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Biomedical subjects

T W Morris

Publications and source records attributed to T W Morris.

At least 73 records · Page 4Linked to original sources
PubMed1986

Incidence of fibrillation with dilute contrast media for intra-arterial coronary digital subtraction angiography.

State-of-the-art imaging technology such as digital subtraction angiography can produce coronary artery opacification with contrast media formulations that contain less than 170 mgI/ml. We examined the effect of electrolyte composition in such formulations on the incidence of fibrillation. Right coronary injections of contrast were made for 25 seconds in anesthetized dogs. This injection is longer than clinical injections, but the model approximates the worst condition of a wedged catheter preventing media washout. Formulations of several mixtures of meglumine and sodium diatrizoate (173 to 141 mgI/ml) and sodium diatrizoate alone (143 mgI/ml) produced fibrillation in only 10 to 20% of the injections. Meglumine diatrizoate (141 mgI/ml) and full strength meglumine/sodium diatrizoate (Angiovist 370) produced fibrillation in 100% and 50% of the injections, respectively. These animal studies demonstrate that dilute contrast media containing few or no sodium ions are more likely to induce fibrillation than Angiovist 370, whereas dilute contrast media containing sodium are the least likely to induce fibrillation.

Angiography↗
PubMed1986

Acute systemic and renal hemodynamic effects of meglumine/sodium diatrizoate 76% and iopamidol in euvolemic and dehydrated dogs.

We examined the acute systemic and renal hemodynamic effects of intravenous meglumine/sodium diatrizoate-76% and iopamidol in euvolemic and dehydrated dogs. The physiologic responses were compared with acute changes in the level of an endogenous heparin-like material (EHM). One of eight dehydrated dogs receiving diatrizoate (2 ml/kg) had an immediate vomiting reflex associated with a very significant decline in all measured renal hemodynamic parameters; none of eight dehydrated dogs receiving iopamidol experienced a similar reaction. EHM levels did not correspond to the magnitude of the physiologic responses following either iopamidol or diatrizoate. Significant differences between iopamidol and diatrizoate were noted when comparing the magnitude of the decrease in systemic pressure (- delta 3.8 +/- 3.02, iopamidol, n = 8; vs. - delta 19.4 +/- 7.3 mm Hg, diatrizoate, n = 8; P less than .03), increased renal plasma flow (+ delta 6.2 +/- 4.9, iopamidol, n = 8; vs. + delta 33.7 +/- 8.0 ml/min, diatrizoate, n = 8; P less than .05), and decreased filtration fraction (- delta 0.09 +/- 0.01, iopamidol, n = 8; vs. - delta 0.14 +/- 0.02, diatrizoate, n = 8; P less than .03). There was no significant difference in the decrease in glomerular filtration rate (- delta 7.4 +/- 1.0, iopamidol, n = 8; vs. - delta 9.3 +/- 1.3, diatrizoate, n = 8; P greater than .05), since the marked drop in filtration fraction occurring with diatrizoate was counterbalanced by the marked increase in renal plasma flow. Acute systemic and renal hemodynamic effects are significantly lessened when comparing iopamidol with diatrizoate.

Animals↗
PubMed1986

Iopamidol and neural tissue metabolism. A comparative in vitro study.

Metrizamide was the first water-soluble contrast medium with a neurotoxicity low enough to allow it to be used routinely in the entire subarachnoid space. However, neurologic complications are still observed in some patients following the use of metrizamide. The cause of this toxicity has not been established, but existing evidence suggests an interference with glucose metabolism. In previous studies, a depression in CO2 production in neural tissue slices was demonstrated when isotonic metrizamide was added but not isotonic iohexol. In addition to iohexol, there is another new, nonionic, monomeric, water-soluble CM, iopamidol, soon to be released for clinical use in the United States. Iopamidol, like iohexol, has shown fewer adverse reactions and seems to be safer for myelography than metrizamide. Direct comparative studies of iopamidol and iohexol are sparse and the cause of their toxicity is not yet understood. This study was performed to determine the effect of iopamidol on neural tissue glucose metabolism as compared with the effects of iohexol and metrizamide. Metrizamide decreased CO2 production in neural tissue slices by 23%. Iopamidol and iohexol did not produce significant depression. Moreover, this model could not demonstrate any significant difference between iopamidol and iohexol in direct comparisons. The new monomeric contrast media, iopamidol and iohexol, thus do not appear to interfere with glucose metabolism. Adverse reactions to these new media are most likely caused by other mechanisms.

Animals↗
PubMed1986

A comparison of clearance and arteriovenous extraction techniques for measurements of renal hemodynamic functions.

