Biomedical subjects
D D Shaw
Publications and source records attributed to D D Shaw.
Contrast media. Directions for the 1990s.
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Hemodynamic effects of gadodiamide injection and gadopentetate dimeglumine in anesthetized dogs.
A nonionic (gadodiamide injection) and an ionic (gadopentetate dimeglumine) contrast medium were compared for their effect on hemodynamics in the anesthetized, open-chest dog. Both agents were administered i.v. over 15 s at dosages of 1.0 and 1.5 mmol/kg, in randomized order. Both contrast agents resulted in transient but statistically significant decreases in aortic pressure, left ventricular pressure, indices of left ventricular contractility and relaxation, and systemic and pulmonary vascular resistance, and increases in aortic blood flow. At each dosage investigated, the changes associated with the administration of gadodiamide injection were of significantly smaller magnitude than those seen after gadopentetate dimeglumine and returned to preadministration levels sooner. The results from this study confirm that gadodiamide injection produces less severe alterations in hemodynamics than gadopentetate dimeglumine.
Knowledge and use of oral rehydration therapy for childhood diarrhoea in Tumpat District.
A community based study was conducted on the understanding and knowledge of childhood diarrhoea and use of oral rehydration therapy (ORT), in four selected villages in Tumpat District, Kelantan. The calculated annual incidence of diarrhoeal disease in children aged 0 to four years in all study villages was 1.38 episodes for each child. The main care-givers of children aged 0 to four years were interviewed and asked to demonstrate how to mix a standard ORS (oral rehydration solution) sachet if they had previously used ORT. Forty percent of care-givers had heard of the locally available ORT and 30% had actually used ORT. Of those who had heard of or used ORT, 10% had good knowledge of what it was and what it was used for, 51% had some knowledge and 39% had either no knowledge or inaccurate knowledge. Of care-givers who had previously used ORT only 20.5% demonstrated the correct volume of water to add to one sachet of ORT, but 82% would discard an unused solution within 24 hours. Significantly more literate women had used ORT than those not literate (p = 0.002). Mothers, particularly those literate, are the primary target group for ORT intervention strategies. Components of health education should include advice on what ORS is, what it is used for, and how to correctly mix a standard sachet.
Iohexol and iopamidol for lumbar myelography.
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The heterochromatin of grasshoppers from the Caledia captiva species complex. I. Sequence evolution and conservation in a highly repeated DNA family.
The restriction enzyme TaqI digests 0.2% of the genomic DNA from the grasshopper Caledia captiva to a family of sequences 168 bp in length (length of consensus sequence). The sequence variation of this "Taq family" of repeat units was examined among four races from C. captiva to assay the pattern of evolution within this highly repeated DNA. The Taq-family repeats are located in C-banded heterochromatin on at least one member of each homologous pair of chromosomes; the locations range from centromeric to telomeric. Thirty-nine cloned repeats isolated from two population 1A individuals along with 11 clones from seven populations taken from three of the races demonstrated sequence variation at 72 positions. Pairwise comparisons of the cloned repeats, both within an individual and between different races, indicate that levels of intraspecific divergence, as measured by reproductive incompatibility, do not correlate with sequence divergence among the 168-bp repeats. A number of subsequences within the repeat remain unchanged among all 50 clones; the longest of these is 18 bp. That the same 18-bp subsequence is present in all clones examined is a finding that departs significantly (P less than 0.01) from what would be expected to occur at random. Two other cloned repeats, from a reproductively isolated race of C. captiva, have sequences that show 56% identity with this 18-bp conserved region. An analysis showed that the frequency of occurrence of an RsaI recognition site within the 168-bp repeat in the entire Taq family agreed with that found in the cloned sequences. These data, along with a partial sequence for the entire Taq family obtained by sequencing uncloned repeats, suggest that the consensus sequence from the cloned copies is representative of this highly repeated family and is not a biased sample resulting from the cloning procedure. The 18-bp conserved sequence is part of a 42-bp sequence that possesses dyad symmetry typical of protein-binding sites. We speculate that this may be significant in the evolution of the Taq family of sequences.
Pharmacokinetics and excretion of iohexol after lumbar myelography in man.
Pharmacokinetics and excretion of iohexol, a new nonionic water-soluble contrast medium, were determined after lumbar myelography. Peak plasma concentrations were obtained 2 to 6 hours after injection and ranged from 29 to 177 microgram/ml. Terminal elimination half-life was 4.0 hours, and over 90% of the dose was recovered in the urine within 24 hours. In one patient with a large lumbar cauda equina tumor, absorption and excretion were delayed; but eventually 99% was recovered indicating a large capacity for reabsorption via the lumbar subarachnoid space. One mild headache of 5 minutes' duration was reported in a 73-year-old woman. No significant changes in vital signs, neurologic examinations, or serum chemistries were observed.
