The impact of increasing body mass index on in vitro fertilization treatment, obstetrical, and neonatal outcomes

BACKGROUND

Citing the risks of administering anesthesia to patients with obesity, few fertility centers offer in vitro fertilization as a treatment modality for patients with body mass indexes ≥40 kg/m2. Although previous studies have assessed clinical pregnancy and cumulative live birth rates in patients who spontaneously conceive with body mass indexes ≥50 kg/m2, there is a paucity of in vitro fertilization, obstetrical, and neonatal outcome data in patients with severe obesity who conceive after in vitro fertilization.

OBJECTIVE

This study aimed to evaluate the impact of increasing body mass index on in vitro fertilization, obstetrical, and neonatal outcomes in patients with obesity undergoing in vitro fertilization.

STUDY DESIGN

This was a retrospective cohort study within an academic fertility center including 2069 fresh in vitro fertilization/intracytoplasmic sperm injection and frozen embryo transfer cycles from January 1, 2012 to April 30, 2020; this cohort was used to determine in vitro fertilization treatment outcomes. A second embedded cohort of 867 fresh in vitro fertilization/intracytoplasmic sperm injection and frozen embryo transfer cycles that resulted in ongoing clinical pregnancies and deliveries within a single tertiary hospital system was used to determine pregnancy, maternal, and neonatal outcomes. All patients with a body mass index ≥40 kg/m2 underwent consultation with a maternal-fetal medicine specialist before starting treatment and a preoperative evaluation with an anesthesiologist before oocyte retrieval. Cycles were grouped by body mass index at cycle start (30-34.9, 35-39.9, 40-44.9, 45-49.9, and ≥50 kg/m2). Log-binomial regression and Poisson regression with an offset were fitted with body mass index of 30 to 34.9 kg/m2 as the reference group, adjusting for potential confounders including oocyte age, patient age, embryo quality, transfer type, and coexisting comorbidities. The primary outcome was live birth rate. Secondary outcomes included fertilization rate, blastulation rate, miscarriage rate, incidence of preeclampsia with severe features, gestational diabetes, labor induction, cesarean delivery, preterm delivery, and birthweight.

RESULTS

There were 2069 fresh in vitro fertilization/intracytoplasmic sperm injection and frozen embryo transfer cycle starts from January 1, 2012 to April 30, 2020. Of these, 1008 cycles were in the 30 to 34.9 kg/m2 group, 547 in the 35 to 39.9 kg/m2 group, 277 in the 40 to 44.9 kg/m2 group, 161 in the 45 to 49.9 kg/m2 group, and 76 in the ≥50 kg/m2 body mass index group. Live birth rate was not significantly different between groups. The body mass index ≥50 kg/m2 group was significantly more likely to experience preeclampsia with severe features when compared with the 30 to 34.9 kg/m2 body mass index group (absolute risk reduction, 2.75; 95% confidence interval, 1.13-6.67). Fertilization rate, blastulation rate, miscarriage rate, incidence of gestational diabetes, labor induction, cesarean delivery, preterm delivery, and neonatal birthweights were not significantly different between groups.

CONCLUSION

Among patients with body mass indexes from 30 to 60 kg/m2 who conceived via in vitro fertilization and received comprehensive prenatal care at a tertiary care hospital, in vitro fertilization, obstetrical, and neonatal outcomes were largely comparable. These data support a collaborative care approach with maternal-fetal medicine specialists and skilled anesthesiologists, reinforcing the notion that in vitro fertilization should not be withheld as a treatment modality from patients with obesity.

Utility of Office Hysteroscopy in Diagnosing Retained Products of Conception Following Early Pregnancy Loss After In Vitro Fertilization

OBJECTIVE

To evaluate the utility of office hysteroscopy in diagnosing and treating retained products of conception in patients with infertility who experience early pregnancy loss (EPL) after in vitro fertilization (IVF).

METHODS

We evaluated a retrospective cohort of 597 pregnancies that ended in EPL in patients aged 18-45 years who conceived through fresh or frozen embryo transfer at an academic fertility practice between January 2016 and December 2021. All patients underwent office hysteroscopy after expectant, medical, or surgical management of the EPL. The primary outcome was presence of retained products of conception at the time of office hysteroscopy. Secondary outcomes included incidence of vaginal bleeding, presence of intrauterine adhesions, treatment for retained products of conception, and duration of time from EPL diagnosis to resolution. Log-binomial regression and Poisson regression were performed, adjusting for potential confounders including oocyte age, patient age, body mass index, prior EPL count, number of prior dilation and curettage procedures, leiomyomas, uterine anomalies, and vaginal bleeding.

