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Biomedical subjects

P B Dobrin

Publications and source records attributed to P B Dobrin.

At least 19 recordsLinked to original sources
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↗
PubMed1989

Effect of twist on flow and patency of vein grafts.

This article examines the effect of twist on flow through reversed vein segments in vitro and its effect on graft patency in vivo. Excised canine superficial femoral veins were perfused in vitro with normal saline solution or canine blood. Perfusion was carried out at five pressures and against three outflow resistances. Increasing increments of twist were applied to the outflow end of the vein. Flow was measured at each level of twist. With both saline solution and blood, flow was unaltered until twist reached 140 to 180 degrees. Flow then decreased sharply, stopping completely at 175 to 200 degrees of twist. In vivo experiments were then performed in 13 dogs. Reversed superficial femoral veins were used as end-to-end grafts to bypass the iliac arteries. Each graft was deliberately twisted 0, 45, 90, 135, or 200 degrees. All grafts were harvested 6 months after surgery. Eighteen of 20 grafts twisted 135 degrees or less remained patent. However, all five grafts twisted 200 degrees were thrombosed within 4 hours of surgery (p less than 0.05). These data suggest that in patients a slight amount of graft twist probably does not reduce flow; however, more than 135 degrees of twist will greatly reduce flow, leading to early graft thrombosis.

Animals↗
PubMed1989

Mechanisms and prevention of arterial injuries caused by balloon embolectomy.

In summary, this article reviews the spectrum of clinical injuries produced by balloon embolectomy The concepts of lateral wall pressure and balloon-artery shear force are presented, and the histologic reactions to passage of embolectomy catheters are described. On the basis of the results of experimental investigations, technical recommendations are made regarding the performance of embolectomy in patients. Attention to these technical details will prevent excessive shear forces and should decrease the incidence of catheter-induced vascular injuries. The following are recommended for performance of balloon embolectomy in patients: 1. Select smallest-sized catheter that will be effective. 2. Use small-bore, long-stroke syringe, such as tuberculin syringe. 3. Whenever possible, fill embolectomy balloons with fluid; air may be preferable in 2F catheters. 4. Before insertion into vessel, fill balloon to check for leaks and for eccentricity. 5. Reject balloons that leak or are markedly eccentric. 6. Insert catheter into vessel, taking care to enter true lumen; do not create false passage. 7. Do not force catheter against resistance: this may cause arterial perforation. 8. Begin to withdraw catheter before balloon is inflated; within first centimeter of motion, inflate balloon. 9. Withdraw catheter slowly and, if possible, continuously. 10. Repeat until lumen is clear, but do not pass catheter excessive number of times. 11. Obtain intraoperative completion arteriogram.

Arteries↗
PubMed1989

Mechanical factors predisposing to intimal hyperplasia and medial thickening in autogenous vein grafts.

Autogenous veins undergo intimal hyperplasia and medial thickening when used as arterial bypass grafts. Exposing veins to arterial pressure and flow subjects them to three static deformations, three static stresses, increased pulsatile deformations, pulsatile stresses, and altered shear stress at the blood-intima interface. All of these occur simultaneously; thus it is unclear which of these nine mechanical factors predispose to the histologic changes that occur in the vein wall. Three sequential experiments were performed in 38 dogs to determine the role of each of these factors. Results showed that intimal hyperplasia is best associated with low flow velocity, a factor correlated with low blood-artery shear stress. By contrast, medial thickening is best associated with increased deformation of the vein wall in the circumferential direction (increased diameter). These findings correlate with clinical responses of vein grafts.

Anastomosis, Surgical↗
PubMed1988

Mechanical and histologic changes in canine vein grafts.

Mechanical and histological studies were performed on dog femoral veins after their implantation as grafts to bypass the ligated femoral arteries. The vein grafts dilated rapidly after implantation with 90% of maximum dilation occurring at 4 weeks. Both the native veins and the vein grafts were highly compliant up to 35-50 mm Hg, but were virtually nondistensible at higher pressures. When implanted with end-to-side anastomoses (end of vein to side of artery), the compliance of the anastomotic region resembled that of the artery rather than that of the vein. This was due to the distensibility of the artery at arterial pressure, as compared with the almost rigid vein. Histologic examination showed that intimal hyperplasia was greater after end-to-side anastomosis than after end-to-end anastomosis (P less than 0.05) and that this increased hyperplasia was reduced by treatment with aspirin and dipyridamole (P less than 0.05). By contrast, medial thickening was increased in all grafts compared with native veins (P less than 0.05), but was not different in end-to-end, end-to-side, and aspirin/dipyridamole-treated end-to-side grafts. These data suggest that intimal hyperplasia and medial thickening are separate responses to different stimuli.

Anastomosis, Surgical↗
PubMed1988

Some mechanical properties of polypropylene sutures: relationship to the use of polypropylene in vascular surgery.

This study was performed to examine some mechanical properties of Polypropylene sutures. Fifty segments of 3-0, 4-0, 5-0, 6-0, and 7-0 sutures were mounted in clamps and were subjected to stepwise elongation. Results showed that suture stiffness (elastic modulus) and breaking stress (tensile strength) correlated directly and linearly with the circumference or "skin" of the filaments and inversely with the cross-sectional area or "core" of the filaments. These data suggest that the strength of the suture may reside in the outer skin. These findings are related to the handling of Polypropylene in surgery, and to suture motion in grafts in patients.

Humans↗