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PubMed1998

Safety and efficacy of pulse and daily calcitriol in patients on CAPD: a randomized trial.

BACKGROUND: Calcitriol therapy is the mainstay of therapy for the treatment of secondary hyperparathyroidism. Oral administration of calcitriol is necessary in CAPD patients, but no studies have directly compared different routes of administration in this patient population. METHODS: To determine if the peak serum calcitriol level (pulse therapy) is more important than the total delivered dose, we randomized CAPD patients with mild to moderate secondary hyperparathyroidism to receive either pulse (3.0 microg twice a week, n = 10) or daily (0.75 microg a day, n = 8) oral calcitriol in comparable weekly doses. The main comparison was the rate of decline of serum intact parathyroid hormone (PTH) levels to reach the desired end-point of 100 pg/ml. The patients were dialysed with low-calcium dialysate and received only calcium-containing phosphate binders. RESULTS: Pharmacokinetic analysis after a single dose of 3.0 microg (pulse) vs 0.75 microg (daily) revealed 1,25(OH)2-vitamin D levels to be higher in the pulse group at 3 and 6 h, but equivalent by 12 h. The area under the curve for 1 week of daily and 1 week of pulse therapy was equal. The patients in the 2 arms had equivalent basal serum levels of PTH (pulse = 562 +/- 291 vs daily = 454 +/- 113 pg/ml), calcium (pulse = 2.32 +/- 0.20 vs daily = 2.32 +/- 0.12 mmol/l) and phosphorus (pulse = 1.32 +/- 0.52 vs daily = 1.35 +/- 0.26 mmol/l). The time required for the PTH to decrease to 100 pg/ml and the rate of decline in PTH were similar (time: pulse = 14.2 +/- 6.8 weeks, daily = 12.2 +/- 7 weeks; rate: pulse = 7.4 +/- 4.2 vs daily = 8.4 +/- 4.2% PTH/week; P = NS). The serum calcium increased similarly in both groups. Hypercalcaemia (> 2.9 mmol/l) was rare (pulse = 3, daily = 2 episodes). CONCLUSIONS: This study demonstrates that pulse and daily calcitriol are similarly effective and safe for the treatment of mild to moderate secondary hyperparathyroidism in CAPD patients despite higher peak levels of 1,25(OH)2-vitamin D with pulse therapy.

Adult↗
PubMed2006

Extracting oscillometric pulses from the cuff pressure: does it affect the pressures determined by oscillometric blood pressure monitors?

OBJECTIVE: Oscillometric noninvasive blood pressure measurement devices determine the pressures by analysing the relationship between the pressure in an occluding cuff and low-amplitude pressure pulses (oscillometric pulses) induced in the cuff by the arterial pressure wave. This paper examines the effects on the pulses and oscillometric pulse amplitude envelope of the filters that extract the pulses from the cuff pressure. METHODS: The cuff pressure and oscillometric pulses extracted by the filter were recorded from a Critikon DINAMAP and a Datex Cardiocap, chosen because of accessibility of the filtered and unfiltered signals. The unfiltered oscillometric pulses were determined by subtracting the cuff pressure from a baseline constructed to represent either the Critikon's step deflation cuff pressure or the Datex's gradual pressure decrease. Waveforms were recorded from a noninvasive blood pressure test simulator and three volunteers. CONCLUSIONS: The filter alters the shape of oscillometric pulses causing a shift in the oscillometric pulse amplitude envelope drawn from the filtered pulses compared with that drawn from the unfiltered pulses in human subjects, but not the test simulator. The pulse shape distortion is dependent on the filter characteristics and the oscillometric pulse shape. Further work is required to explore whether this may help explain why simulators with artificial waveforms cannot validate noninvasive blood pressure monitors and why noninvasive blood pressure monitors may not be accurate in all patient groups.

Blood Pressure↗
PubMed2001

Pulse bifurcations and instabilities in an excitable medium: computations in finite ring domains.

