Urinary incontinence and pelvic organ prolapse.

Urinary incontinence and pelvic organ prolapse commonly coexist. Up to 60% of women presenting with pelvic organ prolapse are also diagnosed with urinary incontinence, and close to 40% of women presenting with urinary incontinence, in turn, are found to have some degree of pelvic organ prolapse. In addition, other disorders of the lower urinary tract, such as voiding dysfunction, are in women frequently associated with pelvic organ prolapse. All women with lower urinary tract symptoms should be screened for pelvic organ prolapse. This is important as pelvic organ prolapse beyond the hymen may either cause or mask lower urinary tract dysfunction. Further, lower urinary tract symptoms do not correlate well with clinical diagnoses of lower urinary tract dysfunction in women with advanced prolapse. Therefore, evaluation and treatment of women with lower urinary tract dysfunction and coexisting pelvic organ prolapse require special considerations. It is important to understand how prolapse may affect lower urinary tract function prior to initiating treatment for either prolapse or urinary symptoms. This is essential when weighing risks against benefits of prolapse correction in a patient who is not bothered by the prolapse itself. Conservative and surgical treatment options are available to address lower urinary tract disorders and prolapse. Treatment plans are generally individualized and determined not just by clinical diagnoses, but also by treatment goals, a patient's age, her level of activity and overall medical condition as well as her preference for treatment. Physicians providing care for women with complex pelvic floor disorders should be familiar with an array of treatment options.

Color-opponent receptive fields derived from independent component analysis of natural images.

Independent Component Analysis (ICA) of images of natural scenes has been shown to generate basis functions, or filters, which resemble spatial [Bell & Sejnowski (1997). Vision Research, 37, 3327-3338; van Hateren & van der Schaaf (1998). Proceedings of the Royal Society of London B, 265, 359-366] and spatiotemporal [van Hateren & Ruderman (1998) Proceedings of the Royal Society of London B, 265, 2315-2320] receptive fields of simple cells of the striate cortex. ICA yields statistically independent components which provide for a redundancy-reduced representation of the data. Using one of several published algorithms [Lee (1998). Independent component analysis: theory and applications. Boston; Kluwer Academic], we applied linear ICA to color images of natural scenes. The resulting independent component filters (ICFs) separate into either luminance or color filters. The luminance filters are localized and oriented edge detectors as reported previously. The color filters resemble either blue-yellow or red-green double-opponent receptive fields with various orientations. An equal number of each type of filter (luminance, red-green, and blue-yellow) is obtained. Thus, ICA predicts that spatiochromatic information is coded in statistically independent luminance, blue-yellow, and red-green opponent pathways with a relatively equal representation and specific spatial profiles at the cortical level.

Cost of cone coupling to trichromacy in primate fovea.

Cone synaptic terminals couple electrically to their neighbors. This reduces the amplitude of temporally uncorrelated voltage differences between neighbors. For an achromatic stimulus coarser than the cone mosaic, the uncorrelated voltage difference between neighbors represents mostly noise; so noise is reduced more than the signal. Here coupling improves signal-to-noise ratio and enhances contrast sensitivity. But for a chromatic stimulus the uncorrelated voltage difference between neighbors of different spectral type represents mostly signal; so signal would be reduced more than the noise. This cost of cone coupling to encoding chromatic signals was evaluated using a compartmental model of the foveal cone array. When cones sensitive to middle (M) and long (L) wavelengths alternated regularly, and the conductance between a cone and all of its immediate neighbors was 1,000 pS (approximately 2 connexons/cone pair), coupling reduced the difference between the L and M action spectra by nearly fivefold, from about 38% to 8%. However, L and M cones distribute randomly in the mosaic, forming small patches of like type, and within a patch the responses to a chromatic stimulus are correlated. In such a mosaic, coupling still reduced the difference between the L and M action spectra, but only by 2.4-fold, to about 18%. This result is independent of the L/M ratio. Thus "patchiness" of the L/M mosaic allows cone coupling to improve achromatic contrast sensitivity while minimizing the cost to chromatic sensitivity.

Lower urinary tract injury during the Burch procedure: is there a role for routine cystoscopy?

