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PubMedDate not supplied

Laparoscopic closure of the nephrosplenic space for prevention of recurrent nephrosplenic entrapment of the ascending colon.

OBJECTIVE: To evaluate outcome after laparoscopic closure of the nephrosplenic space in horses that had previous nephrosplenic entrapment of ascending colon (left dorsal displacement of the left colon; LDDLC). STUDY DESIGN: Retrospective study. SAMPLE POPULATION: Horses that had previous LDDLC. METHODS: Medical records of horses that had LDDLC and subsequent laparoscopic nephrosplenic space closure between 2002 and 2004 were retrieved. Follow-up information was obtained by telephone interview of owners. Preoperative versus postoperative comparisons were: incidence of LDDLC, incidence of colic signs, and incidence of ventral celiotomy. Data were analyzed using a chi2-square test with significance set at P<.05. RESULTS: Ten horses met the inclusion criteria. Mean follow-up was 22 months. No horses had recurrence of LDDLC; however, 3 horses had colic signs subsequently that required surgical intervention. Over the follow-up period there was a significant decrease in the total incidence of colic and ventral celiotomy. Technique modifications included use of different cannula site locations, use of polyglyconate suture material for nephrosplenic space closure, and development of a custom cannula. CONCLUSIONS: Laparoscopic nephrosplenic space closure prevented recurrence of LDDLC, and significantly lowered the overall incidence of colic and ventral celiotomy. The custom-designed cannula provided good access to the operative site and no complications were encountered with use of polyglyconate suture material for nephrosplenic space closure. CLINICAL RELEVANCE: Closure of the nephrosplenic space will prevent LDDLC; however, other surgical lesions can occur.

Animals↗
PubMed2003

Troponin I in the murine myocardium: influence on length-dependent activation and interfilament spacing.

Cyclic AMP-dependent protein kinase (PKA) targets contractile proteins, troponin-I (TnI) and myosin binding protein C (MyBP-C) in the heart and induces a decrease in myofilament Ca2+ sensitivity. Yet, the effect of sarcomere length (SL) change on Ca2+ sensitivity (length-dependent activation: LDA) following PKA-dependent phosphorylation is not clear. To clarify the role of PKA-dependent phosphorylation of TnI and MyBP-C on LDA in the heart, we examined LDA in skinned myocytes from a non-transgenic (NTG) and a transgenic murine model in which the native cardiac isoform (cTnI) was completely replaced by the slow skeletal isoform of TnI (ssTnI-TG) lacking the phosphorylation sites for PKA, while retaining PKA sites on MyBP-C. In NTG myocytes, PKA treatment decreased Ca2+ sensitivity at each SL, but enhanced the impact of SL change on Ca2+ sensitivity. Despite a greater sensitivity to Ca2+ and a reduction in LDA, neither Ca2+ responsiveness nor LDA was affected by PKA treatment in ssTnI-TG myocytes. To determine whether the above observations could be explained by the lateral separation between thick and thin filaments, as suggested by others, we measured interfilament spacing by X-ray diffraction as a function of SL in skinned cardiac trabeculae in the passive state from both NTG and ssTnI-TG models before and following treatment with PKA. Phosphorylation by PKA increased lattice spacing at every SL in NTG trabeculae. However, the relationship between SL and myofilament lattice spacing in ssTnI-TG was markedly shifted downward to an overall decreased myofilament lattice spacing following PKA treatment. We conclude: (1) PKA-dependent phosphorylation enhances length-dependent activation in NTG hearts; (2) replacement of native TnI with ssTnI increases Ca2+ sensitivity of tension but reduces length-dependent activation; (3) MyBP-C phosphorylation by PKA does not alter calcium responsiveness and induces a decrease in myofilament lattice spacing at all sarcomere lengths and (4) length-dependent activation in the heart cannot be entirely explained by alterations in myofilament lattice spacing.

Actin Cytoskeleton↗
PubMed2002

A k-space method for coupled first-order acoustic propagation equations.

