Electrowetting dynamics of microfluidic actuation.

When voltage is suddenly applied to vertical, parallel dielectric-coated electrodes dipped into a liquid with finite conductivity, the liquid responds by rising up to reach a new hydrostatic equilibrium height. On the microfluidic scale, the dominating mechanism impeding this electromechanically induced actuation appears to be a dynamic friction force that is directly proportional to the velocity of the contact line moving along the solid surface. This mechanism has its origin in the molecular dynamics of the liquid coming into contact with the solid surface. A simple reduced-order model for the rising column of liquid is used to quantify the magnitude of this frictional effect by providing estimates for the contact line friction coefficient. Above some critical threshold of voltage, the electromechanical force is clamped, presumably by the same mechanism responsible for contact angle saturation and previously reported static height-of-rise limits. The important distinction for the dynamic case is that the onset of the saturation effect is delayed in time until the column has risen more than about halfway to its static equilibrium height.

Inflammatory-mediated injury and repair in the traumatically injured spinal cord.

Spinal cord trauma activates the immune system and elicits leukocyte recruitment to the site of injury. This increase in immunological activity contributes to acute lesion expansion over a period of days to weeks following the initial trauma. At the same time, inflammatory cells and mediators facilitate endogenous repair processes such as axonal sprouting and remyelination. Thus, to be effective, therapies that target the immune system must limit the destructive effects of neutrophil, macrophage and lymphocyte activation, while simultaneously preserving their reparative functions.

Frequency-dependent electromechanics of aqueous liquids: electrowetting and dielectrophoresis.

Electrowetting on dielectric and dielectrophoretic electromechanical mechanisms dominate microfluidic actuation in the low- and high-frequency limits, respectively. The frequency-dependent relationship between these two mechanisms has been clarified by the Maxwell stress tensor and a simple RC circuit model. In this paper, we report extensive height-of-rise measurements obtained with vertical, parallel, dielectrically coated electrodes to test this relationship using deionized water and solutions containing sugar and salt. For DC and AC (20 Hz to 20 kHz) voltage magnitudes up to approximately 150 V-rms, the data are highly reproducible and, within experimental error, consistent with the square-law predictions of the model. Eventually as voltage is increased, a saturation phenomenon is observed which exhibits a weak dependence on frequency and is probably correlated to contact angle saturation.

Influence of scale on electrostatic forces and torques in AC particulate electrokinetics.

Dielectrophoretic forces and torques move and manipulate biological cells, typically of the order of 10 mum ( approximately 10(-5) m) in diameter and ordinarily suspended in aqueous liquids, using electrodes with dimensions around 100 mum ( approximately 10(-4) m). The ability to exploit these same electromechanical effects for particles below 1 mum, that is, <10(-6) m, creates opportunities for remote manipulation and handling of subcellular components, biological macromolecules, and DNA. In this paper, Trimmer's bracket notation is adapted for systematic examination of the scaling laws governing electrokinetic behaviour. The purpose is to shed light on how critical performance measures relevant to the laboratory on a chip are affected by reducing particle sizes and electrode dimensions into the nanometre range. The scaling methodology facilitates consideration of the effect of electrode structure and particle size reduction on voltage, electric field, heating, and response time. Particles with induced moments, dipolar and quadrupolar, as well as permanent dipoles are examined. Separate consideration is given to electrical torque and its application in electrorotation and particle alignment. An eventual goal of these scaling studies is to identify the lower limit on the size of particles that can be manipulated effectively using electrokinetic phenomena.

Effects of intrapartum zidovudine therapy on fetal heart rate parameters in women with human immunodeficiency virus infection.

OBJECTIVE: To determine the effects of intrapartum maternal administration of zidovudine on fetal heart rate (FHR) parameters in women infected with the human immunodeficiency virus (HIV). METHODS: Term HIV-infected women who delivered at our institution (1995-1998) were identified by medical records coding. Sixty minutes of FHR tracing prior to zidovudine administration and 60 min of FHR tracing 2 h after initiation of therapy were reviewed by 3 perinatologists blinded to patient status. Data were compared with paired t tests; p < 0.05 was considered significant. Inter- and intra-observer FHR interpretation variation were calculated. RESULTS: Ten patients met study criteria. Their demographic data included: Maternal age 26.5 +/- 6.5 years, gestational age 38.9 +/- 1.3 weeks, median parity 2 (range 0-3). Eighty percent were African American. There were no significant differences in FHR parameters after intravenous zidovudine therapy (pretreatment versus 2 h after treatment) with respect to FHR baseline (p = 0.2), FHR variability (p = 0.3), or the number of accelerations (p = 0.1). There was also no difference in the number of variable (moderate or severe), early, or prolonged decelerations following zidovudine infusion. CONCLUSION: Two hours of continuous intrapartum intravenous infusion of zidovudine does not alter any parameter of the FHR in the laboring HIV-infected gravida.

