Search PubMed⌕ Search

Biomedical subjects

P B Dobrin

Publications and source records attributed to P B Dobrin.

At least 19 recordsLinked to original sources
PubMed2001

Mechanical determinants of graft kinking.

Vascular grafts can be twisted inadvertently during implantation. If twisted excessively, they may kink and obstruct flow. In this study, in vitro experiments were performed to identify the mechanical factors that determine graft kinking. These included graft material, graft length, graft diameter, graft wall thickness, perfusion pressure, and flow rate. Six-millimeter-diameter saphenous veins were obtained from humans at autopsy. Six-millimeter standard-wall and 6-mm thin-wall polytetrafluoroethylene (PTFE) grafts also were obtained. Both fixed-length and stretchable PTFE grafts were examined. Grafts 15, 30, 50, and 70 cm in length were evaluated. Finally, PTFE grafts 4, 6, 8, 10, 12, and 14 mm in diameter were studied to determine the effect of diameter. The vessels were mounted horizontally in vitro and were perfused with saline at 50, 100, or 150 mmHg pressure at low (49 mL/min), medium (105 mL/min), and high (239 mL/min) flow rates. Each graft was twisted 90 degrees, then subjected to perfusion for 15 sec. Pressure and flow were interrupted, and an additional 90 degrees twist was imposed for another 15 sec. This sequence was repeated until a visible kink developed. We conclude from our results that, when constructing a bypass, particular care should be taken with vein, short grafts, thin-wall grafts, and large-diameter grafts, as these are especially susceptible to kinking.

Biomechanical Phenomena↗
PubMed1999

Distribution of lamellar deformations: implications for properties of the arterial media.

Most computations of arterial mechanics treat the wall as a mechanically homogeneous body, but there are no data to support or refute this. To evaluate this assumption, experiments were performed that measured the deformation of 4 elastic lamellae located at 4 equidistant points across the thickness of the media. Data were obtained at 25-mm Hg pressure steps between 0 and 200 mm Hg. To satisfy the constraints of incompressibility in an isovolumetric cylinder, the innermost structures must undergo larger deformations than the outermost structures. This manifests as thinning of the wall. Therefore, each experiment was performed twice: once with a vessel segment in its normal cylindrical configuration, and again with a contiguous vessel segment turned inside-out to form an inverted cylinder. The deformations of individual lamellae obtained in normal and inverted vessel segments were averaged to determine their extensions independent of location. Results showed that the extensibilities of the lamellae were equal at all 4 anatomic locations across the media, suggesting equal stiffnesses of the lamellae. Other studies were performed to examine the distribution of the circumferential retractions of the lamellae that occurs when a vessel is extended longitudinally. Results showed that circumferential retraction also was distributed uniformly across the wall. These findings demonstrate that the elastic lamellae behave uniformly in both the circumferential and longitudinal directions at different locations across the wall thickness. Because of the interlocked structure of the elastin, muscle, and collagen in the media, these findings suggest that although the media is histologically heterogeneous, it acts mechanically as a homogeneous material.

Animals↗
PubMed1998

The effect of twist on microvascular anastomotic patency and angiographic luminal dimensions.

BACKGROUND: Microvascular anastomoses must be constructed perfectly in order to be successful. One of the subtle technical errors that can occur during construction is twisting of the anastomosis. In the present study, we examined the effect of twist on the immediate, 2-h postoperative angiographic dimensions and patency of microvascular anastomoses. MATERIALS AND METHODS: Sixty-four Sprague-Dawley rats were assigned randomly to four groups. The femoral arteries were dissected for a distance sufficient to permit the application of an 8.5-mm-long microanastomotic approximator clamp. Microarteriorrhaphies were performed with twists of 0 degrees, 90 degrees, 180 degrees, or 270 degrees. Patency was assessed 2 h after surgery using transabdominal aortic arteriography with run-off. Measurements were recorded for each anastomosis, as well as for the narrowest and widest diameters of the vessels within 10 mm of the anastomosis. RESULTS: Fifty-nine of the 64 rats had technically satisfactory angiograms which permitted measurement of vascular dimensions. The cross-sectional areas of the narrowest areas and the anastomoses were inversely related to the degree of twist, and were significantly reduced at 270 degrees (P < 0.05). Two-hour patency rates were 86% with 0 degrees twist, 82% with 90 degrees twist, 71% with 180 degrees twist, and 33% with 270 degrees twist. The reduction in patency with 270 degrees twist was statistically significant (P < 0.05). CONCLUSIONS: Twists of 0 degrees, 90 degrees, and 180 degrees did not impair patency at a statistically significant level, but twists of 270 degrees did significantly reduce patency of microvascular anastomoses (P < 0.05).

