[Anesthesia in endocrine dysfunction].
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Anesthesia↗
Biomedical subjects
M Sprenger
Publications and source records attributed to M Sprenger.
[Respiratory pattern and respiratory strain in automatic tube compensation and inspiratory pressure support].
STUDY OBJECTIVE: To investigate whether automatic tube compensation (ATC) or conventional pressure support (PS) is suitable to compensate for the work of breathing imposed by the breathing circuit without altering the breathing pattern. METHODS: Breathing pattern and work of breathing were measured in healthy volunteers. After a 20 min period of quiet breathing through a mouth piece (control) the volunteers were breathing through a 8.0 mm ID endotracheal tube (ETT) with four different settings: CPAP at 0 mbar, ATC, PS 5 mbar, PS 10 mbar. Each mode was applied for a 20 min period. At the end of each period data from 10 consecutive breaths were analyzed and averaged. Tidal volume (VT), breathing frequency (f), and minute ventilation (Ve) were determined from the stored gas flow tracings. Work of breathing was assessed as the pressure time product (PTP) calculated from the transdiaphragmatic pressure (Pdi) using a combined esophageal and gastric balloon catheter. RESULTS: During the control period the breathing pattern was as follows: VT = 882 +/- 277 ml, f = 13.7 +/- 5/min, Ve = 11.5 +/- 4.2 L/min. Maximal Pdi was 9.2 +/- 5.4 mbar and PTP was 11.3 +/- 7.1 mbar x s. Breathing CPAP through the ETT resulted in a slight increase in Pdi (10.8 +/- 5.4 mbar) and PTP (14.8 +/- 10.4 mbar x s) with an unchanged breathing pattern. However, for the same amount of unloading from respiratory workload ATC did not alter the breathing pattern, whereas PS 5 mbar and PS 10 mbar resulted in a clear increase in VT (1014 +/- 202 ml, 1336 +/- 305 ml, respectively). CONCLUSION: From the presented data in healthy volunteers it might be concluded that ATC and PS 5 mbar and 10 mbar are suitable modes for unloading the respiratory system from work imposed by the breathing circuit. ATC does not alter the breathing pattern in contrast to PS which results in an increased tidal volume. Therefore, the exact compensation of the work imposed by the ETT during ATC seems to be advantageous over ATC to assess the actual breathing pattern.
Adult↗
Antimicrobial resistance. Is a major threat to public health.
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Animal Husbandry↗
In vivo measurement of changes in venous blood-oxygenation with high resolution functional MRI at 0.95 tesla by measuring changes in susceptibility and velocity.
High-resolution functional imaging experiments at 0.95 Tesla have been performed to determine the changes in oxygen saturation in pial veins during motor activation by measuring both flow and susceptibility changes in the blood. Averaging across subjects, mean values for the change of the oxygenation level, deltaY = 0.16 +/- 0.08 (n = 7) and deltaY = 0.13 +/- 0.09 (n = 4), were obtained from the susceptibility sensitive and the flow sensitive acquisitions, respectively. The results suggest that the increase in blood flow is largely uncoupled from the oxygen consumption. The quoted errors reflect mainly the intersubject variability. In addition, low-resolution echo planar imaging (EPI) measurements were performed on the same volunteers to quantify signal intensity changes. Using the measured change in oxygenation, the observed signal changes in the EPI experiments can be attributed to a 5% venous blood volume.
Adolescent↗
Within-subject reproducibility of visual activation patterns with functional magnetic resonance imaging using multislice echo planar imaging.
