No description available.

No description available.

<p> Increased arterial stiffness and vascular endothelial dysfunction have been identified as independent risk factors for the development and progression of cardiovascular disease. Traditional endurance training has been associated with elevated levels of central arterial compliance and an attenuation of cardiovascular events. As well, the positive benefits of aerobic-based training have been acknowledged as effective modulators of vascular endothelial function. To date, the impact of sprint interval training on cardiovascular health has not been evaluated. Furthermore, the mechanisms responsible for previously observed enhancements in endurance (750 kJ) performance following two weeks of sprint interval training remain unclear, but may be related to changes in vascular structure and function.</p> <p> Nine young healthy males [age: 22 ± 0.5 (mean± SEM)] participated in a two week sprint interval training program consisting of 4-6 30 second maximum effort exercise bouts performed every other day on a cycle ergometer. In addition, each participant was required to complete a 750 kJ time trial on a cycle ergometer as a measure of aerobic exercise performance before (PRE) and after (POST) training. Measurements of supine, resting carotid pulse pressure, carotid cross-sectional compliance, and brachial vascular endothelial function (using flow mediated dilation) were also acquired PRE and POST training.</p> <p> Resting pulse pressure did not show any significant changes with exercise training (PRE= 48.6±1.6, POST= 52.4±2.5 mmHg, p>0.05). Mean brachial artery diameter was not changed with sprint interval training (PRE= 4.29±0.17, POST= 4.38±0.18 mm, p>0.05); however, mean carotid artery diameter increased significantly PRE to POST (PRE= 6.40±0.15, POST= 6.49±0.14 mm, p=0.008). Carotid cross-sectional compliance did not change PRE to POST training (PRE= 0.164±0.010, POST= 0.162±0.007 mm^2/mmHg, p>0.05). Brachial vascular endothelial function measured using flow-mediated dilation did not show a significant change with sprint interval training, however a trend towards improvement was noted (PRE= 4.6±1.8, POST= 6.4±1.0 %, p=0.296). When normalized for shear rate (which was also unaltered with sprint interval training) there were no changes in endothelial function (PRE = 0.158±0.068, POST= 0.198 ± 0.034 %/S^-1, p>0.05). Average brachial post-occlusion blood flow was significantly enhanced following training possibly revealing enhanced resistance vessel function (PRE= 296.0±37.4, POST= 324.8±38.8 ml/min, p=0.04), despite no change in peak brachial blood flow (PRE= 332.0±42.3, POST= 362.6±45.7 ml/min, p>0.05). 750 kJ time trial performance was significantly enhanced with training (PRE = 62.8±4.9; POST= 55.84±3.55 min; p=0.006).</p> <p> In conclusion, sprint interval training did not change resting carotid compliance or brachial endothelial function, despite significant improvements in aerobic performance (750 kJ). However, carotid resting diameters and brachial post occlusion blood flow were significantly increased PRE to POST and a trend towards improvement was seen for brachial flow mediated dilation. The exact mechanisms responsible for such changes remain unknown and require further investigation.</p> / Thesis / Master of Science (MSc)

<p> The Wingate anaerobic test can be used in an exercise training program as a powerful training stimulus for producing metabolic and performance enhancements. Although the acute cardiovascular responses in terms of heart rate (HR), blood pressure (BP), stroke volume (SV), cardiac output (CO), and leg blood flow following a single Wingate have been characterized, the acute cardiovascular recovery pattern in response to multiple Wingate exercise bouts performed in an interval pattern have yet to be described. The purpose of the current investigation was to characterize that acute cardiovascular recovery period following multiple Wingate exercise. We observed the recovery patterns of HR, BP, SV, CO, and leg blood flow for 120 minutes immediately following multiple Wingate exercise. Ten recreationally active males aged 19.8 ± 1.2 years (mean± SD) years performed a single bout of Wingate exercise, and a session of multiple Wingate exercise in random order, on separate days. Cardiovascular measurements were conducted at rest and after two-minutes of recovery and then continued at 15-minute intervals until 120 minutes of recovery. HR was elevated immediately after exercise compared to rest, and declined towards resting values for the remainder of recovery, although HR failed to return to resting values after 120 minutes of recovery. SV was significantly decreased, compared to rest, immediately following exercise from 87.3 ± 5.7 to 60.0 ± 5.6 ml. CO was increased compared to rest at two minutes following multiple Wingate exercise, and continued to increase to a maximum recovery value of 8.1 ± 0.7 L/min at R15. Immediately following exercise systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) were all elevated to 155 ± 3, 73 ± 2, and 100 ± 3 mmHg respectively. Although SBP and MAP returned to resting values 15-minutes after exercise, DBP continued to decrease, resulting in a period of hypotension observed from R15 and R30. Leg blood flow was elevated compared to rest following exercise. Common femoral artery (CFA) blood flow was higher after a single Wingate, than after multiple Wingate exercise (1264 ± 109 and 1036 ± 86 ml/min respectively). Superficial femoral artery (SFA) blood flow (616 ± 55 ml/min) immediately following multiple Wingate exercise was not different following a single Wingate, however the time to return to resting values was longer after multiple Wingate exercise. We attribute the sustained elevations in (SFA) blood flow to increased cutaneous flow for thermoregulation purposes following multiple Wingate exercise.</p> <p> The results of this investigation indicate that the general cardiovascular recovery time is longer after multiple Wingate exercise, than after a single Wingate bout. This type of supramaximal exercise temporarily reduces SV due to elevated SBP and decreases in cardiac preload that are not facilitated by vasodilatation and decreased total peripheral resistance (TPR).</p> / Thesis / Master of Science (MSc)

