Biomedical subjects

Colin K L Phoon

Publications and source records attributed to Colin K L Phoon.

10 recordsLinked to original sources

PubMed2006

Expression of a sorcin missense mutation in the heart modulates excitation-contraction coupling.

Sorcin is a Ca2+ binding protein implicated in the regulation of intracellular Ca2+ cycling and cardiac excitation-contraction coupling. Structural and human genetic studies suggest that a naturally occurring sequence variant encoding L112-sorcin disrupts an E-F hand Ca2+ binding domain and may be responsible for a heritable form of hypertension and hypertrophic heart disease. We generated transgenic mice overexpressing L112-sorcin in the heart and characterized the effects on Ca2+ regulation and cardiac function both in vivo and in dissociated cardiomyocytes. Hearts of sorcin(F112L) transgenic mice were mildly dilated but ventricular function was preserved and systemic blood pressure was normal. Sorcin(F112L) myocytes were smaller than control cells and displayed complex alterations in Ca2+ regulation and contractility, including a slowed inactivation of L-type Ca2+ current, enhanced Ca2+ spark width, duration, and frequency, and increased Na+-Ca2+ exchange activity. In contrast, mice with cardiac-specific overexpression of wild-type sorcin displayed directionally opposite effects on L-type Ca2+ channel function and Ca2+ spark behavior. These data further define the role of sorcin in cardiac excitation-contraction coupling and highlight its negative regulation of SR calcium release. Our results also suggest that additional factors may be responsible for the development of cardiac hypertrophy and hypertension in humans expressing the L112-sorcin sequence variant.

Animals↗

PubMed2006

Finding balance.

Explore the source record for details and available documents.

Attitude to Health↗

PubMed2005

Management of anomalous coronary arteries from the contralateral sinus.

Anomalous origin of the coronary artery from the contralateral sinus of Valsalva, coursing between the aorta and pulmonary artery, has garnered much attention because of its association with sudden death. Current medical opinion is heavily skewed toward "successful" intervention. However, two key issues have not been critically analyzed: what is the true risk of sudden death from an anomalous coronary artery, and how does this risk balance against the risk of surgical intervention? Common misconceptions about risk derive from citations of autopsy data. In fact, the scant available data suggest a far lower absolute risk than commonly cited. The risks of surgical intervention, while likely quite low, remain real, and include aortic valve damage and neurological sequelae. The lack of long-term outcomes data precludes any definite recommendations in most patients. The decision to intervene is thus not straightforward, and should be approached cautiously and only after appropriate counseling of the patient.

Child↗

PubMed2005

Noninvasive localization of nuclear factor of activated T cells c1-/- mouse embryos by ultrasound biomicroscopy-Doppler allows genotype-phenotype correlation.

Ultrasound biomicroscopy (UBM)-Doppler allows study of cardiovascular physiology in the in utero mouse embryo from embryonic day (E)8.25 onward. We determined the accuracy of localization of embryos by transabdominal, noninvasive 40-MHz UBM-Doppler imaging. Nuclear factor of activated T cells c1-/- mice lack semilunar valves, exhibit outflow tract regurgitation, and die in utero. In timed pregnant mice generated from heterozygote crosses, an UBM-derived map of the in situ litter was compared with a definitive laparotomy map, and UBM-Doppler cardiac screen attempted for each embryo. All 109 living and dead (nonresorbed) E10.5 to 17.5 embryos were imaged and accurately localized. All 10 embryos with reversed diastolic aortic flow and 7 of 9 dead embryos genotyped were nuclear factor of activated T cells c1-/-. In 30 embryos followed up serially over 1 to 2 days from E12.5 to E16.5, we again achieved 100% accuracy in localizing at follow-up. Noninvasive localization and UBM-Doppler analysis of in situ mouse embryos can provide accurate genotype-phenotype correlation, along with nontraumatic serial imaging of embryos.

