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At least 595 records · Page 33Linked to original sources
PubMed2007

Patient skin dose in cardiac interventional procedures: conventional fluoroscopy versus pulsed fluoroscopy.

OBJECTIVES: To investigate whether pulsed fluoroscopy reduces a patient's exposure compared with the exposure owing to conventional (continuous) fluoroscopy, we simulated the skin radiation doses of patients at cardiac catheterization facilities with various X-ray systems used in fluoroscopically guided intervention procedures. BACKGROUND: Although many reports have noted that "pulsed fluoroscopy" provides important further reductions in radiation exposure, it has been determined that when comparing dose rates between different vendor systems, "pulsed fluoroscopy" does not reduce patients' exposure as compared with "conventional fluoroscopy". METHODS: We examined 13 X-ray systems; 10 used pulsed fluoroscopy and three used conventional fluoroscopy. The entrance surface doses with fluoroscopy were compared for the 13 X-ray systems by using acrylic plates (20-cm thick) and a skin dose monitor. The X-ray conditions used in the measurements were those normally used in the facilities performing percutaneous coronary intervention. RESULTS: The average surface dose for systems from three different vendors producing conventional fluoroscopy systems was 23.93+/-2.77 mGy/min vs. an average surface dose of 22.52+/-4.50 mGy/min from five vendors of pulsed fluoroscopy systems (25, 30, and 50 pulses/sec) (P=0.646). The average entrance surface dose was significantly (P<0.0001) higher with conventional fluoroscopy and pulsed fluoroscopy at 25, 30, and 50 pulses/sec (23.05+/-3.78 mGy/min) than with pulsed fluoroscopy at 15 pulses/sec (13.86+/-3.22 mGy/min). CONCLUSIONS: Pulsed fluoroscopy did not in itself reduce radiation exposure. In general, the use of pulsed fluoroscopy at a pulse rate lower than 25 pulses/sec should reduce the skin dose in fluoroscopically guided intervention procedures. Nevertheless, some X-ray systems are not designed to reduce the dose rate as the number of pulses per second is decreased. Physicians should be aware of the entrance surface dose of the X-ray system that they use for cardiac IVR.

Cardiac Catheterization↗
PubMedDate not supplied

Fat suppressed MRI of articular cartilage with a spatial-spectral excitation pulse.

We developed a three-dimensional, gradient-recalled-echo imaging technique that incorporates a short-duration spatial-spectral excitation pulse from the family of binomial pulses. Binomial pulses of different orders were tested on phantoms and on normal volunteers to find the composite pulse that produced in the shortest duration the most reliable fat suppression. Composite pulses employing unipolar slice-selective gradients with explicit rewinder gradients between each radio-frequency (RF) pulse were compared with composite RF pulses employing alternating-polarity, slice-select gradients. The advantage of the sequences using the unipolar gradients is improved fat suppression. Images of the knees of volunteers produced with the composite RF pulse have contrast between fat and articular cartilage equivalent to that on images created by the gradient-recalled-echo imaging technique employing a conventional chemsat pulse. The optimum RF pulse consisted of three amplitude- and phase-modulated pulses combined with unipolar slice-select gradients.

Adipose Tissue↗
PubMed1997

Dispersion in magnetization transfer contrast at a given specific absorption rate due to variations of RF pulse parameters in the magnetization transfer preparation.

The effects of RF pulse parameters on magnetization transfer contrast (MTC) were investigated using a magnetization prepared segmented fast gradient echo sequence. MTC was found not to be uniquely determined by the specific absorption rate (SAR). RF pulse parameters (RF amplitude, number of RF pulses and RF duration) also affect MTC. There can be 40% variation in MTC due to differences in RF parameters at SAR = 1 W/kg for a 70-kg subject. Increasing the number of RF pulses is a more efficient way to increase MTC than increasing RF amplitude. This phenomenon is likely caused by the fact that the time scale for magnetization transfer between the free and restricted proton pools is on the same order or longer than the duration of the MT pulse. Accordingly, increase in the MT pulse duration by increasing the number of RF pulses in the MT pulse allows more effective magnetization transfer. Such information can be used as a guide to select RF pulse parameters for a magnetization transfer (MT) pulse. An off-resonance MT pulse designed under this guide for coronary MR angiography improved the depiction of distal vessels.

