Cuffed endotracheal tubes in children reduce sevoflurane and medical gas consumption and related costs.

BACKGROUND: This study aims to evaluate sevoflurane and anaesthetic gas consumption using uncuffed vs. cuffed endotracheal tubes (ETT) in paediatric surgical patients. METHODS: Uncuffed or cuffed ETT were used in paediatric patients (newborn to 5 years) undergoing elective surgery in a randomized order. Duration of assessment, lowest possible fresh gas flow (minimal allowed FGF: 0.5 l/min) and sevoflurane concentrations used were recorded. Consumption and costs for sevoflurane and medical gases were calculated. RESULTS: Seventy children (35 uncuffed ETT/35 cuffed ETT), aged 1.73 (0.01-4.80) years, were enrolled. No significant differences in patient characteristics, study period and sevoflurane concentrations used were found between the two groups. Lowest possible FGF was significantly lower in the cuffed ETT group [1.0 (0.5-1.0) l/min] than in the uncuffed ETT group [2.0 (0.5-4.3) l/min], P<0.001. Sevoflurane consumption per patient was 16.1 (6.4-82.8) ml in the uncuffed ETT group and 6.2 (1.1-14.9) ml in the cuffed ETT group, P=0.003. Medical gas consumption was 129 (53-552) l in the uncuffed ETT group vs. 46 (9-149) l in the cuffed ETT group, P<0.001. The total costs for sevoflurane and medical gases were 13.4 (6.0-67.3)euro/patient in the uncuffed ETT group and 5.2 (1.0-12.5)euro/patient in the cuffed ETT group, P<0.001. CONCLUSIONS: The use of cuffed ETT in children significantly reduced the costs of sevoflurane and medical gas consumption during anaesthesia. Increased costs for cuffed compared with uncuffed ETT were completely compensated by a reduction in sevoflurane and medical gas consumption.

Pioneer venus radar mapper experiment.

Altimetry and radar scattering data for Venus, obtained from 10 of the first 13 orbits of the Pioneer Venus orbiter, have disclosed what appears to be a rift valley having vertical relief of up to 7 kilometers, as well as a neighboring, gently rolling plain. Planetary oblateness appears unlikely to exceed 1/2500 and may be substantially smaller.

Structural and functional organization of a diencephalic sensory-motor interface in the gymnotiform fish, Eigenmannia.

The diencephalic nucleus electrosensorius (nE) of gymnotiform fish comprises a series of finely tuned neuronal filters for control of the jamming avoidance response (JAR) and probably other electromotor tasks as well. The nE receives electrosensory input from the dorsal torus semicircularis (TSd) and octavolateral input from the ventral torus (TSv). The nE, in turn, projects to various hypothalamic and thalamic nuclei, including the prepacemaker nucleus (PPn), which can modulate the frequency of electric organ discharges (EODs) via its unique input to the medullary pacemaker nucleus. Four subdivisions of the nE can now be recognized: 1) The beat-related area (nEb)--a rostral cluster of tightly packed cells which receives TSd input and projects to the inferior lobe, anterior tuberal nucleus, anterior thalamic nucleus, central posterior thalamic nucleus, and PPn. The nEb contains neurons responsive to beat patterns caused by jamming stimuli. Stimulation of the nEb with L-glutamate, however, fails to induce any EOD-frequency shift. 2) The area causing EOD-frequency rises (nE increases)--a horizontal band of cells at the dorsal aspect of the caudal nE which receives TSd input and projects to the PPn and vicinity and to the cerebellum; nE increases stimulation induces slow EOD-frequency rises characteristic of the JAR. Responses of these cells to jamming stimuli are not yet known. 3) The area causing EOD-frequency falls (nE decreases)--a horizontal band of cells at the ventral aspect of the caudal nE which receives TSd input and projects only to the PPn and vicinity; nE decreases stimulation induces slow EOD-frequency falls characteristic of the JAR. The responses of these cells to jamming stimuli are not yet known. 4) The acousticolateral region (nEar)--a complex medial region of the nE which receives input predominantly from the ventral torus and projects to the inferior lobe, anterior tuberal nucleus, central posterior thalamic nucleus, PPn, and cerebellum; the sensory and motor properties of this region are not known in detail, although auditory and mechanosensory responses have been recorded here. Projections to the PPn and its vicinity suggest direct control of electromotor behaviors by the nE, whereas thalamic and hypothalamic projections may provide a substrate for electrosensory influences on neuroendocrine and motivational control centers. The optic tectum projects strongly to the pretectum and various other diencephalic nuclei in the vicinity of the nE, but it does not innervate the nE itself. Accordingly, ablation of the tectum does not affect the performance of the JAR.

