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At least 811 records · Page 45Linked to original sources
PubMed2003

Levetiracetam has no significant gamma-aminobutyric acid-related effect on paired-pulse interaction in the dentate gyrus of rats.

Gamma-aminobutyric acid (GABA)ergic mechanisms of the novel antiepileptic drug, levetiracetam (Keppra), have been both favored and rejected. Since paired-pulse interaction is accepted in functionally assessing GABAergic mechanisms, we investigated whether levetiracetam affects the paired-pulse inhibition/facilitation of the field potentials, evoked in the dentate gyrus of urethane-anesthesized rats. This model revealed a strong paired-pulse inhibition at 20-ms interstimulus interval, a noteworthy paired-pulse facilitation at 80-ms interstimulus interval, and a moderate paired-pulse inhibition at 500-ms interstimulus interval. Bicuculline (3 mg/kg/h, i.v.) and baclofen (10 mg/kg, i.v.) markedly depressed paired-pulse inhibition at 20-ms interstimulus interval, while clonazepam (1 mg/kg, i.p.), diazepam (10 mg/kg, i.v.), and phenobarbital (40 mg/kg, i.v.) enhanced it. Bicuculline also depressed paired-pulse inhibition at 500-ms interstimulus interval. Bicuculline, baclofen, and diazepam reduced paired-pulse facilitation at 80-ms interstimulus interval. Distinct from these GABA(A) receptor- and GABA(B) receptor-related drugs, levetiracetam (17 and 540 mg/kg, i.v.) had no significant effect on either paired-pulse interaction in this model, a result not favoring any major role of GABAergic mechanisms in its antiseizure action.

Animals↗
PubMed1997

Assessment of anastomotic reliability with pulse oximetry in graded intestinal ischemia: an experimental study in dogs.

BACKGROUND/PURPOSE: Pulse oximetry has been proposed as an appropriate and feasible technique in the assessment of intestinal ischemia in recent years. In this study the authors aimed to assess the reliability of anastomoses in the dog small intestine in which there is graded irreversible ischemia as measured by pulse oxymeter. METHODS: In a control group of four dogs, without any devascularization, three small bowel anastomoses were formed in each dog. The study group consisted of 12 dogs. In each animal three intestinal segments with different levels of ischemia were created by ligating the marginal vessels proximally and distally in sequence beginning from the midpoint of the segmental vascular arcade. Preanastomotic pulse oximeter readings between 80% and 90% were assigned to mild ischemia, 70% and 80% to moderate, and 60% and 70% to severe ischemia group. Pulse oximetry measurements were obtained from probes applied to the antimesenteric serosal surfaces at the midpoint of small intestinal segments. A total of 48 intestinal segments (12 nonischemic in the control group and 36 with three different levels of ischemia in the study group) were transected in the midpoint and anastomosed in double layers. Postanastomotic SaO2 values were also noted. The anastomoses were evaluated 48 hours later macroscopically if there was any leakage, and biopsy specimens were obtained for histopathologic ischemic gradings. All results were studied statistically. RESULTS: Histopathologic grades between each group were statistically different (P < .01 for each comparison) except for control and mild ischemia groups (P > .05), worsening as the level of ischemia increased. Pre- and postanastomotic pulse oximetry measurements correlated very well with the histological gradings (r = -0.90, P < .001 and r = -0.93, P < 0.001 respectively). Number of anastomotic leakages were none in control, one in mild, nine in moderate, and 12 (all of the anastomoses) in severe ischemia groups. In the moderate ischemia group with an average preanastomotic pulse reading of 76.75%, each of the leaking anastomoses had a postanastomotic pulse measurement of lower than 70%. The finding that the difference between histopathologic grades of control and mild ischemia groups with average preanastomotic pulse measurements of 96% and 85%, respectively is not statistically significant enables us to suggest that a saturation of at least 85% is necessary for a reliable anastomosis. CONCLUSION: These results suggest clearly that anastomotic reliability can be predicted objectively with pulse oximetry.

Anastomosis, Surgical↗
PubMed1989

A comparison of thermodilution and pulsed Doppler cardiac output measurement in critically ill children.