RESULTS

Of the 597 EPLs included, 129 patients (21.6%) had retained products of conception diagnosed at the time of office hysteroscopy. The majority of individuals with EPL were managed surgically (n=427, 71.5%), in lieu of expectant management (n=140, 23.5%) or medical management (n=30, 5.0%). The presence of retained products of conception was significantly associated with vaginal bleeding (relative risk [RR] 1.72, 95% CI 1.34-2.21). Of the 41 patients with normal pelvic ultrasonogram results before office hysteroscopy, 10 (24.4%) had retained products of conception detected at the time of office hysteroscopy. When stratified by EPL management method, retained products of conception were significantly more likely to be present in individuals with EPL who were managed medically (adjusted RR 2.66, 95% CI 1.90-3.73) when compared with those managed surgically. Intrauterine adhesions were significantly less likely to be detected in individuals with EPL who underwent expectant management when compared with those managed surgically (RR 0.14, 95% CI 0.04-0.44). Of the 127 individuals with EPL who were diagnosed with retained products of conception at the time of office hysteroscopy, 30 (23.6%) had retained products of conception dislodged during the office hysteroscopy, 34 (26.8%) chose expectant or medical management, and 63 (49.6%) chose surgical management. The mean number of days from EPL diagnosis to resolution of pregnancy was significantly higher in patients who elected for expectant management (31 days; RR 1.18, 95% CI 1.02-1.37) or medical management (41 days; RR 1.54, 95% CI 1.25-1.90) when compared with surgical management (27 days).

CONCLUSION

In patients with EPL after IVF, office hysteroscopy detected retained products of conception in 24.4% of those with normal pelvic ultrasonogram results. Due to the efficacy of office hysteroscopy in diagnosing and treating retained products of conception, these data support considering office hysteroscopy as an adjunct to ultrasonography in patients with infertility who experience EPL after IVF.

Premature progesterone elevation during the early and mid-follicular phases in fresh in vitro fertilization (IVF) cycles is associated with lower live birth, clinical pregnancy, and implantation rates

PURPOSE

Evaluate follicular phase progesterone elevation (≥ 1.5 ng/mL) prior to trigger during IVF stimulation and its effects on live birth rate (LBR), clinical pregnancy rate (CPR), and implantation rate (IR) in fresh IVF cycles.

METHODS

This was a retrospective cohort study within an academic clinic. A total of 6961 fresh IVF and IVF/ICSI cycles from October 1, 2015 to June 30, 2021 were included and grouped by progesterone (PR) prior to trigger: PR < 1.5 ng/mL (low PR group) and PR ≥ 1.5 ng/mL (high PR group). Main outcome measures included LBR, CPR, and IR.

RESULTS

Among all cycle starts, 1568 (22.5%) were in the high PR group and 5393 (77.5%) were in the low PR group. Of the cycles which proceeded to an embryo transfer, 416 (11.1%) were in the high PR group and 3341 (88.9%) were in the low PR group. The high PR group had significantly lower IR (RR 0.75; 95% CI 0.64-0.88), CPR (aRR 0.74; 95% CI 0.64-0.87), and LBR (aRR 0.71; 95% CI 0.59-0.85) compared to the low PR group. When stratified by progesterone on the day of trigger (TPR), there was a clinically notable decrease in IR (16.8% vs 23.3%), CPR (28.1% vs 36.0%), and LBR (22.8% vs 28.9%) in the high PR group compared to the low PR group even when TPR < 1.5 ng/mL.

CONCLUSIONS

In fresh IVF cycles in which TPR < 1.5 ng/mL, progesterone elevation ≥ 1.5 ng/mL at any point in time prior to trigger negatively impacts IR, CPR, and LBR. This data supports testing of serum progesterone in the follicular phase prior to trigger, as these patients may benefit from a freeze-all approach.

Sonographic Predictors of Ovarian Torsion in Premenarchal Girls

STUDY OBJECTIVE

To identify preoperative transabdominal sonographic predictors of surgically-confirmed ovarian torsion (OT) in premenarchal girls.

METHODS

Retrospective case-control study of 32 premenarchal girls aged 0-12 undergoing surgery for OT (cases) or a non-torsed ovarian mass (controls) from 2006-2017 at a single academic center. Cases had ICD-9/10 codes for torsion of the ovary, adnexa, ovarian pedicle, or fallopian tube and surgically-confirmed OT; controls had codes for ovarian mass or cyst and surgically-confirmed absence of OT. Preoperative transabdominal ultrasounds were analyzed by three radiologists blinded to final diagnosis. Chi-square, Fisher's exact, and Student's t-test were used for statistical comparisons.

