A Mathematical Model of Granulopoiesis Incorporating the Negative Feedback Dynamics and Kinetics of G-CSF/Neutrophil Binding and Internalization

We develop a physiological model of granulopoiesis which includes explicit modelling of the kinetics of the cytokine granulocyte colony-stimulating factor (G-CSF) incorporating both the freely circulating concentration and the concentration of the cytokine bound to mature neutrophils. G-CSF concentrations are used to directly regulate neutrophil production, with the rate of differentiation of stem cells to neutrophil precursors, the effective proliferation rate in mitosis, the maturation time, and the release rate from the mature marrow reservoir into circulation all dependent on the level of G-CSF in the system. The dependence of the maturation time on the cytokine concentration introduces a state-dependent delay into our differential equation model, and we show how this is derived from an age-structured partial differential equation model of the mitosis and maturation and also detail the derivation of the rest of our model. The model and its estimated parameters are shown to successfully predict the neutrophil and G-CSF responses to a variety of treatment scenarios, including the combined administration of chemotherapy and exogenous G-CSF. This concomitant treatment was reproduced without any additional fitting to characterize drug-drug interactions.

Origin of bistability in the lac Operon

Multistability is an emergent dynamic property that has been invoked to explain multiple coexisting biological states. In this work, we investigate the origin of bistability in the lac operon. To do this, we develop a mathematical model for the regulatory pathway in this system and compare the model predictions with other experimental results in which a nonmetabolizable inducer was employed. We investigate the effect of lactose metabolism using this model, and show that it greatly modifies the bistable region in the external lactose (Le) versus external glucose (Ge) parameter space. The model also predicts that lactose metabolism can cause bistability to disappear for very low Ge. We have also carried out stochastic numerical simulations of the model for several values of Ge and Le. Our results indicate that bistability can help guarantee that Escherichia coli consumes glucose and lactose in the most efficient possible way. Namely, the lac operon is induced only when there is almost no glucose in the growing medium, but if Le is high, the operon induction level increases abruptly when the levels of glucose in the environment decrease to very low values. We demonstrate that this behavior could not be obtained without bistability if the stability of the induced and uninduced states is to be preserved. Finally, we point out that the present methods and results may be useful to study the emergence of multistability in biological systems other than the lac operon.

Stimulus-dependent onset latency of inhibitory recurrent activity

This paper gives an explanation for the experimentally observed onset latencies of the inhibitory responses that vary from a few milliseconds to hundreds of milliseconds in systems where the conduction delays are only several milliseconds in the feedback pathways. To do this we use a simple mathematical model. The model consists of two delay differential equations (DDE) where the nonlinear relation between the postsynaptic potential and the firing frequency of the neuron population arises from the stoichiometry of the transmitter-receptor kinetics. The parameters of the model refer to the hippocampal feedback system, and the modeling results are compared with corresponding experiments.

Information capacity and pattern formation in a tent map network featuring statistical periodicity

We provide quantitative support to the observation that lattices of coupled maps are "efficient" information coding devices. It has been suggested recently that lattices of coupled maps may provide a model of information coding in the nervous system because of their ability to create structured and stimulus-dependent activity patterns which have the potential to be used for storing information. In this paper, we give an upper bound to the effective number of patterns that can be used to store information in the lattice by evaluating numerically its information capacity or information rate as a function of the coupling strength between the maps. We also estimate the time taken by the lattice to establish a limiting activity pattern.

The rate of apoptosis in post mitotic neutrophil precursors of normal and neutropenic humans

Using data on the fraction of post-mitotic neutrophil precursors (CD15+ cells) displaying positive markers for apoptosis in 12 normal humans, and a simple mathematical model, we have estimated the apoptotic rate to be about 0.28/day in this compartment. This implies that the influx of myelocytes into the post-mitotic compartment exceeds twice the granulocyte turnover rate (GTR), and that about 55% of the cells entering this compartment die before being released into the blood. The normal half life of apoptotic post-mitotic neutrophil precursors is calculated to be 10.4 h. Comparable calculations for patients indicate apoptosis rates in the post-mitotic compartment of about 17 times normal for one myelokathexis patient and rates of about 13 times normal for the one cyclical neutropenic patient and two severe congenital neutropenic patients. The estimated half life for apoptotic post-mitotic neutrophil precursors in the myelokathexis patient was about 0.4 h, 1.4 h in the cyclical neutropenia patient, and about 0.6 h in the severe congenital neutropenic patients.

