The effects of inhalation of a novel nitric oxide donor, DETA/NO, in a patient with severe hypoxaemia due to acute respiratory distress syndrome

Aerosolized NONOates have been investigated in animal models in acute pulmonary hypertension, but none have been used in humans. We report the first use of aerosolized diethylenetriamine nitric oxide adduct (DETA/NO), a NONOate, in a patient with severe acute respiratory distress syndrome. Both pulmonary vascular resistance index and mean pulmonary arterial pressure were reduced by a mean of 26% and 18% respectively after the administration of a single dose of DETA/NO (150 micromol). Intrapulmonary shunting also improved. There were no significant changes in systemic arterial pressure or arterial methaemoglobin concentration after DETA/NO inhalation. We conclude that DETA/NO aerosol produced selective pulmonary vasodilation, with an improvement in pulmonary haemodynamics and oxygenation, while having no measurable effect on the systemic circulation.

Determination of optimal data placement for psychometric function estimation: a computer simulation

Psychometric functions are used to relate the responses of a subject to physical stimuli in a variety of psychophysical tasks. However, it is time consuming to obtain data to determine a psychometric function if many stimulus levels and many trials are required. A computer simulation was conducted to determine the minimum number of data points needed for such a determination. The computer simulation also determined the optimal placements of the stimuli and the number of trials per datum point for psychometric function determinations. Results indicate that a 2-point sampling method with 30-50 trials per point at optimal locations can produce a psychometric function with accurate spread and threshold estimates in a yes-no paradigm. However, the 4-point sampling method yields statistically smaller variances of the estimates. For the 2-alternative forced-choice paradigm, at least 120 trials per point are needed for the 2-point sampling method's estimated parameters to differ from the known parameter values by less than 5%. The simulation results suggest that 3-alternative or 4-alternative forced-choice is preferable to 2-alternative. Furthermore, when a criterion-free paradigm is not required, the yes-no paradigm is a better procedure than m-alternative forced-choice for obtaining the corresponding psychometric function because of smaller standard deviation of the estimates and smaller number of trials/point required.

A systematic study of low-resolution recognition in protein--protein complexes

A comprehensive nonredundant database of 475 cocrystallized protein-protein complexes was used to study low-resolution recognition, which was reported in earlier docking experiments with a small number of proteins. The docking program GRAMM was used to delete the atom-size structural details and systematically dock the resulting molecular images. The results reveal the existence of the low-resolution recognition in 52% of all complexes in the database and in 76% of the 113 complexes with an interface area >4,000 A(2). Limitations of the docking and analysis tools used in this study suggest that the actual number of complexes with the low-resolution recognition is higher. However, the results already prove the existence of the low-resolution recognition on a broad scale.

C1 inhibitor removes the entire C1qr2s2 complex from anti-C1Q monoclonal antibodies with low binding affinities

Evidence is presented for a new C1 Inhibitor (C1 INH) function. C1 INH was capable of dislodging the entire C1qr2s2 complex from C1-activating substances that bound weakly to the globular heads of C1q. Two different mouse IgG1 monoclonal antibodies with different affinities for C1q globular heads were compared for their complement-activating properties in the presence of normal human serum. As expected the higher affinity monoclonal antibody (Qu) was more effective in binding C1q and causing C1-mediated C4b deposition. Unexpectedly, time responses of C1 (C1q) binding to immobilized 3C7 reached a peak then gradually decreased. However, C1q remained constantly bound to immobilized Qu. These results indicated that after C1 activation in human serum, the entire C1 complex (including C1q) was dislodged from 3C7, but not from immobilized Qu. The addition of purified C1 INH to purified C1, which had bound to immobilized 3C7, resulted in removal of C1 (C1q). Removal of the entire C1qr2s2 did not occur when C1 INH preparations were first neutralized by the addition of purified activated C1s. In summary, it is suggested that C1 INH plays a prominent role in dislodging the entire C1qr2s2 from immunoglobulin preparations which have a low binding affinity for the globular heads of C1q.

