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Biomedical subjects

D Silver

Publications and source records attributed to D Silver.

At least 19 recordsLinked to original sources
PubMed1992

Helical model of nucleation and propagation to account for the growth of type I collagen fibrils from symmetrical pointed tips: a special example of self-assembly of rod-like monomers.

A model was developed to account for the recent observations indicating that type I collagen fibrils assembled in vivo grow from symmetrical pointed tips. The essential features of the model are (i) a distinctive structural nucleus forms at each end of a growing fibril and growth of the fibril then proceeds by propagation of the two structural nuclei, (ii) the two structural nuclei have similar spiral or helical conformations, and (iii) assembly of each structural nucleus requires two kinds of specific binding steps defined as 3.4 D-period and 0.4 D-period overlaps, but propagation of the nucleus requires only the 3.4 D-period binding step.

Collagen↗
PubMed1992

Heparin-induced thrombocytopenia in open heart surgical patients: sequelae of late recognition.

Most patients undergoing open heart operations have had exposure to heparin for diagnostic and/or therapeutic procedures. Heparin antibody formation and heparin-induced thrombocytopenia with repeat heparin administration can cause high morbidity and mortality from thrombotic complications, especially when delay in diagnosis occurs. From 1981 to 1991, heparin-induced thrombocytopenia was diagnosed in 82 of 4,261 open heart surgical patients (1.9%). Platelet counts less than 100 x 10(9)/L (100,000/microL) or new or recurring thrombotic events prompted suspicion of heparin-induced thrombocytopenia. Heparin-dependent antibody was diagnosed preoperatively in 12 patients (group I) and postoperatively in 70 patients (group II). Heparin was not given postoperatively in group I patients, and complications in this group were limited to bleeding in 3 patients. There were no thromboembolic events and all patients survived. Group II patients had late recognition of heparin-dependent antibody postoperatively, and heparin exposure was continued for varying periods postoperatively. Thirty-seven group II patients (53%) had bleeding complications and 31 (44%) had thromboembolic complications. These complications led to death in 23 group II patients (33%). Heparin-dependent antibody may occur in patients having open heart operations and is a major cause of morbidity and mortality if not diagnosed early with cessation of heparin therapy.

Acute Kidney Injury↗
PubMed1992

Heparin-induced thrombocytopenia in the newborn.

This pilot study was initiated to determine whether heparin-induced thrombocytopenia occurs in the newborn and whether thromboembolic complications in the newborn could be related to heparin-induced thrombocytopenia. Thirty-four infants in whom thrombocytopenia (less than 70,000/mm3) (n = 23), precipitous (30% to 50%) fall in platelet count (n = 5), or thromboses (n = 6) developed while they were receiving heparin were studied. Heparin-associated antiplatelet antibodies were demonstrated in 14 infants by platelet aggregation testing. The average gestational age (29 +/- 6 weeks); birth weight (1300 +/- 945 gm); and platelet count at birth (234,000/mm3 +/- 111,000/mm3) of these 14 infants did not differ statistically from the 20 infants without heparin-associated antiplatelet antibodies. An umbilical artery catheter was inserted in all infants except a single patient from each group. Aortic thrombosis was documented by abdominal ultrasonography in 11 of 13 (85%) infants with heparin-associated antiplatelet antibodies. One patient died with a midgut volvulus before the aorta could be examined. Five aortic thromboses were detected in the 20 infants without heparin-associated antiplatelet antibodies. Bleeding was not associated with the heparin-induced thrombocytopenia. One patient with previously demonstrated thrombocytopenia and heparin-associated antiplatelet antibodies had recurrent thrombocytopenia when reexposed to heparin; her platelet count recovered after heparin withdrawal. Thus heparin-induced thrombocytopenia does occur in preterm and term infants receiving heparin and is associated with arterial thromboses. Therefore infants receiving any form or amount of heparin must be carefully monitored for heparin-induced thrombocytopenia.1+

Autoantibodies↗
PubMed1992

Axillopopliteal bypass for limb salvage.

