Attosecond time-resolved photoelectron holography.

Ultrafast strong-field physics provides insight into quantum phenomena that evolve on an attosecond time scale, the most fundamental of which is quantum tunneling. The tunneling process initiates a range of strong field phenomena such as high harmonic generation (HHG), laser-induced electron diffraction, double ionization and photoelectron holography-all evolving during a fraction of the optical cycle. Here we apply attosecond photoelectron holography as a method to resolve the temporal properties of the tunneling process. Adding a weak second harmonic (SH) field to a strong fundamental laser field enables us to reconstruct the ionization times of photoelectrons that play a role in the formation of a photoelectron hologram with attosecond precision. We decouple the contributions of the two arms of the hologram and resolve the subtle differences in their ionization times, separated by only a few tens of attoseconds.

Non-invasive electrical stimulation of the brain (ESB) modifies the resting-state network connectivity of the primary motor cortex: a proof of concept fMRI study.

An innovative method to obtain fMRI resting-state network maps during non-invasive electrical stimulation of the brain (ESB) was developed and tested. Five healthy volunteers participated in 2 fMRI sessions. In session one, a transcranial direct current stimulator (tDCS) was applied placing the positive electrode (31.5 cm(2)) over the right M1 of the cortex and the negative electrode (31.5 cm(2)) over the left supra-orbital area of the head. In session two, a monophasic pulsed current stimulator (tPCS) was applied using the identical electrode placement. Imaging was performed on a Siemens 3T Tim Trio scanner with a 12-channel head coil. At each session, five consecutive functional scans were obtained: 1) resting-state without stimulation (Rest-1), 2) a motor scan consisting of self-paced, bilateral finger-thumb opposition task, 3) resting-state with ESB (Stim-1), 4) resting-state without stimulation (Rest-2), and 5) resting-state with ESB, replicating Stim-1 (Stim-2). Data were analyzed using AFNI and MATLAB. For motor task fMRI analysis, a general linear model (GLM) determined the voxels in the right and left M1 that were significantly correlated with the motor task paradigm. The resting-state time series from the voxels in the R-M1 were averaged and the resulting time series used as a regressor in a GLM analysis to identify M1 connectivity maps. Connectivity maps were quantified as R(2) values, and then combined to give overlap maps for each of the experimental conditions. Fourier analysis determined the energy in the normalized signal average time courses extracted from L-M1 and R-M1 for each of the resting-state scans. Both tDCS and tPCS lowered the R(2) values and energy of the averaged time course in the right and left M1 ROI. The effect of the tPCS appeared more pronounced and less variable among subjects. Applying non-invasive ESB during fMRI scanning may down regulate the motor cortex's resting-state network connectivity.

Correlation between levels of sex hormones (progesterone, testosterone, and estrogen) and ecophysiological-behavior stages in two species of desert snails (Sphincterochila zonata and Sphincterochila prophetarum) in the Northern Negev Desert.

The steroidal hormonal profiles of two sympatric species of desert snails, Sphincterochila zonata and Sphincterochila prophetarium were determined at three ecophysiological-behavior stages, i.e., aestivation, cryptobiosis, and active-feeding phases. Live snails were collected in their natural habitat every month for 13 months, the corpi removed and extracted with organic solvents and the progesterone, testosterone, and estrogen concentrations determined by radioimmunoassay. In both these hermaphroditic species during aestivation, a peak of testosterone followed by a peak of estrogen was observed. During the brief active intervals, minor peaks of estrogen were also observed but these were much lower than seen during aestivation. Although the two species have different microhabitats during aestivation, there was little difference in the hormonal profile, although S. prophetarum had about two fold higher progesterone concentration than S. zonata.

In vitro evaluation of a retrievable low-profile nitinol vena cava filter.

