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Biomedical subjects

K Chandrasekaran

Publications and source records attributed to K Chandrasekaran.

At least 73 records · Page 4Linked to original sources
PubMed1993

Localization of cytochrome oxidase (COX) activity and COX mRNA in the perirhinal and superior temporal sulci of the monkey brain.

Cytochrome oxidase (COX) activity and COX II mRNA expression were localized in the perirhinal and superior temporal sulci of the rhesus monkey brain. In both regions, a laminar distribution of COX activity and COX II mRNA was observed. COX activity was intense in layers I and IV and were localized to the neuropil. In contrast, COX II mRNA was localized to neuronal cell bodies. In the prorhinal region, highest levels of COX II mRNA was detected in cell bodies of layers II and IV, and in the perirhinal region, in cell bodies of layers III and V-VI. In the superior temporal sulcus, COX II mRNA was detected in cell bodies of layers III and V-VI. Thus, COX II mRNA and COX activity are uniquely localized in the cortical layers and to those neurons that support cortico-cortical connections.

Animals↗
PubMed1993

Visualization of implantable defibrillator patches by two-dimensional echocardiography.

Implantable cardioverter defibrillators are being used with increasing frequency for the management of life-threatening ventricular arrhythmias. In order to determine whether the titanium mesh of the defibrillator patch causes ultrasonographic acoustical interference, 30 patients underwent prospective serial echocardiographic examination. In addition, studies were reviewed to determine whether the defibrillator patches could be visualized with standard two-dimensional echocardiography. In no patient did the anterior patch produce acoustical interference, and, unless specific measures were utilized (such as a standoff pad, a zoom feature, or a 5-MHz transducer), the patches were rarely visualized.

Adult↗
PubMed1993

Nerve growth factor-induced neuronal differentiation is accompanied by differential induction and localization of the amyloid precursor protein (APP) in PC12 cells and variant PC12S cells.

PC12 cells and the morphological variant PC12S cells in culture were examined by immunochemical methods for the presence of the amyloid precursor protein (APP), before and after treatment with the nerve growth factor (NGF). In untreated PC12, untreated PC12S and in NGF-treated PC12 cells, APP was localized in the cytoplasm, whereas in NGF-treated PC12S cells, APP was localized at growth cones, processes and cytoplasm. In PC12 cells, three major forms of APP (695 and 751/770) were detected by Western blot. After NGF treatment, only the level of APP 695 was increased. Immunoprecipitation studies in PC12 cells revealed six protein species, corresponding to immature and mature forms of each of the three APP 695, 751 and 770 proteins. Addition of NGF increased the synthesis of the immature and mature forms of APP695. In PC12S cells, only the higher molecular weight forms of APP (751/770) were detected by both Western blot and immunoprecipitation. Addition of NGF had no effect on their levels. In both cell types, the level of the secreted form of APP showed a significant transient increase after NGF treatment. These results suggest that NGF can differentially regulate the molecular forms of APP and the localization of APP within the cell.

Amyloid beta-Protein Precursor↗
PubMed1993

Doppler echocardiographic assessment of the hemodynamic benefits of rate adaptive AV delay during exercise in paced patients with complete heart block.

