No description available.

Reproducibility of results in biomedical research is an area of concern that should be paramount for all researchers. Importantly, this issue has been examined for experiments concerning cardiac electrophysiology. Specifically, multiple labs have found differences in results when comparing cardiac conduction velocity (CV) between healthy mice and mice that were heterozygous null for the gap junction (GJ) forming protein, Connexin 43. While the results of the comparison study showed differing extracellular ionic concentrations of the perfusates, specifically sodium, potassium, and calcium ([Na+]o, [K+]o, and [Ca2+]o), there was a lack of understanding why certain combinations of the aforementioned ions led to specific CV changes. However, more research from our lab indicates that these changes can predict modifications to a secondary form of cardiac coupling known as ephaptic coupling (EpC). Therefore the work in this dissertation was twofold, 1) to examine the effects of modulating EpC through perfusate ionic concentrations while also modulating GJC and 2) to investigate the effects of modulating all three of the main ions contributed with cardiac conduction (Na+, K+, Ca2+) and the interplay between them. Firstly I designed and tested changes from the use of 3D printed bath for optical mapping procedures. After verification that the bath did not modify electrophysiological or contrile parameters, I studied the effects of physiologic changes to EpC determinants ([Na+]o and [K+]o) on CV during various states of GJ inhibition using the non-specific GJ uncoupler carbenoxolone (CBX). Multiple pacing rates were used to further modify EpC, as an increased pacing rate leads to a decrease in sodium channel availability through modification of the resting membrane potential. with no to low (0 and 15 µM CBX) GJ inhibition, physiologic changes in [Na+]o and [K+]o did not affect CV, however increasing pacing rate decreased CV as expected. When CBX was increased to 30 µM, a combination of decreasing [Na+]o and increasing [K+]o significantly decreased cardiac CV, specifically when pacing rate was increased. Next, the combinatory effects of cations associated with EpC (Na+, K+, and Ca2+) were tested in to examine how cardiac CV reacts to changes in perfusate solution and how this may explain differences in experimental outcomes between laboratories. Briefly, experiments were run where [K+]o was varied throughout an experiment and the values for [Na+]o and [Ca2+]o were at one of two specific values during an experiment. 30 µM CBX was added to half of the experiments to see the changes in the CV-[K+]o relationship with GJ inhibition. With unaltered GJ coupling, elevated [Na+]o maintains CV during hyperkalemia. Interestingly, both [Na+]o and [Ca2+]o must be increased to maintain normal CV during hyperkalemia with reduced GJ coupling. These data suggest that optimized fluids can sustain normal conduction under pathophysiologic conditions like hyperkalemia and GJ uncoupling. Taken as a whole, this dissertation attempts to shed light on the importance of ionic concentration balance in perfusate solutions on cardiac conduction. / Ph. D. / The use of fluid replacement therapy was first used during the outbreak of Blue Cholera in the 1830s. However, after the development of basic fluids for intravenous fluid therapy, there have been very few changes in the fluid recipes. This same principle can be applied to cardiac research, where blood substitute perfusates are used during experimentation. However, there have been disagreements in experimental outcomes between various labs running matching studies which only varied in choice of perfusate solution. Therefore, one of the goals of this dissertation was to explore how changing ionic concentrations in cardiac perfusate solutions affected cardiac electrophysiological parameters. To fully appreciate changes in cardiac conduction, we also had to investigate changes to gap junctional coupling (GJC), which is the canonical determinant of cardiac conduction. Gap junctions are low resistance pathways which allow direct cell-to-cell coupling, which leads to synchronized cardiac conduction and contraction. However, there have been recent studies that have found a secondary form of cardiac coupling, known as ephaptic coupling (EpC), which is controlled through extracellular ionic concentrations, especially sodium, potassium, and calcium ([Na⁺]₀, [K⁺]₀, and [Ca²⁺]₀ respectively) and extracellular nano-domains known as the perinexus. We first investigate making small physiologic changes to [Na⁺]₀ and [K⁺]₀, while also inhibiting GJs to find the relationship between EpC and GJC. The results indicated that these EpC modulators could indeed modulate conduction, but only after GJs were sufficiently inhibited. However, results from this study disagreed with historical work indicating that [K⁺]₀ had a biphasic relationship with CV. Therefore, we then examined the effects of [Na⁺]₀ and [Ca²⁺]₀ on the CV-[K⁺]₀ relationship. Interestingly, it was found that inclusion of [Na⁺]₀ and [Ca²⁺]₀ had varying effects, depending on the level of GJ in the hearts. Specifically, hyperkalemia (high levels of potassium) v is associated with decreases cardiac CV. With a full complement of GJs it was found that increased [Na⁺]₀ was able to maintain cardiac CV at control levels. However, with inhibited GJ coupling, both increased [Na⁺]₀ and [Ca²⁺]₀ were needed to maintain conduction. This indicated that increasing EpC during GJ inhibition could be a possible safety mechanism for cardiac CV. The data in this dissertation aim to provide information to the importance of perfusate composition when regarding scientific data.

