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PubMed1997

Rapid benefit of intravenous pulse loading of clomipramine in obsessive-compulsive disorder.

OBJECTIVE: The authors conducted a randomized, double-blind, placebo-controlled trial of intravenous versus oral pulse loading of clomipramine in patients with obsessive-compulsive disorder to test two hypotheses: 1) intravenous pulse loading will cause greater immediate improvement than oral pulse loading and 2) patients who respond to pulse loading will continue to improve during 8 weeks of oral clomipramine treatment. METHOD: Fifteen patients with DSM-III-R obsessive-compulsive disorder of at least 1 year's duration and baseline Yale-Brown Obsessive Compulsive Scale scores of 17 or higher were enrolled in the study. Yale-Brown scale ratings were made 4.5 days after double-blind oral or intravenous pulse loading of clomipramine, and patients were then given 150 mg/day of oral clomipramine with increases of 25 mg every 4 days to 250 mg/day as tolerated or, in two cases, other selective serotonin reuptake inhibitors (SSRIs). RESULTS: The first hypothesis was confirmed: 4.5 days after the second pulse-loaded dose, six of seven patients given intravenous clomipramine but only one of eight given oral medication responded to the drug. After 8 weeks of oral clomipramine, the results partially supported the second hypothesis: four of six patients who had responded to intravenous clomipramine continued their improvement, but those who had responded to pulse loading did not improve statistically significantly more than those who had not. CONCLUSIONS: Intravenous pulse loading of clomipramine may be a valuable new treatment for obsessive-compulsive disorder, particularly for patients who have failed oral treatment trials.

Administration, Oral↗

PubMed2000

Fos in the suprachiasmatic nucleus of house mouse lines that reveal a different phase-delay response to the same light pulse.

Increased light intensity of a 5-min light pulse is positively correlated with Fos mRNA and Fos protein levels in the suprachiasmatic nucleus (SCN) of hamsters. These findings suggest that the level of Fos activation is proportional to the light intensity and that the magnitude of the phase-shift response depends on the level of Fos activation. However, to what extent different phase-delay responses to the same light pulse are mediated by differential Fos activation is unknown. To elucidate this, the authors used selected house mouse lines that reveal an almost threefold difference in phase-delay responses in constant darkness (DD) between circadian time (CT) 16 and CT 20 to the same light pulse. The authors measured wheel-running activity and subjected male mice of these lines to a 15-min light pulse at CT 16 after 2 weeks in DD. The behavioral response was measured and 10 to 12 days later the animals were again subjected to the same light pulse at CT 16. One hour after the start of the second light pulse, the animals were sacrificed for Fos immunocytochemistry. Results indicate a significant difference between the lines in the phase-delay response (F2,26 = 5.112, p < 0.017) and the level of Fos activation (F2,26 = 27.15, p < 0.0001) after a 15-min light pulse at CT 16. These findings support the hypothesis that the magnitude of the phase-delay response is proportional to the number of cells in the SCN that exhibit Fos induction after the same 15-min light pulse at CT 16 in DD. It also indicates a possible difference in the input pathways among the lines.

Animals↗

PubMed1990

Phase shifts in the circadian rhythm in plasma concentrations of melatonin in rams induced by a 1-hour light pulse.

The effect of a 1-hr light pulse, given at night, on the timing of the circadian rhythm in the plasma concentration of melatonin was examined in Soay rams to investigate the mechanisms involved in determining the duration of the nocturnal peak in melatonin secretion. Animals (n = 8) were housed under short days (LD 8:16) or long days (LD 16:8) and received a light pulse at various times of night. They were released into constant dim red light (DD) on day 1. Blood samples were collected hourly for 30 hr from 1000 hr on day 3, and the plasma concentration of melatonin was determined by radioimmunoassay to assess the timing of the melatonin peak. Control animals (n = 8) were maintained under the same conditions but received no light pulse. Under short days, a light pulse given early in the night caused a phase delay in the melatonin peak, and a light pulse given in the late night caused a phase advance. The mean duration of the melatonin peak was slightly reduced following a light pulse in the early or late night, and slightly increased following a pulse given near the middle of the night. Under long days, both light-pulse treatments given at night caused a phase delay in the melatonin peak, but there was no significant change in duration of the melatonin peak. The duration of the melatonin peak at day 3 under DD in the control animals was similar for all treatments, regardless of the previous entraining photoperiod (mean duration: 12.6-14.8 hr) and was similar to that under short days (14.6 hr), but was significantly longer than that under long days (8.2 hr). Information on the phase response curve in the Soay ram and on the period of the circadian oscillator governing the melatonin rhythm (c 23.0 hr under DD) predicts a close phase relationship between the end of the light phase and the onset of the melatonin peak as observed under normal 24-hr LD cycles. The current results also indicate that light acts to entrain the circadian rhythm influencing the onset and offset of melatonin secretion, and thus dictates the duration of the melatonin peak.

