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Biomedical subjects

T M Chou

Publications and source records attributed to T M Chou.

At least 19 recordsLinked to original sources
PubMed2003

Mean free paths for inelastic electron scattering in silicon and poly(styrene) nanospheres.

The mean free paths for inelastic electron scattering, lambda(in), in silicon [Si] and poly(styrene) [PS] have been measured using off-axis electron holography in a field-emission transmission electron microscope (FEG TEM). The holographic imaging method determines both quantitative wave phase information as well as elastic energy-filtered wave amplitude information. Using the energy-filtered amplitude data, two-dimensional t/lambda(in) images are reconstructed. The present work uses spherical nanoparticles as samples, so the sample thickness at any point in a two-dimensional image can be calculated knowing the center and radius of the projected nanosphere. The thickness contribution to t/lambda(in) is removed to obtain quantitative lambda(in) values. This work finds values of lambda(i)Si = 53.8 +/- 5.5 and 88.6 +/- 6.9 nm, and lambda(PS) = 78.1 +/- 3.4 and 113.0 +/- 5.9 nm for 120 and 200 keV incident electron energies, respectively.

Journal Article↗
PubMed2001

Fractional flow reserve compared with intravascular ultrasound guidance for optimizing stent deployment.

BACKGROUND: Determination of fractional flow reserve (FFR) has been proposed as a means to assess stent deployment. In this prospective, multicenter trial, we evaluate the use of FFR to optimize stenting by comparing it with standard intravascular ultrasound (IVUS) criteria. METHODS AND RESULTS: Eighty-four stable patients with isolated coronary lesions underwent coronary stent deployment starting at 10 atm and increased serially by 2 atm until the FFR was >/=0.94 or 16 atm was achieved. IVUS was then performed. FFR was measured with a coronary pressure wire with intracoronary adenosine to induce hyperemia. The diagnostic characteristics of an FFR <0.94 to predict suboptimal stent expansion by IVUS, defined in both absolute and relative terms, were calculated. Over a range of IVUS criteria, the highest sensitivity, specificity, and predictive accuracy of FFR were 80%, 30%, and 42%, respectively. Receiver operator characteristic analysis defined an optimal FFR cut point at >/=0.96; at this threshold, the sensitivity, specificity, and predictive accuracy of FFR were 75%, 58%, and 62%, respectively (P=0.03 for comparison of predictive accuracy, P=0.01 for concordance between FFR and IVUS). The negative predictive value was 88%. Significantly better diagnostic performance was achieved in a subgroup that received higher doses (>30 microgram) of intracoronary adenosine during pressure measurements, suggesting that FFR might be overestimated in the other group. CONCLUSIONS: A fractional flow reserve <0.96, measured after stent deployment, predicts a suboptimal result based on validated intravascular ultrasound criteria; however, an FFR >/=0.96 does not reliably predict an optimal stent result. Higher doses of intracoronary adenosine than previously used to measure FFR improve these results.

Adenosine↗
PubMed2001

Does higher diastolic augmentation predict clinical benefit from enhanced external counterpulsation?: Data from the International EECP Patient Registry (IEPR).

