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Biomedical subjects

P B Dobrin

Publications and source records attributed to P B Dobrin.

At least 37 records · Page 2Linked to original sources
PubMed1996

Influence of suture technique and suture material selection on the mechanics of end-to-end and end-to-side anastomoses.

Experiments were performed in dogs to evaluate the mechanics of 26 end-to-end and 42 end-to-side artery-vein graft anastomoses constructed with continuous polypropylene sutures (Surgilene; Davis & Geck, Division of American Cyanamid Co., Danbury, Conn.), continuous polybutester sutures (Novafil; Davis & Geck), and interrupted stitches with either suture material. After construction, the grafts and adjoining arteries were excised, mounted in vitro at in situ length, filled with a dilute barium sulfate suspension, and pressurized in 25 mm Hg steps up to 200 mm Hg. Radiographs were obtained at each pressure. The computed cross-sectional areas of the anastomoses were compared with those of the native arteries at corresponding pressures. Results showed that for the end-to-end anastomoses at 100 mm Hg the cross-sectional areas of the continuous Surgilene anastomoses were 70% of the native artery cross-sectional areas, the cross-sectional areas of the continuous Novafil anastomoses were 90% of the native artery cross-sectional areas, and the cross-sectional areas of the interrupted anastomoses were 107% of the native artery cross-sectional areas (p < 0.05). At physiologic pressures, there were no differences in compliance among the three types of anastomosis. These data suggest that when constructing an end-to-end anastomosis in a small vessel, one should use an interrupted suture line or possibly continuous polybutester suture. Forty-two end-to-side anastomoses demonstrated no differences in cross-sectional areas or compliance for the three suture techniques. This suggests that, unlike with end-to-end anastomoses, when constructing an end-to-side anastomosis in patients any of the three suture techniques may be acceptable.

Anastomosis, Surgical↗
PubMed1995

Mechanical factors associated with the development of intimal and medial thickening in vein grafts subjected to arterial pressure. A model of arteries exposed to hypertension.

Arteries exposed to sustained hypertension undergo a moderate degree of intimal thickening and a marked amount of medial thickening. Autogenous veins that are used as bypass grafts undergo similar histological changes. In this study autogenous vein grafts were used as an indirect model of arteries exposed to sustained hypertension. It was hypothesized that it is not pressure per se but rather mechanical changes brought about by exposure to increased pressures that act as a stimulus inducing histological changes. Exposure to arterial pressure increases the following nine mechanical factors: deformation in the circumferential, longitudinal, and radial directions; stresses in each of these three directions; pulsatile deformations and pulsatile stresses; and flow velocity. All of these mechanical changes occur simultaneously. Accordingly, a three-step algorithm was devised to separate each of the nine mechanical factors and correlate them with histological changes. Three sequential experimental studies were performed in 38 dogs following the algorithm. These experiments demonstrated that intimal thickening was best correlated with low flow velocity, a correlate of low shear stress, whereas medial thickening was best correlated with deformation in the circumferential direction.

Animals↗
PubMed1994

Experimental study of determinants of aneurysmal expansion of the abdominal aorta.