To evaluate the pulsed Doppler cardiac output method as a noninvasive means for determining cardiac output in critically ill children, we performed paired pulsed Doppler and thermodilution cardiac output determinations in 17 critically ill children. Commercially available equipment, specifically designed for this purpose, was employed. Forty paired thermodilution and pulsed Doppler determinations were made. There was a significant correlation between the two measurements (pulsed Doppler = 0.84 thermodilution + 0.39; r = 0.79, p less than 0.01). The ranges of thermodilution measurements (1.02 to 6.26 L/min; median 2.77 L/min) and pulsed Doppler measurements (1.13 to 6.35 L/min; median 2.57 L/min) were not different (p = 0.25). However, differences between individual paired thermodilution and pulsed Doppler measurements were large (-3.13 to 2.03 L/min; median 0.12 L/min), and the percentage difference between individual paired thermodilution and pulsed Doppler measurements ranged from 0.41% to 102.5% (median 12.7%). A discrepancy of 15% or more between thermodilution and pulsed Doppler was encountered in 18 (45%) of 40 of paired measurements (95% confidence interval: 29% to 61%), and one fourth of the paired measurements differed by more than 25%. We conclude that, as employed in this study, pulsed Doppler cardiac output determination is not sufficiently representative of the thermodilution output to be employed for hemodynamic monitoring in critically ill children.

Adolescent↗
PubMed1999

A computer-based method for continuous single pulse analysis of intracranial pressure waves.

INTRODUCTION: The single pulse analysis of intracranial pressure waves provides valuable information about the autoregulative processes after head injury. This method has not been used for routine clinical assessment as yet. Current methods for evaluation of intracranial pressure waves are based on spectral analysis or related techniques. This imposes restrictions on the wave sequences available for the investigation of ICP attributes. Therefore, we have developed a computer-based method, which enables continuous analysis of each pulse of the ICP wave, in any clinical setting. METHOD: Firstly, the raw data of the ICP wave is continuously recorded by the Multifunctional Anaesthetic Record System (MARS, Hewlett Packard). The recorded data is then subjected to single pulse wave analysis by our software. Each single pulse is identified by the algorithm. The maximum, minimum and mean value, as well as amplitude and gradient are calculated in each pulse pressure. All conceivable correlations of the listed parameters can be examined. RESULTS: We applied our software in 9 cases with head injury and evaluated the measurements over 59 days (1400 h). More than 7 million single pulse pressures have been analyzed off-line. The software proved to be accurate and easy to apply. It was possible to calculate correlations between the different wave attributes on a broad basis of data. Parameters of special clinical interest were the amplitude of the single pulse pressure and the gradient. CONCLUSION: This method is an improvement on ICP single pulse pressure analysis and facilitates its clinical application. It creates the possibility for continuous long-term analysis of the ICP wave attributes under any clinical condition without loss of data. There are indications that the amplitude and the gradient of the ICP pulse pressure could provide valuable additional information for clinical assessment. However, further evaluation is required.

Craniocerebral Trauma↗
PubMed2000

Transducer resolution enhancement by combining different excitation pulses

This work presents a low-cost solution to improve the axial resolution of an arbitrarily loaded and backed piezoelectric transducer. The proposed solution is based on the use of different excitation pulses and, in particular, the combination of two excitation pulses. The characteristic parameters of the second pulse, i.e. amplitude and time delay with respect to the main pulse, are obtained by studying the waveform of a reference pulse emitted or received by the transducer. This reference pulse is the transducer's response to a generic excitation pulse which has the same shape and duration as the main pulse. The work also presents a procedure to estimate the characteristic parameters of the second excitation pulse by means of the electrical simulator SPICE. Then, to illustrate the effectiveness of the simulation, the simulated and experimental values are compared through two experimental cases.

Journal Article↗
PubMed1997

Steady-state auditory evoked responses to pulsed frequency modulations in children.