A k-space method for large-scale simulation of ultrasonic pulse propagation is presented. The present method, which solves the coupled first-order differential equations for wave propagation in inhomogeneous media, is derived in a simple form analogous to previous finite-difference methods with staggered spatial and temporal grids. Like k-space methods based on second-order wave equations, the present method is exact for homogeneous media, unconditionally stable for "slow" [c(r) < or = c0] media, and highly accurate for general weakly scattering media. In addition, unlike previous k-space methods, the form of the method allows straightforward inclusion of relaxation absorption and perfectly matched layer (PML) nonreflecting boundary conditions. Numerical examples illustrate the capabilities of the present k-space method. For weakly inhomogeneous media, accurate results are obtained using coarser temporal and spatial steps than possible with comparable finite-difference and pseudospectral methods. The low dispersion of the k-space method allows accurate representation of frequency-dependent attenuation and phase velocity associated with relaxation absorption. A technique for reduction of Gibbs phenomenon artifacts, in which compressibility and exponentially scaled density functions are smoothed by half-band filtering, is introduced. When employed together with this smoothing technique, the k-space method provides high accuracy for media including discontinuities, high-contrast inhomogeneities, and scattering structures smaller than the spatial grid resolution.

Acoustics↗
PubMed2006

Developmental and cross-linguistic variation in the infant vowel space: the case of Canadian English and Canadian French.

This article describes the results of two experiments. Experiment 1 was a cross-sectional study designed to explore developmental and cross-linguistic variation in the vowel space of 10- to 18-month-old infants, exposed to either Canadian English or Canadian French. Acoustic parameters of the infant vowel space were described (specifically the mean and standard deviation of the first and second formant frequencies) and then used to derive the grave, acute, compact, and diffuse features of the vowel space across age. A decline in mean F1 with age for French-learning infants and a decline in mean F2 with age for English-learning infants was observed. A developmental expansion of the vowel space into the high-front and high-back regions was also evident. In experiment 2, the Variable Linear Articulatory Model was used to model the infant vowel space taking into consideration vocal tract size and morphology. Two simulations were performed, one with full range of movement for all articulatory paramenters, and the other for movement of jaw and lip parameters only. These simulated vowel spaces were used to aid in the interpretation of the developmental changes and cross-linguistic influences on vowel production in experiment 1.

Child Language↗
PubMed2002

The retrotracheal space: normal anatomic and pathologic appearances.

A variety of diseases can arise from the normal contents of the retrotracheal space or from adjacent structures. Mediastinal diseases in the retrotracheal space typically manifest radiographically as a contour abnormality or an area of increased opacity, although computed tomography (CT) or magnetic resonance (MR) imaging is usually required for diagnosis. The most common aortic arch anomaly, a right subclavian artery that originates from an otherwise normal left-sided aortic arch, appears at posteroanterior chest radiography as an obliquely oriented soft-tissue area of increased opacity that extends superiorly to the right from the superior margin of the aortic arch. CT and MR imaging can reveal associated vascular or mediastinal abnormalities. Aortic aneurysms and pseudoaneurysms can manifest radiographically as fusiform or saccular masslike lesions that protrude into the retrotracheal space. Thoracic MR imaging and spiral CT angiography are the diagnostic procedures of choice for evaluating diverse pathologic conditions of the thoracic aorta. Esophageal diseases can manifest as an abnormality in the retrotracheal space, which may be the initial clue to the diagnosis. At CT, lymphatic malformations in the mediastinum manifest as lobular, multicystic tumors that surround and infiltrate adjacent mediastinal structures. Familiarity with the normal radiologic appearance of the retrotracheal space and with the clinical manifestations of diseases that affect the retrotracheal space and adjacent structures can facilitate detection, diagnosis, and management.

Aortic Arch Syndromes↗
PubMed1998

Estimation of specific hepatic arterial water space.

The aim of this study was to estimate the specific arterial water space and associated blood flow using statistical moments of the frequency versus time outflow profile, with a model with specific spaces for hepatic arterial (HA) and portal venous (PV) flows in parallel with a common space. Studies were performed in the in situ dual-perfused rat liver (n = 6-10), using Krebs-bicarbonate buffer with constant PV flow (12 ml/min) and various HA flow rates (3-6 ml/min). An impulse input-output technique was employed, varying the route of input, using [14C]urea as the reference indicator. Regardless of flow conditions, the frequency outflow profile after HA input was flatter and broader and the mean transit time longer than after PV input. Excellent recovery of marker was obtained in all cases. Applying the above model, the specific arterial space was estimated to be 9.7 +/- 2.3 of total water space and receives approximately 17% of the HA flow, with the remainder mixing with portal blood in the common space. The estimated total water content of liver (0.67-0.72 ml/g liver) agrees well with that determined by desiccation (0.72 +/- 0.01 ml/g liver).

Animals↗
PubMed1987

Liquid thickness vs. vertical pressure gradient in a model of the pleural space.