Anastomosis, Surgical↗
PubMed1998

Characteristics of rectal carcinomas that predict the presence of lymph node metastases: implications for patient selection for local therapy.

BACKGROUND AND OBJECTIVES: It has been estimated that approximately 5% of middle and low rectal adenocarcinomas are amenable to local therapy. However, these treatment modalities are limited by their failure to identify and treat regional nodal metastases. METHODS: This study was undertaken to evaluate the role of tumor size, depth of penetration into the rectal wall, degree of histologic differentiation, DNA ploidy status, and their combination on the presence or absence of metastases in perirectal lymph nodes. Logistic regression was used to quantitatively predict the probability of positive lymph nodes. RESULTS: Tumor size did not correlate with the presence of nodal involvement; however, worsening degree of differentiation, increasing depth of wall penetration and aneuploidy did statistically correlate with the presence of nodal metastases. For any combination of tumor traits, aneuploidy markedly increased the probability of positive lymph nodes over that observed with diploid tumors. CONCLUSIONS: The combination of degree of differentiation, depth of penetration, and ploidy status may be used to identify patients whose tumors may be adequately treated with local measures. For any combination of tumor traits, aneuploidy markedly increased the probability of positive lymph nodes over that observed with diploid tumors.

Adult↗
PubMed1998

Mechanics of spatulated end-to-end artery-to-vein anastomoses.

It previously has been shown that in straight end-to-end artery-to-vein anastomoses, maximum dimensions are obtained with an interrupted suture line. Nearly equivalent dimensions are obtained with a continuous compliant polybutester suture (Novafil), and the smallest dimensions are obtained with a continuous noncompliant polypropylene suture (Surgilene). The present study was undertaken to examine these suture techniques in a spatulated or beveled anastomosis in living dogs. Anastomoses were constructed using continuous 6-0 polypropylene (Surgilene), continuous 6-0 polybutester (Novafil), or interrupted 6-0 polypropylene or polybutester. Thirty minutes after construction, the artery, vein, and beveled anastomoses were excised, restored to in situ length and pressurized with the lumen filled with a dilute suspension of barium sulfate. High resolution radiographs were obtained at 25 mmHg pressure increments up to 200 mmHg. Dimensions and compliance were determined from the radiographic images. Results showed that, unlike straight artery-to-vein anastomoses, there were no differences in the dimensions or compliance of spatulated anastomoses with continuous Surgilene, continuous Novafil, or interrupted suture techniques. Therefore a continuous suture technique is acceptable when constructing spatulated artery-to-vein anastomoses in patients.

Animals↗
PubMed1998

Mechanics of end-to-end artery-to-PTFE graft anastomoses.

