Biomedical subjects

D Lindblom

Publications and source records attributed to D Lindblom.

45 records · Page 3Linked to original sources

PubMed1987

The Björk-Shiley 70 degree convexo-concave prosthesis strut fracture problem (present state of information).

Between June 1980 and June 1983 4028 Björk-Shiley 70 degree convexo-concave prosthetic heart valves were distributed and implanted in Australia, Canada, Europe and South Africa. As of March 1986, a total of 52 outlet strut fractures (1.29%; 70% CL: 1.1%-1.5%) have been reported from 29 implant institutions in 12 countries. The majority (82.7%) occurred in Europe. Intervals between implantation and fracture were 13 days to 45.3 months (mean: 18.4 months; 70% CL: 16.6 months-20.1 months). The mortality rate after strut fracture was 78.7% (70% CL: 72.5%-84.9%). Upon stratification of the fracture by valve sizes and types it becomes evident that 75% (70% CL: 68.8%-81.2%) of all fractures are related to the sizes 29 mm to 33 mm (which virtually represent the same valve size) and predominantly to mitral valves (p less than 0.01). The large valves again have been stratified into two subsets, namely those fabricated from flanges originally machined as Björk-Shiley 60 degree convexo-concave valves (group I) and later produced valves machined initially to 70 degree specifications (group II). In group I the fracture rate was 5.2% (70% CL: 4.2%-6.2%) versus 1.6% (70% CL: 1.1%-2.1%) in group II (p less than 0.01), which identifies the group I 29 mm-33 mm Björk-Shiley 70 degree convexo-concave valves as the highest risk group for strut fracture. The rates are based upon all available information as of March 16, 1986.(ABSTRACT TRUNCATED AT 250 WORDS)

Heart Valve Prosthesis↗

PubMed1987

Three-year clinical results with the Monostrut Björk-Shiley prosthesis.

Between November 1981 and June 1983, 351 patients underwent valve replacement with the Monostrut Björk-Shiley prosthesis. There were 214 aortic valve replacements, 101 mitral valve replacements, and 31 double (aortic and mitral) valve replacements. Four patients had valve implanted in the tricuspid position, and one patient underwent exchange of a valved, extracardiac conduit. Mean age was 61 years (range 2 to 78) and 186 (53%) were male. Concomitant procedures were performed in 52 patients (15%) and 17 (5%) were emergency operations. Early mortality (4.3%) was related to New York Heart Association Functional Class IV, emergency operation, or the presence of a concomitant procedure. Follow-up was 100% and covered 870 patients-years (mean 2.6 years per operative survivor). Postmortem examination was performed in 38 (79%) of the 48 fatalities. Only one patient suffered a sudden, unexplained death. The 3 year survival rate (early mortality excluded) was 88.6% (aortic valve replacement 89.2%, mitral valve replacement 89.3%, and double valve replacement 82.5%). The 3 year freedom from thromboembolism in patients receiving anticoagulants was as follows: aortic valve replacement 97.5%, mitral valve replacement 92.8%, and double valve replacement 100%. There were no instances of valve thrombosis or fatal embolism. In contrast, there were two instances of aortic valve thrombosis among 34 patients having aortic valve replacement without anticoagulation. The 3 year freedom from valve failure (modified Stanford definition) was as follows: aortic valve replacement 96.0%, mitral valve replacement 93.9%, and double valve replacement 89.7%. There were no mechanical failures. In conclusion, the Monostrut Björk-Shiley valve showed a low incidence of complications. There were no mechanical failures, no fatal emboli, and, when anticoagulants were administered, no valve thromboses.

Actuarial Analysis↗

PubMed1986

Characterization and localization of specific oestrogen binding in the human thymus.

Clinical and experimental observations suggest that oestrogens may influence immune reactivity. The oestrogen-binding properties of the human thymus were studied by the use of an aqueous two-phase separation technique. A specific, high-affinity and low-capacity binding was found in 9 out of 10 thymic tissue samples obtained from children and adults of both sexes, their ages ranging from 1 to 42 years. The association constant (+/- SD) for the oestradiol binding in human thymus was 3.7 +/- 1.4 X 10(9) M-1 and was in the same range as the receptor binding in the human uterus. The steroid specificity was found to differ from the classical oestrogen receptor. The concentration of oestrogen-binding sites (+/- SD) was 182 +/- 181 fmol/mg protein and was higher than the receptor concentration of the uterus. According to histochemical analyses the binding is located in the reticulo-epithelial stroma rather than the thymocytes. Data suggest that the human thymus is a target organ for oestrogens which may influence lymphocyte function during therapy.

Adolescent↗

PubMed1986

Mechanical failure of the Björk-Shiley valve. Incidence, clinical presentation, and management.

The experience after implantation of 3,334 Björk-Shiley valves over a 15 year period is described. With a 99.2% follow-up (covering 17,511 patient-years, mean follow-up time 6.3 years) and an autopsy rate of 75% among all fatalities, altogether 19 cases of mechanical failure were documented. There were no mechanical failures among the standard Delrin Björk-Shiley valve (n = 271), the aortic standard Pyrolyte Björk-Shiley (n = 739), or the Monostrut Björk-Shiley valve (n = 377). One of the mitral standard Pyrolyte valves (n = 430) fractured. Among the 1,461 convexo-concave valves, 18 fractured (6/884 with an opening angle of 60 degrees and 12/577 with an opening angle of 70 degrees). The actuarial incidence of mechanical failure at 5 years was 0.6% (with an upper 95% confidence limit of 1.2%) for the 60 degree convexo-concave valve and 2.8% (upper 95% confidence limit of 4.4%) for the 70 degree convexo-concave valve (p less than 0.01). Two groups of valves were especially affected by this complication; the 23 mm aortic 60 degree convexo-concave valve (5 year actuarial incidence 2.2%, upper 95% confidence limit 4.7%) and the 29 to 31 mm mitral 70 degree convexo-concave valve (8.3%, upper 95% confidence limit 14.2%). The hazard function presently indicates a constant (60 degree convexo-concave) or decreasing (70 degree convexo-concave) tendency for mechanical failure. The time interval between the first symptom of mechanical failure and circulatory collapse was significantly (p less than 0.01) shorter after aortic failure than after mitral failure, and no patient with a fractured aortic prosthesis survived long enough to undergo reoperation. The incidence of mechanical failure among patients dying suddenly (but with an autopsy) was 9.6% (95% confidence limits 4.9%-16.6%), and most cases of sudden death were unrelated to the prosthesis. The management of patients with suspected mechanical failure is described. Prophylactic re-replacements are discussed but cannot be generally recommended at present.