An efficient method for small field treatment dose calculation for stereotactic radiosurgery using a LINAC

The normal procedure for a physician-physicist team designing a treatment plan for multiarc stereotactic radiosurgery is the trial-and-error approach of changing the collimator size and the location of the isocenter of radiation and viewing the isodose curves on two-dimensional computed tomography (CT) or magnetic resonance imaging (MRI) image planes. Automatic optimization procedures have also been used to optimize beam weight or beam size. However, either process is very time consuming. To improve the speed of the dose calculation, a random sampling method has been proposed. Unfortunately, the sampled values of an objective function are different from one sample to another. Such a sampling method cannot be used in automatic optimization because the next move in an optimization process is based on the current and past objective function values. To this end, an adaptive method based on the size of the collimators is proposed and used to determine a small volume in the shape of a hollow sphere for which the dose is calculated. With an appropriate choice of an adaptive hollow sphere, the objective function calculated based on such a hollow sphere is the same as that calculated with the traditional three-dimensional (3-D) cube matrix. However, with the new adaptive method, the speed of calculating a dose can be improved by a factor of 4 to a factor of 100. Because of the improvement in the speed of calculating a treatment dose, the new adaptive hollow sphere method for calculating a treatment dose can be used routinely in designing a treatment plan.

Two-dimensional photonic-crystal vertical-cavity array for nonlinear optical image processing

We investigate the electromagnetic properties of a two-dimensional (2-D) photonic-crystal array of vertical cavities for use in nonlinear optical image processing. We determine the 2-D photonic band structure of the array, and we discuss how it is influenced by the degree of interaction between cavities. We study the properties of defects in the 2-D lattice and show that neighboring cavities interact through their overlapping wave functions. This interaction can be used to produce nearest-neighbor nonlinear Boolean functions such asand, or, and xor, which are useful for optical image processing. We demonstrate the use of 2-D photonic bandgap structures for image processing by removing noise from a sample image with a nearest-neighbor and function.

Estimating parameters for psychometric functions using the four-point sampling method

Although a psychometric function describing a subject's responses to some physical stimuli is of considerable value, characterizing such functions is time consuming and, hence, is not carried out routinely in psychophysical experiments. A principal reason for the lack of efficiency in characterizing a psychometric function is the use of sampling methods that either converge on a single point on the psychometric function, such as the PEST method, or which distribute observations uniformly over a wide range, such as the constant stimuli method. As an alternative, a multimodal four-point sampling method has been proposed [C. F. Lam, J. H. Mills, and J. R. Dubno, J. Acoust. Soc. Am. 99, 3689-3693 (1996)]. A psychometric function is then fitted to the four points (each with several trials) to estimate the threshold and slope parameters of the psychometric function. Adaptive methods, such as the up-down methods [H. Levitt, J. Acoust. Soc. Am. 49, 467-477 (1971)], can be used to provide good initial estimates of the threshold and spread parameters of a psychometric function described by a logistic function. In ongoing studies of age-related changes in auditory masking and discrimination, this new four-point sampling method has been applied to determine psychometric functions for absolute thresholds as a function of duration, thresholds in simultaneous and forward masking, frequency discrimination, and intensity discrimination in both young and aged human subjects. Results indicate that a reduction in data collection time of about 50% with no increase in variance can be achieved. This increase in efficiency applies to simple detection tasks by normal hearing subjects as well as to complex discrimination tasks by older subjects with hearing loss.

Relationship between external load and isolated myocyte contractile function with CHF in pigs