Animals↗
PubMed1988

Transmitter release patterns of noradrenergic, dopaminergic and cholinergic axons in rabbit brain slices during short pulse trains, and the operation of presynaptic autoreceptors.

Slices of rabbit brain were field-stimulated either by single electrical pulses or by trains of 4 or 8 pulses at 1 or 100 Hz in order to study transmitter release patterns and the autoinhibition of transmitter release. The slices were preincubated with 3H-noradrenaline (cortex), 3H-dopamine (caudate nucleus) or 3H-choline (caudate nucleus). Slices preincubated with 3H-noradrenaline were superfused with medium containing desipramine 1 mumol/l. The overflow of tritium elicited by single pulses amounted to 0.19% of the tritium content of the tissue. The overflow elicited by 4 pulses/1 Hz was similar, whereas that elicited by 4 pulses/100 Hz was 5.1-fold higher. Yohimbine 10-1000 nmol/l increased up to 2.5-fold the overflow evoked by 4 pulses/1 Hz but did not change the overflow evoked by single pulses or 4 pulses/100 Hz. - Slices preincubated with 3H-dopamine were superfused with medium containing nomifensine 1 mumol/l. The overflow of tritium elicited by single pulses was 0.39% of the tritium content of the tissue. The overflow elicited by 4 pulses/1 Hz was 1.3-fold and the overflow elicited by 4 pulses/100 Hz 1.4-fold higher. Domperidone 1-100 nmol/l and sulpiride 10-1000 nmol/l increased up to 2.4-fold the overflow evoked by 4 pulses/1 Hz but increased only slightly the overflow evoked by single pulses or 4 pulses/100 Hz. - Slices preincubated with 3H-choline were superfused either with physostigmine-free medium or with medium containing physostigmine 1 mumol/l. In physostigmine-free medium, atropine did not increase the evoked overflow of tritium at any stimulation condition. In physostigmine-containing medium, the overflow elicited by single pulses was 0.18% of the tritium content of the tissue. The overflow elicited by 8 pulses/1 Hz was 2.0-fold and the overflow elicited by 8 pulses/100 Hz 2.2-fold higher. Atropine 2-200 nmol/l increased up to 2.4-fold the overflow evoked by 8 pulses/1 Hz but increased only slightly the overflow evoked by single pulses or 8 pulses/100 Hz. In physostigmine-free medium, sulpiride 10-1000 nmol/l did not change the single-pulse-evoked overflow of tritium in the absence but increased it in the presence of nomifensine 1 mumol/l. Single pulses elicit a large release of 3H-noradrenaline, 3H-dopamine and 3H-acetylcholine under the conditions of these experiments. Release elicited by single pulses is not subject to autoinhibition except for a small inhibition by spontaneously released transmitter in the case of dopaminergic and cholinergic axons.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1996

Temporally patterned pulse trains affect directional sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus.

The directional sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus, was studied under free field stimulation conditions with 3 temporally patterned trains of sound pulses which differed in pulse repetition rate and duration. The directional sensitivity curves of 92 neurons studied can be described as hemifield, directionally-selective, or non-directional according to the variation in the number of impulses with pulse train direction. When these neurons were stimulated with all 3 pulse trains, the directional sensitivity curves of 50 neurons was unchanged but that of the other 42 neurons changed from one type into another. When these pulse trains were delivered at high pulse repetition rate and short pulse duration, they significantly sharpened the directional sensitivity of two thirds of the neurons examined by reducing the angular range and increasing the slope of their impulse directional sensitivity curves. These pulse trains also sharpened the slope of the threshold directional sensitivity curves of 25 neurons studied. However, when directional sensitivity of collicular neurons was determined with pulse trains that differed only in pulse repetition rate or in pulse duration, significant sharpening of directional sensitivity was rarely observed in all experimental conditions tested. Possible mechanisms underlying these findings are discussed.