Animals↗

PubMed2003

Brachial-ankle pulse wave velocity and symptomatic cerebral infarction in patients with type 2 diabetes: a cross-sectional study.

BACKGROUND: Recently a new automatic device that measures brachial-ankle pulse wave velocity using an oscillometric method has been developed. However, the practical significance of brachial-ankle pulse wave velocity measurement remains uncertain. The purpose of this study was to examine the association between brachial-ankle pulse wave velocity and symptomatic cerebral infarction in patients with type 2 diabetes. METHODS: One thousand sixty six patients with type 2 diabetes were studied cross-sectionally. Measurements of brachial-ankle pulse wave velocity were made using the automatic device. Logistic regression analysis was used to calculate the odds ratio for cerebral infarction. RESULTS: The presence of symptomatic cerebral infarction was confirmed in 86 patients. In these patients brachial-ankle pulse wave velocity was found to be significantly higher than in patients without cerebral infarction (18.94 +/-; 4.95 versus 16.46 +/-; 3.62 m/s, p < 0.01). The association between brachial-ankle pulse wave velocity and cerebral infarction remained significant after adjustment for traditional risk factors. There was an increasing odds ratio for each tertile of brachial-ankle pulse wave velocity, from the second tertile (odds ratio, 2.28; 95% confidence interval, 1.05 to 4.94), to the third (odds ratio, 2.53; 95% confidence interval, 1.09 to 5.86). CONCLUSION: Overall, we conclude that an increase in brachial-ankle pulse wave velocity is associated with symptomatic cerebral infarction in patients with type 2 diabetes.

Journal Article↗

PubMed1987

Pulsatile release of bioactive luteinizing hormone in prepubertal girls: discordance with immunoreactive luteinizing hormone pulses.

An assessment of pulsatile secretion of luteinizing hormone (LH), measured by both immunoassay (I-LH) and rat interstitial cell testosterone production bioassay (B-LH), as well as of follicle-stimulating hormone and glycoprotein hormone alpha-subunit was carried out in seven normal prepubertal and six normal premenarcheal pubertal girls. Samples were obtained at 20-min intervals for a 6-h period. The hormone secretion profiles were analyzed by several computerized methods yielding pulse frequency and amplitude, interpulse basal levels, and percentage increments, with bio/immuno ratios calculated for peak and basal concentrations. In these prepubertal girls, mean B-LH levels were 12% of I-LH, with B/I ratio of 0.13; 30% of samples were below assay sensitivity (0.10 mIU/ml) for B-LH, but all I-LH (1.25 mIU/ml) were detectable. In the pubertal group, B-LH levels were 30% of I-LH, with mean B/I ratio of 0.24 and undetectable B-LH in 29% of samples. Pulsatile secretion in prepubertal girls was found in five of seven (1/150 min) for B-LH and six of seven (1/212 min) for I-LH; only two of six pubertal girls had detectable pulses. Discordance of B- and I-LH pulses were frequent, with 56% of B-LH pulses lacking an I-LH pulse and 47% of I-LH pulses not having a B-LH pulse. These data demonstrate that both B- and I-LH are secreted episodically in prepubertal girls; I-LH-like material is present in higher concentrations than B-LH in these girls; and substantial discordance of B- and I-LH pulses exist.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1996

Transmission pulse oximetry in the fetal lamb: is there a universal calibration?