RESULTS

From 2016-2017, 32 patients presented with acute abdominal pain or symptoms concerning for ovarian mass requiring ultrasound imaging and subsequent diagnostic laparoscopy-24 (75.0%) had confirmed OT by laparoscopy; eight (25.0%) did not. Mean age in both groups was similar (7.3±2.9 years). Preoperative sonographic variables significantly associated with OT included presence of a simple cyst (20.8% vs 12.5%), ovarian heterogeneity (100% vs 12.5%), presence of peripheralized follicles (70.8% vs 0%), and asymmetry of color Doppler (75.0% vs 37.5%)-all p<0.05. Presence of free fluid, arterial color Doppler, and a whirlpool sign were not predictive of OT.

CONCLUSION

In premenarchal patients, while certain variables on transabdominal sonography predicted surgically-confirmed OT, only the presence of peripheralized follicles was unique to girls with OT. The decision to proceed with diagnostic laparoscopy for suspected OT can be aided by these specific sonographic findings but should ultimately be based on high clinical suspicion.

Mouse oocyte vitrification with and without dimethyl sulfoxide: influence on cryo-survival, development, and maternal imprinted gene expression

PURPOSE

Oocytes and embryos can be vitrified with and without dimethyl sulfoxide (DMSO). Objectives were to compare no vitrification (No-Vitr), vitrification with DMSO (Vitr + DMSO), and vitrification without DMSO (Vitr - DMSO) on fresh/warmed oocyte survival, induced parthenogenetic activation, parthenogenetic embryo development, and embryonic maternal imprinted gene expression.

METHODS

In this prospective controlled laboratory study, mature B6C3F1 female mouse metaphase II oocytes were treated as: i) No-Vitr, ii) Vitr + DMSO/warmed, and iii) Vitr - DMSO/warmed with subsequent parthenogenetic activation and culture to the blastocyst stage. Oocyte cryo-survival, parthenogenetic activation and embryo development, parthenogenetic embryo maternal imprinted gene expression were outcome measures.

RESULTS

Oocyte cryo-survival was significantly improved in Vitr + DMSO versus Vitr - DMSO at initial warming and 2 h after warming. Induced parthenogenetic activation was similar between all three intervention groups. While early preimplantation parthenogenetic embryo development was similar between control, Vitr + DMSO, Vitr - DMSO oocytes, the development to blastocysts was significantly inferior in the Vitr - DMSO oocytes group compared to the control and Vitr + DMSO oocyte groups. Finally, maternal imprinted gene expression was similar between intervention groups at both the 2-cell and blastocyst parthenogenetic embryo stage.

CONCLUSION(S)

Inclusion of DMSO in oocyte vitrification solutions improved cryo-survival and developmental potential of parthenogenetic embryos to the blastocyst stage without significantly altering maternal imprinted gene expression.

Comparison of Short-Duration and Chronic Premenarchal Vulvar Complaints

STUDY OBJECTIVE

To compare clinical characteristics, treatment histories, and microbiology of premenarchal girls who presented to a pediatric gynecology specialty clinic with short-duration and chronic vulvar symptoms.

DESIGN

Retrospective cohort study.

SETTING

Pediatric and adolescent gynecology clinic at a tertiary care children's hospital.

PARTICIPANTS

One hundred eighty-two premenarchal patients ages 2-14 years who presented to a pediatric gynecology specialty clinic with vulvar complaints and who were evaluated with a yeast and/or bacterial culture.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Chronic and short-duration vulvar symptoms, microbiology, and diagnosis.

RESULTS

Patients with chronic symptoms were more likely to present with itching (59/102 (57.8%) vs 34/80 (42.5%); P = .04), redness or rash (53/102 (52.0%) vs 22/80 (27.5%); P = .0009), and discomfort (59/102 (57.8%) vs 30/80 (37.5%); P = .006), compared with patients with short-duration symptoms. Overall, 44.5% of patients had a history of antifungal treatment, with a greater proportion of patients with chronic symptoms having received antifungal treatment compared with those with short-duration symptoms (53/102 (52.0%) vs 28/80 (35.0%); P = .02). Despite a history of antifungal treatment in nearly half of the patients, Candida albicans was isolated in only 3/144 (2.1%) yeast cultures. Bacterial vulvar cultures were positive in 75/159 (47.2%), and there was no difference among the symptom duration groups (38/71 (53.5%) vs 37/88 (42.1%); P = .15).

CONCLUSION

Vulvovaginitis is a common gynecological diagnosis among premenarchal girls with short-duration and chronic vulvar symptoms. Regardless of symptom duration, yeast cultures are rarely positive. Antifungal treatment should be avoided in toilet-trained prepubertal girls.