In recent studies using relatively noninvasive techniques, the vertical gradient in pleural liquid pressure was 0.2-0.5 cmH2O/cm ht, depending on body position, and pleural liquid pressure closely approximated lung recoil (J. Appl. Physiol. 59: 597-602, 1985). We built a model to discover why the vertical gradient in pleural pressure is less than hydrostatic (1 cmH2O/cm). A long rubber balloon of cylindrical shape was inflated in a plastic cylinder. The "pleural" space between the balloon and cylinder was filled with blue-dyed water. With the cylinder vertical, we measured pleural pressure by a transducer through side taps at 2-cm intervals up the cylinder. The pressure was measured with different amounts of water in the pleural space. With a clear separation between the balloon and the container, the vertical gradient in pleural liquid pressure was hydrostatic. As water was withdrawn from the pleural space, the balloon approached the wall of the container. Over an 8-cm-long midregion of the model where the balloon diameter matched the cylinder diameter, the vertical gradient was not hydrostatic and was virtually absent. In this region, the pleural liquid pressure was uniform and equal to the recoil of the balloon. In this section we could not see any pleural space. By scintillation imaging using 99mTc-diethylenetriamine pentaacetic acid in the water, we estimated the thickness of this flat "costal" pleural space to be approximately 20 microns. Radioactive tracer injected at the top of the pleural space appeared by 24 h at the bottom, which indicated a slow drainage of liquid by gravity.(ABSTRACT TRUNCATED AT 250 WORDS)

Body Fluids↗
PubMed1989

Protein clearance from the air spaces and lungs of unanesthetized sheep over 144 h.

We studied the rate, the routes, and the mechanisms for protein clearance from the air spaces and lungs of 20 unanesthetized sheep over 144 h. We instilled 100 ml of autologous serum labeled with 125I-albumin into one lung. At the end of 24, 48, 96, or 144 h, the lungs were removed and the residual native protein and 125I-albumin in the air spaces were determined by bronchoalveolar lavage. Also the fraction of the instilled 125I-albumin remaining in the rest of the lung was measured in the lung homogenate. Clearance of the 125I-albumin from the lung into the plasma, lymph, thyroid, urine, and feces was also determined. The removal of both the 125I-albumin and the native protein from the air spaces was slow, following a monoexponential decline. The removal rate of the 125I-albumin from the air spaces was slightly but significantly faster (1.6%/h) than the clearance rate of the native protein (0.9%/h). Clearance of the 125I-albumin from the lung also followed a slow monoexponential decline at a rate of 1.4%/h. At all time periods, 75% of the 125I-albumin remaining in the lung was located in the air spaces, thus indicating that the pulmonary epithelium is the principal barrier to protein clearance from the normal lung. Macrophages appeared to play a minor role in alveolar protein clearance because the quantity of 125I-albumin present in the phagocytic cells in the air spaces was less than 1% of the instilled 125I-albumin at all time periods. However, macrophages may play some role in protein clearance after 48 h because we visualized phagolysosomes in macrophages, and there was an increase in free iodine in lung lavage, urine, thyroid, and feces after 48 h. However, gel electrophoretic studies showed that most of the 125I-albumin was cleared from the lung as an intact molecule, although only 24.7 +/- 4.7% of the 125I-albumin was cleared by the lymphatics.

Animals↗
PubMed2003

Space-time maps and two-bar interactions of different classes of direction-selective cells in macaque V-1.

We used one-dimensional sparse noise stimuli to generate first-order spatiotemporal maps and second-order two-bar interaction maps for 65 simple and 124 complex direction-selective cells in alert macaque V1. Spatial and temporal phase differences between light and dark space-time maps clearly distinguished simple and complex cell populations. Complex cells usually showed similar direction preferences to light and dark bars, but many of the directional simple cells were much more direction selective to one sign of contrast than the reverse. We show that this is predicted by a simple energy model. Some of the direction-selective simple cells showed multiple space-time-slanted subregions, but others (previously described as S1 cells) had space-time maps that looked like just one subregion of an ordinary simple cell. Both simple and complex cells showed directional interactions (nonlinearities) to pairs of flashed bars (a 2-bar apparent-motion stimulus). The space-time slant of the simple cells correlated with the optimum dX/dT (velocity) of the paired-bar interactions. Some complex cells also showed a space-time slant; the direction of the slant usually correlated with the preferred direction of motion, but the degree of slant correlated with the inferred velocity tuning only when measured by a weighted-centroid calculation. Principal components analysis of the simple-cell space-time maps yielded one fast temporally biphasic component and a slower temporally monophasic component. We saw no consistent pattern for the spatial phase of the components, unlike previous reports; however, we show that principal components analysis may not distinguish between spatial offsets and phase offsets.