In recent years there has been more focus on investigating sex differences across all medical fields, including cardiology. There are sex differences in disease presentation, treatment and baseline function. These differences are critical to understand in order to properly treat both men and women. Even with an increased focus on this field, research has a male bias and there is more work to be done. Cardiac conduction is a highly synchronized process. Electrical signals are passed cell to cell through two mechanisms, ephaptic coupling and gap junctional coupling. These methods of electrical communication rely on gap junctions, sodium channels and the perinexus. When conduction is disrupted it causes arrhythmias. When investigating these three critical determinants of cardiac conduction in guinea pig hearts, we determined that there are sex differences in two of three investigated determinants. It appears that females are more susceptible to sodium channel modulation while males are more susceptible to gap junction modulation. Understanding these differences is critical to clinical care. It has been shown that females have higher mortality following cardiothoracic surgery and the reason for this is unknown. During cardiothoracic surgery the heart is arrested and maintained by a fluid, cardioplegia solution. Cardioplegia solutions contain components that are known to modulate conduction. We investigated the sex differences in cardiac electrophysiology with a focus on cardiac conduction and components of a common cardioplegia solution; we determined that there are electrophysiologic sex differences in response to both magnesium and mannitol. The sex substrates in three of the major determinants of conduction (sodium channels, gap junctions and perinexal width) and the differences in the effects of cardioplegia components on males and females may help to explain the higher mortality of females post cardiothoracic surgery. / Master of Science / In recent years there has been more focus on investigating sex differences across all medical fields, including cardiology. There are sex differences in disease presentation, treatment and baseline function. These differences are critical to understand in order to properly treat both men and women. Even with an increased focus on this field, research has a male bias and there is more work to be done. Cardiac conduction is a highly synchronized process. Electrical signals are passed cell to cell through two mechanisms, ephaptic coupling and gap junctional coupling. These methods of electrical communication rely on gap junctions, sodium channels and the perinexus. When conduction is disrupted it causes arrhythmias. When investigating these three critical determinants of cardiac conduction in guinea pig hearts, we determined that there are sex differences in two of three investigated determinants. It appears that females are more susceptible to sodium channel modulation while males are more susceptible to gap junction modulation. Understanding these differences is critical to clinical care. It has been shown that females have higher mortality following cardiothoracic surgery and the reason for this is unknown. During cardiothoracic surgery the heart is arrested and maintained by a fluid, cardioplegia solution. Cardioplegia solutions contain components that are known to modulate conduction. We investigated the sex differences in cardiac electrophysiology with a focus on cardiac conduction and components of a common cardioplegia solution; we determined that there are electrophysiologic sex differences in response to both magnesium and mannitol. The sex substrates in three of the major determinants of conduction (sodium channels, gap junctions and perinexal width) and the differences in the effects of cardioplegia components on males and females may help to explain the higher mortality of females post cardiothoracic surgery.

