Carotid stiffness, extra-media thickness and visceral adiposity in young adults.

BACKGROUND AND AIMS: Carotid extra-media thickness (EMT) encompasses arterial adventitia and perivascular adipose tissue (PAT). Adventitial remodeling and PAT may contribute independently to functional (stiffness) and structural (remodeling) changes in artery wall properties. Visceral adiposity may contribute to PAT, thereby affecting artery stiffness. We investigated the relationships between carotid artery stiffness, EMT, and visceral adiposity in young, healthy individuals. METHODS: 135 healthy males (20 ± 2 yr, body mass index [BMI] 24.8 ± 3.3 kg/m2) underwent anthropometric and vascular measures on two separate days. Visceral adiposity was assessed using waist circumference and sagittal abdominal diameter (SAD). Brachial and carotid systolic, diastolic, and pulsatile (PP) blood pressures were assessed using an oscillometric cuff and applanation tonometry, respectively. Carotid intima-media thickness (IMT) and EMT were assessed using Doppler ultrasound. Carotid artery stiffness was calculated as ß-stiffness and calibrated to carotid pressures. RESULTS: Separate stepwise multiple regression models demonstrated that carotid PP (ß = 0.205) and EMT (ß = 0.267) accounted for 12.6% of variance in ß-stiffness, while carotid PP (ß = 0.195) and SAD (ß = 0.226) accounted for 10.5% of variance in EMT (p < 0.05). Mediation analyses revealed carotid PP partially mediated the relationship between a) EMT and ß-stiffness, and b) SAD and EMT (p < 0.05). CONCLUSIONS: Carotid PP and EMT, but not IMT, are related to carotid ß-stiffness. Carotid PP and visceral adiposity (SAD) are related to EMT. Carotid PP partially mediates the association between a) EMT and carotid ß-stiffness, and b) SAD and EMT. Our findings suggest visceral adiposity may detrimentally affect subclinical markers of cardiovascular disease risk (carotid PP, EMT) and contribute to artery stiffness.

Manipulation of arterial stiffness, wave reflections, and retrograde shear rate in the femoral artery using lower limb external compression.

Exposure of the arterial wall to retrograde shear acutely leads to endothelial dysfunction and chronically contributes to a proatherogenic vascular phenotype. Arterial stiffness and increased pressure from wave reflections are known arbiters of blood flow in the systemic circulation and each related to atherosclerosis. Using distal external compression of the calf to increase upstream retrograde shear in the superficial femoral artery (SFA), we examined the hypothesis that changes in retrograde shear are correlated with changes in SFA stiffness and pressure from wave reflections. For this purpose, a pneumatic cuff was applied to the calf and inflated to 0, 35, and 70 mmHg (5 min compression, randomized order, separated by 5 min) in 16 healthy young men (23 ± 1 years of age). Doppler ultrasound and wave intensity analysis was used to measure SFA retrograde shear rate, reflected pressure wave intensity (negative area [NA]), elastic modulus (Ep), and a single-point pulse wave velocity (PWV) during acute cuff inflation. Cuff inflation resulted in stepwise increases in retrograde shear rate (P < 0.05 for main effect). There were also significant cuff pressure-dependent increases in NA, Ep, and PWV across conditions (P < 0.05 for main effects). Change in NA, but not Ep or PWV, was associated with change in retrograde shear rate across conditions (P < 0.05). In conclusion, external compression of the calf increases retrograde shear, arterial stiffness, and pressure from wave reflection in the upstream SFA in a dose-dependent manner. Wave reflection intensity, but not arterial stiffness, is correlated with changes in peripheral retrograde shear with this hemodynamic manipulation.

Self-reported sitting time is associated with higher pressure from wave reflections independent of physical activity levels in healthy young adults.

BACKGROUND: Time spent in sedentary pursuits such as sitting (SIT) is associated with an increased risk of cardiovascular disease independent of physical activity (PA). The purpose of this study was to examine the associations of PA and SIT with central hemodynamic burden in young adults. METHODS: Aortic pressure waveforms were obtained using radial applanation tonometry and a generalized transfer function in 70 young healthy men (n = 41) and women (n = 29) (mean age = 23±1 years; body mass index = 24±1kg/m(2)). A wave separation technique that uses a physiologic pseudoaortic flow waveform was used to derive incident/forward wave pressure (Pf) and reflected/backward wave pressure (Pb). Levels of PA (metabolic equivalent, minutes per week) and SIT (sitting time per day) were obtained by self-report using the International Physical Activity Questionnaire. RESULTS: A negative correlation existed between PA and Pf (r = -0.30; P < 0.05) and Pb (r = -0.36; P < 0.05). A positive correlation existed between SIT and Pf (r = 0.39; P < 0.05) and Pb (r = 0.44; P < 0.05). According to results from multiple regression, after adjusting for potential confounders (age, sex, height, heart rate, mean pressure) and PA, associations between SIT and Pf (P < 0.05) and SIT and Pb (P < 0.05) remained. CONCLUSIONS: SIT is associated with higher forward wave pressure and backward wave pressure, 2 novel hemodynamic correlates of cardiovascular disease risk and target organ damage, in young apparently healthy men and women. This association is independent of PA.