Outcomes in a cohort of patients with Stage I twin-to-twin transfusion syndrome.

OBJECTIVE: To determine pregnancy outcomes of patients who present with Stage I twin-to-twin transfusion syndrome (TTTS). METHODS: This was a retrospective review of all patients with TTTS referred to our institution between January 2005 and December 2006. Quintero criteria were used for staging. Laser ablation was not offered to patients with Stage I disease. RESULTS: A total of 155 twin pregnancies were evaluated for TTTS during this period. Forty-two met the criteria for Stage I and were included in the analysis. The overall survival to discharge was 82%. The mean gestational age at the time of consultation was 20.9 +/- 0.4 weeks. A total of 23 cases (54.8%) underwent amnioreduction. Progression of TTTS requiring invasive therapy occurred in four cases. The mean gestational age at delivery was 32.5 +/- 0.62 weeks. When divided according to use of amnioreduction, there were no statistically significant differences between the groups for gestational age at delivery or for birth weight. Those Stage I cases with a CHOP cardiovascular score of 5 or higher delivered almost 3 weeks earlier than the remainder of the cohort. CONCLUSIONS: Progression of TTTS beyond Stage I occurred in only 9.5% of the cohort. Mean gestational age at delivery and survival to discharge did not differ between Stage I patients and those treated with placental laser ablation for more advanced stages of TTTS.

Ovine intramembranous pathway permeability: use of solute clearance to determine membrane porosity.

OBJECTIVE: The contribution of the fetal chorioamniotic membranes (i.e. the intramembranous pathway) to the regulation and maintenance of amniotic fluid (AF) volume and composition has yet to be completely understood. Knowledge of membrane permeability properties is vital to understanding how the intramembranous pathway contributes to the overall maintenance of AF homeostasis. Although there are significant data regarding the regulation of intramembranous water flow, there is little understanding of the regulation of intramembranous solute flow. In the present study, we sought to determine the effect of molecular weight or size of non-polar compounds on intramembranous solute movement in the ovine model. METHODS: Five singleton ovine fetuses (117 +/- 3 days) were chronically prepared with bladder, tracheal, amniotic cavity and femoral arterial and venous catheters and an esophageal occluder. The allantoic membranes were excised. After 5 days' recovery, AF volume was calculated by intraamniotic injection of 99Tc-labelled red blood cells (time -6 to 0 h). At time 0, AF exchange routes were limited to the intramembranous pathway by inflation of the esophageal occluder and external drainage of fetal urine and lung fluid. Following intra-amniotic injection of creatinine (Cr, 1 g, MW 11 000 Da, 4 A) and [125I]albumin (RISA, 250 microCi, MW 69 000 Da, 36 A), maternal and fetal plasma and AF samples were collected at timed intervals during the subsequent 5 h. AF solute clearance (Cl(x)) was determined by the changes in AF total solute content. RESULTS: Cr and RISA disappeared from the AF with a corresponding increase in fetal, though not maternal, plasma levels. The mean Cl(Cr) was significantly greater than Cl(RISA) (2.0 +/- 0.3 ml/min vs. 1.0 +/- 0.2 ml/min; p < 0.04). CONCLUSION: Solute clearance from the amniotic cavity is inversely proportional to solute molecular weight/size. Although the membrane comprising the ovine intramembranous pathway is size restrictive, membrane pores allow passage of non-polar solutes up to 36 A. Knowledge of membrane permeability characteristics is essential for the utilization of the intramembranous pathway for fetal therapeutics.

A simplified index of the plasma sodium threshold for arginine vasopressin secretion-morning fasting, euhydrated sodium levels.