Cardiac fibroblast to myofibroblast phenoconversion is a critical step during the development of cardiac fibrosis. Myofibroblasts chronically remodel extracellular matrix that results in myocardial stiffening, cardiac dysfunction and eventually heart failure. Previously we showed that Meox2, a homeobox transcription factor, can inhibit myofibroblast phenoconversion. Here we show that Zeb2, a repressor of Meox2, plays a crucial role during this phenoconversion process. Zeb2 overexpression significantly upregulates the expression of three key myofibroblast markers: α-SMA, SMemb and ED-A fibronectin in primary rat cardiac myofibroblast. We show that Zeb2 is highly expressed in myofibroblast nuclei whereas it is minimally expressed in fibroblast nuclei. Zeb2 overexpression in myofibroblasts results in a less migratory and more contractile mature myofibroblast phenotype. Moreover, Zeb2 overexpression represses Meox2 expression in endothelial cells. Thus, the current study enhances our understanding of the mechanism behind myofibroblast phenoconversion and provides a basis for developing Zeb2-based novel anti-fibrotic drug in the future. / February 2016

No description available.

Familial amyloidosis with polyneuropathy (FAP) is a neuropathic form of heredofamilial systemic amyloidosis. Clusters of patients have been reported predominantly from Portugal, Japan and Sweden. The present study examines the involvement of the heart in individuals with the Swedish variety of FAP. During long-term ECG recording in 16 patients, a high frequency of disturbances of sinus node function and atrioventricular conduction were observed. Long-term ECG may help considerably in the evaluation of symptoms attributable to disturbances of heart rhythm in FAP. A retrospective survey of 20 patients with FAP treated with a pacemaker showed that the indication for pacing was advanced atrioventricular block (12 cases), dysfunction of the sinus node (5 cases), and atrial fibrillation with a slow ventricular response (3 cases). All patients experienced the effective relief of symptoms attributable to a slow ventricular rate. The long-term prognosis, however, seemed unaffected by this treatment. Histopathological examination of the sinoatrial (9 cases) and atrioventricular (6 cases) parts of the conduction system showed marked amyloid infiltration in all cases, which may explain the high occurrence of disturbances of cardiac rhythm and conduction. Twelve patients were examined by two-dimensional echocardiography and changes of varying degrees, such as highly refractile myocardial echoes (12 cases) and thickened ventricular walls (8 cases) and valves (7 cases), could be observed. Technetium-99m-pyrophosphate scintigraphy of the same patients revealed abnormal myocardial uptake of the isotope only in four. Echocardiography thus seems to be superior to scintigraphy for non-invasive detection of cardiac involvement in FAP. Myocardial samples from regions producing highly refractile myocardial echoes were obtained at in vitro échocardiographie examination of hearts from FAP autopsy cases. Histological examination showed that the highly refractile echoes corresponded to more or less sharply delineated nodules, containing amyloid and collagen in various amounts. / digitalisering@umu

The incidence of cardiovascular diseases including cardiac hypertrophy and failure in pre-menopausal women is lower compared to age-matched men but the risk of heart disease increases substantially after the onset of menopause. It has been postulated that female sex hormones play an important role in cardiovascular health in pre-menopausal women. In animal studies including spontaneously hypertensive (SHR) rats, the development of cardiac hypertrophy is attenuated by 17β-estradiol treatment. Cardiac energy metabolism is crucial for normal function of the heart. In cardiac hypertrophy and heart failure, the