Past studies have demonstrated that the negative relationship between afterload and contractile performance of papillary muscles is shifted downward and to the left with the development of hypertrophy. However, it remained unclear whether a similar load-contractility relationship could be constructed for isolated myocytes, particularly with the development of congestive heart failure (CHF). Accordingly, the effect of incrementally increased external loads on the contractile performance of left ventricular (LV) myocytes isolated from pigs in the normal state (n = 5) and after the development of chronic supraventricular tachycardia (SVT)-induced CHF (SVT-CHF; 240 beats/min, 3 wk; n = 5) was examined. This study used precalibrated microspheres to impose a quantifiable load on isolated myocytes, and myocyte contractility was assessed by videomicroscopy. Steady-state unloaded extent of shortening was 5.4 +/- 0.2 microns in control myocytes (n = 80) and was significantly reduced in the myocytes with the development of SVT-CHF (4.4 +/- 0.2 microns, n = 93; P < 0.05). Inverse relationships between relative resistive load and myocyte contractile function were observed at both normal and CHF states (r2 > 0.85). For myocyte velocity of shortening, the slope of this relationship was significantly reduced in the SVT-CHF state compared with controls (-46.3 x 10(-6) and -34.6 x 10(-6) microns3.microN-1.s-1, respectively; P < 0.05). At higher relative resistive loads (> 0.18 x 10(-6) microN/microns2), the reduction in myocyte shortening extent under an equivalent relative resistive load was significantly greater in the SVT-CHF myocytes compared with controls (62.8 +/- 3.9 vs. 45.6 +/- 4.7%, respectively, P < 0.05). The present study demonstrated for the first time that a load-dependent relationship can be derived for intact isolated LV myocytes in both normal and CHF states. The defect in the capacity of SVT-CHF myocytes to respond to an increased relative resistive load is a likely contributory mechanism for the LV pump dysfunction that occurs in this model of CHF.

Decline in the endocochlear potential corresponds to decreased Na,K-ATPase activity in the lateral wall of quiet-aged gerbils

The ion transport-mediating enzyme, Na,K-ATPase, is abundantly present in the cochlear lateral wall. This enzyme is essential for the generation and maintenance of the endocochlear potential. Diminished enzyme activity has been observed previously in the lateral wall of quiet-aged gerbils. The present study was designed to investigate the impact of the age-related decline in Na,K-ATPase specific activity upon auditory function. Measures of the resting endocochlear potential value and the level of Na,K-ATPase specific activity were made in cochleae obtained from gerbils aged in quiet conditions. Analysis revealed a high degree of correspondence between the level of lateral wall Na,K-ATPase specific activity and the value of the endocochlear potential measured in the round window/turn 1 region of the cochlea. Nonlinear regression models showed a strong relationship between the age-related reductions in enzyme activity and the magnitude of the endocochlear potential. The data suggest that during metabolic presbyacusis a decrease in Na,K-ATPase specific activity can explain most, but not all, of the decline in the endocochlear potential.

Placement of observations for the efficient estimation of a psychometric function

Psychometric functions for different psychophysical tasks describe the relationship between physical stimuli and subjects' responses. Although a psychometric function is of considerable value, characterizing the function is time consuming and, hence, is not carried out routinely in psychophysical experiments. A principal reason for the lack of efficiency in characterizing the psychometric function is the use of unimodal (e.g., Gaussian and uniform) sampling methods. As an alternative, a multimodal four-point sampling method is proposed. A psychometric function is then fitted to the four data points (each with several trials) to estimate the threshold and slope parameters of the psychometric function. Results from three examples demonstrate that a 60% savings in data-collection time can be achieved.

Spatial characterization of contracting cardiac myocytes by computer-assisted, video-based image processing

The goals of the present study were to develop and validate a computer-assisted, video-based image processing (CAVIP) system to measure time-dependent changes in isolated myocyte geometry during contraction and to use the CAVIP system to examine spatial characteristics of the myocyte during contraction in normal myocytes and in myocytes after development of dilated cardiomyopathy (DCM). Myocytes were isolated from the left ventricles of five control pigs and five pigs that developed chronic tachycardia (240 beats/min; 3 wk)-induced DCM. Isolated myocytes were stimulated and recorded using a high-speed camera interfaced with a standard video recording system. There was a significant linear relation between the indexes of time-dependent changes in myocyte length as measured by a conventional video edge-detector system and by the CAVIP system (r > 0.96; P < 0.01). After this validation procedure, dynamic changes in myocyte width and profile area with DCM were examined. Myocyte resting profile area was 33% larger in DCM myocytes compared with controls. However, there was no difference in the rate of area change with contraction between the two groups. Percent changes in myocyte width and profile area at peak contraction were significantly lower in the DCM group (43 and 46% respectively, P < 0.05). Therefore, the present study demonstrated that the CAVIP system provides unique information on time-dependent changes in myocyte geometry during contraction, particularly with the development of cardiomyopathic disease.