OBJECTIVE: This study was undertaken to evaluate the use of intraoperative cystoscopy for the detection of incidental bladder or ureteral injuries during abdominal urethropexy procedures and to determine whether the incidence of injuries warrants the routine use of cystoscopy. METHODS: We reviewed the medical records of 109 consecutive patients who underwent abdominal urethropexy procedures between November 1990 and February 1996 at a teaching institution. Each underwent intraoperative cystoscopy. We determined the incidence of cystotomy and ureteral obstruction and attempted to determine surgical factors that might be associated with an increased risk of injury. RESULTS: Ten of 109 patients (9%) had bladder or ureteral injury, including 1 cystotomy during retropubic dissection, 6 cases of a transvesical suture noted during cystoscopy, 1 cystotomy recognized before closure, 1 case of ureteral obstruction found during cystoscopy, and 1 case of ureteral obstruction not recognized at cystoscopy. Cystoscopy allowed detection of 7 of 9 (78%) otherwise unrecognized events. The only injury that resulted in significant postoperative morbidity was the unrecognized ureteral obstruction. There was no association between incidence of lower urinary tract injuries and surgical risk factors. CONCLUSION: Intraoperative bladder or ureteral injuries during urethropexy procedures are not uncommon, with an incidence of 9% in our series. There is minimal morbidity if these injuries are detected and corrected during the operation, whereas morbidity may be significant if they remain unrecognized. With a potential for unrecognized injury in 8% of Burch procedures without the use of cystoscopy, routine use of cystoscopy during urethropexy procedures appears to be warranted.

Transmitter concentration at a three-dimensional synapse.

Transmitter concentration at a three-dimensional synapse. J. Neurophysiol. 80: 3163-3172, 1998. At intensities from starlight to 1000-fold brighter, the mammalian rod synapse transmits a binary signal, the capture of 0 or 1 photon. Zero is signified by tonic exocytosis, and 1 is signified by a brief pause. The synapse is three dimensional: vesicles discharge at the apex of a deep cleft created by the invagination of four postsynaptic processes. Two horizontal cell spines bearing alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors reach near to the release sites (16 nm), and two bipolar dendrites bearing mGluR6 receptors end far from the release sites (up to 640 nm). We considered two hypotheses for signal transfer: transmitter quanta might be integrated in the cleft and sensed as a steady concentration (high for 0 and low for 1); or quanta might be sensed at the postsynaptic membrane as discrete postsynaptic potentials (PSPs) and integrated within the dendrite. We calculate from a passive diffusion model that the invagination empties rapidly (tau approximately 1.7 ms). Further calculations suggest that a glutamate concentration high enough to hold a bipolar cell in darkness at one end of its response range would require approximately 4,000 vesicles/s. On the other hand, the glutamate pulse from a single vesicle would reach both nearby AMPA receptors (low affinity) and distant mGluR6 receptors (high affinity) at spatiotemporal concentrations matched to their apparent binding affinities. Thus one vesicle could evoke a discrete PSP in all four postsynaptic processes. We calculate from a stochastic model that PSPs could transfer the binary signal at approximately 100 vesicles/s. Thus dendritic integration of unitary PSPs is both plausible and 40-fold more efficient than the alternative mechanism. The rod's deep invagination, rather than serving to pool transmitter, may serve to prevent "spillover" of transmitter to neighboring rods. Spillover, by pooling the noise from neighboring rods, would impair transmission of their binary signals.

Parallel cone bipolar to on-beta ganglion cell pathways in the cat retina: spatial responses, spatial aliasing, and spatial variance.

An important issue in understanding the retina is finding candidate functional roles for different cell pathways and the details of their anatomy and physiology. We consider various spatial properties of the three main cone ==> cone bipolar cell ==> on-beta ganglion cell pathways in the cat retina and possible roles for the particulars of their anatomy. The cone bipolar cells in these pathways have distinct morphologies and modest differences in their convergence, divergence, densities, and synaptic weighting; and it is unclear whether the pathways differ in their spatial properties or in some other manner. Since differences in spatial processing of cells are best studied on a systemwide level, we developed the multirate filter-based method of retinal modeling, a technique for relating the anatomy of multiple cell layers to its systemic effects. We demonstrate that (1) despite the anatomic distinctions among the three main cone bipolar cell pathways, their spatial responses are essentially identical; (2) despite the spatial averaging in the pathways, there is essentially no filtering of the nonaliasing signal components after the cone layer; (3) instead, this averaging combined with prefiltering by the eye's optics and cone gap junctions prevents spatial aliasing; and (4) the averaging and prefiltering combined allow cell responses to be similar despite significant cell-to-cell anatomic differences.

How retinal microcircuits scale for ganglion cells of different size.