Multicenter review of protease inhibitors in 89 pregnancies.

CONTEXT: Despite the success of highly active antiretroviral therapy, the optimal approach for preventing perinatal HIV-1 transmission is not known. OBJECTIVE: A retrospective survey was conducted at six centers in the United States and Puerto Rico from January 1997 to October 1998 to evaluate the effects of protease inhibitor use during pregnancy on maternal and infant safety, prematurity rate, and frequency of perinatal HIV-1 transmission. RESULTS: In the study, 91 live infants, including 3 sets of twins, and 1 neonate who died shortly after birth were born to 89 women. HIV perinatal transmission rate in this series was 0 (95% confidence interval [CI], 0%-3%). Prematurity rate was 19.1%, comparable to rates in earlier reports of HIV-1-infected women. In multiple regression analysis, only cocaine use and premature rupture of membranes were associated with prematurity (p =.03 and.008, respectively). The gestational week during which the protease inhibitors were initiated was not found to be significantly associated with prematurity. Adverse maternal, obstetric, and infant events possibly related to protease inhibitors were uncommon. CONCLUSIONS: Protease inhibitors appeared generally safe in mothers and infants in this series. No perinatal HIV-1 transmission occurred. Further prospective, controlled studies are needed to define the optimal management of HIV-1 in pregnancy.

Genetic analysis reveals ongoing HIV type 1 evolution in infected human placental trophoblast.

To provide a better understanding of the role of placenta in vertical human immunodeficiency virus (HIV) transmission, we have studied the infection of placental trophoblast in a group of 15 mother-neonate pairs. By nested PCR amplification of the C2V3 env gene region, HIV-1 has been found to infect the placenta in five cases (33%). Phylogenetic analysis of the cloned sequences showed that all recovered maternal variants were of the B subtype. Further investigation into the ancestral relationships at the nucleotide level revealed that the trophoblast sequences evolved into a quasispecies population clearly distant from that observed in the mother. As expected, the populations transmitted to the trophoblast were also found to be more homogeneous than those in the mothers when characterized on the basis of pairwise nucleotide sequence distances. With regard to the predicted biological properties, the primary amino acid structure of the V3 loop domain was consistent, with a macrophage-tropic, non-syncytium-inducing phenotype in all patients. We also attempted to determine if any of a number of selected maternal or viral factors was associated with trophoblast infection. However, none of the followed parameters, including maternal age, disease stage, antiretroviral therapy, CCR5delta32 deletion status of the infant, and viral genotype, could be associated with viral transmission. Moreover, in one pair with proven trophoblast infection, HIV was also detected in the cord blood. Taken together, our data suggest that the productive trophoblast infection by HIV-1 in vivo is a relatively frequent event that may bear direct implications for a further transplacental propagation of the virus.

Modulation of NK cell cytolytic activity by macrophages in chronically exercise-stressed mice.

This study was designed to investigate the effects of moderate-intensity endurance training on basal natural killer (NK) cell cytolytic activity in murine splenocytes that were enriched for 1) NK1.1+ cells or 2) macrophages and NK1.1+ cells. Mice were assigned to sedentary (Sed), treadmill control (TM), or treadmill-trained (Trn) groups. Splenocyte number, the percentages of NK1.1+, large granular lymphocytes (NK1.1+, LGL-1+), and other subpopulations did not change in Trn mice. Approximately 70% of cells enriched for NK1.1+ expressed this surface antigen. Lytic units (LU) expressed per LGL-1+ cell were significantly lower in Trn [83.9 +/- 3.2 (SE)] compared with Sed (109.5 +/- 7.5) and TM (101.3 +/- 6.4) groups. When macrophages remained in the in vitro assay, LU per LGL-1(+) cell did not differ across groups. The results indicate that highly enriched NK1.1+ cells from Trn mice had lower NK cell activity compared with Sed mice. No differences in NK cell activity were observed when cells were enriched for NK1.1+ cells and macrophages. These findings support the hypothesis that macrophage modulation of NK cells may be one mechanism contributing to augmented basal NK cell activity in endurance-trained individuals.

A thrombogenic uterine pack for postpartum hemorrhage.

BACKGROUND: A low-lying placenta or placenta previa is frequently associated with postpartum hemorrhage from a low implantation site. We describe the successful use of a thrombin-soaked uterine pack for this condition. CASE: A 30-year-old woman, gravida 3, para 0-0-2-0, had placenta previa diagnosed by ultrasound at 26 weeks' gestation. A repeat examination at 35 weeks demonstrated a low-lying placenta. The patient had an uncomplicated intrapartum course and was delivered by vacuum extraction, but excessive vaginal bleeding was noted 3 hours after spontaneous delivery of the placenta. Oxytocin, prostaglandin, and uterine curettage failed to control the hemorrhage. In an attempt to avoid laparotomy, we placed a thrombin-soaked uterine pack over the bleeding site. There was minimal vaginal bleeding during the following 8 hours, so the pack was removed. The patient had no further complications and was released 3 days after delivery. CONCLUSION: A thrombin-soaked uterine pack may successfully control lower uterine segment bleeding following delivery of a patient with a low-lying placenta. This technique offers the obstetrician another treatment option in selected cases of postpartum hemorrhage.