To determine if rate adaptation of the atrioventricular (AV) delay (i.e., linearly decreasing the AV interval for increasing sinus rate) improves exercise left ventricular systolic hemodynamics, we performed paired maximal semi-upright bicycle exercise tests (EXTs) on 14 chronotropically competent patients with dual chamber pacemakers. Nine patients with complete AV block (CAVB) and total ventricular pacing dependence during exercise comprised the experimental group. Pacemakers in these patients were programmed randomly to rate adaptive AV delay (AVDR) for one EXT and fixed AV delay (AVDF) for the other EXT. AVDF was 156 msec; AVDR decreased linearly from 156-63 msec from rates of 78-142 beats/min. The other five patients had intact AV conduction and comprised the control group who were exercised in identical fashion while their pacemakers were inhibited throughout exercise to assure reproducibility of hemodynamic measurements between EXTs. Cardiac hemodynamics were calculated using measured Doppler echocardiographic systolic aortic valve flows recorded suprasternally with an independent 2-MHz Doppler transducer during a graded ramp exercise protocol. For analysis, exercise was divided into four phases to compare Doppler measurements at submaximal and maximal levels of exercise: rest, early exercise (1st stage), late exercise (stage preceding peak), and peak. Patients achieved statistically similar heart rates between EXTs at each phase of exercise. Although at lower levels of exercise cardiac hemodynamics did not differ, experimental patients (with CAVB) showed a statistically significant benefit to cardiac output at peak exercise with heart rates of 129 +/- 13 beats/min (AVDR: 9.4 +/- 2.8 L/min; AVDF: 8.2 +/- 2.6 L/min, P = 0.002), stroke volume (AVDR: 74.1 +/- 25.6 mL; AVDF: 64.3 +/- 24.4 mL, P = 0.0003), and aortic ejection time (AVDR: 253.3 +/- 35.7 msec; AVDF: 226.7 +/- 35.0 msec, P = 0.002). Duration of exercise, peak rate pressure product, peak aortic flow velocities, and acceleration times did not differ. In contrast, control group patients (intact AV conduction throughout exercise) showed no statistical differences between any hemodynamic parameters measured at any phase of exercise from the first to second exercise test. These data demonstrate that systolic cardiac hemodynamics measured echocardiographically at the high heart rates achieved with peak exercise are improved with AVDR compared to AVDF in chronotropically competent patients with complete AV block. This is due primarily to improved stroke volume and a longer systolic ejection time with AV delay rate adaptation.

Adult↗
PubMed1993

Assessment of aortic regurgitation by transesophageal echocardiography: correlation with angiographic determination.

Transthoracic echocardiographic studies have shown that color Doppler mapping of the aortic regurgitation (AR) jet correlated well with the severity of regurgitation as assessed by contrast aortography. The present study was performed to assess whether these parameters could be similarly applied to measurements determined by transesophageal echocardiography (TEE). In order to determine and validate criteria for the assessment of AR severity, 39 clinically stable patients with a TEE color Doppler study and contrast aortography within a 2-week period were identified. The ratio of the jet area (JA) to left ventricular diastolic area (LVDA) had the best correlation to AR severity as determined by contrast aortography (r = 0.89). Jet length, JA, the ratio of jet width to the width of the left ventricular outflow tract and jet width had r values of 0.88, 0.88, 0.83, and 0.84, respectively. The best sensitivity and specificity for the assessment of AR by TEE were obtained as follows: JA/LVDA ratio of 0%-7% predicts 0-1 + AR; 8%-20% 2-3 + AR, and greater than 20% 4 + AR. Of the three patients miscategorized, none was misgraded by more than one angiographic grade of AR. Jets that measure more than 6 cm in length or have an area of greater than 10 cm 2 have a 100% sensitivity and specificity for diagnosing 4 + AR. In the present study the ratio of JA to LVDA area correlates best with AR severity as determined by angiography.

Aged↗
PubMed1992

Single-plane transesophageal echocardiography for assessing function of mechanical or bioprosthetic valves in the aortic valve position.