BACKGROUND: Enhanced external counterpulsation (EECP) has been demonstrated to be an effective treatment for stable angina in patients with coronary disease. The hemodynamic effects of EECP are maximized when the ratio of diastolic to systolic pressure area is in the range of 1.5 to 2.0. HYPOTHESIS: It is hypothesized that patients undergoing EECP who are able to achieve higher diastolic augmentation (DA) ratios may derive greater clinical benefit. This study examines the relationship between the DA ratio and clinical outcomes in patients undergoing EECP. METHODS: We analyzed demographic, noninvasive hemodynamic, and clinical outcome data on 1,004 patients enrolled in the International EECP Patient Registry (IEPR) for treatment of chronic angina between January 1998 and August 1999. Blood pressure waveforms were recorded from finger plethysmography. Six-month clinical outcomes were obtained by telephone interview. RESULTS: At the end of EECP treatment, 370 (37%) patients had a higher DA ratio (defined as > or = 1.5) and 634 (63%) had a lower DA ratio (defined as < 1.5). Factors associated with a lower DA ratio included age > or =65 years (p <0.001), female gender (p < 0.001), left ventricular ejection fraction < 35% (p < 0.05), hypertension (p < 0.01), prior coronary bypass surgery (p < 0.01), noncardiac vascular disease (p < 0.001), multivessel disease (p < 0.01), congestive heart failure (p < 0.01), current smoking (p < 0.01), unsuitability for further revascularization (p < 0.001), and higher baseline angina class (p < 0.001). There were no significant differences regarding diabetes mellitus, prior coronary angioplasty, prior myocardial infarction, or antianginal medication use between patients with higher or lower DA ratios. Based on a multiple logistic regression model, independent predictors of a DA ratio < 1.5 at the end of EECP included current smoking (odds ratio 3.3; 95% confidence intervals 2.0-5.4); multivessel disease (1.7; 1.3-2.3); female gender (2.2; 1.7-3.0); no prior EECP (1.9; 1.1-3.3); noncardiac vascular disease (2.3; 1.7-2.9); age > or = 65 years (1.7; 1.4-2.2), and patients not suitable for revascularization (1.6; 1.2-2.0). By the end of therapy, there were no significant differences in myocardial infarction, revascularization rates, or nitroglycerin use with respect to higher DA ratios. At 6-month follow-up, patients with higher DA had a trend toward a greater reduction in angina class compared with those with lower DA (p = 0.069). There was a significantly higher rate of unstable angina and congestive heart failure in the group not achieving higher augmentation (p < 0.05). CONCLUSIONS: Patients who are younger, male, nonsmoking, and without multivessel coronary or noncardiac vascular disease are most likely to have higher DA with EECP. Patients with higher DA tended to have a greater reduction in angina class at 6-month follow-up compared with those with lower DA ratios. There is evidence that higher DA ratios are associated with improved short- or long-term clinical outcomes, suggesting that clinical benefit from EECP is associated with the magnitude of DA.

Aged↗
PubMed2001

Power motion imaging can improve image quality in stress conditions with tachycardia.

BACKGROUND: Stress echocardiographic studies are useful, but the evaluation of wall motion is sometimes suboptimal. The recently developed technique of power motion imaging can enhance mobile tissue definition. HYPOTHESIS: The study was undertaken to determine whether power motion imaging improves endocardial definition during tachycardia compared with conventional two-dimensional (2-D) imaging. METHODS: Twenty pigs were studied during pacing rates of 100, 120, and 150 beats/min. We compared power motion imaging with standard 2-D imaging using systolic thickening visualization (STV) scores (3 = excellent definition of systolic thickening approximately 0 = total lack of visualization of systolic thickening) at each heart rate. We calculated the sum of the scores of 22 left ventricular segments as the overall STV score, and also calculated the sum of the scores in 10 parasternal segments and 12 apical segments separately. RESULTS: The overall STV scores in both imaging methods were similar at 100 beats/min, but scores for power motion imaging were significantly higher than those of usual 2-D imaging at 120 and 150 beats/min. Using power motion imaging, the overall STV scores were similar as heart rate was increased; however, while using standard 2-D imaging, STV scores were significantly decreased as heart rate was increased. Findings were analyzed separately by parasternal and apical images. Especially in the parasternal images, the scores were significantly increased as heart rate was increased using power motion imaging. CONCLUSIONS: We conclude that power motion imaging improves the detection of endocardial border in stress condition with tachycardia, and thus this modality is useful for stress echocardiography.

Animals↗
PubMed2001

The use of intra-aortic balloon counterpulsation in patients with cardiogenic shock complicating acute myocardial infarction: data from the National Registry of Myocardial Infarction 2.