Resonance in periodic chemotherapy: a case study of acute myelogenous leukemia

The effects of periodic chemotherapy administration are evaluated within the context of a G(0)model of the cell cycle. Parameters are estimated for normal bone marrow cells and malignant cells in acute myelogenous leukemia (AML). This model explicitly includes the resting G(0)phase and the feedback mechanism that recruits the cells back into the cell cycle. Periodic chemotherapy administration can induce resonance within our model under high cell kill rate where the average cell cycle times may change during the course of treatment, and therapeutic benefits from these resonances cannot be solely based on cell cycle times in untreated tissue. The depletion rate under chemotherapy and the regrowth rate may differ between the cell populations, and our analysis suggests that this favors the tumour cells. We were able to distinguish between the effects of cycle-non-specific, S -phase-specific and M -phase-specific drugs, and found that these can show differences in sharpness and location of the resonance phenomenon. We conclude that resonance chemotherapy (chronotherapy) is unlikely to be efficacious in the treatment of AML.

Dynamic regulation of the tryptophan operon: a modeling study and comparison with experimental data

A mathematical model for regulation of the tryptophan operon is presented. This model takes into account repression, feedback enzyme inhibition, and transcriptional attenuation. Special attention is given to model parameter estimation based on experimental data. The model's system of delay differential equations is numerically solved, and the results are compared with experimental data on the temporal evolution of enzyme activity in cultures of Escherichia coli after a nutritional shift (minimal + tryptophan medium to minimal medium). Good agreement is obtained between the numeric simulations and the experimental results for wild-type E. coli, as well as for two different mutant strains.

Regulation of platelet production: the normal response to perturbation and cyclical platelet disease

An age-structured model for the regulation of platelet production is developed, and compared with both normal and pathological platelet production. We consider the role of thrombopoietin (TPO) in this process, how TPO affects the transition between megakaryocytes of various ploidy classes, and their individual contributions to platelet production. After the estimation of the relevant parameters of the model from both in vivo and in vitro data, we use the model to numerically reproduce the normal human response to a bolus injection of TPO. We further show that our model reproduces the dynamic characteristics of autoimmune cyclical thromobocytopenia if the rate of platelet destruction in the circulation is elevated to more than twice the normal value.

An explanatory model of preterm labor

The purpose of this article is to describe women's explanatory model of their preterm labor (PTL) experiences. Fourteen young adult (20 to 23 years of age) women living in the southeast, who were hospitalized for the treatment of PTL, participated in this naturalistic study. Stress was the dominant theme that all participants used to explain what had precipitated PTL. All women described multiple stressors and chaos in their lives, which preceded their admission to the hospital for PTL. Meanings of PTL were intertwined with dysfunctional families and problematic relationships. All 9 women who delivered at term were able to find a friend or family member to provide support that allowed the women to relax and reduce the stress in their lives. In contrast, women who delivered preterm had no one in their lives that could provide help and support. Women's conceptualizations of PTL suggest that culturally appropriate interventions to reduce stress and mobilize support may help improve birth outcomes after an episode of PTL.

Neural ensemble coding and statistical periodicity: speculations on the operation of the mind's eye

Statistical periodicity is a statistical property of densities which arises in the description of retarded dynamical systems. This property is particularly attractive as a possible mechanism for the ensemble coding of information in the nervous system because it operates rapidly and has high storage capacity. For a population of neurons which exhibits statistical periodicity, information would not be encoded by the periodicity, but rather by the spatio-temporal distributions of neural activity. Statistical periodicity is discussed in relation to the temporal binding hypothesis and to the occurrence of multistability in neural systems.