Treatment planning optimization for multiple arcs stereotactic radiosurgery using a linear accelerator

PURPOSE

Multiarc stereotactic radiosurgery is a technique used to irradiate an intracranial tumor with minimal damage to the surrounding normal tissue. The purpose of this paper is to present a method for and the results from optimizing three dimensional (3D) treatment dose for multiarc stereotactic radiosurgery.

METHODS AND MATERIALS

The normal procedure for a physician-physicist team designing a treatment plan for multiarc stereotactic radiosurgery is the trial-and-error approach of changing the collimator size and the isocenter of radiation by viewing the isodose curves on a two dimensional (2D) computed tomography (CT) or magnetic resonance imaging (MRI) image plane. Not only is this time consuming, but the resulting treatment plan is not optimal in most, if not all, cases. One reason for such nonconformal isodose curves is that the same collimator size is used for all arcs. However, it is very difficult to determine manually the different collimator sizes for different arcs. A derivative free optimization method is used to optimize the collimator size for each arc, as well as the 3D coordinates of the isocenter(s).

RESULTS

One spherical and two ellipsoidal artificial tumors, and one actual tumor, were used to show the utilities of the optimization process. The 90% isodose curves resulting from optimization conform very well with the tumor; whereas the 90% isodose curves from the conventional method either do not envelop the entire tumor when the collimator size is too small, or a large volume of normal tissue is also irradiated by the 90% dose when the next larger collimator size is used.

CONCLUSIONS

When the collimator size for each arc and the location of the isocenters(s) are optimized in a multiarc stereotactic surgery treatment plan, the 90% isodose curve conforms to the tumor much better than when the same collimator size is used for all arcs.

A new sigmoidal function describing the small field dose profile data from a linear accelerator

Dose profile data from small circular fields have been used in treatment dose planning for stereotactic radiosurgery. Generally, a two-dimensional interpolation of the measured beam profiles from circular collimators is used to calculate the dose at any axial depth and radial distance from the central axis. Instead, the dose profile data can be transformed into a sigmoidal form. A new three parameter sigmoidal function was developed to fit the transformed (sigmoidal) dose profile data. The values of the three estimated parameters were found to follow either linearly or exponentially as a function of axial depth. Thus, instead of linear interpolation, these formulas can be used to calculate dose at any axial depth and radial distance from the central axis for circular collimators of various diameters. This new sigmoidal function provides another formula to describe dose profile data from circular collimator of small fields.

Confidence limits for maximum word-recognition scores

Clinical judgments are often made regarding whether maximum word-recognition scores (PBmax) are appropriate in relation to degree of sensorineural hearing loss. In order to determine if word recognition is significantly poorer than expected, it is necessary to consider the lower boundary of PBmax associated with a particular degree of hearing loss for speech materials commonly used to measure word recognition. The purpose of this experiment was to define a confidence limit for PBmax from Northwestern University Test #6 (NU-6) word-recognition scores obtained from a large group of young and aged subjects with confirmed cochlear hearing loss. Word-recognition scores at several speech levels were obtained from 407 ears with a wide range of pure-tone averages. Because the characteristics of the distribution of maximum scores are not known, a procedure was developed using computer simulations to approximate the distribution of word-recognition scores corresponding to PBmax and determine the 95% confidence limit (CL). Results of the simulation were confirmed by comparing means and standard deviations of PBmax derived from experimental and simulation data. Percentages of young and aged subjects with scores outside the 95% CL are equal to their proportions in the entire subject sample. If PBmax determined from a score-level psychometric function is poorer than the 95% CL, PBmax may be considered "disproportionately" poor in relation to the degree of hearing loss. One score measured at a single arbitrary suprathreshold level that is poorer than the 95% CL suggests that the score may underestimate PBmax and that word recognition should be measured at additional levels to obtain a more reasonable estimate of the listener's maximum word-recognition score.

