S1 Intensity Research Articles

Regional differences in arrhythmogenic aftereffects of high intensity DC stimulation in the ventricles.

Regional differences of the aftereffects of high intensity DC stimulation were investigated in isolated rabbit hearts stained with a voltage-sensitive dye (di-4-ANEPPS). Optical action potential signals were recorded from the epicardial surface of the right and left ventricular free wall (RVep, LVep) and from the right endocardial surface of the interventricular septum (IVS). Ten-millisecond monophasic DC stimulation (S2, 20-120 V) was applied to the signal recording spots during the early plateau phase of the action potential induced by basic stimuli (S1, 2.5 Hz). There was a linear relationship between S2 voltage and the S2 field intensity (FI). S2 caused postshock additional depolarization, giving rise to a prolongation of the shocked action potential. With S2 > or = 40 V (FI > or = approximately 20 V/cm), terminal repolarization of action potential was inhibited, and subsequent postshock S1 action potentials for 1-5 minutes were characterized by a decrease in the maximum diastolic potential and a decrease in the amplitude and a slowing of their upstroke phase. The higher the S2 voltage, the larger the aftereffects. The changes in postshock action potential configuration in RVep were significantly greater than those observed in LVep and IVS when compared at the same levels of S2 intensity. In RVep, 12 of 20 shocks of 120 V resulted in a prolonged refractoriness to S1 (> 1 s), and the arrest was often followed by oscillation of membrane potential. Ventricular tachycardia or fibrillation ensued from the oscillation in five cases. No such long arrest or serious arrhythmias were elicited in LVep and IVS. These results suggest that RVep is more susceptible than LVep and IVS for arrhythmogenic aftereffects of high intensity DC stimulation.

Time-course of Spatial-attentional Focusing in the Case of High Processing Demand on the Peripheral Precue

Subjects had to identify pairs of spatially overlapping or neighbouring letters exposed successively at various locations around the central fixation. The first letter (S1) in a pair acted both as a physical precue to indicate the S2 location and as a stimulus letter to be identified. The second letter (S2) in a pair acted only as a letter to be identified. The SOA was varied between 0 and 320 ms in different experiments. Comparison of the time-course functions of S2 identification in the conditions of (1) single pair presentation and (2) presentation of the letter pairs in the context of distractor letters that accompanied S2 in time, but occupied alternative spatial positions, revealed that S2 processing from the covert spatial-attentional focus was open to non-decreasing interference from the distractor letters up to 240 ms SOAs. An unexpected result consisted in equal level of S2 identification regardless of whether S1 had to be identified or not. This shows that if the peripheral precue has to be processed with higher processing demands at the identification level beyond simple location processing (which by itself is sufficient to fulfil the spatial orienting function), then the narrowing down or zooming-in of the attentional area in response to a physical precue can take place as effectively as in the case of a lesser processing demand on that precue. By comparing the relative time-course functions of S1 and S2 identification, it was found that S2 identification gained significant advantage over S1 identification at intermediate SOAs even if the intensity of S1 exceeded that of S2. The results of this investigation refer to the spontaneous, automatic nature of spatial attentional focusing that is evoked by spatially localised transient signals, but also to the possibility of interference between the targets and distractors in the working memory representation.

Hyperlucent Lung in a Patient With Mitral Valve Disease

A 15-year-old boy with rheumatic valvular heart disease was referred for cardiac surgery. His chief complaints were increasing shortness of breath (New York Heart Association class III) and palpitations. He was well otherwise previously. He specifically denied any significant respiratory troubles. He was receiving digoxin, furosemide, and warfarin sodium. On physical examination, he had an irregular pulse (80 beats per minute) and BP of 100/70 mm Hg. Cardiovascular examination showed an increased jugular venous pressure (9 cm above sternal angle), displaced apex to the sixth intercostal space and anterior axillary line, sustained parasternal lift, decreased intensity of S1, a loud pulmonary component of S2, an opening snap, a middiastolic murmur and a loud pansystolic murmur at the apex, and an enlarged liver (4 cm below the costal margin). Chest examination showed reduced expansion on the left side, a resonant percussion note bilaterally, markedly reduced breath sounds on the left side, and fine basal crackles on the right side.

