The Impact of the COVID-19 Pandemic and a Physical Therapy Program on Students' Health Outcomes.

The COVID-19 pandemic affected many aspects of everyday life including school, fitness regimens, and social interactions. The purpose of this study is to understand how COVID-19 restrictions affect the cardiovascular and mental health of Doctor of Physical Therapy (DPT) students as they progressed through the program. Data collection occurred in 16 DPT students (8F:8M, 24±3 years) over a total of 3 visits from 2020 to 2022, during high, moderate, and low COVID-19 restrictions. Outcome measures included VO2max, Venous Occlusion Plethysmography (VOP), %fat mass measured via DEXA, Perceived Stress Scale (PSS) and International Physical Activity Questionnaire (IPAQ). A RM-ANOVA with pairwise comparisons was utilized. Significance was set prior at an α level of 0.05. There was a significant increase (p<0.05) from visit 1 to 2 in VO2max, VOP baseline, BMI, and METs. There was a significant decrease (p<0.05) from visit 2 to 3 in VO2max. Finally, a significant increase in visit 3 was seen from visit 2 in VOP peak. Overall, there was no significant difference observed for PSS and %fat mass (p>0.05). Between high and moderate restrictions, there was an increase in VO2max, VOP baseline, and METs. However, between moderate and low restrictions, only VOP Peak increased. This could be attributed to gyms being closed and limiting the type of physical activity a person could do to exercises like running or walking. When restrictions were lifted, traveling to and from classes, traveling to gyms, and socializing all increased, limiting the time for physical activity.

Near Infrared Spectroscopy is not a Surrogate of Venous Occlusion Plethysmography to Assess Microvascular Resting Blood Flow and Function.

Near-infrared spectroscopy (NIRS) is a non-invasive technique that measures tissue perfusion using red blood cells oxygen saturation and venous occlusion plethysmography (VOP) is the gold standard to assess microvascular blood flow and function. The purpose of this study was to determine if NIRS can surrogate the microvascular blood flow assessment after an ischemic challenge obtained via VOP. Twenty apparently healthy subjects (10 males and 10 females), aged 18 to 35 years, were recruited for this single session study. NIRS probes were placed 40mm apart along the epicondylar muscles on the right forearm and on the tibialis anterior on the right lower leg, while VOP strain gauges were placed on the largest circumference on both right forearm and calf. Blood flow via VOP and NIRS variables (hemoglobin saturation (SO2), oxygenated hemoglobin (HbO2), and deoxyhemoglobin (HHb) slopes) were assessed before and after 5-min ischemic challenge. Person's correlations and intra-class correlations (ICC2k) were conducted for each of the NIRS variables vs VOP. There were moderate associations between of SO2 and HbO2 slopes and VOP (r = 0.59, p < 0.01 and r = 0.53, p < 0.05, respectively) at the lower body during resting conditions. There was a poor agreement between NIRS SO2 and VOP at the resting condition in the lower body (ICC2k = 0.45). There were no other associations between any of the other NIRS variables and VOP of the lower and upper body at resting or post-ischemic conditions. In conclusion, NIRS cannot surrogate VOP for measurements of microvascular blood flow at resting or post-ischemic conditions.

Differences in Blood Flow Patterns and Endothelial Shear Stress at the Carotid Artery Using Different Exercise Modalities and Intensities.

Endothelial dysfunction is the first pathophysiological step of atherosclerosis, which is responsible for 90% of strokes. Exercise programs aim to reduce the risk of developing stroke; however, the majority of the beneficial factors of exercise are still unknown. Endothelial shear stress (ESS) is associated with endothelial homeostasis. Unfortunately, ESS has not been characterized during different exercise modalities and intensities in the carotid artery. Therefore, the purpose of this study was to determine exercise-induced blood flow patterns in the carotid artery. Fourteen apparently healthy young adults (males = 7, females = 7) were recruited for this repeated measures study design. Participants completed maximal oxygen consumption (VO2max) tests on a Treadmill, Cycle-ergometer, and Arm-ergometer, and 1-repetition maximum (1RM) tests of the Squat, Bench Press (Bench), and Biceps Curl (Biceps) on separate days. Thereafter, participants performed each exercise at 3 different exercise intensities (low, moderate, high) while a real-time ultrasound image and blood flow of the carotid artery was obtained. Blood flow patterns were assessed by estimating ESS via Womersley's estimation and turbulence via Reynold's number (Re). Data were analyzed using a linear mixed-effects model. Pairwise comparisons with Holm-Bonferroni correction were conducted with Hedge's g effect size to determine the magnitude of the difference. There was a main effect of intensity, exercise modality, and intensity * exercise modality interaction on both ESS (p < 0.001). Treadmill at a high intensity yielded the greatest ESS when compared to the other exercise modalities and intensities, while Bench Press and Biceps curls yielded the least ESS. All exercise intensities across all modalities resulted in turbulent blood flow. Clinicians must take into consideration how different exercise modalities and intensities affect ESS and Re of the carotid artery.