Animals↗
PubMed1986

Recovery patterns of rat hemopoietic stem cells between pulse doses of 7,12-dimethylbenz(a)anthracene (DMBA) applied in a leukemogenic regimen.

Male Wistar rats received repeated pulse doses of 7,12-dimethylbenz(a)anthracene (DMBA), known to elicit myelodysplasia followed by acute, mostly erythroblastic, leukemia at 10-day intervals. The recovery of spleen colony forming hemopoietic stem cells (CFU-s) surviving the cytocidal action of DMBA was examined between pulses. Recovery after a pulse of 35 mg/kg body weight varied with the organ source of the CFU-s (femoral bone marrow or spleen) and the number of preceding DMBA pulses. After a single DMBA pulse bone marrow CFU-s initially recovered faster than reported for normal bone marrow CFU-s transplanted into chemically conditioned rats. But recovery was followed by regeneration arrest. Population doubling times of marrow CFU-s increased with the number of DMBA pulses. Recovery of splenic CFU-s was slower after a single DMBA pulse than reported for normal spleen CFU-s transplanted into chemically conditioned rats. The CFU-s population doubling times were not significantly different after a single or five DMBA pulses. After three pulses, however, recovery of splenic CFU-s was exceedingly slow until day 5 and subsequently accelerated, but was still slower than after one or five pulses. In the spleen CFU-s recovery was always accompanied by regeneration of total cell numbers with a preference for erythroid regeneration. In the bone marrow this was the case after three DMBA pulses only.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1984

Control of quantal transmitter release at frog's motor nerve terminals. II. Modulation by de- or hyperpolarizing pulses.

Quanta of transmitter were released from motor nerve terminals of the frog by a depolarizing 'releasing pulse'. 'Modulating pulses' were subthreshold for release; pre-pulses were added directly before and post-pulses directly after the releasing pulse. Modulating depolarization pulses enhanced release up to 20-fold, and such hyperpolarizations suppressed release up to 10-fold. Pre- and post-pulses were about equally effective. In a wide range these modulations did not affect the facilitation of a test-EPSC by the preceding releasing pulse; modulation thus is not mediated by changes in Ca-inflow. It is suggested that phasic release is largely controlled by an 'activator' which is generated by depolarization, and that modulating pulses increase this activator when depolarizing, and decrease this activator below its resting level if hyperpolarizing. If an interval was interposed between pre- and releasing pulse, the modulating effect decreased very steeply with increasing interval for the first 2 ms, and much slower for longer intervals. Distributions of delays of quantal releases showed a time course of decay very similar to the decay of modulation with increasing interval. Both decays may reflect the exponential decay of activator. Depolarizing post-pulses increased the minimal synaptic delay and the delay of maximal release, and hyperpolarizing ones had the opposite effects. They are interpreted to modulate the generation and decay of a 'repressor', which is produced by depolarization and is responsible for the minimal synaptic delay and the delayed maxima of release. A speculative scheme of interactions of [Ca]i, activator and repressor is discussed.

Animals↗
PubMed1989

Evaluation of the palmar circulation by pulse oximetry.

