relationships. In 44 subjects (23 females and 21 males; 25 ± 1 years of age), we measured muscle sympathetic nerve activity via peroneal microneurography. In addition, noninvasive aortic pressure waveforms were synthesized from radial pressure waveforms obtained from applanation tonometry. Aortic blood pressure, augmentation index, wave reflection amplitude, and wasted left ventricular energy were calculated. Resting sympathetic activity (bursts/100 heart beats) was not associated with any of the aortic pressure wave reflection characteristics for all patients. However, there was a positive relationship between sympathetic activity and augmentation index (r = 0.46; P = 0.05) in men. Further, sympathetic activity in men was related to wave reflection amplitude (r = 0.53; P<0.05) and wasted left ventricular energy (r = 0.57; P<0.01). In contrast to men, women demonstrated strong inverse relationships between sympathetic activity and augmentation index (r = -0.63), wave reflection amplitude ( r = -0.59), and wasted left ventricular energy (r = -0.58; P<0.01 for all). Our results suggest another possible mechanism by which young women are protected against the development of cardiovascular disease.

Gender differences in vascular function and insulin sensitivity in young adults

To examine influence of insulin resistance and other clinical risk factors for the MetS (metabolic syndrome) on vascular structure and function in young adults. This cross-sectional study was conducted in a cohort of young adults (mean age 22 years) and their siblings participating in a longitudinal study of cardiovascular risk (n=370). Insulin sensitivity was determined by euglycaemic insulin clamp. EDD (endothelium-dependent dilation) was determined by flow-mediated dilation using high-resolution ultrasound imaging of the brachial artery. EID (endothelium-independent dilation) was determined by NTG (nitroglycerine)-mediated dilation. The diameter and cIMT (intima-media thickness) of the carotid artery were also measured. There was no significant difference between males and females for age or body mass index. However, males had significantly higher glucose and triacylglycerol (triglyceride) levels, while the females had significantly higher HDL-C (high-density lipoprotein-cholesterol) and insulin sensitivity (13.00 ± 0.33 compared with 10.71 ± 0.31 mg·kg-1 of lean body mass·min-1, P<0.0001). Although peak EDD was significantly lower (6.28 ± 0.26 compared with 8.50 ± 0.28%, P<0.0001) in males than females, this difference was largely explained by adjustment for brachial artery diameter (P=0.15). Peak EID also was significantly lower in males than females (20.26 ± 0.44 compared with 28.64 ± 0.47%, P<0.0001), a difference that remained significantly lower after adjustment for brachial artery diameter. Males had a significantly greater cIMT compared with females (females 0.420 ± 0.004 compared with males 0.444 ± 0.004 mm, P=0.01), but when adjusted for carotid diameter, there was no significant difference (P=0.163). Although there were gender differences in vascular function and structure in the young adult population examined in this study, many of the differences were eliminated simply by adjusting for artery diameter. However, the lower EID observed in males could not be explained by artery diameter. Future studies need to continue to examine influence of gender on EID and other measures of vascular function.

Long-term exercise training does not alter brachial and femoral artery vasomotor function and endothelial phenotype in healthy pigs

Although the beneficial effects of exercise training on conduit artery endothelial function are well-established in animals and humans with compromised basal function, whether exercise exerts favorable effects on a healthy endothelium is inconclusive. We sought to determine whether long-term exercise training enhances endothelial function in peripheral conduit arteries of healthy pigs. Using a retrospective analysis of data collected in our laboratory (n = 127), we compared in vitro brachial and femoral artery endothelium-dependent and -independent relaxation between a group of pigs that exercise-trained for 16-20 wk and a group that remained sedentary. No differences in vasomotor function were found between the 2 groups (P > 0.05). Additionally, in a subset of pigs (n = 16), expression levels of 18 proteins that are typically associated with the atherosclerotic process were measured by immunoblot analysis of endothelial cell scrapes obtained from the brachial and femoral arteries. We found no differences (P > 0.05) in endothelial gene expression between these exercise-trained and sedentary healthy pigs. These results indicate that pigs exhibiting the classic training-induced adaptations do not demonstrate enhanced endothelium-dependent dilation nor reveal a more atheroprotected endothelial cell phenotype in their brachial and femoral arteries than their sedentary but otherwise healthy counterparts.