Endothelial function is influenced by a variety of factors, including shear stress direction and magnitude. Whereas improvements in endothelial function have mostly been attributed to increased anterograde flow, the results of many interventional models in humans suggest that enhancing blood flow in both anterograde and retrograde directions to create a high shear stress oscillatory stimulus may be optimal for improving endothelial function. Well-controlled studies are necessary to further this theory. The purposes of this study were to determine the brachial artery acute shear stress and endothelial function responses to (1) passive heat stress (HEAT), (2) ECG-gated cuff compressions (CUFF), and (3) ECG-gated rhythmic handgrip exercise (HGEX); and (4) to determine if there is a relationship between the degree of shear stress oscillation and endothelial function, regardless of the stimulus applied. We hypothesized that (1) HEAT would increase anterograde shear stress and decrease retrograde shear stress, leading to an unpredictable change in endothelial function; (2) CUFF would increase both anterograde and retrograde shear stress, leading to an increase in endothelial function; (3) HGEX would increase anterograde and retrograde shear stress and exercise metabolites, leading to an increase in endothelial function; and (4) the change in oscillatory shear index would be positively associated with the change in flow-mediated dilation, such that an increment increase in the degree of shear stress oscillation would be accompanied by a proportional improvement in endothelial function. In separate visits, 10 young healthy males (22±3 years) underwent 10 minutes of unilateral HEAT, CUFF, or HGEX on the left arm (EXP), while the right arm served as a within-subject time control (CON). Non-invasive finger plethysmography was used to measure heart rate (HR) and blood pressure (BP) throughout the testing sessions. Ultrasonography was used to obtain measures of blood velocity and arterial diameter from the brachial artery of both limbs throughout the interventions. Anterograde and retrograde shear stress (SS) and oscillatory shear index (OSI) were calculated at baseline and during each intervention to assess the blood flow pattern changes. Endothelial function was assessed before and after each intervention, in both limbs simultaneously using a flow-mediated dilation (FMD) test. HEAT increased HR during the intervention (P < 0.05), mean BP and diastolic BP after the intervention (P < 0.05), anterograde SS in EXP (rest: 15.2 ± 2.9 vs. HEAT: 29.8 ± 8.5 dynes/cm2, P < 0.05), and FMD% in both limbs (P = 0.000). CUFF did not change HR or BP, increased anterograde (rest: 17.9 ± 4.1 vs. CUFF: 43.0 ± 12.4 dynes/cm2, P < 0.05) and retrograde (rest: -3.1 ± 2.5 vs. CUFF: -22.7 ± 6.0 dynes/cm2, P < 0.05) SS in EXP, but did not change FMD% in either limb (P = 0.248). HGEX increased HR during the intervention (P < 0.05), mean BP during and after the intervention (P < 0.05), anterograde SS in EXP (rest: 18.7 ± 5.9 vs. HGEX: 56.4 ± 11.5 dynes/cm2, P < 0.05), and FMD% in both limbs (P = 0.001). These findings suggest that an anterograde-dominant shear stress stimulus may be effective at improving endothelial function, but the confounding effect of sympathetic nervous system activation may play a more dominant role in the acute control response for shorter duration interventions such as the ones explored in this study. / Thesis / Master of Science (MSc) / It has been well established that the pattern of blood flow can impact arterial function, but the nuances of this relationship remain unclear. Through the use of heating, cuff compression, and exercise, this study sought to determine the optimal shear stress pattern to see beneficial changes in arterial function in the arm of young healthy males. Our results show many real life interventions alter not only the shear stress pattern in the artery, but also involve other systems like the brain and muscle that are crucial to maintaining the body’s physiological balance. It is clear that arterial function is regulated through a variety of different mechanisms, and that the changes we observe will depend on the parameters (e.g. duration, intensity, timing of assessment) of the applied stimulus. More specifically, isolating study designs should be constructed to determine the individual contributions of different human body systems to the arterial regulatory response.

No description available.

A four variable constitutive equation was developed utilizing the method first presented by Schneck and Walburn. Spearman rank correlation coefficients were calculated on whole blood samples within a narrow range of hematocrit to investigate further the effect of the various plasma constituents on whole blood viscosity. Viscosity measurements were made on one hundred anticoagulated blood samples of known hematocrit and chemical composition. The constitutive equation was developed using a power law functional form similar to that employed by Schneck and Walburn. This equation contains two parameters, the consistency index and the non-Newtonian index. A computerized multiple regression technique with apparent viscosity as the dependent variable was used to determine the particular form of these parameters. The one, two and three variable models developed confirmed the results of the previous work of Schneck and Walburn. The four variable model included the total lipids in combination with the concentration of total protein minus albumin and hematocrit. Spearman rank correlation coefficients showed the highest correlations between whole blood viscosity and the plasma constituents to be those of the globulins, total protein and fibrinogen. The constitutive equation developed did not show as high a correlation between experimental data and theory as did the Schneck-Walburn three variable model. The addition of a fourth variable did produce a statistically significant increase over the best three variable model of the present study. / M.S.