Single umbilical artery: accurate diagnosis?

OBJECTIVE: We sought to evaluate the accuracy of ultrasonographic, obstetric, and neonatal diagnosis of a single umbilical artery. STUDY DESIGN: We studied 17,777 consecutive singleton births from women who had undergone ultrasonographic examination at our hospital. A single umbilical artery was confirmed in 37 cases (0.2%) by two clinical methods or by pathologic assessment. Outcome of neonates with a single umbilical artery was compared with the outcome of neonates with either two or three vessel cords. RESULTS: Ultrasonographic diagnosis had a 65% sensitivity and positive predictive value. Obstetricians and pediatricians failed to diagnose 24% and 16% of the cases, respectively. On average, neonates with a single umbilical artery weighed 320 gm less, were delivered 1 week earlier, and had lower Apgar scores than neonates with three vessel cords (p < 0.01 in each case.) CONCLUSION: Although early gestational age may account for some cases not diagnosed by ultrasonography, there is a little justification for missing the diagnosis after delivery. Greater emphasis on clinical examination of the umbilical cord is needed to identify neonates at risk of associated malformations.

Higher-order dielectrophoretic effects: levitation at a field null.

Experiments with certain new micro-electrode structures used to achieve passive dielectrophoretic levitation of small particles and biological cells reveal a pronounced size-dependent effect not anticipated by the conventional dipole-based model. The conventional theory fails to predict this size effect because it neglects higher-order moments such as the quadrupole, hexapole, and octupole. These higher-order moments are in fact responsible for the levitation force achieved by azimuthally periodic electrode structures because, in such geometries, the electric field is zero along the axis so that the induced dipole moment must be zero. For example, the planar quadrupole levitates particles passively along the central axis through the interaction of its field with the induced quadrupolar moment of the particle. The size effect reported with this structure is readily explained in terms of this quadrupolar component of the ponderomotive force exerted on the particle.

Electro-orientation of ellipsoidal erythrocytes. Theory and experiment.

The frequency-dependent orientation of human and llama erythrocytes suspended in isotonic solutions and subjected to linearly polarized electric fields is examined. Human erythrocytes may be represented as oblate spheroids (3.9:3.9:1.1 microns) with two distinguishable orientations, while the llama cells are approximated as ellipsoids with three distinct axes (4.0:2.0:1.1 microns). Under appropriate experimental conditions, both orientations of the human cells and all three orientations of the llama cells are observed. A theoretical cell model which accounts for the membrane as a thin confocal layer of ideal capacitance is used to predict the orientational spectra. The predicted spectra compare favorably in frequency range and orientational sequence with experimental data. Estimates for cell internal conductivity and permittivity are obtained by adjusting the values of these important parameters to achieve the closet fit of the theoretical curves to the data. By the use of this method, the internal conductivity of llama erythrocytes is estimated to be 0.26 S/m (+/- 20%), while the effective internal dielectric constant and conductivity of Euglena gracilis are estimated to be 120 (+/- 10%) and 0.43 S/m (+/- 20%), respectively.

Fetal hemoglobin quantitations using the Hemocue system are rapid and accurate.

OBJECTIVES: To determine whether hemoglobin quantitations using the Hemocue system, a rapid and portable hemoglobin photometer, on fetal blood obtained via funipuncture were accurate compared to the Coulter S-Plus IV. We also examined whether gestational age or extremes in hemoglobin levels significantly affected the accuracy of the Hemocue system. METHODS: We performed fetal hemoglobin quantitations using both systems on 58 specimens obtained between 18-38 weeks' gestation. Correlation between values by both systems was determined by linear regression analysis. The effects of gestational age and hemoglobin extremes on the accuracy of the Hemocue system were evaluated by stepwise regression. RESULTS: The mean Hemocue value was 12.0 +/- 2.4 g/dL (range 3.3-16.4); the mean Coulter value was 11.7 +/- 2.3 g/dL (range 3.6-16.2). The regression equation for Hemocue (y) versus Coulter (x) values was y = 0.72 + 0.97x; r = 0.94 (P < .0001). Neither gestational age nor hemoglobin extremes significantly affected the accuracy of the Hemocue system. CONCLUSION: The Hemocue system is rapid and accurate for fetal hemoglobin quantitation between 18-38 weeks' gestation regardless of extremes in gestational age or hemoglobin levels.