Effects of 1 MHz Therapeutic Ultrasound on Limb Blood Flow and Microvascular Reactivity: A Randomized Pilot Trial.

A randomized, double-blind, placebo-controlled, cross-over study where continuous therapeutic ultrasound (CUS; at 0.4 W/cm2), pulsed therapeutic ultrasound (PUS; at 20% duty cycle, 0.08 W/cm2), both at 1 MHz, and placebo (equipment on, no energy provided) were randomized and applied over the forearm of the non-dominant arm for 5 min in 10 young, healthy individuals. Absolute and peak forearm blood flow (FBF) were measured via Venous Occlusion Plethysmography. FBF was measured before, halfway, and after (immediately and 5 min after) the therapeutic ultrasound (TUS) intervention. Post-ischemic peak FBF was measured 10 min before and 10 min after the TUS intervention. A two-way repeated measures ANOVA (group × time) was selected to assess differences in FBF before, during, and after TUS treatment, and for peak FBF before and after TUS treatment. FBF increased 5 min after TUS in CUS compared to placebo (2.96 ± 1.04 vs. 2.09 ± 0.63 mL/min/100 mL of tissue, p < 0.05). PUS resulted in the greatest increase in Peak FBF at 10 min after US (Δ = 3.96 ± 2.02 mL/min/100 mL of tissue, p = 0.06). CUS at 1 MHz was an effective treatment modality for increasing FBF up to 5 min after intervention, but PUS resulted in the greatest increase in peak FBF at 10 min after intervention.

There are no differences in brachial artery endothelial shear stress and blood flow patterns between males and females during exercise.

Premenopausal females have a lower cardiovascular risk than males. Sex differences on exercise-induced endothelial shear stress (ESS) and blood flow patterns may explain part of this risk reduction. The purpose of this cross-sectional study was to determine the differences in brachial artery exercise-induced ESS and blood flow patterns between males and females. Thirty subjects (13 females) were recruited to perform a three-workload steady-state exercise test based on blood lactate levels (i.e. <2.0, 2.0-4.0, >4.0 mmol/l). ESS and blood flow patterns were estimated at rest and during each workload using Womersley's approximation and Reynolds number, respectively. Both males and females showed an exercise intensity-dependent increase in antegrade and retrograde ESS. There was no significant sex effect or interaction for antegrade ESS (F(1, 30)  = 0.715, p = 0.405 and F(1·672, 60)  = 1.511, p = 0.232, respectively) or retrograde ESS (F(1, 30)  = 0.794, p = 0.380 and F(1·810, 60)  = 1.022, p = 0.361, respectively). Additionally, antegrade blood flow was turbulent during all bouts of exercise while retrograde blood flow became disturbed at moderate and high exercise intensities in both groups. There are no differences in exercise-induced ESS and blood flow patterns between males and females when the exercise load is equivalent. This suggests that the vascular benefits of exercise training are similar in both sexes from a haemodynamic standpoint.

Differences between Males and Females in Determining Exercise Intensity.