This study investigated steady-state auditory evoked responses to pulsed frequency modulations (FM) of a continuous tone in normal children ranging in age from 6 to 12 years. We examined variations in response amplitude and phase as a function of age, recording site, and FM pulse duration. The surface topography of these evoked potentials suggested a relatively broad distribution with maximal responses observed at frontal electrode sites, smaller responses from parietal leads and the smallest responses were evident at the temporal lobe placements. Response parameters varied significantly as a function of pulse duration. Fifty milliseconds pulses elicited responses that were on average 20% larger than 100 ms FM pulses. Mean phase differences suggested that responses to the 100 ms pulses also lagged behind responses to the 50 ms pulses by the equivalent of 20 ms. There were no significant age-related variations in response amplitude. Phase varied with age only in response to the 50 ms FM pulses. The findings indicated that steady-state responses are sensitive to temporal parameters of frequency change present in pulsed modulations. The possibility is raised that this paradigm may be clinically useful in detecting dysfunction of specialized auditory mechanisms involved in frequency modulation analysis.

Acoustic Stimulation↗
PubMed1998

Treatment of spider veins with the 595 nm pulsed-dye laser.

BACKGROUND: Previous attempts to treat spider veins with the conventional 585 nm pulsed-dye laser with a 0.5-ms pulse duration have been relatively ineffective. Recently, a new pulsed-dye laser that is tunable from 585 to 600 nm with a pulse duration 3 times longer than previously available lasers has preliminarily been shown to be effective for treatment of spider veins. OBJECTIVE: Our purpose was to evaluate the effectiveness of multiple treatments with the tunable long-pulse dye laser in treatment of spider veins of the lower extremity. METHODS: Ten female volunteers were treated in two separate areas containing blue or red linear spider veins less than 1.5 mm in diameter. Treatments were administered with the pulsed-dye laser with a 1.5-ms pulse duration and 595-nm light at fluences of 15 and 20 J/cm2, and each subject received a total of 3 treatments at each site, administered at 6-week intervals. Photographs were taken before and 6 weeks after the last treatment. RESULTS: Computer-based image analysis showed clearing of more than three fourths of veins after 3 treatments with 15 or 20 J/cm2. Side effects were minimal and the treatments were well tolerated. CONCLUSION: The 595 nm, 1.5 ms pulse duration, pulsed-dye laser is safe and effective for treating blue or red spider veins of the lower extremities less than 1.5 mm in diameter in nontanned patients with Fitzpatrick skin types I and II. Multiple treatments improve on the results obtained after a single treatment.

Adult↗
PubMed1997

Confirmation of the pulse oximetry gap in carbon monoxide poisoning.

STUDY OBJECTIVES: To demonstrate the degree to which pulse oximetry overestimates actual oxyhemoglobin (O2Hb) saturation in patients with carbon monoxide (CO) poisoning. This phenomenon has been reported in fewer than 20 humans in the English medical literature. METHODS: A retrospective chart review of 191 patients evaluated for CO poisoning at a regional hyperbaric center identified 124 patients 10 years of age and older who had had both arterial blood gas and pulse oximetry measurements and who had received either high-flow oxygen through a nonrebreather mask or 100% inspired oxygen through an endotracheal tube. Blood gas measurements, including direct spectrophotometric determination of O2Hb and carboxyhemoglobin (COHb) saturation values, were compared with finger-probe pulse oximetry readings. RESULTS: Measured O2Hb saturation (mean +/- SD, 88.7 +/- 10.2%; range, 51.4% to 99.0%) decreased linearly and predictably with rising COHb levels (10.7 +/- 10.4%; range, .2% to 46.4%). Pulse oximetry saturation (99.2% +/- 1.3%; range, 92% to 100%) remained elevated across the range of COHb levels and failed to detect decreased O2Hb saturation. The pulse oximetry gap, defined as the difference between pulse oximetry saturation and actual O2Hb saturation (10.5% +/- 9.7%; range, 0% to 40.6%), approximated the COHb level. CONCLUSION: There is a linear decline in O2Hb saturation as COHb saturation increases. This decline is not detected by pulse oximetry, which therefore overestimates O2Hb saturation in patients with increased COHb levels. The pulse oximetry gap increases with higher levels of COHb and approximates the COHb level. In patients with possible CO poisoning, pulse oximetry must be considered unreliable and interpreted with caution until the COHb level has been measured.

