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Biomedical subjects

L J Groome

Publications and source records attributed to L J Groome.

48 records · Page 3Linked to original sources
PubMed1983

Diffusion and convection across heteroporous membranes: a simple macroscopic equation.

Here the problem of identifying a set of macroscopic parameters which describe the transport of a neutral solute across a heteroporous membrane by convection and diffusion is considered. An approximate equation for the solute flux is developed in terms of the membrane boundary conditions and the macroscopic parameters Lp (hydraulic conductivity), sigma s (reflection coefficient), Ps (permeability), and qs (index parameter). The unique feature of this model is that the four macroscopic parameters are (1) expressed in terms of the set of single-pore parameters [Lpi, sigma si, Psi] and the pore-size distribution only, (2) invariant to conditions which alter the volume (Jv) and solute (Js) fluxes, and (3) consistent with simultaneous measurements of Jv and Js. The four-parameter equation for Js is shown to be in good agreement with the exact solution for the extreme case of a membrane composed of two distinct sets of pores which differ greatly in radii.

Cell Membrane↗
PubMed1983

Permeability of the canine visceral pleura.

Fluid and protein movement across the pulmonary endothelial membrane (PEM) and adjacent mesothelial layer of the visceral pleura was quantitatively analyzed in terms of a two-compartment model of fluid exchange. The left lungs of 13 spontaneously breathing anesthetized dogs were enclosed in a water-impermeable membrane, creating a visceral pleural space; fluid flux was determined as the filtration or reabsorption of water and protein in the visceral pleural space. Aortic, pulmonary arterial, left atrial, and pleural pressures were monitored; oncotic pressure was calculated from the protein concentration of plasma and pleural fluid. To determine the hydraulic conductivity (Lp), diffusional permeability (Pd), and the solute and solvent drag reflection coefficients for protein (sigma d and sigma f, respectively), fluid exchange was monitored during two or more experimental periods during which the visceral pleural space contained saline and plasma. The permeability coefficients determined for the PEM of the visceral pleura, Lp = 7.7 (+/- 0.3) X 10(-7) ml X s-1 X mmHg-1 X cm-2, sigma d = 0.93, sigma f = 0.61, and Pd = 2.4 (+/- 1.0) X 10(-6) cm/s, are more restrictive than those previously reported for the devascularized visceral pleura in vitro. We conclude that it is the pulmonary endothelial membrane that determines the rate and composition of visceral pleural fluid flux in response to hydrostatic and oncotic gradients in the intact animal.

Animals↗
PubMed1981

On equations for combined convective and diffusive transport of neutral solute across porous membranes.

The process of combined convection and diffusion of solute across membranes of finite thickness is discussed. An exact solution is available for an open (nonsieving) homoporous membrane. This solution is nonlinear in the volume flux (Jv) for any nonzero volume flow and concentration difference. Extension to the more general case of a partially sieving membrane does not change the nonlinear form of this equation. A linearization of this transport equation about small Jv/Ps yields an approximate equation (the arithmetic mean) that is useful over a reasonable range of conditions near equilibrium. The application of linear nonequilibrium thermodynamics to this process has led to the derivation of a third transport equation, linear in Jv but logarithmic in the concentrations. This finite difference equation is shown to give a less accurate approximation to the exact equation than does the arithmetic mean equation, even in regions near equilibrium. Use of approximate equations may lead to error when the solute reflection coefficient is determined from ultrafiltration experiments or when applied to the individual elements of a membrane array. The early origins of the concept of reflection and sieving coefficients and their relation to one another are discussed. The importance of structural detail in membranes, even at a fine-grained level, and the distinction between the terms "homogeneous" or "black box" and "homoporous" is emphasized. Although structural complexity creates problems in any attempt to write a transport equation without detailed knowledge of the membrane stucture, proper consideration of the local equation and its subsequent integration makes this fact explicit and allows for an assessment of the magnitude of these effects.

Animals↗
PubMed1979

A simple tension-displacement model for hemoglobin cooperativity.

Based on the Perutz view of hemoglobin cooperativity and the methodology of statistical physics, a molecular model for heme-heme interactions is proposed. The motion of the iron atom with respect to the heme plane is assumed to be the important feature of the oxygenation step, and results in an expression for hemoglobin saturation as an explicit function of the internal tension of the hemoglobin molecule. Closure of the equation is obtained with the assumption of linearity between the internal tension and the displacement of the iron atom above the heme plane. All model parameters are physically realizable and are characteristic of the hemoglobin molecule. Finally, the model is capable of discriminating between positive and negative cooperativity.