Demonstration of facilitatory I wave interaction in the human motor cortex by paired transcranial magnetic stimulation.

1. Transcranial magnetic stimulation (TMS) of the human motor cortex results in multiple discharges (D and I waves) in the corticospinal tract. We tested whether these volleys can be explored non-invasively with paired TMS. The intensity of the first stimulus (S1) was set to produce a motor-evoked potential (MEP) of 1 mV in the resting contralateral abductor digiti minimi (ADM) muscle; the second stimulus (S2) was set to 90 % of the resting motor threshold. At interstimulus intervals of 1.1-1.5, 2.3-2.9 and 4.1-4.4 ms the MEP elicited by S1 plus S2 was larger than that produced by S1 alone. 2. Varying the S1 intensity between 70 and 130 % resting motor threshold with S2 held constant at 90 % resting motor threshold showed that the threshold for the first MEP peak was <= 70 % resting motor threshold. The second and third MEP peaks appeared only at higher S1 intensities. The latency of all peaks decreased with increasing S1 intensity. 3. Varying the S2 intensity with S1 held constant to produce a MEP of 1 mV on its own showed that the amplitude of all MEP peaks increased with S2 intensity, but that their timing remained unchanged. 4. Paired TMS in the active ADM (S1 clearly suprathreshold, S2 just above threshold; interstimulus interval, 1 ms) produced strong MEP facilitation. The onset of this facilitation occurred later by about 1.5 ms than the onset of the MEP evoked by S2 alone. No MEP facilitation was seen if the magnetic S2 was replaced by anodal or cathodal transcranial electrical stimulation. 5. It is concluded that the MEP facilitation after paired TMS, at least for the first MEP peak, is due to facilitatory interaction between I waves, and takes place in the motor cortex at or upstream from the corticospinal neurone.

Changes of serum alkaline phosphatase isoenzymes in fasted rats.

Changes of serum alkaline phosphatase (sALP) isoenzymes under fasting conditions were examined using polyacrylamide gel electrophoresis (PAGE), amino-acids (L-phenylalanine (L-Phe), L-homoarginine (L-HArg)) inhibition and wheat germ agglutinin (WGA) treatment. The sALP of non-fasted rats was separated into three bands (S1, S2, S3) by PAGE. The molecular weight (M.W.) of S1 corresponded to that of an isoenzyme found in the ileum. By the addition of L-Phe, the staining intensity of S1 was weakened, S2 and S3 remained unchanged and the total activity of the isoenzymes extracted from intestine decreased. On the other hand, the activity of isoenzymes extracted from kidney and bone decreased by the addition of L-HArg. Therefore, S1 was judged to be derived from intestine. The activities of total sALP and S1 decreased from 16 h of fasting. Total sALP activity and sALP activity of the supernatant prepared by WGA treatment decreased, whereas the ALP activity of the precipitate (difference between total sALP activity and supernatant sALP activity) did not change. The activity band of the precipitate corresponded to that of S3 by PAGE. Therefore, S3 was judged to be derived from bone. In conclusion, under fasting conditions, the activity of S1 decreased while the activities of S2 and S3 remained unchanged.

Damage-induced luminescence in InP

Optical properties of scratched InP specimens were studied by means of cathodoluminescence (CL). A new luminescence band around 942 nm (S1) was detected in the vicinity of scratches. The S1 band is composed of two peaks at 938 and 946 nm. Monochromatic CL images showed that the S1 luminescence is constrained to regions of high residual strain and not related to dislocations or cracks. The S1 intensity increased in samples with a higher Fe content. S1 vanished after 450 K annealing.

Augmentation of the early component of the human blink reflex with closely spaced stimulus pairs