The IRE1α/XBP1s Pathway Is Essential for the Glucose Response and Protection of β Cells

Although glucose uniquely stimulates proinsulin biosynthesis in β cells, surprisingly little is known of the underlying mechanism(s). Here, we demonstrate that glucose activates the unfolded protein response transducer inositol-requiring enzyme 1 alpha (IRE1α) to initiate X-box-binding protein 1 (Xbp1) mRNA splicing in adult primary β cells. Using mRNA sequencing (mRNA-Seq), we show that unconventional Xbp1 mRNA splicing is required to increase and decrease the expression of several hundred mRNAs encoding functions that expand the protein secretory capacity for increased insulin production and protect from oxidative damage, respectively. At 2 wk after tamoxifen-mediated Ire1α deletion, mice develop hyperglycemia and hypoinsulinemia, due to defective β cell function that was exacerbated upon feeding and glucose stimulation. Although previous reports suggest IRE1α degrades insulin mRNAs, Ire1α deletion did not alter insulin mRNA expression either in the presence or absence of glucose stimulation. Instead, β cell failure upon Ire1α deletion was primarily due to reduced proinsulin mRNA translation primarily because of defective glucose-stimulated induction of a dozen genes required for the signal recognition particle (SRP), SRP receptors, the translocon, the signal peptidase complex, and over 100 other genes with many other intracellular functions. In contrast, Ire1α deletion in β cells increased the expression of over 300 mRNAs encoding functions that cause inflammation and oxidative stress, yet only a few of these accumulated during high glucose. Antioxidant treatment significantly reduced glucose intolerance and markers of inflammation and oxidative stress in mice with β cell-specific Ire1α deletion. The results demonstrate that glucose activates IRE1α-mediated Xbp1 splicing to expand the secretory capacity of the β cell for increased proinsulin synthesis and to limit oxidative stress that leads to β cell failure.

The differential diagnosis of longitudinally extensive transverse myelitis

Longitudinally extensive transverse myelitis refers to florid and widespread inflammation of the spinal cord causing T2 hyperintensity on spinal magnetic resonance imaging that is seen to extend over three or more vertebral segments. Whilst rare, longitudinally extensive transverse myelitis is clinically important as it can lead to catastrophic morbidity, and a group of these patients are at risk of further attacks. Early identification and establishment of the underlying aetiology is vital in order to initiate appropriate therapy and optimize outcomes. Whilst longitudinally extensive transverse myelitis is classically associated with neuromyelitis optica, there are many other causes. These include other inflammatory aetiologies, infection, malignancy and metabolic disturbance. Some of these are readily treatable. Laboratory and radiological investigations can help to differentiate these causes. Treatment of longitudinally extensive transverse myelitis hinges on distinguishing inflammatory and non-inflammatory aetiologies and identifying patients who are at high risk of a recurrent course.

Modeling spatiotemporal covariance for magnetoencephalography or electroencephalography source analysis

We propose a new model to approximate spatiotemporal noise covariance for use in neural electromagnetic source analysis, which better captures temporal variability in background activity. As with other existing formalisms, our model employs a Kronecker product of matrices representing temporal and spatial covariance. In our model, spatial components are allowed to have differing temporal covariances. Variability is represented as a series of Kronecker products of spatial component covariances and corresponding temporal covariances. Unlike previous attempts to model covariance through a sum of Kronecker products, our model is designed to have a computationally manageable inverse. Despite increased descriptive power, inversion of the model is fast, making it useful in source analysis. We have explored two versions of the model. One is estimated based on the assumption that spatial components of background noise have uncorrelated time courses. Another version, which gives closer approximation, is based on the assumption that time courses are statistically independent. The accuracy of the structural approximation is compared to an existing model, based on a single Kronecker product, using both Frobenius norm of the difference between spatiotemporal sample covariance and a model, and scatter plots. Performance of ours and previous models is compared in source analysis of a large number of single dipole problems with simulated time courses and with background from authentic magnetoencephalography data.

Dopaminergic modulation and rod contribution in the generation of oscillatory potentials in the tiger salamander retina

The roles of rod and cone input and of dopamine in the generation of oscillatory potentials were studied in tiger salamander retina. Under scotopic conditions, oscillations were elicited with a green, but not a red stimulus. With mesopic background illumination, both stimuli caused oscillations. Addition of quinpirole to a mesopic retina eliminated oscillations while SKF-38393 had no effect. Similarly, addition of sulpiride to a light-adapted retina elicited oscillatory activity, but SCH 22390 had no effect. These results suggest that oscillatory potentials are elicited through activation of the rod pathway and are modulated by dopamine through D2-receptors.