We investigate the instabilities and bifurcations of traveling pulses in a model excitable medium; in particular, we discuss three different scenarios involving either the loss of stability or disappearance of stable pulses. In numerical simulations beyond the instabilities we observe replication of pulses ("backfiring") resulting in complex periodic or spatiotemporally chaotic dynamics as well as modulated traveling pulses. We approximate the linear stability of traveling pulses through computations in a finite albeit large domain with periodic boundary conditions. The critical eigenmodes at the onset of the instabilities are related to the resulting spatiotemporal dynamics and "act" upon the back of the pulses. The first scenario has been analyzed earlier [M. G. Zimmermann et al., Physica D 110, 92 (1997)] for high excitability (low excitation threshold): it involves the collision of a stable pulse branch with an unstable pulse branch in a so-called T point. In the framework of traveling wave ordinary differential equations, pulses correspond to homoclinic orbits and the T point to a double heteroclinic loop. We investigate this transition for a pulse in a domain with finite length and periodic boundary conditions. Numerical evidence of the proximity of the infinite-domain T point in this setup appears in the form of two saddle node bifurcations. Alternatively, for intermediate excitation threshold, an entire cascade of saddle nodes causing a "spiraling" of the pulse branch appears near the parameter values corresponding to the infinite-domain T point. Backfiring appears at the first saddle-node bifurcation, which limits the existence region of stable pulses. The third case found in the model for large excitation threshold is an oscillatory instability giving rise to "breathing," traveling pulses that periodically vary in width and speed.

Journal Article↗
PubMed2002

Effective desynchronization with bipolar double-pulse stimulation.

This paper is devoted to the desynchronizing effects of bipolar stimuli on a synchronized cluster of globally coupled phase oscillators. The bipolar pulses considered here are symmetrical and consist of a positive and a negative monopolar pulse. A bipolar single pulse with the right intensity and duration desynchronizes a synchronized cluster provided the stimulus is administered at a vulnerable initial phase of the cluster's order parameter. A considerably more effective desynchronization is achieved with a bipolar double pulse consisting of two qualitatively different bipolar pulses. The first bipolar pulse is stronger and resets the cluster, so that the second bipolar pulse, which follows after a constant delay, hits the cluster in a vulnerable state and desynchronizes it. A bipolar double pulse desynchronizes the cluster independently of the cluster's dynamical state at the beginning of the stimulation. The dynamics of the order parameter during a bipolar single pulse or a bipolar double pulse is different from the dynamics during a monopolar single pulse or a monopolar double pulse. Nevertheless, concerning their desynchronizing effects the monopolar and the bipolar stimuli are comparable, respectively. This is significant for applications where bipolar stimulation is required. For example, in medicine and physiology charge-balanced stimulation is typically necessary in order to avoid tissue damage. Based on the results presented here, demand-controlled bipolar double-pulse stimulation is suggested as a milder and more efficient therapy compared to the standard permanent high-frequency deep brain stimulation in neurological patients.

Journal Article↗
PubMed1978

Adaptive properties of olfactory receptors analysed with odour pulses of varying durations.

1. The adaptive properties of salamander of olfactory receptors have been analysed in extracellular unit recordings. Stimulation has been by step pulses of odour of varying durations for 1--10 sec. 2. The most common response was a prolonged impulse discharge that continued throughout the duration of the pulse and terminated abruptly within 1 sec of the end of the pulse. The interval for termination was relatively independent of the pulse duration. Pulses were frequently followed by a period of impulse inactivity lasting 1--3 sec, usually independent of previous pulse duration. 3. The impulse discharges were typically slowly adapting. Initially, during the first 1--2 sec, the frequency rose to 5--10 impulses/sec, at threshold concentration. In some cases, the initial level was maintained throughout the pulse, with little or no adaptation. More commonly, there was a distinct initial phasic peak, followed by decay to a lower level of 4--8 impulses/sec, which was maintained during the pulse. It was concluded that most olfactory receptors are slowly adapting, with variable phasic responsiveness dependent on odour concentration and other factors. 4. Reductions in impulse activity, compared with background, during a pulse were rarely seen. Methods for increasing the level of background activity and the use of very long duration pulses were necessary in order to bring out this type of response. Uniformly reduced activity throughout a pulse was seen clearly in only one case. A pattern consisting of a waning and then recovery of impulse frequency during a pulse was also observed in rare cases. 5. The results have shown that olfactory receptor discharges characteristically have a relatively precise relation to step pulses of odour of varying duration. The properties of the response have implications for the steps involved in the overall processes of activation and inactivation of receptor mechanisms at the olfactory mucosa.