Adolescent↗
PubMed2002

Heart rate dependency of pulse pressure amplification and arterial stiffness.

BACKGROUND: Pulse pressure and aortic pulse wave velocity, measures of arterial stiffness, are both important determinants of cardiovascular risk. However, assessment of peripheral pulse pressure does not always provide a reliable measure of changes in central pulse pressure or arterial stiffness. The aim of the present study was to assess the effect of acute changes in heart rate on arterial stiffness and on peripheral and central pulse pressure in healthy subjects. METHODS: Twenty subjects (age range, 20 to 72 years) were studied at cardiac catheterization. Pulse wave analysis was used to determine central pressure, augmentation index (AIx), a measure of systemic arterial stiffness, and aortic pulse wave velocity (PWV) during right atrial pacing (80 to 120 beats/min). RESULTS: Pulse pressure amplification increased during pacing due to a reduction in central pressure augmentation. AIx was significantly and inversely related to heart rate (r = -0.70, P < .001) due to an alteration in the relative timing of the reflected pressure wave, rather than a reduction in arterial stiffness, as PWV did not change. CONCLUSIONS: These data suggest that peripheral pulse pressure does not provide an accurate assessment of changes in central hemodynamics in relation to changes in heart rate, and that aortic stiffness is not affected by acute changes in heart rate.

Adult↗
PubMed2002

Repetitive paired-pulse transcranial magnetic stimulation affects corticospinal excitability and finger tapping in Parkinson's disease.

OBJECTIVES: To study the effect of long trains of a recently established conditioning-test paired-pulse repetitive transcranial magnetic stimulation (rTMS) paradigm on corticospinal excitability and finger tapping speed. METHODS: We applied 900 inhibiting or facilitating paired-pulses or 900 real or sham single stimuli at 1Hz over the motor cortex contralateral to the dominant hand of 9 healthy subjects and contralateral to the more affected hand of 11 patients with Parkinson's disease. RESULTS: In both groups, motor evoked potentials (MEPs) from suprathreshold pulses were larger after facilitating paired-pulses than after inhibiting paired-pulses. After real single-pulse rTMS and after either type of paired-pulse rTMS patients showed an increase in finger tapping frequency on the stimulated hand. Tapping was unchanged contralaterally, after sham stimuli, and in controls. Tremor and tapping frequencies were not correlated, nor was the change in MEP size correlated to the change in tapping frequency. CONCLUSIONS: Repetitive paired-pulses allow selective induction of corticospinal inhibition or facilitation, but do not enhance the transient improvement of finger motility induced by conventional single-pulse rTMS.

Adult↗
PubMed2001

Cell membrane electropermeabilization by symmetrical bipolar rectangular pulses. Part II. Reduced electrolytic contamination.

The paper presents a comparative study of the contamination of a cell suspension by ions released from aluminum cuvettes (Al(3+)) and stainless steel electrodes (Fe(2+)/Fe(3+)) during cell membrane electropermeabilization by unipolar and by symmetrical bipolar rectangular electric pulses. A single pulse and a train of eight pulses were delivered to electrodes at a 2-mm distance, with 100-micros and 1-ms pulse durations, and amplitudes ranging from 0 to 400 V for unipolar, and from 0 to 280 V for bipolar pulses. We found that the released concentrations of Al(3+) and Fe(2+)/Fe(3+) were always more than one order of magnitude lower with bipolar pulses than with unipolar pulses of the same amplitude and duration. We then investigated the viability of DC-3F cells after 1 h of incubation in the medium containing different concentrations of Al(3+) or Fe(2+)/Fe(3+) within the range of measured released concentrations (up to 2.5 mM for both ions), thus separating the effects of electrolytic contamination from the effects of electropermeabilization itself. For Fe(2+)/Fe(3+), loss of cell viability became significant at concentrations above 1.5 mM, while for Al(3+), no effect on cell survival was detected within the investigated range. Still, reports on the biochemical effects of released Al(3+) also suggest that with aluminum cuvettes, electrolytic contamination can be detrimental. Our study shows that electrolytic contamination and its detrimental effects can be largely reduced with no loss in efficiency of electropermeabilization, if bipolar rectangular pulses of the same amplitude and duration are used instead of the commonly applied unipolar pulses.