A high frequency resonance in the responses of retinal ganglion cells to rapidly modulated stimuli: a computer model

Brisk Y-type ganglion cells in the cat retina exhibit a high frequency resonance (HFR) in their responses to large, rapidly modulated stimuli. We used a computer model to test whether negative feedback mediated by axon-bearing amacrine cells onto ganglion cells could account for the experimentally observed properties of HFRs. Temporal modulation transfer functions (tMTFs) recorded from model ganglion cells exhibited HFR peaks whose amplitude, width, and locations were qualitatively consistent with experimental data. Moreover, the wide spatial distribution of axon-mediated feedback accounted for the observed increase in HFR amplitude with stimulus size. Model phase plots were qualitatively similar to those recorded from Y ganglion cells, including an anomalous phase advance that in our model coincided with the amplification of low-order harmonics that overlapped the HFR peak. When axon-mediated feedback in the model was directed primarily to bipolar cells, whose synaptic output was graded, or else when the model was replaced with a simple cascade of linear filters, it was possible to produce large HFR peaks but the region of anomalous phase advance was always eliminated, suggesting the critical involvement of strongly non-linear feedback loops. To investigate whether HFRs might contribute to visual processing, we simulated high frequency ocular tremor by rapidly modulating a naturalistic image. Visual signals riding on top of the imposed jitter conveyed an enhanced representation of large objects. We conclude that by amplifying responses to ocular tremor, HFRs may selectively enhance the processing of large image features.

Simultaneously detected biomagnetic signals and NMR

We have obtained 1H NMR spectra simultaneously with high temporal resolution biomagnetic signals such as the magnetocardiogram (MCG) and magnetomyogram (MMG). The NMR spectra are acquired at measurement fields of 2-50 microT, with corresponding proton Larmor frequencies of 80-2000 Hz. Our measurements demonstrate a method suitable for MR imaging with concurrent measurement of biomagnetic signals that can provide sub-millisecond temporal resolution. The narrow line widths, reduction in susceptibility noise and enhanced spectral resolution at ultra low fields provide a new and extremely sensitive measurement method that may enable direct imaging of biological currents by detecting the phase or frequency shifts produced by magnetic fields arising from those currents. The results of our simultaneous measurements of NMR with MCG and MMG are compared to results from a current phantom to investigate the exciting potential of direct MRI of bioelectric currents.

MUSIC seeded multi-dipole MEG modeling using the Constrained Start Spatio-Temporal modeling procedure

The Constrained Start Spatio-Temporal modeling program (CSST) is an objective multi-dipole, multi-start MEG/EEG analysis procedure that randomly selects from 100 to 100,000 initial dipole configurations, and runs a nonlinear simplex search on each of these configurations employing a reduced Chi-square statistic as the minimization criterion, to obtain a set of dipole configurations that best fit the data [Ranken, 2002]. A parallel version of CSST is implemented in IDL and MPI, making CSST usable on a single computer, or on a Linux cluster. We have now developed a multi-resolution version of MUSIC [Mosher, 1992] [Mosher, 1998] that provides an 80% or more reduction in the number of forward calculations needed to obtain results comparable to a 160,000 point MUSIC scan, on a 2 mm grid that defines a brain volume. The multi-resolution MUSIC scan provides an improved set of initial dipole estimates for the CSST analysis. In preliminary tests on real and simulated MEG data, with model orders ranging between 5 and 7 dipoles, the best performance improvements were obtained by mixing in 1 to 3 dipole locations randomly drawn from the best MUSIC locations, with randomly selected locations from the brain volume to complete the selected model order. We have also developed an improved method for sampling the brain volume for initial configurations. These improvements have led to a 75% reduction in the number of starting configurations required to obtain 5-10 best solutions with equal or lower reduced Chi-square values, when compared to the best solutions from the previous version of CSST.

The influence of brain tissue anisotropy on human EEG and MEG

The influence of gray and white matter tissue anisotropy on the human electroencephalogram (EEG) and magnetoencephalogram (MEG) was examined with a high resolution finite element model of the head of an adult male subject. The conductivity tensor data for gray and white matter were estimated from magnetic resonance diffusion tensor imaging. Simulations were carried out with single dipoles or small extended sources in the cortical gray matter. The inclusion of anisotropic volume conduction in the brain was found to have a minor influence on the topology of EEG and MEG (and hence source localization). We found a major influence on the amplitude of EEG and MEG (and hence source strength estimation) due to the change in conductivity and the inclusion of anisotropy. We expect that inclusion of tissue anisotropy information will improve source estimation procedures.

Scattered-light imaging in vivo tracks fast and slow processes of neurophysiological activation

We imaged fast optical changes associated with evoked neural activation in the dorsal brainstem of anesthetized rats, using a novel imaging device. The imager consisted of a gradient-index (GRIN) lens, a microscope objective, and a miniature charged-coupled device (CCD) video camera. We placed the probe in contact with tissue above cardiorespiratory areas of the nucleus of the solitary tract and illuminated the tissue with 780-nm light through flexible fibers around the probe perimeter. The focus depth was adjusted by moving the camera and microscope objective relative to the fixed GRIN lens. Back-scattered light images were relayed through the GRIN lens to the CCD camera. Video frames were digitized at 100 frames per second, along with tracheal pressure, arterial blood pressure, and electrocardiogram signals recorded at 1 kHz per channel. A macroelectrode placed under the GRIN lens recorded field potentials from the imaged area. Aortic, vagal, and superior laryngeal nerves were dissected free of surrounding tissue within the neck. Separate shocks to each dissected nerve elicited evoked electrical responses and caused localized optical activity patterns. The optical response was modeled by four distinct temporal components corresponding to putative physical mechanisms underlying scattered light changes. Region-of-interest analysis revealed image areas which were dominated by one or more of the different time-course components, some of which were also optimally recorded at different tissue depths. Two slow optical components appear to correspond to hemodynamic responses to metabolic demand associated with activation. Two fast optical components paralleled electrical evoked responses.