To assess the value and limitations of single-plane transesophageal echocardiography in the evaluation of prosthetic aortic valve function, 89 patients (69 mechanical and 20 bioprosthetic aortic valves) were studied by combined transthoracic and transesophageal 2-dimensional and color flow Doppler echocardiography. In the assessment of aortic regurgitation, the transthoracic and transesophageal echocardiographic findings were concordant in 71 of 89 patients (80%). In 8 patients, the degree of aortic regurgitation was underestimated by the transthoracic approach; in each case the quality of the transthoracic echocardiogram was poor. In 10 patients, transesophageal echocardiography failed to detect trivial aortic regurgitation due to acoustic shadowing of the left ventricular outflow tract from a mechanical valve in the mitral valve position. Transesophageal echocardiography was superior to transthoracic echocardiography in diagnosing perivalvular abscess, subaortic perforation, valvular dehiscence, torn or thickened bioprosthetic aortic valve cusps, and in clearly distinguishing perivalvular from valvular aortic regurgitation. Transesophageal echocardiography correctly diagnosed bioprosthetic valve obstruction in 1 patient, but failed to diagnose mechanical valve obstruction in another. In conclusion, transesophageal echocardiography offers no advantage over the transthoracic approach in the detection and quantification of prosthetic aortic regurgitation unless the transthoracic image quality is poor. Transesophageal echocardiography is limited in detecting mechanical valve obstruction and in detecting aortic regurgitation in the presence of a mechanical prosthesis in the mitral valve position. However, it is superior to transthoracic echocardiography in identifying perivalvular pathology, differentiating perivalvular from valvular regurgitation and in defining the anatomic abnormality responsible for the prosthetic valve dysfunction. Combined transthoracic and transesophageal examination provides complete anatomic and hemodynamic assessment of prosthetic aortic valve function.

Adolescent↗
PubMed1992

Localization of cytochrome oxidase (COX) activity and COX mRNA in the hippocampus and entorhinal cortex of the monkey brain: correlation with specific neuronal pathways.

Cytochrome oxidase (COX) activity and COX II mRNA expression were localized in the hippocampal formation and entorhinal cortex of the rhesus monkey brain by means of enzyme histochemistry and in situ hybridization, respectively. Within the hippocampal formation, the terminal field of the perforant pathway showed the highest levels of COX activity, whereas COX II mRNA was localized mainly in neuronal cell bodies. In the entorhinal cortex. COX II mRNA was detected in neuronal cell bodies of layers II and IV. These results indicate that the pattern of localization of COX and its mRNA in entorhinal cortex correlates with the input and output pathways of the hippocampus.

Animals↗
PubMed1992

Differential expression of cytochrome oxidase (COX) genes in different regions of monkey brain.

A frontal pole cDNA library from monkey (Macaca mulatta) brain was screened to identify mRNAs that are expressed more in frontal pole as compared to primary visual cortex. Three cDNA clones, whose greater expression was confirmed by Northern blot analysis, were identified as cytochrome oxidase (COX) subunits I, II, and III (COX I, II, and III). Each clone showed higher levels of mRNA in the frontal pole, dorsal lateral prefrontal cortex, and hippocampus than in the primary visual or somatosensory cortices. COX histochemistry of prefrontal, visual, and somatosensory cortical regions demonstrated heterogeneous distributions, with highest activity in dendrite-rich neuropil of the cortex. A laminar distribution of COX mRNA expression also was demonstrated with in situ hybridization. mRNA was detected in cell bodies and in apical dendrites. These results indicate region specific differences in the distribution of COX activity and in the corresponding mRNA for three of its subunits within the monkey brain. Such differences may be related to differences in the distribution of neuropil as compared with cell bodies among the brain regions studied, and may be relevant to selective vulnerability in Alzheimer's disease.

Animals↗
PubMed1992

Transesophageal echocardiographic recognition of subaortic complications in aortic valve endocarditis. Clinical and surgical implications.

