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Biomedical subjects

L Jiang

Publications and source records attributed to L Jiang.

At least 289 records · Page 16Linked to original sources
PubMed1987

An integrated mechanism for systolic anterior motion of the mitral valve in hypertrophic cardiomyopathy based on echocardiographic observations.

Although many mechanisms have been proposed to explain systolic anterior motion (SAM) of the mitral valve in hypertrophic cardiomyopathy, the precise mechanism of its onset and cessation remain undefined. The Venturi theory, based on increased flow velocity in a narrowed outflow tract, is widely accepted but fails to explain several important characteristics of SAM. It also neglects the potential role of drag forces generated by interposition of the leaflets into the path of ejection and of factors that would decrease the effectiveness of papillary muscle restraint. In order to obtain further insight into the mechanism of SAM, a detailed geometric study of the left ventricle and mitral apparatus was performed with cross-sectional echocardiography in three equal-sized groups of patients with hypertrophic cardiomyopathy and SAM, patients with hypertrophy and no anterior motion, and normal control subjects. A salient finding was that SAM began prior to ejection in patients with hypertrophic cardiomyopathy, which cannot be explained by the Venturi theory. Further, SAM began and was most prominent in the central portion of the leaflet as opposed to its lateral edges; this finding is not predicted by the Venturi mechanism. In addition to outflow tract narrowing, other structural changes unique to patients with SAM included anterior and inward displacement of the papillary muscles, anterior displacement of the mitral leaflets, and elongation of the mitral leaflets, which were, on the average, 1.5 to 1.7 cm longer than in the other subjects (p less than 0.0001). On the basis of these observations, an integrated mechanism for the initiation and resolution of SAM is proposed that would explain observed features such as onset before ejection and central prominence. This mechanism combines the effects of outflow tract narrowing with those of papillary muscle displacement. In particular, anterior and inward displacement of the papillary muscles can be predicted to alter the effectiveness of chordal support so that the central leaflet portions become relatively slack and are more readily displaced anteriorly. The altered distribution of chordal tension can also be predicted to orient the distal leaflets upward into the outflow tract at the onset of systole, prior to aortic valve opening, so that ventricular ejection will actually drag the interposed leaflets anteriorly. The resolution of SAM can be understood in terms of a reverse Venturi effect created by mitral regurgitation, as well as continued traction of the centrally displaced papillary muscles on the lateral leaflet margins.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1985

Variable effects of changes in flow rate through the aortic, pulmonary and mitral valves on valve area and flow velocity: impact on quantitative Doppler flow calculations.

Doppler echocardiographic methods for measuring volumetric flow through the aortic, pulmonary and mitral valves provide the cardiologist with several potentially interchangeable noninvasive methods for determining cardiac output. In addition, comparison of flow differences through individual valves offers the potential to quantitate shunt flow and regurgitant volumes. To date, however, no study has compared the relative accuracies of each of these flow measurements in a controlled experimental setting. Therefore, in this study, Doppler echocardiography was used to measure aortic, pulmonary and mitral valve flows in seven open chest dogs on right atrial bypass where forward cardiac output was precisely controlled with a roller pump. Correlations with roller pump output were better for Doppler measurements of aortic (r = 0.98, SD = 0.3) and mitral (r = 0.97, SD = 0.3) than for pulmonary (r = 0.93, SD = 0.5) valve flow. Interobserver reproducibility was also better for aortic (r = 0.94) and mitral (r = 0.97) than for pulmonary (r = 0.88) valve flow measurements. All valves showed flow-related increases in cross-sectional area, but the slope of this response was variable: 0.05, 0.16 and 0.21 for the aortic, the pulmonary and the mitral valve, respectively. Increased forward flow through the aortic valve, therefore, was manifested primarily by an increase in velocity, whereas increasing flow through the pulmonary and mitral valves produced more significant area changes with correspondingly smaller increases in the velocity component. Recalculation of Doppler-determined outputs, assuming a fixed valve area for the entire range of flows, resulted in a decreased correlation with roller pump output. Both velocity and valve area should be measured at each flow rate for greatest accuracy in volumetric flow calculations.

Animals↗
PubMed1985

A Doppler-two-dimensional echocardiographic method for quantitation of mitral regurgitation.