An anatomical substrate for the inhibitory gradient in the VLVp of the owl.

The interaural difference in the level of sounds is an important cue for the localization of the sound's source. In the barn owl, a keen auditory predator, this binaural cue is first computed in the nucleus ventralis lemnisci laterale, pars posterior (VLVp), a cell group found within the fibers of the lateral lemniscus. Its neurons are excited by inputs from the contralateral ear and inhibited by inputs to the ipsilateral ear and are therefore sensitive indicators of interaural level difference. The excitation arrives by a direct input from the contralateral nucleus angularis, a cochlear nucleus, and the inhibition is mediated by a commissural projection that interconnects the VLVps of the two sides. The dorsally located neurons in the VLVp are more heavily inhibited than those found more ventrally, thus giving rise to a gradient of inhibition. This inhibitory gradient plays a central role in recent models of VLVp function. We present evidence based on standard anterograde tracing methods that this gradient of inhibition is mediated by a dorsoventral gradient in the density of synaptic inputs from the contralateral VLVp, the source of inhibition. Specifically, injection of tracers into one VLVp, regardless of the position of the injection within the nucleus, produced a vertically oriented field of label that was densest along the dorsal margin of the contralateral VLVp and became sparser a more ventral levels. Furthermore, we found that injections into the medial and lateral aspects of the nucleus produced this dorsoventrally graded field of label along the medial and lateral aspects of the contralateral VLVp, respectively. Finally, we confirmed an earlier observation suggesting that the anterior and posterior aspects of one VLVp project to the anterior and posterior aspects of the contralateral nucleus, respectively.

The treatment of hypercholesterolemia with beta-pyridylcarbinol. Part 5. Report on 16 cases with severe hypercholesterolemia treated for 12 years.

A group of 78 patients with severe hypercholesterolemia (-X = 464 mg/dl) and symptoms of vascular disease of the heart, the extremities, or the brain, started a beta-pyridylcarbinol treatment with an average daily dosage of 1.2 g in 1964. In 1976 we could re-examine 12 patients, still on the same therapy. No myocardial infarction has occurred in this group since 1973, only 2 patients have had more attacks of angina pectoris that 1964. In contrast patients discontinuing therapy or replacing beta-pyridylcarbinol by other hypolipidemic drugs had a higher mortality.

Spontaneous discharge of afferents in a neuroma reflects original receptor tuning.

Injured afferent axons trapped in chronic nerve-end neuromas frequently generate spontaneous discharge. We asked whether the patterns of discharge originating at such sites of ectopic electrogenesis bear a consistent relationship to the patterns of discharge characteristic of the corresponding intact afferent types before injury. Nerve-end neuromas were created in electrosensory lateral line nerves in 3 species of weakly electric Gymnotiform fish. Species were chosen in which normal afferent activity occurs at highly characteristic, non-overlapping, species-specific frequencies. Afferent impulse discharge was recorded in vivo from lateral line nerve end neuromas using the nerve-teasing technique. The distribution of firing frequencies of spontaneously active neuroma afferents was relatively uniform within a given fish species, and differed significantly from species to species. Mean values were somewhat lower than for corresponding intact afferents, but the rank order of frequencies across the species was preserved. These data indicate that differential membrane remodelling after axotomy tends to reestablish normal afferent fiber tuning despite failure of regeneration, and in the absence of peripheral electroreceptor reinnervation.

Na+ channel accumulation on axolemma of afferent endings in nerve end neuromas in Apteronotus.