Transmission pulse oximetry is widely used for oxygen monitoring. The use of pulse oximeters is steadily expanding toward situations with low arterial oxygen saturation (Sao2) values. Therefore, we evaluated transmission pulse oximetry in the unanesthetized fetal lamb at low Sao2 levels. In seven fetal lambs, fetal hypoxemia was induced by occlusion of the maternal common iliac artery, four days after the instrumentation of the animal. Two Nellcor prototype transmission Y-sensors (light emitting diodes: 660 and 890 nm) were applied, one around a forelimb muscle and one around a skinfold in the neck, and were connected to Nellcor pulse oximeters. The pulse oximeter was calibrated for the skin measurements. Pulse oximeter saturation readings (Spo2) were compared with sample Sao2 values, over an Sao2 range of 13 to 63%. For the neck sensor the SD of the difference was 5.0% (n = 101). For the muscle sensor the mean difference was 19.5% and the SD of the difference was 5.9% (n = 206). Regression analysis showed a different calibration line for the muscle sensor with the equation: Spo2 = 0.92 x Sao2 + 21.90. Continuous recordings were obtained both from the forelimb muscle and from the neck, but the recordings from the neck showed a substantial loss of signal during the hypoxemia period. We conclude that transmission pulse oximetry is less accurate below an Sao2 of 70% in fetal lambs than above 70% Sao2. At these low levels of Sao2, pulse oximeters may need to be constructed with different calibration lines for various application positions of the body.

Animals↗

PubMed1982

Regulation of luteinizing hormone pulse frequency and amplitude by testosterone in the adult male rat.

Our objective was to gain a better understanding of the role of testosterone (T) in regulating the minute to minute dynamics of LH secretion in the adult male rat. To this end, we examined the patterns of blood LH levels in intact animals and evaluated the effect of small physiological doses of T on mean blood LH and FSH levels and on LH pulse frequency and amplitude in the castrate animal. The intact rat exhibited low frequency (period, approximately 145 min) and low amplitude (approximately 16 ng/ml) LH pulses. After castration, LH pulse frequency (period, approximately 20 min) and amplitude (approximately 118 ng/ml) increased dramatically over that of intact animals. T, administered to castrate rats through Silastic implants, caused a dose-dependent and parallel reduction in mean blood LH and FSH levels. The lowest T dose, which increased mean plasma T levels to 0.5 ng/ml above those of the sham-treated castrates, produced a significant reduction in LH pulse frequency, with a significant increase in pulse amplitude. The next highest T dose caused a reduction in pulse amplitude to a value significantly lower than that in the sham-treated castrates. The highest T dose, which produced steady state mean plasma T levels (approximately 1.6 ng/ml) less than the mean level of the intact group (approximately 2.2 ng/ml), caused a profound reduction in pulse frequency to lower than that of the intact group. These observations demonstrate that T can exert a complex, dose-dependent effect on LH secretory dynamics and imply that one important site of T-mediated negative feedback is the brain's LHRH pulse generator.

Animals↗

PubMed1987

Effects of luteinizing hormone (LH)-releasing hormone pulse amplitude and frequency on LH secretion by perifused rat anterior pituitary cells.

Recent studies have shown that LH secretion in vivo is pulsatile. In the present study, a cell perifusion system was employed to characterize the pituitary response to changes in LHRH pulse amplitude and frequency. Increases in pulse amplitude consistently elevated both mean LH levels and the amount of LH released in response to individual LHRH pulses. The EC50 for LHRH was approximately 3 nM. Increases in pulse frequency also increased mean LH levels, but frequencies of three or more pulses per h were associated with a decrease in the amount of LH released per pulse. Alterations in LHRH pulse characteristics changed qualitative as well as quantitative aspects of LH secretion, with high frequency, high amplitude pulses producing a biphasic response to LHRH. Initially a self-priming response was seen during the second and third hours of stimulation; this was followed by increasing desensitization of the cultures to LHRH. These results, by defining the pituitary response to specific conditions of stimulation, will help to clarify the relationship of LHRH stimulation to LH secretion in vivo.

Animals↗

PubMed1993

Failure of gonadotropin-releasing hormone (GnRH) pulses to increase luteinizing hormone beta messenger ribonucleic acid in GnRH-deficient female rats.