OBJECTIVE: Human pregnancy results in a reduction in plasma osmolality and thus a reduction in the osmotic threshold for arginine vasopressin secretion. Although the functional characteristics of the osmoregulatory system controlling arginine vasopressin secretion have been carefully defined, determination of the osmotic threshold requires a complex, labor-intensive protocol of an intravenous hypertonic saline infusion. To aid in studies of osmotic threshold resetting in pregnancy, we sought to develop a simplified method for determination of this value. STUDY DESIGN: Ten healthy nonpregnant women between the ages of 18 and 40 years were studied over 2 days. All patients were hospitalized, and morning euhydration was ensured by oral water hydration (5-10 mL/kg) the evening before the study. On the first study day, patients were fed a standard no-salt-added diet; plasma osmolality and sodium values were checked just before and 1 and 2 hours after meals. On the second study day, after fasting blood samples were obtained, patients received an intravenous infusion (0.06 mL. kg(-1). min(-1) for 120 minutes) of hypertonic (5%) saline to gradually increase the plasma sodium level. Blood samples were obtained every 15 minutes for measurement of plasma electrolytes and arginine vasopressin. Plasma arginine vasopressin concentrations were regressed against plasma osmolality and sodium concentration to calculate the osmotic threshold for arginine vasopressin secretion. RESULTS: Hypertonic saline injection significantly increased plasma sodium (from 139 +/- 1 to 149 +/- 1 mEq/L) and osmolality (from 284 +/- 2 to 304 +/- 2 mOsm/kg H(2)O). Plasma arginine vasopressin significantly increased (from 5 +/- 1 to 30 +/- 10 pg/mL). The mean sodium and osmolality thresholds for arginine vasopressin secretion were calculated as 137 +/- 2 mEq/L and 285 +/- 15 mOsm/kg H(2)O. The mean morning fasting sodium level was nearly identical to the calculated sodium threshold, whereas the morning fasting osmolality value was significantly different. CONCLUSIONS: The morning fasting, euhydrated sodium level can be used as a simplified index for the plasma osmotic threshold for arginine vasopressin secretion. This index may provide a useful predictive measure for pregnant women in whom the plasma volume does not expand.

Element-specific detection in capillary electrophoresis using X-ray fluorescence spectroscopy.

X-ray fluorescence spectroscopy is demonstrated here as a novel, element-specific detector for capillary electrophoresis. Monochromatic 10 keV X-rays from a synchrotron light source are used to excite core electrons, causing emission of characteristic Kalpha X-ray fluorescence (XRF) lines. Using this technique, XRF energies provide elemental identification, while XRF intensities can be used to quantitate the metal composition of each eluent. An X-ray transparent polymer coupling is used to create a window for the on-line, X-ray detection. This coupling contributes no measurable extra-column variance, and electrophoretic mobilities for the metal complexes used as model solutes are highly reproducible. The combination of XRF detection with capillary electrophoresis (CE-XRF) creates the first on-line detection system that is element-specific, nondestructive, and directly applicable to a broad range of applications including nonelectroactive species. CE-XRF is successfully demonstrated here for high binding-constant complexes of Fe(III), Co(II), Cu(II), and Zn(II). Within a single injection, electropherograms are obtained for each element of interest, with the element identity obtained directly from the emission energy. In contrast with ICPMS, this detection technique is directly on-line and does not require volatilization of the eluent. As a result, element-specific detection is not limited by the sample or the buffer volatility or atomization efficiency. Simultaneous XRF and UV absorbance detection can be used to provide an on-line determination of metal/chelate ratios. Although XRF detection limits are presently only in the 0.1 mM (0.5 ng) range, both collection geometry and incident intensity have yet to be optimized. Further optimization is expected to enhance this detection limit by another 2-3 orders of magnitude. As a result, the advent of XRF detection combined with the separating power of CE presents new possibilities for on-line, element-specific analysis.

Novel technique for assessing amniotic fluid volume: use of a three-dimensional bladder scanner.

OBJECTIVE: Abnormalities of amniotic fluid (AF) volume are associated with significant perinatal morbidity and mortality. Although current ultrasound techniques provide a linear amniotic fluid index (AFI) or 2-D area of AF, these indices have limited correlation with actual AF volume. The bladder volume instrument (BVI) 2500 ultrasound (Diagnostic Ultrasound Corp., Redmond, WA) utilizes a rotating 2 MHz transducer, a computer-defined fluid interface, and computer integration of 12 cross-sectional images to calculate 3-D fluid volume. In term pregnancies with normal AF volume, we previously demonstrated a correlation between the AFI and the 3-D volume as determined by BVI. In the present study, we sought to establish normative gestational values for BVI-determined 3-D volume and the relation to simultaneous AFI determinations. METHODS: Following written informed consent, 73 gravidas (17-41 weeks) with uncomplicated pregnancies and normal

Fetal absorption of intra-amniotic aldosterone: effects on urine composition.