In mammals, cut sensory axons trapped in a nerve end neuroma have been shown to develop hyperexcitability, and to become a source of ectopic afferent discharge and abnormal sensation. We have explored cellular mechanisms underlying neuroma electrogenesis. First we confirmed that ectopic neuroma discharge develops in injured afferents in the electrosensory lateral line nerve of the weakly electric fish Apteronotus, as it does in mammals. Then, using previously characterized antibodies that specifically recognize Na+ channel proteins in this species, we obtained light and electron microscopic evidence of abnormally intense immunolabelling of axolemma at the injury site. Accumulation of excess Na+ channels in afferent endings in neuromas could account for their electrical hyperexcitability.

Head-related transfer functions of the barn owl: measurement and neural responses.

Sounds arriving at the eardrum are filtered by the external ear and associated structures in a frequency and direction specific manner. When convolved with the appropriate filters and presented to human listeners through headphones, broadband noises can be precisely localized to the corresponding position outside of the head (reviewed in Blauert, 1997). Such a 'virtual auditory space' can be a potentially powerful tool for neurophysiological and behavioral work in other species as well. We are developing a virtual auditory space for the barn owl, Tyto alba, a highly successful auditory predator that has become a well-established model for hearing research. We recorded catalogues of head-related transfer functions (HRTFs) from the frontal hemisphere of 12 barn owls and compared virtual and free sound fields acoustically and by their evoked neuronal responses. The inner ca. 1 cm of the ear canal was found to contribute little to the directionality of the HRTFs. HRTFs were recorded by inserting probetube microphones to within about 1 or 2 mm of the eardrum. We recorded HRTFs at frequencies between 2 and 11 kHz, which includes the frequencies most useful to the owl for sound localization (3-9 kHz; Konishi, 1973). Spectra of virtual sounds were within +/- 1 dB of amplitude and +/- 10 degrees of phase of the spectra of free field sounds measured near to the eardrum. The spatial pattern of responses obtained from neurons in the inferior colliculus were almost indistinguishable in response to virtual and to free field stimulation.

Head-related transfer functions of the Rhesus monkey.

Head-related transfer functions (HRTFs) are direction-specific acoustic filters formed by the head, the pinnae and the ear canals. They can be used to assess acoustical cues available for sound localization and to construct virtual auditory environments. We measured the HRTFs of three anesthetized Rhesus monkeys (Macaca mulatta) from 591 locations in the frontal hemisphere ranging from -90 degrees (left) to 90 degrees (right) in azimuth and -60 degrees (down) to 90 degrees (up) in elevation for frequencies between 0.5 and 15 kHz. Acoustic validation of the HRTFs shows good agreement between free field and virtual sound sources. Monaural spectra exhibit deep notches at frequencies above 9 kHz, providing putative cues for elevation discrimination. Interaural level differences (ILDs) and interaural time differences (ITDs) generally vary monotonically with azimuth between 0.5 and 8 kHz, suggesting that these two cues can be used to discriminate azimuthal position. Comparison with published subsets of HRTFs from squirrel monkeys (Saimiri sciureus) shows good agreement. Comparison with published human HRTFs from the frontal hemisphere demonstrates overall similarity in the patterns of ILD and ITD, suggesting that the Rhesus monkey is a good acoustic model for these two sound localization cues in humans. Finally, the measured ITDs in the horizontal plane agree well between -40 degrees and 40 degrees in azimuth with those calculated from a spherical head model with a radius of 52 mm, one-half the interaural distance of the monkey.

Long-term performance summary for the Boot Wetland Treatment System.

The Boot WTS is a 46.5-ha, hydrologically altered cypress-gum wetland in Polk County, Florida. Poinciana Wastewater Treatment Plant No. 3 has discharged advanced secondary treated effluent to the Boot WTS since August 1984. Comprehensive operational monitoring has been ongoing since 1990. The Boot WTS has provided consistent removal of nitrogen and phosphorus. Influent total nitrogen (TN) and total phosphorus (TP) concentrations averaged approximately 10.0 mg/L and 2.5 mg/L at an average hydraulic loading rate (HLR) of 0.2 cm/d. Wetland effluent concentrations for TN and TP averaged 1.8 mg/L and 1.2 mg/L. Available flow and water quality data were used to develop estimates of the first-order removal rate, k, for TN (14 m/y) and TP (1.8 m/y). These removal rates are within the range of values for other forested treatment wetlands. Biochemical oxygen demand (2.2 mg/L) and total suspended solids (4.9 mg/L) in the influent are near background levels for forested wetlands and are not significantly reduced with passage through the system.

