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Biomedical subjects

S E White

Publications and source records attributed to S E White.

At least 19 recordsLinked to original sources
PubMed1999

Knee stability in meniscal bearing total knee arthroplasty.

The effect of a meniscal bearing on knee laxity in anterior cruciate ligament-sacrificing total knee arthroplasty was evaluated in 7 cadaver knees using a knee testing device that measured knee flexion angle as well as laxity to medial-lateral, anterior-posterior [AP], and rotational loads. A standard fixed tibial component and mobile tibial components (AP sliding, rotationally sliding, and AP and rotationally sliding) were used to evaluate AP, rotational, and varus-valgus stability and maximal flexion and extension with the neutrally positioned and malrotated tibial tray. The AP movable components increased AP laxity, and the fixed component decreased rotational laxity significantly when compared with the normal knees. The rotationally movable components did not change knee laxities significantly even when the tibial tray was malrotated. No significant difference among the components was detected when the maximal flexion and extension angles were compared in the neutrally positioned tibial tray. Malrotation of the tibial tray decreased the maximal extension angle in the fixed component. This study showed that the rotationally movable component can achieve near-normal laxity regardless of tibial tray rotation, but AP mobility of the bearing produces AP laxity that could lead to implant failure.

Adult↗
PubMed1999

The molecular evolution of terminal ear1, a regulatory gene in the genus Zea.

Nucleotide diversity in the terminal ear1 (te1) gene, a regulatory locus hypothesized to be involved in the morphological evolution of maize (Zea mays ssp. mays), was investigated for evidence of past selection. Nucleotide polymorphism in a 1.4-kb region of te1 was analyzed for a sample of 26 sequences isolated from 12 maize lines, five populations of the maize progenitor, Z. mays ssp. parviglumis, six other Zea populations, and two Tripsacum species. Although nucleotide diversity in te1 in maize is reduced relative to ssp. parviglumis, phylogenetic and statistical analyses of the pattern of polymorphism among these sequences provided no evidence of past selection, indicating that the region of the gene studied was probably not involved in maize evolution. The level of reduction in genetic diversity in te1 in maize relative to its progenitor is comparable to that found in previous reports for isozymes and other neutrally evolving maize genes and is consistent with a genome-wide reduction of genetic diversity resulting from a domestication bottleneck. An estimate of the age (1.2-1.4 million yr) of the maize gene pool based on te1 is roughly consistent with previous estimates based on other neutral genes, but may be biased by the apparently slow synonymous substitution rate at te1.

Base Sequence↗
PubMed1999

Altered fetal cardiovascular responses to prolonged hypoxia after sinoaortic denervation.

This study examines the role of the peripheral chemoreceptors in mediating fetal cardiovascular responses to prolonged hypoxia secondary to reduced uterine blood flow (RUBF). Fetal sheep were chronically instrumented for continuous heart rate (FHR), blood pressure (FBP), and carotid blood flow (CBF) measurements after bilateral sectioning of the carotid sinus and vagus nerves (denervated, n = 7) or sham denervation (intact, n = 7). Four days postoperatively, uterine blood flow was mechanically restricted, reducing fetal arterial oxygen saturation by 47.3% (P < 0.01). An initial bradycardia was observed in intact (184.0 +/- 10.7 to 160.5 +/- 10.7 beats/min, not significant) but not denervated fetuses, followed by a tachycardia (180.0 +/- 2.2 to 193.7 +/- 2.7 beats/min, P < 0.05). FHR increased in denervated fetuses (175.5 +/- 8.7 to 203. 0 +/- 17.9 beats/min, P < 0.05). FBP increased transiently in intact fetuses from 45.1 +/- 1.0 to 55.4 +/- 3.0 mmHg at 2 h (P < 0.01), whereas denervated fetuses demonstrated a decrease in FBP from 47.1 +/- 4.2 to 37.2 +/- 3.7 mmHg (not significant). CBF increased (P < 0. 05) in both intact and denervated fetuses from 39.3 +/- 2.8 and 29.7 +/- 3.8 ml. min-1. kg-1 to 47.7 +/- 0.4 and 39.1 +/- 0.3 ml. min-1. kg-1, respectively, whereas carotid vascular resistance decreased only in denervated fetuses (1.7 +/- 0.1 to 1.1 +/- 0.02 mmHg. ml-1. min. kg-1, P < 0.05). We conclude that the peripheral chemoreceptors play an important role in mediating fetal cardiovascular responses to prolonged RUBF.

