Maximum nerve conduction

In a 10-month study, monkeys exposed to 1,000 ppm 2-hexanone had abnormal results in electrodiagnostic tests (Johnson et al. 1977). There was a progressive and statistically significant decrease in the maximum motor conduction velocity of the sciatic-tibial nerves starting at 4 months of exposure and a decrease in the maximum conduction velocity of the ulnar nerves starting at 1 month. Decreased amplitude of evoked muscle action potential was also seen at 1,000 ppm. 

Clinical use The indications for levobupivacaine include wound infiltration (0.25 % solution), nerve conduction block (0.25 - 0.5 %), spinal analgesia (0.5 %) and epidural anesthesia (0.5 to 0.75 %). For labour analgesia, lower concentrations of levobupivacaine are recommended when administered as epidural injection (0.125 to 0.25 % up to 25 mg) or infusion (0.25 %). The maximum dose for ilioinguinal or iliohypogastric block in children is 1.25 mg/kg/side (0.25 to 0.5 % solutions). For postoperative pain management, levobupivacaine can be applied epidurally in combination with the opioids fentanyl or morphine or with the a2-agonist clonidine. 

R = / -C H ), in low doses, exhibits the former behavior and is used primarily as an extradural agent in obstetrics. The lowest effective extradural concentration of etidocaine (21, X = CH, R = R = 2H, R = / -C H ), however, shows both adequate sensory and profound motor blockade so that it is useful in surgical situations where maximum neuromuscular blockade is necessary. In an isolated nerve preparation, bupivacaine blocks unmyelinated C fibers which are mainly responsible for pain perception at a much greater extent than the myelinated A fibers which carry motor impulses. It is postulated that absorption of bupivacaine by the vasculature at the site of injection, combined with the slow diffusion of this agent, results in an insufficient amount of the drug penetrating the large A fibers to cause motor conduction blockade. Clinically, motor block can be observed in some procedures. 

Transmembrane action potential of a sinoatrial node cell. In contrast to other cardiac cells, there is no phase 2 or plateau. The threshold potential (TP) is -40 mV. The maximum diastolic potential (MDP) is achieved as a result of a gradual decline in the potassium conductance (gK+). Spontaneous phase 4 or diastolic depolarization permits the cell to achieve the TR thereby initiating an action potential (g = transmembrane ion conductance). Stimulation of pacemaker cells within the sinoatrial node decreases the time required to achieve the TR whereas vagal stimulation and the release of acetylcholine decrease the slope of diastolic depolarization. Thus, the positive and negative chronotropic actions of sympathetic and parasympathetic nerve stimulation can be attributed to the effects of the respective neurotransmitters on ion conductance in pacemaker cells of the sinuatrial node. gNa+ = Na+ conductance. 

In 1984, the Veterans Administration (VA) funded the initial animal studies at the Togus VA Medical Center (Augusta, ME). These were aimed at determining what changes would be required to use a modified cochlear implant with a maximum pulse output of 4.3 mA and 0.4-msec pulse width, to be suitable for FES use in humans. An initial decision was taken to utilize epineuraUy placed electrodes (2.5-mm diameter platinum disks) in preference to epimysial or intramuscular electrodes because it was known that the stimulation currents would be lower and that there would be less movement of the electrodes. In order to determine exactly how low the stimulation currents would be and to determine the stimulation sites, initial anesthetized rabbits studies were conducted [9]. The threshold found for each branch of the split sciatic nerves was of 0.1 to 0.2 mA at 0.2 msec with 50 pps. Maximal stimulation was achieved usually between 0.5 and 1.0 mA. Simultaneous dorsiflexion of both paws as well as co-contraction in the anterior and posterior muscle groups could be achieved. 

The effects of changing the proton content of solutions bathing excitable membranes has been the subject of many reports in the j)ast. (1-7). Two main effects were commonly observed although they differed quantitatively upon changing the nerve preparation a) a shift on the voltage axis of the parameters characterizing nerve excitability (similar to the action of divalent ions (8)), b) a variation of the steady-state maximum conductance of the open channels selective for sodium and potassium ions. A third type of effects concerns phenomena such as the voltage-dependent block of Na" "-channels observed by Woodhull (9) in the node of Ranvier. 

---