Binding Sites↗
PubMed1976

A stochastic model for the transport of oxygen to brain tissue.

Material balances around a small, but finite volume element have formed the basis for previous mathematical models describing the transport of oxygen in the brain microcirculation. Seeking a model which would be both simple and versatile, a stochastic model was proposed based on the assumption that oxygenation of the brain can be described quantitatively by simulating the activity of only one erythrocyte and the oxygen molecules surrounding it. Compared with existing deterministic models, the capillary space-average oxygen partial pressure profiles were in close agreement. Tissue tensions were decidedly different.

Blood Flow Velocity↗
PubMedDate not supplied

Blood pressure changes in normotensive women readmitted in the postpartum period with severe preeclampsia/eclampsia.

The purpose of this study was to determine whether women who had no clinical evidence of preeclampsia at delivery, but who were later readmitted with postpartum severe preeclampsia or eclampsia, differed in mean arterial pressure (MAP) and clinical presentation from women who either remained normotensive or had severe preeclampsia or eclampsia at the time of delivery. Control subjects did not require readmission and were matched (2:1) with study subjects in consecutive order for date of delivery and maternal age, race, and parity. Women in the study group had a significantly greater increase in MAP after delivery than control subjects, and analysis of variance for linear trends demonstrated highly significant differences between the study and control groups in the average intrapartum and postpartum MAPs. Compared to women in either control group, mothers who were readmitted were significantly more likely to demonstrate a > 10-mm Hg increase in MAP between the intrapartum and postpartum periods (delta MAP). Normotensive women with a delta MAP > 10 mm Hg had more than a threefold risk of readmission in the postpartum period with severe preeclampsia or eclampsia. Women who were readmitted reported a significantly greater frequency of headaches and nausea and vomiting than women with intrapartum preeclampsia. In summary, our findings indicate that MAP increase following delivery in normotensive women who were later readmitted with severe preeclampsia or eclampsia.

Analysis of Variance↗
PubMedDate not supplied

Hospital readmission for postpartum endometritis.

This study identified risk factors associated with readmission for postpartum endometritis. The study group consisted of 109 mothers (Group I) who were discharged after delivery and readmitted with endometritis. Control groups consisted of women who had endometritis immediately after delivery but who did not require readmission (Group II, n = 109), and women who had no intrapartum or puerperal infection and also were not readmitted (Group III, n = 109). Subjects in Groups II and III were matched to an index study subject for date of delivery and maternal age, race, and parity; and women in Groups I and III were also matched for route of delivery. Groups were compared in terms of demographic characteristics, intrapartum course, and clinical presentation. The data were analyzed with the t-test, chi2, and multiple logistic regression analyses, and a P value < .05 was considered significant. Women in Groups I and III delivered vaginally more often than mothers in Group II. In addition, mothers in Groups I and III had similar postpartum courses, no evidence of infection on discharge after delivery, and a similar period from delivery until postpartum discharge. Although women in Group I were more likely to have spontaneous rupture of membranes, a shorter latent period, and have fewer bilateral tubal ligations than mothers in Group II, multivariate analysis identified route of delivery as the only significant maternal variable associated with postpartum endometritis requiring readmission. Women who were readmitted for endometritis usually delivered vaginally, and the occurrence of late-onset postpartum endometritis was unrelated to the length of stay following delivery.

Adult↗
PubMedDate not supplied

Pneumonia as a complication of pregnancy.