The effect of closely spaced percutaneous stimuli (S1 and S2) on the early (R1) component of the human blink reflex was studied in three experiments. In all experiments, successive R1 components (called R11, and R12 here) were frequently elicited by S1–S2 pairs with stimulus onset asynchronies (SOAs) as brief as 4 msec. The successive R1s appeared to be under the separate control of S1 and S2, respectively. Experiment 1 (in which S1 was set at each subject’s threshold for R1 elicitation and S2 was set at 80% of that threshold) and Experiment 2 (in which S1 was set at 80% of each subject’s threshold for R1 elicitation and S2 was set at the threshold level) showed that S2 had no effect on either the probability or the amplitude of R11 but that S1 increased both the probability and the amplitude of R12 above control levels established by presentation of S2 alone. Augmentation of R12 was greatest at the shortest SOA tested (4 msec) and decayed to zero at an SOA of about 11–12 msec. Paired stimuli produced no systematic effect on the latency of either R11, or R12. Experiment 3 showed that the probability and amplitude of R11 increased with S1 intensity but were unaffected by S2 intensity over the range tested. The probability and amplitude of R12 increased with S2 intensity and were increased by the presence of S1; the augmentation produced by S1 was greater at the 4- than at the 8-msec SOA, and increased with S2 intensity. There were no systematic effects on the latency of either R1. Reflex augmentation in these experiments is not consistent with the model of temporal integration of stimulus energy. Instead, a percutaneous stimulus appears to evoke a transient excitation of the R1 pathway; a second percutaneous stimulus presented before the excitation decays is more likely to elicit an R1 than otherwise, and the R1 elicited will on the average be larger.

Porphyroblast–fabric relationships: an example from the Appin Group in the Glen Roy area

Synopsis The Neoproterozoic Grampian and Appin groups exposed in the Glen Roy area were deformed during an initial progressive tectono–thermal event of the Grampian orogeny. Prograde regional metamorphism to amphibolite facies accompanied deformation with the thermal peak coinciding with the second phase of folding (F2) and the imposition of an S2 crenulation to transposition fabric. In the pelitic to semipelitic schists of the Lochaber Subgroup (Appin Group), metamorphism resulted in the development of the assemblage: quartz + muscovite + biotite ± garnet, plagioclase (An 13 to 22%), staurolite and opaques. The complexity of porphyroblast–fabric relationships recorded from the schists varies systematically across the area and can be directly related to the intensity of S2. Six progressive stages of S2 crenulation cleavage development are recognized, preserved within multitextured, syn-kinematic garnet porphyroblasts. These stages show a progression from a planar S1 fabric to differentiated S2 crenulation cleavage, through to the development of a differentiated S2 transposition fabric. Porphyroblast–fabric relationships are further complicated by the localized reactivation of S1 in response to movement along the Grampian–Appin lithostratigraphic boundary during F2 folding. Biotite porphyroblasts developed early during the imposition of S2 and were subsequently deformed during D2 to form lenticular mica-fish. Staurolite (rare) nucleation and growth, representing peak metamorphism recorded by these schists, post–dated S2 development.

The effects of selective stellate ganglion manipulation on ventricular refractoriness and excitability.

The effects of selective stellate ganglion stimulation or stellectomy on ventricular excitability were studied in 30 open chest mongrel dogs anesthetized with alpha-chloralose. The effective refractory period (ERP) and strength interval curves (stimulus intensity [S2] = twice the diastolic threshold [ERP], and 2, 3, 5, 7, and 14 mA) were determined using bipolar epicardial electrodes placed in the mid-anterior wall of the right ventricle (RV) and the mid-posterolateral wall of the left ventricle (LV) during left stellate ganglion stimulation (LSGSt, n = 8) or right stellate ganglion stimulation (RSGSt, n = 8), or after left stellectomy (LSGEx, n = 7) or right stellectomy (RSGEx, n = 7). LSGEx prolonged ERP-LV (172 +/- 9 vs 167 +/- 8 msec, P < 0.05) and ERP-RV (163 +/- 10 vs 158 +/- 14 msec, P < 0.05). RSGEx prolonged ERP-LV (168 +/- 17 vs 162 +/- 15 msec, P < 0.01) and ERP-RV (166 +/- 14 vs 160 +/- 13 msec, P < 0.01), and the times of the strength interval curves obtained for each S2 intensity in both ventricles. LSGSt decreased ERP-LV (157 +/- 11 vs 163 +/- 12 msec, P < 0.01) and ERP-RV (147 +/- 18 vs 157 +/- 17 msec, P < 0.05), and the times of the strength interval curves obtained for each S2 intensity in both ventricles. RSGSt did not significantly decreased ERP-LV (152 +/- 11 vs 156 +/- 9 msec); however, it significantly shortened the times of the strength interval curves obtained for S2 intensities of 2 and 7 mA in the LV, and shortened ERP-RV (139 +/- 10 vs 145 +/- 7 msec, P < 0.01) and the times of the strength interval curve for S2 intensities of 2, 3, and 5 mA in the RV. A significant interaction (MANOVA test) was observed between the ventricle studied and the ganglion stimulated for S2 intensities of 2 and 3 mA, and between the effect of stimulation and the ganglion stimulated for S2 intensities of 3 and 14 mA. To conclude, selective stellectomy prolonged epicardial ventricular refractoriness in both the mid-anterior wall of the RV and the mid-posterolateral wall of the LV; the magnitude of the epicardial excitability variations in both areas was different during selective stellate ganglion stimulation.

