BACKGROUND: Age-related declines in endothelial function have been well documented with larger declines observed in middle-aged. Passive heat exposure has been shown to be a promising method to improve vascular endothelial health, with sauna specifically being linked to reduced risk of cardiovascular disease. Increases in blood flow and shear rates associated with heat exposure are often considered to have a major influence on the observed improved endothelial function following heat exposure. The magnitude of these changes in response to sauna have not yet been defined. Therefore, the purpose of this study is to quantify and compare the vascular response to an acute bout of sauna heating in young and middle-aged individuals. METHODS: 10 young (24.9 ± 4.2 years, 6 males and 4 females) and 8 middle-aged adults (55.6 ± 3.9 years 4 males and 4 females) underwent 40 min of sauna exposure at 80 oC. Esophageal and intramuscular temperatures were recorded throughout the duration of the experiment. Brachial and superficial femoral artery blood flow, artery diameter, and shear rates were recorded at baseline and following heat exposure. Brachial artery flow-mediated dilation (FMD) was measured at baseline and following 90 min of recovery. RESULTS: Core and muscle temperatures significantly increased by 1.5 ± 0.53 and 1.95 ± 0.70 °C, respectively (P < 0.05) and the magnitude of increase did not differ between young and middle-aged participants (P0.867 and 0.488, respectively). Shear rate increased by 170– 200% (P < 0.001), while blood flow increased by 180–390% (P < 0.001) in the superficial femoral and brachial artery, respectively, in both groups. Importantly, the changes in shear and flow did not significantly differ between young and middle-aged subjects for either artery (P = 0.190–0.899.) Systolic blood pressure (SBP) was significantly reduced from 135.25 ± 17.50 to 122.38 ± 19.7 mmHg (P = 0.017) only in middle-aged participants and a decrease in diastolic blood pressure was observed from 81.6 ± 13.0 mmHg at baseline to 69.8 ± 8.4 mmHg (P < .001). Heat-induced dilation was strongly correlated to baseline endothelial function in the young (R = 0.86, P = 0.006), but not the old (R = 0.22, P = 0.631). CONCLUSIONS: These results indicate that young and middle-aged adults have similar shear-rate and blood flow responses to acute sauna heating, which significantly reduces blood pressure in middle-aged, but not young individuals. Future heat therapy studies may elicit meaningful cardiovascular benefits from lower magnitudes of chronic passive heat stress.

Carotid artery wall stiffness has been widely considered as an index of vascular health, and has been associated with occurrence of cardiovascular events, such as stroke. In addition, the blood flow patterns in the carotid artery can yield crucial information on atherosclerosis progression and cerebrovascular impairment. Pulse wave imaging (PWI) is a non-invasive ultrasound imaging technique that tracks the propagation of the arterial pulse wave, providing thus regional arterial wall stiffness mapping. Moreover, towards enabling accurate visualization of blood flow patterns, ultrasound-based vector flow imaging (VFI) modalities have been developed. Building upon PWI and VFI techniques, the overall goal of this dissertation is to develop ultrasound-based methodologies that can provide simultaneous imaging of the carotid artery wall mechanics and blood flow dynamics at high temporal and spatial resolutions. The developed techniques are validated through vessel phantom experiments and simulations. Furthermore, their potential to diagnose pre-clinical stages of carotid artery disease and provide additional insights in risk for stroke assessment, is demonstrated in an atherosclerotic swine study and human subjects in vivo. More specifically: A method is presented that analyzes the pattern of arterial wall motion derived by PWI, in order to detect spatial mechanical inhomogeneity across an imaged artery, and provide piecewise arterial wall stiffness estimates. The proposed technique is validated in a phantom consisting of a soft and a stiff segment, while its feasibility is demonstrated to identify inhomogeneous wall properties in atherosclerotic human carotid arteries, as well as provide atherosclerotic plaque mechanical characterization in vivo. Subsequently, PWI is integrated with VFI techniques in the same ultrasound acquisition sequence, in order to enable simultaneous and co-localized imaging of arterial wall stiffness and blood vector flow velocity. The performance of the technique is investigated through experiments and FSI simulations. Moreover, its feasibility was shown to investigate associations between carotid artery Pulse Wave Velocity and blood flow patterns, in vivo. Based on the previously developed PWI and VFI modalities, a novel ultrasound-based technique is developed that combines high frame rate vector flow imaging with a data clustering approach, in order to enable direct and robust wall shear stress measurements. The performance of the proposed method is evaluated through vessel phantom experiments and simulations, while its feasibility is shown to detect pre-clinical stages of carotid artery disease in a swine model in vivo. In addition, a pilot clinical study is presented involving application of the developed modality in normal and atherosclerotic human carotid arteries in-vivo. Moving forward, the developed imaging modalities are used to implement novel clinical biomarkers based on carotid artery arterial wall mechanics and blood flow dynamics, that can potentially assist in risk for stroke assessment. The patterns of those biomarkers are investigated in the common carotid arteries of subjects with low degree of stenosis and medical history of stroke, against subjects without history of stroke. The same biomarkers are also analyzed with respect to stroke symptomatology in atherosclerotic patients with moderate to high degree of stenosis. Moreover, the developed techniques are used to identify vulnerable plaque components in subjects with fully developed plaques, as compared with CTA scans. Finally, a deep learning-based approach for motion tracking of the arterial wall throughout the cardiac cycle is proposed. A neural network is trained to learn the motion patterns of the carotid artery and potentially improve the quality of PWI. The performance of the technique is assessed in vessel phantom experiments and its feasibility is demonstrated in healthy human carotid arteries in-vivo.