myocardium undergoes a metabolic shift from fatty acid as primary cardiac energy source to glucose, which re-introduces the fetal type of metabolism that representing the glucose as a major source of energy. Many studies have reported that the disruption of the balance between glucose and fatty acid metabolism plays an important role in cardiac pathologies including hypertrophy, heart failure, diabetes, dilative cardiomyopathy and myocardial infarction. Glucose enters cardiomyocytes via GLUT1 and GLUT4 glucose transporters and GLUT4 is the major glucose transporter which is insulin-dependent. Cardiac-selective GLUT4 deficiency leads to cardiac hypertrophy. This shows that the decrease in cardiac glucose uptake may play a direct role in the pathogenesis of cardiac hypertrophy. Estrogens modulate glucose homeostasis in the liver and the skeletal muscle. But it is not known whether estrogens affect also cardiac glucose uptake which could provide another mechanism to explain the prevention of cardiac hypertrophy by female sex hormones. In the present study, SHR Rats were ovariectomized (OVX), not ovariectomized (sham) or ovariectomized and treated with subcutaneous 17β-estradiol. After 6 weeks of treatment, body weight, the serum levels of estrogen, insulin, intra-peritoneal glucose tolerance test (IP-GTT), myocardial glucose uptake by FDG-PET (2-(18F)-fluoro-deoxyglucose (18FDG) and Positron Emission Tomography), cardiac glucose transporter expression and localization and cardiac hexokinase activity were analyzed. As results of this study, PET analysis of female SHR revealed decreased cardiac glucose uptake in OVX animals compared to intact that was normalized by estrogen supplementation. Interestingly, there was no change in global glucose tolerance among the treatment groups. Serum insulin levels and cardiac hexokinase activity were elevated by E2 substitution. The protein content of cardiac glucose transporters GLUT-4 and GLUT-1, and their translocation as determined by fractionation studies and immuno-staining did not show any significant change by ovariectomy and estrogen replacement. Also levels of insulin receptor substrate-1 (IRS-1) and its tyrosine phosphorylation, which is required for activation and translocation of GLUT4, was un-affected in all groups of SHR. Cardiac gene expression analysis in SHR heart showed that ei4Ebp1 and Frap1 genes which are involved in the mTOR signaling pathway, were differentially expressed upon estrogen treatment. These genes are known to be activated in presence of glucose in the heart. As a conclusion of this study, reduced myocardial FDG uptake in ovariectomized spontaneously hypertensive rat is normalized by 17β-estradiol treatment. Increased myocardial hexokinase appears as a potential mechanism to explain increased myocardial glucose uptake by 17β-estradiol. Increased cardiac glucose uptake in response to 17β-estradiol in ovariectomized SHR may provide a novel mechanism to explain the reduction of cardiac hypertrophy in E2 treated SHR. Therefore, 17β-estradiol improves cardiac glucose utilization in ovariectomized SHR which may give rise to possible mechanism for its protective effects against cardiac hypertrophy. / Erkrankungen des kardiovaskulären Systems, wie beispielsweise Herzhypertrophie oder Herzinsuffizienz treten bei Frauen vor der Menopause im Vergleich zu gleichaltrigen Männern seltener auf. Das Risiko für eine solche kardiovaskuläre Erkrankung steigt jedoch drastisch mit dem Beginn der Menopause an. Aus diesem Grund wird angenommen, dass weibliche Geschlechtshormone kardioprotektive Wirkungen besitzen. Tierstudien an spontan hypertensiven Ratten (SHR) haben belegt, dass eine Herzhypertrophie durch die Behandlung der Tiere mit 17β-Estradiol abgemildert werden kann. Entscheidend für die Funktion des Myokards ist sein Energiemetabolimus, der sich im Verlauf einer Hypertrophie oder