Stimulation threshold

Pharmacology Therapeutic concentrations of lidocaine attenuate phase 4 diastolic depolarization, decrease automaticity and cause a decrease or no change in excitability and membrane responsiveness. Action potential duration and effective refractory period (ERP) of Purkinje fibers and ventricular muscle are decreased, while the ratio of ERP to action potential duration is increased. Lidocaine raises ventricular fibrillation threshold. AV nodal conduction time is unchanged or shortened. Lidocaine increases the electrical stimulation threshold of the ventricle during diastole. 

Mechanism of Action An antiarrhythmic that increases the electrical stimulation threshold of the ventricles and His-Purkinje system. Decreases myocardial excitability and conduction velocity and depresses myocardial contractility Exerts direct cardiac effects. Therapeutic Effect Suppresses arrhythmias. 

Kornetsky, C., Esposito, R.U., McLean, S., and Jacobson, J.O. (1979) Inracranial self-stimulation thresholds a model for the hedonic effects of drugs of abuse. Arch Gen Psychiatry 36 289-292. 

Kometsky, Conan, Ralph U. Esposito, Stafford McLean, and Joseph O. Jacobson. 1979. "Intracranial Self-Stimulation Thresholds A Model for the Hedonic Effects of Drugs of Abuse." Archives of General Psychiatry 36 289-92. 

Stimulation Thresholds Observed in a Rat Model of Cocaine Withdrawal." Neu ropsychopharmacology 7 213-24. 

Wise, Roy A., and Elizabeth Munn. 1995. "Withdrawal from Chronic Amphetamine Elevates Baseline Intracranial Self-Stimulation Thresholds." Psychopharmacology 117 130-36. 

The sensory evaluation differentiates between the stimulation threshold (a just detectable level where a perceptible but not yet definable deviation of the sample from the standard is observed) and the recognition threshold, a level where the odor is identifiable or creates odor problems (a no longer tolerable quality deterioration caused by a definite off odor and/or taste). The difference between a perceptible and identifiable level is usually only one to two steps of a geometric dilution series. Therefore, only undifferentiated odor and taste thresholds are given in Table 13-6, because of the very different sensitivities of individual testers. The perceptible (stimulation) levels of a less sensitive tester can overlap with the identifiable (recognition) level of another more sensitive tester. 

The muscle is stimulated with a monophasic rectangular stimulus of 3 ms duration and at 1.5 times the stimulation threshold using a 1831A stimulator... 

Markou, A. and Koob, G. (1993) Intracranial self-stimulation threshold as a measure of reward, in Behavioral Neuroscience A Practical Approach, Vol. 2 (Sahgal, A., ed.), IRL Press, Oxford, pp. 93-115. 

FIGURE 37.3 Neural strength-duration curve depicting stimulation threshold vs. duration. 

The electric field strength at the cathode increases with current density but decreases as a function of the square of the distance between the electrode surface and the tissue. In the case of a thick, fibrous capsule developing at the tip of the electrode, the stimulation threshold inevitably increases, and sometimes it may be impossible to obtain myocardial electrical activation (exit block). For this reason, inflammation after lead implantation is the crucial factor that must be controlled to achieve a chronic, low-stimulation threshold. 

Thuesen L, Jensen PJ, Vejby-Christensen H et al (1989) Lower chronic stimulation threshold in the carbon-tip than in the platinum-tip endocardial electrode a randomized study. Pacing Clin Electrophysiol 12(10) 1592-1595... 

The current standard pacemaker lead utilizes many of the innovations described above and possesses a low coil resistance coupled with a high electrode impedance and a steriod-eluting tip (de Voogt, 1999). The steroid reduces the inflammatory reaction to the implanted lead that can increase the stimulation threshold over time (Mitrani et al., 1999 Crossley, 2000). 

D. J. Schaefer, J. D. Bourland, J. A. Nyenhuis, K. S. Foster, W. F. Wirth, L. A. Geddes, and M. E. Riehl, 1994, Determination of Gradient-Induced, Human Peripheral Nerve Stimulation Thresholds for Trapezoidal Pulse Trains, abstract, Society of Magnetic Resonance, Second Meeting, San Francisco, p. 101. 

By definition, the stimulation threshold is the lowest voltage or current necessary to consistently evoke cardiac depolarization outside the refractory period of the heart. By convention the term consistently refers to at least five consecutive beats. Although in clinical practice only voltage (volts = V) and pulse duration (milliseconds = ms) are used, nevertheless, a number of derived parameters are often described in lead studies but are of little value in day-to-day management. These include current (milliamperes = mA), energy (microjoules = pJ) and charge (microcoulombs = pC). These parameters are discussed later in this chapter. 

In recent years, titanium, titanium oxide, titanium alloys, iridium oxide coated titanium and especially titanium nitride in a variety of shapes and sizes, have become very popular for use as cathode materials, because of low stimulation thresholds and acceptable polarization losses (15-18). 

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