The usual method of substantiating collateral circulation of the hand is with Allen's test. We used the pulse-detecting capability of the pulse oximeter to assess the presence of collateral circulation of the hand. Thirty-one patients undergoing radial artery cannulation for intraoperative monitoring were evaluated before cannulation with a modified Allen's test and by pulse oximetry. After the collateral circulation of the hand was tested by the modified Allen's test, a pulse oximeter probe was placed on the index finger. Both radial and ulnar arteries were occluded until no perfusion was detected by the pulse oximeter. The test was repeated twice on each hand, once for each artery. The time to reperfusion after arterial release was recorded. Reperfusion times greater than 15 seconds were considered abnormal. This sequence was repeated postoperatively after the radial artery cannulae were removed. A total of 68 tests were performed before cannulation; 3 showed an abnormal Allen's test, a finding confirmed by pulse oximetry evaluation. The Allen's test was indeterminate 13 times. In all of these cases, pulse oximetry demonstrated collateral blood flow. When collateral circulation was determined to be present by Allen's test, it was also found to be present with pulse oximetry. Three days after cannulation was discontinued, 8 patients had abnormal Allen's test results, a finding again confirmed by pulse oximetry evaluation. Of 15 patients with indeterminate Allen's test results, 12 had collateral blood flow determined by pulse oximetry and 3 had abnormal results. The ability of pulse oximetry to detect collateral circulation was significantly different (P less than 0.001) when compared with Allen's test both before and after radial artery cannulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Control of luteinizing hormone-releasing hormone pulse generation in nonhuman primates.

1. The pulsatile release of luteinizing hormone-releasing hormone (LHRH) is critical for reproductive function. However, the exact mechanism of LHRH pulse generation is unclear. The purpose of this article is to review the current knowledge on LHRH pulse generation and to discuss a series of studies in our laboratory. 2. Using push-pull perfusion in the stalk-median eminence of the rhesus monkey several important facts have been revealed. There is evidence indicating that LHRH neurons themselves have endogenous pulse-generating mechanisms but that the pulsatility of LHRH release is also modulated by input from neuropeptide Y (NPY) and norepinephrine (NE) neurons. The release of NPY and NE is pulsatile, with their pulses preceding or occurring simultaneously with LHRH pulses, and the neuroligands NPY and NE and their agonists stimulate LHRH pulses, while the antagonists of the ligands suppress LHRH pulses. 3. The pulsatile release of LHRH increases during the estrogen-induced LH surge as well as the progesterone-induced LH surge. These increases are partly due to the stimulatory effects of estrogen and progesterone on NPY neurons. 4. An increase in pulsatile LHRH release occurs at the onset of puberty. This pubertal increase in LHRH release appears to be due to the removal of tonic inhibition from gamma aminobutyric acid (GABA) neurons and a subsequent increase in the inputs of NPY and NE neurons to LHRH neurons. 5. There are indications that additional neuromodulators are involved in the control of the LHRH pulse generation and that glia may play a role in coordinating pulses of the release of LHRH and neuromodulators. 6. It is concluded that the mechanism generating LHRH pulses appears to comprise highly complex cellular elements in the hypothalamus. The study of neuronal and nonneuronal elements of LHRH pulse generation may serve as a model to study the oscillatory behavior of neurosecretion.

Animals↗
PubMed1999

Temporally patterned pulse trains affect duration tuning characteristics of bat inferior collicular neurons.

This study examines the effect of temporally patterned pulse trains on duration tuning characteristics of inferior collicular neurons of the big brown bat. Eptesicus fuscus, under free-field stimulation conditions. Using a 50% difference between maximal and minimal responses as a criterion, the duration tuning characteristics of inferior collicular neurons determined with pulse trains of different pulse durations are described as band-pass, long-pass, short-pass, and all-pass. Each band-pass neuron discharged maximally to a specific pulse duration that was at least 50% larger than the neuron's responses to a long- and a short-duration pulse. In contrast, each long- or short-pass neuron discharged maximally to a range of long- or short-duration pulses that were at least 50% larger than the minimal responses. The number of impulses of an all-pass neuron never differed by more than 50%. When pulse trains were delivered at different pulse repetition rates, the number of short-pass and band-pass neurons progressively increased with increasing pulse repetition rates. The slope of the duration tuning curves also became sharper when determined with pulse trains at high pulse repetition rates. Possible mechanisms underlying these findings are discussed.