A noninvasive method to accurately quantitate the severity of mitral insufficiency would be of major clinical value. In theory, in the absence of confounding variables, regurgitant mitral flow should represent the difference between forward mitral blood flow and aortic blood flow. Since Doppler-two-dimensional echocardiographic (D2DE) methods for measuring transvalvular mitral and aortic flow have been validated, it should be possible to use mitral and aortic flows derived by this method to calculate regurgitant mitral flow. To assess the validity and accuracy of this combined approach for quantitation of regurgitant flow, we developed an open-chest canine preparation in which we could simulate, vary, and accurately measure degrees of mitral regurgitation. Seven animals were anesthetized and prepared to allow controlled right heart output. Mitral regurgitation was than simulated by placing a flexible conduit incorporating a one-way valve and electromagnetic flowmeter between the left ventricular apex and left atrium. Flow through the tube (effective mitral regurgitation) was varied between 0.2 and 1.8 liters/min and forward cardiac output ranged between 0.5 and 4 liters/min. Transmitral and transaortic flows were calculated by previously reported Doppler methods. Doppler-derived estimates of forward flow through the aortic valve correlated well with the flow measured by flowmeter (r = .92), and regurgitant flow and regurgitant fraction calculated by the D2DE approach also compared well with those measured by flowmeter (r = .84 and .83, respectively). This study demonstrates that mitral regurgitant flow and regurgitant fraction calculated by the D2DE method provide an acceptable measure of both absolute regurgitant flow and the regurgitant fraction in the experimental setting.

Animals↗
PubMedDate not supplied

Solution structure determination of endothelin-1 in methanol/water by NMR and molecular modelling methods.

To understand the structural requirements for the biological activity of endothelin peptides and to develop receptor selective endothelin analogues further, the solution structure of the bicyclic 21 amino acid residue vasoactive peptide, endothelin-1, has been determined in methanol-d3/water using high-resolution 1H-NMR spectroscopy. To our knowledge, this solvent system has not previously been used in NMR studies of endothelin and/or endothelin-like peptides. Two-dimensional DQFCOSY, TOCSY and NOESY spectra were acquired along with a series of one-dimensional spectra. A total of 219 distance constraints and 5 angle constraints were derived from the NMR data. These were incorporated into structure calculations using distance geometry (DIANA) followed by simulated annealing and molecular dynamics. The resulting structures are characterized by an alpha-helical conformation, Lys9-His16, and residues Ser5-Asp8 form a type I beta-turn. The N-terminal region, which was not extensively constrained by NMR data, showed no preferred conformation. The C-terminal tail showed less extensive conformational averaging but no descriptive conformation could be observed. The results obtained in this study are in good agreement with previous proposals.

Amino Acid Sequence↗
PubMedDate not supplied

Immunodiagnostic differentiation of alveolar and cystic echinococcosis using ELISA test with 18-kDa antigen extracted from Echinococcus protoscoleces.

Immunoblotting analysis was carried out using crude extracts of Echinococccus multilocularis and E. granulosus. A total of 214 serum samples were examined for the detection of antibody responses against 18-kDa polypeptides (Eg18 and Em18). Of 44 sera from patients with alveolar echinococcosis (AE) 91% were positive against both Eg18 and Em18, compared with 10% and 13%, respectively, of 70 cystic echinococcosis (CE) samples and 13% and 17% of 29 cysticercosis samples. A relatively purified 18-kDa antigen was extracted from E. granulosus protoscoleces and an 18-kDa-ELISA test which is simple, fast and highly sensitive and specific has been established. A comparative ELISA analysis, using the purified 18-kDa antigen and pooled AE and CE serum, indicated that there are significant differences in antibody levels between AE and CE sera. The maximum ratio for the evaluation of AE to CE was 2.26. The 18-kDa-ELISA was positive for 91% (40/44) and 11% (8/70) of AE and CE sera, respectively, and there was no cross-reactivity with cysticercosis sera or healthy controls. The overall diagnostic values of 18-kDa-ELISA for AE sera were sensitivity 91%, specificity 94%, positive predictive value 83% and negative predictive value 97%. We conclude that (i) the 18-kDa antigenic component may not be species specific but (ii) levels of antibody to the 18-kDa antigen are significantly different between AE and CE sera. Therefore, the 18-kDa antigen can be a reliable serological marker for differentiation of AE from CE.

Animals↗
PubMedDate not supplied

Three-dimensional echocardiographic reconstruction of right ventricular volume: in vitro comparison with two-dimensional methods.