Modeling the fine structure of the 2f1-f2 acoustic distortion product. I. Model development

The fine structure of the 2f1-f2 acoustic distortion product (ADP) as a function of frequency has been measured in human subjects and shows a series of sharp peaks and valleys (rippling) with peak-to-valley level differences of up to 15-20 dB. In order to delineate the cause of the ADP rippling pattern, a computer model was developed to simulate the behavior of the ADP, specifically the ADP fine structure. The ADP model includes the middle ear and cochlea. The middle ear was treated as a simple signal delivery system in both the forward and reverse directions. The ADP was assumed to be generated within the cochlea by nonlinear elements taken to be the outer hair cells (OHCs), and an array of ADP generators was used to simulate the OHCs along the basilar membrane (BM). The magnitude and phase of the output of each of the ADP generators were functions of the local responses of the two primary traveling waves. The traveling waves were calculated from a passive transmission line model of the BM using the WKB approximation, coupled to a second-order resonance to mimic the contribution from active OHC feedback. The system output of ADP in dB was proportional to the weighted vectorial sum of all the components, arriving at the stapes. Parameters such as lateral coupling and feedback gain were examined.

Modeling the fine structure of the 2f1-f2 acoustic distortion product. II. Model evaluation

In a previous article, a vector sum model was developed that successfully reproduces the ADP rippling pattern when a nonuniformity is introduced in the active damping factor, a parameter that is inversely related to the energy gain contribution of the outer hair cells [OHCs, Sun et al., J. Acoust. Soc. Am. 96, 2166-2174 (1994)]. Here, the mean of the damping factor is increased nonlinearly with input level, mimicking the saturation of the active feedback of the OHCs. The passive damping factor in the transmission line model was also nonlinearly increased with input level to reproduce the frequency shift of the peak of the traveling wave observed in experimental data. The resulting model simulates an ADP that is compatible with data from human subjects wherein the ADP fine structure does not saturate with level. Moreover, the model suggests that the shifting of the ADP pattern with level is a direct result of the peak shift of the traveling wave, thus implicating the nonlinear damping factors as the underlying basis of this phenomenon. The input/output (I/O) functions of the simulated ADP emissions at specific frequencies were also examined. The resulting functions show a variety of shapes, depending on the pattern of ADP fine structure around the I/O frequency, and the way the fine structure shifts as primary levels increase. These I/O functions are also similar to those observed in human subjects, even with regard to overall slopes which approximate one. Thus the model illustrates how cubic distortion generators coupled with damping on linearities can yield I/O function slopes on the order of one, rather than the expected three.(ABSTRACT TRUNCATED AT 250 WORDS)

Predictor-corrector with cubic spline method for spectrum estimation in Compton scatter correction of SPECT

In single photon emission computed tomography (SPECT), Compton scattered photons degrade image contrast and cause erroneous regional activity quantification. A predictor-corrector and cubic spline (PCCS) method for the compensation of Compton scatter in SPECT is proposed. Using spectral information recorded at four energy windows, the PCCS method estimates scatter counts at each window and constructs the scatter spectrum with cubic spline interpolation. We have shown in simulated noise-free situations that this method provides accurate estimation of scatter fractions. A scatter correction employing PCCS method can be implemented on many existing SPECT systems without hardware modification and complicated calibration.

An efficient method for computer-aided dosage form design

It is desirable to have slow-release dosage form to be taken once daily, or at most twice daily, as compared to three or four times in a single day. However, the existing computer-aided dosage form design method requires a large amount of computer time when applied to nonlinear disposition drugs. This large commitment of computer time makes it inconvenient to study the feasibility for prolonged-release products containing such drugs. Instead of evaluating all possible combinations of the amount of dose and release rates that produce acceptable steady-state plasma concentrations, only the contour of the dose-release rate domain needs to be determined. An image boundary tracking method has been used to determine such contours. When combined with several modifications of the numerical solution process, the acceptable dose and release rate constants can be determined efficiently. When this modified boundary tracking method was applied to phenytoin, which exhibits nonlinear disposition, the required computer time was reduced to about 5% of the previous method, making the dosage form feasibility assessment practical.