PURPOSE: To evaluate the clot-trapping ability, stability, and migration of a new low-profile, retrievable inferior vena cava (IVC) filter in an in-vitro model. MATERIALS AND METHODS: The SafeFlo IVC filter consists of two superelastic nitinol wires that form a double-ring platform and spiral filter. The filter is collapsed into a 5-6-F catheter and delivered into the IVC model. The in-vitro model closely simulates the physical parameters of flow in the human IVC. Human blood clots of 2-mm and 4-mm diameters and 3-cm lengths were injected into the flow system in sets of five clots. Filter delivery and retrieval were performed in every series. Filtration was evaluated in IVC models of 20-mm and 24-mm lumen diameter in vertical and horizontal positions. Stability and migration of the filter were evaluated by direct vision of maintenance of position and shape before and after clot trapping. RESULTS: Filter delivery and retrieval were straightforward and repeatable in a total of 20 procedures. The filters maintained shape and position throughout the study. A total of 248 clots were injected and 225 (90.7%) were trapped. The individual tests in horizontal and vertical positions with either clot size demonstrated trapping rates of 85.7%-97.1%. CONCLUSIONS: The SafeFlo IVC filter is a stable and effective filter in an in-vitro model. The filter design is amenable to simple delivery and retrieval.

Quadriceps femoris muscle torques and fatigue generated by neuromuscular electrical stimulation with three different waveforms.

BACKGROUND AND PURPOSE: Neuromuscular electrical stimulation is used by physical therapists to improve muscle performance. Optimal forms of stimulation settings are yet to be determined, as are possible sex-related differences in responsiveness to electrical stimulation. The objectives of the study were: (1) to compare the ability of 3 different waveforms to generate isometric contractions of the quadriceps femoris muscles of individuals without known impairments, (2) to compare muscle fatigue caused by repeated contractions induced by these same waveforms, and (3) to examine the effect of sex on muscle force production and fatigue induced by electrical stimulation. SUBJECTS: Fifteen women and 15 men (mean age=29.5 years, SD=5.4, range=22-38) participated in the study. METHODS: A portable battery-operated stimulator was used to generate either a monophasic or biphasic rectangular waveform. A stimulator that was plugged into an electrical outlet was used to generate a 2,500-Hz alternating current. Phase duration, frequency, and on-off ratios were kept identical for both stimulators. Participants did not know the type of waveform being used. Torque was measured using a computerized dynamometer. A maximal voluntary isometric contraction (MVIC) of the right quadriceps femoris muscle set at 60 degrees of knee flexion was determined during the first session. In each of the 3 testing sessions, torque of contraction and fatigue elicited by one waveform were measured. Order of testing was randomized. Torque elicited by electrical stimulation was expressed as a percentage of average MVIC. A mixed-model analysis of variance was used to determine the effect of stimulation and sex on strength of contraction and fatigue. Bonferroni-corrected post hoc tests were used to further distinguish between the effects of the 3 stimulus waveforms. RESULTS: The results indicated that the monophasic and biphasic waveforms generated contractions with greater torque than the polyphasic waveform. These 2 waveforms also were less fatiguing. The torques from the maximally tolerated electrically elicited contractions were greater for the male subjects than for the female subjects. DISCUSSION AND CONCLUSION: Muscle torque and fatigue of electrically induced contractions depend on the waveform used to stimulate the contraction, with monophasic and biphasic waveforms having an advantage over the polyphasic waveform. All tested waveforms elicited, on average, stronger contractions in male subjects than in female subjects when measured as a percentage of MVIC.

Effect of long-term electrical stimulation on motor recovery and improvement of clinical residuals in patients with unresolved facial nerve palsy.

PURPOSE: This study investigated the efficacy of a pulsatile electrical current to shorten neuromuscular conduction latencies and minimize clinical residuals in patients with chronic facial nerve damage caused by Bell's palsy or acoustic neuroma excision. SUBJECTS: The study group included 12 patients (mean age 50.4 +/- 12. 3 years) with idiopathic Bell's palsy and 5 patients (mean age 45.6 +/- 10.7 years) whose facial nerves were surgically sacrificed. The mean time since the onset of paresis/paralysis was 3.7 years (range 1-7 years) and 7.2 years (range 6-9 years) for the Bell's and neuroma excision groups, respectively. METHOD AND PROCEDURES: Motor nerve conduction latencies, House-Brackmann facial recovery scores, and a 12-item clinical assessment of residuals were obtained 3 months before the onset of treatment, at the beginning of treatment, and after 6 months of stimulation. Patients were treated at home for periods of up to 6 hours daily for 6 months with a battery-powered stimulator. Stimulation intensity was kept at a submotor level throughout the study. Surface electrodes were secured over the most affected muscles. Groups and time factors were used in the analyses of the 3 outcome measures. RESULTS: No statistical differences were found between the two diagnostic groups with respect to any of the 3 outcome measures. Mean motor nerve latencies decreased by 1.13 ms (analysis of variance test, significant P = 0.0001). House-Brackmann scores were also significantly lower (Wilcoxon signed rank test, P = 0.0003) after treatment. Collective scores on the 12 clinical impairment measures decreased 28.7 +/- 8.1 points after 6 months [analysis of variance test, significant P = 0.0005). Eight patients showed more than 40% improvement, 4 better than 30%, and 5 less than 10% improvement in residuals score. CONCLUSION: These data are consistent with the notion that long-term electrical stimulation may facilitate partial reinnervation in patients with chronic facial paresis/paralysis. Additionally, residual clinical impairments are likely to improve even if motor recovery is not evident.