Even though there are physiological differences between males and females, heart rate (HR), ratings of perceived exertion (RPE), power output (PO), oxygen consumption (VO2), and blood lactate (BL) levels have been used as measures of exercise intensity independently of sex. The purpose of this study was to determine differences between sexes in different exercise intensity models. Thirty (15 females) young, healthy individuals were scheduled for two testing visits 48-72 hours apart. During the first testing visit, a graded exercise test (GXT), with BL obtained at the end of each exercise step, was administered on a stationary bicycle to determine peak PO and VO2max. BL during the GXT was used to determine three 5-min steady-state workloads (low: 0-2 mmol/L; moderate: 2-4 mmol/L; and high: >4 mmol/L) for the second test. HR, %HRmax, RPE, PO, %POmax, VO2, %VO2max, and BL were obtained at the end of each steady-state workload. A two-way repeated measures ANOVA was performed to compare all exercise intensity variables obtained during the second test between males and females (α=0.05). Only RPE, %PO, and BL did not differ between sexes on all 3 exercise intensities. HR, %HR, and PO differ between sexes on at least 2 exercise intensities. Females have higher HR and %HR than males for similar %PO. VO2 and %VO2max differ between sexes on at least 1 exercise intensity. Based on the current results, traditional exercise intensity markers are different between males and females. BL and %PO appear to be markers that might be used independently of sex.

Acute dietary nitrate does not reduce resting metabolic rate or oxidative stress marker 8-isoprostane in healthy males and females.

To investigate changes in resting metabolic rate and 8-isoprostane, an oxidative stress biomarker, following acute dietary nitrate supplementation in healthy males and females. In a randomised, double-blind, cross-over study, 10 males and seven females (age range 19-25 years) underwent protocol familiarisation (visit 1), baseline assessments (visits 2 and 4) and assessments following supplementation, placebo or 6.2 mmol nitrate, 2 hours prior to visits 3 and 5. Participants completed a 30-minute RMR test with visits 2 and 3 on consecutive days, separated by a week-long washout period concluding with visits 4 and 5 on consecutive days. Plasma nitrate/nitrite (NOx) significantly increased (p ≤ 0.05) following dietary nitrate consumption compared to baseline values. No significant effect on resting metabolism (p = 0.194) or 8-isoprostane (p = 0.660) was observed following dietary nitrate supplementation. Dietary nitrate increases NO bioavailability, but acute supplementation does not effect resting metabolism or 8-isoprostane in healthy males and females.

Characterization of blood flow patterns and endothelial shear stress during flow-mediated dilation.

INTRODUCTION: Endothelial dysfunction is considered the first step in the development of atherosclerosis. Flow-mediated dilation (FMD) has been the most common assessment of endothelial function in research but it has failed in obtaining a widespread use in clinical settings due to a lack of standardization and a large inter-subject variability. Normalization of FMD to endothelial shear stress (ESS) has been proposed to solve its technical limitations. However, studies have not considered the characteristic of the blood flow during FMD under pulsatile conditions in their ESS estimations. METHODS: A total of 26 young healthy subjects (15 females and 11 males) underwent FMD testing. Microhematocrit measurement was used to determine blood viscosity (µ). ESS was calculated by Womersley's approximation, ESS = µ*2K*Velocity/Diameter, where K is a function of Womersley's parameter (α). Blood flow patterns were determined by critical Reynolds number. Statistical analysis included repeated measures ANOVA to detect ESS differences during FMD until peak dilation. Significance was established at P≤0.05. RESULTS: The mean (SD) FMD% and time to peak dilation were 7·4 (3·1) % and 35 (9·3) seconds, respectively. ESS was significantly reduced during FMD until peak dilation (P<0·001). Turbulent blood flow was the only pattern observed until peak dilation in 96·15% of the sample. CONCLUSION: Peak FMD dilation in a young healthy population is triggered mostly by high-ESS under turbulent flow conditions. Due to the pulsatile nature of blood flow and the appearance of a turbulent pattern during FMD, ESS should be estimated by Womersley's approximation rather than Poiseuille's law.

Comparison between cuff-based and radial tonometry exercise-induced central blood pressure.

