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At least 19 recordsLinked to original sources
PubMed1992

The chronaxie for myocardium and motor nerve in the dog with chest-surface electrodes.

The chronaxie (i.e., the duration for a stimulating current having twice the rheobasic, or minimum, value) was determined for ventricular myocardium in 12 pentobarbital-anesthetized dogs. Current was applied transthoracically via chest-surface electrodes located at the optimal axillary site for producing inspiration by stimulation of the phrenic nerve (electroventilation). In four dogs the chronaxie for motor-nerve was determined using electrodes at the same location. After using hand-held electrodes to identify the optimal stimulation site for electroventilation, 4.1 cm diameter electrodes were applied bilaterally to the optimal site on the thorax. In 12 dogs, the threshold current for producing ventricular ectopic beats was determined for single rectangular current pulses ranging from 0.1-10 ms in duration. From these data, strength-duration curves were determined and the average chronaxie for ventricular myocardium was found to be 1.82 ms. In four dogs the relationship between inspired volume and maximum stimulus intensity was determined using a 0.8 s burst of stimuli (60/s) with pulse durations ranging from 20-500 microseconds. From these data, strength-duration curves for current were constructed and the average chronaxie for motor-nerve was found to be 0.17 ms. The results of this study show that, because of the differing chronaxies, the current required to produce inspiration with short-duration stimuli is much less than that required to evoke an ectopic heart beat.

Animals↗
PubMed1989

Dietary-induced changes in lipid and fatty acid composition can modify chronaxie values in the rat sciatic nerve.

The present investigation aimed at clarifying the possible correlations among dietary lipids, peripheral fatty acid composition of nerve lipids and an index of the nervous tissue excitability, the chronaxie. The experiments were performed on female albino rats fed diets containing olive oil (OO) and fish oil (FO) along two generations. Total lipids fatty acid composition of the sciatic nerves from the two groups differed in the proportions of 18:1(n-9), 20:1(n-9), 22-1, 20:5(n-3) and 22:6(n-3). Also the lipid class composition showed significant differences among FO and OO specimens (free cholesterol more concentrated in the OO lipids; triacylglycerols more concentrated in the FO ones). The sciatic nerve isolated from FO rats showed a significant decrease in the chronaxie values if compared to the OO specimens. These results could follow from dietary-induced changes in the perineural permeability and/or possible modifications in the cable properties of the peripheral nerve fibers related to the myelin sheath composition.

Animals↗
PubMed1977

Electroneuronography in prognosis of intratemporal facial palsy, as compared to measurements of rheobase and chronaxy.

Electroneuronography is compared to indicrect chronaximetry in the prognosis of intratemporal facial palsies. In 86 patients, the two methods were found to be congruent and in a number of cases complementary in determining impending degeneration. Both techniques are described and their results evaluated statistically. Our observations indicate that electroneuronography allows to some extent a quantitative evaluation by means of numeric parameters whereas the results of chronaximetry only give a qualitative account of nerve degeneration depending largely on the examiner's experience. Both methods, however, have a certain margin of failure and for more accurate diagnosis and prognosis simultaneous use of both methods is advocated.

Action Potentials↗
PubMed1979

[Electrodiagnostical determination of strength-duration curves during pregnancy, labour, puerperium, and their evaluation (author's transl)].

Electrodiagnostical determination of Rheobase and Chronaxy has been carried out on 10 women during pregnancy, beginning labour and puerperium. Rheobase and Chronaxy were marked in a Strength-Duration Curves scheme as well as some other points within that scheme. As a base of rise of the gained curves the actual rise at the point of the chronaxy was calculated. Our results show that with all 10 women the t-Difference-Test showed a significantly much lower curve during labour than that obtained during pregnancy. The same applied to the rise of the curve obtained during labour, which was significantly much lower than that during puerperium. There was no significant difference between the curves obtained during pregnancy and puerperium. The significance of the decline of the actual rise at the point of the Chronaxy of the Strength-Duration Curve before starting of labour as a physiological method of functional diagnostic will be discussed there under.

Chronaxy↗
PubMed1976

[Diagnostic importance of electrophysiologic tests in Bell's palsy: report on a longterm follow-up study in 100 cases (author's transl)].

The present study is based upon the results of repeated electrodiagnostic tests carried out in a series of 100 cases of Bell's palsy (Determination of Rheobase and Chronaxy). The first symptoms of denervation can be observed during the second week after the onset of the paralysis. This seems to be the critical period in which the ultimate consequences of the lesion are determined: partial or total recovery or complete irreversible denervation. In cases showing a rapid increase of chronaxy during the 2nd week, prognosis is rather poor because a difference of 240% between the affected and the normal side indicates a progressive denervation. Cases in which the difference of chronaxy values during the 2nd week is increased upto 240% (i.e. partial denervation) recover incompletely in 15% of the cases. Estimation of prognosis in Bell's palsy and timing of a facial nerve decompression must be based on reliable facts, such as the results of repeated electrodiagnostic tests (modified measurement of Rheobase and Chronaxy) carried out at least every secont but preferably every day during the first 3 weeks after the onset of the paresis.