Object localization in cluttered acoustical environments.

In nature, sounds from objects of interest arrive at the ears accompanied by sound waves from other actively emitting objects and by reflections off of nearby surfaces. Despite the fact that all of these waveforms sum at the eardrums, humans with normal hearing effortlessly segregate one sound source from another. Our laboratory is investigating the neural basis of this perceptual feat, often called the "cocktail party effect", using the barn owl as an animal model. The barn owl, renowned for its ability to localize sounds and its spatiotopic representation of auditory space, is an established model for spatial hearing. Here, we briefly review the neural basis of sound-localization of a single sound source in an anechoic environment and then generalize the ideas developed therein to cases in which there are multiple, concomitant sound sources and acoustical reflection.

Stimulus discrimination in the diencephalon of Eigenmannia: the emergence and sharpening of a sensory filter.

Neuronal reliability and sensitivity to behaviorally relevant stimulus patterns were investigated in a higher-order nucleus of the diencephalon believed to participate in the jamming avoidance response (JAR) of the weakly electric fish, Eigenmannia. The fish raises or lowers its frequency of electric organ discharge (EOD) to minimize interference from a neighboring fish's EOD. Proper JARs require determination of the sign of the difference frequency (Df) between the neighboring fish's EOD and the fish's own EOD. Bastian and Yuthas (1984) recently described diencephalic neurons within the nucleus electrosensorius that are able to make this determination. In the present study, response properties of such neurons were compared with those of lower-level 'sign-selective' cells found in the torus semicircularis and the optic tectum (Heiligenberg and Rose 1985) as well as with properties of the intact behavior. Most sign-selective cells within the nucleus electrosensorius show a high degree of selectivity for one sign of the difference frequency; cells with either sign preference were found in approximately equal numbers. The sign preference and the degree of sign selectivity is most often independent of the spatial orientation of the jamming stimulus. In contrast, the responses of toral and tectal cells are less robust and consistent and are often highly dependent on the geometry of the jamming stimulus. Determination of the sign of the difference frequency requires the analysis of amplitude modulations coupled with modulations in phase (timing) differences between pairs of areas of the body surface. The most sensitive cells recorded in the nucleus electrosensorius can determine the sign of the difference frequency with timing differences of 1 microsecond or less, roughly comparable to the behavioral threshold of 400 ns (Carr et al. 1986). The best toral/tectal response required at least a 16 microseconds modulation. Cells within the nucleus electrosensorius thus code the sign of Df with a high degree of reliability and sensitivity. Ambiguities persist, however, which suggest that single cells at this level cannot completely account for the behavioral discrimination. Additional processing may be necessary to transform a still primarily sensory code into a motor program for control of the JAR (Rose et al. 1988).

From distributed sensory processing to discrete motor representations in the diencephalon of the electric fish, Eigenmannia.

During their jamming avoidance response (JAR), weakly electric fish of the genus Eigenmannia shift their electric organ discharge (EOD) frequency away from a similar EOD frequency of a neighboring fish. The behavioral rules and neural substrates for stimulus recognition and motor control of the JAR have been extensively studied (see review by Heiligenberg 1986). The diencephalic nucleus electrosensorius (nE) links sensory processing within the torus semicircularis and optic tectum with the mesencephalic prepacemaker nucleus which, in turn, modulates the medullary pacemaker nucleus and hence the EOD frequency. Two separate areas within the nE responsible for JAR-related EOD frequency rises and frequency falls, respectively, were identified by iontophoresis of the excitatory amino acid L-glutamate. Bilateral lesion of the areas causing EOD frequency rises resulted in elimination of JAR-related frequency rises above a baseline frequency obtained in the absence of a jamming stimulus. Similarly, bilateral lesion of the areas causing frequency falls resulted in a loss of JAR-related frequency falls below the baseline frequency. Whether these areas are also responsible for non-JAR-related frequency shifts is not known. The strength of response and spatial extent of the areas causing frequency shifts varied among fish and also varied in individual fish, reflecting the strength of JAR-related frequency shifts and the balance of activities in frequency-rise and frequency-fall areas. Local application of bicuculline-methiodide or GABA demonstrated a tonic inhibitory input to each area and suggests a reciprocal inhibitory interaction between the two ipsilateral areas, possibly accounting for much of the individual plasticity. The nE thus is a site for neuronal transformation from distributed, topographically organized processing within the laminated structures of the torus and tectum to discrete cell clusters which control antagonistic motor responses.