Algorithms↗
PubMed1996

Coding of peripersonal space in inferior premotor cortex (area F4).

1. We studied the functional properties of neurons in the caudal part of inferior area 6 (area F4) in awake monkeys. In agreement with previous reports, we found that the large majority (87%) of neurons responded to sensory stimuli. The responsive neurons fell into three categories: somatosensory neurons (30%); visual neurons (14%); and bimodal, visual and somatosensory neurons (56%). Both somatosensory and bimodal neurons typically responded to light touch of the skin. Their RFs were located on the face, neck, trunk, and arms. Approaching objects were the most effective visual stimuli. Visual RFs were mostly located in the space near the monkey (peripersonal space). Typically they extended in the space adjacent to the tactile RFs. 2. The coordinate system in which visual RFs were coded was studied in 110 neurons. In 94 neurons the RF location was independent of eye position, remaining in the same position in the peripersonal space regardless of eye deviation. The RF location with respect to the monkey was not modified by changing monkey position in the recording room. In 10 neurons the RF's location followed the eye movements, remaining in the same retinal position (retinocentric RFs). For the remaining six neurons the RF organization was not clear. We will refer to F4 neurons with RF independent of eye position as somatocentered neurons. 3. In most somatocentered neurons (43 of 60 neurons) the background level of activity and the response to visual stimuli were not modified by changes in eye position, whereas they were modulated in the remaining 17. It is important to note that eye deviations were constantly accompanied by a synergic increase of the activity of the ipsilateral neck muscles. It is not clear, therefore, whether the modulation of neuron discharge depended on eye position or was a consequence of changes in neck muscle activity. 4. The effect of stimulus velocity (20-80 cm/s) on neuron response intensity and RF extent in depth was studied in 34 somatocentered neurons. The results showed that in most neurons the increase of stimulus velocity produced an expansion in depth of the RF. 5. We conclude that space is coded differently in areas that control somatic and eye movements. We suggest that space coding in different cortical areas depends on the computational necessity of the effectors they control.

Animals↗
PubMed1998

Neurotransmitter involvement in development and maintenance of the auditory space map in the guinea pig superior colliculus.

Neurotransmitter involvement in development and maintenance of the auditory space map in the guinea pig superior colliculus. J. Neurophysiol. 80: 2941-2953, 1998. The mammalian superior colliculus (SC) is a complex area of the midbrain in terms of anatomy, physiology, and neurochemistry. The SC bears representations of the major sensory modalites integrated with a motor output system. It is implicated with saccade generation, in behavioral responses to novel sensory stimuli and receives innervation from diverse regions of the brain using many neurotransmitter classes. Ethylene-vinyl acetate copolymer (Elvax-40W polymer) was used here to deliver chronically neurotransmitter receptor antagonists to the SC of the guinea pig to investigate the potential role played by the major neurotransmitter systems in the collicular representation of auditory space. Slices of polymer containing different drugs were implanted onto the SC of guinea pigs before the development of the SC azimuthal auditory space map, at approximately 20 days after birth (DAB). A further group of animals was exposed to aminophosphonopentanoic acid (AP5) at approximately 250 DAB. Azimuthal spatial tuning properties of deep layer multiunits of anesthetized guinea pigs were examined approximately 20 days after implantation of the Elvax polymer. Broadband noise bursts were presented to the animals under anechoic, free-field conditions. Neuronal responses were used to construct polar plots representative of the auditory spatial multiunit receptive fields (MURFs). Animals exposed to control polymer could develop a map of auditory space in the SC comparable with that seen in unimplanted normal animals. Exposure of the SC of young animals to AP5, 6-cyano-7-nitroquinoxaline-2,3-dione, or atropine, resulted in a reduction in the proportion of spatially tuned responses with an increase in the proportion of broadly tuned responses and a degradation in topographic order. Thus N-methyl--aspartate (NMDA) and non-NMDA glutamate receptors and muscarinic acetylcholine receptors appear to play vital roles in the development of the SC auditory space map. A group of animals exposed to AP5 beginning at approximately 250 DAB produced results very similar to those obtained in the young group exposed to AP5. Thus NMDA glutamate receptors also seem to be involved in the maintenance of the SC representation of auditory space in the adult guinea pig. Exposure of the SC of young guinea pigs to gamma-aminobutyric acid (GABA) receptor blocking agents produced some but not total disruption of the spatial tuning of auditory MURFs. Receptive fields were large compared with controls, but a significant degree of topographical organization was maintained. GABA receptors may play a role in the development of fine tuning and sharpening of auditory spatial responses in the SC but not necessarily in the generation of topographical order of the these responses.