BACKGROUND: Secondary involvement of the mitral-aortic intervalvular fibrosa and the anterior mitral leaflet (subaortic structures) can occur in patients with aortic valve endocarditis. The secondary involvement of these structures occurs as a result of direct extension of the infection from the aortic valve or as a result of an infected aortic regurgitant jet striking the ventricular surfaces of the mitral-aortic intervalvular fibrosa and the anterior mitral leaflet. The abscess of mitral-aortic intervalvular fibrosa can expand to form an aneurysm. Subsequently, this mitral-aortic intervalvular fibrosa aneurysm can develop a perforation and communicate with the left atrium, resulting in the systolic regurgitation of blood from the left ventricular outflow tract into the left atrium. Secondary infection can also occur on the ventricular surface of the anterior mitral leaflet and result in the formation of an aneurysm or perforation of anterior mitral leaflet. METHODS AND RESULTS: This study examines the utility of transesophageal echocardiography in the detection of these subaortic complications in 55 consecutive patients with aortic valve endocarditis. A total of 24 patients (44%) had involvement of subaortic structures, including four with an abscess in the mitral-aortic intervalvular fibrosa, four with mitral-aortic intervalvular fibrosa aneurysm, seven with perforation of the mitral-aortic intervalvular fibrosa with communication into the left atrium, two with an aneurysm of the anterior mitral leaflet, and seven with perforation of the anterior mitral leaflet. The transesophageal echocardiographic findings were confirmed at surgery in 20 patients and at necropsy in two. By comparison, transthoracic echocardiography visualized these lesions in five of 24 patients (21%), including none of four with mitral-aortic intervalvular fibrosa abscesses, two of four with mitral-aortic intervalvular fibrosa aneurysms, one of seven with mitral-aortic intervalvular fibrosa perforations, one of two with anterior mitral leaflet aneurysms, and one of seven anterior mitral leaflet perforations. Eccentric mitral regurgitation-type systolic jets were noted in eight additional patients by transthoracic color flow imaging, and this finding suggested the possibility of these unusual subaortic complications. If these patients are included, then transthoracic echocardiography suggested the presence of these subaortic complications in 13 of 24 patients (54%). CONCLUSIONS: The results indicate that 1) involvement of the subaortic structures in patients with aortic valve endocarditis may be more common than previously recognized, 2) patients with aortic valve endocarditis and eccentric jets of mitral regurgitation on transthoracic echocardiography should undergo further evaluation by transesophageal echocardiography to exclude these unusual complications, 3) precise recognition of these complications is of value in the optimal medical and surgical management of these patients, and 4) these complications may be responsible for unexplained congestive heart failure and hemodynamic deterioration in some patients with aortic valve endocarditis.

Abscess↗
PubMed1992

The role of transesophageal echocardiography in the acute onset of paraplegia.

BACKGROUND AND PURPOSE: Acute paraplegia must be investigated promptly to exclude reversible causes. In this report we illustrate the usefulness of transesophageal echocardiography in identifying the vascular etiologies of acute paraplegia. CASE DESCRIPTIONS: Two patients presented with acute paraplegia, one spontaneously and the other after removal of an intra-aortic balloon pump catheter. Through the use of transesophageal echocardiography, we excluded aortic dissection and identified protruding atherosclerotic plaques in the descending thoracic aorta of each patient. Embolization of atheromatous material from the thoracic aorta was considered the most likely etiology of paraplegia in both cases. CONCLUSIONS: Embolization from atherosclerotic plaques in the thoracic aorta may be an underestimated cause of acute paraplegia. Transesophageal echocardiography provides a safe, rapid, and reliable tool for investigating a vascular etiology of acute paraplegia.

Aged↗
PubMed1992

Clinical application of magnetic resonance imaging of the heart and great vessels.

This report reviews the clinical applications of magnetic resonance imaging, (MRI) for the heart and great vessels based on the first 120 patients studied with 1.5 Tesla scanner. Cine scans were obtained in 85% of patients studied with the remainder having T1 spin-echo imaging. MRI provides high-resolution multiplanar images for defining abnormalities in cardiac structure and is especially useful for congenital heart disease. Cine MR evaluates cardiac dynamic functions such as left ventricular volumes and ejection fraction, left ventricular segmental wall motion, and valvular function. It is also useful for detection of aortic and pulmonary arterial disease and diseases of the pericardium. It is concluded that MR has broad applications for diagnosis of cardiac and great-vessel disorders.

Aorta, Thoracic↗
PubMed1992

Diagnosis of superior vena caval obstruction by transesophageal echocardiography.

Superior vena caval (SVC) syndrome may be caused by extravascular compression or intravascular obstruction. Knowing the mechanism of SVC syndrome enables the physician to choose appropriate treatment. Transesophageal echocardiography (TEE) is a safe bedside procedure that is excellent for evaluating the SVC and its surrounding structures. We report the valuable role of TEE in demonstrating the mechanism of SVC syndrome.

Aged↗