No previous studies have directly compared timed urine collections (UV/P) vs. arteriovenous (A-V) extraction methods for determination of renal function in whole kidney preparations. We examined different markers and techniques for assessing renal plasma flow (RPF), filtration fraction (FF), and glomerular filtration rate (GFR) in both steady-state and rapidly changing conditions following 2 ml/kg bolus intravenous injections of either Renografin 76% (meglumine/sodium diatrizoate-76%) or hypertonic mannitol 25%. During steady-state conditions, excellent correlations were obtained when comparing markers and techniques. Thus, timed urinary clearances of inulin vs. 99m-technetium DTPA (Tc) had a correlation coefficient (R) of .96 (P less than .01; n = 16), and the A-V extraction technique of inulin vs. Tc as determinants of GFR showed a correlation of R = .98 (P less than .01; n = 15). The timed urinary clearance of inulin vs. the A-V extraction of inulin for glomerular filtration gave a correlation of R = .93 (P less than .01; n = 15). The clearance of para-aminohippurate (PAH) divided by the extraction of PAH vs. flow determinations using the electromagnetic flowmeter gave a correlation of R = .92 (P less than .01; n = 16). The anticipated decrease in GFR following contrast medium and hypertonic mannitol was observed using the A-V extraction technique, whereas an artifactual, exaggerated increase in GFR was observed using the timed urine collection technique. Similarly, we noted an exaggerated increase in RPF using CPAH/EPAH as the methodology. We conclude that rapid changes in renal hemodynamics may be measured accurately using the A-V extraction technique but not with clearance techniques requiring timed urine collections.

Animals↗
PubMed1986

The effect of subarachnoid metrizamide and iohexol on cerebral glucose metabolism in vivo.

We studied the effect of metrizamide and iohexol on local cerebral glucose utilization (LCGU) using autoradiography. Metrizamide or iohexol was introduced into the subarachnoid space of rabbits and positioned over the right hemisphere for 3 or 6 hours. Using the unexposed (left) hemisphere as an internal control, we calculated relative changes in LCGU. In the three metrizamide-exposed animals the LCGU was decreased over the contrast media-exposed right temporoparietal cortex (L-R difference was positive). There was no significant changes in LCGU and no positive L-R difference after treatment with iohexol (three animals). We conclude that metrizamide does affect glucose metabolism in vivo, and this effect is dependent on localization of the contrast medium. The clinically safer drug, iohexol, in similar concentration and higher osmolality, did not decrease glucose metabolism.

Animals↗
PubMed1986

Incidence of fibrillation with isotonic contrast media for intra-arterial coronary digital subtraction angiography.

Intra-arterial digital subtraction angiography (DSA) can produce coronary artery opacification with isotonic contrast media. In this study we have examined the importance of electrolyte composition in isotonic formulations on the incidence of fibrillation. Right coronary injections of media were made for 25 s in anesthetized dogs. Isotonic meglumine diatrizoate and iohexol produced fibrillation in more than 68% of the injections, while sodium diatrizoate, saline, meglumine/sodium ioxaglate and iohexol with added sodium diatrizoate never produced fibrillation. These animal studies demonstrate a significantly higher risk of fibrillation (p less than 0.005) with isotonic nonionic and ionic media not containing sodium ions.

Angiography↗
PubMed1986

Recent advances in contrast agents.

Intravascular contrast agents are remarkably safe and inexpensive. With the recent approval of three new low-osmolality, high-cost contrast media, questions arise as to toxicity, side effects, and choice of particular agents for particular patients and examinations. This article examines the nature and the etiology of the effects of all currently available contrast agents in order to achieve an improved understanding of the relative advantages, disadvantages, and utility of each.

Animals↗
PubMed1985

Glomerular filtration response to acute ureteral obstruction in the dog.

In order to assess the glomerular filtration responses to acute ureteral obstruction in the dog we employed an established method that does not require timed urine collections. Our results show a 57 per cent increase in renal blood flow (baseline: 203.8 +/- 50.9 vs. 319 +/- 69.4 ml./min. at 105 minutes; no. = 7) that was associated with a monophasic decrease in filtration fraction to -70 per cent at 120 minutes (0.26 +/- 0.025 vs. 0.08 +/- 0.007) and an increase in ureteral pressure to 63.1 +/- 6.1 mm. Hg at 120 minutes. A biphasic GFR response was noted with an initial small increase (baseline: 32.5 +/- 7.5 vs. 36.3 +/- 11.0 ml./min. at 2 minutes) followed by a continual decline to -55 per cent at 120 minutes (to 14.5 +/- 2.6 ml./min.). This investigation has confirmed the results of micropuncture studies showing maintenance of GFR early after complete ureteral ligation.

Animals↗
PubMed1984

Systemic response to excretory urography. Work in progress.

Ninety-seven patients who were undergoing excretory urography for suspected genitourinary tract abnormalities were continuously monitored for systemic blood pressure and pulse rates before (control) and after rapid intravenous injections of contrast material (1.5 ml/kg meglumine iothalamate, 60%) using a Bard pressure monitor. We report the systemic responses observed. Clinically obvious reactions to contrast medium were recorded and compared with the blood pressure and pulse rate responses. The most common response to rapid infusion of contrast medium was a transient hypotension. An increase in systemic pressure had a high association with nausea and vomiting. Significant hypotension (mean blood pressure less than 60 mm Hg) was observed in six patients (6%), but no overt clinical manifestations were present.