Five adult male volunteers were studied to investigate the effect of opiate receptor blockade on the physiological response to a maximum of 60 minutes of stationary cycling at 70% V02peak in a hot (33 0 C/65% RH) environment. Exercise bouts were conducted following the administration of naloxone (4mg IV) 5 minutes prior to exercise with a follow-up 4mg dose at 25 minutes of exercise. In the placebo trial, volume-matched doses of saline were administered at the same points. No significant drug effect was observed on rectal or mean skin temperature during exercise. Post-exercise skin temperature was significantly (P<.001) higher on naloxone versus saline. Forearm blood flow (FBF) was consistently higher from minute 25 of exercise until test termination, although only the minute 25 and minute 55 data points were significantly elevated (P<.05, P<.005, respectively) . The rectal temperature threshold at which FBF plateaued was higher on naloxone (P=.054), and the FBF: rectal temperature slope was higher on naloxone throughout the trial. No significant changes were observed in heart rate or estimated mean arterial pressures, although both were consistently lower on naloxone. Gross sweat response was not altered by the drug. Plasma Beta-Endorphin was significantly (P<.Ol) higher on naloxone versus saline, and Beta-Endorphin was significantly elevated in the naloxone trial only. The observation that FBF was significantly higher on naloxone without inducing compensatory heart rate or blood pressure changes suggests that the opioids may be involved in the blood volume shifts that occur during prolonged exercise in the heat. / Master of Science

Angle-closure glaucoma is a leading cause of blindness in the United States and around the world. New research has indicated that intraocular pressure is not the only risk factor associated with glaucomatous optic neuropathy. In recent years, a vascular deregulation in ocular blood flow has been considered a possible risk factor in glaucoma. A laser peripheral iridoplasty is a standard treatment option in non-pupillary block angle-closure glaucoma. The present study employed a secondary retrospective design and utilized patient’s data from an ophthalmologist’s practice. The purpose of this study was to examine the effect of laser peripheral iridoplasty on pulsatile ocular blood flow in primary angle-closure glaucoma and primary angle-closure suspects. A sample of 30 eyes from 17 patients was analyzed for this study. A significant increase in pulsatile ocular blood flow was found among primary angle-closure suspects. Additional data analysis was performed through SPSS software to examine the effect on these variables by age, sex and medical history as a total sample and in each group. Primary angle-closure suspects who were 51-60 years old showed a significant increase in intraocular pressure after laser treatment, however, primary angle-closure glaucoma patients who were 71-80 years old showed a significant decrease in intraocular pressure. Furthermore, a significant increase in pulsatile ocular blood flow was found in female subjects among primary angle-closure suspects, supporting the need for gender medicine research. Lastly, the pulsatile ocular blood flow increased significantly among primary angle-closure suspects who were also suffering from cardiovascular disease. Among primary angle-closure glaucoma patients who were suffering from both cardiovascular disease and diabetes mellitus, a significant decrease in intraocular pressure was observed.

Cerebrovascular diseases are by far the largest causes of death in the UK, as well as one of the leading causes of adult disability. The brain's healthy function depends on a steady supply of oxygen, delivered through the microvasculature. Cerebrovascular diseases, such as stroke and dementia, can interrupt the transport of blood (and hence oxygen) rapidly, or over a prolonged period of time. An interruption in flow can lead to ischaemia, with prolonged interruptions leading to tissue death and eventual brain damage. The microvasculature plays a key role in the transport of oxygen and nutrients to brain tissue; however, its role in diseases such as dementia is poorly understood, primarily due to the inability of current clinical imaging techniques to resolve microvessels, and due to the complexity of the underlying microvasculature. Therefore, in order to understand cerebrovascular diseases, it is necessary to be able to resolve and understand the microvasculature. In particular, generating large-scale models of the human microvasculature that can be linked back to contemporary clinical imaging is important in helping plug the current imaging gap that exists. A novel statistical model is proposed here that generates such large-scale models efficiently. Homogenization theory is used to generate a porous continuum capillary bed (characterised by its permeability) that allows for the efficient scaling up of the microvasculature. A novel order-based density-filling algorithm is then developed which generates morphologically accurate penetrating arterioles and venules, also demonstrating that the topology of the vessels only has a minor influence on CBF compared to diameter. Finally, the capillary bed and penetrating vessels are coupled into a large voxel-sized model of the microvasculature from which pressure and flux variations through the voxel can be analysed. A decoupling of the pressure and flux, as well as a layering of flow, was observed within the voxel, driven by the topology of the penetrating vessels. Micro-infarctions were also simulated, demonstrating the large local effects they have on the pressure and flux, whilst only causing a minor drop in CBF within the voxel.