Action Potentials↗
PubMed1999

The perceptual effects of current pulse duration in electrical stimulation of the auditory nerve.

In cochlear implants employing pulsatile stimulation, loudness is controlled by current amplitude and/or pulse duration. Five experiments were conducted with cochlear implantees to investigate the hypothesis that perceptual effects other than loudness result from changes in pulse duration for durations from 50 to 266 microseconds. In experiment 1, five subjects' ability to discriminate equally loud pulse trains employing differing pulse durations was measured at four electrode positions. In 11 of the 20 cases, subjects could significantly discriminate these stimuli. In experiments 2 and 3, discrimination was measured of dual-electrode stimuli which differed in overall temporal pattern but had an equal temporal pattern on each of the individual electrodes (separated by 0 to 9 mm). Discrimination was compared for stimuli employing short or long pulse durations and, in experiment 3, employing different pulse durations on each electrode. When the pulse duration was longer, six out of seven subjects could either combine temporal information across electrode positions at wider electrode separations (experiment 2) or had better discrimination at the same electrode separation (experiment 3). This result was consistent with the hypothesis that longer pulse durations result in a greater spread of excitation than equally loud stimuli using shorter pulse durations. In experiment 4, pulse rate discrimination was compared for stimuli with differing pulse durations, and in four out of five subjects, there was no effect of pulse duration. Finally, the dB change in current per doubling of pulse duration for threshold and equally loud stimuli was calculated for nine subjects (52 electrodes). Values ranged from -5.9 to -2.0 dB/doubling, and were significantly correlated with the absolute intensity of the stimulus. This result was hypothesized to be due to a relationship between the neural charging characteristics and the distance of the excited neural elements from the electrode.

Adult↗
PubMed1990

Radio-frequency ablation: effect of voltage and pulse duration on canine myocardium.

The purpose of this investigation was to examine in vivo the relationship of radio-frequency (RF) pulse voltage and duration on the volume of tissue injury. RF 500-kHz pulses of 20-, 40-, and 60-V amplitude (RMS) were applied to the epicardium of 18 dogs for pulsing periods of 5-20 s. Systematic and quantitative tissue analysis was then performed after 30 days. No chronic lesions were evident on microscopic examination for 20-V RF pulse applications up to 15 s. Application of 20-V pulses for 20 s produced small lesions having a volume of 2.4 +/- 0.7 mm3. At 40 V, the volume of tissue injury ranged from 39.1 +/- 10.3 mm3 for 5 s of pulse application to 128.8 +/- 24.8 mm3 for 20 s of pulse application. Over the first 15 s of 40-V pulse application, the volume of tissue injury increased as pulse application time increased. There was no further increase in tissue injury for 40-V pulsing durations greater than 15 s. At 60 V, volumes of tissue injury ranged from 122.7 +/- 33.5 mm3 at 5 s to 313.6 +/- 73.7 mm3 at 20 s. Lesion size increased significantly for pulse durations of up to 10 s. Thereafter, 60-V pulses yielded little increase in tissue injury. In addition, persistent 60-V pulsing for periods greater than 9 s duration resulted in arcing and tissue vaporization in 28% of the applications. Thus RF energy is limited in its ability to create safe and effective tissue injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Disruption of GnRH pulses by anti-GnRH serum and phentolamine obliterates pulsatile LH but not FSH secretion in ovariectomized rabbits.

