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Biomedical subjects

C E Miller

Publications and source records attributed to C E Miller.

At least 73 records · Page 4Linked to original sources
PubMed1990

Finite element analysis of bioelectric phenomena.

This article reviews the application of finite element methods to models of bioelectric phenomena. The models represent the electrical fields created in the body as a result of membrane current sources or external current applied for diagnostic or therapeutic purposes. We formulate the governing equations for these models and then derive the finite element equations for the generalized bioelectric problem. The 32 papers reviewed here, all those appearing in the literature to date, cover the areas of electrocardiology, therapeutic and functional electrical stimulation in the cerebellum, cochlea, spinal cord, and peripheral nerves, cardiac defibrillation, electrical impedance tomography, bidomain cardiac models, electroporation, and therapeutic electrical stimulation of bone. For each, we summarize the purpose of the study, the model details and assumptions, the major results, and the applicability of the study. The models are then considered as a group to critique the appropriateness of the finite element method, the means of implementation, and the factors affecting accuracy, thus providing an overview of the state of finite element modeling of bioelectric phenomena.

Central Nervous System Diseases↗
PubMed1988

Dissimilar plasmids isolated from Pseudomonas diminuta MG and a Flavobacterium sp. (ATCC 27551) contain identical opd genes.

The opd (organophosphate-degrading) gene derived from a 43-kilobase-pair plasmid (pSM55) of a Flavobacterium sp. (ATCC 27551) has a sequence identical to that of the plasmid-borne gene of Pseudomonas diminuta. Hybridization studies with DNA fragments obtained by restriction endonuclease digestion of plasmid DNAs demonstrated that the identical opd sequences were encoded on dissimilar plasmids from the two sources.

Base Sequence↗
PubMed1988

Autoregulation in the developing postnatal intestinal circulation.

The relationships among perfusion pressure, blood flow, and oxygen uptake were determined in in vitro ileal loops from 3- and 35-day-old swine. Arterial perfusion of the ileal loops was achieved using a reservoir perfusion apparatus that allowed direct manipulation of perfusion pressure. The hematocrit, partial pressure of oxygen, and partial pressure of carbon dioxide of the blood used to perfuse the gut loops were standardized. During steady-state perfusion at an arterial pressure of 100 mmHg and venous pressure of 0 mmHg, ileal loops from 3-day-old swine demonstrated a higher blood flow (55 vs. 27 ml.min-1.100 g-1, 3 vs. 35 day old) and lower arteriovenous oxygen content difference (3.5 vs. 6.6 ml O2/dl). Oxygen uptake was not statistically different between groups (1.99 vs. 1.76 ml O2.min-1.100 g-1). During perfusion pressure reduction from 150 to 25 mmHg (in successive decrements of 25 mmHg), pressure-flow autoregulation was present in ileal loops from 35-day-old swine but not in ileal loops from 3-day-old swine. Similarly, tissue oxygen uptake was more effectively maintained in ileal loops from older swine during perfusion pressure reductions. We speculate that the efficacy of intrinsic regulation of intestinal hemodynamics and oxygenation is dependent, in part, on postnatal age.

Aging↗
PubMed1988

Effects of arterial hypoxia and isoproterenol on in vitro postnatal intestinal circulation.

We have previously speculated that intestinal vasodilation and hyperemia that occur in response to moderate arterial hypoxia in newborn swine in vivo are mediated by factors intrinsic to the intestinal circulation. To test this speculation, we vascularly perfused in vitro loops of jejunum from postnatal swine with control (PO2 98 +/- 4 mmHg) and hypoxic (PO2 38 +/- 2 mmHg) blood obtained from donor swine. In response to hypoxic perfusion, jejunal vascular resistance decreased 12 +/- 2, 13 +/- 3, 33 +/- 5, and 42 +/- 3% in in vitro loops from 1-, 7-, 14-, and 30-day-old swine, respectively, whereas jejunal oxygen uptake decreased 53 +/- 6, 29 +/- 6, 31 +/- 4, and 13 +/- 6% in these age groups. To clarify whether this age-dependent vasodilation was unique to the stimulus of arterial hypoxia or a response characteristic of the postnatal swine intestine to other vasodilator stimuli, we also determined the effect of intra-arterial isoproterenol infusion at rates of 0.01, 0.1, and 1.0 micrograms/min on jejunal hemodynamics and oxygenation in vitro. In jejunal loops taken from 7- and 30-day-old swine, isoproterenol caused a similar degree of vasodilation at each drug-infusion rate. We conclude that vasodilation of the postnatal swine intestine in response to moderate arterial hypoxia is mediated, at least in part, by intrinsic vascular regulation. We speculate that the age dependency of hypoxic vasodilation may reflect a relative inability of the intestine from very young swine to respond to the stimulus of arterial hypoxia.