Commissural connections mediate inhibition for the computation of interaural level difference in the barn owl.

In the barn owl (Tyto alba), the posterior nucleus of the ventral lateral lemniscus (VLVp) is the first site of binaural convergence in the pathway that processes interaural level difference (ILD), an important sound-localization cue. The neurons of VLVp are sensitive to ILD because of an excitatory input from the contralateral ear and an inhibitory input from the ipsilateral ear. A previously described projection from the contralateral cochlear nucleus, can account for the excitation. The present study addresses the source of the inhibitory input. We demonstrate with standard axonal transport methods that the left and right VLVps are interconnected via fibers of the commissure of Probst. We further show that the anesthetization of one VLVp renders ineffective the inhibition that is normally evoked by stimulation of the ipsilateral ear. Thus, one cochlear nucleus (driven by the ipsilateral ear) appears to provide inhibition to the ipsilateral VLVp by exciting commissurally-projecting inhibitory neurons in the contralateral VLVp.

Representation of multiple sound sources in the owl's auditory space map.

The barn owl's inferior colliculus contains a retina-like map of space on which a sound generates a focus of activity whose position corresponds to the location of the sound source. When there is more than one source of sound, the sound waves sum and may generate spurious binaural cues that degrade the auditory image. We investigated the signal conditions under which neurons in the owl's auditory space map are able to resolve two simultaneously active sound sources. We recorded from space map neurons responding to sounds from a pair of speakers separated in azimuth by 45 degrees and mounted on a rotatable arm. Stimuli consisted of a sum of sinusoids or pseudorandom noise bursts emitted simultaneously and at equal overall levels. The characteristics of the sounds in each speaker were varied, and the neuron's response was plotted as a function of the speaker pair's position. When the speakers emitted different sets of summed sinusoids, the cells responded to each speaker separately; that is, the cells were able to resolve two separate targets. However, when the speakers emitted identical summed sinusoids generating binaural cues that were identical to those of a single phantom source between the two speakers, the neurons responded when the speakers were on either side of their receptive fields. By manipulating the amplitude at which each speaker emitted the various frequencies, we could control the position, number, and size of the phantom sources detected by the cell. The cells also resolved two separate sources when they emitted noise bursts that were statistically independent or temporally reversed versions of one another. Since the overall spectra of such waveforms are identical, we suggest that the space map relies on differences between noise bursts that exist over brief time spans.

Simulated motion enhances neuronal selectivity for a sound localization cue in background noise.

In nature, sound sources move and signals are accompanied by background noise. Noting that motion helps the perception of visual stimuli, we tested whether motion similarly facilitates the detection of acoustic targets, at the neuronal level. Auditory neurons in the central nucleus of the barn owl's inferior colliculus (ICc), due to their selectivity for interaural phase difference (delta phi), are sharply tuned to the azimuth of sound sources and are arrayed to form a topographic map of delta phi. While recording from single ICc neurons, we presented tones that simulated either moving or stationary sound sources with and without background noise. We found that the tuning of cells in the ICc for delta phi was sharper for stimuli that simulated motion than for those that simulated stationary targets. The neurons signaled the presence of a tone obscured by noise better if the tone moved than if the tone remained stationary. The resistance to noise observed with moving stimuli could not be reproduced with the temporal modulation of the stimulus amplitude, suggesting that a change of position over time was required.

Representation of temporal features of complex sounds by the discharge patterns of neurons in the owl's inferior colliculus.