It has been hypothesized that the secretion of gonadotropins, i.e. luteinizing hormone (LH) and follicle-stimulating hormone (FSH), is driven by a synchronized neural network ('pulse generator'). This network, regulated in part by alpha-adrenergic activity, ultimately generates bursts of hypothalamic gonadotropin-releasing hormone (GnRH) release. In this study, we used the push-pull (PP) perfusion technique in ovariectomized rabbits to investigate three aspects of the ('GnRH/gonadotropin pulse generator') hypothesis. The objectives were to determine: (1) if plasma LH and FSH pulses occur concomitantly with mediobasal hypothalamic (MBH-) GnRH pulses, (2) changes in the patterns of pulsatile LH and FSH secretion when pulsatile MBH GnRH signals are interrupted by either local immunoneutralization of GnRH or intravenous infusion of the alpha-adrenergic antagonist phentolamine (PHEN, 4 mg/kg BW), and (3) whether third cerebroventricular (3VT-) GnRH patterns reflect neuronal GnRH release from the MBH. We found that while both plasma LH and FSH patterns were pulsatile, MBH GnRH pulses were significantly coupled only with LH pulses (94% coincidence). Both the local immunoneutralization of MBH GnRH pulses and the PHEN-induced suppression of MBH GnRH pulses obliterated the pulsatile secretion of LH, but not FSH. Neither MBH GnRH nor plasma LH or plasma FSH pulses were concurrent with 3VT GnRH pulses. However, the PP perfusion of the 3VT appeared to alter the pulsatile release of MBH GnRH and pituitary LH. The results support the hypothesis that in the absence of ovarian signals, the 'pulse generator' is maintained by tonic alpha-adrenergic input and that a 'cellular unity' of MBH GnRH release (GnRH pulses) drives the gonadotrophs to secrete LH in pulses. In contrast, the pulsatile release of FSH appears to involve additional nonovarian regulatory events to those controlling LH secretion.

Animals↗
PubMed2005

Noninvasive assessment of local pulse pressure: importance of brachial-to-radial pressure amplification.

The advocated SphygmoCor procedure uses a radial-to-aorta transfer function with calibration on brachial instead of radial artery pressure to assess the central pulse pressure. We compared these values with carotid artery pulse pressures obtained from a validated calibration method, assuming mean minus diastolic blood pressure constant throughout the large artery tree. From 44 healthy subjects (21 males; 22 to 68 years) pressure waves were obtained at the radial, brachial, and carotid artery with applanation tonometry. Using the calibration method, radial and carotid artery pressures were assessed from brachial artery waves and pressures. The effect of brachial-to-radial pulse pressure amplification, brachial pulse pressure, mean pressure, age, gender, height, body mass index, and smoking on differences between the 2 methods was assessed. Brachial artery pressure was 118+/-12/72+/-10 mm Hg. SphygmoCor central pulse pressure was 9.7+/-4.6 mm Hg lower (P<0.001) than the carotid artery pulse pressure (33.0+/-6.8 versus 42.7+/-8.9 mm Hg). The difference between the 2 methods strongly depended (P<0.001) on brachial-to-radial artery pulse pressure amplification (5.8+/-5.1 mm Hg; 12+/-11%) and less on brachial artery pulse pressure (P=0.005). After calibration of the radial pressure wave with radial instead of brachial artery pressures, the difference between SphygmoCor central pulse pressure and carotid pulse pressure decreased with 4 mm Hg. The advocated SphygmoCor procedure systematically underestimates the central pulse pressure with brachial-to-radial pulse pressure amplification as important determinant. Therefore, calibration of radial artery pressure waves on brachial artery pressures should be avoided. The underestimation of central aortic pulse pressure caused by the radial-to-aorta transfer function itself is much less than previously reported.

Adult↗
PubMed1991

A pulsatile gonadotropin-releasing hormone stimulus is required to increase transcription of the gonadotropin subunit genes: evidence for differential regulation of transcription by pulse frequency in vivo.