Forty-one axillopopliteal bypass grafts have been placed in 30 patients for limb salvage in the past 12 years. The mean patient age was 65.6 years; 8 were women; 19 smoked; and six had diabetes. Sixteen grafts were straight axillopopliteal bypass grafts, and 25 were sequential axillopopliteal bypass grafts. Cumulative life-table primary patency rates at 1, 2, and 3 years were 70%, 56%, and 43%, respectively; secondary patency rates were 73%, 57%, and 50%, respectively. Corresponding limb salvage rates were 86%, 69%, and 69%, respectively. Ringed polytetrafluoroethylene (PTFE) graft patency at 3 years was 61% versus 40% for unsupported PTFE grafts (p = 0.35). Ringed PTFE axillofemoral grafts with sequential femoropopliteal saphenous vein grafts had a 3-year patency of 67%. Graft patency was restored in 25% of occluded grafts by thrombectomy and in 80% of occluded grafts by thrombectomy with graft revision (p = 0.21). Cumulative 3-year patient survival was 48%. The 30-day operative mortality rate was 20%; patients operated on for graft infection had a 30-day operative mortality rate of 36%. The data support the use of axillopopliteal bypass for limb salvage when standard revascularization techniques are contraindicated. Long-term patency is enhanced by use of externally supported PTFE and sequential femoropopliteal saphenous vein.

Aged↗
PubMed1991

An overview of venous thromboembolism prophylaxis.

This symposium reviewed the risk factors and problems associated with venous thromboembolism in surgical patients, especially those patients having total hip replacement. The importance of venous thromboembolism prophylaxis was emphasized by a theoretical analysis indicating that venous thromboembolism in patients having hip replacement not only saves lives but is also effective. A discussion of the pharmacology of low-molecular-weight heparin (LMWH) included a review of its role, clinically and experimentally, in venous thromboembolism prophylaxis. Three of the discussants presented their favorable experiences with LMWH in reducing the incidence of venous thromboembolism in patients having hip replacement. It can be concluded that LMWH does reduce the incidence of venous thromboembolism in patients having hip replacement without causing an increase in blood loss. If its effectiveness and safety remain substantiated, LMWH may soon become the preferred agent for venous thromboembolism prophylaxis.

Humans↗
PubMed1991

Mood variability in adolescents: a study of depressed, nondepressed and comorbid patients.

In a study to examine the variability of mood in psychiatrically disturbed adolescents, 30 inpatients aged 13-17 reported on current depressive symptoms three times a day for seven consecutive days, using a set of visual analog scales (the Adolescent Mood Scale: AMS) to record DSM-IIIR and other depressive symptoms. Ten of the patients had no depressive diagnosis; 11 had both a depressive and an 'externalizing' diagnosis (mainly conduct disorders and substance abuse disorders), and nine had depressive diagnoses but no externalizing disorder. Variability was defined in terms of (1) range of AMS scores; (2) amount of change from one test point to the next; (3) rhythmicity, measured by the autocorrelation function across 21 test points. All three groups had high levels of depressive symptoms throughout the week. On all measures of severity of depression, the depressed girls were more depressed than the depressed boys, irrespective of comorbidity. Measures of variability, however, showed no effect of sex, but comorbid patients were more likely to have a wide range of mood scores, and reported a 45% greater amount of mood change. Only five subjects had a significant lag1 autocorrelation function, and there was no indication of diurnal rhythmicity. Implications for research and diagnosis are discussed.

Adolescent↗
PubMed1991

Recovery of neuromuscular function during reperfusion of the ischemic extremity: effect of mannitol and superoxide dismutase.

The ability of mannitol and superoxide dismutase (SOD) to improve the recovery of peripheral nerve and skeletal muscle function and to influence metabolism during reperfusion after 4 hours of complete ischemia was investigated in an autoperfused canine hind-limb model. Study groups included control subjects (n = 7), subjects given 5000 units/kg of SOD intra-arterial bolus immediately before reperfusion and 10,000 units/kg infusion during first hour of reperfusion (n = 7), and subjects given 150 mg/kg isosmolar mannitol intra-arterial bolus before reperfusion and 1 gm/kg intravenous infusion during the first hour of reperfusion. Function was evaluated by determining isometric twitch and tetanic contractile force of paw dorsiflexion by stimulating the peroneal nerve or the anterior tibial muscle. Metabolic responses (oxygen consumption and lactate clearance) and blood flow were not influenced by either treatment protocol. However, mannitol significantly reduced muscle damage and significantly improved neuromuscular contractile function compared to control and SOD treatment regimens.