Aging↗
PubMed1986

Decreased gestational sac volumes in pregnancies induced by human menopausal gonadotropin.

Mean gestational sac volumes of 9 singleton pregnancies induced by human menopausal gonadotropin (hMG) measured by ultrasound were compared with mean gestational sac volumes obtained from 37 normal singleton pregnancies, 6 to 8 weeks from the last menstrual period. HMG-induced gestational sacs were smaller at 6 and 7 weeks of gestation, compared with normal pregnancies. Despite the initial lag in gestational sac volume, hMG-induced pregnancies subsequently demonstrated appropriate fetal growth as measured by crown-rump length measurements between 8 and 12 weeks. These pregnancies also demonstrated normal fetal growth patterns in the second and third trimesters of pregnancy, as assessed by clinical evaluation and ultrasound. These preliminary data suggest that early growth development in hMG-induced pregnancies may be different from that in spontaneously occurring pregnancies.

Embryonic and Fetal Development↗
PubMed1985

Structural implications of basilar membrane compliance measurements.

Static point-load measurements of basilar membrane compliance were made in the basal region of the excised guinea pig cochlea. Points on a radial line across the basilar membrane were displaced in one-half micron increments and the force required to maintain each increment recorded. The results are interpreted in terms of the material layers of the basilar membrane and displayed as compliance curves. In addition, a beam model of the basilar membrane, including the arches of Corti and the actual geometry of the pectinate zone, is constructed from anatomical data. The free parameters in this model are the modulus of elasticity of the transverse filaments and the effective spring stiffness of the arches. Compliance curves for the model are generated with a finite element approach and the parameters are obtained by requiring optimal agreement with the experimental measurements. The results show that the separation between fiber layers in the pectinate zone is relevant to the effective moment of inertia of the cross section and that the longitudinal coupling between the heads of the arches provides a rigidity to the arcuate zone not seen in the pectinate zone where longitudinal coupling is minimal. The elastic modulus calculated for the filaments is 1.8 GPa, approximately one-half that of keratin, while the cells and ground substance are five orders of magnitude softer.

Animals↗
PubMed1982

The effect of labor on the rheologic response of chorioamniotic membranes.

A study of chorioamniotic membranes was undertaken in 2 term populations. One group of women delivered vaginally after normal labor (N = 41), the other by elective cesarean section (N = 41). Rheologic properties were measured in an experimental environment. The membranes in each group responded similarly while intact. Those membranes subject to labor, however, ruptured earlier in cyclic testing. They also required more time to dissipate applied stress. This stress response pattern is similar to that seen with rupture of amorphous materials in which multiple flaws or cracks are aggravated by stress testing. The clinical problem of premature rupture of the membranes may occur by a phenomenon that produces flaws in their structure. The data suggest that these flaws may be aggravated by labor-like uterine activity.

Amnion↗
PubMed1980

L-Glutamic acid as a mediator of sexual morphogenesis in Volvox capensis.

In Volvox capensis the development of sexual individuals is in response to low concentrations (68 nM) of L-glutamic acid rather than to such species-specific glycoproteins as have been isolated in Volvox carteri or are believed to exist in a number of other species. V. capensis grows equally as well in light and in darkness in a medium supplemented with sodium acetate; however, L-glutamic acid is active as an inducer of the sexual form only in populations grown in the light. The site of action of L-glutamic acid and its biochemical role in the sexual response are unknown. Attempts to induce the sexual response by using the other L-amino acids, various analogs of glutamic acid, compounds of similar structure (e.g., gamma-aminobutyric acid), and intermediates of biochemical pathways known to involve L-glutamic acid (e.g., alpha-ketoglutarate or pyroglutamic acid) have been unsuccessful. L-Glutamic acid is produced by V. capensis as a natural product of the digestion of the glycoproteinaceous parental matrix at the time young spheroids escape. As a population increases, so does the level of L-glutamic acid produced at each succeeding generation until the threshold of sensitivity is reached and the induction of sexual forms is effected. This serves as a mechanism for ensuring the production of sexual spheroids and their zygotes, the only phase in the life cycle resistant to drying. Thus, Volvox is especially adapted to an existence in ephemeral pools of water resulting from seasonal rains.