Aluminum↗
PubMed2000

Effects of pulsed electric fields on ovalbumin solutions and dialyzed egg white.

Ovalbumin solutions (2%, pH 7.0, 200 ohm.cm) and dialyzed fresh egg white (pH 9.2, 200-250 ohm.cm) were subjected to 50-400 exponential decay pulses with an electric field strength of 27-33 kV/cm. The pulse width was ca. 0.3 micros (at a capacitance of 20 nF) or 0.9 micros (at 80 nF), and the corresponding dissipated energy was 0.7 or 2.3 J/(pulse.mL) of solution. The sample temperature was maintained below 29 degrees C. While the four sulfhydryl groups of native ovalbumin did not react with DTNB, they became reactive immediately after pulse processing, indicating either partial protein unfolding or enhanced SH ionization. The extent of SH reactivity increased with dissipated energy, 3.7 SH groups becoming reactive after 100 or 200 pulses at 31.5 kV/cm and 80 nF. However, SH reactivity was reversible, since only 0.79 or 0.2 SH group was found to remain reactive 30 min or 8 h after pulse processing. The fourth derivatives of UV spectra of ovalbumin were determined, before and 15-30 min after pulse processing, to assess possible polarity and conformation changes in the environment of tyrosine and tryptophan. No differences were observed. Thermal gels prepared from fresh or dialyzed egg white had markedly different mechanical and water retention characteristics. Pulse processing of dialyzed egg white (200 pulses, 30 kV/cm, 80 nF) only slightly reduced its gelling properties. Thus electric pulses known to induce significant microbial inactivation did not cause notable changes in the proteins investigated.

Animals↗
PubMed2000

Masimo signal extraction pulse oximetry.

OBJECTIVE: To describe a new pulse oximetry technology and measurement paradigm developed by Masimo Corporation. INTRODUCTION: Patient motion, poor tissue perfusion, excessive ambient light, and electrosurgical unit interference reduce conventional pulse oximeter (CPO) measurement integrity. Patient motion frequently generates erroneous pulse oximetry values for saturation and pulse rate. Motion-induced measurement error is due in part to widespread implementation of a theoretical pulse oximetry model which assumes that arterial blood is the only light-absorbing pulsatile component in the optical path. METHODS: Masimo Signal Extraction Technology (SET) pulse oximetry begins with conventional red and infrared photoplethysmographic signals, and then employs a constellation of advanced techniques including radiofrequency and light-shielded optical sensors, digital signal processing, and adaptive filtration, to measure SpO2 accurately during challenging clinical conditions. In contrast to CPO which calculates O2 saturation from the ratio of transmitted pulsatile red and infrared light, Masimo SET pulse oximetry uses a new conceptual model of light absorption for pulse oximetry and employs the discrete saturation transform (DST) to isolate individual "saturation components" in the optical pathway. Typically, when the tissue under analysis is stationary, only the single saturation component produced by pulsatile arterial blood is present. In contrast, during patient motion, movement of non-arterial components (for example, venous blood) can be identified as additional saturation components (with a lower O2 saturation). When conditions of the Masimo model are met, the saturation component corresponding to the highest O2 saturation is reported by the instrument as SpO2. CONCLUSION: The technological strategies implemented in Masimo SET pulse oximetry effectively permit continuous monitoring of SpO2 during challenging clinical conditions of motion and poor tissue perfusion.

Artifacts↗
PubMed2002

Accuracy of fetal pulse oximetry.