Ganglion cell receptive field centers are small in central retina and larger toward periphery. Accompanying this expansion, the distribution of sensitivity across the centers remain Gaussian, but peak sensitivities decline. To identify circuitry that might explain this physiology, we measured the density of bipolar cell synapses on the dendritic membrane of beta (X) and alpha (Y) ganglion cells and the distribution of dendritic membrane across their dendritic fields. Both central and peripheral beta cells receive bipolar cell synapses at a density of approximately 28/100 microns2 of dendritic membrane; central and peripheral alpha cells receive approximately 13/100 microns2. The distribution of dendritic membrane across the dendritic field is dome-like; therefore, the distribution of bipolar cell synapses is also dome-like. As the dendritic field enlarges, total postsynaptic membrane increases with field radius, but only linearly. Consequently, density of postsynaptic membrane in the dendritic field declines, and so does density of synapses within the field. The results suggest a simple model in which the receptive field center's Gaussian profile and peak sensitivity are both set by the density of bipolar cell synapses across the dendritic field.

Mammalian rod terminal: architecture of a binary synapse.

The mammalian rod synapse transmits a binary signal (one photon or none) using tonic, rapid exocytosis. We constructed a quantitative, physical model of the synapse. Presynaptically, a single, linear active zone provides docking sites for approximately 130 vesicles, and a "ribbon" anchored to the active zone provides a depot for approximately 640 vesicles. Postsynaptically, 4 processes invaginate the terminal: 2 (known to have low affinity glutamate receptors) lie near the active zone (16 nm), and 2 (known to have high affinity glutamate receptors) lie at a distance (130-640 nm). The presynaptic structure seems designed to minimize fluctuations in tonic rate owing to empty docking sites, whereas the postsynaptic geometry may permit 1 vesicle to evoke an all-or-none response at all 4 postsynaptic processes.

Network simulations of retinal and cortical contributions to color constancy.

A biologically-based neural network simulation is used to analyze the contributions to color perception of each of several processing steps in the visual system from the retina to cortical area V4. We consider the effects on color constancy and color induction of adaptation, spectral opponency, non-linearities including saturation and rectification, and spectrally-specific long-range inhibition. This last stage is a novel mechanism based on cells which have been described in V4. The model has been tested with simulations of several well known psychophysical color constancy and color induction experiments. We conclude from these simulations the following: (1) a simple push-pull spectrally specific contrast mechanism, using large surrounds analogous to those found in V4, is very effective in producing general color constancy and color induction behavior; (2) given some spatio-temporal averaging, receptor adaptation can also produce a degree of color constancy; (3) spectrally opponent processes have spatial frequency dependent responses to color and brightness contrast which affect the contribution of the V4 mechanism to color constancy in images with nonuniform backgrounds; and (4) the effect of the V4 mechanism depends on the difference between center and surround while the effect of adaptation depends on the total sum of inputs from both center and surround and therefore the two stages cooperate to increase the range of stimulus conditions under which color constancy can be achieved.

A multistage neural network for color constancy and color induction.

A biologically-based multistage neural network is presented which produces color constant responses to a variety of color stimuli. The network takes advantage of several mechanisms in the human visual system, including retinal adaptation, spectral opponency, and spectrally-specific long-range inhibition. This last stage is a novel mechanism based on cells which have been described in cortical area V4. All stages include nonlinear response functions. The model emulates human performance in several psychophysical paradigms designed to test color constancy and color induction. We measured the amount of constancy achieved with both natural and artificial simulated illuminants, using homogeneous grey backgrounds and more complex backgrounds, such as Mondrians. On average, the model performs as well or better than the average human color constancy performance under similar conditions. The network simulation also displays color induction and assimilation behavior consistent with human perceptual data.

Rheology of the vitreous body: Part 2. Viscoelasticity of bovine and porcine vitreous.

The viscoelastic properties of the vitreous body from bovine and porcine eyes were determined by microrheometry. Each vitreous sample was sectioned into anterior, central and posterior segments. The rheological properties of each species and region were compared with each other and with the viscoelastic properties of human vitreous reported earlier. The results showed significant variations among species, as well as between regions in all species. All regions of human vitreous have significantly different rheological properties from those of the cow, and from the anterior and posterior regions of the pig; however, the viscoelastic behavior of the central porcine region closely resembles that of the human. In comparing the three species, the major differences found are in those parameters characterizing "viscous" or dissipative properties; values of "elastic" or energy storage properties were similar.