PURPOSE: Non-invasive central blood pressure assessed during exercise may provide better cardiovascular prognostic than measurements taken at rest. Radial tonometry is the only technique validated to perform this type of assessment; however, it relies on the experience of the tester. Cuff-based devices have been developed to avoid operator dependency, although these systems have yet to be validated during exercise. The purpose of this study was to compare exercise-induced central blood pressure estimations between a cuff-based device and radial tonometry. METHODS: Twenty young healthy subjects were recruited to perform a three-workload steady-state exercise test at blood lactate levels of < 2, 2-4, and > 4 mmol/L, respectively. Central systolic and diastolic blood pressure (cSBP and cDBP, respectively), central pulse pressure (cPP), and augmentation index (AIx) were assessed at rest and during each workload with a cuff-based device and radial tonometry. Statistical analysis included Bland-Altman analysis for agreement between techniques. Agreement was considered when 95% of the data set for each central blood pressure parameter was within 1.96 standard deviations from the mean difference. Significance was considered at α = 0.05. RESULTS: Central blood pressure measurements with the cuff device were obtained only at rest and during low-intensity exercise. During low-intensity exercise, all measurements showed agreement between both devices (cSBP 95% CI [- 6.0 to 10.7], cDBP 95% CI [- 4.5 to 6.3], cPP 95% CI [- 4.7 to 8.3], and AIx (95% CI [- 20.1 to 22.2]). CONCLUSION: A cuff-based device can estimate central blood pressure at low-intensity exercise, without operator dependency, and showing agreement to radial tonometry.

Blood flow patterns during incremental and steady-state aerobic exercise.

BACKGROUND: Endothelial shear stress (ESS) is a physiological stimulus for vascular homeostasis, highly dependent on blood flow patterns. Exercise-induced ESS might be beneficial on vascular health. However, it is unclear what type of ESS aerobic exercise (AX) produces. The aims of this study are to characterize exercise-induced blood flow patterns during incremental and steady-state AX. We expect blood flow pattern during exercise will be intensity-dependent and bidirectional. METHODS: Six college-aged students (2 males and 4 females) were recruited to perform 2 exercise tests on cycle-ergometer. First, an 8-12-min incremental test (test 1) where oxygen uptake (VO2), heart rate (HR), blood pressure (BP), and blood lactate (La) were measured at rest and after each 2-min step. Then, at least 48-hr. after the first test, a 3-step steady state exercise test (test 2) was performed measuring VO2, HR, BP, and La. The three steps were performed at the following exercise intensities according to La: 0-2 mmol/L, 2-4 mmol/L, and 4-6 mmol/L. During both tests, blood flow patterns were determined by high-definition ultrasound and Doppler on the brachial artery. These measurements allowed to determine blood flow velocities and directions during exercise. RESULTS: On test 1 VO2, HR, BP, La, and antegrade blood flow velocity significantly increased in an intensity-dependent manner (repeated measures ANOVA, P<0.05). Retrograde blood flow velocity did not significantly change during test 1. On test 2 all the previous variables significantly increased in an intensity-dependent manner (repeated measures ANOVA, P<0.05). CONCLUSIONS: These results support the hypothesis that exercise-induced ESS might be increased in an intensity-dependent way and blood flow patterns during incremental and steady-state exercises include both antegrade and retrograde blood flows.

Internal validation of an automated system for brachial and femoral flow mediated dilation.

BACKGROUND: Flow Mediated Dilation (FMD) has immense potential to become a clinical, non-invasive biomarker of endothelial function and nitric oxide bioavailability, which regulate vasomotor activity. Unfortunately, FMD analysis techniques could deviate significantly in different laboratories if a validation process is not involved. The purpose of this study was to provide validation to the assessment of FMD analysis in our laboratory and to standardize this process before reporting results of FMD. METHODS: Brachial and femoral arteries FMD were performed on 28 apparently healthy participants (15 male and 13 female, ages 18-35 years). For the intratester reliability study, nine subjects were asked to come to the lab for a second brachial FMD within 48 h. All FMD procedures were performed by the same investigator, while the FMD analyses were performed by 2 independent testers who were blind to each other's analyses. FMD analyses included baseline artery diameter measurements, peak artery diameter after 5 min of ischemia, and FMD. Analysis was completed via an automated edge detection system by both testers after training of the methodical process of analysis to minimize variability. Intratester and intertester reliability were determined by using coefficient of variation (CV) between first and second visit (intratester) and between results obtained by both testers (intertester). RESULTS: The intratester CVs for tester 1 and 2 were 3.28 and 2.62%, 3.74 and 3.27%, and 4.95 and 2.38% for brachial baseline artery diameter, brachial peak artery dilation, and brachial FMD, respectively. In the intertester CVs were 2.40, 3.16, and 3.37% for brachial baseline artery diameter, peak artery dilation, and FMD, respectively and 4.52, 5.50, and 3.46% for femoral baseline artery diameter, peak artery dilation, and FMD, respectively. CONCLUSION: All CVs were under or around 5%, confirming a strong reliability of the method. Our laboratory has shown that the FMD protocol is reproducible due to the significantly low coefficient of variation. This is one step closer to use FMD as a biomarker for endothelial function in our laboratory.