Acoustic Stimulation↗
PubMed2006

Competition for pulsed resources: an experimental study of establishment and coexistence for an arid-land grass.

In arid environments, episodically-pulsed resources are important components of annual water and nutrient supply for plants. This study set out to test whether seedlings have an increased capacity for using pulsed resources, which might then improve establishment when in competition with older individuals. A second aim was to determine whether there is a trade-off in competitive strategies when resources are supplied continuously at low concentrations, or as pulses with pronounced inter-pulse periods. A glasshouse experiment used a target-neighbour design of size-asymmetric competition, with juveniles of Panicum antidotale (blue panicgrass) introduced into contrasting densities of adult plants. Stable isotopes of nitrogen were used for measuring plant resource uptake from pulses, and tolerance to inter-pulse conditions was assessed as the mean residence time (MRT) of nitrogen. A higher root/shoot ratio and finer root system enhanced the capacity of juveniles to use resources when pulsed, rather than when continuously supplied. Higher resource uptake during pulses improved the establishment of juvenile Panicum in mixed cultures with older individuals. However, a trade-off was observed in plant strategies, with juveniles showing a lower MRT for nitrogen, which suggested reduced tolerance to resource deficit during inter-pulse periods. Under field conditions, higher utilization of pulsed resources would lead to the improved seedling establishment of Panicum adjacent to "nurse" plants, whereas mature plants with well-developed roots, exploiting a greater soil volume, maintain more constant resource uptake and retention during inter-pulse periods.

Aging↗
PubMed1995

Effects of bicuculline and baclofen on paired-pulse depression in the dentate gyrus of epileptic patients.

Paired-pulse field responses were recorded from the granule cell layer of the dentate gyrus in brain slices from temporal lobe epileptic patients. Paired-pulse depression (PPD) was examined using perforant path stimulation of low to moderate intensity at an inter-stimulus interval (ISI) of 20 ms. The paired-pulse ratio (PS2/PS1) was expressed as the population spike amplitude of the second response (PS2) relative to that of the first response (PS1). Representative tissue response from each patient biopsy were divided into two groups that were significantly different based on the magnitude of the highest paired-pulse ratio recorded for each biopsy specimen: the strong paired-pulse depression group (PS2/PS1 = 0.12 +/- 0.03; n = 15) and the weak paired-pulse depression group (PS2/PS1 = 0.68 +/- 0.06; n = 13). Paired-pulse ratios from the strong PPD group were relatively independent of stimulus intensity, whereas, PPD was dependent on stimulus intensity in the weak PPD group; i.e., PPD was greatest at the lowest intensity and reached a plateau at higher intensities. Bicuculline (20 microM) and low concentrations of baclofen (0.1-0.2 microM) reduced paired-pulse depression in the strong PPD group, but did not significantly change the paired-pulse ratio in the weak PPD group. Paired-pulse facilitation was observed in some cases after inhibition was blocked pharmacologically. The number of population spikes was increased in the presence of bicuculline but was unchanged by baclofen. In the strong PPD group, baclofen significantly altered the EPSP-population spike (E-S) relationship by increasing the slope of the relationship for the second response, without having an effect on the slope of the first response. Baclofen had no effect on the E-S relationship of either response in the weak PPD group. The data are consistent with (1) less inhibition in the weak PPD group compared to the strong PPD group, (2) reduction of feedback inhibition in the strong PPD group by bicuculline and by low concentrations of baclofen, and (3) the occurrence of paired-pulse facilitation when inhibition was pharmacologically reduced in the dentate gyrus of temporal lobe epileptic patients. The results are also consistent with the presence of GABAB receptors on human inhibitory interneurons that, when activated by baclofen, result in disinhibition of granule cells through feedback circuits. Although inhibition may be compromised in some epileptic human biopsy specimens, the presence of strong inhibition in other patients' biopsy material suggest the re-evaluation of the role of inhibition in epilepsy.

