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Controlled cross circulation was performed in six pairs of dogs to assess hemodynamic changes in the donor dog. Cardiopulmonary bypass was performed for 45 minutes, with an aortic cross clamp time of 3 5 minutes. Anesthesia was maintained in the donor dog with 1.8% end-tidal isoflurane. Parameters before and after controlled cross circulation were compared using a Wilcoxon Signed Rank Test. Donor left ventricular dP/dt max, pulmonary capillary wedge pressure, blood volume, systemic vascular resistance, heart rate, total protein, platelet count, and white blood cell count did not change significantly. Donor cardiac output, end diastolic volume, central venous pressure, stroke volume, mean arterial blood pressure, and packed cell volume all decreased significantly (p<O.05). Recipient blood volume and donor cardiac performance (LV dP/dt max/end diastolic volume) increased significantly (p<O.05). / Master of Science

An experimental investigation was done on oxygen transfer into a laminar flow of whole blood and saline solutions downstream of an abrupt pipe expansion. This was used as the experimental model for regions of separated flow in the arterial system. The flow was fully-developed prior to the expansion with Reynolds numbers between 160 to 850. The results showed high transfer rates over most of the region downstream of the step, with maximum transfer occurring near the reattachment point. In addition, oscillations of the transfer rate were measured at the larger Reynolds numbers of 450 and 850. / Master of Science

Suspension of the body in the head-down posture (90° below the horizontal) for traction and added resistance to exercise has generated considerable interest in recent years. However, recent investigators of inversion have cautioned individuals not to participate in such activities until further research could be performed on the effects of exercise in the head-down position. The purpose of this investigation was to examine the acute metabolic and hemodynamic responses of men at rest and during exercise in the inverted posture (90° head-down tilt) versus the supine and standing postures. The parameters investigated were oxygen consumption(V̇O₂), heart rate(HR), systolic blood pressure (SBP), and diastolic blood pressure(DBP). Eleven male recreational athletes underwent 6 sessions of postural change. The baseline posture was sitting and the critical positions were supine, standing, and inverted. The subjects were asked to remain in each of these postures for three minutes. In the first 2 sessions, oxygen consumption(V̇O₂), was measured at rest and during 45° hip-f1exion respectively, The V̇O₂ in the inverted posture at rest was found to be 1.7% greater than the V̇O₂ in the standing and the supine postures. V̇O₂ in the inverted posture during exercise was 7% and 36.5% greater than in the supine and standing postures, respective1y. A statistical significance in HR at rest in the standing posture versus the inverted and supine postures was observed. During 45° hip-flexion activity, the HR in the standing posture was found to be significantly faster than the supine posture. The HR in the inverted posture was significantly faster than the supine posture as well. At rest, there was no significant increase in SBP as re1ated to posture. During exercise, the SBP was significant1y greater; at rest in each of the postures. Both postural and exercise factors significantly affected the DBP. The post-hoc analyses showed supine resting DBP was significantly lower than in the other two resting postures. During exercise, the standing BP was significantly greater than the supine and inverted DBP. These data demonstrate: A) V̇O₂ in the supine and inverted postures is significantly greater than in the standing postures. B) a statistically significant increase in HR occurs in the standing posture as compared to the supine and inverted postures; however, it does not appear to be clinically significant, C) with the arms maintained in the anatomical position for all postural changes, the SBP was not significantly affected by the change of posture, but was significantly increased with exercise. D) and DBP in the standing posture was statistically greater than in the other two postures and DBP in the inverted posture was significantly elevated above that found in the supine posture. / Master of Science