The natural history and the factors determining the expansion of aneurysms have not been elucidated. To study the respective roles of elastolysis, collagenolysis, inflammatory cells, and hypertension in the pathogenesis of aneurysms, two previously described in vivo experimental models were used. An isolated segment of the abdominal aorta was infused with 15 units of pancreatic elastase. The maximal diameter of the aorta was measured before and after infusion and the isolated aorta was excised for classic histologic and immunohistologic studies. Twelve hours after the infusion of elastase the mean diameter of the aorta increased by 30%. The aorta had a cylindric form and only collagen fibers remained. Two and a half days after the infusion the aorta was spherical in shape and the diameter increased by 300% (3.09 +/- 0.08 mm) (p < 0.05). The entire aortic wall was invested by inflammatory cells. Six days after infusion the diameter increased by 421% (4.38 +/- 0.03 mm) (p < 0.05), and immunohistochemical staining showed numerous T lymphocytes and macrophages. Between 6 and 12 days, after perfusion inflammation decreased, the final diameter was 4.23 +/- 0.14 mm (not significant). Sixteen rats had thioglycollate and plasmin infusion, which are nonspecific activators of inflammation. Nine days after infusion the diameter of the aorta had increased by 288%; the elastic fibers of the media were fragmented and rare and the entire aortic wall was invaded by inflammatory cells, predominantly macrophages. The diameter of the aorta increased progressively. Two groups of 17 hypertensive rats (renovascular and spontaneous hypertension) received an aortic infusion of 15 units of pancreatic elastase. Elastolysis overlapped the limits of the infusion and inflammation persisted after 2 weeks. The mean diameter of the aorta (F = 11, p < 0.01) and the mean length of the aneurysms (F = 11.2, p < 0.001) were significantly increased. This study demonstrates that elastolysis and especially collagenolysis are determinants of aneurysmal expansion. Inflammation may be a promoting factor in the degradation of the aortic wall. Hypertension increases the hemodynamic stress to the aorta and activates mural inflammation.

Animals↗
PubMed1994

Morphology predicts rapid growth of small abdominal aortic aneurysms.

This study evaluated CT scans of small abdominal aortic aneurysms (AAAs) (< 5 cm) to assess anatomic features associated with rapid expansion. Serial CT scans obtained at least 10 months apart (mean 15 months) from patients with small AAAs were reviewed. Each cross-sectional image of the AAAs was analyzed using a computer-assisted design program. The circumference of the AAA in each CT image was divided into eight equal arcs, from which the apparent radius of curvature (Rc) for each segment was calculated. Flattening of the wall curvature results in an increased segmental Rc. The CT scans of nine patients with expanding AAAs (expansion > or = 0.5 cm/yr) were compared to those of 10 patients with stable AAAs (expansion < or = 0.2 cm/yr). To adjust for differences in AAA size, the Rc for each segment was normalized by dividing each individual Rc by the average of the eight Rcs (RcAvg) calculated for that cross-sectional CT image. Analysis of variance showed that the left posterolateral segments in expanding AAAs had larger Rc/RcAvg ratios than those segments in stable AAAs (1.14 +/- 0.19 vs. 0.80 +/- 0.09, p < 0.02). Laplace's law indicates that the left posterolateral segment in AAAs that grow more rapidly is subjected to greater wall tension. Flattening in the curvature of the left posterolateral wall segment was significantly associated with an increased rate of expansion in small AAAs. This finding, readily derived from standard CT scan images, may predict which small AAAs are more prone to rapid expansion.

Aortic Aneurysm, Abdominal↗
PubMed1994

Failure of elastin or collagen as possible critical connective tissue alterations underlying aneurysmal dilatation.

Previous studies in the authors' laboratory have demonstrated that degradation of arterial elastin produces vessel dilatation, decreased vessel distensibility, and vessel elongation which can cause tortuosity. By contrast, degradation of collagen produces increased vessel distensibility and rupture. However, neither degradation of elastin nor of collagen produced the true gross enlargement characteristic of human aneurysms. The present study was performed to identify the connective tissue critical to aneurysm formation. Vessel dimensions were measured repeatedly in human arteries during progressive enzymatic degradation. Experiments were performed on six intact human common, external and internal iliac arteries, and two aneurysmal human common iliac arteries. The vessels were mounted in vitro and subjected to pressure steps up to 200 mmHg while diameters were measured. Repeated pressure-diameter curves were obtained for up to 18 h during treatment with elastase or collagenase. Degradation of elastin produced moderate dilatation (6-10% at 100 mmHg) with decreased vessel distensibility; this occurred as the load was shifted to remaining collagen. Degradation of collagen produced greater dilatation (10-23% at 100 mmHg), increased distensibility, and vessel rupture. These findings suggest that the critical element in both the gross enlargement and rupture of aneurysms resides in collagen. They also suggest that, in vessels obtained from patients with a family history of aneurysms, defects should be sought in: (i) the structure of collagen; (ii) increased susceptibility of collagen to degradation by endogenous mechanisms; (iii) increased endogenous collagenolytic activity; or (iv) decreased inhibition of endogenous collagenolytic activities.