A decidual cast following therapy with norethisterone.
A case is presented of a decidual cast following progesterone therapy, an extraordinarily rare event.
Iohexol: a new, nonionic agent in adult peripheral arteriography.
The safety and efficacy of iohexol, a new nonionic contrast agent, were compared with a diatrizoate (Renografin-76) in a double-blind, parallel study of peripheral arteriography by femoral puncture in 60 patients. Extra-large field serial peripheral arteriography was used and a posterior tibial nerve block was applied to all patients in the study. Similar changes in blood chemistry were observed following the injection of iohexol and diatrizoate but these changes did not require corrective measures. Significantly more patients complained of a sensation of severe heat after receiving diatrizoate (38%) than after the injection of iohexol (10%) (p = 0.001). Four patients in the diatrizoate group experienced one or more adverse reactions, including mild urticaria. Only mild nausea was reported by a single patient in the iohexol group. Overall, 100% of the studies were diagnostic but more of the radiographs taken after the injection of iohexol were rated excellent than after the injection of diatrizoate.
Lumbar myelography with iohexol and metrizamide: a comparative multicenter prospective study.
Diagnostic quality of radiographs and adverse reactions associated with the use of metrizamide and iohexol as contrast agents in lumbar myelography were compared in a prospective randomized double blind study in 350 patients at seven centers. The contrast media were administered in comparable volumes at a concentration of 180 mg I per ml. Overall quality of radiographic visualization was graded good or excellent in 95% of 175 metrizamide studies and in 98% of 175 iohexol studies. Ninety-three patients examined using metrizamide (53%) and 130 patients examined using iohexol (74%) experienced no discomfort during or after myelography. Postmyelographic headache was associated with 38% of metrizamide examinations and 21% of iohexol examinations. Nausea and vomiting were also more common with metrizamide. Five patients examined using metrizamide (3%) experienced transient confusion and disorientation following lumbar myelography. No such reactions were observed following iohexol myelography.
Increased chromosomal mutation rate after hybridization between two subspecies of grasshoppers.
Hybridization between two chromosomally distinct subspecies of the grasshopper Caledia captiva results in a high incidence of novel chromosomal rearrangements among the backcross progeny. Rearrangements are restricted to those chromosomes derived from the F1 hybrid parent. Chromosomal involvement is nonrandom with the same rearrangement occurring repeatedly in different backcrosses. A single individual can also generate an array of different rearrangements among its offspring. Several of the rearrangements have also been found in natural populations. The nonrandom and recurrent nature of these chromosomal mutations at high frequencies provides a plausible explanation for the establishment and fixation of chromosomal rearrangements in natural populations.
Human pharmacologic trials with iohexol.
Injections of iohexol in two series of volunteers, 20 in 1980 and 16 in 1982 are briefly reported. Intravenous injections of iohexol in doses from 125 to 1500 mg I/kg body weight were well tolerated. Iohexol was completely excreted in unchanged form. The results indicate that iohexol may safely be used in clinical trials.
Assessment of healing of long-bone fractures by intraosseous venography.
Intraosseous venography with compression of the soft tissue was performed following fracture of the radius in 13 dogs to assess the repair process. Two angiographic criteria were analyzed: (a) intraosseous venous crossing of the fracture ("medullary crossing") and (b) capillary blush of the proximal osseous fragment ("proximal blush"). The bone strength of the fractured and intact radii was compared. Venograms obtained immediately after fracture showed contrast material reaching but not crossing the fracture line, indicating that the entire intramedullary venous network had been disrupted. When Parafilm was interposed between the bone fragments to prevent healing, proximal blush was seen at 4 weeks and medullary crossing at 6-7 weeks; bone strength was 13-14% of normal. With no barrier, proximal blush appeared at 5 weeks and medullary crossing at 10-11 weeks; bone strength was 30-40% of normal. The authors conclude that medullary crossing can be seen in the presence of decreased bone strength if the healing process is uneven across the fracture line, as occurred with Parafilm. If the animal model reproduces the clinical situation, this finding challenges the predictive value of intraosseous venography.
Role of peripheral vasodilation in the hypotensive response to left ventriculography in anesthetized dogs.
