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Biomedical subjects

N D Johnson

Publications and source records attributed to N D Johnson.

At least 37 records · Page 2Linked to original sources
PubMed1991

Caval thrombolysis in neonates using low doses of recombinant human tissue-type plasminogen activator.

Four neonates suffered caval thrombosis secondary to indwelling central catheters. Dissolution of thrombus with recombinant tissue plasminogen activator (rt-PA) as a low-dose infusion (0.05 mg/kg/hr) directly into thrombus was successful in three patients. rt-PA was ceased after three days in the fourth patient because of catheter malposition. Thrombolysis was achieved between four and ten days. Rethrombosis occurred in one patient despite heparin prophylaxis. Plasminogen activator infusions were titrated to maintain fibrinogen levels above 100 mg/dl. One neonate suffered an intracranial haemorrhage. Regional rt-PA is an alternative to thrombectomy in critically ill neonates.

Humans↗
PubMed1990

Prothrombinex-induced thrombosis and its management with regional plasminogen activator in hepatic failure.

Fulminant hepatic failure causes a bleeding diathesis as a result of impaired synthesis of hepatic clotting factors, thrombocytopenia, fibrinolysis and disseminated intravascular coagulation. Administration of clotting factor concentrates can cause thrombosis in patients with acute hepatic failure. Regional infusion of recombinant tissue-type plasminogen activator may be used to induce local thrombolysis. A case report of a five-year-old child is presented and the literature is reviewed.

Blood Coagulation Disorders↗
PubMed1990

Vesicoureteric reflux in children: prediction with color Doppler imaging. Work in progress.

Unlike gray-scale sonography, color Doppler ultrasonography allows reliable visualization of the ureteric jet phenomenon. A study was undertaken to determine whether any measurable parameter predicts the presence of vesicoureteric reflux. Measurements of mean urine jet velocity, longitudinal angle, transverse angle, and distance of the origin of the jet from the midline of the bladder were obtained on 31 infants and children (62 ureters) with a proved urinary tract infection. Of these measurements, only the distance of the ureteric orifice from the midline of the bladder was found to correlate with vesicoureteric reflux (mean distance in the reflux group, 10.25 mm +/- 2.40 (standard deviation [SD]); in the nonreflux group, 7.98 mm +/- 2.40 [P = .004]). The authors conclude that the more laterally positioned the ureteric orifice, the more likely it is to reflux. Color Doppler ultrasound measurement of the laterality of the ureteric orifice may be useful for predicting which children with a urinary tract infection would benefit from voiding cystourethrography.

Child↗
PubMed1988

Complex infantile and congenital hip dislocation: assessment with MR imaging.

Twenty-five magnetic resonance hip studies were performed on 19 infants with congenital hip dislocation. These patients had a poor initial treatment response, a teratologic dislocation, or a late presentation. Detailed images of single hips obtained with small surface coils resulted in excellent visualization of all the clinically important soft-tissue and cartilaginous structures of the hip. No other imaging modality demonstrates all of these structures simultaneously.

Acetabulum↗
PubMed1988

Pediatric musculoskeletal magnetic resonance imaging.

MRI has demonstrated clinical applicability and improved diagnostic capability in the musculoskeletal system to a degree rivaling its success in the neurologic system. For certain regions such as the joints, the superficial nature of these structures is ideal for the application of localized radiofrequency coils, enabling considerably improved signal, spatial resolution, and detectable contrast. The multiplanar capability is often invaluable in assessing such regions as the weight-bearing surfaces of the hips. It has been shown to be the most sensitive single test for diagnosing avascular necrosis, and has yielded very high resolution images of the internal architecture of the joints and soft tissues in an entirely noninvasive manner and without the need for the administration of exogenous contrast agents. Short TE images are quite useful in evaluating fatty background regions of interest, such as the bone marrow and subcutaneous tissue, whereas long TR and TE studies are frequently more suitable for soft tissue pathology. The lack of ionizing radiation and the continued failure of intensive research to disclose any deleterious effects at the levels used for clinical diagnostic imaging make this tool especially appealing for application to the pediatric population. With the continual development of new pulsing sequences, contrast agents, and further advances in imaging/spectroscopic correlation, magnetic resonance imaging of the musculoskeletal system is ensured of a solid role in the clinical diagnostic evaluation of the pediatric population.

Bone Diseases↗
PubMed1983

Chitosan: a new hemostatic.

Chitosan is a deacetylated derivative of arthropod chitin. We found that it formed a coagulum in contact with defibrinated blood, heparinized blood, and washed red cells. When knitted DeBakey grafts were treated with chitosan, they were impermeable to blood. Examination of these grafts at 24 hours revealed no rebleeding. Examination at one, two, three, and four months showed the grafts to be encased in smooth muscle with a living endothelial lining and an abundant vasa vasorum. Control grafts showed the usual fibrous healing.

Animals↗
PubMed1981

Respiratory distress in newborn infants: contribution to current mortality.

