[Ultrasonographic assessment of hemidiaphragm paralysis secondary to interscalene block]. / Evaluación ultrasonográfica de la parálisis hemidiafragmática secundaria a bloqueo interescalénico.

BACKGROUND: In shoulder surgery, interscalene brachial plexus block has an incidence of 100% hemidiaphragm palsy due to phrenic nerve block. Controling the hemidiaphragm becomes a security ventilation parameter. OBJECTIVE: identify and evaluate with ultrasound hemidiaphragm paralysis after interscalene block. METHODS: This prospective study included 50 patients scheduled for shoulder surgery with interscalene block using neurostimulation. Diaphragmatic movement was evaluated by ultrasound prior to placement of block and the end of the surgical procedure to make the comparison between the two measurements. RESULTS: Comparing the duration of the respiratory cycle at the start and the end of the surgical procedure, both normal and forced ventilation, there is a statistically significant difference of p < 0.001, as with the depth of the hemidiaphragm was found p < 0.001. 90% of patients had no adverse events, 8% had Horner's syndrome and 2% periauricular hypoesthesia. Hemidiaphragm paralysis was found in all cases, with a volume of 30 mL local anesthetic. CONCLUSIONS: Ultrasound is a reliable tool that allows real time viewing of the respiratory cycle and measurements of the diaphragm dome it serves to identify diaphragmatic hemiparesis.

Detection of biologically active botulinum neurotoxin--A in serum using high-throughput FRET-assay.

INTRODUCTION: The goals of this project were to compare fluorescent resonance energy transfer (FRET) assays using a customized FRET substrate (substrate-substrate-A, SSA) with a commercially available FRET substrate (SNAPtide); optimize the assay conditions for SSA for lowest level of detection; and apply SSA to detect botulinum neurotoxin-A (BoNTA) in serum samples. METHODS: Biological activity of BoNTA and light-chain-A (LCA) was verified by murine phrenic nerve-hemidiaphragm bioassay and western blot before use in both FRET assays. The reaction conditions were optimized to determine the smallest amount of toxin that could be detected. A range of serum samples was investigated for interference in the SSA-based FRET assay. Detection of BoNTA from rat serum samples was performed over time. RESULTS: We found that BoNTA and LCA were able to cleave the substrates whereas mutated LCA and a different serotype of BoNT, BoNTB, could not. SSA had significantly more arbitrary fluorescing units compared to the FRET substrate SNAPTide, and the SSA assay could detect 0.1nM of BoNTA or LCA comfortably (p=<0.05) in a 20-µl reaction. No significant interference was observed when serum was present in the reaction buffer. Due to negligible background noise, the SSA FRET assay could detect BoNTA from spiked rat serum even after 256min. DISCUSSION: The greatest advantage of the FRET assay is its extreme rapidity, its cost effectiveness, and unlike ELISA, its ability to detect biologically active toxin. SSA is a better FRET substrate for detecting BoNTA toxin (detected 0.1nM concentration). Because serum present in the assay reaction did not cause any appreciable interference, the assay can be used to detect BoNTA in serum samples. Therefore, the SSA FRET assay can be used for pharmacokinetic and pharmacodynamic studies, screening inhibitors, and detecting BoNTA in serum samples.

Functional assessment of Ca(2+)-current in the mouse motor nerve terminals.

