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Biomedical subjects

G Johnson

Publications and source records attributed to G Johnson.

At least 397 records · Page 22Linked to original sources
PubMed1988

Cell responses to biomaterials. II: Endothelial cell adhesion and growth on perfluorosulfonic acid.

We report here the use of perfluorosulfonic acid (Nafion) as a substratum for the growth of bovine aortal endothelial cells. This support which can be generated in a number of forms is at least as efficient in maintaining the growth of endothelial and other cell types as tissue culture grade polystyrene (TCP) and represents an advance in this regard over polytetrafluoroethylene (Teflon). The mechanism underlying the different cell attachment capacities of these three polymers is not readily related to their different protein binding patterns. While Nafion adsorbs more total protein from serum than Teflon or TCP, it adsorbs relatively less of the major cell adhesive proteins, vitronectin and fibronectin, than does Teflon. Both Nafion and Teflon had comparable but low thrombogenic potential by in vitro tests. Teflon or expanded Teflon (Gore-tex) coated with a thin film of Nafion assumes the cell supportive characteristics of Nafion and hence the modification of these surfaces by the induction of a stable bond between Teflon (in various forms) and Nafion may provide a composite vascular graft material which has all the desirable qualities of both materials.

Animals↗
PubMed1988

Multiline chemical-shift (MULCH) imaging.

A fast chemical-shift imaging technique is presented. The method involves saturating all spins outside a plane, selectively exciting individual lines, phase encoding along each line, sampling the FID without gradients, and interleaving interrogation of multiple lines. A 64 X 64 array of spectra with 5 Hz resolution can be obtained in 17 min.

Magnetic Resonance Spectroscopy↗
PubMed1988

19F NMR imaging of blood oxygenation in the brain.

Perfluorocarbon (PFC) emulsions have been developed as oxygen carrying blood substitutes. High fluorine concentrations allow them to be used in 19F NMR imaging of blood vessels. Furthermore, 19F relaxation times in PFCs are dependent on oxygen tension (pO2) so that NMR imaging may provide a noninvasive method of measuring spatially localized pO2 values in vivo. Using these principles, we have formed 19F images and calculated pO2 maps of the cat brain.

Animals↗
PubMed1988

Determination of whole blood apparent viscosity: experience with a new hemorheologic technique.

A new experimental technique of determining apparent blood viscosity at low rates of shear using a porous bed viscometer (PBV) was evaluated in a study of 213 blood samples from 43 mongrel dogs. Viscosity was measured over a wide range of hematocrit (Hct), 6.5-51%, and plasma fibrinogen (Fib), 11-597 mg%, levels significantly altered (P less than 0.0005) by isovolemic hemodilution. Viscosity was highly correlated with Hct and Fib (r = 0.89), which confirmed the results of previous investigations. An important finding was the ability of the PBV to detect the non-Newtonian behavior of whole blood that occurs under low shear conditions at higher Hct levels. In a subgroup of 10 animals, viscosity was also measured by a precision cone and plate viscometer (CPV) at various shear rates. Although the PBV and CPV measurements showed excellent correlation (r = 0.92), a marked nonlinear deviation of the plotted data from the regression of Hct vs viscosity measured by the PBV at Hct levels greater than or equal to 30% was noted which could not be identified by the CPV. The PBV technique affords valid measurements of the apparent viscosity of normal canine blood. Moreover, the device is apparently sensitive to the anomalous rheologic properties of whole blood attributable to shear-dependent changes in red blood cell aggregation that can become physiologically significant in low-flow states.

Animals↗
PubMed1988

19F imaging of cerebral blood oxygenation in experimental middle cerebral artery occlusion: preliminary results.

Fluorine (19F) nuclear magnetic resonance may be used to image cerebral perfusion in cats receiving perfluorocarbon blood substitutes. 19F relaxation times in these blood substitutes are dependent on oxygen tension (PO2) and may be used to calculate and spatially map cerebrovascular PO2 values in vivo. We have applied this noninvasive method to experimental middle cerebral artery (MCA) occlusion. Following MCA occlusion a perfusion defect is evident in the sylvian region, followed by the appearance of collaterals. Signal from the ipsilateral rete mirabilis is increased. Calculated cortical vascular PO2 values indicate a relative reduction in oxygenation in the ischaemic hemisphere. PO2 maps show a perfused hypoxaemic zone adjacent to the perfusion defect. These changes are partly reversed with reperfusion.

