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Biomedical subjects

P R Harvey

Publications and source records attributed to P R Harvey.

At least 19 recordsLinked to original sources
PubMed1996

Echo-volumar imaging (EVI) at 0.5 T: first whole-body volunteer studies.

Improvements in the echo-volumar imaging (EVI) technique and its application in whole-body studies are described. Using an in-house built 0.5 T echo-planar imaging system, complete modulus three-dimensional image data are acquired in 102 ms with real-time display. Hardware limitations have restricted the maximum array size achievable to 64 x 32 x 8 voxels. Representative voxel dimensions are x = 6.0 mm; y = 4.0 mm, and z = 10.0 mm. Results on human volunteers are presented, showing cardiac, liver, and bladder images. Also shown are the first EVI gastric filling and emptying results.

Echo-Planar Imaging↗
PubMed1996

Accumulation of unconjugated bilirubin in cholesterol pellets implanted in swine gallbladders.

BACKGROUND & AIMS: Most cholesterol gallstones have a pigmented center, but it is unclear whether its presence is primary or secondary. This study was performed to determine if bilirubin would accumulate in a gallstone model consisting of cholesterol pellets. METHODS: Cholesterol was compressed into pellets at 2500 psi, producing a pellet that behaved like human cholesterol gallstones in regard to penetration of solutes into the stone. Pellets were implanted into gallbladders of pigs and harvested after 4 weeks. Bilirubin species were measured by high-performance liquid chromatography. RESULTS: The proportions of bilirubin species in bile were not changed by the presence of pellets, i.e., diconjugates (mean +/- SD, 1.9% +/- 1.0% vs. 0.7% +/- 0.8%), monoconjugates (83.8% +/- 5.5% vs. 87.8% +/- 6.6%), and unconjugated bilirubin (14.2% +/- 5.3% vs. 11.5% +/- 5.6%) were similar at the time of implantation and removal. The cut surfaces of the pellets were pigmented. Pellets contained 5.46 +/- 1.38 micrograms bilirubin/g sample at harvesting, and 98.6% +/- 2.3% of bilirubin in pellets was unconjugated. In in vitro studies, there was a large increase in unconjugated bilirubin in the bile. Pellets also became pigmented in vitro, but there was considerable variability in the bilirubin species present in the pellets. CONCLUSIONS: Unconjugated bilirubin accumulates in cholesterol pellets and pigments them. This provides a mechanism by which cholesterol gallstones could become secondarily pigmented.

Analysis of Variance↗
PubMed1995

Active acoustic screening: reduction of noise in gradient coils by Lorentz force balancing.

We have designed and constructed a quiet gradient set with restricted access for the combined purposes of evaluating the principles of active acoustic screening, recently introduced by Mansfield, Glover, and Bowtell, and for EPI studies of the head at 3.0 T. The design utilizes the return paths of the conductors in a closed arc loop arrangement to eliminate net Lorentz forces thereby attenuating acoustic noise especially at low frequency. This design should significantly reduce the dangers to patients of high noise levels, especially in high field magnetic resonance imaging systems.

Acoustics↗
PubMed1995

Evidence of preservation injury to bile ducts by bile salts in the pig and its prevention by infusions of hydrophilic bile salts.

Preservation injury to bile ducts is a serious problem in liver transplantation, especially when preservation exceeds 12 hours. The authors hypothesized that the injury was caused by contact of bile ducts with bile salts during cold preservation and might be preventable by infusion of more hydrophilic bile salts. Swine livers were harvested after intraportal infusions of saline (control), of the hydrophobic bile salt taurodeoxycholate, or of the hydrophilic bile salts tauroursodeoxycholate or dehydrocholate. The effect of infusing a combination of hydrophilic and hydrophobic bile acids was also studied. Bile samples were taken before and during the infusions. Then livers were perfused with UW solution, ducts were flushed retrograde with UW, and livers were stored at 0 to 1 degree C for 20 hours. Bile ducts were harvested after preservation, and coded microscopic slides of the specimens were examined by light microscopy. There was large variability in baseline bile salt concentration. Injury after preservation consisted of sloughing and pyknosis of surface and glandular epithelium. The histologic injury score determined after preservation was directly related to bile salt concentration in bile ducts at the time of flushing. During bile salt infusions, the infused bile salt replaced most or all of the other bile salts present in bile. Severe postpreservation injury of intrahepatic ducts occurred after taurodeoxycholate infusions, but injury was minimal when either of the two hydrophilic bile salts was infused. The mixture of bile acids produced intermediate results. Retrograde flushing with UW does not prevent injury to intrahepatic ducts. The authors conclude that the injury is caused by contact with bile salts, is dependent on bile salt concentration and composition, and is preventable.