Modeling complex neutrophil dynamics in the grey collie

We have developed a mathematical model for the peripheral regulation of neutrophil production mediated by granulocyte colony-stimulating factor. We have used that model to show that the pattern of neutrophil oscillations in nine grey collies is consistent with the hypothesis that cyclical neutropenia is due to an oscillatory stem cell input to the neutrophil regulatory system, and not due to autonomous oscillations in the peripheral neutrophil regulatory system. In the process of interfacing our model with the laboratory data, we have estimated parameters for the peripheral neutrophil control system consistent with higher than normal apoptotic cell loss within the recognizable neutrophil precursors. This is in agreement with other experimental data. Our estimated model parameters also predict that the peripheral neutrophil production system is globally stable in the grey collies we studied. This further supports our hypothesis that the origin of the oscillatory behavior in cyclical neutropenia is in the stem cell population, consistent with other clinical and experimental evidence.

Alienation from self and others: the psychosocial problem of rural alcoholic women

The purpose of this study was to describe women's perspectives in becoming and being alcohol dependent. Using grounded theory techniques, 14 adult Black and White women receiving treatment for alcohol addiction at rural substance abuse centers participated in an intensive interview. Data analysis focused on the identification of the basic psychosocial problem and the process of becoming alcohol dependent. The results are presented in 2 parts. Part 1, "Alienation From Self and Others," focuses on the basic psychosocial problem faced by women in becoming alcohol dependent. Part 2, "Running Away to Nowhere," on page 142 of this issue of Archives, describes the process used by women to resolve this problem.

Running away to nowhere: rural women's experiences of becoming alcohol dependent

The purpose of this study was to describe women's perspectives in becoming and being alcohol dependent. Part 1, "Alienation From Self and Others," on page 134 in this issue of Archives, describes the study methods, the sample, and the basic psychosocial problem faced by rural, alcoholic women. Part 2, "Running Away to Nowhere," focuses on the basic psychosocial process that women used to resolve the pain caused by their "Alienation From Self and Others." The article concludes with suggestions for nursing intervention.

Cost effectiveness of a high-risk pregnancy program

This article presents an evaluation of an innovative community-based, case-management program for high-risk pregnant women and their infants. A 7-year analysis of the Medicaid claims from 182,196 pregnant women and those for 140,088 infants was conducted. The findings showed improved birth outcomes and a steady decrease in the cost of care for both pregnant women and their infants. Recommendations are made concerning implementation of this program in other settings with other clients.

Hematopoietic dynamics in grey collies

Using Lomb periodogram analysis we have quantified variations in the peripheral neutrophil and platelet counts of the cyclical neutropenia animal model-the grey collie. We found that the amplitudes of the oscillations in these two cell lineages vary concomitantly. Further, the power spectrum and the shape of the oscillations in the absolute neutrophil counts vary together with the amplitude of the oscillations. As the amplitude of the oscillations increases, the height of the second subharmonic increases, giving rise to a distorted oscillation with two peaks per cycle. The particular dynamics of the absolute neutrophil counts can be reproduced by a combination of a delayed peripheral feedback, representing the peripheral control of granulopoiesis through granulocyte colony stimulating factor, together with a sinusoidal input representing an oscillatory input from the pluripotential stem cells to the granulocytic lineage. The same pluripotential stem cell input is probably responsible for the sinusoidal oscillations observed in the other cell lineages.

Occurrence of periodic oscillations in the differential blood counts of congenital, idiopathic, and cyclical neutropenic patients before and during treatment with G-CSF

Using techniques developed in astrophysics to deal with unequally sampled data sets, we have analyzed serial differential cell counts from 45 congenital, idiopathic, and cyclic neutropenic patients before and during treatment with recombinant human G-CSF (rhG-CSF). Our results show that the occurrence of significant cycling in the absolute neutrophil count (ANC) of neutropenics not classified as cyclical is much more prevalent than had been previously thought, and that not all the patients classified as cyclic show significant ANC periodicity. In these patients, cycling in more than one cell line may be involved. The range of periods encountered in these patients is much broader (between 11 and 52 days) than is usually associated with classical cyclical neutropenia, and there is no obvious connection between the range of periods and the patient's diagnostic category. Administration of rhG-CSF is able to induce significant cycling in neutropenic patients that were not cycling prior to treatment. In patients who had significant cycling before treatment, rhG-CSF may either decrease the period to between 11 and 14 days, or may obliterate any statistical evidence of cycling.