OBJECTIVES: Amniotic fluid (AF) volume and composition are maintained by a balance of fetal fluid production and resorption. Ovine fetal resorption of peptide hormones (e.g., arginine vasopressin) from the amniotic cavity has been demonstrated, with resultant effects on fetal urine production. The present study was undertaken to determine whether intra-amniotically administered steroid hormones could be absorbed from the amniotic cavity into fetal plasma and whether intra-amniotic aldosterone administration would affect fetal renal sodium and potassium excretion. METHODS: Seven singleton fetuses (132 +/- 2 days) were prepared with bladder, vascular, and amniotic cavity catheters. After a 5-day recovery period, a bolus of aldosterone was injected into the amniotic cavity. Fetuses were monitored for an additional 24 hours during which time maternal, fetal, and AF samples were collected at timed intervals. RESULTS: After intra-amniotic aldosterone injection, AF aldosterone concentrations increased at 30 minutes and remained elevated for 4 hours after the aldosterone bolus. In response to increased AF aldosterone, fetal plasma aldosterone levels significantly increased by 30 minutes, peaked at 1 hour (17 +/- 4 to 758 +/- 160 pg/mL), and remained elevated for a minimum of 4 hours. Fetal urine sodium excretion significantly decreased and potassium excretion increased. Maternal plasma aldosterone levels increased significantly (25 +/- 10 to 401 +/- 56 pg/mL) but to levels below fetal values. Amniotic fluid and fetal and maternal aldosterone concentrations and fetal urine sodium and potassium excretion returned toward basal levels by 24 hours. CONCLUSION: The steroid hormone aldosterone can be absorbed from the amniotic cavity into the fetal circulation and can alter fetal urine electrolyte excretion. These results suggest that the amniotic cavity is a potential route of in utero pharmacologic fetal therapy.

Human amniotic fluid mathematical model: determination and effect of intramembranous sodium flux.

OBJECTIVE: A recently described mathematical model of human amniotic fluid dynamics used known and estimated rates of fetal fluid production (lung liquid and urine) and composition (osmolality) to enable calculation of previously unmeasured routes of amniotic fluid resorption, including fetal swallowing and intramembranous (across the amnion) water flow. This "osmolar" model assumed that only free water resorption occurred across the intramembranous route. We hypothesized that intramembranous flow also may include solutes and electrolytes because significant concentration gradients exist between amniotic fluid and fetal plasma. We used mass balance analysis to determine the direction and magnitude of intramembranous sodium flux and to assess the ability of a newly described "sodium" model to predict changes in amniotic fluid volume in response to changes in intramembranous electrolyte flow. Mathematical modeling was used to predict changes in amniotic fluid volume in response to changes in intramembranous electrolyte flow. STUDY DESIGN: Model predictions were calculated using published values for human amniotic fluid and fetal urine composition and volume. Ovine studies were used to derive lung fluid volumes and composition. Fetal swallowing and intramembranous flow were independently determined using net amniotic fluid osmolar (osmolality model) and sodium (sodium model) balance. Differences between osmolality and sodium model predictions were normalized to calculate the net intramembranous sodium flux, assuming a net balance of intramembranous osmotic solute flow. RESULTS: Both sodium and osmolality models predicted swallowed volume to be greater than intramembranous flow until 28 to 32 weeks' gestation, after which the relationship reversed. However, the sodium model predicted greater intramembranous flow and lower swallowing rates compared with the osmolality model at all gestational ages. Osmolar mass balance required daily intramembranous sodium flux into the amniotic fluid, which increased with gestational age. Furthermore, assuming stable swallowing and intramembranous water flow, the model predicts that 5% increases or decreases in amniotic fluid solute concentrations caused by intramembranous flux result in polyhydramnios or oligohydramnios, respectively. CONCLUSION: Sodium and osmolality models demonstrate similarities in determinations of amniotic fluid dynamics. However, mass balance equations demonstrate a net intramembranous flow of sodium into the amniotic fluid under normal conditions. Mathematical modeling suggests that small alterations in daily intramembranous sodium flux may evoke large changes in amniotic fluid volume.