Within-subject reproducibility of visual brain activation using multislice echo planar functional magnetic resonance imaging (fMRI) was tested. Ten healthy subjects underwent fMRI with visual stimulation on three occasions: two studies in one scanning session (without repositioning); and a third study 1 h to 2 weeks later. Following a three-dimensional matching procedure, activation was measured and compared between sessions on a voxel-by-voxel basis. Data were filtered to full-width-at-half-maximum of 4.0 x 4.0 x 5.0 mm and a conservative Bonferroni-corrected significance threshold was applied to correlation maps. For reproducibility, change in centre of mass of the activated volume, a ratio of the number of pixels and a ratio of the number of overlapping pixels was calculated. Further, reproducibility was tested varying significance thresholds and at different filter widths. Average changes in centre of mass of the activated volume were 2.63 and 3.96 mm between Studies 1 and 2 and 1 and 3, respectively. The reproducibility of the number of activated voxels was 90% and 88% (Studies 1 and 2 and 1 and 3). The ratio of overlapping pixels was 74% between Studies 1 and 2 and 64% between Studies 1 and 3. Varying the significance threshold showed that at a certain range, the overlap reached a maximum, and increasing the filter widths increased reproducibility. It is concluded that fMRI with visual stimulation can be used to measure brain activity with reasonably good reproducibility on a routine clinical system equipped with echo planar imaging. Difficulties remain in separating the contribution of motion, repositioning errors, and true physiological changes.
Adolescent↗
Visual activation patterns in patients with optic neuritis: an fMRI pilot study.
We studied the use of functional MRI (fMRI) with visual stimulation in nine patients with unilateral optic neuritis. Eight healthy subjects served as controls. Patients showed reduced activation upon stimulation of the affected eye, on average 33% (range 0 to 156%) of the average monocular activation in the control group. Decreased activation was also seen for the unaffected eye (61% of control values, range 3 to 133%). We conclude that fMRI with visual stimulation is feasible in patients with optic neuritis and deserves future study.
Adult↗
PcMYB1, a novel plant protein containing a DNA-binding domain with one MYB repeat, interacts in vivo with a light-regulatory promoter unit.
Light regulatory unit 1 (LRU1) is necessary for and sufficient to mediate light-dependent activation of the chalcone synthase (CHS) minimal promoter in Petroselinum crispum. This composite promoter unit consists of at least two distinct cis-acting elements, designated ACECHS and MRECHS, both of which are required for light induction. The ACGT-containing element ACECHS interacts with common plant regulatory factors (CPRFs) which belong to the basic region/leucine zipper (bZIP) class of transcription factors. Here, we demonstrate that MRECHS, originally identified as an in vivo DNA footprint, is a MYB recognition element. This element possesses a functional core that is essential for light responsiveness and is specifically recognized by two distantly related MYB-like proteins: MYB305 and the novel factor MYB1 from P. crispum. PcMYB1 was identified by both its specific binding to MRECHS in vitro and recognition of MRECHS in vivo. The deduced amino acid sequence revealed that PcMYB1 contains only one MYB-like repeat. This portion of the protein constitutes the DNA-binding domain. Mutational analysis of PcMYB1 in combination with sequence comparison suggests the presence of a helix-turn-helix structure containing a recognition helix that is sufficient for sequence-specific binding. The structure of this distinct MYB-like DNA-binding domain appears to be conserved in proteins from all three eukaryotic phyla.
Acyltransferases↗
Test-retest analysis with functional MR of the activated area in the human visual cortex.
PURPOSE: To investigate the intersubject and intrasubject variability of the activated area in the visual cortex with functional MR imaging. METHODS: Double-section gradient-echo MR images were acquired at 1.5 T in 28 healthy volunteers using the fast low-angle shot (FLASH) technique. Visual stimulation was obtained with light-emitting diode (LED) goggles. Eighteen volunteers were studied twice. The size of the activated areas in the visual cortex and the increase in signal were measured. A reproducibility ratio for size (R[size]) and for location (R[overlap]) was calculated on a scale of 0.0 to 1.0. RESULTS: Activation was seen in 89% of the subjects. The size of the activated area was widely variable among subjects: mean, 460 +/- 284 mm2; range, 0 to 1029 mm2 in the first study in all volunteers. Signal increases ranged from 3.2% to 10.9%, with a mean of 6.6 +/- 1.7%. The mean values of intrasubject variability testing were R(size) = 0.83 +/- 0.16 and R(overlap) = 0.31 +/- 0.11. CONCLUSION: Functional MR imaging with the FLASH technique is useful in identifying certain cortical areas that have quite variable locations among subjects. This study provides reference data for the intrasubject and intersubject variability of the activation pattern of the visual cortex.