Adult↗
PubMed1984

Contrast media induced fibrillation: comparison of Angiovist 370 and Renografin 76. Work in progress.

Angiovist 370, a new formulation of meglumine/sodium diatrizoate, is being marketed for coronary arteriography. Angiovist 370 contains no significant calcium chelator additives, but according to manufacturer specifications may have a pH as low as 6.0. The contact times required to produce ventricular fibrillation with Angiovist 370 and with Renografin 76 were compared using a canine right coronary arteriography model. The fibrillation contact time was 32.2% longer for the Angiovist 370 than for the Renografin 76. The lower pH therefore does not appear to increase the risk of contrast media induced fibrillation. The increased contact time and safety factor with the Angiovist 370 is most likely related to the absence of calcium chelators in the formulation.

Animals↗
PubMed1984

Lumbar myelography with metrizamide in rabbits. An investigation of contrast media penetration and resorption.

Neurotoxicity from subarachnoid contrast media is probably related to their specific pharmacologic effects and to their penetration into the central nervous system. The lack of a barrier between the cerebrospinal fluid and the extracellular fluid of the brain and cord allows water-soluble contrast media to diffuse into the neural tissue. The aim of this investigation was to develop a method that allows one to quantify the neural tissue penetration for a given contrast medium in relation to the cerebrospinal fluid concentration and contact time and apply this to the use of metrizamide. The result shows a good correlation between iodine concentration in the lumbar cerebrospinal fluid and that in the lumbar cord suggestive of a simple diffusion. When time of sacrifice (contact time) is added as a covariant there is also some indication of retention of metrizamide in the neural tissue. The investigation also demonstrates that the resorption of the contrast medium in the rabbit in this experimental model is mainly in the lumbo-sacral region.

Animals↗
PubMed1983

Reactions to intravenous contrast media. Part I: Severe and fatal cardiovascular reactions in a canine dehydration model.

Investigations into the nature of severe and fatal reactions to contrast media have been severely limited by their unpredictable occurrence in the clinical setting and the absence of suitable laboratory models. The authors report their experience with a canine dehydration model. Intravenous administration of 2 ml/kg of 76% sodium methylglucamine diatrizoate resulted in vomiting, shock, inappropriate slowing of the heart rate, and death. ECG findings indicated suppression of sinoatrial node automaticity, a decrease in the rate of atrioventricular conduction, and depression of myocardial contractility. These results suggest two possible mechanisms: (a) enhanced vagal tone as the result of stimulation of the vasomotor center of the medulla or (b) accentuation of direct contrast-induced myocardial toxicity.

Animals↗
PubMed1983

Reactions to intravenous contrast media. Part II: Acute renal response in euvolemic and dehydrated dogs.

Growing concern about acute renal failure as the result of contrast agents prompted an investigation into the renal effects of intravenous contrast materials in euvolemic and dehydrated dogs. Bolus injection of hypertonic agents induced marked reductions in filtration fraction and glomerular filtration rate in both groups of animals; however, these changes were transient, returning to near-base-line values within 30 minutes after injection. The most striking differences between euvolemic and dehydrated animals appeared to be related to prerenal factors such as hypovolemia and contrast-induced hypotension.

Animals↗
PubMed1983

Work in progress: reduction of calcium activity by radiopaque contrast media.

An in vitro examination of the effects of radiopaque contrast media anions, cations, additives, and ionic strength on ionic calcium level using ion-specific electrodes was made. The calcium-binding additives sodium citrate and sodium EDTA produced the largest reduction in ionic calcium. At the same iodine concentration the anions diatrizoate, iothalamate, metrizoate, and ioxaglate reduced ionic calcium by essentially the same amount. Sodium compounds reduced ionic calcium more than did meglumine compounds, a difference that is probably related to dissociation. The nonionic compounds iohexol and iopamidol did not reduce ionic calcium significantly. Ionic strength appears to have little direct effect on ionic calcium at and above physiologic levels. All ionic contrast media bind significant amounts of ionic calcium at the high concentrations achieved during selective arteriography. Since the anions are only weak calcium binders supplemental calcium can restore the level of ionic calcium.

Angiography↗
PubMed1983

Comparison of iohexol and meglumine-Na diatrizoate in cerebral angiography.

A double blind investigation comparing meglumine-Na diatrizoate (290 mg I/ml) and iohexol (300 mg I/ml) showed that patients receiving iohexol experienced significantly less discomfort. Patients who received diatrizoate commonly showed transient episodes of hypertension while those who received iohexol either showed no changes or transient episodes of hypotension. No significant changes in heart rate were observed in either group.

Blood Pressure↗