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Biomedical subjects

M J Buckley

Publications and source records attributed to M J Buckley.

At least 109 records · Page 6Linked to original sources
PubMed1989

Stress shielding effect of rigid internal fixation plates on mandibular bone grafts. A photon absorption densitometry and quantitative computerized tomographic evaluation.

The use of rigid internal fixation reconstruction plates in combination with bone grafts provides many advantages in mandibular reconstruction. These advantages include ease of adaptability at the time of surgery as well as immediate postoperative function for the patient. Disadvantages may include a "stress shielding" or disuse osteoporosis effect on the underlying bone graft as a result of the rigidity of the reconstruction plate. This study evaluated the stress shielding effects on bone grafts in primate mandibles. Bilateral bone grafts stabilized with rigid fixation plates were performed in 4 Macaca fascicularis monkeys. Three months after the bone grafting procedure one plate was removed from each monkey. The monkeys were then killed 1, 4, 6 and 8 months after plate removal. Photon absorption densitometry and computerized tomography were used to evaluate stress shielding. The results of this study indicate that the stress shielding effect occurs if the plate is not removed from the area of bone grafting postoperatively.

Absorptiometry, Photon↗
PubMed1989

Histomorphometric evaluation of stress shielding in mandibular continuity defects treated with rigid fixation plates and bone grafts.

Histomorphometric techniques were used to evaluate the stress shielding effect in bilateral bone grafts in 4 Macaca fascicularis monkeys. Bilateral continuity defects were created and grafted by replacing the resected portion of the mandible and iliac crest bone into the defect area. Both sides were plated with rigid internal fixation plates. Three months after bone grafting, the plate was removed from one side while the other plate was left in place. The animals were sacrificed at 1, 4, 6, and 8 months after plate removal and the grafted areas removed for histomorphometric analysis. This study documents decreased bone volume as well as smaller interlabel width on the plated side, suggesting a stress shielding effect as a result of the rigid internal fixation plate.

Animals↗
PubMed1989

Complications of orthognathic surgery: a comparison between wire fixation and rigid internal fixation.

This retrospective review compares the results of using rigid internal fixation (RIF) and wire fixation for orthognathic surgery patients. The records of two groups of demographically similar patients who underwent comparable surgery, performed by the same four attending surgeons at the same institutions during the same time period (1983 to 1986), were evaluated for complications and unanticipated treatment results. The most striking finding of this study is the general similarity between the two groups. However, differences in frequency of excessive weight loss and persistent restriction of mandibular opening suggest a benefit from early mobility of the mandible that comes with RIF. Because there was no concomitant increase in complications or unexpected results of treatment, the introduction of RIF for orthognathic surgery may offer patients some potential advantages.

Humans↗
PubMed1989

Octogenarians with aortic stenosis. Outcome after aortic valve replacement.

To assess the outcome of aortic valve replacement for aortic stenosis in octogenarians, we retrospectively studied 64 patients, aged 80-89 years, who underwent aortic valve replacement for aortic stenosis from 1974 to 1987. Mean aortic valve gradient was 61 +/- 22 mm Hg, and valve area was 0.5 +/- 0.2 cm2. Concurrent coronary artery bypass grafting was performed in 29 patients, mitral valve replacement in two, and both procedures in two. Serious, comorbid, noncardiac conditions were infrequent. In-hospital mortality was 9.4%. Outcomes were classified as 1a) uncomplicated; 1b) complicated (technically complicated surgery, temporary encephalopathy, discharge to a rehabilitation facility, or some combination thereof) but with ultimately good results; or 2) unfavorable (death or permanent, severe neurological deficit). There were 28 (44%) patients in group 1a, 24 (38%) in group 1b, and 12 (19%) in group 2. Of 18 patients with preoperative left ventricular ejection fraction less than 50%, two (11%) were in group 2. Of 31 patients undergoing aortic valve replacement only, two (6%) were in group 2, compared with 10 of 33 (30%) patients who had concomitant coronary artery bypass grafting, mitral valve replacement, or both (p = 0.02). Late follow-up at 28 +/- 5 months revealed four cardiac and seven noncardiac deaths, with actuarial 1- and 5-year survival rates of 83 +/- 5% and 67 +/- 10%, respectively. With few exceptions, survivors were free of cardiac symptoms. Thus, short- and long-term outcomes after aortic valve replacement for aortic stenosis in otherwise healthy octogenarians is generally favorable, even in the presence of preoperative left ventricular systolic dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗
PubMed1988

The automatic implantable cardioverter-defibrillator: efficacy, complications and survival in patients with malignant ventricular arrhythmias.