Heart disease is the main cause of death today, and studying causes and treatments are of great interest. Blood flow simulations using computational fluid dynamics shows promise in providing insight into this area. This study builds upon previous work by Larsson et al. and Kronborg et al. who have developed a program for simulating the blood flow through patient specific left ventricles. More specifically we aimed to improve the accuracy of their blood flow simulation by accounting for the protruding structure of the endocardial wall, previously disregarded in the model due to the limitations in spacial accuracy of echocardiography. These structures, consisting of trabeculae carneae and papillary muscles, have been shown to have a significant impact on the blood flow. In a recent study, Sacco et al. proposed a solution were a porous layer could mimic the effects on the blood flow from these structures in a rigid heart model. Our study aimed to apply this modification to the left ventricle of the dynamic model using the Navier-Stokes-Brinkman flow equation and a subdomain defining the porous region. This study has been working towards the end goal of fully implementing the porous layer into the heart simulation. The equations needed have been formulated and simulations have been run on flow in a more simple setting to verify the model. The simulations show promise in being able to recreate the results from Sacco et al. but further development is needed before the porous model can be tested in the dynamic left ventricle model, most notably defining the porous subdomain in the dynamic model. We conclude that the porous domain will affect the flow, possibly breaking up vortices and reducing the wall shear stress. Confirming this requires additional studies, but the implementation of a porous domain would likely result in a more accurate simulation.

Yes / Venous abnormalities contribute to the pathophysiology of several neurological conditions. This paper reviews the literature regarding venous abnormalities in multiple sclerosis (MS), leukoaraiosis, and normal-pressure hydrocephalus (NPH). The review is supplemented with hydrodynamic analysis to assess the effects on cerebrospinal fluid (CSF) dynamics and cerebral blood flow (CBF) of venous hypertension in general, and chronic cerebrospinal venous insufficiency (CCSVI) in particular.CCSVI-like venous anomalies seem unlikely to account for reduced CBF in patients with MS, thus other mechanisms must be at work, which increase the hydraulic resistance of the cerebral vascular bed in MS. Similarly, hydrodynamic changes appear to be responsible for reduced CBF in leukoaraiosis. The hydrodynamic properties of the periventricular veins make these vessels particularly vulnerable to ischemia and plaque formation.Venous hypertension in the dural sinuses can alter intracranial compliance. Consequently, venous hypertension may change the CSF dynamics, affecting the intracranial windkessel mechanism. MS and NPH appear to share some similar characteristics, with both conditions exhibiting increased CSF pulsatility in the aqueduct of Sylvius.CCSVI appears to be a real phenomenon associated with MS, which causes venous hypertension in the dural sinuses. However, the role of CCSVI in the pathophysiology of MS remains unclear.

No description available.

Many epidemiological studies have named pinching, deviated wrist postures, and repetitive motion as ergonomic risk factors in the development of carpal tunnel syndrome (CTS). Evidence suggests that hypervascularization of the median nerve and increased intraneural blood flow proximal to the carpal tunnel result in response to ergonomic risk factors (finger pressing and deviated wrist postures). The purposes of this study were to 1) determine the effect of a pinch posture, with and without force exerted by the finger, thumb, or both and 2) determine the effect of repetitive wrist flexion and extension on intraneural blood flow velocity in the median nerve proximal to the carpal tunnel. Eleven healthy and eleven CTS symptomatic individuals participated in this study and completed three components: 15 pinch posture force trials, 3 repetitive wrist motion trials, and 3 static wrist posture trials. Intraneural blood flow was measured using pulse wave Doppler during each trial. Main effects of pinch posture force (F4,80 = 21.397, p < 0.001) and wrist posture (F2,40 = 14.545, p < 0.001) were observed. Trials where force was applied by the finger (2.21 cm/s), thumb (2.22 cm/s) or both (2.34 cm/s) produced higher intraneural blood flow velocities than trials with no force (1.79 cm/s) or relaxed hand (1.89 cm/s). Trials performed in flexion (2.24 cm/s) were greater than neutral (2.06 cm/s) and extension (1.97 cm/s). No interactions or main effects of time were found in response to repetitive wrist motion. These results suggest that at low force levels (6 N) it’s not how the force is applied but rather that the force is being applied that has an effect on the median nerve. Additionally these results suggest that the contribution of repetitive motion to the development of CTS may not be directly to the median nerve. / Thesis / Master of Science (MSc)