The purpose of this study was to characterize voltage-gated Ca2+ channels on the mouse motor nerve terminals. Mouse diaphragm and triangularis sterni preparations were used for this study in order to assess the functional Ca2+ channels in the transmitter release. The results showed that omega-conotoxin MVIIC (CTx-MVIIC, 0.5-1 microM) but not omega-conotoxin GVIA (1 mM) markedly inhibits not only the nerve-evoked muscle contractions accompanied by a decrease in the amplitude of end plate potentials (epps) in the mouse phrenic-nerve diaphragm but also the Ca(2+)-waveforms in the nerve terminals of triangularis sterni. The inhibitory effects of CTx-MVIIC were considered to be specifically presynaptic rather than myogenic, since none of the electrical properties of muscle fibers including action potentials, resting membrane potentials and the miniature endplate potential, were affected. Moreover, Na(+)- and K(+)-waveforms of the nerve terminals were unaffected by CTx-MVIIC. At a saturating concentration of 3-5 mM, CTx-MVIIC exerted a maximal inhibitory effect by 38% of 3,4-diaminopyridine-prolonged epps area and inhibited only the slow component of Ca(2+)-current, respectively, and the remaining fast component could be inhibited by subsequent addition of cadmium chloride (Cd2+). All of these findings indicate that at least two components (a slow CTx-MVIIC sensitive component and a fast Cd2+ sensitive component) of the mouse motor nerve terminals would cooperate in the induction of the transmitter release from motor nerve endings.

Ciguatera and mannitol: in vivo and in vitro assessment in mice.

Mannitol (1 g/kg i.v.) is currently the treatment of choice for acute ciguatera, but confirmation of this treatment's apparent efficacy awaits further experimental or controlled clinical evidence. In mice, mannitol (1 g/kg i.v.) administered before or after i.p. ciguatoxin did not influence the signs of intoxication or the time to death. The effects of oral ciguatoxin differed from those following i.p. ciguatoxin, but again i.v. mannitol provided no detectable benefit. Development of hypothermia was rapid in mice receiving i.p. or oral ciguatoxin and was unaffected by i.v. mannitol. A sublethal i.p. dose of ciguatoxin initially retarded (day 0-4) but then accelerated (day 4-12) the growth of mice. Mannitol (i.v.) had no influence on these effects of ciguatoxin on the growth of mice. Ciguatoxin inhibited responses of isolated diaphragms to nerve stimulation (ED50 = 9 x 10(-11) M), while directly stimulated diaphragms were inhibited by five-fold higher concentrations. Mannitol (50 mM) added to the organ bath did not influence the ciguatoxin-induced inhibition of diaphragm responses to nerve stimulation in vitro. Responses of isolated diaphragm to nerve stimulation were normal in preparations removed from ciguatoxin-treated mice displaying pronounced dyspnoea (gasping). However, responses to nerve stimulation were reduced in preparations removed from mice immediately following death from ciguatoxin. Mannitol (i.v.) partially protected the phrenic nerve-diaphragm from this effect of ciguatoxin in vivo. We conclude that the lethal effects of ciguatoxin in mice probably stem from a central action, and suggest that species differences may account for the absence of any marked beneficial effect of i.v. mannitol in the mouse model for ciguatera in humans.

Assessment of neuromuscular blockade produced by atracurium in the rat diaphragm preparation. Measurements of tetanic fade, depression and recovery profile.

The effect of atracurium, a relatively new muscle relaxant, on neuromuscular transmission, in the rat diaphragm preparation, was studied, by analysing the characteristic features of tetanic fade and recovery pattern following a blocking concentration of atracurium (10 microns). Tetanic fade (TF) and peak tetanic tension (Tp) and its depression by atracurium, were analysed and the results were interpreted in terms of atracurium action at the neuromuscular junction. Atracurium reduced the sustained tetanic tension, elicited at 50 Hz for 0.5 s duration, and produced a marked tetanic fade in 38 s. Atracurium also reduced the peak tetanic tension by 40%, of the control value, in 38 s. Maximum tetanic tension was 5.7 g tension, and the time taken to completely block the tetanus was 4.75 +/- 0.15 min (means +/- SE, n = 8). Recovery from atracurium-induced blockade occurred in 30s (tetanic fade) and in 3-4 min (peak tetanic tension). It was concluded that atracurium produces a profound tetanic fade, at a time when the peak tetanic tension is reduced by only 40%. The data presented indicate that atracurium has a rapid onset of blockade, intermediate duration and a quick recovery profile at the rat neuromuscular junction.