A method for the analysis of biological transduction phenomena

Biological transduction can be defined as the triggering of a cellular response by the binding of molecules of effector substances to specific cellular sites. An example of biological transduction, analyzed in this report, is the triggering of T-cell proliferation by the binding of T-cell growth factor (TCGF) to specific TCGF-binding sites on responsive T-cells. Sigmoidal or S-shaped curves often result when measurements of biological response are plotted as a function of concentration of effector substance. Such curves suggest that effector molecules must bind a critical number of cellular sites, and this critical number of bound complexes must undergo secondary events (cross-linking, association, internalization, second messenger release, etc.) in order to initiate the biological response. The method described here estimates the critical number of cellular sites (R) and the probability of these secondary events (PS/B) as follows: (1) The total number of cellular sites (N) is estimated from binding data, and the probabilities (PB) of effector molecules binding to a site are estimated from response data. (2) The response data are assumed to follow the summed binomial distribution function, which is equated to the incomplete beta function. (3) R and PS/B are estimated by applying nonlinear regression to the incomplete beta function. The T-cell data to which the method was applied gave N = 15,000, R = 5, and PS/B = 7.22 x 10(-4). These results show that the binding of very few TCGF molecules is required for activation of T-cells and that the probability of the secondary events leading to cell proliferation is much smaller than the probability of TCGF binding to T-cells. The method described can be used to analyze any biological transduction experiments where both binding and biological response data are available.

Effect of refraction on optical microscopic measurement of internal blood-vessel diameter and its correction

In optical microscopic measurement of internal blood-vessel diameters, the effect of refraction must be taken into account to ensure accuracy of the result. This effect is discussed and an analytical correction formula derived. Phantom blood vessels with known internal and external diameters were used to test the validity of the correction formula. The errors obtained prior to correction were reduced significantly after correction.

Diabetes-associated impairment of hepatic insulin receptor tyrosine kinase activity: a study of mechanisms

Insulin receptor tyrosine kinase activity solubilized from liver of control and streptozotocin diabetic rats was studied using histone H2b and poly-Glu-Tyr (4:1) as phosphoacceptors. Both substrates inhibited autophosphorylation and exogenous kinase activity when added before, but not after, receptor activation with ATP. When H2b was added before ATP, insulin stimulated exogenous kinase activity of diabetic-derived receptors was significantly higher (approximately 50%) than control values at low H2b concentrations, but significantly lower (approximately 50%) than control values at high H2b concentrations, suggesting a decrease in the apparent Km and maximal velocity of the diabetic receptor tyrosine kinase toward H2b. When receptors were allowed to maximally autophosphorylate before the addition of H2b, the maximal H2b kinase activity of diabetic-derived receptors was only approximately 25% lower than that of controls. These effects were not attributable to altered ATP kinetics. Insulin receptor kinase activity toward the substrate poly-Glu-Tyr (4:1) was unaltered by insulinopenic diabetes. Insulin receptor alpha-beta dimers were not detectable in either control or diabetic-derived preparations. We conclude that the impairment of hepatic insulin receptor kinase activity associated with insulinopenic diabetes reflects a decreased ability to maximally activate, which is enhanced when the receptor is activated in the presence of some substrates, e.g. H2b. Impaired signalling by the diabetic-derived receptor appears to be dependent on the type of substrate and its concentration.

Computer-assisted localization of nervous system injuries

Expert systems to assist in neurological diagnosis require a representation of anatomical relationships. In order to test one representational method, a prototype expert system was developed. It accepts patient signs of neurological dysfunction and identifies the site of nervous system injury. The system's knowledge base is contained in a semantic network which represents nervous system anatomy and the physical signs of injuries. When provided with an individual's physical signs, the network is searched by a simple algorithm; the anatomical locations which best explain the physical signs are the system's output. Medical expert systems which require anatomical reasoning can use a direct representation of spatial relationships to avoid the difficulties of encoding clinical associations in the form of If-Then rules.