Acoustic Stimulation↗
PubMed1983

Reduced space constant in slowly conducting regions of chronically infarcted canine myocardium.

Experiments were performed to test the hypothesis that a reduction in the space constant contributes to slow conduction in the infarcted myocardium of dogs 5-8 days after coronary artery occlusion and reperfusion. Standard microelectrode techniques were used to measure action potential characteristics and conduction velocity parallel to fiber orientation in normal and infarcted ventricular epicardial strips superfused in a tissue bath. The space constants were determined by measuring the decay of the transmembrane steady state electrotonic potential with distance from a suction electrode current source. In eight normal epicardial preparations, conduction velocity ranged between 0.305 and 0.603 m/sec, and the space constant was between 0.712 and 1.202 mm. In 10 infarcted epicardial preparations, in regions of slow conduction (0.032-0.299 m/sec), the space constant was reduced to values between 0.281 and 0.917 mm. Action potential amplitude and maximum rate of depolarization were also reduced in infarcted myocardium. There was a direct relationship between conduction velocity and space constant and maximum rate of depolarization. In infarcted tissues, two types of slow conduction occurred. Slow conduction was uniform down to a velocity of approximately 0.181 m/sec, and a space constant of 0.523 mm. Below these values, conduction was discontinuous with prepotentials associated with the action potential upstroke. Indirect evidence from our studies suggests that a depression in action potential depolarization and an increase in effective axial resistance contribute approximately equally to uniform slow conduction in the infarcted myocardium.

Action Potentials↗
PubMed1997

Algebraic theory of recombination spaces.

A new mathematical representation is proposed for the configuration space structure induced by recombination, which we call "P-structure." It consists of a mapping of pairs of objects to the power set of all objects in the search space. The mapping assigns to each pair of parental "genotypes" the set of all recombinant genotypes obtainable from the parental ones. It is shown that this construction allows a Fourier decomposition of fitness landscapes into a superposition of "elementary landscapes." This decomposition is analogous to the Fourier decomposition of fitness landscapes on mutation spaces. The elementary landscapes are obtained as eigenfunctions of a Laplacian operator defined for P-structures. For binary string recombination, the elementary landscapes are exactly the p-spin functions (Walsh functions), that is, the same as the elementary landscapes of the string point mutation spaces (i.e., the hypercube). This supports the notion of a strong homomorphism between string mutation and recombination spaces. However, the effective nearest neighbor correlations on these elementary landscapes differ between mutation and recombination and among different recombination operators. On average, the nearest neighbor correlation is higher for one-point recombination than for uniform recombination. For one-point recombination, the correlations are higher for elementary landscapes with fewer interacting sites as well as for sites that have closer linkage, confirming the qualitative predictions of the Schema Theorem. We conclude that the algebraic approach to fitness landscape analysis can be extended to recombination spaces and provides an effective way to analyze the relative hardness of a landscape for a given recombination operator.

Algorithms↗
PubMed1969

Elastic properties of the centrilobular emphysematous space.

Bronchograms were performed using finely particulate lead on emphysematous lungs obtained at necropsy. X-ray films were taken of these lungs at distending pressures of 0, 5, 10, and 20 cm H(2)O. The volumes of individual centrilobular emphysematous spaces were calculated at each distending pressure from measurements made on these bronchograms and pressure-volume curves were constructed for each space. The pressure-volume characteristics of seven normal lungs and one lung with centrilobular emphysema was also measured. The normal lungs, the lung with centrilobular emphysema, and the centrilobular emphysematous spaces were compared by expressing the volume of air contained in them at each distending pressure as a per cent of the volume contained at 20 cm H(2)O distending pressure. We conclude that centrilobular emphysematous spaces have a high residual volume, are less compliant than normal lung tissue, and are much less compliant than the emphysematous lungs which contain them. Furthermore, these spaces undergo little volume change in the tidal breathing range and probably add a relatively nondistensible series dead space to the surrounding lung parenchyma.

Bronchography↗
PubMedDate not supplied

Management of buccal space masses.