Hypotension after left ventriculography (LVG) is believed to result from direct myocardial toxicity, peripheral vasodilation, or a combination of both. The contribution of each has not been established. Thus, LVG was performed in anesthetized dogs under conditions in which peripheral vascular reactivity (PVR) was altered pathophysiologically (aortic coarctation) or pharmacologically (acetylcholine infusion). Ventricular pressure (LVP), its first derivative (dP/dt), aortic pressure (AoP), and carotid and femoral flows were monitored. When PVR was normal, LVG was associated with significant hemodynamic changes which reached a maximum 25-35 seconds after injection. Left ventricular and aortic diastolic pressures were decreased by 22 and 48%, whereas carotid and femoral systolic flows were increased by 41 and 59%. During acetylcholine infusion, LVG did not cause systolic hypotension and peripheral flows were maintained strikingly constant. Similarly, LVG also was associated with insignificant changes in systolic pressures and carotid flow in the presence of aortic coarctation. These results demonstrate that the hypotension attendant with LVG is directly related to the augmentation in peripheral flow, suggesting that the response is mediated almost exclusively by peripheral vasodilation.
A comparison of chromosomal and allozymal variation across a narrow hybrid zone in the grasshopper Caledia captiva.
A hydrid zone between the Moreton and Torresian taxa of the grasshopper Caledia captiva in S.E. Queensland has been characterised in terms of allozyme and chromosome variation within the same individuals.--On chromosomal criteria (pericentric rearrangements), the zone is asymmetrical with evidence of high levels of introgression of Torresian chromosomes into the Moreton taxon. This is apparent from the analysis of two independent transects across the hydrid zone. Major changes in chromosomal frequency occur over distances of less than 0.5 km. and the level of introgression differs between the two transects, with much higher levels in the northern Moreton populations, characterised by an acrocentric X-chromosome, when compared with the southern metacentric-X Moreton populations. Chromosome analysis of samples taken from the same transect over two years has revealed no major changes in the structure of the zone. Moreover, a Moreton population located only 0.5 km. from the null point was found to be stable over 6 generations with evidence for a new balanced genome having originated following the differential incorportation of Torresian chromosomes.--Contrary to the chromosomal situation, the same hybrid zone was found to be symmetrical with respect to allozyme variation with evidence of movement of diagnostic alleles in both directions across the zone. The alleles are independent and not tightly linked to any of the pericentric rearrangements. Thus these 5 alleles are acting as markers of the background genome and reveal the relatively free movement of genes which are located outside the pericentric rearrangements.--It is proposed that the hybrid zone in Caledia captiva is unstable and is moving slowly in a westerly direction into the Torresian territory. This is due to the ability of the Moreton taxon to incorporate more readily into its genome those Torresian chromosomes or chromosome segments which increase the fitness of the Moreton taxon. On chromosomal criteria, the Torresian taxon does not share the same capacity.--It is suggested that, so long as the two taxa retain their ability to hybridise with subsequent asymmetrical introgression, the zone will continue to move westwards and eventually lead to the selective incorporation of the Torresian genome into the Moreton taxon. This will result in a polymorphic situation with clinal variation in chromosomal frequencies. The structure of the zone is dependent upon a fine balance between genomic reorganisation in recombinant genotypes and the relative dispersal capacities of the two hydridising taxa.
Distinguishing ischemic from fibrotic myocardium during ventriculograpy by means of physiological potentiation.
Physiological potentiation during ventriculography is more helpful than the routine ventriculogram in predicting postoperative ventricular function. The authors describe a control device which allows the operator to flexibly program a pacing stimulus, thus making it possible to obtain both a resting beat and an optimum potentiated beat during a single ventriculographic study.
Regional distribution of coronary blood flow during left ventriculography in anesthetized dogs.
Changes in total and regional left coronary blood flow in response to ventriculography were studied using electromagnetic and microsphere techniques. Correlation of coronary flows by these methods showed excellent agreement (r = 0.947). Ventriculography produced a characteristic triphasic response in total flow and in endocardial/epicardial perfusion ratios. Changes in coronary flow can be explained as a result of hypotension and vasodilatation.
Accuracy of estimates of contrast media concentration.
An animal model was used to prepare 18 experimental roentgenograms with differing dilutions of Conray 400 in each renal pelvis. Fifty radiologists were asked to estimate the iodine concentrations after they had been shown examples with known iodine concentrations. It was found there was a great deal of variation in the ability of individual subjects to accurately estimate the iodine concentration present. When the urinary iodine was less than 25 mg/ml, contrast estimations became grossly unreliable. At higher concentrations, the average performance of the sixty subjects was fairly clos to observed densotimetric readings. This study demonstrates that the ability to estimate iodine concentration is similar to other perceptive abilities in demonstrating both thereshold sensitivity and a near normal distribution among observes of the ability to judge perceptable differences in contrast media density.