Animals↗

PubMed2004

Embryonic heart failure in NFATc1-/- mice: novel mechanistic insights from in utero ultrasound biomicroscopy.

Gene targeting in the mouse has become a standard approach, yielding important new insights into the genetic factors underlying cardiovascular development and disease. However, we still have very limited understanding of how mutations affect developing cardiovascular function, and few studies have been performed to measure altered physiological parameters in mouse mutant embryos. Indeed, although in utero lethality due to embryonic heart failure is one of the most common results of gene targeting experiments in the mouse, the underlying physiological mechanisms responsible for embryonic demise remain elusive. Using in utero ultrasound biomicroscopy (UBM), we studied embryonic day (E) 10.5 to 14.5 NFATc1-/- embryos and control littermates. NFATc1-/- mice, which lack outflow valves, die at mid-late gestation from presumed defects in forward blood flow with resultant heart failure. UBM showed increasing abnormal regurgitant flow in the aorta and extending into the embryonal-placental circulation, which was evident after E12.5 when outflow valves normally first develop. Reduced NFATc1-/- net volume flow and diastolic dysfunction contributed to heart failure, but contractile function remained unexpectedly normal. Among 107 NFATc1-/- embryos imaged, only 2 were observed to be in acute decline with progressive bradyarrhythmia, indicating that heart failure occurs rapidly in individual NFATc1-/- embryos. This study is among the first linking a specific physiological phenotype with a defined genotype, and demonstrates that NFATc1-/- embryonic heart failure is a complex phenomenon not simply attributable to contractile dysfunction.

Animals↗

PubMed2003

Ultrasound biomicroscopy-Doppler in mouse cardiovascular development.

The ability to modify the mouse genome has yielded new insights into the genetic control of mammalian cardiovascular development. However, it is far less understood how genetic factors and their consequent structural changes alter cardiovascular function, a void largely due to the lack of effective noninvasive techniques to assess function in the developing mouse cardiovascular system. In this review, we discuss the recent advances in ultrasound biomicroscopy (UBM)-Doppler echocardiography for analyzing cardiovascular function in the embryonic mouse in utero. "Cardiovascular function" encompasses broad aspects of physiology, including systolic and diastolic cardiac function, distribution of blood flow among various embryonic vascular beds, and vascular bed properties (impedance). A wide range of physiological measurements is possible using UBM-Doppler, but it is clear that the limitations of any single measurement warrant a multi-parameter approach to characterizing cardiovascular function. We further discuss the prospects for UBM-Doppler analysis of alternative vertebrate systems increasingly studied in developmental biology. The ability to correlate cardiovascular physiological phenotypes with their corresponding genotypes should lead to the elucidation of mechanisms underlying normal development, as well as embryonic disease and death.

Animals↗

PubMed2003

Onset of cardiac function during early mouse embryogenesis coincides with entry of primitive erythroblasts into the embryo proper.

When cardiac function and blood flow are first established are fundamental questions in mammalian embryogenesis. The earliest erythroblasts arise in yolk sac blood islands and subsequently enter the embryo proper to initiate circulation. Embryos staged 0 to 30 somites (S) were examined in utero with 40- to 50-MHz ultrasound biomicroscopy (UBM)-Doppler, to determine onset of embryonic heartbeat and blood flow and to characterize basic physiology of the very early mouse embryonic circulation. A heartbeat was first detected at 5 S, and blood vascular flow at 7 S. Heart rate, peak arterial velocity, and velocity-time integral showed progressive increases that indicated a dramatically increasing cardiac output from even the earliest stages. In situ hybridization revealed an onset of the heartbeat coincident with the appearance of yolk sac-derived erythroblasts in the embryo proper at 5 S. Early maturation of the circulation follows a tightly coordinated program.

Animals↗

PubMed2003

Sudden cardiac death: a 2400-year-old diagnosis?