Adult↗
PubMed1995

Responses of pontine neurons of the big brown bat, Eptesicus fuscus, to temporally patterned sound pulses.

Under free field stimulation conditions, this study examined the responses of pontine neurons of Eptesicus fucus to temporally patterned sound pulses by means of repetitive single pulses and pulse trains. Among 93 pontine neurons isolated, 90 always discharged less than 5 impulses to sound pulses presented during this study and 3 discharged impulses throughout the whole duration of each presented pulse. Responses to sound pulses at different repetition rates were examined in 65 neurons. The number of impulses of individual neurons discharged to each pulse varied within a given repetition rate and among different repetition rates. Although these pontine neurons showed different degrees of habituation to high repetition rates, more than 25% could follow the highest repetition rate tested (100 pps). However, they did not always discharge maximal number of impulses to this repetition rate. The total number of impulses discharged by a neuron was also affected by pulse duration. Thus, each pontine neuron discharged maximally to a specific combination of pulse repetition rate and duration. Using a 50% difference between the maximal and minimal responses as a criterion, the function with respect to repetition rate and duration can be described as band-pass, high-pass, all-pass and irregular. These response properties reflect more those of inferior collicular neurons than auditory cortical neurons. This study also showed that response latencies of pontine neurons examined were lengthened by increasing pulse repetition rate and duration. In addition, whereas minimum thresholds of pontine neurons were elevated by increasing repetition rate, they were lowered by increasing pulse duration.

Acoustic Stimulation↗
PubMed2004

Peak exercise oxygen pulse and prognosis in chronic heart failure.

Cardiopulmonary variables, particularly peak oxygen consumption (peak VO(2)) corrected for total and lean body weight, have been confirmed to predict prognosis in patients with chronic systolic heart failure (HF). Only limited data are available on the prognostic ability of maximal oxygen (O(2)) pulse, an indicator of stroke volume and arteriovenous O(2) difference, especially when corrected for lean body mass. Cardiopulmonary exercise tests were performed in 209 consecutive patients with mild-to-moderate HF (mean ejection fraction 23%), followed for 19 +/- 12 months to determine the impact of maximal O(2) pulse in relation to other cardiopulmonary variables on major clinical events (13 cardiovascular deaths and 15 urgent transplantations). Compared with patients with clinical events, those without major events had a higher peak O(2) pulse (11.4 +/- 4.1 vs 9.2 +/- 2.3 ml/beat, p <0.0001) and body fat-adjusted peak O(2) pulse (15.6 +/- 5.6 vs 11.9 +/- 3.4 ml/beat, p <0.0001). In multivariate analysis, a low peak O(2) pulse was the strongest independent predictor of clinical events (chi-square 10.5, p <0.01). Although peak O(2) pulse was a stronger predictor for clinical events than any other exercise cardiopulmonary variable, including peak VO(2), peak VO(2) lean (defined as the VO(2) corrected for lean body mass), and percentage of predicted peak VO(2), this relation was further strengthened by correcting peak O(2) pulse for percent body fat (chi-square 12.4, p <0.001). In most subgroups (including women, obese subjects, those receiving beta blockers, and those with class III HF), peak O(2) pulse lean was similar to or superior to peak VO(2) lean for predicting major clinical events. Especially in patients who were class III HF and who were receiving beta blockers, peak VO(2) (cutoff 14 ml/kg/min) poorly predicted prognosis; risk stratification was best with peak O(2) pulse lean (cutoff 14 ml/beat). These data indicate the potential usefulness of peak O(2) pulse and lean body mass-adjusted O(2) pulse for predicting prognosis in patients with systolic HF.

Adult↗
PubMed1999

Validity of the PULSES profile compared with the Functional Independence Measure for measuring disability in a stroke rehabilitation setting.