Two-dimensional echocardiographic measures of right ventricular volume are limited by the asymmetric and crescentic shape of that ventricle and the difficulty in obtaining standardized views. We have developed a three-dimensional echocardiographic system that automatically integrates images and positional data and calculates right ventricular volume without the need for geometric assumptions or standardized views and a surfacing algorithm that takes advantage of the full three-dimensional data set. The accuracy of this system was studied and compared with two-dimensional methods in 12 gel-filled excised human right ventricles (18 to 74 ml). Volumes calculated by three-dimensional echocardiography correlated well with actual values (r = 0.99) and agreed more closely with them than did those obtained by two-dimensional methods (p < 0.02).

Algorithms↗
PubMedDate not supplied

Hyperthermia prevents metabolic and cerebral flow responses to hypoxia in the fetal sheep.

OBJECTIVE: Fetal brain temperature has been found to decrease during hypoxia, strongly suggesting a reduction in cerebral O2 consumption and increases in cerebral blood flow. These responses may protect the brain in part against hypoxic injury. This study was undertaken to examine whether these compensatory mechanisms are lost during fetal hyperthermia. METHODS: Intermittent fetal hypoxemia was induced by administering low-O2 gas mixtures to nine near-term ewes. Fetal brain and body core temperature responses were measured with and without fetal hyperthermia induced by circulating warm water through a plastic coil looped about the fetus in utero. RESULTS: In normothermic fetuses, fetal brain temperature relative to core decreased during a 30-minute period of hypoxia and then returned to normal during recovery. This response may be explained by a combination of cerebral hypometabolism and increased cerebral blood flow. However, in hyperthermic fetuses (intrauterine warming for 1 hour, raising body core and brain temperatures 0.66 +/- 0.06 and 0.61 +/- 0.10 C, respectively) a subsequent period of hypoxia no longer induced a reduction in brain temperature relative to body core. CONCLUSION: When temperature of the fetal sheep is elevated, as may occur with maternal fever, prolonged exercise, and elevated environmental temperatures, the fetal brain is less well protected against hypoxic injury.

Amniotic Fluid↗
PubMedDate not supplied

Kinetics of uptake, transport, and accumulation of liposome-associated fluorescent dolichol esters in human fibroblasts.

The anthroyl and n-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino (NBD) hexanoyl esters of dolichol were synthesized and incorporated into phospholipid liposomes. Fluorescence spectrometric methods were used to estimate the kinetics and dynamics of the incorporation and turnover of these esters in normal human fibroblasts. For anthroyl dolichol a saturable uptake of 2.5 x 10(3) pmol/10(6) fibroblasts was obtained. Half-maximum uptake was seen at a labeling concentration of 19 microM. The time required for half-maximum uptake of fluorescence (t1/2) was about 10 h. Over 50% of the anthroyl dolichol taken up remained in fibroblasts 24 h after the labeling medium was removed. Uptake was higher for esters of 9 isoprenes than for those with 16-21. Dolichol labeled with the NBD fluorophore appeared to enter fibroblasts in higher concentration than the same dolichol labeled with anthracene. Uptake was not influenced by the presence of agents that disrupt lysosome function (leupeptin and chloroquine) prior to or during fluorescence labeling. The amount of fluorescent dolichol in the (i) lysosomes and endosomes and (ii) nuclei of labeled fibroblasts was determined after Percoll density gradient centrifugation and cell lysis in culture, respectively. Most of the fluorescent dolichyl ester (and most of the free alcohol form) taken up by fibroblasts was recovered in lysosomes.

Biological Transport↗
PubMedDate not supplied

Improved exercise tolerance following enhanced external counterpulsation: cardiac or peripheral effect?

The effect of treatment with enhanced external counterpulsation (EECP) on exercise hemodynamics and myocardial stress perfusion in 27 patients with chronic stable angina was studied. A majority (22/27 or 81%) of patients improved their exercise tolerance after EECP treatment, and a similar percentage (21/27 or 78%) of patients improved their radionuclide stress perfusion images. Post-EECP maximal exercise heart rate and blood pressure, while demonstrating a linear relation with exercise duration, did not increase significantly despite the increased exercise duration. This suggests that the increase in exercise duration after treatment with EECP is due to both improved myocardial perfusion and altered exercise hemodynamics. EECP therapy thus appears to exert a "training' effect, decreasing peripheral vascular resistance and the heart rate response to exercise. Coronary disease patients may improve their exercise tolerance after EECP because of both improved myocardial perfusion and a decrease in cardiac work load.

Aged↗