Animals↗
PubMed1999

Increased cerebral extracellular adenosine and decreased PGE2 during ethanol-induced inhibition of FBM.

Adenosine and PGE2 are neuromodulators, both of which inhibit fetal breathing movements (FBM). Although circulating PGE2 has been implicated as a mediator of ethanol-induced inhibition of FBM in the late-gestation ovine fetus, a role for adenosine has not been examined. The objective of this study was to determine the effect of maternal ethanol infusion on ovine fetal cerebral extracellular fluid adenosine and PGE2 concentrations by using in utero microdialysis and to relate any changes to ethanol-induced inhibition of FBM. Dialysate samples were obtained from the fetal parietal cortex over 70 h after surgery to determine steady-state extracellular fluid adenosine and PGE2 concentrations. On each of postoperative days 3 and 4, after a 2-h baseline period, ewes received a 1-h infusion of ethanol (1 g/kg maternal body wt) or an equivalent volume of saline, and the fetus was monitored for a further 11 h with 30-min dialysate samples collected throughout. Immediately after surgery, dialysate PGE2 and adenosine concentrations were 3.7 +/- 0.7 and 296 +/- 127 nM, respectively. PGE2 did not change over the 70 h, whereas adenosine decreased to 59 +/- 14 nM (P < 0.05) at 4 h and then remained unchanged. Ethanol decreased dialysate PGE2 concentration for 2 h (3.3 +/- 0.3 to 1.9 +/- 0.4 nM; P < 0.05) and increased adenosine concentration for 6 h (87 +/- 13 to a maximum of 252 +/- 59 nM, P < 0.05). Ethanol decreased FBM incidence from 47 +/- 7 to 16 +/- 5% (P < 0.01) for 8 h. Saline infusion did not change dialysate adenosine or PGE2 concentrations or FBM incidence. These data are consistent with the hypothesis that fetal cerebral adenosine, and not PGE2, is the primary mediator of ethanol-induced inhibition of FBM at 123 days of gestation in sheep.

Adenosine↗
PubMed1999

The adenosine A(1)-receptor antagonist 8-CPT reverses ethanol-induced inhibition of fetal breathing movements.

Administration of either ethanol or adenosine inhibits fetal breathing movements (FBM), eye movements, and low-voltage electrocortical activity (LV ECoG). The concentration of adenosine in ovine fetal cerebral extracellular fluid increases during ethanol-induced inhibition of FBM. The purpose of this study was to determine the effect of a selective adenosine A(1)-receptor antagonist, 8-cyclopentyltheophylline (8-CPT) on the incidence of FBM during ethanol exposure. After a 2-h control period, seven pregnant ewes received a 1-h intravenous infusion of ethanol (1 g/kg maternal body wt), followed 1 h later by a 2-h fetal intravenous infusion of either 8-CPT (3.78 +/- 0.08 microg. kg(-1). min(-1)) or vehicle. Ethanol reduced the incidence of FBM from 44.0 +/- 10.4 to 2.7 +/- 1.3% (P < 0.05) and 51.2 +/- 7.6 to 11.9 +/- 5.0% (P < 0.05) in fetuses destined to receive 8-CPT or vehicle, respectively. In the vehicle group, FBM remained suppressed for 7 h. In contrast, during the first hour of 8-CPT infusion, FBM returned to baseline (31 +/- 11%) and was not different from control throughout the rest of the experiment. Ethanol also decreased the incidence of both low-voltage electrocortical activity and eye movements, but there were no differences in the incidences of these behavioral parameters between the 8-CPT and vehicle groups throughout the experiment. These data are consistent with the hypothesis that adenosine, acting via A(1) receptors, may play a role in the mechanism of ethanol-induced inhibition of FBM.

Animals↗
PubMed1999

The effect of varus tilt on contact stresses in total knee arthroplasty: a biomechanical study.

