High Frequency Impulse Research Articles

Effect of ischemia and cooling on the response to high frequency stimulation in rat tail nerves.

In normal rat tail nerves the effect of temperature and ischemia on the response to long-term high frequency stimulation (HFS) (143 Hz) was studied. The effect of temperature was studied in two consecutive tests at 14 degrees C and 35 degrees C. Prior to the HFS the peak-to-peak amplitude (PP-amp) of the compound nerve action potential was 139 +/- 20 microV (mean +/- SD) and 127 +/- 37 microV at 35 degrees C and 14 degrees C, respectively (NS). After 15 min of HFS the PP-amp was reduced to 45.3 +/- 20.5% of baseline level at 14 degrees C as compared with 80.8 +/- 10.2% at 35 degrees C (p < 0.001). Applying ischemia to the rat tail, an additional fall of the PP-amp was seen after 15-20 min of HFS at both low (20 Hz) and high (143 Hz) stimulation frequencies. In conclusion, ischemia and cooling result in an impaired ability to transmit high frequency impulses.

Simulation of triggered earthquakes in the laboratory

The experiments were conducted for the study of stick-slip at the contact between two granite blocks. Three cases were studied under the following conditions: 1) the increase of load at a constant rate; 2) the additional application of sinusoidal oscillations in the frequency range from 1 to 30 Hz; 3) subjection to the impulse in the kilohertz frequency range. The imposition of sinusoidal oscillations with the amplitude of 15% of the maximal load caused the reduction of time by 10% for the discussed in terms of durability. The high frequency impulse influence increased this effect and also caused essential changes in the amplitude of elastic oscillations generating during the stick-slip. The trigger phenomena should be integrated in prediction models of the time and magnitude of earthquakes.

Reduced capability of transmitting high frequency impulses in tail nerves of diabetic rats.

The effect of long-term (40 min) high frequency stimulation (143 Hz) of sensory-motor tail nerves was studied in normal and in streptozotocin-diabetic rats. The study comprised a 6-week period, repeating the test at 2-week intervals. In the initial (prediabetic) study, single experiments showed a mild depression of the peak-to-peak amplitude during high frequency stimulation, which reversed completely during a subsequent rest period. In normal rats, the amplitude depression was unchanged in repeated tests over a 6-week period. Diabetic rats showed a greater amplitude depression during high frequency stimulation. The difference was statistically significant after 2 weeks, but showed no further change at subsequent tests. The greater decrease in the amplitude in diabetic rats may reflect a depression of the axon membrane function, which may be the functional correlate to the inhibition of the Na/K ATPase activity in diabetes, described by others. Monitoring of the axon membrane functional capacity may have clinical implications in the control of peripheral neuropathies.

Prebreakdown currents of vacuum tubes with increased pressure stressed with AC voltage

Prebreakdown currents at AC are mainly determined by emission currents, if the capacitive current component is compensated. Under certain conditions, which are dealt with in this study, HF (high-frequency) impulse currents are superimposed. The shape of the HF impulse current curve as a function of time was recorded with a high time resolution. The steepness of relevant current jumps has been evaluated. On the basis of the results the phenomenon of HF impulse currents is interpreted as a consequence of changing gas attachment to the metallic electrodes. >

High frequency alternating current ablation of an accessory pathway in humans

High frequency alternating current ablation of an accessory pathway was performed in a patient with incessant circus movement tachycardia using a right-sided, free wall accessory pathway. Antiarrhythmic drugs, antitachycardia pacing and transvenous catheter ablation using high energy direct current shocks could not control the supraventricular tachycardia. A 7F bipolar electrode catheter with an interelectrode distance of 1.2 cm was positioned at the site of earliest retrograde activation during circus movement tachycardia. At this area, two alternating current high frequency impulses were delivered with an energy output of 50 W through the distal tip of the bipolar catheter, while the patient was awake. After the first shock supraventricular tachycardia terminated and accessory pathway conduction was absent without altering anterograde conduction in the normal atrioventricular (AV) conduction system. No reports of pain or other complications were noted. In short-term follow-up of 5 months, the patient had been free of arrhythmias without antiarrhythmic medication. Thus, high frequency alternating current ablation was performed for the first time in the treatment of an arrhythmia incorporating an accessory pathway in a human. This technique may be an attractive alternative to the available transcatheter ablation techniques and to antitachycardia surgery.

Section of fibular nerve affects activity pattern and contractile properties of soleus motor units in adult rats.