Previous results have shown that the pattern of GnRH pulses (amplitude and frequency) can differentially regulate expression of gonadotropin subunit cytoplasmic messenger RNA (mRNA) concentrations. The present study examined the effect of GnRH pulses on alpha, LH-beta and FSH-beta transcription rates as determined by nuclear runoff transcription assay. GnRH pulses (saline to controls) were given to castrate, testosterone-replaced male rats, and the rate of subunit gene transcription was measured in isolated pituitary nuclei. The effect of GnRH treatment duration was examined by giving GnRH pulses (25 ng/pulse at 30-min intervals) for 1, 4, or 24 h. The basal transcription rates [expressed as parts per million (ppm)] were 82 +/- 25 for alpha; 39 +/- 19 for LH-beta and 27 +/- 6 ppm for FSH-beta, and transcription rates of all 3 subunits were elevated at 1 h (3-5-fold vs. saline controls). After 4 h of GnRH pulses, alpha and FSH-beta transcription rates were reduced vs. 1 h, but LH-beta mRNA synthesis rate was maintained. At 24 h, the alpha transcription rate was still increased (66%), but LH-beta and FSH-beta transcription rates had fallen to basal levels despite the continuing pulsatile GnRH stimulus. The second experiment investigated the effect of the duration of GnRH pulses (25 ng/pulse, every 30 min for 4 h or 24 h), on cytoplasmic subunit mRNA concentrations to assess if the initial 4-h increase in transcription rate would induce a rise in cytoplasmic mRNAs. After 4 h of GnRH pulses, alpha and LH-beta mRNAs were unchanged, but FSH-beta mRNA had increased by 36% (P less than 0.05) compared to controls. All 3 subunit mRNAs were increased (approximately 2-fold) by 24 h of GnRH pulses. Administering GnRH pulses for 4 h followed by 20 h of saline pulses did not increase alpha mRNA; LH-beta was slightly increased (P less than 0.05), but FSH-beta mRNA concentrations were similar to levels seen after 24 h of continued GnRH pulses. The third experiment examined the effects of a continuous GnRH infusion and different GnRH pulse frequencies on gonadotropin subunit transcription rates. GnRH (25 ng/pulse) was given at intervals of 8, 30, or 120 min for 4 h (saline to controls). The continuous GnRH infusion (200 ng/h) did not increase the transcription rate of any of the three subunit mRNAs. alpha-subunit transcription rate was increased 2.7- or 4-fold by GnRH pulses given every 8 or 30 min, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Statistical evaluation of coincident prolactin and luteinizing hormone pulses during the normal menstrual cycle.

The purpose of this work was 2-fold. First, we sought to develop statistical criteria by which it could be established that the coincident occurrence of pulses of two different hormones exceeds that which would occur by chance alone, thereby suggesting that secretion of the two hormones is either coupled or controlled from a single source generator. Using computer simulations of uncoupled pulse generators operating at different frequencies, we were able to derive the appropriate statistical criteria and to apply them to achieve our second objective, to determine whether the occasional coincidence of plasma LH and serum PRL pulses that occurs throughout the menstrual cycle in normal women exceeds that which would happen by chance. The results of the computer simulations indicated that pulses emanating from two completely independent oscillators will occur coincidently at a predictable rate, despite the fact that the generator sources are not coupled; moreover, the rate of coincidence is increased when the pulse frequency of one of the source generators is increased. Using this knowledge and the statistical criteria we derived, we analyzed the coincidence of LH and PRL pulses in five normal women during their early follicular, late follicular, and midluteal phases and in another five women during their late luteal phase. We found that the number of PRL pulses that occurred coincidently with LH pulses consistently exceeded that which would be predicted if the two pulse generators were operating completely independently of one another; however, only during the late follicular and late luteal phases was the coincidence level between LH and PRL pulses sufficiently high in a sufficient number of women to conclude that there was coupling between the pulse sources. These studies suggest, first, that stringent and rigorous statistical criteria must be applied to the analysis of spontaneously coincident secretory phenomena before it can be deduced that two pulse generators are indeed coupled, and second, that the pulse generators governing the secretion of PRL and LH are probably coupled, at least during certain phases of the menstrual cycle.