Rheology of the vitreous body: part 3. Concentration of electrolytes, collagen and hyaluronic acid.

The vitreous body from bovine, porcine, and human eyes was analyzed for concentration of selected components. Each vitreous sample was sectioned into anterior, central, and posterior segments. The segments were analyzed for concentration of Ca+2, Cl-, Na+, and K+, as well as of Collagen and Hyaluronic acid. The four electrolytes showed significant differences between species, but no significant regional variations. The two macromolecules showed significant differences with respect to both species and region within the vitreous. Comparison of these results with previously determined rheological values for the three species revealed a number of unexpected results, such as higher polymer concentrations on average being associated with lower values of viscosity parameters. The results are analyzed in terms of possible compositional differences among species and effects of electrolytes on the viscoelastic behavior of the vitreous' macromolecules.

Rate of quantal transmitter release at the mammalian rod synapse.

Under scotopic conditions, the mammalian rod encodes either one photon or none within its integration time. Consequently the signal presented to its synaptic terminal is binary. The synapse has a single active zone that releases neurotransmitter quanta tonically in darkness and pauses briefly in response to a rhodopsin isomerization by a photon. We asked: what minimum tonic rate would allow the postsynaptic bipolar cell to distinguish this pause from an extra-long interval between quanta due to the stochastic timing of release? The answer required a model of the circuit that included the rod convergence onto the bipolar cell and the bipolar cell's signal-to-noise ratio. Calculations from the model suggest that tonic release must be at least 40 quanta/s. This tonic rate is much higher than at conventional synapses where reliability is achieved by employing multiple active zones. The rod's synaptic mechanism makes efficient use of space, which in the retina is at a premium.

Signal sampling and propagation through multiple cell layers in the retina: modeling and analysis with multirate filtering.

The retina is a multilayered structure. Each layer consists of one or more classes of cell, each at its own density and with its own anatomic and physiologic properties. Signals converge from many cells in one layer onto single cells in another layer, and a signal from a single cell diverges to many cells in the next layer. In this methods paper we develop a general approach to retinal analysis and modeling that incorporates multiple cell classes, their densities, and related anatomic properties. The method is based on multirate filtering, a branch of signal processing in which signals of different sampling rates are manipulated. By drawing a correspondence between cell density and signal sampling rate, we define multirate models that incorporate different cell densities, convergence, divergence, variation in dendritic field shape, cell-to-cell variation in synaptic weights, and other anatomic features. We develop the multirate approach and apply it to the cat cone-->cone bipolar CBb1-->on-beta ganglion cell pathway as an example. We calculate the spatial frequency responses of the CBb1 and on-beta cells based on the cone spatial frequency response and find that the attenuation of high frequencies in the cones prevents aliasing that would otherwise occur in CBb1 and on-beta cells. We compare the calculations with cat psychophysics. We show that the optics of the cat eye are insufficient in themselves for the prevention of aliasing in these cells; additional attenuation by the cone-cone gap junctions and the cone aperture is necessary. By including this postreceptoral filtering, we demonstrate that the highest spatial frequency that can be passed by the retina without aliasing is determined not always only by the densities of cones, bipolar cells, and ganglion cells but also by the synaptic and the dendritic weighting between these cells.

Efficient coding of natural time varying images in the early visual system.

We investigate the hypothesis that the early visual system efficiently codes natural time varying images, first by tracking part of the image, then by matching the spatiotemporal properties of the neural pathway to those of the tracked image. A representation for the time varying image is formulated which consists of two spatiotemporal components, a velocity field component and a stationary component. We show, using digitized sequences of natural images, that the spatiotemporal spectrum and other attributes of the image markedly differ before and after tracking. The temporal frequency bandwidth and velocity distribution of the velocity field component are diminished in the region of tracking and broaden with increasing eccentricity from this region. On the other hand, the spectrum of the stationary component is unaffected by tracking. Comparison of the properties of the tracked image to those of the M and P pathways suggests that each pathway transmits different attributes of the tracked image. A retinal architecture which varies with eccentricity also matches the properties of the tracked image.

Rheology of the vitreous body. Part I: Viscoelasticity of human vitreous.