A review of infants with respiratory distress born at the Mercy Maternity Hospital, Melbourne, during the years from 1975 to 1977 showed that live-born infants totalled 13304; 288 (2.2%) had respiratory distress. Of the 13304 infants, 197 died; 75 (38.1%) were infants with respiratory distress. Hyaline membrane disease was the cause of the respiratory distress in 153 (53.1%) infants; 58 (37.9%) infants with that problem died. Hyaline membrane disease accounted for 58 (77.3%) of the 75 deaths in infants with respiratory distress. Assisted ventilation was required in 147 (51.0%) infants with respiratory distress and chronic complications of its use acceptable as bronchopulmonary dysplasia occurred in only 8.2% and retrolental fibroplasia in only 3.4%; it is suggested that assisted ventilation was commenced too late in 23 (34.0%) infants. Twenty-eight (42.0%) infants with respiratory distress died despite correct usage of assisted ventilation. This number attests to the dangers of prematurity; hence the decision to deliver an infant prematurely should not be taken lightly.

Australia↗
PubMed1981

IgG antibodies to phosphorylcholine exhibit more diversity than their IgM counterparts.

An amino acid sequence analysis of the N-terminal immunoglobulin heavy and light chain variable regions (VH and VL) from 16 hybridoma proteins which bind phosphorylcholine as well as the complete sequence analysis of 9 of these VH regions is presented. There seem to be more VH regions participating in the phosphorylcholine response than can be encoded directly by germ-line VH gene segments. Moreover, the V regions from IgG antibodies are considerably more variable than those from their IgM counterparts. These observations raise the possibility that a somatic mechanism for V region diversification produces greater diversity in IgG than in IgM antibodies.

Amino Acid Sequence↗
PubMed1981

Late objective assessment of venous value surgery.

To evaluate the contribution of an isolated femoral venous value to venous hemodynamics, ten patients (12 limbs) who had undergone femoral valve transposition without saphenous vein stripping or ligation of perforators were followed up for 12 to 18 months after surgery. Ascending and descending venography were performed to document anatomic patency. Dynamic venous pressures and venous refilling times were recorded to evaluate muscle pump function and cutaneous congestion, respectively. Signs of venous hypertension and the need for elastic support were noted. No patient attained normal venous pressure at any time after surgery. Normalization of venous refilling time was transient: nine of 12 limbs had reverted to preoperative abnormal levels at 12 to 18 months and all required elastic support. Femoral value reconstruction performed alone for venous stasis is not sufficient. In postthrombotic venous ulcer, incompetent calf perforators remain a central problem.

Femoral Vein↗
PubMed1981

Recognition and surgical management of patent but hemodynamically failed arterial grafts.

During a five-year period, 34 patients had persistence or recurrence of abnormal hemodynamic measurements in limbs after arterial reconstruction depsite graft patency documented by arteriography. Initial operations included aortofemoral (four), femorofemoral (ten), femoropopliteal (18), and femorotibial (two) bypass. Immediate postoperative hemodynamic failure was documented in seven patients by a mean ankle/brachial systolic pressure index increase of only 0.05 +/- 0.04 following the initial reconstruction. The remaining 27 patients had delayed hemodynamic failure; mean increase in ankle pressure was only 0.06 +/- 0.05 from the preoperative period until time of detection of failure (average duration 2.5 years). In all 34 patients, arteriography demonstrated patency of the initial graft. In conjunction with the vascular laboratory examination, arteriography identified the cause of hemodynamic failure to be inadequate inflow in 10 patients, poor outflow in 16, combined inflow and outflow obstruction in one, and graft stenosis in seven. Unrecognized stenosis in areas proximal (two patients) and distal (three patients) to the bypass emphasized the importance of complete biplanar arteriography before initial operation. Reoperation was successful in correcting hemodynamic failure in 26 patients (76.5%) with a mean increase in ankle index of 0.41 +/- 0.15. Operation was technically not feasible in four patients and was not performed in another four patients because of concomitant medical problems. In two of these patients, progression to graft thrombosis was documented. The results of this study suggest that early objective recognition of an anatomically patent but hemodynamically failed graft is possible by frequent noninvasive testing. Prompt investigation by arteriography defines the cause and location of failure, and reoperation restores normal limb hemodynamics. Most important, reoperation permits salvage of the majority of these patent grafts prior to ultimate failure from thrombosis.

Adult↗
PubMed1981

Assessment of a modified technique of distal splenorenal shunting.

Warren's distal splenorenal shunt has been effective in treatment of recurrent variceal hemorrhage. To simplify the operative procedure, two alterations in the technique were used in this study. The first was to approach the splenic and renal veins simultaneously through a single inframesocolonic retroperitoneal incision in the plane of the pancreatic fusion fossa. The second was abandonment of the portoazygos disconnection. Since 1974, twenty-nine patients have undergone this modified operation. The patients ranged in age from 21 to 76 years. Fourteen patients had alcoholic cirrhosis, 13 had nonalcoholic cirrhosis, and the etiology was unknown in two. There were 14 Child's class A patients, 12 class B, and three class C. Significant ascites was present at operation in seven patients. Hepatofugal flow was demonstrated angiographically in four patients. The follow-up period ranged from 6 months to 6 years; 19 patients were followed up for 1 year or longer. There were three early postoperative deaths (10.3%), and one patient died 2 months postoperatively. Recurrent variceal bleeding was seen early in one patient and late (2 months) in another. Only one of the surviving patients developed encephalopathy. Technical modification to simplify performance of the distal splenorenal shunt did not compromise the results of the operation. However, four of seven patients with ascites died either immediately or early after the procedure, and two of these four patients also had hepatofugal flow. Ascites and hepatofugal flow may adversely influence the results of the operation.

Adult↗