OBJECTIVES: To test the validity of the PULSES profile for measuring the disability of stroke rehabilitation patients and to compare it with the Functional Independence Measure (FIM); and to determine the ability of the PULSES score to predict discharge home from a stroke rehabilitation setting. STUDY DESIGN: Retrospective cohort. SETTING: A tertiary stroke rehabilitation unit. PATIENTS: One hundred ninety-seven patients admitted consecutively to a stroke rehabilitation unit from September 1992 to April 1995. METHODS: The PULSES profile was tested for internal consistency. Criterion validity was evaluated by comparing with the FIM. Construct validity was tested using the multimethod-multitrait matrix method and by performing logistic regression to determine if admission PULSES score was predictive of discharge home. RESULTS: Internal consistency of the PULSES profile was supported with a Cronbach's alpha of .74. There was a high correlation between the PULSES and FIM admission and discharge scores of -.82 and -.88, respectively. The multimethod-multitrait matrix correlations demonstrated good convergent and divergent validity for the correlation of the PULSES profile items and the FIM subcategories. Multivariate logistic regression determined the admission PULSES total score to be an independent variable in the model to predict discharge home. CONCLUSIONS: The PULSES profile is a valid measure for assessing disability in the stroke rehabilitation setting. The PULSES profile correlates highly with the FIM. The admission PULSES total score is predictive of discharge home from a stroke rehabilitation program.

Activities of Daily Living↗
PubMed2000

Effects of pre-acclimation to aluminium on the physiology and swimming behaviour of juvenile rainbow trout (Oncorhynchus mykiss) during a pulsed exposure.

Anthropogenic acidification of the freshwater environment causes aluminium to be mobilised into the aquatic environment. When pH falls below 5.5, exposure to aluminium concentrations as low as 12.5 microg.l(-1) can cause serious physiological disturbances in freshwater fish. However, under constant laboratory exposures fish can acclimate and recover physiological status within 5-30 days. In reality, fish in the wild are likely to experience chronic sub-lethal exposure, with occasional elevations (pulses) to much higher levels. The experiment described here investigated the effects of an environmentally realistic, 4-day pulse exposure to a high level of aluminium (36 microg.l(-1)) in two groups of juvenile rainbow trout. One group was exposed to a lower level of aluminium (24 microg.l(-1)) for 16 days before and 10 days after the pulse ('aluminium-acclimated' fish). A second group was exposed to pH 5.2 alone for 16 days before and 10 days after the pulse ('aluminium-naïve' fish). A third group exposed to pH 5.2 alone for 30 days (no aluminium added) acted as controls. Triplicate groups of 24 juvenile rainbow trout (2.3-16.7 g) were randomly allocated to one of these three treatments. Swimming behaviour was monitored throughout and samples were taken on days 14, 20, 22, 26 and 30 for assessment of physiological status. No treatment effects were recorded in the control group (pH 5.2 alone). Fish in the 'aluminium-acclimated' treatment became hypo-active upon initiation of the exposure to 24 microg.l(-1) aluminium, but recovered after just 4 days of this exposure. Subsequent challenge on day 16 with the 36 microg.l(-1) aluminium 'pulse' caused these fish to became hypo-active again, but they recovered normal swimming behaviour whilst still subject to the 4-day pulse. The 'aluminium-naïve' fish also became hypo-active during the pulse exposure (36 microg.l(-1) aluminium). However, they did not exhibit any recovery of swimming behaviour, either during the pulse, or even 6 days after the cessation of the pulse, despite a rapid depuration of gill aluminium load (within 2 days of the pulse finishing). Mortality was low in the aluminium-acclimated fish (4%) and significantly higher in the aluminium-naïve fish (26%). Haematological disturbances were most extreme in the aluminium-naïve fish and had not recovered to control levels 6 days after the end of the pulse. This study provides new evidence, using behavioural responses, that previous exposure to low levels of aluminium may be an important factor abating the impact of aluminium on fish in the natural environment.