Herzinsuffizienz vom primären Fettsäurestoffwechsel auf Glucosemetabolismus umschaltet. Diese Situation entspricht der des fetalen Herzens. Viele Studien haben belegt, dass eine Störung der Balance zwischen Glucose- und Fettsäurestoffwechsel oftmals ein erstes Anzeichen für einen pathologischen Zustand des Herzens, wie z.B. Hypertrophie, Herzinsuffizienz, Diabetes, dilative Kardiomyopathie und Myokardinfarkt ist. Im gesunden Herzen gelangt Glucose über die zwei Glucosetransporter GLUT1 und GLUT4 in die Zellen des Myokards, wobei der insulinabhängige Glut4-Transporter der Hauptglucosetransporter ist. Eine GLUT4-Defizienz führt daher ebenfalls zu einer Herzhypertrophie was wiederum zeigt, dass eine verminderte Glucoseaufnahme im direkten Zusammenhang mit pathologischen Zuständen des Herzens steht. Bisherige Studien haben gezeigt, dass Östrogen an der Glucosehomöostase in Leber und Skelettmuskeln beteiligt ist. Jedoch ist wenig darüber bekannt, ob Östrogen ebenfalls in die kardiale Glucosehomöostase eingreift und inwiefern die kardioprotektive Wirkung des Östrogens in diesem Zusammenhang steht.In der vorliegenden Arbeit wurden weibliche SH-Ratten ovariektomiert (OVX), nicht ovariektomiert (sham) oder ovariektomiert und zusätzlich subkutan mit 17β-Estradiol behandelt. Nach einer Behandlungszeit von 6 Wochen wurden dann das Körpergewicht, die Serumspiegel von Östrogen, Insulin und IPGTT bestimmt, und die Glucoseaufnahme des Myokards mittels FDG-PET analysiert. Zusätzlich wurden Expression und zelluläre Lokalisation der kardialen Glucosetransporter sowie die kardiale Hexokinaseaktivität untersucht. Es konnte gezeigt werden, dass sich eine verminderte Glucoseaufnahme des Herzens bei ovariektomierten Tieren durch Östrogen-Supplementation normalisieren lässt. Eine Abweichung bezüglich der Glucosetoleranz der einzelnen Gruppen konnte nicht beobachtet werden. Jedoch konnte ein erhöhter Insulinspiegel des Serums und eine erhöhte kardiale Aktivität des Enzyms Hexokinase durch die Behandlung mit Östrogen bei den ovariektomierten Tieren beschrieben werden. Durch Fraktionierungen und immunhistologische Untersuchungen konnte kein signifikanter Unterschied in Bezug auf die Menge sowie die Translokation der Glucosetransporter GLUT1 und GLUT4 im Myokard zwischen den einzelnen Behandlungen der Tiere beschrieben werden. Ferner konnte zwischen den einzelnen Tiergruppen auch kein Unterschied zwischen dem Insulin Rezeptor Substrat-1 (IRS-1) und seiner Tyrosin-phosphorylierten Form festgestellt werden, die für die Aktivierung und Translokation des GLUT4 benötigt werden. Analysen der Genexpression in den Herzen der SH-Ratten konnten allerdings zeigen, dass die Gene ei4Ebp1 und Frap1, die im mTOR Signalweg involviert sind, bei den Östrogen-supplementierten Tieren ein abweichendes Expressionsmuster aufweisen. Über diese Gene ist bekannt, dass sie in der Gegenwart von Glucose im Herzen aktiviert werden und bei der Entstehung einer Herzhypertrophie mitwirken. Basierend auf den PET-Analysen und der Hexokinaseaktivität lässt sich als Resultat dieser Arbeit aussagen, dass Östrogen die kardiale Glucoseaufnahme in SH-Ratten fördert. Diese Ergebnisse könnten einen Hinweis auf einen noch unbekannten Mechanismus geben, um die protektive Wirkung des Östrogens im Hinblick auf die Herzhypertrophie zu erklären. Hinsichtlich der Tatsache, dass keine Veränderungen in der Translokation der GLUT4-Transporter in der Plasmamembran bei den einzelnen Behandlungen der Tiere zu verzeichnen sind, jedoch Veränderungen der Glucoseaufnahme durch die PET-Analysen dargestellt werden konnten, besteht jedoch noch Erklärungsbedarf. Es liegen diverse Studien vor, die diesen Unterschied damit erklären könnten, dass der GLUT4-Transporter in einer inaktiven Form in der Plasmamembran vorliegt bis die Glucoseaufnahme durch den GLUT4-Transporter mittels der Insulin Signaltransduktionskaskade reguliert wird.