BACKGROUND: Cardiogenic shock complicating acute myocardial infarction (AMI) remains the leading cause of death in patients hospitalized with AMI. Although several studies have demonstrated the importance of establishing and maintaining a patent infarct-related artery, it remains unclear as to whether intra-aortic balloon counterpulsation (IABP) provides incremental benefit to reperfusion therapy. The purpose of this study was to determine whether IABP use is associated with lower in-hospital mortality rates in patients with AMI complicated by cardiogenic shock in a large AMI registry. METHODS: We evaluated patients participating in the National Registry of Myocardial Infarction 2 who had cardiogenic shock at initial examination or in whom cardiogenic shock developed during hospitalization (n = 23,180). RESULTS: The mean age of patients in the study was 72 years, 54% were men, and the majority were white. The overall mortality rate in all patients who had cardiogenic shock or in whom cardiogenic shock developed was 70%. IABP was used in 7268 (31%) patients. IABP use was associated with a significant reduction in mortality rates in patients who received thrombolytic therapy (67% vs 49%) but was not associated with any benefit in patients treated with primary angioplasty (45% vs 47%). In a multivariate model, the use of IABP in conjunction with thrombolytic therapy decreased the odds of death by 18% (odds ratio, 0.82; 95% confidence interval, 0.72 to 0.93). CONCLUSIONS: Patients with AMI complicated by cardiogenic shock may have substantial benefit from IABP when used in combination with thrombolytic therapy.

Aged↗
PubMed2001

Tamoxifen is an acute, estrogen-like, coronary vasodilator of porcine coronary arteries in vitro.

Tamoxifen is a mixed estrogen antagonist and agonist. Observational data from breast cancer studies associate tamoxifen use with lesser rates of myocardial infarction. The authors sought to determine the acute vasoactive properties of tamoxifen compared with estradiol. Isolated coronary ring segments from female pigs were studied in organ baths. KCl-precontracted ring segments were exposed to increasing doses of both tamoxifen and estradiol (log-9-log-5 M ). Ring segments were also exposed to tamoxifen and estradiol in the presence of inhibitors of nitric oxide, glybenclamide, the hormone receptor antagonists ICI 182,780 and flutamide, and after de-endothelialization. Tamoxifen caused acute dilation of coronary arteries but less than estradiol. Tamoxifen-and estradiol-induced acute vasodilation was not nitric oxide- or endothelium-dependent, but was adenosine triphosphate-sensitive potassium channel-dependent. Tamoxifen-induced vasorelaxation was inhibited by antagonism of the classic estrogen receptor and antagonism of the androgen receptor with flutamide, whereas estrogen-induced vasorelaxation was inhibited partially by classic estrogen receptor antagonism but not by androgen receptor antagonism. Tamoxifen attenuated both the sensitivity of vasoconstriction to endothelin-1 and the maximal response. Tamoxifen and estradiol are both acute coronary vasodilators, with similar mechanisms of action. Tamoxifen also attenuates coronary vasoconstriction. Such properties may account for some of the observed cardiovascular clinical benefits seen in observational studies of tamoxifen use.

Animals↗
PubMed2001

Comparative effects of ACE inhibitors and an angiotensin receptor blocker on atherosclerosis and vascular function.

BACKGROUND: Both angiotensin-converting enzyme inhibitors (ACE-I(s)) and angiotensin receptor blockers (ARB(s)) provide vascular protection. This study was designed to compare ACE-I(s) with widely differing tissue affinity (captopril and quinapril) and an ARB (losartan) on vascular protection against the adverse effects of high cholesterol. METHODS AND RESULTS: Forty-two New Zealand rabbits on a 0.5% cholesterol diet were randomized into control, captopril (10 mg/kg/d), quinapril (0.3 mg/kg/d), and losartan (8 mg/kg/d) groups for 14 weeks. Captopril, quinapril, and losartan significantly attenuated aortic lipid lesions (P=0.001). Captopril and quinapril were more effective than losartan in preserving vascular relaxation. CONCLUSIONS: Captopril, quinapril, and losartan had similar protective effects against atherogenesis. Captopril and quinapril were more effective than losartan in preserving vascular function. Increased bradykinin by ACE inhibition may be responsible for this improved vascular endothelial function.