Vaginal physiology in postmenopausal women: pH value, transvaginal electropotential difference, and estimated blood flow

Basal vaginal physiologic study, including pH values in various locations, transvaginal electropotential difference, and blood flow estimation, was done twice in a group of 34 untreated postmenopausal women. Plasma hormone levels (gonadotropins and estrogens) and vaginal cytology were also obtained to confirm the estrogen deficiency state. The pH values in the vaginal fornices were significantly lower than those in the middle portion of the vagina. Sexually active women had significantly lower pH values than sexually inactive women. The transvaginal electropotential difference and estimated blood flow values were lower than those of premenopausal women reported in the literature, indicating impaired vaginal transport mechanism and decreased vaginal blood flow. The close approximation of the data obtained in the two measurements one month apart attests the reproducibility of the methods used.

Denaturation behavior of antithrombin in guanidinium chloride. Irreversibility of unfolding caused by aggregation

The structural stability of the protease inhibitor antithrombin from bovine plasma was examined as a function of the concentration of guanidinium chloride (GdmCl). A biphasic unfolding curve at pH 7.4, with midpoints for the two phases at 0.8 and 2.8 M GdmCl, was measured by far-ultraviolet circular dichroism. Spectroscopic and hydrodynamic analyses suggest that the intermediate state which exists at 1.5 M GdmCl involves a partial unfolding of the antithrombin molecule that exposes regions of the polypeptide chain through which slow, intermolecular association subsequently takes place. The partially unfolded molecule can be reversed to its fully functional state only before the aggregation occurs. Upon return of the aggregated state to dilute buffer, the partially unfolded antithrombin remains aggregated and does not regain the spectroscopic properties, thrombin-inhibitory activity, or heparin affinity of the native inhibitor. This behavior indicates that the loss of the functional properties of the proteins is caused by the macromolecular association. Comparative experiments gave similar results for the human inhibitor. Analyses of bovine antithrombin in 6 M GdmCl indicated that the second transition reflects the total unfolding of the protein to a disulfide-cross-linked random coil. This transition is spectroscopically reversible; however, on further reversal to dilute buffer, the molecules apparently are trapped in the partially unfolded, aggregated, intermediate state. The results are consistent with the existence of two separate domains in antithrombin which unfold at different concentrations of GdmCl but do not support the contention that the thrombin-binding and heparin-binding regions of the protein are located in different domains [Villanueva, G. B., & Allen, N. (1983) J. Biol. Chem. 258, 14048-14053].

Low-dose oral contraception and blood pressure in women with a past history of elevated blood pressure

Sixty-one women with a past history of elevated blood pressure (high-risk group) associated with oral contraceptive use (27 patients), unknown etiology (17 patients), or preeclampsia (17 patients) used a low-dose oral contraceptive containing 0.4 mg of norethindrone and 35 micrograms of ethinyl estradiol for 3 to 24 months. The highest blood pressures recorded in the past were 141.0 +/- 14.9 (mean +/- SD) mm Hg systolic and 98.3 +/- 8.0 diastolic. Sixty-one women without a past history of elevated blood pressure (low-risk group), selected from a pool of 616 low-risk patients, were matched with the high-risk group for race, initial age, initial body weight, duration of use, history of smoking, and family history of hypertension. The blood pressures in the high-risk group before and after oral contraceptive therapy were significantly higher than those in the low-risk group. Despite these differences, the mean systolic and diastolic blood pressures in these two groups of women using the low-dose oral contraceptive did not rise when compared with their own baseline blood pressures. Five high-risk patients (8.2%) discontinued therapy because of the redevelopment of hypertension; however, blood pressures at discontinuance were comparable to the previous highest blood pressures.

Computer modeling of the recombination reaction of rhodopsin

Various mechanistic schemes for the recombination reaction of rhodopsin were designed and tested using computer modeling and simulation with data from kinetics experiments. The reaction schemes were mathematically modeled by systems of nonlinear first-order ordinary differential equations (ODEs) with unknown rate constants. Each model was fitted to the experimental data by using a modified simplex algorithm for parameter (rate constant) estimation and Gear's method for solving stiff systems of ODEs. The recombination reaction of rhodopsin was best modeled by branched, multistep reaction schemes which included formation of noncovalent complexes, acid-base equilibria, and acid and base-catalyzed dehydration of a Schiff base intermediate. The biochemical bases for these models are discussed.