BACKGROUND: The goal of this investigation was to evaluate the agreement of fetal pulse oximetry to saturation readings from hemoximetry at low oxygen saturation. METHODS: Fetal oxygen saturation measurements obtained by pulse oximetry were compared with those obtained by hemoximetry in fetal scalp blood samplings. The prospective observational trial included fetuses with non-reassuring fetal heart rate tracings suggestive of hypoxia and requiring fetal scalp blood samplings. Arterial oxygen saturation was determined by a blinded pulse oximeter (N400, FS14; Nellcor Puritan Bennett, Pleasanton, CA, USA) and continuously stored on a notebook computer. Saturation from fetal scalp blood samples was measured by hemoximetry (Bayer Diagnostics 865; ABL 625, Radiometer). Data analysis focussed on the absolute and relative difference between hemoximetry and pulse oximetry of fetuses, showing the most distinct difference in neonatal outcome. Normal outcome was defined as spontaneous delivery and umbilical artery pH >or= 7.20 + Apgar 5 >or= 7 (n = 42). In contrast, a group of neonates with combined respiratory and metabolic acidemia at birth was defined by pH <or= 7.16 and an additional base excess <or= -9.4 mmol/l in the umbilical artery (n = 18). RESULTS: The correlation coefficient between hemoximetry and pulse oximetry measurements was r = 0.72; p = 0.002 in the acidemic group. The median of absolute differences in saturation was + 5.2% (95%CI 2.5-10.3) saturation. The absolute differences ranged from -21% to + 36% saturation. The median of relative differences amounted to 23% (95%CI 15.1-55.0). The relative differences ranged from -30% to + 217%. Observing the saturation distribution in the two groups (hemoximetry and pulse oximetry, respectively) presented a median hemoximetry pulse oximetry of 38% (42%) in the normal and 26% (39%) in the acidemic group. In this small group of cases, the correlation coefficient between pH and saturation from pulse oximetry in fetal scalp blood from the samplings was r = 0.19. CONCLUSION: Fetal pulse oximetry tends to overestimate arterial oxygen saturation compared with hemoximeter values.

Adult↗
PubMed2002

Single-pulse coherently controlled nonlinear Raman spectroscopy and microscopy.

Molecular vibrations have oscillation periods that reflect the molecular structure, and are hence being used as a spectroscopic fingerprint for detection and identification. At present, all nonlinear spectroscopy schemes use two or more laser beams to measure such vibrations. The availability of ultrashort (femtosecond) optical pulses with durations shorter than typical molecular vibration periods has enabled the coherent excitation of molecular vibrations using a single pulse. Here we perform single-pulse vibrational spectroscopy on several molecules in the liquid phase, where both the excitation and the readout processes are performed by the same pulse. The main difficulty with single-pulse spectroscopy is that all vibrational levels with energies within the pulse bandwidth are excited. We achieve high spectral resolution, nearly two orders of magnitude better than the pulse bandwidth, by using quantum coherent control techniques. By appropriately modulating the spectral phase of the pulse we are able to exploit the quantum interference between multiple paths to selectively populate a given vibrational level, and to probe this population using the same pulse. This scheme, using a single broadband laser source, is particularly attractive for nonlinear microscopy applications, as we demonstrate by constructing a coherent anti-Stokes Raman (CARS) microscope operating with a single laser beam.

Lasers↗
PubMed1998

Paired pulse analysis of ATP and noradrenaline release from sympathetic nerves of rat tail artery and mouse vas deferens: effects of K+ channel blockers.