OBJECTIVE: To identify risk factors for the development of antepartum pneumonia and to describe maternal and perinatal outcome in pregnant women with pneumonia. METHODS: The study group consisted of 59 women with antepartum pneumonia. Pneumonia was defined by the presence of lower respiratory tract symptoms, radiographic findings, no other source of infection, and at least two of the following: oral temperature > or =38 degrees C, white blood cell count > or =15,000/ml, auscultatory findings, and/or positive sputum cultures. For comparison, a control group (n = 118) of pregnant women was formed by selecting the first mother who delivered immediately before and after an index study subject. RESULTS: Mothers in the study group were significantly more likely than women in the control group to have either a history of asthma (P = 0.022) or an admission hematocrit < or =30% (P < 0.001). Women with pneumonia were also more likely to receive a tocolytic agent (P < 0.001) and/or beta-methasone to enhance fetal lung maturity (P < 0.001). In addition, study subjects delivered at an earlier mean gestational age (P = 0.002) and had infants who weighed significantly less (P = 0.003) than mothers in the control group. Multivariate analysis indicated that women with asthma or anemia had more than a five-fold increase in the risk of developing pneumonia during pregnancy (P = 0.013), and mothers with pneumonia were significantly more likely to deliver before 34 weeks gestation (P = 0.04). CONCLUSIONS: Pneumonia during pregnancy was associated with maternal anemia and asthma. In addition, preterm labor with tocolysis and/or beta-methasone was more common in women with pneumonia, and these women were more likely to deliver preterm and have low birthweight infants compared to women without pneumonia.

Anemia↗
PubMedDate not supplied

Reproductive risks of cocaine.

Cocaine use during pregnancy in the USA has increased dramatically in the past decade, and has resulted in an associated increase in a variety of maternal and perinatal complications. However, a number of confounding factors make it difficult to determine the direct impact of perinatal cocaine use on maternal and fetal outcome. Many substance-abusing women use multiple drugs while pregnant, receive inadequate prenatal care and are predisposed to other health problems that impact on perinatal outcome. As a result of the rapid clearance of cocaine and limitations of available screening methods, the identification of individual users can be difficult. Furthermore, the determination of accurate prevalence rates of cocaine use during pregnancy has been frustrated by sampling bias. Cocaine has profound systemic and cardiovascular effects in both the mother and the fetus, and as a result a number of complications (i.e. fetal malformations, preterm labour, placental abruption) have been attributed to perinatal cocaine exposure. In addition, maternal cocaine use has been associated with a number of neonatal abnormalities, including cardiopulmonary effects, somatic changes and neurobehavioural sequelae. It is estimated that US $500 million dollars in additional health expenditure resulted from increased neonatal hospital costs and longer lengths of stay for cocaine-exposed neonates. This article reviews the reproductive risks associated with prenatal cocaine use. The pharmacology and physiology of cocaine in relation to pregnancy is discussed, and the impact of this substance on the growth and development of the fetus and infant is reviewed.

Abnormalities, Drug-Induced↗
PubMedDate not supplied

The antiphospholipid antibody syndrome: an overview.

The antiphospholipid antibody syndrome is characterized by the presence of maternal anticardiolipin antibodies and/or the lupus anticoagulant in association with recurrent pregnancy loss, thrombotic events, and/or thrombocytopenia. This disorder occurs rarely, but pregnant patients with antiphospholipid antibodies are at risk for adverse maternal and perinatal outcomes. This article reviews the antiphospholipid antibody syndrome, including its pathophysiology, clinical sequelae, diagnostic criteria, medical treatment, and nursing care.

Antiphospholipid Syndrome↗
PubMedDate not supplied

Clinical presentation of women readmitted with postpartum severe preeclampsia or eclampsia.

OBJECTIVE: To identify symptoms that prompted a group of women readmitted for postpartum severe preeclampsia or eclampsia to seek medical care. DESIGN: Retrospective, case-control. SETTING: Tertiary-care teaching hospital. SUBJECTS: The study group consisted of 53 women readmitted in the postpartum period with severe preeclampsia or eclampsia. The control group was matched two-to-one with an index study participant and consisted of 106 women who had intrapartum severe preeclampsia or eclampsia. MAIN OUTCOME MEASURES: Patient symptoms, physical findings, laboratory assays. RESULTS: Neurologic complaints, malaise, and nausea and vomiting were reported more often in women who were readmitted than in mothers with intrapartum preeclampsia (all p values less than .001). Headaches were positively correlated with systolic, diastolic, and mean arterial blood pressure in women who were readmitted (all p values less than .05), although there was no relationship between blood pressure and headaches in the control group. In addition, multivariate analysis revealed that study participants were more likely to deliver at full term, have headaches and malaise, have normal platelet values, and develop seizures than mothers in the control group, chi 2 = 155.7, p < .001. CONCLUSIONS: Women readmitted for postpartum severe preeclampsia or eclampsia have a clinical presentation that differs from that of intrapartum preeclampsia or eclampsia.

Adolescent↗