The bioengineering of changing lifestyle and wearable technology: a mini review.

Chronic diseases are a major health concern at the national and global level. According to the CDC, 86% of US health dollars go toward the treatment of chronic diseases. Many chronic diseases are manageable or preventable if individuals make appropriate lifestyle choices. Wearable technology – both consumer and medical – provides a unique opportunity to track lifestyle choices, such as increasing physical activity. It is estimated the market for consumer wearables will grow from $9.2 billion in 2014 to $30 billion by 2018. With such a potential market growth, it is important to understand the potential benefits and limitations of wearable technology to impact chronic disease management and prevention.

Flow-mediated dilation is associated with endothelial oxidative stress in human venous endothelial cells.

Flow-mediated dilation (FMD) is recognized as a non-invasive endothelial function bioassay. However, FMD's relationship with endothelial cell oxidative stress in humans is yet to be determined. Here, we sought to determine if FMD was associated with endothelial nitric oxide synthase (eNOS) and endothelial oxidative stress in humans. Twenty-seven apparently healthy young men (26.5±5.9 years) underwent brachial artery FMD testing and endothelial cell biopsy from a forearm vein. Non-normalized FMD (%) and three different brachial artery FMD normalizations were performed: (1) peak shear rate (%/SR); (2) area under the SR curve until peak dilation (%/AUC); and (3) AUC 30 seconds before peak dilation (%/AUC30). Immunofluorescence quantification was used to assess eNOS expression and nitrotyrosine (NT), a criterion marker of endothelial oxidative stress. Values for eNOS and NT expression were reported as a ratio of endothelial cell to human umbilical vein endothelial cell average pixel intensity. NT expression was significantly correlated with FMD normalized by AUC30 (r = -0.402, p<0.05). Other FMD normalizations and non-normalized FMD were not significantly correlated with NT expression (r range = -0.364 to -0.142, all p>0.05). There were no significant correlations between eNOS expression and normalized and non-normalized FMD (r range = -0.168 to -0.066, all p>0.05). In conclusion, brachial artery FMD is associated with venous endothelial cell oxidative stress. However, this association is observed only when FMD is normalized by AUC30.

Validity of a novel wristband tonometer for measuring central hemodynamics and augmentation index.

BACKGROUND: Central hemodynamic and augmentation indices are independent predictors of cardiovascular events and all-cause mortality that can be estimated noninvasively by pulse wave analysis. The purpose of this study was to assess the reliability and validity of a newly engineered wristband tonometer for acquiring radial artery pressure waveforms. METHODS: Radial artery pulse pressure waveforms were evaluated with an established pencil-type and a novel wristband tonometer in 31 participants (aged 30.2±9.5 years) resting in a supine position. Pulse wave analysis was executed using the same validated generalized transfer function (SphygmoCor) for both tonometers. RESULTS: A significant difference in time to data acquisition between tonometers was observed (-70.2±147.7 s; P < 0.05; wristband faster). The wristband tonometer had significantly lower within-subject coefficients of variation (CV) compared with the pencil-type tonometer in aortic pulse wave height (-2.67% ± 5.51%; P < 0.05) and time to reflection (-2.26% ± 6.16%; P < 0.01). No other differences in CV were observed. Slight but statistically significant mean differences between tonometers were observed in aortic systolic blood pressure (ASBP; 0.43±1.08 mm Hg; P < 0.05; wristband lower), aortic pulse pressure (APP; 0.43±0.96 mm Hg; P < 0.05; wristband lower), and round-trip travel time of the reflected pressure wave (Δtp; 3.58±12.86 ms; P < 0.05; wristband higher). However, ASBP, APP, and Δtp measurements were highly correlated (r = 0.9970, r = 0.9953, and r = 0.8838, respectively, P <0.0001) between tonometers; within-subject and between tonometer significant mean differences were within clinical ranges. CONCLUSIONS: This novel, hands-free platform may be interchangeable with the commonly used pencil-type tonometer, heralding new directions in noninvasive in vivo vascular research and clinical application.