Continuous image and electrophysiological recording with real-time processing and control

Collecting continuous video together with multichannel electrophysiological data and other experimental modalities requires high bandwidth and storage capacities, as well as accurate synchronization to detect correlations between different recorded events. Often, experiments are highly complex, with many variables requiring immediate analysis and feedback during the course of the experiment. In addition, output channels require real-time control with high time resolution. We have explored several approaches to a system that can perform the above functions. The design of our system considered a number of issues, including time intervals between control and acquisition events, longest continuous recording period, data transfer bottleneck considerations, file archiving and format, and real-time display and processing. To demonstrate the system, we describe an experiment for characterizing rapid evoked scattered light changes in neural tissue, in vivo, using simultaneous electronic image acquisition and electrophysiological recording.

Conductivity tensor mapping of the human brain using diffusion tensor MRI

Knowledge of the electrical conductivity properties of excitable tissues is essential for relating the electromagnetic fields generated by the tissue to the underlying electrophysiological currents. Efforts to characterize these endogenous currents from measurements of the associated electromagnetic fields would significantly benefit from the ability to measure the electrical conductivity properties of the tissue noninvasively. Here, using an effective medium approach, we show how the electrical conductivity tensor of tissue can be quantitatively inferred from the water self-diffusion tensor as measured by diffusion tensor magnetic resonance imaging. The effective medium model indicates a strong linear relationship between the conductivity and diffusion tensor eigenvalues (respectively, final sigma and d) in agreement with theoretical bounds and experimental measurements presented here (final sigma/d approximately 0.844 +/- 0.0545 S small middle dots/mm(3), r(2) = 0.945). The extension to other biological transport phenomena is also discussed.

A focusing image probe for assessing neural activity in vivo

We describe a compact, focusing image probe to record rapid optical changes from neural tissue. A gradient index (GRIN) lens served as a relay lens from tissue to a microscope objective which projected an image onto a CCD camera. The microscope objective and camera assembly was adjusted independently from the GRIN lens, allowing focus changes without disturbing the probe/tissue interface; firm contact minimized movement and specular reflectance. Fiber optics around the probe perimeter provided diffuse illumination from a 780 nm laser, or 660 and 560 nm light emitting diodes. To characterize depth-of-field, we imaged a black suture through increasing tissue thicknesses. Light modulation by the suture remained detectable down to 900 microm using 780 nm illumination. We acquired images from cardiorespiratory areas of the rat dorsal medulla, at different depths and illumination wavelengths. Images illuminated at 560 nm were dominated by vasculature flow patterns, while 660 nm illumination revealed different spatial patterns which preceded vascular flow by 40 ms and may represent cardiac-related neural activity. Using 780 nm light, image sequences triggered by the cardiac R-wave showed vascular perfusion changes with delayed and broader responses at deeper levels. Electrical stimulation within the vagal bundle caused fast optical changes which track the electrical response, with a different spatial distribution from hemodynamic signals.

Bayesian inference applied to the electromagnetic inverse problem

We present a new approach to the electromagnetic inverse problem that explicitly addresses the ambiguity associated with its ill-posed character. Rather than calculating a single "best" solution according to some criterion, our approach produces a large number of likely solutions that both fit the data and any prior information that is used. Whereas the range of the different likely results is representative of the ambiguity in the inverse problem even with prior information present, features that are common across a large number of the different solutions can be identified and are associated with a high degree of probability. This approach is implemented and quantified within the formalism of Bayesian inference, which combines prior information with that of measurement in a common framework using a single measure. To demonstrate this approach, a general neural activation model is constructed that includes a variable number of extended regions of activation and can incorporate a great deal of prior information on neural current such as information on location, orientation, strength, and spatial smoothness. Taken together, this activation model and the Bayesian inferential approach yield estimates of the probability distributions for the number, location, and extent of active regions. Both simulated MEG data and data from a visual evoked response experiment are used to demonstrate the capabilities of this approach.