Adenosine↗
PubMed1995

Effect of deoxycholate on immunoglobulin G concentration in bile: studies in humans and pigs.

Because an increase in biliary deoxycholate levels seems to be a risk factor for cholesterol gallstone formation, we determined the relationship between deoxycholate levels and levels of the pronucleating protein, immunoglobulin G (Ig) in human gallbladder bile. Patients with cholesterol gallstones had a higher concentration of biliary IgG compared with a pigmented stone group and control patients. This was associated with the simultaneous presence of two conditions in the cholesterol stone group, supersaturated bile and a high deoxycholate/cholate ratio. The other patient groups met only one of the two conditions. Next, animal studies were performed to determine if model biles mimicking the two conditions could affect IgG secretion by the gallbladder. Gallbladders were exposed in vivo and then in an Ussing chamber to model biles. The voltage clamp technique was used to monitor functional integrity of the preparation. Three different model biles were tested: (1) taurodeoxycholate (TDC), 80%; taurocholate (TC), 20%; and cholesterol saturation index (CSI), 1.2; (2) TDC, 20%; TC, 80%; and CSI, 1.2; and (3) TDC, 80%; TC, 20%; and CSI, 0.6. IgG concentrations became significantly higher in group 1 than in the other two groups. The concentration of mucous glycoprotein was also significantly greater in group 1 when compared with group 2. Plasma cells were increased in number in mucosal and submucosal layers in group 1. We conclude that cholesterol supersaturated model bile with high content of TDC induces gallbladder epithelial alterations, which increase the luminal concentration of IgG and mucous glycoprotein.

Animals↗
PubMed1995

A rapid, simple high capacity cholesterol crystal growth assay.

Cholesterol crystal "nucleation time", more recently referred to as cholesterol crystal observation time, is defined as the first appearance of cholesterol crystals from isotropic crystal-free biles on light microscopy. This test is used to assess the potency of nucleating agents. Crystal appearance has conventionally been determined by polarizing light microscopy and crystal growth by counting the number of crystals. In this study we adapted a spectrophotometric method to a microtiter plate reader to generate cholesterol crystal growth curves. Model biles were prepared with a cholesterol saturation of 1.2 to 1.3 and total lipid concentration of 10.7 g/dl (taurocholate, 125 mM; cholesterol, 16.8-18.4 mM; phospholipid, 43 mM). Pronucleating IgM samples were used to establish and validate the assay. Cholesterol crystal growth curves were generated by reading absorption at 630 nm daily on a Dynatech microplate reader. Results were correlated to cholesterol crystal counts as determined by polarizing light microscopy. Standard curves generated from absorbencies of known masses of cholesterol crystals were used to quantify the mass of cholesterol crystals formed over the observation period. The assay was applied to known pronucleating biliary immunoglobulins. Results obtained were similar to our previous report that biliary IgM is more potent than biliary IgG. We conclude that using microplates and a microtiter plate reader provides a rapid high capacity method for detecting cholesterol crystal growth to assess potential nucleating agents in nucleation assays.

Bile↗
PubMed1995

Cholesterol microcrystals associated with concanavalin A-binding glycoproteins contribute artifactually to nucleating activity assays.

Concanavalin A (Con A) affinity chromatography is the standard procedure to separate cholesterol nucleating biliary proteins from lipids and pigment. We observed that even after extensive washing following application of bile, lipid contaminants remain. We have determined the contribution of lipid contamination to cholesterol nucleation and assessed a modified procedure to remove lipids from the column. Human gallbladder bile was spiked with [3H]cholesterol and [14C]phospholipid and applied to two sets of Con A-Sepharose columns. One column was washed in the usual manner with Tris-HCl buffer and the other with buffer containing 10 mM taurocholate prior to eluting bound glycoproteins with alpha-D-methylmannopyranoside. Eluted proteins were added to heated abnormal bile at a final concentration of 250 micrograms/ml to study the effect on cholesterol nucleation. A separate aliquot (20 microliter) of the protein solutions was counted for radioactivity. Cholesterol nucleating activity was less in samples from columns washed with 10 mM taurocholate than in samples from columns not washed with the bile salt. Lipid radioactivity was associated with Con A-binding proteins prepared without taurocholate, but not in those prepared with taurocholate wash. Light microscopy revealed the presence of cholesterol microcrystals and vesicles in some Con A-binding protein preparations prepared without a taurocholate wash. However, pellets from ultracentrifuged Con A preparations prepared without a bile salt wash revealed cholesterol crystals in all samples (n = 6). Washing with taurocholate did not affect recovery of protein mass and appearance of bands on SDS-PAGE gel showed an identical pattern in the two groups. This modified procedure to prepare potential nucleating proteins from gallbladder bile should eliminate erroneous results that may arise due to lipid contamination.