Cardiac pacing has been the only effective treatment in the management of patients with symptomatic bradycardia caused by sinus node dysfunction or atrioventricular block for decades. Conventional dual-chamber pacing is performed by implanting two leads in right atrial (RA) appendage and right ventricular (RV) apex separately. RV apex is the most commonly applied pacing site because it can be easily reached and allows a chronically stable position and stimulation thresholds. However, large randomized clinical trials have suggested that right ventricular apical (RVA) pacing may cause abnormal ventricular contraction and reduce pump function and lead to myocardial hypertrophy, in particular in patients with impaired left ventricular (LV) function. Recent studies have also reported a reduced LV systolic function in patients with pacing indications and preserved ejection fraction. The deleterious effects of RVA pacing on LV function may be related to the abnormal electrical and mechanical activation pattern or ventricular dyssynchrony. During RVA pacing, conduction of the electrical wave front propagates slowly through ventricular myocardium rather than through the His-Purkinje conduction system, comparable to left bundle branch block (LBBB). In addition , RVA pacing alters ventricular synchrony and loading conditions which may result in diastolic heart failure with abnormal LV relaxation, high filling pressure and low cardiac output state. Furthermore, it is possible that left atrial (LA) remodeling and reduction of atrial function may occur during RVA pacing . However, it is not been carefully studied. / Echocardiography is a convenient, non-invasive and established tool to assess cardiac function in clinical practice. Conventional two-dimensional echocardiography is useful to assess cardiac chamber size, volume and function. With the development of real time three-dimensional echocardiography (RT3DE) and color tissue Doppler imaging (TDI), echocardiography provides further valuable information and more accurate measurements which include myocardial velocity and parameters of dyssynchrony. In the present study, the main echocardiographic parameters including the maximal left atrial volume (LAVmax), pre-atrial contraction volume (LAVpre) and the minimal left atria l volume (LAVmin) were assessed by two-dimensional echocardiography. Peak systolic (Sm-la), peak early diastolic (Em-la), peak late diastolic (Am-la) velocities of left atrium (LA) and atrial conduction time (from onset of P wave on electrocardiogram to onset of atrial velocity) were measured by TDI. / In a cross-sectional study, ninety-eight patients who had been implanted with RVA-based dual-chamber pacemakers were enrolled. Four patients with pacing dependent were excluded. Eventually 94 patients were included in the final analysis. Echocardiography was performed (iE33, Philips) during intrinsic ventricular conduction (V-sense) and RVA pacing (V-pace) modes with 15 minutes between switching modes. We aimed to investigate if RVA pacing has any acute effects on atrial remodeling and function in patients with preserved ejection fraction (LV ejection fraction> 45%). The result showed that during V-pace, LA volumes increased significantly when compared with V-sense (LAVmax: 52.0 +/- 18.8 vs. 55.2 +/- 21.1 ml, p = 0.005; LAVpre: 39.8 +/- 16.4 vs. 41.3 +/- 16.6 ml, p = 0.014; LAVmin: 27.4 +/- 14.0 vs. 29.1 +/- 15.1 ml, p = 0.001) . TDI parameters showed significant reduction in Sm-la (3.0 +/- 1.1 vs. 2.7 +/- 0.9 cm/s, p < 0.01), Em-la (2.7 +/- 1.1 vs. 2.4 +/- 1.0 cm/s, p = 0.001). However, there was no change in Am-la. / In a prospective study, patients with symptomatic bradycardia, preserved ejection fraction, and received RVA pacing were recruited. Echocardiography was performed at both baseline and one year follow up through a standard protocol by experienced echocardiographers. LA volumes and velocities as well as intra- and interatrial dyssynchrony were measured offline with the use of dedicated software. The objectives of this study were to investigate: (1) if RVA pacing has any deleterious effects on LA remodeling and function during long-term follow up; (2) if RA appendage pacing has separate effects on atrial pump function, intra- and interatrial dyssynchrony; (3) if atrial