Diffusion imaging with hyperpolarized 3He Gas

We used MRI of hyperpolarized 3He to demonstrate some novel aspects of gas diffusion. Two different techniques were used. First, a slice was burned into a one-dimensional image by inverting the spins in the slice and diffusion was studied by measuring the magnetization as it filled the depleted slice. A diffusion coefficient was determined by the fit of these data. Second, one-dimensional diffusion images were made using a Stejskal-Tanner PGSE method. This was done with and without a temperature gradient present, showing that the effect of temperature can be dynamically monitored by such diffusion images. Copyright 1997 Academic Press. Copyright 1997Academic Press

Retinotopic organization of human visual cortex: departures from the classical model

Retinotopic mapping strategies similar to those used for invasive electrophysiological studies to identify multiple visual areas in monkeys have been adapted for noninvasive studies in humans, using magnetic recordings of brain activity in conjunction with anatomical magnetic resonance imaging. The retinotopic organization of the primary visual area (V1) in the left hemisphere of human subjects was examined by presenting a small patterned stimuli near the vertical and horizontal meridians in the lower right visual field. In contrast with the classical model of V1 retinotopy, our results suggest that the representation of the horizontal meridian does not necessarily correspond in a one-to-one manner with the base of the calcarine fissure and that some lower field stimuli can activate regions in the lower bank of the fissure. The results also indicate significant individual variability in the details of how V1 maps around the calcarine fissure.

Neuromagnetic source imaging with FOCUSS: a recursive weighted minimum norm algorithm

The paper describes a new algorithm for tomographic source reconstruction in neural electromagnetic inverse problems. Termed FOCUSS (FOCal Underdetermined System Solution), this algorithm combines the desired features of the two major approaches to electromagnetic inverse procedures. Like multiple current dipole modeling methods, FOCUSS produces high resolution solutions appropriate for the highly localized sources often encountered in electromagnetic imaging. Like linear estimation methods, FOCUSS allows current sources to assume arbitrary shapes and it preserves the generality and ease of application characteristic of this group of methods. It stands apart from standard signal processing techniques because, as an initialization-dependent algorithm, it accommodates the non-unique set of feasible solutions that arise from the neuroelectric source constraints. FOCUSS is based on recursive, weighted norm minimization. The consequence of the repeated weighting procedure is, in effect, to concentrate the solution in the minimal active regions that are essential for accurately reproducing the measurements. The FOCUSS algorithm is introduced and its properties are illustrated in the context of a number of simulations, first using exact measurements in 2- and 3-D problems, and then in the presence of noise and modeling errors. The results suggest that FOCUSS is a powerful algorithm with considerable utility for tomographic current estimation.

Mapping function in the human brain with magnetoencephalography, anatomical magnetic resonance imaging, and functional magnetic resonance imaging

Integrated analyses of human anatomical and functional measurements offer a powerful paradigm for human brain mapping. Magnetoencephalography (MEG) and EEG provide excellent temporal resolution of neural population dynamics as well as capabilities for source localization. Anatomical magnetic resonance imaging (MRI) provides excellent spatial resolution of head and brain anatomy, whereas functional MRI (fMRI) techniques provide an alternative measure of neural activation based on associated hemodynamic changes. These methodologies constrain and complement each other and can thereby improve our interpretation of functional neural organization. We have developed a number of computational tools and techniques for the visualization, comparison, and integrated analysis of multiple neuroimaging techniques. Construction of geometric anatomical models from volumetric MRI data allows improved models of the head volume conductor and can provide powerful constraints for neural electromagnetic source modeling. These approaches, coupled to enhanced algorithmic strategies for the inverse problem, can significantly enhance the accuracy of source-localization procedures. We have begun to apply these techniques for studies of the functional organization of the human visual system. Such studies have demonstrated multiple, functionally distinct visual areas that can be resolved on the basis of their locations, temporal dynamics, and differential sensitivity to stimulus parameters. Our studies have also produced evidence of internal retinotopic organization in both striate and extrastriate visual areas but have disclosed organizational departures from classical models. Comparative studies of MEG and fMRI suggest a reasonable but imperfect correlation between electrophysiological and hemodynamic responses. We have demonstrated a method for the integrated analysis of fMRI and MEG, and we outline strategies for improvement of these methods. By combining multiple measurement techniques, we can exploit the complementary strengths and transcend the limitations of the individual neuro-imaging methods.

Temporal dynamics of visual-evoked neuromagnetic sources: effects of stimulus parameters and selective attention

Results are reviewed from several neuromagnetic studies which characterize the temporal dynamics of neural sources contributing to the visual evoked response and effects of attention on these sources. Different types of pattern-onset stimuli (< or = 2 degrees) were presented sequentially to a number of field locations in the right visual field. Multiple dipole models were applied to a sequence of instantaneous field distributions constructed at 10 ms intervals. Best-fitting source parameters were superimposed on Magnetic Resonance images (MRI) of each subject to identify the anatomical structure(s) giving rise to the surface patterns. At least three sources, presumably corresponding to different visual areas, were routinely identified from 80-150 ms following the onset of visual stimulation. This observation was consistent across subjects and studies. The temporal sequence and strength of activation of these sources, however, were dependent upon the specific stimulus parameters used to evoke the response (e.g., eccentricity) and on the relevance of the stimulus to the subject. In addition, our results provide evidence for the recurrence of activity in striate and extrastriate regions, following the initial cycle of responses.