Effects of drive train stimulus intensity on ventricular refractoriness in humans.

The strength-interval relation between the intensity of premature stimulus and the ventricular effective refractory period (VERP) has been well characterized. The effects of variation in the intensity of the basic drive train stimuli (S1) on VERP are not as well defined. This relation was studied in 44 patients undergoing clinically indicated electrophysiological study. The outputs of two stimulus isolation units were connected in parallel, allowing the intensity of S1 to be varied independently of intensity of the extrastimulus (S2). To prevent confounding effects from cycle length change, continuous overdrive pacing was performed for 3 minutes before each measurement of VERP. The effect of S1 intensity on VERP was assessed in 24 patients with S2 intensity kept constant at twice threshold. VERP shortened from 232 +/- 19 msec at an S1 intensity of 1.5 times threshold to 219 +/- 20 msec at 5 mA and 211 +/- 19 msec at 10 mA (p less than 0.0001 for baseline versus 5 mA and for 5 mA versus 10 mA). Autonomic blockade with atropine and propranolol blunted but did not completely eliminate this effect. To assess whether the effect of S1 intensity on VERP was independent of S2 intensity, S2 strength-interval curves were generated in 10 patients at low (1.5 times threshold) and high (10 mA) S1 intensities. All portions of the strength-interval curve were shifted to the left by an increase in S1 intensity. The time course of change in VERP after an abrupt increase in S1 intensity was assessed in an additional 10 patients. VERP changed slowly, requiring 18 +/- 28 seconds to shorten by 2 msec and 64 +/- 46 seconds to decrease by 10 msec after a change in S1 intensity from 1.5 times threshold to 10 mA. In a final group of 10 patients, VERP was measured using an eight-beat drive train and a 4-second intertrain interval. With this more conventional protocol, VERP shortened by 14 +/- 8 msec with an increase in S1 intensity from 1.5 times threshold to 10 mA. Increasing S1 intensity results in clinically significant, progressive shortening of VERP in man. This effect is independent of S2 intensity. The prolonged time course of the change in VERP after an increase in S1 intensity and the attenuation of this effect by autonomic blockade are consistent with stimulation of sympathetic nerve terminals and catecholamine release as a result of intense stimulation.

The Ventricular Excitability‐Interval Relationship in Early Diastole in Humans: The Influence of the Electrode Configuration During Bipolar Stimulation

The purpose of this study was to determine the relationship between ventricular excitability and the extrastimulus (S2) coupling interval in early diastole in humans. The influence of the electrode configuration during bipolar stimulation was examined. Ventricular strength-interval curves were constructed using an eight beat drive train at a cycle length of 600 msec, 2-msec decrements in the S2 coupling interval, and 0.2-mA increments in the current intensity of S2 at each coupling interval. A transient dip in the excitation threshold was observed in early diastole during bipolar pacing when the distal electrode was the anode in six of 17 patients (35%). In contrast, this type of dip was not observed when the distal electrode was the cathode. The excitation threshold at the trough of the dip ranged from 1.0 to 2.2 mA. Unipolar strength-interval curves indicated that a dip occurred with anodal but not cathodal pacing. We postulated that the dip might interfere with the accurate determination of the ventricular effective refractory period by resulting in transient loss of ventricular capture during decremental scanning of diastole with S2. A gap in ventricular capture was produced in all six patients who demonstrated a dip in the bipolar strength-interval curve by selecting an S2 current intensity that fell within the dip. In conclusion, the bipolar strength-interval curve may display an early diastolic dip in the excitation threshold, depending on the electrode configuration.(ABSTRACT TRUNCATED AT 250 WORDS)