Periodic chronic myelogenous leukaemia: spectral analysis of blood cell counts and aetiological implications

Of 24 published clinical reports of periodic chronic myelogenous leukaemia (PCML), 21 had sufficient data to analyse for periodicity, and 12 showed significant periodicity (p < or = 0.05) using the Lomb periodogram. Leucocyte oscillations had periods T ranging from 37 to 83d. When data were also reported for platelets and reticulocytes there was no significant difference between their periods and those of the leucocytes. These data and their analysis provide strong circumstantial evidence for a haemopoietic stem cell origin of PCML. Namely, the known chromosomal changes in CML patients may, on occasion, also be accompanied by a destabilization resulting in an oscillatory efflux into the leucocyte, platelet and erythrocytic pathways.

Women's evaluation of the labor and delivery experience

The purpose of this study was to identify how women described and evaluated their labor and delivery experience and what factors were related to their responses. Sixty Lamaze-prepared, married multigravidae, aged 21 to 37 years, participated in this qualitative field study. Detailed, open-ended tape-recorded interviews were conducted on the postpartum unit of a community hospital or in the women's homes early during the postpartum period. Women evaluated their labor and delivery experience according to how well they perceived they had managed their own childbirth performance. Women who managed well viewed childbirth as positive, whereas women who had difficulty or managed poorly viewed it as both positive and negative. Women who managed well thought their own performance and the nature of labor and delivery (physical aspects) went well; women who had difficulty thought labor and delivery and the performance of others went well, but women who managed poorly had problems identifying anything that went well. There was overall agreement that the baby was the best part of the experience and that pain and pushing were the worst parts. Since women's evaluation of their labor and delivery experience may be related to the quality of their subsequent mothering, it is important to enhance their perceptions of their own performance, and thus their evaluation of the childbirth experience.

Pica: sorting it out

Pica, a culture-bound illness, has occurred for centuries. The ingestion of nonfood substances such as starch, cornstarch, clay, dirt, and other material is fairly common, although the distribution of the condition varies by cultural and socioeconomic factors. The underlying cause of pica is not known, although the condition often is associated with pregnancy. There is conflicting evidence about the association of nutrient deficiencies and pica. This article presents a clinical example of pica in a pregnant 33-year-old African American woman. Implications for culturally appropriate care are discussed.

Women's experiences of preterm labor: a feminist critique

Using a feminist perspective, women's experiences of preterm labor (PTL) were critiqued and compared with the medical establishment's perspective on PTL as described in the medical literature. Interview data from 29 women who participated in a larger study on the PTL experience were revisited and examined based on principles of feminist theory. The persistent "medicalization" of women's bodies was discussed and used as a framework to explore several issues: (a) the diagnosis of PTL and what it means to be at risk for this phenomenon; and (b) the treatment of PTL including the role of medications, activity, and home monitoring for uterine contractions. Based on the differences that emerged when PTL--was examined from two divergent standpoints--the women's perspective and the physician's perspective--some alternative approaches to PTL management that place women's lives at the center of the treatment process were suggested.

The preterm labor experience: a balancing act

The purpose of the study was to identify how women described, interpreted, and managed their preterm labor experience. Ten married, middle-class women participated in an in-depth, tape-recorded interview in the hospital after preterm labor was stabilized; periodically over the telephone after discharge from the hospital; and in the hospital, home, or via telephone after birth, for a total of 31 interviews. Using qualitative data analysis techniques, the findings were conceptualized as five recursive stages: becoming aware that something was wrong and feeling unbalanced, making sense of the experience as they sought to understand why preterm labor occurred, trying different strategies to re-create a balance in their lives, addressing other life stressors that threatened restoring balance, and emerging from the preterm labor experience with added growth. An increased understanding of the preterm labor experience from the women's perspective can be helpful to health care professionals and others who support women during pregnancy.