Gonadotropin subunit gene transcription and messenger RNA (mRNA) levels are differentially regulated by GnRH pulse frequency and amplitude in the male rat. The rapid changes of subunit mRNA levels and LH and FSH secretion during the estrous cycle, particularly the rapid rise in LH-beta subunit mRNA on proestrus afternoon, suggest that physiological changes in the pattern of GnRH action may also be important in female rats. However, in the absence of a GnRH-deficient female model the role of varying GnRH stimulation remains to be determined. We have characterized a GnRH-deficient model by administering the alpha-adrenergic antagonist phenoxybenzamine (PBZ) to ovariectomized (OVX) rats. Initial experiments showed that PBZ given 24 h earlier abolished the afternoon LH surge in OVX estradiol (E2) replaced rats whereas LH responses to exogenous GnRH were preserved. A PBZ regimen of 15 mg/kg ip at OVX followed by 10 mg/kg at 24 h and 5 mg/kg at 48 h prevented the increase in alpha, LH-beta, and FSH-beta mRNAs and LH and FSH secretion for 72 h post-OVX. LH and FSH responses to GnRH pulses were preserved suggesting that PBZ blocked the post-OVX increase in hypothalamic GnRH secretion. The suppressive effect of PBZ appeared to be specific to the hypothalamic-pituitary-ovarian axis as plasma PRL, TSH, and corticosterone were not decreased compared to controls. We have used this GnRH-deficient OVX female model to investigate the effects of exogenous GnRH pulses on subunit mRNA expression. GnRH pulses (5-250 ng/30 min for 12-24 h) were administered via an intraatrial catheter beginning 24 h after OVX and the first PBZ injection (OVX+PBZ+saline pulses to controls). Expression of alpha and FSH-beta mRNAs and LH and FSH secretion were increased by GnRH pulse doses of 5-25 ng to values similar to or greater than those in OVX controls though the higher doses of GnRH/pulse did not increase FSH-beta mRNA or plasma FSH. However, LH-beta mRNA levels were not increased by GnRH pulses. GnRH pulses were also given to rats replaced with proestrus concentrations of estradiol alone or in combination with progesterone (P). Again, no demonstrable increases in LH-beta mRNA expression were observed. alpha-mRNA concentrations were further increased in the presence of E2 alone, and P in combination with E2, produced an augmented response of FSH-beta subunit mRNA. These data suggest that ovarian steroid hormones act directly on the gonadotrope to augment alpha and FSH-beta mRNA responses to GnRH.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2001

A possible role of neuropeptide Y as a mediator of undernutrition to the hypothalamic gonadotropin-releasing hormone pulse generator in goats.

To understand central mechanisms for nutritional infertility, the activity of the GnRH pulse generator was directly assessed in ovariectomized (OVX) goats under several experimental conditions by recording characteristic increases in the multiple-unit activity (volleys). When estradiol (E(2))-treated animals were fasted for 4-5 days, the activity of the GnRH pulse generator was gradually suppressed, and the volley interval at the end of fasting was significantly prolonged, compared with that during the feeding period (67.4 vs. 49.3 min, n = 5, P < 0.01). On the other hand, such a significant effect on the pulse generator was not observed in OVX goats. In the second experiment, the animals received a bolus intracerebroventricular injection of several doses (0, 2, 5, and 20 microg/400 microl) of neuropeptide Y (NPY). Exogenous NPY dose-dependently inhibited the pulse generator activity. At the highest dosage, the 1st posttreatment volley interval was significantly longer than that of the pretreatment (112.4 vs. 32.6 min, n = 5, P < 0.01) in OVX goats. The suppressive effect of NPY was similarly observed in OVX+E(2) goats. Further, when NPY was infused (10 microg/200 microl.h for 6 h) into OVX goats, the activity of the GnRH pulse generator was almost completely inhibited during the infusion period. Hypothalamic sites responding to fasting were immunohistochemically evaluated using an antibody for Fos in castrated goats. Fos-immunoreactive neurons were found in areas adjacent to the third ventricle. Double-labeling immunohistochemistry revealed that a subpopulation of NPY neurons in the arcuate nucleus was activated in response to fasting. These results demonstrate that: 1) the activity of the GnRH pulse generator is suppressed by fasting in the presence of E(2); 2) exogenous NPY inhibits the activity of the GnRH pulse generator regardless of the presence of E(2); and 3) several hypothalamic neurons or regions, including those containing NPY in the arcuate nucleus, are activated by fasting. Collectively, these observations suggest that NPY acts as a mediator of undernutrition to the GnRH pulse generator.