Reversible opening of the blood-brain barrier by anti-bacterial antibodies

The leukocyte adhesion molecule CR3 (CD11b/CD18, Mac-1) promotes leukocyte transmigration into tissues by engaging an unknown cognate ligand on the surface of vascular endothelial cells. Filamentous hemagglutinin (FHA), an adhesin of the bacterium Bordetella pertussis, binds to CR3. We hypothesized that FHA mimics the native ligand for the CR3 integrin on endothelial cells and predicted that anti-FHA antibodies should bind to endothelial cells, interfere with leukocyte recruitment, and induce endothelial permeability. Anti-FHA monoclonal antibodies bound to cerebral microvessels in sections from human brain and upon intravenous injection into rabbits. Antibody binding correlated with the ability to recognize two polypeptides in extracts of human cerebral vessels that were also bound by CD18. In vivo, antibody binding not only interfered with transmigration of leukocytes into cerebrospinal fluid but also induced a dose-dependent reversible increase in blood-brain barrier permeability sufficient to improve delivery of intravenously administered therapeutic agents to brain parenchyma.

Interactions between the subunits of transducin and cyclic GMP phosphodiesterase in Rana catesbiana rod photoreceptors

In bullfrog (Rana catesbiana) rods the activity of cyclic GMP (cGMP) phosphodiesterase was stimulated 10 times by washing disc membranes with an isotonic, GTP-containing buffer. This stimulation was maintained following hydrolysis of GTP and after removal of guanine nucleotides. At least 60-70% of the inhibitory gamma subunit of cGMP phosphodiesterase (P gamma) was physically released from membranes by these washing procedures. When cGMP phosphodiesterase was activated by a hydrolysis-resistant GTP analogue, P gamma was found in the supernatant complexed with the transducin alpha subunit (T alpha) using three chromatography systems. When GTP was used to activate cGMP phosphodiesterase, P gamma was also found in the supernatant complexed with GDP.T alpha. This complex was also isolated using the same three chromatography systems, indicating that P gamma remained tightly bound to T alpha even after bound GTP was hydrolyzed. Interaction with the beta,gamma subunits of transducin, which remained associated with disc membranes, was required for the release of P gamma from the GDP.T alpha complex, which resulted in the deactivation of active cGMP phosphodiesterase. We conclude that during activation of cGMP phosphodiesterase, P gamma is complexed with T alpha (both GTP and GDP forms) in the supernatant and that, following GTP hydrolysis, beta,gamma subunits of transducin are necessary for the release of P gamma from the complex and the resulting inactivation of cGMP phosphodiesterase in frog photoreceptors.

Control of Ca2+ in rod outer segment disks by light and cyclic GMP

Photons absorbed in vertebrate rods and cones probably cause electrochemical changes at the photoreceptor plasma membrane by changing the cytoplasmic concentration of a diffusible transmitter substance, reducing the Na+ current flowing into the outer segment of the cell in the dark, to produce the observed membrane hyperpolarization that is the initial excitatory response. Cyclic GMP has been proposed as the transmitter because a light-activated cyclic GMP phosphodiesterase (PDE) has been found in rod disk membranes and because intracellularly injected cyclic GMP reduces rod membrane potentials. Free Ca2+ has also been proposed because increasing external [Ca2+] quickly and reversibly reduces the dark current and divalent cationophores increase the Ca2+ sensitivity. Ca2+ efflux from rod outer segments (ROS) of intact retinas occurs simultaneously with light responses. Vesicles prepared from ROS disk membranes become more permeable on illumination, releasing trapped ions or molecules, but intact outer segment disks have not previously been found to store sufficient Ca2+ in darkness and to release enough in light to meet the theoretical requirements for control of the dark current by varying cytoplasmic Ca2+ (refs 14-18). We now report experiments that show the required Ca2+ storage and release from rod disk membranes suspended in media containing high-energy phosphate esters and electrolytes approximating the cytoplasmic composition of live rod cells. Cyclic GMP stimulates Ca2+ uptake by ROS disks in such media.

Intestinal parasitic infestation among parturients in Trinidad and Tobago

1. In this limited survey, 42.5% of parturients were found to be infested with intestinal parasites. 2. Hookworm, Trichuris and Entamoeba infestations were the most common. 3. Race, social class and locality influenced in the incidence of the different types of infestations. 4. Those infested with hookworm had longer labor, smaller babies and higher incidence of prematurity.