On some occasions vascular surgeons are called upon to construct an end-to-end anastomosis using prosthetic graft material. If a spatulated anastomosis is not fashioned, three important variables that are under the surgeon's control could affect anastomotic dimensions: (1) selection of graft material, (2) graft size relative to the native vessel, and (3) suture technique. Accordingly, studies were performed on 36 nonspatulated, end-to-end artery-to-polytetrafluoroethylene (PTFE) grafts to evaluate the effects of graft size and suture technique on anastomotic dimensions. Size-matched (3 mm) and slightly oversized (4 mm) grafts were anastomosed end-to-end to 3 mm pig carotid arteries using (1) running polypropylene (Surgilene) sutures, (2) running polybutester (Novafil) sutures, or (3) interrupted sutures. After 30 min the vessels were excised, filled with contrast material, and radiographs were obtained to measure anastomotic dimensions. Results showed that, at every comparable pressure, 4 mm grafts produced larger anastomoses than did 3 mm grafts. In addition 4 mm grafts produced smoother anastomoses without a constricted or "pinched" appearance at the graft-artery junction. Marked compliance mismatch was observed with both sized grafts. There was no significant difference in the dimensions of the anastomoses or compliance mismatch with the three different suture techniques. These studies indicate that, when using PTFE grafts for end-to-end anastomoses, a graft that is slightly larger than the artery is preferable to provide the largest and smoothest anastomosis, and that any of the three suture techniques may be used.

Anastomosis, Surgical↗
PubMed1998

Chronic loading and extension increases the acute breaking strength of polypropylene sutures.

Polypropylene sutures provide satisfactory strength for construction of vascular anastomoses, but occasionally they break. Experimental studies show that they break at reduced forces when they are subjected to chronic loads. Moreover, in patients, sutures are subject to acute loads superimposed on chronic loads. For example, an episode of hypertension applies acute load that is added to the baseline chronic load in a suture that has been used to close an arteriotomy. The purpose of the present study was to examine the breaking force of 6-0 polypropylene sutures subjected to acute loads after they had been loaded with chronic loads. One hundred sixty-five 6-0 polypropylene sutures were subjected to 50-175 g chronic loads in vitro. After 38 days they were subjected to additional increasing acute loads until they broke. Five hundred ninety other sutures were subjected to "injuries" of manipulation before chronic loading. A stray knot was simulated by placing a knot in the center of 90 sutures. Nurse's tugs used to straighten folded sutures in the operating room were simulated by applying brief loads of 75-275 g to 452 other sutures. Intraoperative injuries were simulated in 48 other sutures by pinching them with DeBakey forceps. Surprisingly, chronic loading of polypropylene sutures increased their acute breaking force. It is suggested that this may have resulted from increased orientation of crystals in the core of the filaments. By contrast, disturbing the outer surface of the filament by placing a stray knot, or pinching with forceps decreased acute breaking strength. These data suggest that if polypropylene sutures do not break soon after they have been placed in a patient, they may gain strength over time.

Materials Testing↗
PubMed1998

Peripheral aneurysms and arteriomegaly: is there a familial pattern?

PURPOSE: Studies have shown that 11% to 18% of patients with an abdominal aortic aneurysm (AAA) have a first-degree relative with an AAA. A familial pattern among patients with peripheral arterial aneurysms and arteriomegaly has not been reported. The objective of this study was to examine familial patterns among patients with peripheral arterial aneurysm and arteriomegaly and compare them with patterns among patients with AAA. METHODS: Pedigrees were constructed for first-degree relatives of patients who received the diagnosis of peripheral arterial aneurysm, arteriomegaly, or AAA from 1988 through 1996. The presence of aneurysms and risk factors was confirmed for patients and relatives by means of telephone interviews and review of hospital and physician records. RESULTS: Seven hundred three first-degree relatives older than 50 years were contacted for 140 probands with peripheral arterial aneurysm, AAA, or arteriomegaly. There were differences in risk factors for hernia and diabetes mellitus among the probands with peripheral arterial aneurysm, AAA, or arteriomegaly but none for relatives. Patients with peripheral arterial aneurysm (n = 40) had a 10% (4/40) familial incidence rate of an aneurysm, patients with AAA (n = 86) had a 22% (19/86) familial incidence rate, and patients with arteriomegaly (n = 14) had a 36% (5/14) familial incidence rate. AAA (24/28, or 86%) was the aneurysm diagnosed most commonly among first-degree relatives. Most aneurysms (85%) occurred among men. CONCLUSION: There appears to be a gradation of familial patterns from peripheral arterial aneurysm to AAA to arteriomegaly among patients with degenerative aneurysmal disease, and there appears to be a predominance among men. Relatives of patients with any of the 3 lesions-peripheral arterial aneurysm, AAA, arteriomegaly--most frequently have AAA. Relatives of patients with AAA, peripheral arterial aneurysm, or arteriomegaly may be screened by means of a physical examination for peripheral aneurysmal disease. Screening by means of ultrasound examination of the aorta should be limited to first-degree relatives of patients with aortic aneurysms or arteriomegaly.