Summation of Excitation with a Single Conditioning Stimulus in the Canine Heart

A subthreshold stimulus was reported to become effective in producing a propagated ventricular response when preceded by another subthreshold stimulus or stimuli, a phenomenon that is known as summation of excitation but has not been studied systematically. Effect on summation of current intensity and coupling interval of a conditioning stimulus (Sc, protocol #1) and that of stimulation site of Sc (protocol #2) were determined in anesthetized, open-chest dogs. Effective refractory period (ERP) was determined with an extrastimulus (S2) at a ventricular pacing cycle length (S1S1) of 500 msec. Pulse width of S1, S2 and Sc was 2 msec. For pacing protocol #1 (12 dogs), current intensity of S1 and S2 was equal (twice diastolic threshold, 2, 5, or 15 mA), and that of Sc was equal to or lower than that of S1. S1S2 interval was fixed 1 msec shorter than ERP, and Sc was delivered 5 msec prior to S2. The S1Sc interval was shortened in 2 msec steps. Summation was present if Sc plus S2 evoked a propagated response. Prevalence of summation increased along with an increase in current intensity of Sc (P less than 0.01). For pacing protocol #2 (7 dogs), current intensity of S1, S2 and Sc was equal (twice diastolic threshold, 5 or 10 mA). As the distance between site of Sc and that of S2 increased, prevalence of summation decreased (P less than 0.01). Summation did not occur when Sc was delivered at a site only 5 mm away from the site of S2. In conclusion, summation of excitation with a single conditioning stimulus was both time and strength dependent, and limited in development spatially.

Application of static SIMS to the study of rubber cross‐linking

AbstractStatic SIMS has been used to analyze the sulfur cross‐links at the surface of compounded polyisoprene rubbers. Linear relationships were found between the normalized intensities of S1− ions and the total cross‐link densities and between the intensities of the S4− clusters and the percentages of the polysulfidic cross‐links.

Contingent negative variation in processes of expectancy, motor preparation and time estimation

The Contingent Negative Variation (CNV) was compared in four paradigms inducing distinct processes. All paradigms comprised empty intervals of 4 sec bounded by two 100 msec stimuli (S1 and S2) or by S1 and the response (a button press). In paradigm ID (Intensity Discrimination), the S1–S2 interval was followed, after another delay, by a choice response depending on the intensity of S2. In paradigm RT (Reaction Time), the S1–S2 interval was followed by a simple reaction time. In paradigm TP (Time Production), the subjects had to produce a response 4 sec after S1. In paradigm TR (Time Reproduction), the duration of the S1–S2 interval was estimated by the subjects and was to be reproduced after S2. Electrodes were placed on Cz, Fz and Pz in 12 human subjects. The largest CNVs were obtained in paradigm TR. Motor preparation before S2 had no effect on CNV amplitude. Discussion focuses upon the relations between CNV, temporal processes and activation.

Current noise generated by electrogenic ion pumps.

Active ion transport by ATP- or light-driven pumps involves a sequence of elementary steps such as binding and release of ions, as well as conformational transitions of the pump protein. At the microscopic level the individual reaction steps occur at random intervals, and therefore the current generated by electrogenic pumps fluctuates around a mean value. In this paper, a theoretical treatment of the electrical noise associated with active ion transport is given. The analysis, which is based on the calculation of the correlation function, yields the spectral intensity S1 of current noise as a function of frequency, f. The shape of S1(f) contains information on the rate constants as well as on the magnitude of the charge displacements occurring during single reaction steps. The contribution of electrogenic pumps to the total voltage noise of the cell may be estimated from S1(f) and from the frequency-dependent impedance of the cell membrane.