Peripheral nerve excitation and plantar flexion force elicited by electrical stimulation in males and females.

STUDY DESIGN: Two-group (gender) posttest only using a sample of convenience. OBJECTIVES: Our study examined the effect of gender on selected stimulus properties, perceived pain thresholds, and maximally tolerated level of contraction of the plantar flexor muscle group. BACKGROUND: There is a dearth of literature regarding gender as a factor that may influence the outcome following the application of neuromuscular electrical stimulation. Data from other disciplines suggest that males and females may not have similar tolerance to electrical stimulation. METHODS AND MEASURES: Eleven women (mean age, 28.3 years +/- 5.6 years) and 9 men (mean age, 33.2 years +/- 6 years) participated in a single session of electrical stimulation. A pair of 4.5 x 4.5 cm, self-adhesive, synthetic, polymer electrodes was placed over the medial and lateral heads of the gastrocsoleus muscle group. Electrical stimulation was provided by a battery-powered pulsatile stimulator generating a symmetric biphasic waveform, 200-mu second phase duration, and pulse rate of 50 pulses per second. During testing, the subjects were seated on a specially constructed chair that incorporated a foot pedal attached to a piezoelectric force transducer to measure plantar flexion force. Stimulation amplitude was increased slowly until 4 thresholds (sensory, motor, pain, and maximal pain) were sequentially achieved. At each threshold, stimulus peak voltage, peak current, and phase charge used to elicit that threshold were recorded. Plantar flexion force was also recorded when stimulation was sufficient to achieve pain and maximal pain thresholds. RESULTS: The peak voltage, peak current, and phase charge needed to elicit the 4 thresholds did not differ between women and men at any threshold examined (2-factor ANOVA; Newman-Keuls post hoc tests). However, significantly higher stimulus peak voltage, peak current, and phase charge were recorded for each of the 4 thresholds (sensory, motor, pain, and maximal pain tolerance) for both groups. The plantar flexion force elicited by electrical stimulation was significantly lower in female subjects than in male subjects at both pain threshold and maximally tolerated stimulation levels. CONCLUSIONS: Gender can influence the magnitude of electrically induced plantar flexion contraction force. We hypothesize that females may require longer conditioning periods to achieve therapeutic levels of muscle contraction.

The first gene in the biosynthesis of the polyketide antibiotic TA of Myxococcus xanthus codes for a unique PKS module coupled to a peptide synthetase.

The polyketide antibiotic TA is synthesized by the Gram negative bacterium Myxococcus xanthus in a multi-step process in which a unique glycine-derived molecule is used as a starter unit and elongated through the condensation of 11 acetate molecules by polyketide synthases (PKSs). Analysis of a 7.2 kb DNA fragment, encoding the protein that carries out the first condensation step, revealed that the fragment constitutes a single open reading frame, referred to as Ta1, which lacks the 5' and 3' ends and displays two regions of similarity to other proteins. The first 1020 amino acid residues at the N terminus of the polypeptide are similar to sequences of the large family of enzymes encoding peptide synthetases. They are followed by a second region displaying a high degree of similarity to type I PKS genes. The genetic analysis of this open reading frame is compatible with the proposed chemical structure of TA. The data indicate that the genes encoding TA have a modular gene organization, typical of a type I PKS system. The unusual feature of Ta1 is that the first PKS module of TA resides on the same polypeptide as the peptide synthetase functional unit.