The spiking pattern evoked in cells of the owl's inferior colliculus by repeated presentation of the same broadband noise was found to be highly reproducible and synchronized with the temporal features of the noise stimulus. The pattern remained largely unchanged when the stimulus was presented from spatial loci that evoke similar average firing rates. To better understand this patterning, we computed the pre-event stimulus ensemble (PESE)-the average of the stimuli that preceded each spike. Computing the PESE by averaging the pressure waveforms produced a noisy, featureless trace, suggesting that the patterning was not synchronized to a particular waveform in the fine structure. By contrast, computing the PESE by averaging the stimulus envelope revealed an average envelope waveform, the "PESE envelope," typically having a peak preceded by a trough. Increasing the overall stimulus level produced PESE envelopes with higher amplitudes, suggesting a decrease in the jitter of the cell's response. The effect of carrier frequency on the PESE envelope was investigated by obtaining a cell's response to broadband noise and either estimating the PESE envelope for each spectral band or by computing a spectrogram of the stimulus prior to each spike. Either method yielded the cell's PESE spectrogram, a plot of the average amplitude of each carrier-frequency component at various pre-spike times. PESE spectrograms revealed surfaces with peaks and troughs at certain frequencies and pre-spike times. These features are collectively called the spectrotemporal receptive field (STRF). The shape of the STRF showed that in many cases, the carrier frequency can affect the PESE envelope. The modulation transfer function (MTF), which describes a cell's ability to respond to time-varying amplitudes, was estimated with sinusoidally amplitude-modulated (SAM) noises. Comparison of the PESE envelope with the MTF in the time and frequency domains showed that the two were closely matched, suggesting that a cell's response to SAM stimuli is largely predictable from its response to a noise-modulated carrier. The STRF is considered to be a model of the linear component of a system's response to dynamic stimuli. Using the STRF, we estimated the degree to which we could predict a cell's response to an arbitrary broadband noise by comparing the convolution of the STRF and the envelope of the noise with the cell's post-stimulus time histogram to the same noise. The STRF explained 18-46% of the variance of a cell's response to broadband noise.

Responses to simulated echoes by neurons in the barn owl's auditory space map.

The natural acoustical environment contains many reflective surfaces that give rise to echoes, complicating the task of sound localization and identification. The barn owl (Tyto alba), as a nocturnal predator, relies heavily on its auditory system for tracking and capturing prey in this highly echoic environment. The external nucleus of the owl's inferior colliculus (ICx) contains a retina-like map of space composed of "space-specific" auditory neurons that have spatially limited receptive fields. We recorded extracellularly from individual space-specific neurons in an attempt to understand the pattern of activity across the ICx in response to a brief direct sound and a simulated echo. Space-specific neurons responded strongly to the direct sound, but their response to a simulated echo was suppressed, typically, if the echo arrived within 5 ms or less of the direct sound. Thus we expect there to be little or no representation within the ICx of echoes arriving within such short delays. Behavioral tests using the owl's natural tendency to turn their head toward a sound source suggested that owls, like their space-specific neurons, similarly localize only the first of two brief sounds. Naive, untrained owls were presented with a pair of sounds in rapid succession from two horizontally-separated speakers. With interstimulus delays of less than 10 ms, the owl consistently turned its head toward the leading speaker. Longer delays elicited head turns to either speaker with approximately equal frequency and in some cases to both speakers sequentially.

Binaural cross-correlation predicts the responses of neurons in the owl's auditory space map under conditions simulating summing localization.

Summing localization describes the perceptions of human listeners to two identical sounds from different locations presented with delays of 0-1 msec. Usually a single source is perceived to be located between the two actual source locations, biased toward the earlier source. We studied neuronal responses within the space map of the barn owl to sounds presented with this same paradigm. The owl's primary cue for localization along the azimuth, interaural time difference (ITD), is based on a cross-correlation-like treatment of the signals arriving at each ear. The output of this cross-correlation is displayed as neural activity across the auditory space map in the external nucleus of the owl's inferior colliculus. Because the ear input signals reflect the physical summing of the signals generated by each speaker, we first recorded the sounds at each ear and computed their cross-correlations at various interstimulus delays. The resulting binaural cross-correlation surface strongly resembles the pattern of activity across the space map inferred from recordings of single space-specific neurons. Four peaks are observed in the cross-correlation surface for any nonzero delay. One peak occurs at the correlation delay equal to the ITD of each speaker. Two additional peaks reflect "phantom sources" occurring at correlation delays that match the signal of the left speaker in one ear with the signal of the right speaker in the other ear. At zero delay, the two phantom peaks coincide. The surface features are complicated further by the interactions of the various correlation peaks.