The upper and lower bounds of rate constants for general mammillary compartment systems

The upper and lower bounds of rate constants for general mammillary three and four compartment systems have been derived. It is further proposed that the midpoints of the bounds can be used as initial estimates for parameter estimation. Numerical examples are given demonstrating the closeness of the calculated midpoints to the "known" rate constants of both the three and four compartment systems.

Discriminating somatic evoked potentials using a pairwise procedure

Generally, investigators use only the magnitude spectra of a signal for processing or for discriminant analysis, with the phase information discarded. However, it is not difficult to generate two different time domain signals having identical magnitude spectra in the frequency domain. Thus the phase information should not be neglected. This paper presents the results of a simulation study of a discriminant analysis procedure for paired variables, e.g. magnitude and phase pairs. The procedure is then applied to discriminating somatic evoked potentials from normal and damaged spinal cords with excellent results.

Classification of somatic evoked potentials through maximum entropy spectral analysis

Maximum entropy (ME) spectra are currently considered to be superior to spectra calculated by means of Fast Fourier Transforms (FFT) because the former offer higher resolution. However, in terms of classification of somatic evoked potentials (SEPs), FFT spectra are found to be better than ME spectra. An even better set of parameters for discriminating SEPs is the set of reflection coefficients derived in the process of calculating the ME spectra. They permit separation of SEPs obtained from monkeys with dorsal column lesion from SEPs obtained from normal monkeys, as well as distinguishing between SEPs obtained from large nerve fiber stimulation and SEPs from stimulation of all nerve fibers.

The effects of low spinal injury on the latencies of cortical evoked responses from forelimb stimulation

A previous report showed that following spinal cord transaction well below the C7 level in cats, later components of the cortical somatic evoked potential (SEP) (40 msec or longer) produced in response to median or radial nerve stimulation were abnormal (Katz et al., 1977). Evidence presented here shows that early components of the radial nerve SEP are also altered following spinal cord transection. Latencies of both early and late components were increased as higher functional transections of the spinal cord were made. This monotonic increase in latency of the primary components supports the hypothesis that the results may be due to increasing loss of excitatory input. Correlation of latency change with level of injury may serve as a useful diagnostic tool.

Automatic generation of steady state enzyme rate equation and the associated constraint equations

A computer algorithm is presented to derive initial velocity rate equation for general enzyme raction mechanisms, including sequential as well as complicated random mechanisms. The method is based on the theory of graph and the theory of prime number. In complicated mechanisms, there are many pathways and hence many cycles. The values of the rate constants are constrained according to the principle of detailed balance: the product of rate constants in the clockwise direction of a cycle must equal to the product of the rate constants in the counter-clockwise direction of the same cycle. An algorithm is presented to derive the appropriate constraint equations. These constraint equations are arranged so that when the rate equation is used for estimating rate constants, the resulting rate constants would satisfy the principle of detailed balance automatically.

The effects of low spinal injury on somatosensory evoked potentials from forelimb stimulation

Spinal cord transection below C6 in anesthetized cats results in an alteration in the configuration of the SEP following direct or percutaneous stimulation of the median or radial nerves. The most significant alterations were in components occurring at latencies from 40 to 60 msec. The results of these experiments support the general conclusion that the spinal cord and supraspinal structures act as a functional unit and that the SEP is not solely determined by input over segmental pathways In addition, the alteration in the SEP produced by median nerve stimulation following spinal cord injury below C6 may serve clinically as a monitor of events at the site of injury in cases where an SEP from lower limb stimulation is no longer obtainable.

Enzyme kinetics. Systematic generation of valid King-Altman patterns

One of the most generally applicable algorithms for the derivation of steady-state rate equations for complex enzyme reaction mechanisms is that of King and Altman. Several modifications of this algorithm have been suggested; however, each requires the generation of numerous valid and invalid patterns and the subsequent elimination of those that are invalid. A method is presented, employing topological theory of linear graphs, for the systematic generation of only those patterns which are valid. This method is readily adaptable to use on a digital computer. An independent method for the calculation of the number of valid patterns is also presented. This calculation can be used to substantiate the accuracy of the patterns obtained. This calculation is also adaptable to computerization. Examples are included to demonstrate both the generation of patterns and the calculation of their number for specific enzyme mechanisms.