Animals↗
PubMed1988

The characterization of experimental gliosis by quantitative nuclear magnetic resonance imaging.

Quantitative nuclear magnetic resonance imaging techniques were used to study the development of astrocytic gliosis following a cortical freezing injury in 4 cats, and the findings compared with the histological and ultrastructural appearances of the affected white matter. In the first week after lesioning, the acutely oedematous white matter was apparent as a region of signal abnormality with very prolonged T1' and T2' relaxation times. Following resolution of this oedema, the images remained normal for a period of approximately three months. After this latent period they became abnormal once again, and the abnormal signal was most evident in images emphasizing differences between tissues in T1' and proton density, but not T2'. The light and electron microscopic appearances of the corresponding tissue were of astrocytic gliosis in each animal. Measurement of the relaxation times, T1' and T2', of the abnormal regions revealed an increase in T1' without a corresponding change in T2'. The T2' magnetization decay characteristics were consistently monoexponential, in contrast to the clearly biexponential T2 decay which has previously been demonstrated in the presence of acute vasogenic oedema. These findings suggest that the pattern of change of the relaxation times and T2 magnetization decay might provide a means of distinguishing between lesions in multiple sclerosis which are predominantly gliotic, and those containing significant amounts of oedema.

Animals↗
PubMed1988

Serial gadolinium enhanced magnetic resonance imaging in multiple sclerosis.

Serial gadolinium-DTPA (Gd-DTPA) enhanced magnetic resonance imaging (MRI) was performed in 9 patients with multiple sclerosis (MS). On the first scan enhancing lesions were seen in 7 patients, all of whom were in acute relapse. Most enhancing lesions were asymptomatic. On the second scan (3 to 5 weeks later), persisting enhancement was seen in only 12/54 lesions which enhanced on the first scan. No lesion showed persisting enhancement on the third scan (after 6 months). Enhancement occurred in all 12 new lesion areas seen on the unenhanced second scan and in 8 of 15 new lesions seen on the third scan. Enhancement was also seen in 4 older lesions which had been nonenhancing on earlier scans. Relaxation time measurements demonstrated a high water content in some nonenhancing lesions, which could be due to a subtle blood-brain barrier disturbance not detected with Gd-DTPA. The results show that blood-brain barrier impairment is a consistent finding in new MS lesions detected with MRI. Gd-DTPA is a useful marker of new and biologically active lesions and should prove of value in monitoring therapeutic trials in MS.

Adult↗
PubMed1988

Air embolism and the radial arterial line.

A clinical case of apparent air embolism through a radial artery line served as the impetus to conduct a study in primates to investigate the possibility of air embolism from the radial artery into the cerebral circulation. Using 133Xe cerebral scanning, we demonstrated that greater than 2 ml of air in the radial artery would result in retrograde passage of air into the vertebral system and then into the brain.

Animals↗
PubMed1988

Indium-111 platelet kinetics in patients with diabetes mellitus.

We performed in vitro aggregation and indium-111 labeled platelet kinetic and biodistribution studies in seven patients with diabetes mellitus and in five control subjects. All subjects were male. All diabetic patients were poorly controlled at the time of study with blood glucose greater than 140 mg % and hemoglobin A1c greater than 10%. In vivo kinetic and biodistribution studies were performed following reinjection of autologous platelets labeled with indium-111 oxine in a dose of approximately 50 microCi (42-67 microCi). Images obtained at 4 and 24 h were computer-analyzed to determine splenic and hepatic uptake, and platelet survival times were calculated using four mathematical models. Unexpectedly, diabetic patients with fewer vascular complications tended to have shorter platelet survival times than patients with advanced vascular disease. However, no significant differences were observed between diabetic and control groups for any of the parameters of platelet function evaluated.

