Synchrony suppression in complex stimulus responses of a biophysical model of the cochlea.

A minimal biophysical model of the cochlea is used to investigate the validity of the hypothesis that a single compressive nonlinearity at the hair cell level can explain some of the suppression phenomena in cochlear responses to complex stimuli. The dependencies of the model responses on the amplitudes and frequencies of two-tone stimuli resemble in many respects the behavior of the experimental data, and can be traced to explicit biophysical parameters in the model. Most discrepancies between theory and experiment stem from simplifications in parameters of the minimal model that play no direct role in the hypothesis. The analysis and simulations predict further results which, pending experimental verification, may provide a more direct test of the influence of the compressive nonlinearity on the relative amplitudes of the synchronous response components, and hence of its role in synchrony suppression. For instance, regardless of the overall absolute levels of a two-tone stimulus applied to this type of model, the ratio of the amplitudes at the input and the ratio of the corresponding responses at the output remain approximately constant and equal (the output ratio changes by at most 6 dB in favor of the stronger tone). Other nonlinear responses to multitonal stimuli can also be reproduced, such as "spectral edge enhancement" [Horst et al., Peripheral Auditory Mechanisms (Springer, Berlin, 1985)] and some aspects of three-tone suppression [Javel et al., Mechanisms of Hearing (Monash U.P., Australia, 1983)]. In contrast to the complex behavior of suppression with increasing sound intensity and the drastic influence of the compressive nonlinearity on the absolute response measures on the auditory nerve (e.g., average rate and synchrony profiles), the percepts of complex sounds are relatively stable. This suggests that the invariant relative response measures are more likely used in the encoding and CNS extraction of the spectrum of complex stimuli such as speech.

Localization of parathyroid adenomas in patients who have undergone surgery. Part I. Noninvasive imaging methods.

The authors evaluated computed tomography (CT), ultrasound (US), technetium/thallium scintigraphy, and magnetic resonance (MR) imaging as localization procedures in 53 patients with proved parathyroid adenomas and previous unsuccessful parathyroid surgery. CT had the highest overall sensitivity (47%), followed by US (36%) and scintigraphy (27%). There is still too little data to assess MR imaging. Adenoma size affected the sensitivity of CT, scintigraphy, and MR imaging but not US. When all three studies were used, at least one study depicted a lesion in 78% of patients, but definitive localization (two positive studies) was achieved in only 31%.

Localization of parathyroid adenomas in patients who have undergone surgery. Part II. Invasive procedures.

The authors studied intraarterial digital subtraction angiography (DSA), conventional selective angiography, parathyroid venous sampling (PVS), and intraoperative ultrasound (US) as localization procedures for parathyroid adenomas in 53 patients with proved parathyroid adenomas and previous unsuccessful parathyroid surgery. PVS had the highest overall sensitivity as a single study (80%), followed by intraoperative US (78%), angiography (60%), and DSA (49%). Invasive procedures permitted successful localization of adenomas in 41 of 43 patients studied (95%). False-positive studies were uncommon. The optimum sequence of invasive localization procedures is determined by clinical factors and not by the sensitivity of individual tests. The authors recommend DSA be performed first, followed by angiography, PVS, and intraoperative US, in that order.

A biophysical model of cochlear processing: intensity dependence of pure tone responses.

A mathematical model of cochlear processing is developed to account for the nonlinear dependence of frequency selectivity on intensity in inner hair cell and auditory nerve fiber responses. The model describes the transformation from acoustic stimulus to intracellular hair cell potentials in the cochlea. It incorporates a linear formulation of basilar membrane mechanics and subtectorial fluid-cilia displacement coupling, and a simplified description of the inner hair cell nonlinear transduction process. The analysis at this stage is restricted to low-frequency single tones. The computed responses to single tone inputs exhibit the experimentally observed nonlinear effects of increasing intensity such as the increase in the bandwidth of frequency selectivity and the downward shift of the best frequency. In the model, the first effect is primarily due to the saturating effect of the hair cell nonlinearity. The second results from the combined effects of both the nonlinearity and of the inner hair cell low-pass transfer function. In contrast to these shifts along the frequency axis, the model does not exhibit intensity dependent shifts of the spatial location along the cochlea of the peak response for a given single tone. The observed shifts therefore do not contradict an intensity invariant tonotopic code.

Performance of one- and two-dimensional models for a slow flow system in a long, permeable tubule.

A radially symmetric slow flow system in a long cylinder with moderate wall leakage is considered, with physical parameters taken from the renal proximal tubule. Dimensional analysis yields a simplified system which, under certain assumptions, is well-posed, and possesses a unique solution if a solution exists. A lumped parameter analysis generates a one-dimensional model identical to a typical one-dimensional model in a special case. The one- and two-dimensional models agree well in the situations examined. When the wall fluxes are of a certain class, the concentration to which the solution tends as the fluid proceeds down the tubule can be computed algebraically.

Lipid emulsions as contrast agents for hepatic sonography: an experimental study in rabbits.