The contact stress produced in the tibiofemoral joint from a varus-tilted tibial component was tested in five total knee prostheses. Peak and mean stresses were measured with a digital electronic sensor under compressive load at 15 degrees and 90 degrees flexion. Stresses were measured with the tibial component tilted 0 degrees and 5 degrees in the mediolateral direction. At a 5 degree tilt, the Advantim, the Miller-Galante II, and the Omnifit prostheses, which have a flat configuration on the femoral and tibial surfaces in the coronal plane, had significantly greater stresses than the LCS and the Profix prostheses, which have tibial and femoral components with matching curved surfaces in the coronal plane. These results suggest that the femoral component surface should have a radius of curvature that matches that of the tibial articular surface in the coronal plane to achieve a large contact area even in varus-valgus tilting.

Arthroplasty, Replacement, Knee↗
PubMed1999

Evaluation of tibial component fixation in specimens retrieved at autopsy.

Fixation of the tibial component was evaluated in eight knees retrieved at autopsy by comparing their radiographs with measurements of micromovement between the component and the tibial plateau. Micromovement in the one cemented Miller-Galante and seven cementless Ortholoc components, which had been implanted for a range of 3 days to 57 months, was measured with linearly variable differential transducers under anteroposterior shear and axial compressive loads. Micromovement between the tibial component and the screws and between the tibial component and the bone after the screws were removed also was measured in the cementless specimens. Minimal micromovement in most of the implants suggests that the tibial components were well fixed. Micromovement between the tibial tray and the screws also was minimal in the cementless components. Removing the screws did not significantly affect micromovement, except in the specimen retrieved 3 days after surgery and in the specimen with a complete radiolucent line under the component. The cementless tibial components fixed with screws, pegs, and stem were as stable as the component secured with cement. Partial radiolucencies were not associated with greater micromotion than that of bone ingrown areas, but the component with complete radiolucency did have greater micromotion than that of all of the other specimens.

Biomechanical Phenomena↗
PubMed1998

Contact stress analysis in meniscal bearing total knee arthroplasty.

The effect of a mobile meniscal bearing on tibiofemoral contact stress was tested with a standard fixed tibial component and with movable tibial components (anteroposterior sliding, rotationally sliding, and anteroposterior and rotationally sliding). A digital electronic sensor was used to detect tibiofemoral contact location in five cadaver knees, then the location was reproduced while peak and mean stresses were measured under compressive load at 0 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion. Stresses were measured when the tibial component was normally aligned and at 15 degrees internal and 15 degrees external rotation. To evaluate the effect of excessive overhang of the polyethylene articular surface, undersurface stress of the rotationally sliding component was also measured with a 30 degrees and a 45 degrees malrotated tibial tray. Uppersurface stresses of the fixed-bearing components were significantly higher at full extension than those recorded in components with rotational mobility. Undersurface stresses were always lower than uppersurface stresses, but correlated with uppersurface stresses. Undersurface stresses of the rotationally sliding component gradually increased as the malrotation angle of the tray increased. A mobile meniscal bearing surface appears to offer an advantage over a standard fixed component when rotational malalignment of the tibial component occurs. However, with severe rotational malalignment, edge contact markedly increases undersurface stresses, which could cause deformity and subluxation.

Adult↗
PubMed1998

Multivariate prediction of skeletal Class II growth.

Prediction of craniofacial growth is one of the keys to successful orthodontic treatment and stability. Despite numerous attempts at growth forecasting, our ability to accurately predict growth is limited. The present study outlines a possible new approach to prediction of craniofacial growth that differs from any previous attempt because of both the methods used and type of patients studied. The purpose of this study is to create and test prediction equations for forecasting favorable or unfavorable patterns of growth in skeletal Class II preadolescents. The subjects for this study include 19 females and 12 males from the Bolton growth center in Cleveland, Ohio. The patients were all untreated orthodontically, had lateral cephalometric headfilms taken biannually from the ages of 6 through 18 and had a Class II skeletal relationship at age 8. Twenty-six skeletal and dental landmarks were identified and digitized, and 48 linear, angular, and proportional measurements were calculated. The subjects were divided into two groups based on anterior-posterior changes in the relationship between the maxilla and mandible. Eleven patients were in the favorable growth group, with an average improvement of 4.13 degrees in the ANB angle; 20 patients were in the unfavorable growth group with an average increase of 0.16 degrees in the ANB angle. The following prediction formula was created with Bayes theorem and assuming a multivariate Gaussian distribution: P(Good¿Fn) = ke (-(0.5)) ¿Fn - mu(ng)¿sigma(g)(-1)¿Fn - mu(ng)¿T. The equation's sensitivity and specificity was calculated from serial cephalometric data from ages 6, 8, 10, and 12. The results obtained with this equation indicate 82.2% sensitivity, 95% specificity with a overall positive predictive value of 91%. This corresponds to 17.8% of patients being incorrectly identified as Poor Growers and only 5% of our patients were incorrectly identified as Good Growers. We conclude that this prediction formula improves the ability to predict favorable or unfavorable patterns of growth in this sample of skeletal Class II preadolescents.