Age and exercise training alter signaling through reactive oxygen species in the endothelium of skeletal muscle arterioles.

Exercise training ameliorates age-related impairments in endothelium-dependent vasodilation in skeletal muscle arterioles. Additionally, exercise training is associated with increased superoxide production. The purpose of this study was to determine the role of superoxide and superoxide-derived reactive oxygen species (ROS) signaling in mediating endothelium-dependent vasodilation of soleus muscle resistance arterioles from young and old, sedentary and exercise-trained rats. Young (3 mo) and old (22 mo) male rats were either exercise trained or remained sedentary for 10 wk. To determine the impact of ROS signaling on endothelium-dependent vasodilation, responses to acetylcholine were studied under control conditions and during the scavenging of superoxide and/or hydrogen peroxide. To determine the impact of NADPH oxidase-derived ROS, endothelium-dependent vasodilation was determined following NADPH oxidase inhibition. Reactivity to superoxide and hydrogen peroxide was also determined. Tempol, a scavenger of superoxide, and inhibitors of NADPH oxidase reduced endothelium-dependent vasodilation in all groups. Similarly, treatment with catalase and simultaneous treatment with tempol and catalase reduced endothelium-dependent vasodilation in all groups. Decomposition of peroxynitrite also reduced endothelium-dependent vasodilation. Aging had no effect on arteriolar protein content of SOD-1, catalase, or glutathione peroxidase-1; however, exercise training increased protein content of SOD-1 in young and old rats, catalase in young rats, and glutathione peroxidase-1 in old rats. These data indicate that ROS signaling is necessary for endothelium-dependent vasodilation in soleus muscle arterioles, and that exercise training-induced enhancement of endothelial function occurs, in part, through an increase in ROS signaling.

Enhanced external counterpulsation creates acute blood flow patterns responsible for improved flow-mediated dilation in humans.

Enhanced external counterpulsation (EECP) is a FDA-approved treatment for patients with coronary artery disease and unstable angina. Although beneficial effects of EECP have been linked to central/cardiac adaptations, recent findings have shown peripheral/vascular effects. Here, we sought to determine EECP-induced blood flow patterns and their association with vascular function. The present study was designed to investigate endothelium-mediated arterial vasodilation changes after one 45-min session of either EECP or Sham EECP in 18 randomly assigned apparently healthy, young men (25±4 years). Brachial (b) and femoral (f) flow-mediated dilation (FMD) were assessed before and within 10 min after completing EECP or Sham. After 20 min of EECP, peak blood flow velocity (V) and brachial and femoral artery diameters (D) were recorded live for 2 min. In addition, a blood sample was drawn from the earlobe to determine hematocrit and then to calculate blood viscosity (µ) and density (ρ), Reynolds number (Re=V*D*ρ/µ), and endothelial shear stress (ESS=2µ*V/D). EECP increased retrograde shear stress and retrograde-turbulent blood flow in the femoral artery and antegrade-laminar shear stress in the brachial artery. fFMD was increased after EECP compared with Sham and baseline (fFMD=13.1±3.7 vs. 7.9±4.6% and 7.8±4.5%, respectively, P<0.05) and bFMD was increased after EECP compared with baseline (bFMD=10.6±4.8 vs. 7.0±3.5%, P<0.05), despite different blood flow patterns. These results provide novel evidence that a single session of EECP-induced blood flow patterns improve endothelial function in peripheral muscular conduit arteries.

Analysis of both pulsatile and streamline blood flow patterns during aerobic and resistance exercise.