Animal Nutritional Physiological Phenomena↗

PubMed1985

Evidence for decreased luteinizing hormone-releasing hormone pulse frequency in men with selective elevations of follicle-stimulating hormone.

To examine the hypothesis that the frequency of endogenous pulsatile LHRH stimulation controls the relative secretion of FSH and LH from the pituitary, we studied men with elevated FSH levels and normal LH levels to determine whether they have an altered frequency of pulsatile LHRH secretion compared to normal men. Because peripheral blood measurements of LHRH do not reflect the pulsatile characteristics of hypothalamic LHRH secretion, and it is generally accepted that the pulse frequency of LH secretion is an index of the frequency of endogenous LHRH pulsation, we used LH pulse frequency as the indicator of LHRH pulse frequency. Frequent blood sampling was performed to characterize LH pulse patterns in five men with selective elevations of FSH and seven age-matched normal men. Beginning at 0800-0930 h, blood samples were obtained every 10 min for 24 h through an indwelling iv catheter. Serum LH and FSH levels were measured by RIA in each sample, and the pattern of LH secretion was determined. Testosterone (T), estradiol, sex hormone-binding globulin, and free T were measured in a pooled serum sample from each man. Men with selective elevations of FSH had fewer LH pulses per 24 h (mean +/- SEM, 10.6 +/- 0.5) than the control group (12.9 +/- 0.6; P less than 0.01). There was no statistically significant difference in LH pulse amplitude (23 +/- 4 vs. 17 +/- 3 ng/ml). There were no statistically significant differences in T (4.9 +/- 0.5 vs. 6.1 +/- 0.5 ng/ml), estradiol (23 +/- 7 vs. 31 +/- 5 pg/ml), sex hormone-binding globulin (7.7 +/- 1.4 vs. 7.7 +/- 1.2 ng bound dihydrotestosterone/ml), or free T (0.16 +/- 0.02 vs. 0.23 +/- 0.04 ng/ml) in these men vs. normal subjects. We conclude that 1) compared to normal men, men with selectively elevated FSH levels have decreased LH pulse frequency, which suggests decreased LHRH pulse frequency; and 2) the relative secretion rates of LH and FSH by the pituitary may be regulated by the frequency of pulsatile LHRH secretion from the hypothalamus.

Adult↗

PubMed1993

Differential effects of glucose stimulation upon rapid pulses and ultradian oscillations of insulin secretion.

To determine the effect of glucose stimulation on the rapid 8- to 15-min pulses and the ultradian 80- to 170-min oscillations of insulin secretion, peripheral concentrations of glucose, insulin, and C-peptide were measured at 2-min intervals over 2 h (i.e. rapid experiments), at 15-min intervals over 8-20 h (i.e. ultradian experiments) in 17 normal subjects during saline infusion, or during constant glucose infusion at a rate of 3 mg/(kg.min) (i.e. low dose) or 6 mg/(kg.min) (i.e. high dose). In the ultradian experiments, insulin secretory rates (ISR) were calculated by deconvolution of the plasma C-peptide concentrations. Significant oscillations with 125- to 166-min periods were detected in all glucose and ISR profiles. The numbers of ISR oscillations per 24 h were similar during saline infusion and low and high dose glucose infusion. In contrast, the amplitude of the ISR peaks increased progressively from 14 +/- 1 pmol/min during saline infusion to 50 +/- 7 pmol/min and further to 97 +/- 9 pmol/min during low and high dose glucose infusions, respectively. When expressed as percent increment, the amplitude of the ISR oscillations increased significantly from 31 +/- 5% during saline infusion to 41 +/- 4% during low dose glucose infusion and 44 +/- 3% during high dose glucose infusion (P < 0.05). In all profiles obtained from the 2-min sampling experiments, rapid pulses of glucose, insulin, and C-peptide were apparent. The number of insulin pulses during saline and glucose infusions corresponded to a mean periodicity of 10 min. The amplitude of these rapid insulin pulses increased from 17.3 +/- 2.9 to 39.8 +/- 11.8 pmol/L (P < 0.01) in response to glucose. In contrast to the ultradian oscillations, the relative amplitude of the rapid insulin pulses decreased significantly from 28.8 +/- 3.4% during saline infusion to 13.6 +/- 1.6% during high dose glucose infusion (P < 0.01). Our findings demonstrate that the pancreatic response to glucose stimulation is different for the rapid pulses and the ultradian oscillations. When the rate of glucose stimulation is increased, the absolute amplitude of both the rapid pulses and the ultradian oscillations increases. However, when expressed as percent increment, the amplitude of the rapid pulses decreases during glucose stimulation, whereas the amplitude of the ultradian oscillations increases. These findings suggest that the two oscillatory modes have a different origin and physiological significance.