Transvaginal sonography of the forewaters in the assessment of amniotic fluid volume in patients with oligohydramnios.

OBJECTIVE: To determine whether the forewaters should be considered in the assessment of amniotic fluid (AF) volume in patients beyond 37 weeks' gestation. METHODS: Sixty patients were prospectively studied and designated as having oligohydramnios or normal AF volume based upon on the standard four-quadrant AF index (AFI) of < or = 5 cm or > 5 cm, respectively. The distance between the internal os and the fetal head was measured transvaginally. This measurement was first added to the standard AFI and subsequently interchanged with the lowest of the two lower abdominal quadrant measurements. Statistical analysis included Student's t-test with p < 0.05 considered significant. RESULTS: Thirty patients were classified as oligohydramnios and 30 normal AF volume. The two subgroups did not differ as to maternal age, parity, gestational age at sonographic examination, incidence of meconium-stained amniotic fluid or 5-min Apgar scores < 7, or birth weight. No significant difference was noted between the mean forewaters measurement of patients with oligohydramnios and controls (0.2 +/- 0.1 and 0.4 +/- 0.1 cm, respectively). In patients with oligohydramnios, there was no significant difference between the standard AFI and the AF volume with the forewaters in each of the methods assessed (2.7 +/- 0.3, 2.9 +/- 0.3, and 2.7 +/- 0.3 cm, respectively). CONCLUSION: We conclude that various permutations of the AFI, which include sonographic assessment of the forewaters, do not impact on the diagnosis of oligohydramnios.

Effects of a butterfly scale microstructure on the iridescent color observed at different angles.

Multilayer thin-film structures in butterfly wing scales produce a colorful iridescence from reflected sunlight. Because of optical phenomena, changes in the angle of incidence of light and the viewing angle of an observer result in shifts in the color of butterfly wings. Colors ranging from green to purple, which are due to nonplanar specular reflection, can be observed on Papilio blumei iridescent scales. This refers to a phenomenon in which the curved surface patterns in the thin-film structure cause the specular component of the reflected light to be directed at various angles while affecting the spectral reflectivity at the same time by changing the optical path length through the structure. We determined the spectral reflectivities of P. blumei iridescent scales numerically by using models of a butterfly scale microstructure and experimentally by using a microscale-reflectance spectrometer. The numerical models accurately predict the shifts in spectral reflectivity observed experimentally.

Ovine fetal adaptations to chronically reduced urine flow: preservation of amniotic fluid volume.

Adequate amniotic fluid (AF) volume is maintained by a balance of fetal fluid production (lung liquid and urine) and resorption (swallowing and intramembranous flow). Because fetal urine is the principle source of AF, alterations in urine flow and composition directly impact AF dynamics. Intra-amniotic 1-desamino-8-D-arginine vasopressin (DDAVP) is rapidly absorbed into fetal plasma and induces a marked fetal urinary antidiuresis. To examine the effect of intra-amniotic- DDAVP-induced fetal urinary responses on AF volume and composition, six chronically prepared ewes with singleton fetuses (gestation 128 +/- 2 days) were studied for 72 h after a single intra-amniotic DDAVP (50-microgram) injection. After DDAVP, fetal urine osmolality significantly increased at 2 h (157 +/- 13 to 253 +/- 21 mosmol/kg) and remained elevated at 72 h (400 +/- 13 mosmol/kg). Urinary sodium (33.0 +/- 4.5 to 117.2 +/- 9.7 meq/l) and chloride (26.0 +/- 2.8 to 92.4 +/- 8.1 meq/l) concentrations similarly increased. AF osmolality increased (285 +/- 3 to 299 +/- 4 mosmol/kg H2O), although there was no change in fetal plasma osmolality (294 +/- 2 mosmol/kg). Despite a 50% reduction in fetal urine flow (0.12 +/- 0.03 to 0.05 +/- 0.02 ml.kg-1.min-1 at 2 h and 0.06 +/- 0.01 ml.kg-1.min-1 after 72 h), AF volume did not change (693 +/- 226 to 679 +/- 214 ml). There were no changes in fetal arterial blood pressures, pH, PCO2, or PO2 after DDAVP. We conclude the following. 1) Intra-amniotic DDAVP injection induces a prolonged decrease in fetal urine flow and increases in urine and AF osmolalities. 2) Despite decreased urine flow, AF volume does not change. We speculate that, in response to DDAVP-induced fetal oliguria, reversed intramembranous flow (from isotonic fetal plasma to hypertonic AF) preserves AF volume.