Adult↗
PubMed1993

Gonadotropin-releasing hormone pulse generator activity during pubertal transition in girls: pulsatile and diurnal patterns of circulating gonadotropins.

To delineate the activity of the GnRH pulse generator during pubertal transition, 40 healthy girls 7-18 yr of age were studied. Ten were prepubertal (PP), 7 were in early puberty (EP), and 23 were in late puberty (LP, all postmenarcheal). Serum concentrations of LH and FSH were measured with immunofluorometric assays, which have a sensitivity about 100-fold that of RIA, in samples taken at 10-min intervals for 24 h during basal conditions, during Nal-Glu antagonist suppression, and in response to GnRH stimulation (10 micrograms). Serum levels of androstenedione, testosterone, and estradiol were measured with RIA. A pulsatile pattern of LH and FSH secretion was found in girls of all ages. PP girls had irregular LH pulses with low amplitudes during the daytime, but increased amplitude LH and FSH pulses were evident within 1 h after sleep-onset. Older PP girls had more regular and higher amplitude pulses throughout sleep than younger PP girls. The sleep-related LH and FSH pulses in PP girls were abolished with Nal-Glu GnRH antagonist treatment, reflecting endogenous GnRH pulse activities. The PP group had the most pronounced amplification of LH secretion with sleep yielding a sleep-wake ratio of 4, which decreased to 2 in the EP group and to 1 in the LP group. The emergence of regular daytime LH pulses along with a further amplification of pulsatile activity during sleep was closely related to the onset of breast development. By the age of 16 yr, an LH secretory pattern characteristic of adult women in the early follicular phase, i.e. a decrease in LH concentration during sleep, was established. Mean 24-h LH concentrations increased 40-fold from PP to LP consequent to a 9-fold increase in pulse amplitude and a 4-fold increase in pulse number (both P < 0.0001). Mean FSH concentrations (24 h), which were 20-fold higher than corresponding LH concentrations in the PP group, increased only 3-fold from the PP to the LP group. FSH pulse secretion appears to be predominantly GnRH dependent in PP girls in contrast to girls after ovarian activation, as indicated by the increased FSH responses to both GnRH antagonist suppression and GnRH stimulation in the PP as compared to the EP and LP groups. We conclude that the GnRH pulse generator is functionally active in prepubertal girls with selective expression of LH and FSH pulses after the onset of sleep. The onset of puberty is associated with a greater increase in LH pulse amplitude than frequency.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed2004

Recognition of calls with exceptionally fast pulse rates: female phonotaxis in the genus Neoconocephalus (Orthoptera: Tettigoniidae).

Male Neoconocephalus robustus and Neoconocephalus bivocatus produce remarkably fast calls, with pulse rates of approximately 175-200 Hz. The temporal call patterns differ significantly between the two species. Male N. robustus produce calls with a single pulse rate of 200 Hz. In N. bivocatus, pulses are repeated with alternating periods, resulting in distinct pulse pairs: approximately 175 pulses s(-1) are grouped into 87 pulse pairs s(-1). In order to identify the temporal parameters used to recognize calls with such fast pulse rates, female call recognition in both species was tested during phonotaxis on a walking compensator. Female N. robustus were attracted to calls without amplitude modulation. Amplitude-modulated signals were equally attractive, as long as the silent intervals were short enough. The maximally tolerated interval duration varied with pulse duration. Female N. bivocatus did not require the paired-pulse pattern but were attracted to call models in which each pulse pair was merged into one long pulse. Females used the pulse rate to recognize such signals: pulse rates close to 87 Hz were attractive, largely independent of the duty cycle. Thus, females of the sibling species N. robustus and N. bivocatus used qualitatively different call recognition mechanisms.

Acoustic Stimulation↗
PubMed2006

High-intensity pulsed electric field variables affecting Staphylococcus aureus inoculated in milk.