Adult↗
The functional basis of ocular dominance: functional MRI (fMRI) findings.
Changes in cortical metabolism and cerebral perfusion may be recorded non-invasively with functional magnetic resonance imaging (fMRI). In pilot experiments, using fMRI with photic stimulation, we found differences between activated areas when the left or the right eye was stimulated separately. In this study we investigated whether this could be explained by ocular dominance. We studied 26 healthy volunteers (mean age 23.3 +/- 3.5 years). Ocular dominance was determined by means of the near-far alignment test. fMRI-measurements consisted of a double-slice gradient echo sequence. Slices were acquired placed parallel on either side of the calcarine fissure. Visual stimulation was done with goggles with two LED matrices (red light, 8 Hz); each in front of one eye. In each subject, the left and right eye were stimulated separately and together, in a randomly alternating order. Twenty-two subjects showed activation, of whom eight subjects had a dominant left eye and 14 a dominant right eye. In general the size of the activated area was bigger upon stimulation of the dominant eye. The difference with the area upon stimulation of the non-dominant eye was statistically significant in the right eye dominant group. These results indicate that the dominant eye actually activates a larger area of the primary visual cortex than the non-dominant eye. This provides for the first time a functional basis for the concept of ocular dominance.
Adult↗
Nitroglycerin versus epoprostenol: effects on hemodynamics, oxygen delivery, and hepatic venous oxygenation after liver transplantation.
Our objective was to determine the effects of vasodilatory treatment with epoprostenol (PGI2) and nitroglycerin (NTG) on systemic oxygen delivery index (DO2) and hepatic venous oxygen saturation (SvhO2) after liver transplantation. This prospective study used repeated-measures design. Fifteen adult patients undergoing orthotopic liver transplantation (OLT) were enrolled. Postoperatively, a fiberoptic pulmonary artery catheter was inserted into the right hepatic vein and a timed infusion of PGI2 and NTG was sequentially performed in random order at the following rates: PGI2 at 5 ng/kg/minute and NTG at 0.1 microgram/kg/minute. Each step in each sequence lasted 45 minutes, followed by a control interval of 45 minutes. Measurements were taken at the end of each period when hemodynamic function was stable. Systemic hemodynamics, DO2, oxygen uptake index (VO2), mixed venous oxygen saturation (SvO2), and SvhO2 were assessed. We found that PGI2 induced an increase of cardiac index (+18%, p < .05); DO2 (+16%, p < .05); and SvhO2 (+11%, p < .05). Mean arterial pressure was decreased during PGI2 infusion (-9%, p < .05), as well as during infusion of NTG (-10%, p < .05). NTG significantly decreased DO2 (-6%, p < .05) and SvhO2 (-4%, p < .05). Neither drug affected VO2. We conclude that PGI2 induced vasodilation and increased systemic oxygen delivery in parallel with SvhO2, suggesting a corresponding increase of hepatic oxygen supply. NTG induced systemic vasodilation and significantly impaired hepatic venous oxygen saturation and DO2. Thus, if vasodilatory therapy is indicated in the patient after liver transplantation, PGI2 appears to be better than NTG in improving DO2 without impairing splanchnic oxygenation.
Adult↗
Transesophageal cardiac pacing during magnetic resonance imaging: feasibility and safety considerations.