Adaptation, Physiological↗
PubMed2003

The pulse length-dependence of inertial cavitation dose and hemolysis.

Gas-based ultrasound (US) contrast agents increase erythrocyte sonolysis, presumably via enhancing inertial cavitation (IC) activity. The amount of IC activity (IC "dose") and hemolysis generated by exposure to 1.15 MHz US were examined with different US pulse lengths, but with the same delivered acoustic energy, for Optison and Albunex. The hypotheses were that 1. at longer pulse lengths, IC would generate more bubbles that could nucleate additional IC activity; 2. if the interval between pulse pairs were short enough for the next pulse to hit derivative bubbles before their dissolution, more IC could be induced; and 3. hemolysis would be proportional to IC activity. Two types of studies were performed. In the first, bubble generation after each burst of IC activity was quantified using an active cavitation detector (ACD), for different pulse lengths (5, 10, 20, 30, 50, 100 or 200 cycles), but the same pressure level (3 MPa) and total "on" time (173.16 ms). Low concentrations of either Optison or Albunex were added into the tank with high-intensity and interrogating transducers orthogonal to each other. For pulse lengths > 100 cycles, and pulse repetition intervals < 5 ms, a "cascade" effect (explosive bubble generation) was observed. In the second, IC was measured by passive detection methods. IC dose and hemolysis were determined in whole blood samples at a pressure level (3 MPa) and interpulse interval (5 ms) that induced the "cascade" effect. Each blood sample was mixed with the same number of contrast microbubbles (Optison approximately 0.3 v/v % and Albunex approximately 0.5 v/v %), but exposed to different pulse lengths (5, 10, 20, 30, 50, 100 or 200 cycles). With Optison, up to 60% hemolysis was produced with long pulses (100 and 200 cycles), compared with < 10% with short pulses (5 and 10 cycles). Albunex generated considerably less IC activity and hemolysis. The r(2) value was 0.99 for the correlation between hemolysis and IC dose. High pulse-repetition frequency (PRF) (500 Hz) generated more hemolysis than the low PRF (200 Hz) at 3 MPa. All experimental results could be explained by the dissolution times of IC-generated bubbles.

Albumins↗
PubMed1997

Pulsed brachytherapy as a substitute for continuous low dose rate: an in vitro study with human carcinoma cells.

PURPOSE: Pulsed dose rate (PDR) brachytherapy as a substitute for continuous low dose rate (CLDR) has the potential to be a useful option in brachytherapy. However, the frequency and duration of pulses that will produce results practically equivalent to CLDR is still an open and important question. This study was designed to compare the survival of human tumor cells, cultured in vitro, and exposed to continuous or pulsed irradiation where the pulse frequency was varied. METHODS AND MATERIALS: Three different human carcinoma cells, derived from cervical and breast cancers, were exposed to CLDR gamma rays, or to pulsed irradiations with the same overall dose rate. Pulsed regimens used were 3.8 min every hour, 7.6 min every 2 h, 11.4 min every 3 h, 15.2 min every 4 h, 22.8 min every 6 h, and 45.6 min every 12 h. For each comparison between CLDR and PDR, the overall dose and the overall time were the same. Experimental design was such that significant differences in biological effectiveness, if present, would be detected. RESULTS: For the cell lines investigated, hourly pulses resulted in cell survival indistinguishable from CLDR. However, as the pulse interval was increased, cell survival progressively decreased compared with CLDR, and the pulsed regimes were no longer equivalent to continuous low dose rate. CONCLUSIONS: This study provides some evidence to support the suggestion that a 10-min pulse, repeated every 1 to 2 h, would be functionally equivalent to a continuous low dose rate irradiation, at least in terms of early responding endpoints. Longer intervals between pulses might result in loss of equivalence in some cases.

Brachytherapy↗