Aneurysm↗
PubMed1993

Necrotizing infections of the perineum.

During a 6-year period, 10 patients were treated for severe necrotizing infections of the perineum (Fournier's gangrene) at the Edward Hines Veterans Administration Hospital (Hines, Ill). All were male, and their average age was 60 years. When known, duration of symptoms was 2 to 5 days. Prodromal signs such as edema, erythema, and pain frequently developed into rapidly spreading, full-thickness cutaneous gangrene in less than 24 hours. All patients had significant concomitant disease; 60% were diabetic. All patients had expedient and aggressive initial debridement, usually within 24 hours of presentation to the surgical service. Each patient had a "second-look" debridement within 1 or 2 days. Debridement was done an average of 2.6 times per patient. The cause of the infection was noted in seven patients--five with perirectal abscess and two with urethral trauma. Suprapubic catheters were placed in both patients with urethral trauma. Diverting colostomy was done on two patients who had perirectal abscess as a nidus; eight patients were treated without colostomy. Polymicrobial bacteriologic flora were found in all patients, with a predominance of Escherichia coli, Bacteroides sp, and staphylococci. Broad spectrum antibiotics and early nutritional supplementation were given. Hospital stay averaged 4 weeks (range, 3 to 12 weeks). One patient died (mortality of 10%). Successful management of these patients requires expedient diagnosis, aggressive nutritional supplementation, and early and repeated debridement as clinically indicated. We have not found diverting colostomy to be a necessary part of the management of these patients even when the nidus is perirectal.

Adult↗
PubMed1992

Chronic histologic changes after vascular clamping are not associated with altered vascular mechanics.

The mechanical properties of arteries, along with the histologic and scanning electron microscopy characteristics of the nonatherosclerotic canine arteries, were investigated six months after vascular clamping. Different vessel clamps were applied to 73 sites on the carotid and femoral arteries in five anesthetized dogs. Each clamp was applied for 30 minutes with (a) sufficient force to just occlude blood flow or (b) as tightly as the clamp could be placed. After six months the vessels were excised, filled with barium sulfate suspension, and pressurized in 25 mmHg steps up to 150 mmHg. High resolution contact radiographs were taken at each pressure. These were magnified 35x and measured. Scanning electron microscopy and conventional histology disclosed that the clamped sites exhibited serrated clamp "tracks" in the intima, intimal hyperplasia, and, in a few cases, fractured elastic lamellae. These histologic changes were seen more frequently in the femoral artery than in the carotid artery (p less than .01). The mechanical properties, as determined from radiographic measurements, demonstrated that, for all types of clamps, the luminal diameter, pressure-diameter relationship, and compliance of the clamped vessels were not significantly different from nonclamped control regions (ANOVA). These studies demonstrate that careful application of clamps to nonatherosclerotic arteries produces persistent morphologic changes, but these are not associated with altered mechanical properties of the vessel wall.

Animals↗
PubMed1992

Correlation of inflammatory infiltrate with the enlargement of experimental aortic aneurysms.

Inflammatory cells often are seen in the walls of human aortic aneurysms, but their significance is uncertain. To investigate their actions an in vivo model of arterial aneurysms was developed in the rat. Fifteen units of hog pancreatic elastase were infused for 2 hours into the isolated abdominal aorta in 26 rats. The vessels were measured in vivo and were excised for conventional histologic and immunohistologic study at selected intervals. In untreated control rats the diameter of the aorta was 1.04 +/- 0.02 mm. Immediately after infusion with elastase the aorta dilated 26% to 1.31 +/- 0.02 mm (p = NS), with no histologically demonstrable remaining elastic lamellae. Two and one half days after infusion the aorta dilated nearly 300% to 3.09 +/- 0.08 mm (p less than 0.05). These vessels exhibited large numbers of activated macrophages and T cells in the media. Three and 4 days after infusion the vessels dilated 388% to 4.04 +/- 0.09 mm and 367% to 3.82 +/- 0.31 mm, respectively. These vessels also exhibited numerous inflammatory cells in the media. Six days after infusion the vessels enlarged 421% to 4.38 +/- 0.03 mm (p less than 0.05), and the infiltrate persisted staining immunohistologically for macrophages, polymorphic neutrophils, and T lymphocytes. Twelve days after infusion the aneurysms remained enlarged but stable at 4.23 +/- 0.14 mm (p = NS). At this time the number of inflammatory cells regressed to control levels. The temporal correlation between inflammatory infiltrate and aneurysmal enlargement suggests that inflammatory cells may participate in the destruction of the aneurysmal vessel wall thereby promoting progressive enlargement.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