Aging results in lower exercise tolerance, manifested as decreased Critical Power (PCRIT). Aging is also associated with reduced physical activity, decreased muscle mass, and altered muscle blood flow, all of which may contribute to the age-related decrease in PCRIT. Purpose: The purpose of this study was to determine if the age-related decrease in PCRIT occurs independently of changes in physical activity and muscle mass and if it is related to impaired muscle blood flow. Methods: 10 Old (63.1 ± 2.5 years, 5 female and 5 male) and 10 Young (24.4 ± 4.0 years, 5 female and 5 male) physically active volunteers enrolled in this study. Physical activity was measured with accelerometry. Leg muscle mass was quantified with dual x-ray absorptiometry (DEXA). PCRIT and the maximum power achieved during a graded exercise test (PGXT) during single-leg knee extension exercise were determined over the course of 4 visits. On the fifth visit, vascular function of the leg was assessed with the passive leg movement (PLM) hyperemia. Subsequently, subjects performed knee extension exercise at 10 watts (W), 20 W, 90% PCRIT, and 100% PGXT while blood flow and blood pressure were measured at the femoral artery for each intensity. Results: Young and Old subjects did not differ in daily step count (Old = 13001.1  2464.0 vs Young = 13527.0  3213.8 steps, P = 0.735) or in leg lean mass (9.06  0.62 g/kg, P = 0.901). The Old subjects had a lower mass-specific PCRIT (Old = 3.20  0.94 vs Young = 4.60  0.87 W/kg, P = 0.004), vascular function (mass-specific Passive Leg Movement (PLM): Old = 79.4  38.3 vs Young = 128.8  34.9 ml/min/kg, P = 0.010) and leg blood flow at 90% PCRIT (mass-specific: Old = 378  122 vs Young = 522  124 ml/min/kg, P = 0.014) and 100% PGXT (mass-specific: Old = 391  109 vs Young = 544  136 ml/min/kg, P = 0.013). When normalized for leg muscle mass, PCRIT was strongly correlated to peak leg blood flow in response to PLM (R2 = 0.53; P < 0.001) and leg blood flow during knee extension exercise at 90% PCRIT (R2 = 0.36; P = 0.007). Conclusion: The age-related decline in PCRIT is associated with major decreases in muscle endurance and is correlated with concomitant reductions in vascular function in healthy active adults. Future research should determine if interventions known to improve vascular function can ameliorate exercise tolerance in Old adults.

A Calibrated Cuff Plethysmography device was built, tested for verification, and used to experiment on human subjects to measure the cardiovascular response of consuming a beet supplement, specifically looking at arterial compliance and pressure-area curves. Each subject was tested four times. A baseline was measured under normal conditions and after five-minute hyperemia conditions. 10 subjects were given 6 ounces of water mixed with either purple Kool-Aid (control), a SuperBeets supplement, or a SuperBeets Sport supplement and after 45 minutes, measurements were taken undergoing normal and hyperemia conditions once more. The verification testing demonstrated the calibration of the device was effectively able to measure volume changes using a stationary metal pipe and IV bag, showing an average percent error of 3.11%. Data collected during the patient experiment resulted in the expected arterial compliance curves as well as pressure-area curves, when measurements were taken properly, and the subject didn’t move. These tests were able to validate the use of the device for measuring arterial compliance and seeing distinctions between normal and hyperemic conditions. However, many issues were presented and are thoroughly addressed in this paper for future research using the same device.