Artifacts↗
PubMed1994

Fetal weight estimation by echo-planar magnetic resonance imaging.

Fetal weight was estimated in utero in eleven singleton pregnancies by measurement of fetal volume with echo-planar imaging (EPI), a form of magnetic resonance imaging, and by ultrasound measurements. EPI estimates of fetal volume were closely correlated with actual birthweight (R = 0.97). The median difference (expressed as a percentage of actual birthweight) between actual and EPI-estimated birthweights was 3.0% (range 0.6-9.9); this discrepancy was significantly smaller than that found for ultrasonographic estimates (6.5% [1.7-17.8]; p < 0.01).

Birth Weight↗
PubMed1994

Avoiding peripheral nerve stimulation: gradient waveform criteria for optimum resolution in echo-planar imaging.

Adaptation of Mansfield and Harvey's theory of magnetically induced neural stimulation indicates that, for trapezoidal gradient waveforms and at the relatively low modulation frequencies commonly used in echo-planar imaging, an increase in rise time even to the point of creating a triangular waveform can prove advantageous over the use of simple sinusoidal modulation. For example, a higher image resolution is in principle possible before the neural stimulation limit is reached. For higher modulation frequencies and fast ramp trapezoidal waveforms, the peak gradient can be lower than that for a sinusoidal waveform by a factor approaching 2/pi for equal resolution. This means that by using a multimode resonant gradient drive, the amplifier power requirements are greatly relaxed. The signal sampling bandwidth required is also lower, because, due to the trapezoidal nonlinear sample pattern, sample points are spaced linearly during the waveform plateaus.

Echo-Planar Imaging↗
PubMed1994

The effects of hepatic preservation at 0 degrees C compared to 5 degrees C: influence of antiproteases and periodic flushing.

The optimal preservation temperature for liver allografts is unknown. We evaluated the effect of small differences in preservation temperature, 5 degrees C vs 0 degrees C, on outcome of prolonged preservation. Livers of Wistar rats were preserved at these temperatures in UW solution for 40 h. Function was studied during reperfusion on the isolated perfused rat liver system at 37 degrees C. To compare the effects of a small reduction in temperature with known beneficial strategies, the effects of including antiproteases and periodic flushing of the graft with UW solution during cold preservation at 5 degrees C were also studied. Aspartate transaminase (AST) and alanine transaminase release after 4 h of reperfusion were much higher in the livers stored at 5 than at 0 degrees C (P < 0.0005). Addition of antiproteases to the preservation solution or periodic flushing reduced AST release but neither treatment at 5 degrees C was as good as simple storage at 0 degrees C. Cumulative bile production after 4 h of reperfusion was significantly greater in the 0 degrees C preserved group than in liver at 5 degrees C or 5 degrees C with periodic flushing. The addition of antiproteases resulted in slightly increased bile production (not significant). Platelets and WBCs in the perfusate decreased during reperfusion. This effect was more pronounced in the 5 degrees C preserved livers than in those stored at 0 degrees C. Antiproteases in the preservation solution appeared to inhibit platelet and WBC loss. Perfusate flow was significantly higher in the 0 degrees C group. We conclude that small differences in preservation temperature even at these low temperatures are important in postreperfusion liver function.

Adenosine↗
PubMed1994

Resonant trapezoidal gradient generation for use in echo-planar imaging.

Two passive filter circuit designs are compared which enable series resonant trapezoidal drive of the modulated read gradients used in both echo-planar and echo-volumar imaging. Using simple circuit simulation software, details of the expected power requirements and performance have been evaluated for peak operating currents of up to 1000 A. The circuits evaluated were of a 7th order design incorporating a 110 microH gradient coil operating at fundamental frequencies between 800 Hz and 2000 Hz. Results indicate that the simpler circuit design is not necessarily the most efficient. In addition, by suitable modification of the input waveform algorithm, it can be shown that the shape of the resonant gradient waveform may be varied entirely under software control from triangular to trapezoidal, the minimum ramptime being specified by the highest harmonic accommodated in the circuit. The energy storage, non-dissipative nature of the circuit design also means that the gradient ramptime is effectively independent of amplifier power capabilities, making a fast rise trapezoidal waveform as easy to implement as either triangular or sinusoidal waveforms. Using the approach outlined above, trapezoidal gradient modulation at peak current amplitudes in excess of 320 A and risetimes less than 60 microseconds have been easily produced in this laboratory for use in echo-planar imaging and for investigations into ways of optimising gradient performance before the onset of peripheral nerve stimulation.