Adolescent↗
PubMed1998

Effect of partial release of the posterior cruciate ligament in total knee arthroplasty.

Appropriate tension of the posterior cruciate ligament, which often is tight in deep flexion, is difficult to achieve after posterior cruciate ligament retaining total knee arthroplasty. Kinematics and maximum flexion after partial release of the posterior cruciate ligament were evaluated in this study. A partial release improved the maximum flexion angle and maintained anteroposterior stability without causing undesirable changes in kinematics, whereas full resection of the posterior cruciate ligament caused unfavorable anteroposterior instability. Partial posterior cruciate ligament release eliminated excessive rollback movement caused by a tight posterior cruciate ligament and also shifted the point of articular surface contact anteriorly. These results indicate that partial release of the posterior cruciate ligament may improve knee function in patients with a tight posterior cruciate ligament after total knee arthroplasty.

Arthroplasty↗
PubMed1998

Prostaglandin E2 inhibition of fetal breathing movements is not sustained during prolonged reduced uterine blood flow in sheep.

Fetal breathing movements (FBM) are inhibited by both exogenous prostaglandin E2 (PGE2) and ethanol in sheep. Maternal ethanol exposure in late-gestation sheep also increases fetal [PGE2]. However, during prolonged reduced uterine blood flow (RUBF) when [PGE2] in fetal plasma is already elevated, FBM are not inhibited by ethanol. These experiments were designed, therefore, to test the hypothesis that the FBM response to PGE2 is also diminished during RUBF. PGE2 (594+/-19 ng.min(-1).kg(-1) fetal body weight) was infused for 6 h into the jugular vein of RUBF (PO2 = 14+/-1 mmHg (1 mmHg = 133.3 Pa); n = 7) and control (PO2 = 22+/-1 mmHg (p < 0.01); n = 7) ovine fetuses, and the effect on FBM, electrocortical (ECoG), and electroocular activities was determined. The infusion of PGE2 increased plasma [PGE2] from 881+/-162 to 1189+/-114 pg.mL(-1) in RUBF fetuses and from 334+/-72 to 616+/-118 pg.mL(-1) (p < 0.05) in control fetuses. FBM were initially inhibited by PGE2 from 22.5+/-9.4 and 17.9+/-6.5% of the time to 6.9+/-2.4 and 0.5+/-0.4% (p < 0.01) in RUBF and control fetuses, respectively. FBM remained inhibited in control fetuses throughout the infusion but returned to baseline incidence in RUBF fetuses in the last 2 h of the infusion. These results are consistent with the hypothesis that one component of the adaptative mechanisms of the fetus to prolonged RUBF is an altered response of FBM to exogenous PGE2. We speculate that the lack of a sustained inhibition in FBM during RUBF with infusion of PGE2 may be a result of an alteration in brainstem receptor function or number or local PGE2 removal.

Animals↗
PubMed1998

Fetal endocrine responses to prolonged reduced uterine blood flow are altered following bilateral sectioning of the carotid sinus and vagus nerves.