Transection of the common fibular (FIB) nerve caused an immediate reduction in the total amount of soleus (SOL) motor unit activity, which declined further during the following 10 days and then remained stable at less than half of normal values. In addition, there was an immediate reduction in median impulse rate from about 20.0 to 14.9 Hz followed by a return to normal values during the first 10 days. Short interval (3-4 ms) double discharges, occurring either in isolation or at the same regular intervals as single impulses, were observed 2-5 days after FIB nerve section in a few motor units. Brief, high frequency impulse bursts with interspike intervals of 12-16 ms were observed in a few units from the third day and until the end of the experiment (up to 31 days). It was not established whether the high frequency discharge pattern occurred only in a fixed population of the SOL motor units, or whether the units could switch between high and low frequency activity. Two months after FIB nerve section, the SOL muscle in the same leg contracted faster than normal (mean isometric twitch contraction time 29.6 ms, n = 4; vs. 38.7 ms, n = 8), contained a larger than normal percentage of type II fibres (13-36 vs. 0-0.2%) and weighed less than the contralateral SOL muscles (180 vs. 206 mg). SOL muscles (n = 4) in the opposite leg were comparable to normal SOL muscles except for a small reduction in mean isometric twitch contraction time (35.5 ms).

Conductivity of dorsal column fibers during experimental spinal cord compression and after decompression at various stimulus frequencies.

The effects of spinal cord compression on conduction of dorsal column fibers at various stimulus frequencies were analyzed in pentobarbital anesthetized cats. The responses to L6 dorsal root stimulation at 1 to 500 Hz were recorded from the L2 cord dorsum. The L4 cord segment was compressed gradually until the compound action potential (CAP) at 1 Hz was flat. There was no significant change of CAP at any frequency during the first part of compression, but there was progressive conduction failure, which was more severe with increased stimulus frequency, at a later stage. After decompression, the CAPs at all frequencies recovered progressively for 1 hour but slowly thereafter. However, marked differences were observed in recovery rate at different stimulus frequencies. The recovery rate at 500 Hz was much slower than that at 1 Hz, whereas the recovery rate at 100 Hz exceeded those at 1 Hz. Serial analysis of a train of high frequency impulses revealed the following different response patterns with stimulus frequencies after decompression. At 333-500 Hz the amplitude of CAPs decreased progressively, whereas at 33-125 Hz it increased up to 110-134% of the first CAP and then reached an almost steady level. At 200-250 Hz the amplitude increased transiently and then decreased progressively. The latency increased with decreased amplitude, and decreased with increased amplitude. Conduction failure at a high stimulus frequency (500 Hz) was observed at the compression site. In contrast, augmentation of CAPs at moderately high stimulus frequency (100 Hz) was observed rostral to the compressing site. The conduction failure at high stimulus frequency indicates incomplete impairment of spike generation in axons injured by mechanical compression and that these axons can transmit impulses at a low stimulus frequency. High frequency stimulation may be useful for monitoring of the function of the CNS axons. The mechanism underlying the augmentation of CAPs at moderately high stimulus frequency is briefly discussed.

The initial burst of impulses in responses of toad muscle spindles during stretch.

The responses of muscle spindles in the iliofibularis muscle of the cane toad Bufo marinus were examined during constant velocity stretch of the passive muscle. Spindles were found to show an 'initial burst' of high frequency impulses at the onset of stretch. Associated with the initial burst was a steep passive tension rise in the whole muscle, the short-range elastic component (Hill, 1968), called here the passive stiffness. The size of the initial burst was found to depend on muscle length in a similar way as whole-muscle tetanic tension. Repetitive stretch was found to reduce both the initial burst and passive stiffness. The time taken for both to return to their control values was 3 and 10 s respectively. If immediately following repetitive stretch the muscle, and hence the spindle, was held stretched for 3 s, the initial burst in response to a subsequent stretch from a shorter length remained reduced in size for 300 s. The depression could be reversed by a brief period of fusimotor stimulation. Hypertonic Ringer solutions were found to increase the initial burst and passive stiffness, while both were reduced in hypotonic solutions. Low concentrations of caffeine (1.5 mM) produced a similar decrease in both the initial burst and the passive stiffness. Calcium-free Ringer solution left the stiffness unchanged, and increased the whole dynamic response of the spindle. Metabolic exhaustion and poisoning of the muscle caused the initial burst to increase while decreasing the active tension. It is concluded that the initial burst is an intrafusal manifestation of the passive short-range stiffness of extrafusal muscle which is thought to be due to the formation of stable cross-bridges between the actin and myosin filaments of myofibrils.