Sudden cardiac death is one of the most important causes of mortality in the modern industrialized world. Although it has been described for at least several centuries, we believe in fact that Hippocrates provided a concise, but historically compelling, description of sudden cardiac death in his Aphorisms II, 41: "Those who are subject to frequent and severe fainting attacks without obvious cause die suddenly." This would be the earliest description of sudden cardiac death known. The Aphorism was analyzed in the context of genuine Hippocratic writings as well as ancient Greek culture. The Aphorism describes recurrent syncope in otherwise healthy individuals. Therefore, only certain select cardiac conditions are likely described by this Aphorism. Such conditions-long QT syndrome, hypertrophic cardiomyopathy, congenital coronary artery syndromes, and arrhythmogenic right ventricular dysplasia, chief among them-are linked by a final common pathway of an arrhythmic death. Relying solely on clinical experience based on careful history-taking and keen powers of observation, Hippocrates was the first to describe sudden cardiac death due to a select group of cardiac conditions. This analysis establishes such conditions as being an important cause of sudden death 2400 years ago, much as they are among the most important causes of sudden death today.

Death, Sudden, Cardiac↗

PubMed2003

Do paediatric cardiologists discuss cardiovascular risk factors with patients and their families?

Atherosclerotic disease of the heart likely has its origins in childhood. The promotion of cardiovascular health in children, however, has been studied only for those practicing in general paediatrics. We hypothesised that paediatric cardiologists do not consistently discuss cardiovascular risk factors with patients and their families. We therefore, carried out a nationwide survey of paediatric cardiologists to determine how often they discussed atherosclerosis and 4 modifiable risk factors, specifically weight, smoking, diet and nutrition, and physical activity. Only two-fifths reported that they discussed atherosclerotic disease frequently to always. For patients with cardiovascular disease, weight was discussed frequently to always by 59%, smoking by 61%, diet and nutrition by 63%, and physical activity by 92%. In contrast, for patients without cardiovascular disease, weight was discussed frequently to always by 35%, smoking by 46%, diet and nutrition by 39%, and physical activity by 62%. These differences are statistically significant (p < 0.003 by chi2 analysis). Cardiovascular risk factors were discussed more consistently as children grew older (p < 0.0001). Respondents stated that, in their opinion, the promotion of cardiovascular health was a role more appropriate for providers of primary care than for paediatric cardiologists (p < 0.0001). Constraints of time, and the perceived role of the cardiologist, were the most common barriers to anticipatory guidance. We suggest that these findings indicate that paediatric cardiologists can assume a more prominent role in preventive cardiology and education, although their precise role or roles, and the optimal methods of anticipatory guidance, remain controversial.

Cardiology↗

PubMed2002

Spatial velocity profile in mouse embryonic aorta and Doppler-derived volumetric flow: a preliminary model.

Characterizing embryonic circulatory physiology requires accurate cardiac output and flow data. Despite recent applications of high-frequency ultrasound Doppler to the study of embryonic circulation, current Doppler analysis of volumetric flow is relatively crude. To improve Doppler derivation of volumetric flow, we sought a preliminary model of the spatial velocity profile in the mouse embryonic dorsal aorta using ultrasound biomicroscopy (UBM)-Doppler data. Embryonic hematocrit is 0.05-0.10 so rheologic properties must be insignificant. Low Reynolds numbers (<500) and Womersley parameters (<0.76) suggest laminar flow. UBM demonstrated a circular dorsal aortic cross section with no significant tapering. Low Dean numbers (<100) suggest the presence of minimal skewing of the spatial velocity profile. The inlet length allows for fully developed flow. There is no apparent aortic wall pulsatility. Extrapolation of prior studies to these vessel diameters (300-350 microm) and flow velocities (~50-200 mm/s) suggests parabolic spatial velocity profiles. Therefore, mouse embryonic dorsal aortic blood flow may correspond to Poiseuille flow in a straight rigid tube with parabolic spatial velocity profiles. As a first approximation, these results are an important step toward precise in utero ultrasound characterization of blood flow within the developing mammalian circulation.

Animals↗