dysfunction and dyssynchrony can predict atrial high rate episodes (AHREs) burden in the first year of RVA pacing. The main findings of this study were: (a) at one year follow up, LA volumes and indexes were increased with reduction in passive emptying fraction and total emptying fraction. Atrial velocities showed significant reduction when compared with baseline; (b) in multivariate regression analysis, the ratio of transmitral early diastolic filling velocity to mitral annular early diastolic velocity (E/e') > 15 at one year and reduction of LV ejection fraction ≥ 5% were independent predictors of reduction of Am-la > 30%; (c) high percent of RA appendage pacing prolonged atrial conduction and induced intra- and interatrial dyssynchrony. (d) Am-la < 5.3 cm/s can predict AHREs burden which had a sensitivity of 71% and specificity of 75%. / In conclusion, our studies suggest even short-term RVA pacing induces LA dilatation and impaired passive atrial function, though it did not have direct effect on active atrial contractility. However, chronic RVA pacing results in LA remodeling and reduces atrial function with decreased contractility. This was more likely to occur in those with impaired LV ejection fraction and evidence of diastolic dysfunction. Atrial dysfunction and interatrial dyssynchrony can predict AHREs burden after chronic RVA pacing. Therefore, measures that may minimize such adverse effect of pacing on atrial function need to considered for patients receiving RVA pacing, such as the use of new pacing modalities. / Xie, Junmin. / "December 2010"--Abstract. / Adviser: Yu Cheuk Man. / Source: Dissertation Abstracts International, Volume: 73-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 142-161). / 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, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Based on data from my in-vitro investigation in the non-pulsatile flow test rig, my best estimate for the random (inter-reading) error was +/-10.0% (95% c.i.) for single and +/-5.8% for triplicate readings and the systematic (between catheters) error was +/-11.6%. Thus, the overall error was +/-15.3% for a single, and +/-13.0% for triplicate readings. / For the in-vitro model, a test rig through which water circulated at different rates with ports to insert catheters into a flow chamber was assembled. Flow rate was measured by an externally placed transonic flow probe and meter. The meter was calibrated by timed filling of a cylinder. Arrow and Edwards 7Fr thermodilution catheters, connected to a Siemens SC9000 cardiac output monitor, were tested. Thermodilution readings were made by injecting 5 mL of ice-cold water. Measurement error was divided into random and systematic components, which were determined separately. Between-readings (random) variability was determined for each catheter by taking sets of 10 readings at different flow rates. Coefficient of variation (CV) was calculated for each set and averaged. Between-catheters systems (systematic) variability was derived by plotting calibration lines for sets of catheters. Slopes were used to estimate the systematic component. Performances of three cardiac output monitors were compared: Siemens SC9000, Siemens Sirecust 1261, and Philips MP50. After the constant rate model, I also developed a pulsatile model and did a similar evaluation. / For the in-vivo model, ten domestic pigs, weight 27--32kg, were anaesthetized with propofol and ketamine infusion. The aortic flow probe was surgically placed via a left thoracotomy. A pulmonary artery catheter sheath was inserted in the right internal jugular vein. Both Arrow and Edwards catheters were used. A 10 ml, room temperature, saline injectate was used and cardiac output was calculated using the Seimens SC9000 monitor. Sets of cardiac output readings were taken over 5 minute intervals of stable haemodynamics. Catheters were frequently changed and cardiac output increased (e.g. Dopamine and Adrenaline) and decreased (e.g. Trinitrate and Beta-Blocker) using drug infusions. Baseline (e.g. no drug intervention) and drug treatment data were analyzed separately. / For the pulsatile model, the best estimate for the random (inter-reading) error (95% c.i.) was +/-16.7% for single and +/-9.7% for triplicate readings and the systematic (between