Serotonergic modulation of the feeding behavior of the medicinal leech

Hungry medicinal leeches, Hirudo medicinalis, bite warm surfaces and ingest blood meals averaging 890% of their weight. Satiation lasts 12–18 months during which leeches avoid warm surfaces and will not bite. The segmental nervous system of the leech is distinguished by a population of neurons which contain serotonin (5-Hydroxytryptamine, 5-HT) at high concentrations. Some of these identified 5-HT neurons directly activate the effectors responsible for three physiological components of feeding: salivary secretion, bite-like movements and pharyngeal peristalsis. A localized warming of the lip is sufficient to initiate ingestion and synaptically excites anterior 5-HT cells into high frequency impulses or bursts. Distension of the body wall terminates ingestion and also hyperpolarizes these 5-HT neurons. Serotonin treatment produces hyperphagic behavior by the leech, while a specific pharmacological lesion of its 5-HT cells produces the anorexic behavior of satiation. This anorexia is transiently reversed by 5-HT treatment. Serotonin plays an obligatory role in the initiation and expression of leech feeding behavior by its differential modulation of central neuronal networks and peripheral glands and muscles.

Short-latency scalp somatosensory evoked potentials and central spine to scalp propagation characteristics during peroneal and median nerve stimulation in multiple sclerosis

Peripheral (cauda-lumbar, wrist-Erb, Erb-cervical) and central (cauda-vertex, cervical-scalp) nervous impulse propagation velocities and times to peroneal and median nerve stimulation were investigated in 34 patients suffering from definite (17 cases), probable (6 cases) and possible (11 cases) forms of multiple sclerosis (MS). In 6 cases short- and intermediate-latency scalp somatosensory evoked potentials to peroneal nerve stimulation were recorded with ‘open’ (1–5000 Hz, −6 dB) bandpass filters and subsequently digitally filtered through a ‘narrow’ bandpass (200–5000 Hz, −6 dB). The lumbar response was abnormal in 2.95% of legs, while the Erb response was always within normal limits. The cauda-vertex conduction was altered in 75% of the examined limbs (86.2% definite, 58.3% probable, 63.6% possible MS). Absent scalp responses to peroneal stimulation were often encountered during narrow bandpass recording (54.9%), while a slowed central conduction was less frequent (33.3%). Scalp responses when recorded with open bandpass were always identifiable, being delayed in 3 out of 6 cases. In 5 of these the short-latency wavelets were either absent or showed a prolonged interpeak time even when open filter records were normal. Median nerve SEPs were altered in 60.3% of cases, more frequently because of a delayed scalp response or of a prolonged cervical-scalp conduction time than because of an absent cervical or scalp response. When peroneal and median nerve data were considered together, the rate of abnormality rose to 88.2% of patients. Due to their length, afferent pathways from the lower limb might suffer from a loss of high frequency impulse coding as an early sign of defective impulse propagation.

Diagnosis of Acute Nerve Compression in the Cat with High Frequency Nerve Trains Evoked Responses

High frequency nerve trains were evaluated from above and below the site of compression before, during, and after acute compression of the sciatic nerves of six adult cats. Acute nerve compression reduced the ability of axons to conduct high frequency impulse trains: the longer the compression, the lower the frequency of impulses that could be conducted through the region of compression without a decrement in latency and amplitude. Possible mechanisms for alterations of nerve trains and the possible clinical and experimental use of nerve trains analysis are discussed.

THE INFLUENCE OF MOTOR NERVE TETANIZATION ON THE EFFECT OF ORGANOPHOSPHORUS CHOLINESTERASE INHIBITORS ON NEUROMUSCULAR TRANSMISSION

1. The changes in the activity of synaptic cholinesterases (ChE) of the ant. tibial muscle in the anaesthetized cat were detected by recording the changes of the blocking activity of acetylcholine (ACh) and comparing them with the blocking activity of carbaminoylcholine (carbachol) injected intra-arterially or intravenously. After the administration of organophosphorus inhibitors (OPI) of ChE the ACh blocking dose diminished 500 to 2000-fold but the carbachol blocking dose did not change. In 4-6 h after the injection of OPI the ACh blocking dose increased again 8 to 15-fold, but the dose of carbachol still remained unchanged. The transmission of high frequency impulses improved after OPI in parallel with the decrease of the ACh blocking activity. Thus the synaptic ChE is partly restored in a few hours after its irreversible inhibition with OPI. 2. Tetanization of the motor nerve (50-60 Hz, 10 min), started simultaneously with the intravenous injection of OPI (armine Gd-42), diminished the impairment of neuromuscular transmission. On the side of tetanization the ACh blocking action was less pronounced and the transmission of high frequency impulses better than on the control side. Thus the tetanization produced some protection of synaptic ChE against inhibition by OPI. The protective effect of tetanization was absent when the tetanization was performed before the injection of OPI or was started 10-20 min after the injection of OPI. 3. The protective effect of tetanization was also observed on the isolated phrenic nerve diaphragm preparation of the rat. 4. The possible mechanisms of the protective effect of tetanization are discussed.