Analysis of Variance↗
PubMed1991

Complete external iliac artery disruption after percutaneous aortic valvuloplasty in two young children: successful repair with hypogastric artery transposition.

The majority of vascular injuries in young children are iatrogenic. This is a report of two complete external iliac artery disruptions occurring during percutaneous transfemoral balloon aortic valvuloplasty in a 2-year-old and a 5-year-old child. The damaged external iliac artery was bypassed by extensively mobilizing the hypogastric surgery and rotating it upward to anastomose it to the proximal common femoral artery. Normal limb pulses, function, and growth were noted in follow-up.

Anastomosis, Surgical↗
PubMed1990

Children's understanding of private keys in referential communication.

A private key is a referential utterance used to inform selectively. The ambiguity of the utterance conceals meaning from nonselected audience members. The purpose of this study was to examine three aspects of children's understanding of the use of private keys. Experiment 1 concerned children's sensitivity to information in the context of utterance (i.e., the common ground). Experiment 2 examined appreciation of audience design and the speaker's intent. Experiments 3, 4, and 5 explored some reasons for children's problems in understanding private keys. The results show that even first graders are sensitive to common ground information and the speaker's intent. However, audience design is troublesome even for second graders in some situations, probably because they fail to assess the knowledge of the audience members. Private keys are important theoretically because they represent an aspect of referential communication involving the uses of ambiguous utterances that have been ignored by developmental researchers.

Attention↗
PubMed1990

The relation between item identification difficulty and elaborative conceptual processing for children and adults.

The four experiments concerned the relation between the difficulty of item identification processes, elaborative conceptual processing, and developmental differences in cued recall. Elaborative conceptual processing was manipulated by asking related ("How many are related?"), category ("How many are vehicles?"), and analytic ("How many usually carry freight?") orienting questions about four-word stimuli in which the words were categorically related (Bus-Airplane-Car-Train). The measures of elaborative processing were the speed and accuracy of question answers. Cued recall for the targets (Train) was assessed for one-word (Bus) or two-word (Bus-Airplane) cues, which were varied to determine if elaborative processing affected cue discriminability or constructability, or both. The difficulty of item identification was varied in several ways. In Experiment 1, the graphemic information was degraded in the acquisition stimuli, or the retrieval cues, or the stimulus words were intact. In Experiments 2 and 3, acquisition presentation time was varied and the stimuli were read by the experimenter or the subject. Experiment 4 featured pictures to determine generalizability. The results showed that elaborative conceptual processing facilitates recall. Most important, item identification processes limit elaborative conceptual processing for both words and pictures, and more for children than for college students.

Adolescent↗
PubMed1990

Heparin-induced thrombocytopenia in patients who undergo open heart surgery.

To determine whether heparin-dependent antiplatelet antibodies (HAAb) have an effect on morbidity and/or mortality rates, we reviewed the cases of 3438 patients who underwent open heart surgery from 1981 to 1989. Forty-six patients (1.3%) had HAAb. The patients were divided into two groups: those patients who were known to have HAAb before surgery (group I) and those patients who were diagnosed with HAAb after surgery (group II). Group I patients (n = 5) were pretreated with platelet-inhibiting drugs before reexposure to heparin during cardiopulmonary bypass and were maintained with strict abstinence from heparin afterward. Their lowest observed platelet counts ranged from 42,000/mm3 to 89,000/mm3 (median, 63,00/mm3). Thromboembolic complications did not occur, and all patients survived. Group II patients (n = 41) who were diagnosed to have HAAb after surgery had not been pretreated with platelet-inhibiting drugs before surgery. Lowest platelet counts ranged from 11,000/mm3 to 128,000/mm3 (median, 42,000/mm3). Bleeding complications occurred in 21 patients (51%), and thromboembolic complications occurred in 13 patients (32%). Hospital mortality in group II patients was 37%. Late recognition of HAAb was associated with an increase in morbidity and mortality rates. Thromboembolic complications of HAAb, which had been diagnosed before surgery, were eliminated, and bleeding was reduced by pretreatment with platelet-inhibiting drugs and strict abstinence from heparin after surgery.