Staphylococcus aureus is an important milk-related pathogen that is inactivated by high-intensity pulsed electric fields (HIPEF). In this study, inactivation of Staph. aureus suspended in milk by HIPEF was studied using a response surface methodology, in which electric field intensity, pulse number, pulse width, pulse polarity, and the fat content of milk were the controlled variables. It was found that the fat content of milk did not significantly affect the microbial inactivation of Staph. aureus. A maximum value of 4.5 log reductions was obtained by applying 150 bipolar pulses of 8 mus each at 35 kV/cm. Bipolar pulses were more effective than those applied in the monopolar mode. An increase in electric field intensity, pulse number, or pulse width resulted in a drop in the survival fraction of Staph. aureus. Pulse widths close to 6.7 micros lead to greater microbial death with a minimum number of applied pulses. At a constant treatment time, a greater number of shorter pulses achieved better inactivation than those treatments performed at a lower number of longer pulses. The combined action of pulse number and electric field intensity followed a similar pattern, indicating that the same fraction of microbial death can be reached with different combinations of the variables. The behavior and relationship among the electrical variables suggest that the energy input of HIPEF processing might be optimized without decreasing the microbial death.

Animals↗
PubMed1994

Intraocular photodisruption with picosecond and nanosecond laser pulses: tissue effects in cornea, lens, and retina.

PURPOSE: Nd:YAG laser photodisruption with nanosecond (ns) pulses in the millijoule range is an established tool for intraocular surgery. This study investigates tissue effects in cornea, lens, and retina to assess whether picosecond (ps) pulses with energies in the microjoule range can increase the surgical precision, reduce collateral damage, and allow applications requiring more localized tissue effects than can be achieved with ns pulses. METHODS: Both ps and ns Nd:YAG laser effects on Descemet's membrane, in the corneal stroma, in the lens, and at the retina were investigated in vitro in bovine and sheep eyes and in cataractous human lens nuclei. For each tissue, the optical breakdown threshold was determined. The morphology of the tissue effects and the damage range of the laser pulses were examined by light and scanning electron microscopy. The cavitation bubble dynamics during the formation of corneal intrastromal laser effects were documented by time-resolved photography. RESULTS: The optical breakdown threshold for ps pulses in clear cornea, lens, and vitreous is, on average, 12 times lower than that for ns pulses. In cataractous lens nuclei, it is lower by a factor of 7. Using ps pulses, Descemet's membrane could be dissected with fewer disruptive side effects than with ns pulses, whereby the damage range decreased by a factor of 3. The range for retinal damage was only 0.5 mm when 200 microJ ps pulses were focused into the vitreous. Picosecond pulses could be used for corneal intrastromal tissue evaporation without damaging the corneal epithelium or endothelium, when the pulses were applied in the anterior part of the stroma. The range for endothelial damage was 150 microns at 80 microJ pulse energy. Intrastromal corneal refractive surgery is compromised by the laser-induced cavitation effects. Tissue displacement during bubble expansion is more pronounced than tissue evaporation, and irregular bubble formation creates difficulties in producing predictable refractive changes. CONCLUSIONS: The use of ps pulses improves the precision of intraocular Nd:YAG laser surgery and diminishes unwanted disruptive side effects, thereby widening the field of potential applications. Promising fields for further studies are intrastromal corneal refractive surgery, cataract fragmentation, membrane cutting, and vitreolysis close to the retina.

Animals↗
PubMed1997

Do pulse checks cause a significant delay in the initial defibrillation sequence?