Ninety-four patients underwent surgery for automatic implantable cardioverter-defibrillator implantation. Ninety patients were discharged from the hospital with the device and were followed up for a mean period of 17 +/- 10 months. Forty-six patients experienced at least one discharge of the device under circumstances consistent with a malignant ventricular arrhythmia. One sudden death occurred. Complications included perioperative death (3 patients), post-operative ventricular tachycardia (12 patients) and atrial fibrillation (8 patients), perioperative myocardial infarction (1 patient) and device discharges for sinus tachycardia and supraventricular arrhythmias (17 patients). Six and 12 month survival rates by life table analysis were 98.7 and 95.4%, respectively. Thus, the automatic implantable cardioverter-defibrillator is a highly effective and relatively low risk treatment modality for patients with refractory life-threatening ventricular arrhythmias.

Adolescent↗
PubMed1988

Thallium kinetics in rat cardiac transplant rejection.

Cardiac transplant rejection is a very complex process involving both cellular and vascular injury. Recently, thallium imaging has been used to assess acute transplant rejection. It has been suggested that changes in thallium kinetics might be a sensitive indicator of transplant rejection. Accordingly, thallium kinetics were assessed in vivo in acute untreated rat heterotopic (cervical) transplant rejection. Male Lewis rats weighing 225-250 g received heterotopic heart transplants from syngeneic Lewis rats (group A; n = 13), or allogeneic Brown Norway rats (group B; n = 11). Rats were imaged serially on the 2nd and the 7th postoperative days. Serial cardiac thallium content was determined utilizing data collected every 150 sec for 2 hr. The data were fit to a monoexponential curve and the decay rate constant (/sec) derived. By day 7 all group B hearts had histological evidence of severe acute rejection, and demonstrated decreased global contraction. Group A hearts showed normal histology and contractility. However, thallium uptakes and washout of the two groups were the same. Peak thallium uptake of group B was +/- 3758 1166 counts compared with 3553 +/- 950 counts in the control group A (P = 0.6395); The 2-hr percentage of washout was 12.1 +/- 1.04 compared with 12.1 +/- 9.3 (P = 1.0000); and the decay constant was -0.00002065 +/- 0.00001799 compared with -0.00002202 +/- 0.00001508 (P = 0.8409). These data indicate that in vivo global thallium kinetics are preserved during mild-to-severe acute transplant rejection. These findings suggest that the complex cellular and extracellular processes of acute rejection limit the usefulness of thallium kinetics in the detection of acute transplant rejection.

Animals↗
PubMed1988

Osteoblasts increase their rate of division and align in response to cyclic, mechanical tension in vitro.

Bone adapts to physical deformation in vivo, yet the mechanism of the adaptive process remains unknown. One reason for this perplexity has been the difficulty in examining the effects of a well-defined deformation regimen on individual bone cells. With the utilization of novel, flexible-bottomed cell culture plates, one can study the effects of cyclic strain on the morphologic and biochemical adaptations of individual osteoblasts in vitro. Avian, calvarial osteoblast-like cells, from passes 2-5, responded to cyclic strain, by increasing their rates of DNA synthesis and cell division during the first 72 h after initiation of a continuous deformation regimen comprised of 3 cycles per min of 0-24% elongation. In addition, within hours after initiation of the deformation regimen, cells oriented 90 degrees to the applied strain field at the periphery of the culture plate in the region of maximum strain and elongation.

Animals↗
PubMed1987

Aortic dissection.

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Aortic Dissection↗
PubMed1987

Degree of reversibility of left ventricular systolic dysfunction after aortic valve replacement for isolated aortic valve stenosis.

To determine whether a low preoperative left ventricular (LV) ejection fraction (EF) returns to normal late after aortic valve replacement for aortic stenosis, 42 patients with critical aortic stenosis (valve area 0.7 cm2 or less), LV systolic dysfunction (EF 0.45 or less), angiographically normal coronary arteries, and no other significant valvular disease were studied at 10 to 84 months (mean 41 +/- 21) postoperatively. All patients survived aortic valve replacement and were discharged clinically improved. There were 4 late deaths; these patients were older (79 +/- 6 vs 64 +/- 13 years, p = 0.007) and had lower preoperative mean valve gradients (51 +/- 6 vs 68 +/- 23 mm Hg, p = 0.003) than late survivors. Of 23 survivors who returned for follow-up radionuclide angiography and Doppler echocardiography, 21 were asymptomatic. EF returned to normal (0.50 or more) in 14 patients (group 1) and remained low in 9 patients (group 2). Doppler peak prosthetic valve gradient was 24 +/- 8 mm Hg in group 1 and 25 +/- 10 mm Hg in group 2 (difference not significant). Six of the 9 patients in group 2 underwent early postoperative radionuclide imaging, and LVEF was normal in 4 (0.65 +/- 0.14 early vs 0.41 +/- 0.06 late, p = 0.02). Of 77 preoperative and intraoperative variables analyzed, only paroxysmal nocturnal dyspnea (0 of 14 vs 4 of 9, p = 0.01) distinguished group 1 from group 2. Thus, LVEF does not always normalize after aortic valve replacement for AS, implying impaired myocardial contractility.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Myocardial temperature variation: effect on regional function and coronary flow in dogs.