Tension band arthrodesis of small joints in the hand.

Two-hundred three patients underwent 290 tension band arthrodeses of the metacarpophalangeal and proximal interphalangeal joints of the hand. Nine patients (3%) failed to achieve bony union, four had painless pseudarthroses, and one patient had a small finger amputation. Twenty-five fusions (9%) required hardware removal. There were 10 superficial infections (all responded to oral antibiotic therapy), and three fusions were malrotated. Tension band arthrodesis is our choice for fusion of the metacarpophalangeal and proximal interphalangeal joints. It is reliable and provides stable fixation, pins do not protrude, and external splinting is unnecessary in the cooperative patient.

Abnormal second-trimester ultrasounds: an indication for karyotype.

There are limited data on the risks of aneuploidy for normal-appearing fetuses with amniotic fluid volume (AFV) abnormalities. The purpose of this study was to determine the relative risks of aneuploidy associated with second-trimester abnormal AFVs and fetal structural anomalies in a cohort of 2,823 singleton, viable fetuses. Compared to gravidas younger than 35 with normal ultrasounds, normal fetuses had an increased incidence of aneuploidy with polyhydramnios, increased AFV, i.e. subjectively increased but normal by maximum vertical pocket (MVP) and/or amniotic fluid index (AFI), oligohydramnios, and decreased AFV, i.e. subjectively decreased but normal by MVP and/or AFI. These included: increased AFV [odds ratio = 12.9, 95% confidence interval (CI) = 4.1-39.4], polyhydramnios (odds ratio = 4.6, CI = 0.6-36.8), and decreased AFV (odds ratio = 3.8, CI = 1.1-13.1). There were no aneuploidies among the 28 normal fetuses with oligohydramnios. Anomalous fetuses had a markedly increased incidence of aneuploidy (odds ratio = 13.4, CI = 7.2-24.9). We conclude that fetal structural anomalies as well as isolated AFV abnormalities were associated with an increased risk for aneuploidy.

Dual-frequency dielectrophoretic levitation of Canola protoplasts.

A novel dual-frequency excitation technique is introduced which permits investigation of the low-frequency dispersion of Canola plant protoplasts using feedback-controlled dielectrophoretic levitation. The upper and intermediate frequency spectra obtained using the new technique are generally consistent with previous work. However, below some cross-over frequency f(OL), the protoplasts exhibit an apparent positive dielectrophoretic response that is not predicted by conventional theory. This cross-over frequency is linearly related to suspension conductivity, virtually independent of the suspension pH, and inversely proportional to the square of the cell radius. Examination of the complex Clausius-Mossotti polarization coefficient reveals that the observed positive dielectrophoretic response can not be accounted for in terms of Maxwell-Wagner polarization associated with a conventional layered model for the protoplast. The failure of straightforward enhancements to the protoplast model in explaining the low frequency behavior may indicate the presence of an electrophoretic contribution to the net observable force on the particle. To account for such fluid mechanical effects, it will be necessary to modify the existing dielectrophoretic force formulation.

Biparietal diameter and femur length discrepancies: are maternal characteristics important?

We examined whether gestational age, maternal race or height can be used to explain discrepancies between biparietal diameter- and femur length-derived gestational ages by analyzing ultrasound scans from 8041 consecutively scanned, singleton pregnancies, using multiple regression analysis. While a consistent association was noted between differences of more than 3 weeks and less than 3 weeks and advancing gestational age, neither maternal height nor race were significantly related. We conclude that, first, discrepancies between gestational age by biparietal diameter and femur length are rare (5%) and, second, the presence of discrepancies should not be dismissed on the basis of maternal stature or race and should alert the clinician to possible abnormal fetal growth or development.

Preconceptional planning.

Preconceptional counseling has become an important part of obstetrical care. The concept of preconceptional planning is discussed in detail, with an emphasis on particular high-risk groups. The role of genetics and fetal diagnosis is also examined.

Dielectrophoretic spectra of single cells determined by feedback-controlled levitation.

In this paper we have utilized the principle of dielectrophoresis (DEP) to develop an apparatus to stably levitate single biological cells using a digital feedback control scheme. Using this apparatus, the positive DEP spectra of both Canola plant protoplast and ligament fibroblast cells have been measured over a wide range of frequencies (1 kHz to 50 MHz) and suspending medium conductivities (11-800 muS/cm). The experimental data thus obtained have been interpreted in terms of a simple spherical cell model. Furthermore, utilizing such a model, we have shown that various cellular parameters of interest can be readily obtained from the measured DEP levitation spectrum. Specifically, the effective membrane capacitance of single cells has been determined. Values of 0.47 +/- 0.03 muF/cm2 for Canola protoplasts and 1.52 +/- 0.26 muF/cm2 for ligament fibroblasts thus obtained are consistent with those determined by other existing electrical methods.