The feasibility and safety of transesophageal cardiac pacing during clinical MRI at 1.5 Tesla is considered. An MRI compatible pace catheter was developed. In vitro testing showed a normal performance of the pulse generator, image artifacts that extended less than 11 mm from the catheter, and a less than 5% increase in noise. Cardiac stimulation induced by MRI was not observed and, theoretically, is not expected. Potentially, tissue around the catheter tip may become heated. This heating (delta tau) was monitored. Eight dogs were exposed to MRI during pacing. For low RF radiation exposure, a time-averaged squared B1 field below 0.08 p tau 2 (SAR < 0.03 W/kg), delta tau was below 1 degree C. For high RF radiation exposure, but at normal RF radiation specific absorption rate (0.4 W/kg) delta tau was 5 degrees C. Thus, transesophageal atrial pacing during MRI at low RF exposure seems to be possible to perform cardiac stress studies or to correct unstable heart rates.
Animals↗
Assessment of flow in the right human coronary artery by magnetic resonance phase contrast velocity measurement: effects of cardiac and respiratory motion.
Flow in the human right coronary artery was determined using magnetic resonance phase contrast velocity quantification. Two methods were applied to reduce respiratory motion: Imaging during breath holding, which is fast, and retrospective respiratory gating, which has a high temporal resolution (32 ms) in the cardiac cycle. Vessel cross-sectional area, through-plane velocity, and volume flow were determined in six healthy subjects. In-plane vessel displacement during the cardiac cycle, caused by cardiac contraction, was about 2-4 mm within a time frame of 32 ms in systole and early diastole. The motion resulted in blurring of images obtained during breath holding caused by the large acquisition time window (126 ms) within the cardiac cycle. Therefore, only with a high temporal resolution correct velocity images over the entire cardiac cycle could be obtained. The time- and cross-sectionally averaged velocity was 7 +/- 2 cm/s, and the volume flow was 30 +/- 10 ml/min.
Adult↗
Motion induced phase shifts in MR: acceleration effects in quantitative flow measurements--a reconsideration.
Magnetic resonance phase difference techniques are commonly used to study flow velocities in the human body. Acceleration is often present, either in the form of pulsatile flow, or in the form of convective acceleration. Questions have arisen about the exact time point at which the velocity is encoded, and also about the sensitivity to (convective) acceleration and higher order motion derivatives. It has become common practice to interpret the net phase shifts measured with a phase difference velocity technique as being the velocity at a certain (Taylor) expansion time point, chosen somewhere between the RF excitation and the echo readout. However, phase shifts are developed over the duration of the encoding magnetic field gradient wave form, and should therefore be interpreted as a more or less time-averaged velocity. It will be shown that the phase shift as measured with a phase difference velocity technique represents the velocity at the "gravity" center of the encoding bipolar gradient (difference) function, without acceleration contribution. Any attempt to interpret the measured phase shift in terms of velocity on any other time point than the gradient gravity point will automatically introduce acceleration sensitivity.
Acceleration↗
In vivo validation of magnetic resonance blood volume flow measurements with limited spatial resolution in small vessels.
The accuracy of magnetic resonance phase contrast volume flow measurements in small blood vessels is expected to be smaller than in large vessels, because of partial volume effects at the vessel boundary. Accuracy was validated in the dog femoral artery, diameter 3.5 +/- 0.7 mm, using an ultrasonic transit-time flowmeter (TT). The number of pixels per vessel diameter (ND) ranged from 1.6 to 4.8. The vessel cross-section was determined using a threshold in the magnitude image. Between the two methods the correlation coefficient was 0.95 (range 10-200 ml/min). The proportional difference (PD), (QTT-QMR)/1/2(QTT+QMR), was 0.8%, showing no systematic difference between the methods. The PDs standard deviation was 27%, and 19% for flow rates above 30 ml/min. Only a significant decrease of the PDs variance was found at the highest ND values, suggesting other sources of error than partial volume effects. It is concluded that with an ND value of about 3, accurate blood volume flow rates can be determined.
Animals↗
Functional analysis of a light-responsive plant bZIP transcriptional regulator.