Incremental changes in the temperature (28-42.5 degrees C) of the anterior left ventricular wall in a canine, working, beating right heart bypass preparation (constant preload, afterload, and heart rate) were produced to measure the effect of regional temperature on myocardial function and blood flow. Circumferential-axis segment lengths were measured with sonomicrometry in both the temperature-varied, left-anterior descending coronary artery (LAD)-supplied myocardium and the normothermic (38 degrees C) circumflex-supplied myocardium. Fast thermistors (time constant less than 0.25 s) continuously monitored midmyocardial temperature in both areas. A Silastic loop with heat exchanger, thermistors, strain gauge, and flow probe was inserted into the LAD and allowed precise control of regional myocardial temperature. Nine-micron microspheres injected into left atrium were used to evaluate coronary flow and distribution. In six anesthetized dogs, relative to normothermic control (38 degrees C), regional systolic shortening decreased 42.2 +/- 10% at 41 degrees C and increased 23.3 +/- 6% at 31 degrees C. There was no significant change in coronary blood flow or distribution at the three temperatures. Pressure-length areas varied inversely with myocardial temperature. These data demonstrate that there is a reversible inverse relationship between midwall T and ventricular function when heart rate, preload, and after-load are controlled.

Animals↗
PubMed1987

Augmentation of pulmonary blood flow by a right atrial balloon pump after the Fontan operation.

The Fontan principle of right ventricular exclusion is frequently applied to complex congenital lesions. Results are adversely affected by increases in pulmonary vascular resistance and/or ventricular end-diastolic pressure. Survival depends on means to increase pulmonary blood flow. To address this problem, we have developed a triple-balloon catheter that is passed via the femoral vein to the right atrium. Inflation is sequenced so that small balloons located at the junction of each vena cava with the atrium inflate first. Then the larger central balloon inflates, ejecting blood from the right atrium to the pulmonary arteries. The pump is timed to inflate during ventricular systole. In this study, we tested the catheter in vivo in eight dogs. Tricuspid atresia was created and right ventricular exclusion accomplished. Pulmonary blood flow was measured with a flow probe in the right atrium-to-pulmonary artery conduit, at central venous pressures of 15, 20, and 25 mm Hg. Pulmonary blood flow was increased by balloon pumping in every instance (p less than .05). Maximal augmentation of pulmonary blood flow (25.5%) was achieved at a central venous pressure of 15 mm Hg with a balloon ratio of 1:2. Less augmentation was achieved at a central venous pressures of 20 mm Hg (8.4% to 13.0%) and a 25 mm Hg (4.4% to 5.3%) and at balloon ratios of 1:4 and 1:8. We conclude that (1) a triple-balloon pump in the right atrium can significantly augment pulmonary blood flow after right ventricular exclusion and (2) most effective augmentation can be achieved without excessive volume loading. Pulsatile augmentation of pulmonary blood flow with this device should improve survival after Fontan operations.

Animals↗
PubMed1986

Influence of coronary artery obstruction on cardiac prostaglandin metabolism during experimental cardioplegic arrest.

In order to test the influence of coronary artery obstruction on cardiac prostaglandin metabolism during surgically induced cardioplegia (CP), we have measured transcardiac veno-arterial gradients of prostacyclin and thromboxane A2 (TXA A2) during experimental canine cardiopulmonary bypass. Cardiac arrest was induced by infusion of 500 ml of hypothermic (8 degrees C), hyperkalemic (25 meq) crystalloid CP solution into the aortic root with (group I) and without (group II) occlusion of the left anterior descending artery (LAD). After 30 minutes of cardioplegic arrest the LAD occlusion in group I was released and a second set of CP infusion was applied in both groups. Transcardiac gradients were obtained 5 seconds after onset of the first and second CP washouts. Significant prostacyclin and TXA A2 gradients were observed at both times. Prostacyclin gradients did not differ between group I and group II. In contrast, TXA A2 gradients were significantly higher during the second CP washout in group I as compared to the unoccluded group (group I 918 +/- 221, group II 244 +/- 144 pg/ml, p less than 0.05). The results of our study suggest that cardiac TXA A2 metabolism during cardioplegic arrest is increased distal to a coronary artery obstruction. Cardiac TXA A2 production might contribute to the increased ischemic myocardial injury observed in this setting.

6-Ketoprostaglandin F1 alpha↗