Activity Cycles↗

PubMed2004

Relationship between growth hormone (GH) pulses in the peripheral circulation and GH-releasing hormone and somatostatin profiles in the cerebrospinal fluid of goats.

Growth hormone (GH) is secreted in a pulsatile manner, but the underlying mechanisms of GH pulse generation remain to be resolved. In the present study, we investigated the relationship between GH pulses in the peripheral circulation and GH-releasing hormone (GHRH) and somatostatin (SRIF) profiles in the cerebrospinal fluid (CSF) of male goats. The effects of an intracerebroventricular (icv) injection of neuropeptide Y (NPY), galanin and ghrelin were also analyzed. Blood and CSF samples were collected every 15 min for 8 hr from the jugular vein and third ventricle, respectively. GH pulsatility in the goat was found to consist of distinct large pulses of 5 hr periodicity and small pulses of 1 hr periodicity. GHRH and SRIF in the CSF fluctuated in a pulsatile manner with 1 hr periodicity, and most of the descending phase of SRIF pulses were associated with the initiation of GH pulses. Icv injections of NPY, galanin and ghrelin stimulated GHRH release without affecting SRIF release. In addition, NPY suppressed, and galanin and ghrelin induced large GH pulses, although ghrelin was much more effective than galanin. These results suggest that an hourly fall in SRIF is involved in generating intrinsic circhoral rhythm of GH pulsatility. The mechanisms underlying the generation of large GH pulses of 5 hr periodicity remain unknown, while direct action of NPY and/or ghrelin on the pituitary might be involved.

Analysis of Variance↗

PubMed2006

Picosecond-pulse wavelength conversion based on cascaded second-harmonic generation-difference frequency generation in a periodically poled lithium niobate waveguide.

The wavelength conversion of picosecond optical pulses based on the cascaded second-harmonic generation-difference-frequency generation process in a MgO-doped periodically poled lithium niobate waveguide is studied both experimentally and theoretically. In the experiments, the picosecond pulses are generated from a 40 GHz mode-locked fiber laser and two tunable filters, with which the lasing wavelength can be tuned from 1530 to 1570 nm, and the pulse width can be tuned from 2 to 7 ps. New-frequency pulses, i.e., converted pulses, are generated when the picosecond pulse train and a cw wave interact in the waveguide. The conversion characteristics are systematically investigated when the pulsed and cw waves are alternatively taken as the pump at the quasi-phase-matching wavelength of the device. In particular, the conversion dependences on input pulse width, average power, and pump wavelength are examined quantitatively. Based on the temporal and spectral characteristics of wavelength conversion, a comprehensive analysis on conversion efficiency is presented. The simulation results are in good agreement with the measured data.

Journal Article↗

PubMed2006

Investigation of crystallization and amorphization dynamics of phase-change thin films by subnanosecond laser pulses.

We report experimental results on amorphization and crystallization dynamics of reversible phase-change (PC) thin-film samples, GeSbTe and GeBiTe, for optical disk data storage. The investigation was conducted with subnanosecond laser pulses using a pump-and-probe configuration. Amorphization of the crystalline films could be achieved with a single subnanosecond laser pulse; the amorphization dynamics follow closely the temperature kinetics induced in the irradiated spot. As for crystallization of the samples initially in the amorphous state, a single subnanosecond pulse was found to be insufficient to fully crystallize the irradiated spot, but we could crystallize the PC film (in the area under the focused spot) by applying multiple short pulses. Our multipulse studies reveal that the GeSbTe crystallization is dominated by the growth of nuclei whose initial formation is slow but, once formed, their subsequent growth (under a sequence of subnanosecond pulses) happens quickly. In the case of GeBiTe samples, the crystalline nuclei appear to be present in the material initially, as they grow immediately upon illumination with laser pulses. Whereas our amorphous GeSbTe samples required approximately 200 pulses for full crystallization, for the GeBiTe samples approximately 15 pulses sufficed.