Angiotensin Receptor Antagonists↗
PubMed2000

Use of fractional myocardial flow reserve to assess the functional significance of intermediate coronary stenoses.

The goal of the present study was to compare the use of pressure-derived myocardial fractional flow reserve for detecting ischemia with nuclear stress imaging in patients undergoing stent placement for intermediate coronary lesions. We demonstrated that myocardial fractional flow reserve detects ischemia in intermediate coronary lesions accurately when compared with nuclear stress imaging.

Adult↗
PubMed2000

Anti-SSA/Ro and anti-SSB/La autoantibodies bind the surface of apoptotic fetal cardiocytes and promote secretion of TNF-alpha by macrophages.

Despite the near universal association of congenital heart block and maternal Abs to SSA/Ro and SSB/La, the intracellular location of these Ags has made it difficult to substantiate their involvement in pathogenicity. To define whether components of the SSA/Ro-SSB/La complex, which translocate during apoptosis, are indeed accessible to extracellular Abs, two approaches were taken: immunoprecipitation of surface biotinylated proteins and scanning electron microscopy. Human fetal cardiocytes from 16-24-wk abortuses were cultured and incubated with staurosporine to induce apoptosis. Surface biotinylated 48-kDa SSB/La was reproducibly immunoprecipitated from apoptotic, but not nonapoptotic cardiocytes. Surface expression of SSA/Ro and SSB/La was further substantiated by scanning electron microscopy. Gold particles (following incubation with gold-labeled sera containing various specificities of anti-SSA/Ro-SSB/La Abs and murine mAb to SSB/La and 60-kDa SSA/Ro) were consistently observed on early and late apoptotic cardiocytes. No particles were seen after incubation with control antisera. To evaluate whether opsonized apoptotic cardiocytes promote inflammation, cells were cocultured with macrophages. Compared with nonapoptotic cardiocytes or apoptotic cardiocytes incubated with normal sera, apoptotic cardiocytes preincubated with affinity-purified Abs to SSB/La, 52-kDa SSA/Ro, or 60-kDa SSA/Ro increased the secretion of TNF-alpha from cocultured macrophages. In summary, apoptosis results in surface accessibility of all SSA/Ro-SSB/La Ags for recognition by circulating maternal Abs. It is speculated that in vivo such opsonized apoptotic cardiocytes promote an inflammatory response by resident macrophages with damage to surrounding conducting tissue.

Antibodies, Antinuclear↗
PubMed2000

Comparative effects of pretreatment with captopril and losartan on cardiovascular protection in a rat model of ischemia-reperfusion.

