Articles: biological-models.
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Clinical Trial
A graphic approach for prediction of arterial oxygen tension at different concentrations of inspired oxygen.
A rapid, simple method for predicting the arterial oxygen tension (PaO2) at any fractional concentration of inspired oxygen (FIO2) is presented. The method is based on a nomogram interrelating PaO2, arterial carbon dioxide tension (PaCO2) and FIO2, allowing rapid determination of the arterial to alveolar oxygen tension ratio a/A PO2. The applicability of the nomogram and its reliability for predicting the PaO2 at any FIO2 were studied prospectively in nine consecutive patients requiring mechanical ventilation (16 trials). ⋯ Retrospectively, we analyzed the nomogram's ability to predict the PaO2 +/- 9.6 mm Hg (2 SD) at varying FIO2. The overall sensitivity of this method was 85 percent (126 predictions out of 149 trials). We conclude that appropriate levels of supplemental oxygen can be rapidly and reliably chosen using the nomogram in selected patients.
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Comparative Study
Monotonic dichotomous regression estimates: a burn care example.
Methods for estimating a dichotomous response regression function are discussed. A smoothed nonparametric monotonic estimator is developed and a procedure for estimating its variance is given. In an institutional differences study, the probability of death from a burn injury is related to the severity of the burn injury for patients treated at several specialized burn care units.
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A chronic model for investigation of spinal anesthesia in the dog is described. This model incorporates the use of a chronically implanted catheter in the lumbar subarachnoid space. An 18-gauge thin-walled Crawford needle is passes percutaneously into the subarachnoid space. ⋯ Durations of motor blockade were longest for dibucaine and tetracaine, followed in order of decreasing duration by bupivacaine, lidocaine, chloroprocaine, and mepivacaine. The durations of subarachnoid conduction motor blockades in the dog are qualitatively similar to reported values for spinal anesthesia in man. Therefore, the technique described may provide a useful model to evaluate factors that may influence spinal anesthesia.
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The authors used the scanning electron microscope to study the surface ultrastructure of the ependyma in six control rabbits and six rabbits subjected to bilateral jugular vein ligation four to five days previously. Whereas in the control rabbits the mean CSF pressure was 27 mm H2O, it rose to 71.5 mm H2O in the experimental animals. The ependymal lining of the fourth ventricle, third ventricle and the inferior horn of the lateral ventricle was examined. ⋯ While a marked reduction in ciliary density and appearance of pits were noticeable in the former, almost total replacement of globular excrescences by pleomorphic microvilli was noted in the infundibular region. The morphological alterations in the ependyma that occurred in experimental animals suggested a modification in its function from a surface capable of propelling cerebrospinal fluid by ciliary movement to one capable of increased ependymoabsorption. Increased incidence of macrophage-like supraependymal cells was noted in the experimental rabbits.
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The multichannel cochlear prosthesis requires an electrode stimulus configuration which produces a stimulus field spatially localized to each electrode. In this paper, a three-dimensional discrete resistance model of the cochlea was developed which exhibits electrical response properties similar to those observed during electrical stimulation of the cochlea. The model results suggest that the spatial attenuation of current within the cochlea varies greatly in magnitude, depending on the stimulus configuration. ⋯ Therefore the efficacy with which a particular stimulus configuration differentially excites local terminal auditory nerve fiber populations cannot be deduced from scalar voltage measurements which have previously been recorded in the literature. Consequently physiological experiments were performed in the cat to measure the current distributions in the terminal nerve fiber region for monopolar and bipolar stimulation of the scala tympani, and also for stimulation between the scala tympani and the scala vestibuli. The mean length constants measured in the basal turn for these stimuli were found to be 12, 3, and 7.5 mm, respectively.