Echo-Planar Imaging↗
PubMed1994

A three-year follow-up of children imaged in utero with echo-planar magnetic resonance.

A 3-year follow-up study was carried out on 20 children examined in utero with echo-planar magnetic resonance imaging when fetal compromise had been demonstrated or was suspected. There was no demonstrable increase in the occurrence of disease or disability (including hearing deficit) that could be related to echo-planar imaging techniques.

Child, Preschool↗
PubMed1993

Effect of human biliary immunoglobulins on the nucleation of cholesterol.

We have previously identified that either biliary immunoglobulin IgA or IgM is a pronucleating protein which can accelerate the precipitation of cholesterol from bile. In this study we purified the biliary immunoglobulins (IgA, IgG, and IgM) to homogeneity by affinity chromatography to investigate the relative cholesterol nucleating potency of each immunoglobulin. Each immunoglobulin was added to slow nucleating heated abnormal biles in a dose-response manner to give a final concentration of protein in the range of 62.5-625 micrograms/ml bile. Cholesterol-nucleating activity was measured by noting the first day of cholesterol crystal formation as well as the number of crystals formed over the observation period. Biliary IgM and IgG appear to be more potent pronucleators than IgA. Isolated serum IgM from patients with Waldenstrom's macroglobulinemia as well as serum IgG from patients with and without cholesterol gallstones were shown to have pronucleating activity and acted in a dose-response manner. Commercial IgG unlike commercial IgM retains nucleating activity. The concentration of biliary immunoglobulins was measured by an enzyme-linked immunoassay (ELISA) in the gallbladder bile of patients with and without cholesterol gallstones. Biliary IgG concentrations in bile were higher in cholesterol gallstones patients than in pigmented gallstone patients and controls. We conclude that immunoglobulins particularly IgG and IgM are important pronucleating proteins and could play a role in the pathogenesis of cholesterol gallstones.

Albumins↗
PubMed1993

Limits to neural stimulation in echo-planar imaging.

Simple electrical circuits are used to model neural stimulation. The stimulation current is evaluated for a variety of magnetically induced waveforms and for sinusoidal stimulation as a function of frequency. Experimental results obtained using a small scale magnetic stimulator show that the transient response rather than the steady-state behavior determines the stimulation characteristics thus suggesting a nonlinear model. We show that a nonlinear circuit changes a steady-state current solution into a repeated transient solution and thereby better explains our experimental results. Our model also shows that for very short times and high frequencies, contrary to the current widely held view, neural stimulation is independent of the magnetic field switching rate dB/dt, but depends on the final magnetic field value, Bm. At lower frequencies and rise-times, there may be a small advantage in using square wave over sine wave gradient modulation for whole body echo-planar imaging (EPI). It is found that the peak stimulation fields Bm, for both sinusoidal and trapezoidal waveforms are equal for equal risetimes. This means that for a given image array size and imaging time, trapezoidal modulation EPI ultimately can be made to operate below the neural triggering threshold while the equivalent sine modulation EPI version transcends the threshold.

Echo-Planar Imaging↗
PubMed1993

Evidence of the existence of a soluble mediator of cold preservation injury.