The rheological properties of the vitreous body of the eye are believed to be a function of composition and to differ among species, as well as to vary regionally within the vitreous. These properties are essential to the mechanical functioning of the eye. Although there are gross, qualitative data on vitreous rheology available in the literature, quantitative rheological measurements on human vitreous and on eyes of other species are sparse and incomplete. The aim of the research reported in this series of papers is to study the rheological behavior of human, bovine, and porcine vitreous, to measure the macromolecular and electrolyte content of these samples, and to correlate and compare these values for the different species as a function of location in the vitreous. In this paper, the rheological model used to correlate viscoelasticity of the vitreous is presented, and a detailed description of the rheological instrumentation and methods of analysis used is given. Data on the rheological properties of human vitreous, as a function of location within the eye, are presented. The results show that in the human eye there are significant differences in a number of the viscoelastic parameters as a function of location within the vitreous body.

Temporal differences between color pathways within the retina as a possible origin of subjective colors.

We propose a model of temporal signal processing within the retina based on temporal differences between the color pathways which may explain the phenomenon of subjective color. We quantify the model by inferring impulse response functions from physiological data, and predict the output of the different color pathways to temporally modulated achromatic signals which produce the sensation of color. Certain achromatic temporally modulated signals create imbalances between the color pathways which are analogous to those produced by stationary chromatic signals.

Global spatiochromatic mechanism accounting for luminance variations in contrast sensitivity functions.

Psychophysical luminance and chromatic spatial contrast sensitivity functions (CSF's) exhibit a number of variations that depend on the average luminance of the stimulus grating. The contrast sensitivity at each spatial frequency and the maximum resolvable spatial frequency decrease with decreasing average luminance. Most prominently, luminance CSF's have peaks that shift toward lower frequencies, broaden, and disappear as luminance decreases. Chromatic CSF's are flat at low frequencies and do not exhibit luminance-related variations in shape. In this paper, we account for the luminance-dependent variations of CSF's by incorporating them into an earlier model that accounts for the basic high-luminance shapes of psychophysical luminance and chromatic spatial CSF's. These variations are modeled by increasing the spatial extent of a global center mechanism while decreasing the inhibitory effect of a global surround on that center. The results support the hypothesis that the global center mechanism changes size as a means of maintaining the dynamic range and controlling the signal-to-noise ratio as luminance varies.

Definitive irradiation in carcinoma of the vagina: long-term evaluation of results.

A retrospective analysis of 165 patients with histologically confirmed carcinoma of the vagina is reported. Actuarial disease-free 10-year survival was: Stage 0 (16 patients)--94%, Stage I (50 patients)--75%, Stage IIA (49 patients)--55%, Stage IIB (26 patients)--43%, Stage III (16 patients)--32%, Stage IV (8 patients)--0%. All but one of the in situ lesions were controlled with intracavitary therapy. Of the patients with Stage I disease, 86% showed no evidence of vaginal or pelvic recurrence. Most of them received interstitial or intracavitary therapy or both; the addition of external beam irradiation did not significantly increase survival or tumor control. In Stage IIA (paravaginal extension) 61% of the tumors were controlled with a combination of brachytherapy and external beam irradiation. Ten of 16 Stage III tumors were controlled in the pelvis. Two of the patients with Stage IV disease had no recurrence in the pelvis with relatively high doses of irradiation. The total incidence of distant metastases was 16% in Stage I, 30.6% in Stage IIA, 46.1% in Stage IIB, 62% in Stage III, and 50% in Stage IV. The dose of irradiation delivered to the primary tumor or the parametrial extension was critical in achieving successful results. The incidence of grade 2-3 complications (12%) is correlated with the stage of the tumor and type of treatment given. More effective irradiation techniques including the optimization of dose distribution by judicious combination of external irradiation and interstitial brachytherapy will be necessary to enhance loco-regional tumor control. The high incidence of distant metastases underscores the need for earlier diagnosis and effective systemic cytotoxic agents if survival is to be significantly improved in these patients.

Quantitative studies of color constancy.

In order to study color constancy, the color appearance of the center of a center-surround paradigm was measured by using multiple-alternative forced-response matching. The center was presented with (1) no surround, (2) an adjacent chromatic surround, or (3) a chromatic surround separated from the center by an achromatic gap. The center and the surrounds were presented under various simulated illuminants ranging from illuminant A to illuminant D75. We found that when no surround is present, color constancy fails; however, when surrounds are present, some degree of color constancy is displayed. We also found that color constancy is poor when chromatic induction is minimal. In addition, it was determined that, if the ratios of R, G, and B of the center to R, G, and B of the surround remain constant as the illuminant changes, color constancy results. (R, G, and B correspond to the outputs of the retinal color mechanisms).