This study was undertaken to determine if checking for a pulse between initial defibrillations causes a clinically significant delay in the administration of the defibrillations. Ten emergency department nurses and 10 emergency medicine resident physicians were timed delivering three successive defibrillations (200, 300 and 360 J) to a manikin under three randomly assigned scenarios: (1) without pulse checks; (2) with pulse checks performed by an assistant; and (3) with pulse checks performed by the participant. All participants performed the three defibrillation scenarios using three different models of defibrillators. Repeated measures analysis of variance was used to compare mean defibrillation times for the three scenarios. The mean time was 20.4 +/- 1.0 s for defibrillation without pulse checks; 20.2 +/- 1.2 s with pulse checks by an assistant and 22.0 +/- 2.0 s with pulse checks by the participant. There was a statistically significant difference between no pulse checks and pulse checks by the participant. No statistically significant difference was noted between no pulse checks and pulse checks by an assistant. We conclude that checking for a pulse does cause a statistically significant delay in the administration of defibrillations. This difference, however, is not likely to be clinically relevant.

Analysis of Variance↗
PubMed2000

Similarity in bilateral photoplethysmographic peripheral pulse wave characteristics at the ears, thumbs and toes.

The characteristics of the photoplethysmography (PPG) pulse signal are body site specific, with pulses from the various peripheral sites showing differences in pulse transit time, strength and shape, and variation of each over time. The aim of this study was to determine the similarity in the right-left pulse characteristics for a group of normal subjects with pulses obtained simultaneously from six peripheral sites (cars, thumbs and big toes). A multi-site photoplethysmography pulse measurement and analysis system is described and comprised six sets of pulse probes and amplifiers, arranged and electronically matched in pairs for the right and left side comparisons. Two sets of data were collected: firstly a set of validation data to test the electronic matching of right left channels, and secondly a set of physiological data for pulses from 40 normal subjects. The right-to-left side similarity in pulse waveform shape at the three segmental levels (ears, thumbs and toes) was assessed using two types of analysis: root mean square error (RMSE) providing a measure of differences, and cross correlation analysis providing a measure of the degree of similarity. Very low levels of RMSE and correlation coefficients close to unity were obtained for the system validation data, demonstrating good right-left channel matching. The RMSE was an order of magnitude lower than that calculated for the normative physiological data, where median RMSE levels were between 0.053 and 0.060 relative to a peak-to-peak pulse amplitude of unity. The median correlation coefficients were greater than 0.98 for all three segmental levels studied, with the maximum values approaching those of the validation data. We have shown that pulses from the right and left sides of normal subjects are highly correlated at each segmental level. We have obtained a normative range of pulse data, with which specific (vascular) patient groups can be compared.

Adolescent↗
PubMed1975

[Orbital pulse analyses in healthy subjects and patients with cerebral arteriosclerosis].

81 normotensive persons were examined with the ophthalmodyamographic method. The measuring device was fixed with a constant, hypodiastolic pressure, and orbital volume pulses were registered and analysed according to qualitative and quantitative pulse criteria. Pulse criteria of younger persons were compared to those of older patients, pulses of persons with a normal vascular system were compared to pulses of persons suffering from cerebral vascular sclerosis. The most important results can be summarized as follows: 1. In old age pulses with arciform ascent or deep-seated anacrotic inflection are found more often. 2. The applanation of the dicrotic wave is seen more often in older patients and most often in patients with cerebral arteriosclerosis. Yet it is not specific for regressive changes of the arterial wall. 3. Pulses of the peripheral type with decrement of the incisura are found more often in younger persons with unimpaired blood vessels, presumably because of the more viscous-plastic properties of the vascular wall. 4. The quotient of dicrotism increases in old age. 5. The mean value of pulse wave transmission time, as a rule, diminishes in older persons, but non-hypertensive patients with cerebral arteriosclerosis have an increased pulse wave transmission time when compared to persons of the same age group without vascular changes. 6. Concerning the diagnostic value of differences between left and right it is important to notice that physiological differences of pulse criteria are considerable as far as amplitudes and height of discrotism are concerned; they are less prominent as to the period of rapid ejection (time between beginning of steep ascent and primary peak) and practivally below the measurable range as to semi-amplitude time (time that passes until half of the maximum amplitude is reached) and pulse wave transmission time. That means: measurable differences in regard to semi-amplitude time or pulse wave transmission time are reliable diagnostic criteria whereas differences in amplitudes and height of discrotism may bring false positive results.

Adult↗