Reductions in self-injury produced by transcutaneous electrical nerve stimulation.

Transcutaneous electrical nerve stimulation is used to reduce pain but also may be useful for self-injurious behavior (SIB). In the current investigation, a microcurrent electromedical device, classified as a transcutaneous electrical nerve stimulator (TENS), was applied with a man with Down syndrome who displayed SIB that persisted in the absence of social contingencies. Although clinically significant results were not maintained, a clear difference in the rates of SIB during active and inactive TENS was observed.

The effects of selected stimulus waveforms on pulse and phase characteristics at sensory and motor thresholds.

BACKGROUND AND PURPOSE: The purposes of this investigation were to determine the effect of five commonly used voltage waveforms (four pulsed and one sinusoidal) on excitation of sensory and motor nerves and to characterize variables associated with reaching threshold. SUBJECTS: Eighteen healthy subjects were stimulated during one session via surface electrodes placed over the forearm and leg. METHODS: Stimulation amplitude was increased at a constant rate, and the threshold of sensory and motor excitation was determined. Measured variables included peak voltage, peak current, phase charge, and total pulse charge. RESULTS: Three-factorial, repeated-measures analysis of variance and Newman-Keuls tests revealed that phase charge varied the least during excitation induced by the five waveforms. Total pulse charge markedly increased when bursts of 10 symmetrical pulses, 25 symmetrical pulses, or amplitude-modulated waveforms were used. Monophasic and symmetrical biphasic waveforms required the least amount of total pulse charge. All measurements were higher during motor threshold than during sensory threshold, and the measurements were higher in the leg than in the forearm. CONCLUSION AND DISCUSSION: The authors concluded that all five studied waveforms were effective at threshold excitation of peripheral sensory and motor nerves. Of the five waveforms, the symmetrical biphasic waveform, having a low total pulse charge, may be the preferred waveform, and the 25 symmetrical pulses and amplitude-modulated waveforms may be considered the least preferred due to high total pulse charge.

Effects of electrode size on basic excitatory responses and on selected stimulus parameters.

Recent data have implicated the size of surface electrodes as an important factor affecting peripheral nerve excitation. Therefore, we studied the effects of electrode size on the basic excitatory responses and on stimulus characteristics. Four different sizes of self-adhesive surface electrodes were applied over the medial and lateral gastrocnemius muscle of 20 healthy subjects. The excitatory levels were sensory threshold, motor threshold, pain threshold, and maximally tolerated painful stimulation. Stimulus parameters included a symmetric biphasic waveform, 200 microseconds phase duration, and a pulse repetition rate of 50 pps. Amplitude was increased until the appropriate excitatory response was achieved. At this amplitude level, the computerized recording system collected data of stimulus peak current, peak voltage, and phase charge as well as isometric plantar flexion force. Repeated measure analysis of variance and Newman-Keuls post hoc tests revealed that increasing electrode size significantly decreased voltage but increased current and phase charge magnitudes. With increasing electrode area, the ratios of voltage/current decreased nonlinearly, while the ratios of charge/voltage increased nonlinearly. The comfort of stimulation for the same amount of plantar flexion force improved significantly as electrode size became larger. We concluded that electrode size affects the stimulus parameters, comfort, and force generation associated with electrically induced excitatory responses. Electrode size should be considered an integral part of the attempt to improve subject response to transcutaneous electrical stimulation.

The electrical effect of two commonly used clinical stimulators on traumatic edema in rats.

The purposes of this study were to determine the effect of electrical stimulation on traumatic rat hind-paw edema and to establish whether there would be a difference in edema reduction when two types of stimulators were used. The animals were divided into a control group (n = 15) and two experimental groups, one group receiving monophasic pulsed current (MPC group, n = 15) and the other group receiving symmetrical biphasic pulsed current (SBPC group, n = 14). The right hind-paw volume of all groups was measured prior to traumatization and at 24, 48, 72, and 96 hours posttrauma. Following the 24-, 48-, and 72-hour measurements, 1 hour of electrical stimulation was administered to the experimental groups. The control group received sham treatment. Results revealed significant edema reduction in all groups over the 96-hour period, with each group's greatest change in paw volume occurring 48 hours posttrauma. At the final paw volume measurement, there was no significant difference between the MPC and control groups or between the MPC and SBPC groups. The SBPC group, however, showed less reduction in edema than did the control group. One hour of electrical stimulation per day over 3 consecutive days failed to demonstrate significant edema reduction in either the MPC group or the SBPC group as compared with the control group. The results of this study demonstrated that the electrical stimulation characteristics and procedures currently used in the clinic do not significantly reduce extant edema caused by trauma in rat hind limbs.