Blood Platelets↗
PubMed1988

The Effect of Temperature on the Level and Biosynthesis of Unsaturated Fatty Acids in Diacylglycerols of Brassica napus Leaves.

Experiments on the effects of temperature on the levels of unsaturated fatty acids and their rates of desaturation in Brassica napus leaf lipids have shown that significant differences occur in the composition of all diacylglycerols in the leaf between plants grown at high and low temperatures. In the major thylakoid diacylglycerols, monogalactosyl-diacylglycerol and digalactosyldiacylglycerol, not only is there an increase in the level of unsaturation at low temperatures, but there is a change in the balance between molecular species of chloroplastic origin (16/18C) and cytosolic origin (18/18C). Radioactivity tracer data indicate that at low temperatures there are two distinct phases of desaturation in the fatty acids of the major diacylglycerols of these leaves. A rapid phase, which appears in plants grown at low temperatures and results in the desaturation of palmitic acid to hexadecadienoic acid and oleic acid to linoleic acid may explain the high levels of unsaturated fatty acids found in the leaf diacylglycerols from plants grown at low temperatures. The appearance of this rapid phase is controlled by the temperature at which the plant is grown and is not subject to rapid variations in environmental temperature.

Journal Article↗
PubMed1988

Quality of life after cystectomy. Comparison between patients with conduit and those with continent caecal reservoir urinary diversion.

A questionnaire survey was carried out to assess the quality of life of 60 patients who had undergone cystectomy because of bladder carcinoma. Urinary diversion was by a continent caecal reservoir in 20 patients and by a conduit in 40. The patients' replies showed that cystectomy could cause severe problems in all aspects of life. Diversion with a continent caecal reservoir was associated with fewer stoma-related problems and seemed to allow the patients greater freedom to continue activities such as sport, travel and social life. Sexual problems, disturbed relationships with partners and emotional and mental problems were common and did not differ between the two groups of patients. It is recommended that patients judged to be prone to mental and emotional disturbance after cystectomy should be identified pre-operatively and given extra psychological support.

Adult↗
PubMed1988

Magnetic resonance imaging of the optic nerve in optic neuritis.

Magnetic resonance imaging (MRI) of the optic nerves using the STIR (short inversion time inversion recovery) sequence was performed in 37 adult patients with a recent or past attack of optic neuritis. MRI revealed high-signal regions in 84% of symptomatic and 20% of asymptomatic nerves. The mean longitudinal extent of lesions was 1 cm. Slow or poor visual recovery was associated with more extensive lesions, or lesions within the optic canal. Disk swelling was usually associated with anterior lesions but also occurred with lesions in the canal. Visual evoked potentials were even more sensitive than MRI in detecting lesions and are still the investigation of choice in suspected demyelinating disease involving the optic nerve.

Adult↗
PubMed1988

Magnetic resonance imaging in central nervous system sarcoidosis.

We performed brain MRIs on 21 patients with CNS sarcoidosis. Brain CTs were performed in 18 of these. Parenchymal lesions were seen in 17 of 21 with MRI, compared with 9 of 18 with CT. MRI detected a greater number of parenchymal lesions in cases where both CT and MRI were positive, and some lesions appeared more extensive with MRI than with CT. The most common MRI pattern was one of periventricular and multifocal white matter lesions (14 cases). Such a pattern is not specific, and other recognized causes for it were identified in four cases. It is likely, however, that sarcoid tissue causes this pattern in some cases, and confirmation was obtained from cerebral biopsy in one. In six patients, the white matter changes were indistinguishable from those seen in multiple sclerosis. Contrast-enhanced CT in two patients showed diffuse meningeal involvement not seen with MRI. MRI is the investigation of choice in detecting parenchymal changes in the brain of patients with CNS sarcoidosis and may prove useful in monitoring treatment in such cases.

Adolescent↗
PubMed1988

Macroscopic and radiographic examination of proximal root surface caries.