Stimulus Omission and Dishabituation of the Skin Conductance Response

Three experiments investigated the effects on the skin conductance response of S2 omission following 15 S1-S2 presentations. These effects were examined at omission and on the following S1-S2 (re-presentation) trial. In Experiment 1 (N = 36), S1 was a 5-sec slide of a snake and S2 was 1 sec of either 65 or 105 dB white noise. The S1-S2 interval was 4 sec. Both frequency and amplitude of omission responses were a positive function of S2 intensity, and responding to S2 re-presentation was reliably higher than on the preomission trial. Experiment 2 (N = 36) used the same S1, an S2 of 105dB, and two additional groups which controlled for stimulus omission and spontaneous recovery. Omission of S2 again produced increased responding to its re-presentation. In Experiment 3 (N = 72), S1 and S2 were moderately intense tones (80dB) and lights (1089 cd/cm2. The procedure for the experimental and two control groups was essentially the same as in Experiment 2, except that S1 modality was counterbalanced across subjects. The experimental group displayed significantly larger responses to S2 on the re-presentation trial than the control groups regardless of its modality. The results are discussed in terms of theories of habituation with special emphasis on the concept of priming utilized by Wagner (1976) and Ohman (1979).

反射喚起と先行刺激抑制効果の独立性 ヒトの驚がく性瞬目反射を指標として

In the present study, the relationship between startle elicitation and lead-stimulus inhibition was examined. The amplitude of the human startle eyeblink reflex increased linearly with increases in the intensity of reflex-eliciting noise (S2). A lead-stimulus (S1), a pip tone of 70dB, inhibited the reflex at both conditions with lead times of 100ms (Experiment 1) and 250ms (Experiment 2). The amplitude of the reflex was reduced by an equal amount regardless of the intensity of S2 in both experiments. The results show that the lead-stimulus inhibition is independent of the reflex elicitation.

The correlates of an abnormal first heart sound in mitral-valve-prolapse syndromes.

In 52 patients with mitral-valve prolapse we studied the intensity of the first heart sound (S1) in relation to the timing of the prolapse and to the presence of leaflet tip coaptation. Sixteen normal subjects served as controls. With two-dimensional echocardiography, three distinct groups were identified. Sixteen patients had early systolic mitral prolapse coincident with initial mitral-leaflet coaptation at the S wave on electrocardiography. Twenty-one had middle to late systolic mitral prolapse. Fifteen had flail mitral leaflet without normal leaflet coaptation at the free margins. The intensity of S1 was expressed as the ratio of the S1 amplitude to that of the aortic component of the second heart sound. This ratio was greater in the patients with early prolapse (6.2 +/- 3.1, mean +/- S.D.) than in the controls (1.4 +/- 0.7) (P less than 0.01). The ratio was reduced in patients with flail valves (0.3 +/- 0.5) (P less than 0.01) and did not differ between patients with middle to late prolapse (1.3 +/- 0.6) and controls. We conclude that the amplitude of S1 may provide a clue to the type and timing of mitral-valve prolapse.

Reflex inhibition and reflex elicitation by acoustic stimuli differing in abruptness of onset and peak intensity

The rat’s acoustic startle reaction to a loud tone (S2) was inhibited by white-noise preliminary stimuli (S1) varying in rise/decay time (5 and 100 msec) and intensity (70, 80, and 90 dB). The amount of inhibition was linearly related to the intensity of S1 but was unaffected by its rise/ decay time. In contrast, the response directly elicited by S1 was affected by both variables, being greater with greater intensity and with the more abrupt onset. These data reveal that reflex elicitation and reflex inhibition are the products of different neural mechanisms.

Inhibition of the human eyeblink reflex: an evaluation of the sensitivity of the Wendt-Yerkes method for threshold detection.

In two experiments, human subjects showed a reduced eyewink reflex to an airpuff (S2) if it was preceded by a light flash or a noise burst (S1). The first (N=6) showed that a light inhibited the blink maximally at a 100-msec lag. In the second (N=8), thresholds for noise pips were established with the method of limits. Then the pips were presented in multiples of threshold values as S1 100 msec before S2. Sujbects pressed a button whenever they heard the sound, on S1-S2 pairs, on S1 alone, or on S2 alone trials. Eyeblinks to S2 declined in amplitude and increased in latency as S1 intensity increased. The threshold S1 (approximately 2 dB over a 50-dB background) produced reliable inhibition in 7 of 8 subjects, and a weaker S1 which never evoked a button press was sufficient to produce reliable inhibition for the group as a whole. Inhibition in any particular trial was unrelated to button pressing. The sensitivity of the reflex technique and its relative invariance to task demands suggest its usefulness as a behavioral psychophysical procedure.