Lesions in the substance of the cheek--the buccal space--may present diagnostic and management difficulties. The buccal space, that potential fascia space lying within the bulk of the cheek, is anatomically described. While the history and physical characteristics of the buccal mass and selected radiographic and special procedures may suggest a specific cause, the diagnosis is often elusive and requires removal of the mass for histologic evaluation. The surgical approach to a mass in the cheek is governed by its location within the buccal space and by the index of suspicion of malignancy. The preauricular, submandibular approach is the authors' choice for most buccal space lesions. Five case reports are presented to illustrate features in the diagnosis and management of a buccal space mass.

Adenoma↗
PubMed1990

Residual lower first premolar extraction space.

Residual lower first premolar extraction space was examined in 43 subjects, 16 male and 27 female, 5 years after extraction; 16 subjects were treated mechanically, 27 had no active treatment. Forty per cent of extraction sites had residual spaces averaging 0.62 mm left and 0.71 mm right. Various parameters were measured to try to establish reasons for non-closure of spaces. These included buccal space condition and incisal space condition measured on the pre-extraction models, and alveolar atrophy assessed on final models. The angulation of second premolars and canine to the maxillary plane and molar space were measured on 60 degrees cephalograms. Changes in these three parameters were measured after superimposing a tracing of the pre-extraction film on the final film. Angulation of lower incisors to the maxillary plane was measured on pre-extraction 90 degrees cephalograms, and change in lower incisor angulation and position measured after superimposing a tracing on the final 90 degrees film.

Alveolar Process↗
PubMed2006

Transcriptional and structural impact of TATA-initiation site spacing in mammalian core promoters.

BACKGROUND: The TATA box, one of the most well studied core promoter elements, is associated with induced, context-specific expression. The lack of precise transcription start site (TSS) locations linked with expression information has impeded genome-wide characterization of the interaction between TATA and the pre-initiation complex. RESULTS: Using a comprehensive set of 5.66 x 10(6) sequenced 5' cDNA ends from diverse tissues mapped to the mouse genome, we found that the TATA-TSS distance is correlated with the tissue specificity of the downstream transcript. To achieve tissue-specific regulation, the TATA box position relative to the TSS is constrained to a narrow window (-32 to -29), where positions -31 and -30 are the optimal positions for achieving high tissue specificity. Slightly larger spacings can be accommodated only when there is no optimally spaced initiation signal; in contrast, the TATA box like motifs found downstream of position -28 are generally nonfunctional. The strength of the TATA binding protein-DNA interaction plays a subordinate role to spacing in terms of tissue specificity. Furthermore, promoters with different TATA-TSS spacings have distinct features in terms of consensus sequence around the initiation site and distribution of alternative TSSs. Unexpectedly, promoters that have two dominant, consecutive TSSs are TATA depleted and have a novel GGG initiation site consensus. CONCLUSION: In this report we present the most comprehensive characterization of TATA-TSS spacing and functionality to date. The coupling of spacing to tissue specificity at the transcriptome level provides important clues as to the function of core promoters and the choice of TSS by the pre-initiation complex.

Animals↗
PubMed2005

Threshold current of an insulated needle in the intrathecal space in pediatric patients.

A threshold current of <1 mA has been suggested to be sufficient to produce a motor response to electrical stimulation in the intrathecal space. We designed this study to determine the threshold current needed to elicit motor activity for an insulated needle in the intrathecal space. Twenty pediatric patients aged 7.3 +/- 3.9 yr scheduled for lumbar puncture were recruited. After sedation with propofol, patients were turned to the lateral position and an 18-gauge or 20-gauge introducer needle was placed at the L4-5 level through which an insulated 24-gauge Pajunck unipolar needle (with a Sprotte tip and stylet) was inserted. The needle was advanced into the intrathecal space as suggested by the presence of a "pop." At this point, a nerve stimulator was attached to the insulated needle and the current was gradually increased until motor activity was evident. The needle hub was checked for cerebrospinal fluid. If cerebrospinal fluid was not present, the needle was advanced further until cerebrospinal fluid was present. The threshold current was retested. The mean current in the intrathecal space required to elicit a motor response was 0.6 +/- 0.3 mA (range, 0.1-1 mA). In 19 patients, the twitches were observed at the L4-5 myotomes and 1 patient had twitches at L2. Twitches were observed unilaterally in 19 children and bilaterally in one child. This confirms the hypothesis that the threshold current in the intrathecal space is <1 mA and that it differs significantly from the threshold currents reported for electrical stimulation in the epidural space.

Adolescent↗