Cyclical neutropenia and other periodic hematological disorders: a review of mechanisms and mathematical models

Although all blood cells are derived from hematopoietic stem cells, the regulation of this production system is only partially understood. Negative feedback control mediated by erythropoietin and thrombopoietin regulates erythrocyte and platelet production, respectively, but the regulation of leukocyte levels is less well understood. The local regulatory mechanisms within the hematopoietic stem cells are also not well characterized at this point. Because of their dynamic character, cyclical neutropenia and other periodic hematological disorders offer a rare opportunity to more fully understand the nature of these regulatory processes. We review the salient clinical and laboratory features of cyclical neutropenia (and the less common disorders periodic chronic myelogenous leukemia, periodic auto-immune hemolytic anemia, polycythemia vera, aplastic anemia, and cyclical thrombocytopenia) and the insight into these diseases afforded by mathematical modeling. We argue that the available evidence indicates that the locus of the defect in most of these dynamic diseases is at the stem cell level (auto-immune hemolytic anemia and cyclical thrombocytopenia seem to be the exceptions). Abnormal responses to growth factors or accelerated cell loss through apoptosis may play an important role in the genesis of these disorders.

Adolescents' description and management of pregnancy and preterm labor

OBJECTIVE

To describe adolescents' experiences with pregnancy and preterm labor.

DESIGN

Naturalistic inquiry, a qualitative study using intensive, open-ended, tape-recorded interviews and constant comparative data analysis.

SETTING

Antepartum units of two hospitals in the southeastern section of the United States.

PARTICIPANTS

Eight African American and five white adolescents, ages 14-19 years, hospitalized for preterm labor.

RESULTS

The findings are broadly conceptualized as (a) describing pregnancy and preterm labor and (b) managing pregnancy and preterm labor. "Responding to Pregnancy" consisted of descriptions of the adolescents' reactions to pregnancy (initial concern and dislike) and pathophysiologic responses that put the adolescents at risk for preterm labor. "Responding to Preterm Labor" included the various ways that adolescents became aware of preterm labor and their various understandings of the causes and consequences of preterm labor. Vignettes illustrate how adolescents managed pregnancy and preterm labor with ease or with difficulty. Adolescents who received support from others, especially their mothers, tended to deliver near or at full-term.

CONCLUSIONS

Nurses can use the findings from this study as a guide for assessing and monitoring adolescents throughout pregnancy. Advanced practice nurses may have the educational background and philosophy of care to provide the most appropriate prenatal care to pregnant adolescents. Research is needed to further explore stressful experiences and support in adolescents' lives and how these are related to preterm labor and birth.

Cyclical neutropenia and the peripheral control of white blood cell production

Cyclical neutropenia (CN) is an interesting dynamic hematological disease in which the neutrophils spontaneously oscillate from approximately normal levels to near zero with a period between 19 and 21 days. In the only known animal model for this disorder, the grey collie, the disease's single apparent difference from human CN is the smaller period of 11-15 days. CN can be treated using the cytokine G-CSF which decreases the period (to about 14 days in humans), increases the mean value, and elevates the amplitude of the oscillations. After reviewing the clinical and laboratory data on this disease, we examine the proposition that CN is due to a loss of stability in the peripheral negative feedback control of neutrophil production. This is accomplished by the development of a physiologically realist mathematical model for the system. We conclude that there is no consistent way in which such a destabilization can give rise to either the clinical or laboratory characteristics of CN. Rather it seems more likely that the oscillations of CN are generated within the pluripotential stem cell population.

Hematopoietic model with moving boundary condition and state dependent delay: applications in erythropoiesis

An age-structured model for erythropoiesis is extended to include the active destruction of the oldest mature cells and possible control by apoptosis. The former condition, which is applicable to other population models where the predator satiates, becomes a constant flux boundary condition and results in a moving boundary condition. The method of characteristics reduces the age-structured model to a system of threshold type differential delay equations. Under certain assumptions, this model can be reduced to a system of delay differential equations with a state dependent delay in an uncoupled differential equation for the moving boundary condition. Analysis of the characteristic equation for the linearized model demonstrates the existence of a Hopf bifurcation when the destruction rate of erythrocytes is modified. The parameters in the system are estimated from experimental data, and the model is simulated for a normal human subject following a loss of blood typical of a blood donation. Numerical studies for a rabbit with an induced auto-immune hemolytic anemia are performed and compared with experimental data.