The purpose of the study was to compare macroscopic and radiographic examination of proximal root surface caries of extracted teeth from patients aged 65-95 years. Although the study conditions for macroscopic and radiographic diagnosis favored more sensitive evaluations than routine clinical conditions, there was a 24% disagreement in diagnosis. This finding indicates that under routine clinical conditions it is difficult to register with certainty all superficial root carious lesions. Even in the absence of clinically detectable root surface caries, preventive measures should be considered for elderly people with exposed root surfaces.

Aged↗
PubMed1988

Noninvasive determination of healing of major lower extremity amputation: the continued role of clinical judgment.

Various tests are used preoperatively to differentiate patients who require an above-knee amputation (AKA) from those whose vascular supply is adequate to heal a below-knee procedure (BKA). This 15-month study of 109 amputations compared four of these methods: segmental Doppler systolic pressure measurements, transcutaneous oxygen measurement (tcPO2), fluorescein angiography, and skin thermometry. There were 66 BKAs (85% healed primarily) and 43 AKAs (93% healed primarily). The actual level of amputation was determined by the operating surgeon without consideration of the preoperative test results, and the incidence of healing was then related to the test parameters. The average skin temperature at the amputation site was higher (93.7 degrees F) in the group that healed primarily compared with those who required operative stump revision (89.9 degrees F) (p less than 0.001). The mean midcalf tcPO2 was also higher in the BKA group that healed (PO2 = 36.6 mm Hg) compared with those who failed (PO2 = 16.4 mm Hg) (p less than 0.001). Qualitative skin fluorescence was less successful in differentiating success from failure. Of the 63 BKAs that fluorescein predicted would heal, eight failed (13%). Doppler pressures at the thigh, popliteal, midcalf, or ankle level were unreliable in predicting healing of a BKA. Formulation of indexes relating absolute pressures to the brachial systolic pressure did not improve the value of this examination. From this review it is concluded that the skin temperature and tcPO2 obtained at the site of proposed amputation were the most reliable prognostic noninvasive examinations.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1988

The effect of allopurinol and catalase on cardiovascular hemodynamics during hemorrhagic shock.

The primary objective of this study was to determine the effect that the xanthine oxidase inhibitor allopurinol (ALLO) and the hydrogen peroxide scavenger catalase (CAT) have on the cardiovascular compensatory ability of the dog to respond to severe hemorrhagic hypotension. Twenty-four mongrel dogs were anesthetized with sodium pentabarbitol and surgically prepared to monitor 1) average arterial blood pressure (AAP), 2) central venous pressure (CVP), 3) heart rate (HR), 4) cardiac index (CI = CO/kg), and hindlimb skeletal muscle blood flow (MBF). Total body vascular conductance (TBC) and skeletal muscle vascular conductance (MVC) were calculated by dividing the CI or MBF by the difference between the AAP and CVP. Eight animals were placed into each of the following three groups, bled over a 1-hr period of time to an AAP of 50 mm Hg and monitored for an additional 2 hr. Group I controls received an intravenous volume of lactated Ringer's equivalent to that volume given to groups II and III. Group II was pretreated 24 hr prior to hemorrhage with 100 mg/kg ALLO orally and received a bolus injection of 25 mg/kg 15 min prior to hemorrhage plus an intravenous infusion of 5 mg/kg/hr over the 3-hr study. Group III was given the same ALLO treatment as group II plus an additional 5-mg/kg/hr intravenous infusion of CAT throughout the duration of the 3-hr study. The results show that the intense compensatory increase in total body vascular tone which occurs during severe hypovolemia is significantly reduced at the 60-, 120-, and 180-min periods in the ALLO/CAT group; however, when ALLO alone was used this effect lasted only through the 120-min period. A similar, but statistically less convincing, picture was seen in the skeletal muscle vascular bed. Thus, the ALLO/CAT group seemed to inhibit some free radical mechanisms better than the ALLO group during and immediately following hemorrhage. Allopurinol alone lost its effectiveness before the 3 hr, which suggests that a free radical mechanism may play an early role in the pathophysiologic shock sequence. As shock continues, however, other factors seem to override the free radical mechanism. One possible explanation for this early tissue protective action of allopurinol and catalase is the inhibition of the oxygen free-radical-induced microvascular swelling and plugging.

Administration, Oral↗