Estimating the elastic modulus of non-atherosclerotic elastic arteries.

BACKGROUND: Non-invasive measurements of the diameter and wall thickness of arteries in vivo, combined with recordings of pressure, permit the assessment of some mechanical aspects of arteries in vivo. However, arteries are anisotropic cylinders with complex elastic properties which can only be determined by a detailed evaluation. Many of the parameters required to calculate the anisotropic circumferential elastic modulus cannot be obtained in patients in vivo, or can be obtained only with difficulty. AIMS: Experiments were performed to assess the true anisotropic circumferential elastic modulus, and to find simpler methods of estimation. METHODS: One hundred and twenty dog carotid arteries were mounted in vitro and were extended to four lengths, 120, 130, 160 and 180% of the retracted length. The different lengths were applied in random order. The vessels were pressurized in steps while the longitudinal force and vessel diameter were measured. When a reproducible mechanical behavior was observed, the pressure, diameter and longitudinal force were recorded. These values were used to calculate the longitudinal elastic modulus, the circumferential-longitudinal Poisson's ratio and the true anisotropic circumferential elastic modulus with respect to the dimensions of the fully unloaded vessel. A number of simpler expressions were then evaluated for their value as approximations of the true anisotropic modulus. RESULTS: Excellent estimates were obtained with a variety of expressions. CONCLUSIONS: These methods may be useful for non-invasive assessments of the elastic properties of non-atherosclerotic arteries in patients.

Animals↗
PubMed1991

Efficacy of intraperitoneal antibiotics in the treatment of severe fecal peritonitis.

A study was performed with rabbits to examine the efficacy of treatments for fecal peritonitis and, specifically, to determine whether it is beneficial to include antibiotics in the saline used to irrigate the peritoneum. A standardized inoculum of human stool suspension was placed in the peritoneal cavity of the rabbits. Fifty-six rabbits were studied to compare the effect of treatments begun 2 hours after peritoneal soiling. The administration of no treatment resulted in 100% mortality (14 of 14). Parenteral cefotetan 25 mg/kg intramuscularly (IM) twice a day (BID) with no other treatment reduced mortality to 50% (p less than 0.05). Cefotetan 25 mg/kg IM BID plus irrigation of the peritoneum with plain saline further reduced mortality to 21% (3 of 14, p less than 0.05). Cefotetan 25 mg/kg IM BID plus irrigation of the peritoneum with saline containing cefotetan 1.0 mg/mL reduced mortality to 14% (2 of 14, p = not significant). These treatments also produced a progressive decrease in the number of intraperitoneal abscesses from 24.0 +/- 2.1 (mean +/- SEM) in the animals receiving no treatment to 9.7 +/- 1.2 abscesses in the animals receiving peritoneal irrigation with saline containing cefotetan (p less than 0.001). A second experiment then was performed specifically to examine the efficacy of intraperitoneal antibiotics. A lethal fecal inoculum was determined in rabbits receiving conventional therapy, i.e., parenteral antibiotics (cefotetan) and irrigation of the peritoneum with plain saline. With two hours delay before treatment, cefotetan 25 mg/kg IM BID and irrigation with plain saline produced 80% mortality (11 of 14). Cefotetan 25 mg/kg IM BID plus cefotetan 1.0 mg/mL in the saline washout reduced mortality to 21% (3 of 14, p = 0.003) and markedly reduced the number of intraperitoneal abscesses from 13.4 +/- 0.7 in the animals receiving irrigation with plain saline to 8.1 +/- 0.8 in the animals receiving irrigation with saline containing cefotetan (p less than 0.0001). Thus, intraperitoneal irrigation with antibiotics was highly effective. Serum antibiotic levels drawn 30 minutes after irrigation were 112.7 +/- 22.4 micrograms/mL in animals that received irrigation with plain saline, and 101.7 +/- 15.2 micrograms/mL in animals that received irrigation with saline containing cefotetan. These serum levels were not significantly different. With 6 hours delay before treatment, all therapy was less effective. Cefotetan 25 mg/kg IM BID and irrigation with plain saline resulted in 100% mortality (14 of 14). With 6 hours delay, cefotetan 25 mg/kg IM BID and irrigation with saline containing cefotetan reduced mortality to 80% (11 of 14).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Pathophysiology of arterial aneurysms.