This thesis investigates the effect of acute isometric handgrip exercise on cognitive function in young healthy adults / Acute whole-body exercise transiently improves cognitive function which may be mediated by increased cerebral blood flow (CBF) and arousal. Interestingly, small muscle mass exercise, like isometric handgrip exercise (IHG) may stimulate the same physiological responses as whole body-exercise and improve cognitive function. However, these effects are poorly understood, and whether sex-based differences exist in the cognitive response to IHG is unknown. Therefore, the purpose of this study was to investigate whether acute IHG improves cognitive function in young healthy adults and examine potential sex differences in the cognitive response to IHG. We hypothesized that acute IHG would improve cognitive function compared to a control condition, and that females would have greater improvements in cognitive function due to a lower exercise pressor response. To test this, 30 participants (n=15 females, mean age=23.8±3.3 years;BMI=25.3±4.1 kg/m2) completed either IHG or a control condition in a randomized-crossover design separated by at least 2 days. IHG consisted of four sets of 2-min unilateral squeezing a handgrip dynamometer at 30% maximal voluntary contraction separated by 3-min of rest. The control condition watched a nature documentary for 20-min. Hemodynamics (systolic blood pressure, diastolic blood pressure, mean arterial pressure, and heart rate) were assessed throughout. Executive function, working memory, and processing speed were assessed via the 4-Choice, Corsi Block, and N-Back tests. Arousal was assessed using the Felt Arousal Scale (FAS). Middle cerebral artery blood velocity (MCAv) was assessed using transcranial Doppler ultrasound. Compared to the control condition, IHG significantly increased MAP (∆ 26 ± 17 mmHg; P<0.001), HR(∆ 18 ±13 bpm; P<0.001), MCAv (∆ 5.27 ± 19.4 cm/s; P<0.001), cerebrovascular resistance (∆ 0.71 ±0.69 mmHg/cm/s; P=0.003), and arousal (∆ 2 ± 2 FAS score; P<0.001). Cerebrovascular resistance was calculated as MAP/MCAv. Overall, despite increases in MCAv and arousal, there was no effect of IHG on cognitive performance, and no sex differences were observed in the cognitive response to IHG. These findings stand in opposition to emerging work and suggests that increased CBF and arousal via acute IHG are an insufficient stimulus to enhance cognitive function in young adults. Furthermore, there seems to be no moderating effect of biological sex on the cognitive response to acute IHG. / Thesis / Master of Science (MSc) / It is well known that whole-body exercise, such as running, swimming, or lifting weights, improves cognitive function. Cognitive function encompasses our ability to pay attention, remember new information, and make important decisions. We sought to investigate whether isometric handgrip exercise (IHG) could improve cognitive function in young adults, because it may be a new and accessible way to improve cognitive abilities. We also wanted to know if IHG had a different effect on cognitive function in females compared to males. To test cognitivefunction, participants played computer games that measured how their cognitive abilities were affected by IHG. In particular, we examined how IHG impacted a participant’s memory, decision making, and speed to completion. Our results show that IHG increased blood flow to the brain and made participants feel more alert compared to a control condition, however, IHG did not improve performance on the computer games. Males and females also did not differ in terms of their performance on the cognitive tests. Overall, a single session of IHG did not improve cognitive function in young adults. Although IHG did not improve cognitive function in young adults, it should be investigated in other individuals, such as older adults and people with hypertension, who may stand to gain more from IHG.

Cerebral hemodynamics monitoring is vital in the neuroscience intensive care unit to assess brain health. Diffuse optical methods using near-infrared light, e.g., near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS), allow for non-invasive prolonged monitoring of cerebral hemoglobin oxygenation and blood flow. For patients suffering from cerebral fluid or tissue volume buildup, intracranial pressure (ICP) is monitored invasively as its elevation compromises cerebral perfusion. The critical closing pressure (CrCP) is a transcranial doppler (TCD) derived non-invasive parameter that correlates with ICP; however, its use is limited due to discomfort during extended TCD measurement. I expanded on Sutin’s preliminary study using DCS to estimate CrCP and found high correlations between DCS obtained CrCP against TCD (R2: 0.77-0.83) in stroke patients. The use of DCS to monitor CrCP is advantageous because its sensors are comfortable to wear and easy to use continuously without the need of a specialized operator. However, the low DCS signal-to-noise ratio (SNR) limits the depth sensitivity and temporal resolution of CrCP measures. Following these encouraging results, I built a low-cost wireless cerebral oximeter based on multi-distance continuous wave NIRS called FlexNIRS, which exhibits high SNR (NEP < 70 fw/Hz0.5) and high sampling rate (266 Hz). This device not only quantifies cerebral oxygenation but resolves the pulsatile blood volume signal at large source-detector separations (33 mm). Using the relationship between blood flow and volume, I augmented pulsatile DCS blood flow measurements with FlexNIRS pulsatile signals. I experimentally demonstrated the high fidelity (R2: 0.98) and > 50-fold SNR improvement of the method, resulting in a one order of magnitude increase in the temporal resolution of CrCP estimates. / 2024-06-12T00:00:00Z