OBJECTIVES: We sought to assess the comparative effects of pretreatment with captopril and losartan on myocardial infarct size and arrhythmias in a rat model of ischemia-reperfusion. BACKGROUND: Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs) inhibit the renin-angiotensin system in different ways. However, the comparative effects of pretreatment with ACE inhibitors or ARBs on acute myocardial infarct size and arrhythmias are unknown. METHODS: We randomly assigned 117 female Sprague-Dawley rats into three groups: group N was the normal control; group C was given 40 mg/kg body weight per day of captopril in drinking water; and group L was given 40 mg/kg per day of losartan in drinking water. After 10 weeks of pretreatment, 25 rats in each group were subjected to 17 min of left anterior descending coronary artery occlusion and 2 h of reperfusion with hemodynamic and electrocardiographic monitoring. Fourteen rats in each group had blood samples drawn and aortic rings removed to study vascular reactivity. RESULTS: Mortality during ischemia and reperfusion was lower in combined groups L and C than in group N (4.2% vs. 19.2%, p = 0.042). Rats treated with losartan had significantly higher levels of angiotensin II in their plasma. Hemodynamic variables were not significantly different among the three groups. The thresholds of ventricular fibrillation (VF) before occlusion and after reperfusion were significantly higher in groups L and C than in group N (1.99 +/- 0.24 and 1.93 +/- 0.27 vs. 1.23 + 0.17 mA, p = 0.04; 2.13 +/- 0.25 and 1.78 +/- 0.22 vs. 0.95 +/- 0.11 mA, p = 0.001). The average episodes of ventricular tachycardia (VT) and VF per rat were significantly less in groups L and C than in group N (0.96 +/- 0.2 and 1.2 +/- 0.3 vs. 2.8 + 0.4 mA, p < 0.001). Myocardial infarct size was significantly smaller in groups L and C than in group N (34 +/- 3% and 35 +/- 3% vs. 44 +/- 3%, p = 0.031, 0.043). Endothelium-dependent vasorelaxation induced by a calcium ionophore (A23187) was increased in both groups but was only statistically significant in group C (p = 0.020). CONCLUSIONS: Losartan and captopril have similar cardiovascular protective effects in a rat model of ischemia-reperfusion. They increased the threshold of VF, decreased mortality and decreased episodes of VT and VF, as well as decreased myocardial infarct size.

Angiotensin II↗
PubMed2000

Acute occlusion of left internal mammary artery graft during dual-chamber pacemaker implantation.

A patient who had undergone bypass surgery 5 yr earlier, including left internal mammary artery (LIMA) grafting to the left anterior descending artery, underwent transvenous dual-chamber permanent pacemaker implantation for persistent advanced atrioventricular block. Intraoperative LIMA graft obstruction occurred, resulting in anterior myocardial infarction that was treated successfully by primary percutaneous transluminal coronary angioplasty and stenting. This is the first report of the occurrence of this complication during pacemaker implantation.

Aged↗
PubMed2000

Intracoronary measurement of pulsus alternans.

Pulsus alternans is typically found in patients with left ventricular systolic dysfunction. We describe a woman with biventricular systolic dysfunction and pulsus alternans in the right ventricle, pulmonary artery, and aorta. Coronary angiography revealed an intermediate stenosis in the proximal left anterior descending (LAD) coronary artery. Pulsus alternans was demonstrated in the mid LAD using a 0.014" guidewire-mounted pressure sensor. An abnormal fractional flow reserve was measured in the LAD. Cathet. Cardiovasc. Intervent. 51:335-338, 2000.

Aged↗
PubMed2000

Teleconferencing with dynamic medical images.

Dynamic images, a sequence of static images displayed in rapid succession and perceived as a continuous motion by the human eye, are widely used in medicine. One of the primary objectives of telemedicine is the transmission of such images to a distant location to manage clinical problems remotely. A broad variety of methods is available to acquire, store, transmit, and display these images. However, the context of the clinical problem determines which of these methods can be deployed in a telemedicine solution. This paper discusses the advantages and disadvantages of the different technologies and presents an example of a teleconferencing system for interventional cardiology. This system acquires cardiac angiography and intravascular ultrasound images and transmits them over an existing Internet connection to a distant location. It is specifically optimized for clinical conferencing, where time is limited for each case presentation during the conference, compared to the relatively long time available for the conference preparation. The system takes advantage of this characteristic by transmitting the images well in advance of the clinical conference and displaying them synchronously in both locations during the conference. This allows for the preservation of the original image quality.

Blood Vessels↗
PubMed2000

Development of a molecular probe to baboon interleukin-10 mRNA for in situ hybridization during experimental schistosomiasis.