A study was designed to determine whether soluble mediators of injury are released during cold preservation. A first set of livers consisting of three groups was stored in cold Euro-Collins solution. These were a control group stored for 10 min (group 1), an experimental group stored for 16 hr (group 2), and an "antiprotease" group to which a cocktail of antiproteases had been added, which was also stored for 16 hr (group 3). The preservation solution in these livers was washed out at the end of preservation, and this effluent was concentrated and infused into a second set of livers that were all cold-stored for 4 hr. Then, the second-set livers were either perfused-fixed at 4 degrees C with universal fixative or reperfused at 37 degrees C for 180 min in the isolated perfused rat liver (IPRL). Morphometric assessment of sinusoidal lining cells (SLC) on light and electron microscopy showed an increased degree of microcirculatory injury in livers preserved with concentrates from livers of the experimental group. On light microscopy, only 2.2 +/- 0.4% (mean +/- SD) of the SLC had a normal flattened morphology compared with 11.9 +/- 2.0% in the control group, and 10.7 +/- 2.3% of the SLC appeared completely detached from the underlying hepatocytes compared with 2.6 +/- 0.8% in the control group, the differences being statistically significant (P < 0.05). This injury was prevented by the addition of antiproteases to EC solution. Similar results were obtained in the IPRL model, in which a number of typical changes related to cold preservation injury were noted in livers preserved with concentrates from the experimental group. Compared with controls, livers preserved with concentrates from the experimental group had early and significant alterations in markers of microcirculatory injury, including a reduction in portal flow and an increase in creatinine kinase-BB isoenzyme release, followed by an increase in perfusate transaminases, LDH, and a decrease in bile production. Again the injuries were largely prevented by the addition of antiproteases. There were no differences among groups in the degree of white cell and platelet adherence during reperfusion. Experiments using UW solution showed similar results, indicating that the soluble mediator(s) is not specific for a particular preservation solution. These observations are consistent with the hypothesis that soluble mediators are produced during the hypothermic period, and are responsible for a significant part of cold preservation injury, and that proteolytic reactions are involved in this type of injury.

Alanine Transaminase↗
PubMed1993

Prediction of the outcome of transplantation in man by platelet adherence in donor liver allografts. Evidence of the importance of prepreservation injury.

We examined platelet adhesion in thirty human donor livers to determine if the degree of platelet adhesion could predict outcome of transplantation. Wedge liver biopsies were taken at the start of the donor operation (biopsy 1) and 1 hr after reperfusion in the recipient (biopsy 2). Biopsies were stained with a monoclonal antibody against platelet glycoprotein Ib and graded for platelet adhesion. Hematoxylin and eosin-stained sections were examined for polymorphonuclear leukocyte adhesion and necrosis. Platelet adhesion was much more frequent and extensive than expected in biopsy 1. Nine of 30 biopsies showed moderate or high-grade platelet adhesion. Thus in this study endothelial cell damage was present in about one-third of donors before the donor operation. The injury was not detectable by routine microscopic or clinical examination or biochemical tests. The degree of platelet adhesion in biopsy 1 predicted development of PMN adhesion and necrosis in biopsy 2 and postoperative transaminase concentrations and prothrombin times in recipients. During preservation and implantation some livers converted from low to either moderate or high grades of platelet adhesion. The grade of platelet adhesion in biopsy 2 predicted postoperative outcome as measured by transaminase and PT levels. Patients whose platelet grade converted to a higher level during preservation and implantation did not do as well as patients who remained at a low adhesion grade. These findings strongly suggest that the degree of platelet adhesion is an important determinant in assessing outcome and may provide a means of measuring the status of liver allografts prior to transplantation.

Age Factors↗
PubMed1993

Role of platelets in hepatic allograft preservation injury in the rat.

Cold preservation of liver allografts injuries hepatic sinusoidal lining cells. This injury is exacerbated on reperfusion, in part because of adhesion of leukocytes. Platelets also adhere to activated endothelial surfaces. In this study we examined the role of platelets in preservation injury. Our specific aim was to determine whether the degree of platelet adhesion on reperfusion of preserved rat livers was related to duration of cold or warm ischemia and whether platelet adhesion resulted in injury to allografts. We also examined the effect of prior activation of platelets on adhesion and injury. Rat livers were preserved at 1 degree C for different time periods in University of Wisconsin solution and then reperfused for 3 hr on the isolated perfused rat liver system with Krebs-Henseleit solution to which unactivated isolated rat platelets were added. Other livers were rewarmed before reperfusion or reperfused with activated platelets. Platelets were lost from the circulation in all studies; the percentage reduction of circulating platelets was dependent on the length of preservation. The initial platelet concentration did not affect the rate of reduction of platelets in the circuit. Rewarming before reperfusion increased platelet adherence, and prior activation also increased adherence. With electron microscopy we determined that platelets adhered in small aggregates to endothelial cells or endothelial cell remnants. Adherent platelets appeared more activated and contained fewer granules than did unperfused platelets. Liver injury as measured by release of transaminases into perfusate was worsened by longer periods of cold preservation and by addition of rewarming to the protocol. The presence of platelets under these circumstances aggravated injury. Prior activation of platelets also increased the extent of injury. These studies show that platelets have an important role in cold preservation-reperfusion injury.

Alanine Transaminase↗