Biomedical subjects

Meihua Li

Publications and source records attributed to Meihua Li.

5 recordsLinked to original sources

PubMed2003

Uniformity in dynamic baroreflex regulation of left and right cardiac sympathetic nerve activities.

Functional laterality of cardiac sympathetic nerve stimulation in chronotropic and inotropic effects is well known. Whether left (LSNA) and right (RSNA) cardiac sympathetic nerve activities show laterality during dynamic baroreflex activation remains to be determined. In nine anesthetized, vagotomized, and aortic-denervated rabbits, we randomly perturbed intracarotid sinus pressure (CSP) in both carotid sinus regions while simultaneously recording LSNA and RSNA. The baroreflex neural arc transfer function from CSP to LSNA and from CSP to RSNA revealed derivative characteristics, i.e., the magnitude of LSNA and RSNA responses became greater as the input frequency of CSP perturbation increased. The average slope of increasing gain in the frequencies between 0.03 and 0.3 Hz showed no difference between LSNA and RSNA responses (9.7 +/- 2.9 vs. 9.7 +/- 3.1 dB/decade, means +/- SD). The amplitude ratio and phase difference between LSNA and RSNA approximated unity and zero radians, respectively, in the frequencies from 0.01 to 1 Hz. In addition, the LSNA-RSNA relationship during stepwise CSP perturbation from 40 to 160 mmHg showed a straight line (r(2) ranged from 0.969 to 0.999). These findings indicate no laterality in the dynamic as well as static baroreflex regulation of LSNA and RSNA as far as grouped axonal activity is concerned.

Adrenergic Fibers↗

PubMed2003

Intravenous angiotensin II does not affect dynamic baroreflex characteristics of the neural or peripheral arc.

Although the elevation of angiotensin II (Ang II) associated with cardiovascular diseases has been considered to suppress the arterial baroreflex function, how Ang II affects dynamic arterial pressure (AP) regulation remains unknown. The aim of the present study was to elucidate the acute effects of Ang II on dynamic AP regulation by the arterial baroreflex. In seven anesthetized Japanese white rabbits, we randomly perturbed intra-carotid sinus pressure (CSP) according to a binary white noise sequence while recording renal sympathetic nerve activity (RSNA) and AP. We estimated the neural arc transfer function from CSP to RSNA and the peripheral arc transfer function from RSNA to AP before and after 30-min intravenous administration of Ang II (100 ng/kg/min). Ang II increased mean AP from 75.7 +/- 3.1 to 95.5 +/- 5.1 mmHg (p < 0.01), while it did not affect mean RSNA (from 5.9 +/- 1.3 to 5.7 +/- 1.2 a.u.). The neural arc transfer functions did not differ before or after Ang II administration (dynamic gain: -0.94 +/- 0.04 vs. -0.94 +/- 0.13, corner frequency: 0.06 +/- 0.01 vs.0.06 +/- 0.01 Hz, pure delay: 0.16 +/- 0.01 vs. 0.17 +/- 0.02 s). The peripheral arc transfer function did not differ before or after Ang II administration (dynamic gain: 1.18 +/- 0.05 vs. 1.06 +/- 0.11, natural frequency: 0.07 +/- 0.01 vs. 0.08 +/- 0.01 Hz, damping ratio: 1.19 +/- 0.06 vs. 1.24 +/- 0.19, pure delay: 0.83 +/- 0.06 vs. 0.78 +/- 0.05 s). Intravenous Ang II hardly affects the dynamic characteristics of neural and peripheral arc around the physiological operating pressure.

Algorithms↗

PubMed2002

Genome-wide analysis of gene expression in intestinal-type gastric cancers using a complementary DNA microarray representing 23,040 genes.

To shed light on mechanisms that underlie development and/or progression of intestinal-type gastric cancer, we compared expression profiles of cancer cells obtained by laser-capture microdissection of 20 intestinal-type gastric tumors with expression of genes in corresponding noncancerous mucosae, by a cDNA microarray consisting of 23,040 genes. We identified 61 genes that were commonly up-regulated and 63 that were commonly down-regulated in the cancer tissues. Altered expression of 12 of those genes was associated with lymph node metastasis. A "predictive score," based on expression profiles of five of the genes that were able to distinguish tumors with metastasis from node-negative tumors in our panel, correctly diagnosed the lymph node status of nine additional gastric cancers. This genome-wide information contributes to an improved understanding of molecular changes during the development of intestinal-type gastric cancers. It may help clinicians predict metastasis to lymph nodes and assist researchers in identifying novel therapeutic targets for this type of cancer.

Adenocarcinoma↗

PubMed2002

Input-size dependence of the baroreflex neural arc transfer characteristics.

Static characteristics of the baroreflex neural arc from pressure input to sympathetic nerve activity (SNA) show sigmoidal nonlinearity, whereas its dynamic characteristics approximate a derivative filter where the magnitude of SNA response becomes greater as the input frequency increases. To reconcile the static nonlinear and dynamic linear components, we examined the effects of input amplitude on the apparent linear transfer function of the neural arc. In nine anesthetized rabbits, we perturbed isolated carotid sinus pressure by using binary white noise while varying the input amplitude among 5, 10, 20, and 40 mmHg. With increasing input amplitude, the transfer gain at 0.01 Hz decreased from 1.21 +/- 0.27 to 0.49 +/- 0.28 arbitrary units/mmHg (P < 0.01). Moreover, the slope of the transfer gain between 0.03 and 0.3 Hz decreased from 14.3 +/- 3.7 to 6.5 +/- 2.5 dB/decade (P < 0.01). We conclude that the model consisting of a sigmoidal component following rather than preceding a derivative component explains the observed results and thus can be used as a first approximation of the overall neural arc transfer characteristics.

Acoustic Stimulation↗

PubMed2002

An accurate iterative reconstruction algorithm for sparse objects: application to 3D blood vessel reconstruction from a limited number of projections.

Based on the duality of nonlinear programming, this paper proposes an accurate row-action type iterative algorithm which is appropriate to reconstruct sparse objects from a limited number of projections. The cost function we use is the Lp norm with p approximately 1.1. This norm allows us to pick up a sparse solution from a set of feasible solutions to the measurement equation. Furthermore, since it is both strictly convex and differentiable, we can use the duality of nonlinear programming to construct a row-action type iterative algorithm to find a solution. We also impose the bound constraint on pixel values to pick up a better solution. We demonstrate that this method works well in three-dimensional blood vessel reconstruction from a limited number of cone beam projections.

Algorithms↗