Mathematic modeling of human amniotic fluid dynamics.

OBJECTIVE: We sought to develop a model quantifying the relative contributions of fetal swallowing and intramembranous flow to amniotic fluid dynamics during human gestation. We then used the model to simulate the impact of absent swallowing on amniotic fluid volume. STUDY DESIGN: The model was developed with published data for normal human amniotic fluid volume and composition, human fetal urine flow rate and composition (11 to 42 weeks), and extrapolated data from ovine lung fluid production. Fetal swallowing and intramembranous flow were calculated with assumptions that (1) swallowed fluid is isotonic to amniotic fluid, (2) intramembranous flow is free water diffusion, and (3) 50% of lung fluid is swallowed. The model was then applied to simulate absent fetal swallowing and variable (0%, 50%) proportions of swallowed lung fluid were used as a representation of esophageal atresia-tracheal fistula variations. RESULTS: Fetal swallowed volume and intramembranous flow linearly increase until 28 to 30 weeks. Daily swallowed volume then exponentially increases to a maximum of 1006 ml/day at term, whereas intramembranous flow continues on a linear trend to reach 393 ml/day at term. With absent swallowing and variable amounts of lung fluid swallowed (0%, 50%), predicted amniotic fluid volume is similar to normal values through 20 weeks, exceeds the 95% confidence interval for normal amniotic fluid volume at 29 to 30 weeks' gestation (approximately 2000 ml), and then exponentially increases. Predicted amniotic fluid osmolality (280 to 257 mOsm/kg) is slightly lower than actual values although within the clinically normal range. CONCLUSIONS: This model indicates that the normal reduction in amniotic fluid volume beginning at 34 weeks results from the marked increase in swallowed volume during the third trimester. Additionally, this model correlates well with the timing of the initial clinical presentation of polyhydramnios observed in some fetuses with conditions that result in absent or reduced swallowing or gastrointestinal atresia. Modeling of amniotic fluid dynamics can predict normal changes in fetal fluid exchange and may aid in understanding of amniotic fluid imbalances.

Amniotic fluid index as a predictor of latency after preterm premature rupture of the membranes.

To determine if latency following preterm premature rupture of membranes can be predicted using the amniotic fluid index, a retrospective observational study was performed using patient records to identify those admitted with a diagnosis of preterm premature rupture of membranes. Fifty-one patients with initial evaluation within 48 hours of rupture and gestational age 26 to 34 weeks were identified. Amniotic fluid index was evaluated along with a biophysical profile; these were followed serially until delivery. Delivery was accomplished because of spontaneous labor or chorioamnionitis. Amniotic fluid index at initial evaluation was stratified into three groups: Low (less than 5.0), reduced (4.0 to 7.9), and normal (8.0 or higher). Latency in days from preterm premature rupture of membranes to delivery was evaluated for these groups. A difference was noted in that latency was significantly longer in the group with normal versus low or reduced amniotic fluid index groups. The amount of residual amniotic fluid, as measured by the amniotic fluid index, following preterm premature rupture of membranes, is predictive of latency.

Conditional task-related responses in monkey dorsomedial frontal cortex.

Dorsomedial frontal cortex (DMFC) was studied in monkeys trained to make visually guided eye or arm movements. Portions of DMFC are involved in the execution of learned, goal-directed behaviors. Many neurons discharge with both eye and hand movements as well as when motor responses are withheld, provided these behaviors are related to the successful execution of the learned task. Similar movements, when carried out at times unrelated to the task, are not accompanied by neuronal activity. Electrical microstimulation produces either arrest of task-related, but not task-unrelated motor acts, or triggers task-related movements. The nature of stimulation elicited responses depends on the task the animal has been trained on and is altered by new training.