Although ACC exerted a strong effect on the haemodynamic changes after SA, SA per se did not have much influence on ACC. The incidence and severity of ACC remained unchanged compared with the pre-spinal state. As long as maternal blood pressure were well controlled, the uterine blood flow indices were not affected by ACC. / Although there are many publications on ACC, most publications have considered ACC as a single entity, or reported its effects in terms of just a few end-point measures. The information published so far on ACC remains fragmented. This will be readdressed by taking a multidisciplinary approach with input from the fields of anaesthesia, obstetrics and radiology to non-invasively assess the haemodynamic changes associated with ACC. / Aortocaval compression occurs when parturients lie in the supine position with the gravid uterus compressing the aorta and the inferior vena cava. This interferes with venous return to the heart to reduce cardiac output, resulting in hypotension, uterine hypo-perfusion and fetal acidosis. Under neuraxial anaesthesia when the compensatory mechanisms via the sympathetic nervous outflow are blocked, the effects from ACC are exaggerated and results in maternal and fetal morbidity. / Intermittent IVC compression was responsible for most of the haemodynamic effects, presenting mainly as a reduction in cardiac output. Blood pressure or heart rate changes are poor indicators for IVC compression, and most patients were asymptomatic. Patients who have moderate to severe ACC have a higher incidence of hypotension after SA and consume a higher amount of phenylephrine for maintaining BP. / The research was conducted on non-labouring term parturients presenting for elective Caesarean section under spinal anaesthesia. Measurements were performed to assess the patency of blood vessels and haemodynamic responses to lateral tilts, using ultrasound and non-invasive haemodynamic monitors. / This research has achieved the following: (1) Qualitative measurements of compression of the aorta and IVC with US imaging and Doppler US; (2) Development of a new simple bedside method for detecting ACC using US; (3) Quantitative measurements of physiological responses in the maternal and fetal circulation associated with ACC; (4) Investigation of the effects of spinal anaesthesia per se on ACC. / Lee, Wee Yee Shara. / Adviser: Khaw Kim Sun. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3446. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 234-254). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Cardiovascular activities may increase the brain blood flow improving neuronal activities leading to improved cognition. Consequently, the effects of an acute bout of moderate intensity aerobic exercise on brain hemodynamics and its correlation with cognitive color-word Stroop task performance were tested. The Stroop tasks were congruent (color matches word) and incongruent (color does not match word). Prefrontal (PFC) and motor cortex (MC) blood flow was recorded by fNIRS (functional near-infrared spectroscopy) while the subject was performing the Stroop tasks before and after the 30 minutes of exercise or equivalent time of rest controls (checking for practice effects). Ninety human subjects of age 24± 6, 20 ADHD (attention-deficit hyper-activity disorder), 27 High-BMI (>25), 29 males were recruited. Reaction time ‘RT' decreased (p<0.05) after exercise for both the congruent (12%) and incongruent (10%) Stroop tasks, compared to 8% with practice alone. Accuracy did not change after practice or exercise. HR changes after exercise correlated (p<0.05) with better accuracy and faster RT for the incongruent Stroop task. In general, a metabolic lag occurred in the neuronal deoxy- hemoglobin (Hb) signals behind the systemic oxy-Hb signals. PFC showed the highest effect sizes of Stroop task-responsive systemic hemodynamic changes compared to baseline irrespective of rest or exercise. Yet, PFC showed most significant (p<0.001) neuronal hemodynamic changes between the before and after exercise sessions, and these changes were opposite for right and left PFC, and opposite for congruent and incongruent Stroop tasks. Correlating the RT and mistakes with hemodynamics for both the Stroop tasks revealed that, after exercise, neuronal hemodynamic changes occurred at both PFC and MC associated with faster RT (p<0.05), and systemic hemodynamic responses occurred at PFC correlated (p<0.05) with mistakes. Overall, it was concluded that exercise changed the neuronal hemodynamic changes affecting speed; however, neuronal metabolic changes did not occur sufficiently to help improve accuracy in all subjects.

Hemodynamic factors play a role in atherogenesis and the localization of atherosclerotic plaques. The human aorta and coronary arteries are susceptible to arterial disease, and there have been many studies of flows in models of these vessels. However, previous work has been limited in that investigations have not modeled both the geometry and flow conditions in specific individuals. The first aim of the research was to develop a methodology that combined computational fluid dynamics (CFD) and magnetic resonance imaging (MRI) to simulate the blood flow patterns found in the human aorta. The methodology included MR image processing, 3D model reconstruction and flow simulation using in vivo velocity boundary conditions obtained from phase contrast (PC)-MRI scanning. The CFD simulations successfully reproduce the unusual right-hand helical flow pattern that has been reported in the ascending aorta, giving confidence in the accuracy of the methodology. The second aim was to investigate the causes of the right-hand helical flow. It was found that the correct flow dynamics could only be produced by including the specific aortic motion caused by the beating heart; and it is concluded that this is a significant factor in producing the observed in vivo helical flow patterns. The entrance flows of coronary arteries are expected to be affected by flow in the aortic root, and the third aim was to explore these effects using models that include aorta and coronary arteries. The simulation results demonstrate that a pair of axial vortexes with different rotating directions exists in the entrance segments of the right and left coronary arteries during systole and early diastole, producing asymmetrical wall shear stress (WSS) distributions. The last aim of the research was to examine possible relationships between WSS distributions induced by the entry flow patterns and the frequency distributions of atherosclerosis in the proximal segments of coronary arteries reported in the clinical literature. A close correspondence between low WSS and higher frequency of plaque occurrence was observed. The tools developed in this study provide a promising avenue for future study of cardiovascular disease because of the ability to investigate phenomena in individual human subjects.