Chronaxy↗
PubMedDate not supplied

Existence of a strength-duration curve for spinal cord motor evoked potentials in cats.

A new technique has been developed to estimate the chronaxie of fibers carrying action potentials that are responsible for short latency motor evoked potentials (MEPs). In a 6-cat study, electrical stimuli were applied to the exposed motor cortex, and spinal cord potentials (at the vertebral level of T9/10 and L2/3) were recorded with needle electrodes using signal averaging. From a plot of MEP amplitude versus stimulus current amplitude for stimuli of 70, 100, 200 and 500 microseconds duration, it was possible (by extrapolation and using the linear relationship between charge and duration) to estimate chronaxie for the first 2 prominent peaks in MEP recordings. Mean chronaxie values ranging from 190 to 337 microseconds were obtained. This study describes acquisition of strength-duration curves for short latency MEP peaks, but does not address the origin of these peaks.

Animals↗
PubMed1990

Correlation between histology and nerve excitability after reinnervation of paralyzed strap muscles in the rabbit.

We have recently shown that the mean muscle chronaxie for nerve pedicle implanted into denervated rabbit strap muscle is comparable to that of normal nerve. This study correlates excitability with histologic characteristics of muscles reinnervated via nerve-muscle pedicles (NMP) and direct nerve implants (DNI). Strength duration curves were measured in 13 rabbits 3.5 to 5 months after reinnervation by NMP (n = 6) and DNI (n = 7). Following this, control (n = 5) and reinnervated straps were harvested immediately before the animals were killed and frozen in liquid nitrogen. The material was submitted for hematoxylin-eosin stains as well as trichrome stains for general morphology, myofibrillar ATPase and NADH for fiber typing, and cholinesterase for determination of denervated fibers. In all animals with low chronaxie, expected type grouping from reinnervation was noted (n = 10). By contrast, the three animals in which chronaxie was abnormally elevated demonstrated fibrosis, inflammation, and absence of or poor type grouping. This suggests that type grouping is necessary for excitability after reinnervation of paralyzed striated muscles.

Animals↗
PubMed1979

[Electrodiagnostical investigations during pregnancy, labour, puerperium, and in impending early delivery (author's transl)].

Electrodiagnostical investigations measuring the Rheobase and the Chronaxy have been carried out on 100 women, 36 during pregnancy, 21 during labour, 29 in puerperium and 14 with impending early delivery. As the results show, the rheobase values, which were determined during pregnancy, were significantly much higher, than those during labour or impending early delivery. The rheobase values were significantly lower during 19th--30th week of pregnancy than during 30--40th week, and the latter were significantly much higher, than those during labour or impending early delivery. In puerperium there was no significant difference of the rheobase values to those during labour, but a significant difference to the values obtained during pregnancy. The chronaxy values show no significant differences during pregnancy and labour and during pregnancy and impending early delivery. Only the chronaxy values in puerperium were significantly lower than in pregnancy as well as in labour.

Chronaxy↗
PubMed1985

Effect of electrode size on brain stimulation.

Behaviorally determined strength-duration curves of many brain pathways differ from those of peripheral nerves, or single fibers. The chronaxies measured using short-duration pulses are much shorter than those measured with long pulses. A suggested explanation for this was that the pathways have mixed populations of long- and short-chronaxie elements. We attempted to test this hypothesis by stimulating with electrodes of different surface area, on the assumption that they would fire different proportions of long-chronaxie elements at short pulse durations where their thresholds are high. For a given current a large electrode delivers a lower maximum current density than a small one. Electrode size was found to have no detectable effect on the shape of the strength-duration curve. An attempt to discover the characteristics needed to modulate neurons having a basically hyperbolic strength-duration curve so as to produce the empirical curve revealed that the process has a zero rheobase and is thus presumably a direct influence of current on the threshold of the stimulated axons. A probable candidate for this process is the accumulation of potassium iontophoretically driven from cells in the vicinity of the electrode.

Animals↗
PubMed1975

Which elements are excited in electrical stimulation of mammalian central nervous system: a review.

(1) There are data on the amount of current necessary to stimulate a myelinated fiber or cell body and/or its axon a given distance away from a monopolar electrode over the entire range of practical interest for intracranial stimulation. Data do not exist for other electrode configurations. (2) Currents from a monopolar cathode of more than 8 times threshold may block action potentials in axons. Therefore, only axons lying in a shell around the electrode are stimulated. Elements very close to the electrode may not be stimulated. Close to an electrode small diameter axons may be stimulated and larger ones may not be. (3) Most, and perhaps all, CNS myelinated fibers have chronaxies of 50-100 musec. When gray matter is stimulated, the chronaxie is often 200-700 musec. It is not clear what is being stimulated in this case. Current-duration relations should be determined for many more responses. (4) There are no current-distance or current-duration data for central finely myelinated or unmyelinated fibers. (5) It takes less cathodal current than anodal to stimulate a myelinated fiber passing by a monopolar electrode. When a monopolar electrode is near a cell body, on the opposite side from the axon, often the lowest threshold is anodal, but sometimes cathodal. Stimulation of a neuron near its cell body is not well understood, but in many cases the axon is probably stimulated. (6) Orientation of cell body and axons with respect to current flow is important. For an axon it is the component of the voltage gradient parallel to the fiber that is important. (7) The pia has a significant resistance and capacitance. Gray matter, white matter, and cerebrospinal fluid have different resistivities, which affect patterns of current flow. (8) More is known about stimulation of mammalian CNS than most workers are aware of. Much of what is unknown seems solvable with current methods.