The present study examines the effect of carotid sinus/vagosympathetic denervation on fetal endocrine responses to prolonged reduced uterine blood flow (RUBF). Fetal sheep had vascular catheters inserted following bilateral sectioning of the carotid sinus and vagus nerves (denervated, n = 7) or sham denervation (intact, n = 7). Uterine blood flow was mechanically restricted at 126.1 +/- 0.7 days (mean +/- S.E.M.) for 24 h, decreasing arterial oxygen saturation by 47.3 +/- 2.6% (P < 0.01). Fetal plasma samples were obtained at -1, 3, 6, 12 and 24 h for subsequent analyses of arginine vasopressin (AVP), angiotensin II and catecholamines. The AVP response to prolonged RUBF was markedly attenuated in denervated fetuses (15.6 +/- 3.6 to 34.9 +/- 6.0 pg/ml) when compared with intact (10.0 +/- 1.4 to 127.3 +/- 28.4 pg/ml). In contrast, intact fetuses demonstrated no change in plasma angiotensin II concentrations with RUBF whereas denervated fetuses demonstrated a marked increase from 47.5 +/- 18.9 to 128.7 +/- 34.2 pg/ml. The norepinephrine and epinephrine responses to prolonged RUBF were attenuated in denervated fetuses (950.1 +/- 308.9 and 155.8 +/- 58.5 to 1268.3 +/- 474.6 and 290.6 +/- 160.2 pg/ml respectively) when compared with intact (1558.3 +/- 384.4 and 547.3 +/- 304.7 pg/ml to 3289.2 +/- 1219.8 and 896.8 +/- 467.8 pg/ml respectively). These results support a role for the peripheral chemoreceptors in mediating fetal endocrine responses to prolonged RUBF, which may in part lead to the altered cardiovascular responses observed in denervated fetuses under these conditions.

Angiotensin II↗
PubMed1997

Failure of magnesium sulfate infusion to inhibit uterine activity in pregnant sheep.

OBJECTIVES: Our purpose was to determine the effect of magnesium sulfate infusion on nonlabor uterine contractures and corticotropin-induced preterm uterine contractions in pregnant sheep. STUDY DESIGN: Fetal and maternal vascular catheters and uterine electromyographic electrodes were surgically placed in 15 pregnant sheep between 118 and 125 days' gestation. After 3 to 5 days of recovery, magnesium sulfate was infused into 7 ewes with a 0.11 gm/kg bolus over 20 minutes, followed by 0.08 gm/kg/hr. In 8 animals labor was induced with use of an intrafetal corticotropin infusion, after which 4 ewes received magnesium sulfate and 4 received saline solution. Continuous recordings of uterine electromyographic activity, amniotic pressure, fetal heart rate, blood pressure, and tracheal pressure were made. Maternal and fetal magnesium, calcium, albumin concentrations, and blood gases were determined before and during the infusion. RESULTS: Maternal magnesium concentrations increased from an average of 0.94 +/- 0.03 mmol/L to 2.73 +/- 0.1 mmol/L at the end of the bolus, remaining elevated (2.44 +/- 0.17 mmol/L) for 8 hours. Fetal magnesium concentrations (0.89 +/- 0.03 mmol/L before the bolus) did not change with the maternal infusion. In ewes not in labor, uterine contractures occurred 3.7 +/- 0.7 times per 2 hours before and did not change significantly with the infusion of magnesium sulfate. During corticotropin-induced preterm labor uterine contractions were present 13 +/- 3.2 times per hour before infusions and were unchanged by infusion of magnesium sulfate to the ewes. CONCLUSIONS: Magnesium sulfate infusion in pregnant sheep has no effect on either nonlabor uterine contractures or on corticotropin-induced preterm uterine contractions.

Adrenocorticotropic Hormone↗
PubMed1997

Patellofemoral joint after total knee arthroplasty. Effect on contact area and contact stress.

Compressive contact stress between the patella and the anterior femur and between the quadriceps tendon and anterior femur was measured before and after total knee arthroplasty in 5 cadaver knee specimens using a digital electronic sensor. Contact stresses were measured in the normal knee and after total knee arthroplasty with an unresurfaced patella, a dome-shaped patella, and a conforming patella. Patellofemoral contact stresses did not change significantly after total knee arthroplasty when the patella was not resurfaced, but they increased significantly after the patella was resurfaced with both the dome-shaped and the conforming components. The conforming patella had the highest contact stresses because it tilted at flexion angles greater than 90 degrees and applied load to a small area on the superior portion of the patellar component. The conforming patella markedly decreased tendofemoral contact force because the thicker superior pole of the patella tented the quadriceps tendon at flexion angles greater than 120 degrees. This further increased patellofemoral contact force in deep knee flexion.

Arthroplasty, Replacement, Knee↗