Staff evaluation of a high-risk pregnancy program

A southeastern state implemented a multidisciplinary health care program for Medicaid eligible, medically high-risk pregnant women and their infants as part of a statewide effort to reduce perinatal morbidity and mortality. The purpose of this study was to obtain the staff's evaluation of this high-risk-pregnancy program. Clinical, supervisory, and clerical staff (N = 182) completed a questionnaire about the operation of the program and its perceived benefits. Staff identified program strengths: nurse case management, interdisciplinary structure, quality care, and positive health outcomes. Staff also identified program limitations including limited staff and time, inflexible protocols, administrative tasks, and narrow enrollment criteria. The majority of staff reported that the following barriers interfered with the effective operation of the program: paperwork, limited support, time, difficulty locating patients, and mandated time frames for patient contact. The majority of staff also reported that transportation most interfered with patient access to the program. The findings of this study support the need for ongoing staff evaluation of all perinatal health care programs.

Age-structured and two-delay models for erythropoiesis

An age-structured model is developed for erythropoiesis and is reduced to a system of threshold-type differential delay equations using the method of characteristics. Under certain assumptions, this model can be reduced to a system of delay differential equations with two delays. The parameters in the system are estimated from experimental data, and the model is simulated for a normal human subject following a loss of blood. The characteristic equation of the two-delay equation is analyzed and shown to exhibit Hopf bifurcations when the destruction rate of erythrocytes is increased. A numerical study for a rabbit with autoimmune hemolytic anemia is performed and compared with experimental data.

Women's evaluation of their childbirth performance

OBJECTIVE

To describe women's evaluation of their own performance during labor and delivery.

METHODS

Participants (N = 60) were Lamaze-prepared, married multigravidae, aged 21-37 years who responded to open-ended questions in tape-recorded interviews during their postpartum hospital stay. Qualitative data analysis was used to identify themes.

FINDINGS

Women evaluated their childbirth performance as managing well (45%), having difficulty (35%), and managing poorly (20%). The following helped them to manage well: short, fast labors; minimal pain; Lamaze; husband's encouragement; being informed; feeling strong; medication; and nurses' and physicians' encouragement, help with Lamaze, and information. Women who had managed well before and who were confident about managing well again tended to evaluate their childbirth performance positively. A significant difference was seen in mean labor length: Women who managed well had the shortest labors and women who managed poorly had the longest.

CONCLUSIONS & IMPLICATIONS FOR NURSING

The women confirmed the notion that they had important work to do; they identified their own performance as one of the most important or the most important component of the childbirth experience.

Global stability in a delayed partial differential equation describing cellular replication

Here we consider the dynamics of a population of cells that are capable of simultaneous proliferation and maturation. The equations describing the cellular population numbers are first order partial differential equations (transport equations) in which there is an explicit temporal retardation as well as a nonlocal dependence in the maturation variable due to cell replication. The behavior of this system may be considered along the characteristics, and a global stability condition is proved.

Fluctuations in circulating cell numbers following chemotherapy or bone marrow transplant

We study the effect of noise on the behaviour of a dynamic cell population model in which cell replication and maturation take place simultaneously. We assume that the maximum proliferative potential v fluctuates uniformly about a mean value of v, and show that a decrease in v and/or the input flux uin into the population can lead to an increase in the variance in the cellular efflux uf. We draw a qualitative correspondence between this behaviour and the commonly observed increase in the variance of circulating blood cell numbers following chemotherapy and radiotherapy, both of which lead to a decrease in v and uin, and bone marrow transplant which probably corresponds to a decrease in uin.

Women's evaluations of their labor and delivery nurses

OBJECTIVE

To document women's evaluations of their labor and delivery nurses.

DESIGN

An exploratory, qualitative study using open-ended, intensive, tape-recorded interviews.

SETTING

Postpartum unit of a 400-bed midwestern hospital, except for two interviews in the women's homes.

PARTICIPANTS

Sixty-one Lamaze-prepared, married, multigravidae, aged 21-37 years.

RESULTS

Ninety percent of the women evaluated their nurses favorably, 10% unfavorably. Nurses were evaluated favorably because of their positive participation (80%), acceptance (78%), information giving (75%), encouragement (65%), presence (53%), and competence (7%).