Common plant regulatory factor 1 (CPRF1) is a parsley basic region/leucine zipper (bZIP) transcription factor that recognizes specific nucleotide sequences containing ACGT cores. Such a sequence is contained within LRU1, the composite light regulatory unit that is necessary and sufficient for light-dependent activity of the parsley chalcone synthase (CHS) promoter. After light treatment of both etiolated and green seedlings, CPRF1 mRNA levels increased prior to CHS mRNA accumulation. The change in CPRF1 mRNA leads to a light-responsive increase in CPRF1 protein. Transient expression analysis in parsley protoplasts using the CPRF1 promoter fused to the beta-glucuronidase (GUS) open reading frame indicated that light-dependent CPRF1 mRNA accumulation was under transcriptional control. The 5' untranslated region of the CPRF1 gene includes a cis-acting nucleotide sequence that contains two ACGT elements at a distance of 12 bp between their palindromic centers. This feature is reminiscent of as-1 and octopine synthase (ocs) elements identified in promoters from plant pathogens. This double ACGT Element element, designated dACECPRF1, stimulated transcription when placed 5' to a heterologous core promoter. CPRF1 bound to dACECPRF1 DNA as well as to the ACGT element from the CHS promoter in vitro. Cotransfection experiments demonstrated that CPRF1 interacts with these elements in vivo and that overexpression of CPRF1 actually reduced light-dependent transcription from the CHS promoter. CPRF1 thus appears to contribute to the regulation of the CPRF1 gene and to interfere with the activities of light-regulated promoters.
Acyltransferases↗
Phase-contrast cine MR imaging of normal aqueductal CSF flow. Effect of aging and relation to CSF void on modulus MR.
Cine phase-contrast MR imaging was used to study pulsatile CSF flow in the aqueduct in 11 young controls (mean age 30 years) and 9 old controls (mean age 69 years). A high-resolution gradient echo technique and an oblique imaging plane, perpendicular to the aqueduct, was used to avoid volume averaging. Phantom studies confirmed that the technique was accurate. Aqueductal velocity and flux in old controls was higher than in young controls, but the differences were not significant. For all controls together, the averaged peak velocity was 4.2 +/- 1.5 cm/s in rostral and -7.8 +/- 4.9 cm/s in caudal direction; for the flux it was 0.16 +/- 0.10 cm3/s in rostral and -0.29 +/- 0.19 cm3/s in caudal direction. Phase-contrast measurements were significantly related to flow-void on modulus MR images, but not with ventricular size or cortical atrophy. The present technique avoids underestimation of aqueductal flow, and therefore reveals higher aqueductal velocity and flux values than previous studies. Factors other than age or atrophy seem to determine aqueductal CSF flow.
Adult↗
Nontriggered magnetic resonance velocity measurement of the time-average of pulsatile velocity.
The feasibility of the determination of the time-average of pulsatile velocity obtained via a nontriggered magnetic resonance (MR) acquisition is studied. The advantage of this method, in comparison with a triggered acquisition, is a considerable reduction (approximately 15x) in acquisition time. However, pulsatility causes image artifacts, known as ghosts, and the Fourier transform technique required for the imaging procedure accomplishes time-averaging of the complex MR signal. Both effects can result in errors in the velocity determined. Calculations show that these errors depend on the velocity time function and the acquisition parameters. In vivo comparison of triggered and nontriggered MR velocity measurements in the femoral artery of volunteers (n = 7) shows larger statistical and systematic errors in the latter, which depend on the excitation angle. Therefore, this nontriggered average velocity measurement is only useful as a fast and rough estimation of the time-averaged velocity.
Blood Flow Velocity↗
Influence of health care systems on the market for picture archiving and communication systems.
An analysis is given of the relation between health care systems and the PACS market. Two driving forces exist in the market: quality and price. It is argued that the quality driven market is mainly independent of the health care system and will be the force that drives the introduction of the health care system and will be the force that drives the introduction of PACS in the forthcoming years. Finally a change of focus is suggested from only archiving and communication to a more general concept of image networking, serving more goals than only the goal of working filmlessly.
Delivery of Health Care↗