Blood flow-induced endothelial shear stress (ESS) during aerobic (AX) and resistance (RX) exercise can regulate endothelial function. However, non-invasive in vivo ESS estimation is normally obtained only according to Poiseuille's laws for streamline flow, rather than using Womersley's approximation for pulsatile flows. Here, we sought to determine brachial and femoral artery blood flow patterns, based on ESS, flow direction, and flow turbulence, using both pulsatile and streamline flow approximations during low- and moderate-intensity AX and RX. We performed high-resolution ultrasound imaging and Doppler peak blood flow velocity (V) measurements of the brachial and femoral arteries in eight young, healthy men during rest and two intensities of AX and RX at 40 and 70% of VO2max and 1-RM, respectively. Microhematocrit measurement was used to determine blood density (ρ) and viscosity (µ). ESS was calculated using Poiseuille's law, ESS = 2µ × SR (V/artery diameter), and Womersley's approximation, ESS = 2 Kµ × SR, where K is a function of Womersley's parameter α. Turbulence was determined using Reynolds number (Re). Re was calculated using Re = V × artery diameter × ρ/µ and normalized to resting steady-state values (nRe). ESS increases in a dose-dependent manner in the femoral and brachial arteries during both AX and RX when using either streamline or pulsatile approximations. However, our findings indicate that ESS is underestimated when using Poiseuille's law. Secondly, turbulence increases in conduit arteries with exercise intensity in a dose-dependent manner in both retrograde and antegrade flows during both AX and RX.

Redox balance in the aging microcirculation: new friends, new foes, and new clinical directions.

Cardiovascular aging is associated with a decline in the function of the vascular endothelium. Considerable evidence indicates that age-induced impairment of endothelium-dependent vasodilation results from a reduction in the availability of nitric oxide (NO(•) ). NO(•) can be scavenged by reactive oxygen species (ROS), in particular by superoxide radical (O(2) (•-) ), and age-related increases in ROS have been demonstrated to contribute to reduced endothelium-dependent vasodilation in numerous large artery preparations. In contrast, emerging data suggest that ROS may play a compensatory role in endothelial function of the aging microvasculature. The primary goal of this review is to discuss reports in the literature which indicate that ROS function as important signaling molecules in the aging microvasculature. Emphasis is placed upon discussion of the emerging roles of hydrogen peroxide (H(2) O(2) ) and peroxynitrite (ONOO(•-) ) in the aging microcirculation. Overall, existing data in animal models suggest that maintenance in the balance of ROS is critical to successful microvascular aging. The limited work that has been performed to investigate the role of ROS in human microvascular aging is also discussed, and the need for future investigations of ROS signaling in older humans is considered.

Association of age with timing and amplitude of reflected pressure waves during exercise in men.

BACKGROUND: Increased elastic conduit artery stiffness with aging is associated with early wave reflection and increased wasted left ventricular pressure energy (LVE(W)). The effects of aging on central hemodynamics during exercise have not been well characterized. This study sought to investigate changes in central hemodynamics during cycle exercise in young, middle-aged, and older men. METHODS: Central blood pressure and wave reflection characteristics were measured noninvasively using radial artery applanation tonometry at rest and during cycling exercise (45, 55, and 65% of predicted maximum heart rate (HR(max))) in 14 young (24 ± 1 years), 16 middle-aged (49 ± 2 years) and 13 older (73 ± 2 years) men. RESULTS: Repeated measures analysis of variance revealed significant group-by-time interactions for heart rate, central diastolic blood pressure (DBP), central pulse pressure (PP), PP amplification (PPA), central aortic pressure augmentation (AP), aortic augmentation index (AI(X)), and LVE(W). Magnitude of change from baseline was significantly different in the older group compared to young and middle-aged groups in response to exercise at 65% of predicted HR(max) for AP (+3 ± 1 mm Hg vs. -7 ± 1, P < 0.001 and -3 ± 1 mm Hg, P < 0.001) and LVE(W) (+724 ± 215 dynes s/cm(2)·min vs. -494 ± 199, P < 0.001 and -315 ± 192, P < 0.001). CONCLUSIONS: This study suggests that changes in the timing and amplitude of reflected pressure waves during exercise alter the hemodynamic response to exercise with aging. In response to exercise, AP and LVE(W) increased in older subjects while young and middle-aged subjects exhibited a decline in AP and no change in LVE(W).