Adult↗

PubMed1985

The Monostrut Björk-Shiley heart valve.

To avoid the possibility of a fracture of the welded two-armed outflow strut of the Björk-Shiley heart valve, since 1982 it has been machined from one piece of Haynes 25 in the form of a monostrut valve without welds. Of the first 864 patients with a monostrut Björk-Shiley valve implanted, 268 have now been followed up to 3 years. The clinical findings, as well as absence of hemolysis, excellent hemodynamics even with a narrow aortic root as demonstrated by transseptal cardiac catheterization and excellent functional improvement are reported. No valve thrombosis in patients receiving anticoagulant therapy was observed with valves in either the aortic or the mitral position and there was no case of mechanical failure.

Adolescent↗

PubMed1985

The monostrut strength.

The fatigue endurance limit for Haynes 25 from which the Björk-Shiley (B-S) valve is made is 4900 kg per square centimeter (70000 pounds per square inch). A welded strut may have a variation of fatigue endurance limit from 4900 kg per square centimeter (70000 pounds per square inch) in an incomplete weld with phase segregation. To avoid a weld with this variation, the monostrut has been developed, where the valve is made by electrochemical machining from one piece of Haynes 25. The homogenous outflow monostrut will then have a stable fatigue endurance limit of 4900 kg per square centimeter (70000 pounds per square inch). In a pulse duplicator at a pulse rate of 120 and a peak ventricular pressure of 200 mmHg, the maximum inservice tensile stresses for the 29 mm valve outflow strut do not exceed 700 kg per square centimeter (9800 pounds per square inch). Therefore, a seven times safety limit is present for the monostrut under maximal physiological stress conditions. The struts in the B-S monostrut valve cannot be fractured even under extreme experimental conditions and never under peak physiological conditions.

Equipment Design↗

PubMed1984

Specific binding of 17 beta-estradiol in the human thymus.

Many observations suggest that estrogenic preparations can depress cell-mediated immune reactions. Since cell-mediated immunity is thymus-dependent, the estrogen-binding properties of human and mouse thymus tissue were studied with the use of an aqueous two-phase separation system. A high-affinity and low-capacity estrogen binding was found in human thymus tissue from six prepubertal children of both sexes and two grown women. A similar specific binding was found in the mouse thymus and in the human uterus. The association constant (Ka) for the binding in the human thymus was 16.01 +/- 8.98 X 10(9)M-1. The human uterus, which is known to possess estrogen receptors, had Ka values in the same range. The binding seems to be located in the reticuloepithelial cells of the thymus. Data suggest that the human thymus is a target organ for estrogens, which may influence lymphocyte function during therapy.

Adult↗

PubMed1984

Mechanical heart valves in children.

Longterm follow-up of 17 children, who consecutively underwent replacement of one cardiac valve with the Björk-Shiley prosthesis, is presented. The children's mean age was 8 years (range 4-12 years) and body weight 23.5 kg (range 15.0-38.4 kg) at the time of surgery 1970-80. Nine of the 17 operations (53%) were second-stage cardiac surgery. The operations comprised 2 aortic and 7 mitral valve replacements, 2 implantations of prosthesis in aortoventricular plasties (Konno's operation), 4 in the functional mitral orifice of transpositions (3 congenitally corrected and one operated on a.m. Mustard) and 2 valved conduits included in the repair of complex malformations. Two deaths were associated with surgery, but were not related to the valve prosthesis per se. One patient died 37 months postoperatively, due to mechanical valve failure (early and late mortality 12% and 6%, respectively). All survivors were followed at least two years, 9 were followed at least 5 years and 6 at least 10 years (mean 7.7 years). Anticoagulation was maintained without pertinent problems. There was one thromboembolic episode (0.87%/patient year). Two patients were reoperated because of "outgrown prosthesis" after 8 and 11 1/2 years. Morbidity otherwise was low and 9 patients (53%) had no complications at all. We conclude that the mechanical valve is a suitable substitute for a seriously diseased cardiac valve in childhood. However, if valve replacement is performed in early life, the later need of exchange of the outgrown prosthesis must be faced.

Age Factors↗

PubMed1977

75Se-Selenite scrintigraphy in the clinical staging of malignant lymphomas.

The value of 75Se-selenite scintigraphy in clinical staging was investigated in 45 patients with Hodgkin's disease and in 28 patients with non-Hodgkin's lymphoma. Of these, 9 patients had recurrence of previously treated lymphomas. The scintigraphic results were compared with clinical, cytologic, histologic and radiographic findings in different anatomic regions. 75Se-selenite scintigraphy resulted in 6 to 20 per cent false negative findings, 15 to 43 per cent false positive and 12 to 20 per cent equivocal evaluations, the accuracy being least in the abdominal region. The relatively high rediation dose delivered by 75Se-selenite, furthermore, makes it less attractive for use in the primary diagnosis of malignant lymphomas.

Abdomen↗