Animals↗
PubMed1979

Central gray and medial hypothalamic stimulation: correlation between escape behavior and unit activity.

A chronic experiment and an acute one were carried out in the same rat in order to get information on the neuronal events correlated with the escape latency (EL) induced by an electrical stimulation in the mesencephalic central gray (CG) or in the medial hypothalamus (MH). Escape latencies as well as unitary MH and CG neuronal responses (104 units in 25 rats) were studied as functions of the intensity and the pulse duration of a 50 pulses/sec stimulation train. The CG and/or the MH neuronal firing rate was either synchronized or diffusely altered, either inhibited or activated, by the CG or the MH stimulations. Many neuronal firing rate alterations were highly correlated with the escape speed (ES = 1/EL) induced by the same stimulation. Intensity duration trade-off functions were computed from both the EL and the unit recordings. Chronaxie determinations were performed from these data: the behaviorally determined chronaxies did not differ from the unitary ones (limit values: 0.05-0.42 msec). The discussion bear on the possible role of the observed neuronal alterations induced by CG or MH stimulations in relation to their behavioral effects.

Animals↗
PubMed1990

Effect of pacing rate on the human atrial strength-duration curve.

The effect of rapid pacing on the atrial constant voltage stimulation threshold in humans has not been defined at rates applicable to those of antitachycardia pacing. The effect of pacing rate on the atrial strength-duration relation was determined in 10 patients at pacing rates between 125 and 300 beats/min to explore excitability over the range of rates used for permanent antitachycardia pacing systems. Two points that define the strength-duration curve were measured at each pacing rate: rheobase voltage--the lowest stimulus voltage that results in capture at a pulse duration of 2 ms; and chronaxie pulse duration--the threshold pulse duration at twice rheobase voltage. A permanent, tined, J-shaped pacing lead with a high current density and low polarization electrode was positioned in the right atrial appendage for cathodal stimulation. A constant voltage output, incorporating a fast recharge pulse designed to minimize electrode polarization, was used for stimulation. There was a significant increase in rheobase voltage (p = 0.009), chronaxie pulse duration (p = 0.001) and minimal threshold stimulus energy (p = 0.05) at pacing rates greater than 225 beats/min. A rheobase voltage greater than 5 V occurred in three patients at pacing rates greater than or equal to 275 beats/min. At a pacing rate of 300 beats/min, rheobase voltage had increased in 8 of 10 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗
PubMed1992

Comparison of rectangular and exponential current pulses for evoking sensation.

There exists a paucity of quantitative information comparing the stimulating currents for different waveforms. Thus, the objectives of this study was to compare the threshold peak current (I) for sensation using rectangular and exponential; that is, capacitor-discharge, cathodal pulses of equivalent pulse duration (d). In 10 human subjects, stimuli were applied to the skin of the forearm, and I was determined alternately for each current waveform at each of several pulse durations (d). Strength-duration curves for sensation were obtained using d of 0.01-50 ms. The threshold peak current (Ir) for a rectangular pulse of duration d was compared to the threshold peak current (Icd) for a capacitor-discharge pulse of duration d, where d was the time constant; that is, the time required for the current to decrease to 1/e, or 37% of its peak value. Chronaxie, the pulse duration at which I is twice the infinite-duration current asymptote (i.e., the rheobase), was calculated for each waveform and subject using the Weiss-Lapicque expression for excitability. Icd was found to be always higher than Ir of equivalent duration. Chronaxie for the capacitor-discharge pulse was, on the average, twice that for the rectangular pulse (p less than 0.01). Moreover, the ratio Icd/Ir increased with decreasing d. These results indicate that these two waveforms are not equivalent on the basis of an equal-charge requirement for excitation, particularly at the short pulse durations. Furthermore, they suggest the need of a better expression to describe the excitability characteristics of tissues.

Adult↗
PubMedDate not supplied

Strength-duration properties of single units driven by electrical stimulation of the lateral hypothalamus in rats.

Cathodal strength-duration functions were measured for 27 single units which were driven by electrical stimulation of the lateral hypothalamus. The distribution of chronaxies of these units showed four clusters at about 0.1, 0.25, 0.4 and 0.5 msec. These chronaxies are not fundamentally different from those previously reported for peripheral nerve. Two units fired repetitively during a long-duration stimulation pulse. Anodal strengitation. The data are discussed with reference to behaviorally determith duration properties were obtained from 14 units. Four units were not excited by anodal pulses of any strength or duration, four were excited during an anodal pulse (anode-make excitation) but not at the termination of the pulse (anode-break excitation), and six showed both anode-make and anode-break excitation. The data are discussed with reference to behaviorally determined strength-duration functions for brain stimulation reward.

Action Potentials↗