Comparison of the effects of electrical stimulation and exercise on abdominal musculature.

The purpose of this study was to test the effect of electrical stimulation and volitional exercise on abdominal muscle strength and endurance. Changes of voltage, current, and tissue resistance were analyzed to determine tissue conditioning to stimulation. Subjects were randomly assigned to a control, stimulation (S), volitional exercise, or exercise combined with stimulation (ES) groups. Maximal voluntary isometric contraction and endurance data were recorded. In the three experimental groups, the number of repetitions and time of sustained contraction were increased by a predetermined amount during 4 weeks of training. The S and ES groups were stimulated using a biphasic, symmetrical pulse waveform having 200 microsec phase duration and 50 pulses per second. The ES group demonstrated the largest significant increases in abdominal strength, while the S group was the second best mode. No significant change in endurance occurred among the groups. Voltage and current increased significantly whereas tissue resistance decreased. It was concluded that combined exercise and stimulation may prove to be the most effective method of improving abdominal strength. J Orthop Sports Phys Ther 1987;8(12):567-573.

High voltage stimulation. Effects of electrode size on basic excitatory responses.

The purpose of this study was to examine the effects of electrode size on thresholds of sensory and motor excitation, strongest motor excitation without pain perception, and strongest motor excitation coupled with maximally tolerated painful stimulation. A high voltage stimulator with monophasic pulsatile current was applied to the quadriceps femoris muscles of 14 healthy subjects. Voltage output, pulse-charge density, and isometric muscle torque were measured during random application of four electrode pairs measuring 3 X 3, 6 X 6, 9 X 9, and 5 X 16.2 cm. Results indicated a dependence of the measured variables on electrode size; the larger electrodes required greater voltage output but less pulse-charge density than the smaller electrodes. The two largest electrodes evoked significantly greater non-painful and maximally tolerated painful muscle torques. Maximal volitional contraction increased 13.3% after completion of all stimulations. Electrode size should be considered by physical therapists when administering transcutaneous electrical nerve stimulation.

Optimization of pulse duration and pulse charge during transcutaneous electrical nerve stimulation.

The main effects and interaction of pulse duration and pulse charge on sensory, motor and painful stimulation were examined on six male subjects. Surface electrodes were placed over the triceps brachii muscle. Pulse duration was varied between 5 and 1000 µs. Peak current, muscle torque and four excitatory responses were determined. Sequential order of sensory, motor and painful stimulation was evidenced. Selective excitation of these different physiological responses was easier and required less charge as pulse duration became shorter. The greatest non-painful torque was reached at 100 µs pulse duration. The most suitable range for motor stimulation was 20 to 200 µs. For painful stimulation, a 5 to 10 µs duration was favoured. A range of 20 to 100 µs was recommended for sensory stimulation.

Electromyographic response of the elbow flexors to a changing, dislocating force.

The electromyographic (EMG) outputs of the biceps brachii, brachialis, and brachioradialis muscles of 14 subjects were monitored during the application of an externally generated, dislocating force across the elbow joint. Subjects were seated in an apparatus designed to maintain the right upper extremity at 90 degrees shoulder flexion and 180 degrees elbow extension. The dislocating force was increased from 0-22 Newtons (N) at an average rate of 2N/sec to determine if a minimum load were necessary before muscles would be activated. Although no muscle was found to be significantly more active than any other over the entire load range, post hoc analysis showed that both the brachialis and brachioradialis were significantly more active at loads above 18N than below. The biceps brachii showed no significant increase in activity. The practice of strengthening muscles as a means of protecting joint integrity can be questioned by these results since the muscles under study did little to resist elbow joint dislocation at loads up to 18N.