Studies were performed to evaluate the contributions of elastin and collagen to the formation of arterial aneurysms. Dog carotid arteries and human external and internal iliac arteries were excised, mounted horizontally in a tissue bath, and were pressurized. Vessel diameter and longitudinal force were measured. the vessels were treated with elastase or collagenase. Those treated with elastase dilated, but never ruptured. Those treated with collagenase dilated still more and, in every case, ruptured. Circumferential stability resulted from recruitment of previously non-loaded collagen fibers, and from a change in geometry from a cylinder to a sphere. The laminated thrombus lining the lumen has little intrinsic strength and therefore does not confer strength to the aneurysmal wall. Treatment with elastase also reduces the retractive force exerted by the vessel in the longitudinal direction. Therefore loss of elastin permits the vessel to elongate and to become tortuous. In aged human arteries collagen also contributes a small portion of the retractive force. Progressive enlargement of aneurysms results from continued failure of wall connective tissues reflecting a) genetically defective collagen and or b) activity of the immune system.

Aneurysm↗
PubMed1991

Poststenotic dilatation.

Partial narrowing of arteries produces poststenotic dilatation. This appears as a dilation of the vessel wall 1 to 3 centimeters distal to the area of a partial stenosis. When a stenotic band is placed in dogs, poststenotic dilatation develops rapidly, often within eight to ten days. Moderate stenoses that produce a bruit and thrill are effective in eliciting poststenotic dilatation, whereas very tight and very mild stenoses usually are ineffective. Thus, development of poststenotic dilatation requires the presence of flow disturbances sufficient to produce an audible bruit and a palpable thrill. Although the exact flow disturbance is uncertain, statis, increased lateral pressure, cavitation, abnormal shear stresses and turbulence all have been postulated to be the cause of poststenotic dilatation. Of these, experimental studies support abnormal shear stresses and turbulence as the most likely causes. Whatever the flow disturbance, it must make the wall vibrate to produce poststenotic dilatation. Vibrations are thought to produce alterations in wall elastin and possibly in vascular smooth muscle tone. This leads to dilatation of the vessel. If the dilatation is slight, removal of the stenosis may cause reversal of poststenotic dilatation with recovery beginning within hours of correction of the stenosis. If the dilated area is enlarged to twice normal diameter, it may exhibit permanent aneurysmal changes and, therefore, requires resections with reanastomosis. Arteries that are dilated to as little as one-third more than normal size may contain areas of ulceration with overlying thrombus. These vessels also may require resection with reanastomosis.

Anastomosis, Surgical↗
PubMed1990

Longitudinal retractive force in pressurized dog and human arteries.

Experiments were performed to examine longitudinal retractive force in pressurized arteries in vitro. This force opposes vessel elongation and prevents the development of tortuosity. Common carotid arteries were excised from six adult dogs and external iliac arteries were excised from six elderly male humans at autopsy. Each vessel was mounted in a tissue bath at in situ length and was pressurized. Longitudinal retractive force was measured under control conditions and after treatment with elastase or collagenase. Results showed that, in the dog vessels, elastin provides all of the longitudinal retractive force. In the aged human vessels, both elastin and collagen provide longitudinal retractive force, with elastin contributing the much greater part.