Effect of procaine on asphyxial rigidity

Procaine (0.2–0.5%) was applied to the motor nerve of the gastrocnemiussoleus muscle of cats showing either “secondary” or “late” tone after asphysiation of the cord for appropriate periods of time. The drug tended to abolish the responses both to sinusoidal slow and fast (0.2–2 cycle/sec) stretch of the muscle before the muscle action potentials elicited by a single shock to the sciatic nerve started to decline. Although secondary tone in contrast to the late tone is characterized by considerable γ-efferent activity, both forms of asphyxial rigidity were similarly affected by procaine. It was, therefore, postulated that, in addition to the selective effect of procaine on the γ-efferents, this local anesthetic also affects the transmission of high frequency impulse trains in the Ia fibers, which represent the sensory input for the myotatic reflex underlying the response of the muscle to stretch. Evidence was obtained that in the concentrations and time of application used to affect the stretch responses procaine impedes the transmission of high frequency trains of impulses.

Some observations on allergy in neurites

Experiments were performed on guinea pigs. It was shown that the antigen, normal horse serum, acted on the nerve of a sensitized animal to depress its conductivity. The conduction of high frequency impulses was the first to be affected. No such changes occurred when the antigen acted on the nerve of a non-sensitized animal.

On the treatment of muscle atrophy with very high frequency impulses.

The sciatic nerves of 10 rabbits were severed on both sides and very high frequency impulses were administered to their gastrocnemius muscle groups unilaterally. In 3 to 62 days after the beginning of the stimu-ation, the muscles groups were cut out at the insertion of the tendons on both sides and weighed, for estimating the degree of muscle atrophy in comparison. The results obtained were as follows: 1. The weight of the gastrocnemius muscles on the treated side in comparison with that of the muscles on the other side was always larger and apparently showed that such a treatment was effective in controling muscle atrophy. 2. The impulse treatment should be begun in a short period after the cutting off of the nervous control and should be continued in daily administration more than two months.

Décharges réticulaires induites par la polarisation du cervelet: Leurs rapports avec le tonus postural et la réaction d'éveil

1. 1. Spikes discharges were led with wire microelectrodes from the medial reticular formation of the medulla in decerebrate or “encéphale isolé” cats. 2. 2. Three types of spontaneous reticular activity are observed: ( a) low frequency (2–5/sec.), irregular discharges; ( b) high frequency (up to 50–100/sec.), continuous discharge; ( c) outbursts of high frequency impulses. 3. 3. When patterns of type ( c)_are recorded in the decerebrate animal, inhibition of extensor rigidity occurs in the ipsilateral limbs, synchronously with the reticular outbursts. Sometime, but not constantly, a correlation between spontaneous reticular discharges and EEG patterns is observed. 4. 4. Strong increase of reticular discharge and inhibition of extensor hypertonus are elicited in the decerebrate animal by surface positive polarisation (0,5 to 1,5 mA) of the medial part of the cerebellar anterior lobe. The cerebellar origin of these effects is shown by control experiments. 5. 5. The same intensities of cerebellar polarisation yield strong increase in the reticular discharge and generalized EEG arousal, when applied during the spontaneously occurring sleep of the “encéphale isolé” cat. The arousal is abolished by doses of intravenous chloralosane (1,75 mg/kg.) which do not prevent the EEG arousal by reticular or sensory stimulations. The cerebellar origin of these effects is shown by other control experiments. 6. 6. Sometimes units of the medial reticular formation are completely inhibited by cerebellar polarization (up to 0,5 mA), too weak for eliciting clear-cut increase of reticular discharge or generalized EEG arousal. 7. 7. The relations of these findings with the reticular influence on both cortical and bulbospinal spheres are discussed.

Die gravitationelle Deklination, ihre Bestimmung und ihre Elimination

The gravitational declination appears here as the analogue of the wellknown magnetic declination. The photographic recording theodolit in connection with a high frequency impulse transmitter allows, by a method of simultaneousness on two fieldstations, its direct and connected measurement and its elimination with regard to geodetic directions. The method has been based on linear equations, with the only request of horizontal angle measurements to a plain system of stars, abstracting from any transportable clocks. The method promises a higher accuracy and a multiple as great working velocity, comparatively to the state at present.