CONCLUSIONS

Although technical competence is important, manner, provision of supportive care, and acceptance of each woman as a unique human being may be a nurse's most important characteristics.

Women's views of the preterm labor experience

This study used a naturalistic approach to describe the childbearing woman's views of her preterm labor and delivery experience. Specifically, the aim was to identify how women describe, interpret, and manage preterm labor and subsequent preterm or term delivery. The views of 20 women who were hospitalized for preterm labor (before 37 weeks) were documented with semistructured, tape-recorded, in-depth interviews during their hospitalization for preterm labor and after delivery. Qualitative data analysis focused on the process of becoming a preterm labor patient and on living with a diagnosis of preterm labor. Women either waited for a period of time before seeking care or sought care immediately for the symptoms they were experiencing. Women interpreted the experience by identifying causes of preterm labor and by worrying about the outcome for the baby. Managing preterm labor required extensive, moderate, or limited changes in their lives. Women who delivered at term appeared to have more tangible help than those who delivered preterm. A better understanding of women's preterm labor experiences will provide clues to nurses on how to improve the care they provide.

Strategies for change: nursing implementation of the birthing room

Nurses were primary participants in introducing the birthing room for maternity care in their respective institutions. Based on tape-recorded interviews, this paper is a report on how the idea of a birthing room was initiated, the resistance it encountered, the eight strategies used to implement the idea, and appropriation of the idea by physicians. Although the examples are specific to the development of a birthing room, the strategies can be used by nurses to initiate other changes in perinatal health care delivery. In addition, increased collaboration between nurses and physicians may make some strategies obsolete.

Stability properties of proliferatively coupled cell replication models

To address the possibility that proliferative disorders may originate from interactions between multiple populations of proliferating and maturing cells, we formulate a model for this process as a set of coupled nonlinear first order partial differential equations. Using recent results for the asymptotic behaviour of the solutions to this model, we demonstrate that there exists a region of coupling coefficients, maturation rates, and proliferation rates that will guarantee the stable coexistence of coupled cellular populations. The analysis shows that increases in the coupling between populations may ultimately lead to a loss of stability. Furthermore, the analysis indicates that increases (decreases) in the maturation and/or proliferation rates above (below) critical levels will lead either to instability in the populations or the destruction of one population and the persistence of the other.

A deterministic approach to survival statistics

Survival functions of the form p(t) = exp[-(lambda t) gamma], gamma greater than 0 can be generated by deterministic nonlinear, asymptotically stable (chaotic) dynamical systems. These systems thus provide an alternative to stochastic interpretations of failure time data. We use this approach to analyze cancer patient survival statistics. In this manner we are able to obtain fresh insights into the implications of negative and positive clinical trials.

Women's choice of childbirth setting

As part of a larger study on women's views of the childbirth experience, this study was focused on women's choice of childbirth setting. Sixty-one Lamaze-prepared, married multigravidae between the ages of 21 and 37 and experiencing a normal pregnancy were interviewed twice: at 36-38 weeks gestation in their homes and during their postpartum stay in the hospital. Data were collected using (a) two semistructured interview guides consisting of open-ended questions about choosing a caregiver and the place of birth and about describing the actual childbirth experience, (b) a self-administered sociodemographic questionnaire, and (c) an obstetrical and infant data form. The tape-recorded interviews were transcribed verbatim. Qualitative data analysis was focused on reasons for choosing a hospital and a physician, reasons for choosing or not choosing a birthing room, and the outcomes of the decisions. An understanding of women's childbirth needs as reflected in their choices can suggest areas where flexibility might be built into maternity care programs.

Women's expectations of the labor and delivery nurse

Sixty-one, Lamaze-prepared, married multigravidae identified their expectations of the labor and delivery nurse in semistructured interviews conducted at 36 to 38 weeks' gestation. Findings indicate variations in the amount of involvement women expected from the nurses during labor and delivery: limited (n = 17), moderate (n = 22), or extensive (n = 22). Women varied in the amount of time they wanted nurses present, who they expected to make caregiving decisions, and whether or not they wanted nurses to assist them in managing labor and delivery.