Journal Article↗

PubMed2005

Diffraction characteristics of 10 fs laser pulses passing through an aperture.

Results are presented on experimental and theoretical work performed to compare diffraction phenomena for ultrashort 10 fs pulses and continuous-wave propagation modes illuminating different-sized pinholes and slits. Results demonstrate that 10 fs pulses do not produce high-frequency diffraction like that produced with continuous-wave illumination. The diffraction through a 1 mm pinhole of temporally stretched pulses obtained by using fused silica plates whose frequency spectrum remains the same is compared with those of 10 fs pulses. The overall diffraction intensity profiles are, however, nearly identical in this case. The simulations of diffraction patterns for 100 fs, 10 fs, and 1 fs incident pulse were compared theoretically for different aperture sizes and frequencies. Calculations indicate that the lack of high-frequency diffraction for the mode-locked case is due to the broadband nature of the ultrashort laser pulses; i.e., the distribution of the frequency contained in the pulse ends up washing out when objects are illuminated with pulses of broad frequency content. The results of this work have important application in biomedical imaging and remote imaging applications, to name only a few.

Journal Article↗

PubMed2006

Observations in collinear femtosecond-nanosecond dual-pulse laser-induced breakdown spectroscopy.

In the work reported herein, we have combined a short-lived femtosecond laser-induced plasma (LIP) and a longer-lived nanosecond LIP in a collinear pulse configuration to examine the source(s) of atomic emission and signal-to-noise enhancement in dual-pulse laser-induced breakdown spectroscopy (LIBS). Initial studies indicate that the primary source of dual-pulse LIBS enhancement in the collinear configuration may in large part be a matter of pulse focus; focusing on the sample surface, for example, yields atomic emission enhancements whose lifetime correlates reasonably well with the femtosecond LIP emissive lifetime, suggesting that plasma-plasma coupling may play an important role at that pulse focus. At a second "optimal" focal position above the sample surface, alternatively, atomic emission and signal-to-noise enhancements correlate quite well with the nitrogen and oxygen atomic emission reductions previously seen following use of a femtosecond air spark and a nanosecond ablative pulse in the orthogonal dual-pulse configuration, suggesting that pressure or number density reductions due to femtosecond LIP formation in air may be significant at that pulse focus.

Equipment Design↗

PubMed1995

Effect of routine emergency department triage pulse oximetry screening on medical management.

PURPOSE: To determine the utility of routine triage pulse oximetry screening in emergency department (ED) patients. DESIGN: Prospective study using pulse oximetry to measure oxygen saturation of ED patients at triage. Saturation values were disclosed to physicians only after they completed medical evaluations and were ready to discharge or admit each patient. We measured changes in medical management initiated after disclosure of pulse oximetry values. SETTING AND PARTICIPANTS: The study included 14,059 consecutive patients presenting to triage at a university ED. MEASUREMENTS: Changes in select diagnostic tests: chest radiography, CBC count, spirometry, arterial blood gases, pulse oximetry, and ventilation-perfusion scans; treatments: antibiotics, beta-agonists, supplemental oxygen; and hospital admission and final diagnoses that occurred after disclosure of triage pulse oximetry values. RESULTS: Of 1,175 patients having triage pulse oximetry values less than 95%, physicians ordered repeat pulse oximetry on 159 (13.5%), additional chest radiography on 5.4%, CBC count on 3.1%, arterial blood gases on 2.9%, spirometry on 0.9%, and ventilation-perfusion scans on 0.3%. Physicians ordered 178 new therapies on 134 patients (11.4%), including supplemental oxygen for 6.5%, antibiotics for 3.9%, and beta-agonists for 1.8%. Thirty-five patients (3.0%) initially scheduled for hospital discharge were subsequently admitted. Physicians changed or added diagnoses in 77 patients (6.6%). CONCLUSIONS: Providing physicians with routine triage pulse oximetry measurements resulted in significant changes in medical treatment of these patients.

Adolescent↗