A nucleic acid probe complementary to baboon interleukin 10 (IL-10) mRNA was developed for in situ hybridization. Highly conserved IL-10 protein sequences from several mammals were aligned to design oligonucleotide primers flanking a 270-bp sequence of the target cDNA. RNA was isolated from stimulated peripheral blood mononuclear cells (PBMC). IL-10 cDNA was reverse-transcribed from the total PBMC RNA and amplified with the polymerase chain reaction (PCR). Cloning and sequencing of the PCR product confirmed it to be of baboon IL-10 origin, with 97.8% identity to human and 100% identity to macaque mRNA sequences. The baboon IL-10 DNA probe hybridized in Southern blots to a 7.9-Kbp or 8.6-Kbp band after digestion of genomic baboon DNA with Bam H1 or Eco R1, respectively. Preliminary results with an antisense riboprobe derived from this sequence showed the presence of IL-10 mRNA in sections of granulomatous tissues.

Animals↗
PubMed2000

Serial laparoscopic biopsies of liver and spleen from Schistosoma-infected baboons (Papio spp.).

PURPOSE: To obtain large, serial biopsy samples from the liver and spleen by using laparoscopy. Large samples were needed for measurement of inflammatory mediators during various stages of schistosomiasis. METHODS: Each of the seven female baboons (Papio sp.) underwent as many as three laparoscopies, for a total of 19 laparoscopic procedures. This process permitted sampling of the liver, spleen, and mesenteric lymph nodes before and at 6 and 9 weeks after infection with Schistosoma mansoni. All surgery was performed through three trocar sites. Postoperative care included preemptive analgesia. After surgery, we monitored the animals' appetite and measured the core body temperature and activity by using implanted radiofrequency transmitters. RESULTS: We obtained samples of the liver and splenic biopsies during all 19 laparoscopic procedures. The mean weight of the liver biopsies was 3.7 g and that of the spleen samples was 5.3 g. We encountered small adhesions during 5 of the 12 reoperations. Eating and activity rapidly returned after surgery. CONCLUSIONS: Laparoscopy permitted collection of large, serial biopsies with apparently limited stress to the animals. Laparoscopy can be used for biopsies in studies to characterize disease response, confirm normal organ histology prior to drug toxicity studies, determine target-organ drug concentrations in pharmacokinetic studies, and measure drug residues. This refinement likely will reduce required animal numbers by decreasing the effect of surgery compared to that of the experimental conditions, enhance animal well-being, and permit repeated measurements in an animal that serves as its own control.

Analgesics, Opioid↗
PubMed1999

Should the electrocardiogram be used to guide therapy for patients with left bundle-branch block and suspected myocardial infarction?

CONTEXT: Recently, an algorithm based on the electrocardiogram (ECG) was reported to predict myocardial infarction (MI) in patients with left bundle-branch block (LBBB), but the clinical impact of this testing strategy is unknown. OBJECTIVE: To determine the diagnostic test characteristics and clinical utility of this ECG algorithm for patients with suspected MI. DESIGN: Retrospective cohort study to which an algorithm was applied, followed by decision analysis regarding thrombolysis made with or without the algorithm. SETTING: University emergency department, 1994 through 1997. PATIENTS: Eighty-three patients with LBBB who presented 103 times with symptoms suggestive of MI. MAIN OUTCOME MEASURES: Myocardial infarction determined by serial cardiac enzyme analyses and stroke-free survival. RESULTS: Of 9 ECG findings assessed, none effectively distinguished the 30% of patients with MI from those with other diagnoses. The ECG algorithm indicated positive findings in only 3% of presentations and had a sensitivity of 10% (95% confidence interval, 2%-26%). The decision analysis showed that among 1000 patients with LBBB and chest pain, 929 would survive without major stroke if all received thrombolysis compared with 918 if the ECG algorithm was used as a screening test. CONCLUSIONS: The ECG is a poor predictor of MI in a community-based cohort of patients with LBBB and acute cardiopulmonary symptoms. Acute thrombolytic therapy should be considered for all patients with LBBB who have symptoms consistent with MI.

Algorithms↗