An ultrasound contrast agent capable of increasing hepatic echogenicity would be useful for the detection of hepatic tumors and metastases. Fatty liver is known to produce increased liver echogenicity. Intravenously administered lipid emulsions are phagocytosed by cells of the reticuloendothelial system the liver with transient hepatic lipid accumulation. We examined the effectiveness of three lipid emulsions of differing particle size as potential ultrasound contrast agents using a rabbit liver model. None of the tested emulsions showed any consistent ability to alter liver echogenicity at maximum tolerable doses. Lipid emulsions do not appear to have potential as contrast agents for ultrasound examination of the liver.

Vertebral bone mineral content in osteogenesis imperfecta.

Quantitative computed tomography of the lumbar spine was carried out in 28 patients with osteogenesis imperfecta (OI) in order to measure vertebral trabecular bone mineral concentration (BMC). The patients ranged in age from 6-73 years, and included 3 of the 4 major clinical subtypes of the disease. The findings underscore the heterogeneity of osteogenesis imperfecta even among family members with the same disease type. In addition, cross-sectional analysis of Type I OI patients suggests that BMC during young adulthood averages about 70% of normal, and subsequently falls more rapidly than in normal patients. BMC tends to be lower in the more severe forms of OI. Decreased BMC was not found in a few otherwise normal relatives with scoliosis or joint laxity.

Nutrient foramina in the phalanges of the hands.

The normal distribution and size of nutrient foramina in the terminal and middle phalanges of the fingers, which appear as radiolucencies on hand radiographs, is described. In a study based on the antero-posterior (AP) hand films of 218 patients, we found no evidence that the foramina were more frequently seen in childhood. When age is disregarded in statistical analysis, the foramina are more frequently observed in women than in men. In both sexes foramina are seen most often in the middle phalanges. We have found that the upper limit of normal of foraminal diameters is 1 mm (uncorrected for enlargement) and this permits recognition of enlargement of the foramina which can occur in disorders such as Gaucher's disease, sickle cell anemia and thalassemia.

Vertebral body bone mineral content in hyperprolactinemic women.

Hyperprolactinemia with amenorrhea and galactorrhea generally has a benign clinical course without treatment. Prolonged amenorrhea due to early surgical castration or premature menopause is, however, associated with reduced bone mass and increased risk of fractures. Previous studies in hyperprolactinemic women suggested an association with decreased cortical bone density. To determine whether hyperprolactinemia is associated with reduced trabecular bone mineral, we studied 13 hyperprolactinemic women and matched normal women by quantitative computed tomographic scans of the vertebral bodies. No patient had taken bromocriptine and one patient had previously unsuccessful transsphenoidal surgery. Each patient was matched with a normal woman on the basis of race, age +/- 52 weeks, parity, exercise, tobacco use, oral contraceptive (OCP) use, and alcohol use. No subject was currently taking OCPs. Calcium, phosphorus, and protein intakes were estimated from a 3-day diet diary. The mean duration of amenorrhea was 98.9 +/- 79.7 (SD) months. The mean height, weight, serum 25-hydroxyvitamin D (25,OHD), serum 1,25 dihydroxyvitamin D [1,25(OH)2D] and daily intakes of calcium, phosphorus, and protein were not different. The bone mineral content for each patient fell within +/- SD of the mean of the normal subjects. The mean bone mineral content (mg K2HPO4 eq/ml) of the patients was 10% less than in the normal subjects (144.6 +/- 31.4 (SD) vs. 160.1 +/- 26.6, P less than 0.05). The slope of the regression of bone mineral content and age (mg K2HPO4 eq/ml X yr) was similar in patients (-2.4 +/- 1.1) and normal subjects (-2.3 +/- 1.0). We conclude that hyperprolactinemia is associated with reduced bone mineral content, but does not necessarily produce persistent acceleration of the age-related decline in bone density.

Use of a microcomputer to store information on radiology cases.

A microcomputer program for storage of qualitative patient data has been applied to CT and special procedures case data. Different vocabularies have been established and utilised for these two case categories. Experience over two years involving more than 10,000 cases is discussed. Utility for statistical, research, and patient care purposes is demonstrated.

Characterization of tongue shape.

Mathematical techniques are described for analyzing tongue shapes obtained with ultrasound images. The surface of the mid-sagittal section of the tongue was approximated by discrete points. In turn, these points were used to approximate position, slope and curvature of the tongue surface at a fixed time during speech. Two approaches were employed. The first method involved the use of finite difference approximations to derivatives of the function of tongue position. The second utilized a curve fit. Both methods were examined for reliability. Results of these analyses on a simple, single speech sound are discussed.

A microcomputer approach to storage of qualitative patient data using key words.

A microcomputer program is presented which stores and retrieves qualitative patient information, such as diagnosis and physical findings. Users can design and enter a key word list and modify it as needed. Using those key words, up to 5000 patient entries can be made on a single floppy disk. Application of the program to CT scan study results is discussed.