catheters) error was +/-21.1 %. Thus, the overall error was +/-26.9% for a single, and +/-23.2% for triplicate readings. / I set out to evaluate in the pig model two types of measurement errors, random and systematic errors, which I defined using the test rig in-vitro, the coefficient of variation (CV) was +2.8% (95% c.i.), with random error (95% c.i.) of + 5.5%. But if the ranges of cardiac output was widened, the error was increased to + 19.3% . The systematic component ofthe error (95% c.i.) was +20.0%. / There was a good linear regression relationship between the two methods (e.g. thermodilution and flow probe). The mean correlation coefficient was 0.95 (0.9--0.99, 95% c.i.) based on data from 8 pigs'. However, there were significant systematic errors due to calibration of the measurement systems between pig experiment and catheter testings. By eliminating the systematic errors based on the calibration line corrections, I was able to draw modified Bland and Altman plots for the 8 pigs. The bias was eliminated and become 0 L/min. The limits of agreement or percentage errors of this analysis, were within the +/-30% limits. / Thermodilution cardiac output, measured using a pulmonary artery catheter and cardiac output monitor, is the reference standard against which all new methods of cardiac output measurement are judged. There has been a recent decline in the use of pulmonary artery thermodilution cardiac output in favour of less invasive methods. When validating these new methods comparisons are made using Bland and Altman analysis with single bolus thermodilution as the accepted reference method. 95% confidence intervals and percentage errors are generated that rely on a precision of +/-20% (Stetz et al (1982)) for thermodilution measurements. However, this precision is now being questioned as it is based on data collected over 30-years ago. Lack of precision of this reference standard, and uncertainty about its true values, causes difficulty when validating new cardiac output technology. Thus, the aim of this thesis was to reappraise the error of thermodilution by testing currently available catheters in both in-vitro and in-vivo settings. / When testing in haemodynamically unstable conditions (e.g. high and low flow states), the percentage error was increased by about +/-15% in the treatment groups comparing with baseline group data. This finding was in agreement with the growing world opinion that thermodilution may not be as accurate as originally thought, in extreme haemodynamic conditions, such as hypovolaemia or high cardiac output states. / Yang, Xiaoxing. / Adviser: Lester August Hall Critchley. / Source: Dissertation Abstracts International, Volume: 73-06, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 165-178). / 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, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Iroquois homeobox (Irx) family members, a group of highly conserved homeodomain containing transcription factors, are involved in the patterning and the proper functions of vertebrate organs. They can act as transcriptional activators or repressors in a context-dependent manner. Preliminary data indicated that Irx3 and Irx5 are functionally redundant during cardiac morphogenesis, and they physically interact with other cardiac transcription factors. At E14.5, outflow tract septation failure and ventricular septation failure were observed in Irx3/5DKO mouse hearts. Loss of Irx3/5 in neural crest and endothelial cell lineages led to outflow tract septation failure and ventricular septal defect. In adult mice, Irx3 is expressed in the atrioventricular conduction system, and loss of Irx3 leads to slower ventricular conduction velocity. qRT-PCR analysis and immunofluorescence staining revealed that the expression of gap junction proteins, Cx40 and Cx43, are affected by the loss of Irx3. Over-expression of Irx3 and a dominant repressor form of Irx3, Irx3-EnR, resulted in Cx40 upregulation, indicating that Irx3 acts as an indirect positive regulator of Cx40. Irx3-EnR over-expression in vivo resulted in postnatal onset of atrial enlargement, ventricular hypertrophy, and conduction failure. Taken together, this study demonstrates the significance of Irx3/5 in both cardiovascular development and cardiac electrophysiology.