Journal Article↗
PubMed1980

An improved WKB calculation for a two-dimensional cochlear model.

The finite difference calculations of Neely [E.D. thesis, California Institute of Technology, Pasadena, CA (1977)] and the WKB solution of Steele and Taber [J. Acoust. Soc. Am. 65, 1001-1006 (1979)] generally agree, except in the "phase plateau" region, where both are irregular. In the present work, an improvement in the accuracy of the WKB procedure is gained by using a closed-form integral which gives the phase and damping functions in the short wavelength region. The present results agree qualitatively with the preceding but show a smooth variation with frequency and distance along the cochlea.

Cochlea↗
PubMed1980

Effect of meconium on the strength of chorioamniotic membranes.

A population of 1320 patients was reviewed to assess the clinical significance of antepartum meconium staining on the occurrence of premature rupture of the membranes. Specimens of amniotic membranes were studied by tensile strength testing from 2 population groups. The results of the retrospective review showed no difference in the incidence of premature rupture of the membranes between the populations with clear amniotic fluid and those with meconium-stained fluid at time of amniorrhexis. The tensile strength testing demonstrated that the study population with antepartum meconium-stained fluid had significantly lower stress tolerance. This investigation demonstrated a significant decrease in stress tolerance of human chorioamniotic membranes associated with a meconium-stained fluid environment, but this loss of stress tolerance is not apparently significant in clinical practice.

Adult↗
PubMed1979

Deformation and creep in the human chorioamniotic sac.

This paper presents a review of physical principles involved in deformation and creep in the human chorioamniotic membrane. These are definable rheological properties found in many materials. Experimental data are presented on 66 human fetal membranes. A difference in the stress tolerance between preterm and term membranes is demonstrated. A computer model has been devised which allows for the calculation of changes in thickness of the membrane at the point of fracture. This computer model allows for the study of the physical property of the tissue in ways which have not previously been suggested. The model suggests that the pathophysiology related to rupture of the membrane is based on changes in the thickness of this tissue occurring secondary to acute and chronic stress applications. The data derived in these experiments suggest a possible physical model for rupture of the membranes; they also introduce questions regarding the anatomic and biochemical makeup of the chorion and the amnion and the respective role that each plays in maintaining the integrity of the human chorioamniotic sac.

Extraembryonic Membranes↗
PubMed1979

Probabilistic theories of coalition formation in groups.

Chertkoff's (1967) and Walker's (1973) theories of coalition formation for decision making, which attempt to predict the probabilities of the occurrence of coalitions in three-person group systems, are extended to apply to certain situations involving groups larger than these triads. These two extended theories and Komorita's (1974) weighted probability theory, which attempts to predict the probabilities of occurrence of coalitions in groups of any size, are compared according to how well they can account for the results of a number of previously reported experiments, both on triads and on larger groups. In general, this comparison shows that: (a) Chertkoff's theory cannot account for the results; (b) Walker's theory can account only for the results of experiments in which all the minimal winning coalitions are equal in size; and (c) Komorita's theory can account only for the results of experiments in which there is some difference in size among the minimal winning coalitions. It is suggested that the theories of Chertkoff and Walker do not attribute enough importance to size as a factor in coalition formation, while weighted probability theory attributes too much importance to this factor.

Decision Making↗
PubMed1978

Pitfalls in the ultrasonographic diagnosis of the pancreatic pseudocyst.

A pseudocyst of the pancreas typically presents ultrasonographically as a cystic structure in the upper abdomen. We have seen numerous cases which presented similar sonographic features suggestive of a pancreatic pseudocyst in which this diagnosis proved false. A knowledge of the ultrasonographic differential diagnosis of the pancreatic pseudocyst therefore becomes important.

Adult↗