Age Factors↗
PubMed1990

Balloon embolectomy catheter-induced arterial injury: a comparison of four catheters.

This study compared four brands of balloon embolectomy catheters with respect to their mechanical characteristics and the histologic responses they elicit. Seventy-two 4F Becton-Dickinson, Edwards, Electro-Catheter, and Shiley catheters were studied. In vitro studies of penetration forces demonstrated that the forces required for arterial puncture were greatest for Shiley (295 +/- 22 gm) and least for Edwards catheter tips (217 +/- 11 gm) (p less than 0.05). This indicates that the Shiley catheter is least likely to puncture vessels in patients. Studies of balloon eccentricity showed that none of the balloons distended with excessive eccentricity. Studies of balloon emptying time demonstrated that the silicon Becton-Dickinson balloon required more than two times as long (5.7 +/- 1.2 seconds) as all other balloons to empty. Balloon emptying time reflects the ability of the surgeon to rapidly adapt the balloon to changing vessel diameter in patients. Shear forces were studied in cylindrical segments of arteries in vitro. Initial shear forces were significantly different among all catheters, Becton-Dickinson greater than Edwards greater than Shiley greater than Electro-Catheter (p less than 0.05). In contrast, during catheter withdrawal dynamic shear forces were similar among the four brands of catheters. Balloon embolectomies were performed in vivo in the common carotid and common femoral arteries in 18 anesthetized dogs. Histologic examinations of the vessels exposed to 50, 100, and 200 gm shear forces showed that myointimal hyperplasia increased with rising shear forces for all catheters (p less than 0.05), but that there were no differences in the degree of myointimal hyperplasia elicited by the different brands of catheters.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Surgical manipulation and the tensile strength of polypropylene sutures.

Laboratory studies were performed on 509 size 6-0 polypropylene sutures to examine the effects of surgical manipulation on suture tensile strength. Results showed that dragging sutures over the torn edge of the foil package, permanently kinking sutures, or axially twisting them up to four times did not decrease tensile strength. Similarly, the tug exerted by operating room nurses on polypropylene sutures did not decrease their tensile strength. Two manipulations, however, did decrease breaking strength. The presence of a stray knot reduced suture strength 17%, and grasping sutures with DeBakey forceps decreased suture strength in a dose-dependent fashion. When experienced surgeons grasped sutures with forceps out of direct vision, their grasping forces were well below that which alters tensile strength. Nevertheless, these results demonstrate that sutures that have acquired a stray knot should be discarded and that sutures should not be grasped with mechanical devices such as forceps.

Plastics↗
PubMed1989

The value of continuous 72-hour peritoneal lavage for peritonitis.

Studies were performed in 120 rabbits to determine whether 72-hour peritoneal lavage is beneficial or harmful in the treatment of peritonitis. Results showed that against a high concentration fecal inoculum (90 percent mortality), peritoneal lavage containing gentamicin and clindamycin reduced mortality to 10 to 20 percent (p less than 0.05). Parenteral antibiotics alone and lavage not containing antibiotics did not decrease mortality. By contrast, against a low fecal inoculum (30 percent mortality), peritoneal lavage containing gentamicin and clindamycin did not alter mortality. However, lavage not containing antibiotics increased mortality to 70 to 80 percent (p less than 0.05). These data demonstrate that continuous peritoneal lavage may be helpful in the treatment of peritonitis provided the lavage solution contains antibiotics and may be harmful if it does not contain antibiotics.

Animals↗
PubMed1989

Pathophysiology and pathogenesis of aortic aneurysms. Current concepts.

From an engineering point of view, the development of an arterial aneurysm is a classic case of material failure that may involve two factors: excessive applied load and inadequate material strength. The author describes a hypothesis that explains how atherosclerosis could increase the pressure load on the vessel and at the same time decrease the capacity of the wall to bear that load. It will be of interest to learn precisely what the genetic trait is that causes the atherosclerotic aorta to fail structurally in some patients while allowing the vessel to remain intact and develop occlusive lesions in others.

Animals↗