Acute Kidney Injury↗
PubMed1990

Concept availability in the causal inferences of children and adults.

What supplies the concepts in causal inferences in story comprehension? This question was examined in 5 experiments. Elementary school children and college students listened to stories containing a "premise" sentence describing a character's intent in initiating a series of actions, followed by an unexpected "outcome." After each story, the subjects were asked inference questions about the reason for the outcome (Experiments 1-4) or asked to explain the outcome (Experiment 5). In the various experiments, the availability of object concepts for an inference was manipulated by providing 0 or 2 clues preceding the outcome, additional filler information that diluted the clue information, a mention of an object in the premise or no mention, and an object title for each story or no title. The results suggested that the availability of an object concept in sentences prior to the outcome was a critical determinant of whether an object inference occurred, especially for children. Given availability, the thematic prominence of the object influences whether the object will be used in an inference.

Adolescent↗
PubMed1989

Reexposure to heparin of patients with heparin-associated antibodies.

Four patients with heparin-associated antiplatelet antibodies who were not receiving platelet function-inhibiting agents received heparin during surgery, angiography, or hemodialysis. Three of the four patients had complications that were attributed to heparin-induced platelet aggregation. The complications included a superficial femoral artery thrombosis, a thrombotic stroke after a carotid endarterectomy, and recurring thrombosis of a graft inserted for dialysis. Nine patients received aspirin (325 mg b.i.d.) or dipyridamole (Persantine) (200 to 300 mg daily) before reexposure to 5000 to 12,000 units of heparin during 11 vascular procedures. The procedures included two carotid endarterectomies, three aortofemoral bypasses, one femoropopliteal bypass, two femorotibial in situ saphenous vein bypasses, one iliofemoral thrombectomy, one bilateral iliac artery angioplasty, and one axillobifemoral bypass. Platelet counts averaged 173,000/mm3 before heparin reexposure, fell to an average of 86,000/mm3 within 24 hours of heparin reexposure, and returned to normal within 48 hours after the reexposure. None of these patients had a thromboembolic or hemorrhagic complication. Patients with heparin-associated antiplatelet antibodies are at risk for developing thrombocytopenia and thromboembolic complications on reexposure to heparin. The platelet function-inhibiting agents, aspirin and Persantine, protect the patients from the thromboembolic complications but not the thrombocytopenia associated with limited heparin reexposure.

Angiography↗
PubMed1989

Transaxillary or supraclavicular decompression for the thoracic outlet syndrome. A comparison of the risks and benefits.

The difficult exposure with the transaxillary resection of the first rib (TAR) prompted an analysis of the TAR versus the supraclavicular approach (SCR) for decompressing the thoracic outlet in patients with thoracic outlet syndrome (TOS). Thirty-seven patients underwent 30 TAR and 15 underwent SCR for TOS. The operating time was similar for the two groups. Mean blood loss was 61 cc for the SCR group and 218 cc for the TAR group. There was one complication in the SCR group, a urinary tract infection, whereas the TAR group had 21 complications including pneumothorax (13), laceration of subclavian vessel (3), winged scapula (3), pleural effusion (1), and wound infection (1). Postoperative hospitalization averaged 3 and 5 days, respectively, for the SCR and TAR patients. All SCR patients and all but one TAR patient were improved or asymptomatic immediately postoperatively. Ninety-three per cent and 81 per cent, respectively, of SCR and TAR patients were improved at 2 months, whereas 100 per cent and 83 per cent, respectively, remained improved at a mean follow-up of 3 years. The significantly fewer complications, decreased blood loss and shorter postoperative hospitalization, noted in the SCR patients supports this approach as the preferred form of management for TOS.

Adult↗
PubMed1989

Thrombocytopenia associated with heparin-coated catheters in patients with heparin-associated antiplatelet antibodies.

Thrombocytopenia was associated with the presence of heparin-coated pulmonary artery catheters in 12 patients with heparin-associated antiplatelet antibodies. The thrombocytopenia persisted so long as the heparin-coated catheters were in place, even when all other sources of heparin were discontinued. The high morbidity and mortality associated with heparin-induced thrombocytopenia mandates that heparin administration cease and that all heparin-coated catheters be removed from patients with heparin-associated antiplatelet antibodies.

Aged↗