1. The paired pulse stimulus paradigm - two pulses of equal strength delivered at variable interpulse intervals was used to study the release of ATP and noradrenaline (NA) from post ganglionic sympathetic nerves of rat tail artery and mouse vas deferens. 2. Excitatory junction currents (EJCs) were used to measure the release of ATP, and differential pulse amperometry to measure that of NA. 3. At interpulse intervals of 0.1 - 1 s paired pulse stimulation caused an increase in the size of the second EJC, both in rat tail artery and mouse vas deferens. As the interpulse interval was increased to 10 s or more, the two EJCs became of equal size. 4. In both preparations the K+ channel blockers tetraethylammonium (TEA, 20 mM) and 4-aminopyridine (4-AP, 1 mM) prolonged the duration of the nerve terminal spike and greatly amplified the first EJC of the pair. 5. In the presence of TEA and 4-AP in rat tail artery paired pulse stimulation caused a dramatic depression of the second EJC without markedly affecting the nerve terminal spike. The depression of the second EJC decreased with increasing interpulse intervals, and also when external Ca2+ was reduced to 0.2 mM. In mouse vas deferens, TEA and 4-AP caused only a modest depression of the second EJC. 6. In rat tail artery in the presence of TEA and 4-AP paired pulse stimulation caused a depression of the NA oxidation current evoked by the second pulse, which was similar in magnitude and time course to that of the EJC. Similar TEA and 4-AP induced depression of the second pulse response was also observed when the purinergic and noradrenergic components of the contractile response were investigated. 7. The results show that in rat tail artery K+ channel blockers cause a dramatic paired pulse depression of the release of ATP and NA. The similarity in the depression of the EJC, the NA oxidation current, and the purinergic and noradrenergic components of the contractile response is compatible with the hypothesis that ATP and NA are released in parallel from the same neuronal sources.

4-Aminopyridine↗
PubMed2003

Modelling and optimization of inactivation of Lactobacillus plantarum by pulsed electric field treatment.

AIMS: The effect of critical pulsed electric field (PEF) process parameters, such as electric field strength, pulse length and number of pulses, on inactivation of Lactobacillus plantarum was investigated. METHODS AND RESULTS: Experiments were performed in a pH 4.5 sodium phosphate buffer having a conductivity of 0.1 S m-1, using a laboratory-scale continuous PEF apparatus with a co-linear treatment chamber. An inactivation model was developed as a function of field strength, pulse length and number of pulses. Based on this inactivation model, the conditions for a PEF treatment were optimized with respect to the minimum energy required to obtain a certain level of inactivation. It was shown that the least efficient process parameter in the range investigated was the number of pulses. The most efficient way to optimize inactivation of Lact. plantarum was to increase the field strength up to 25.7 kV cm-1, at the shortest pulse length investigated, 0.85 micros, and using a minimum number of pulses. The highest inactivation of Lact. plantarum at the lowest energy costs is obtained by using the equation: E=26.7tau0.23, in which E is the field strength and tau the pulse length. An optimum is reached by substituting tau with 5.1. CONCLUSIONS: This study demonstrates that the correct choice of parameters, as predicted by the model described here, can considerably improve the PEF process. SIGNIFICANCE AND IMPACT OF THE STUDY: The knowledge gained in this study improves the understanding of the limitations and opportunities of the PEF process. Consequently, the advantage of the PEF process as a new option for non-thermal decontamination can be better utilized.

Electric Stimulation↗
PubMed2001

Local pulse pressure is a major determinant of large artery remodelling.

1. The aim of the present brief review is to show that the pulsatile component of blood pressure is a stronger determinant of large artery remodelling than the steady component (i.e. mean blood pressure). 2. Pulse pressure, which is a strong determinant of cardiovascular events, including coronary heart disease and stroke, is increased when large arteries stiffen. Local pulse pressure, measured with applanation tonometry in normotensives and patients with essential hypertension, explains a significant part of the variance of intima-media thickness at the site of the carotid artery, a proximal elastic artery, whereas mean blood pressure does not contribute. Local pulse pressure has no influence on intima-media thickness at the site of the radial artery, a distal muscular artery that undergoes very little stroke change in diameter. 3. The decrease in carotid pulse pressure is also a major determinant of the regression of carotid intima-media thickness after antihypertensive treatment. Local pulse pressure can influence not only intima-media thickness, but also internal diameter. Indeed, there is a significant association between the lumen enlargement of the ascending aorta in patients with Marfan syndrome and pulse pressure. In addition, carotid pulse pressure is positively correlated with carotid internal diameter in normotensives and hypertensives, and the decrease in carotid internal diameter during long-term antihypertensive treatment is influenced by the decrease in carotid pulse pressure and not by the reduction in mean blood pressure. 4. We suggest that the effects of pulse pressure on large artery remodelling may explain part of its predictive value on cardiovascular events.

Antihypertensive Agents↗