Aged↗
PubMed1998

Incidence, timing, and causes of cerebral ischemia during carotid endarterectomy with regional anesthesia.

PURPOSE: Controversy exists regarding the best technique to identify cerebral ischemia during carotid endarterectomy (CEA). Regional anesthesia allows continuous evaluation of neurologic function and therefore can help determine the incidence, timing, and causes of cerebral ischemia. METHODS: The timing and clinical manifestations of any neurologic event during CEA and as long as 30 days afterward was determined by review of operative reports, hospital charts, and outpatient records of consecutive patients who underwent CEA under regional anesthesia over a 68-month period. RESULTS: Two hundred patients underwent CEA; indications were asymptomatic stenosis > 60% in 25%, transient ischemic attack with stenosis > 50% in 52%, and prior stroke with stenosis > 50% in 23%. Eight patients (4%) were converted to general anesthesia for non-ischemic reasons. Of the remaining 192 patients, 183 (95.5%) underwent the procedure with regional anesthesia and no shunt, 2% had cerebral ischemia and underwent shunt placement, and 2.5% had cerebral ischemia, were converted to general anesthesia, and underwent shunt placement. Cerebral ischemia developed in nine patients after carotid cross-clamping, manifested by loss of consciousness in four, confusion in two, dysarthria and confusion in one, and decreased contralateral motor strength in two. Immediate cerebral ischemia developed in four of the nine patients within 1 minute of cross-damping; all four underwent shunt placement. In five of the nine patients, cerebral ischemia occurred between 20 and 30 minutes after cross-clamping; all occurred during relative intraoperative hypotension (average reduction of 35 mm Hg in the systolic pressure). All awake patients in whom ischemic symptoms developed immediately regained and maintained normal neurologic function with shunt placement. Five of 26 patients (19%) with contralateral occlusion required a shunt; none had postoperative ischemia. The mean carotid cross-clamp time was 27 minutes. Postoperative (30 day) complications included a 0.5% stroke rate, a 0.5% rate of postoperative transient ischemic attack, a 0.5% rate of worsening of preexisting acute stroke, and a 0.5% rate of myocardial infarction (no deaths). Of the nine patients who had intraoperative ischemic changes, none had a postoperative neurologic deficit; the three patients who had postoperative neurologic changes had no intraoperative ischemic symptoms. CONCLUSIONS: CEA with regional anesthesia allows continuous neurologic monitoring and can be performed safely even when contralateral occlusion coexists; intraoperative shunting for ischemia is necessary in 4.5% of all cases and in 19% of patients with contralateral occlusion. Intraoperative ischemia was flow-related in our patients; it occurred early from ipsilateral carotid clamping and late from reduced collateral flow as a result of hypotension. Monitoring should be continued throughout cross-clamping to identify late cerebral ischemia. Postoperative cerebral ischemia is not associated with intraoperative ischemia, if corrected.

Aged↗
PubMed1997

Intimal hyperplasia following thrombectomy versus thrombolysis in occluded vein grafts.

Although the histologic effects of balloon catheter thromboembolectomy in arteries are well described, little is known about its effects on arterialized vein grafts. A chronic canine model was used to compare the intimal hyperplasia that develops following balloon catheter thrombectomy versus thrombolytic therapy when each treatment was used to open experimentally occluded reversed autogenous vein grafts. Eleven of 12 dogs survived to the time of graft thrombosis and treatment. Ten grafts in one group of animals were treated with shear force-controlled balloon catheter thrombectomy, and eleven grafts in another group of animals were treated with infusion of urokinase (average 355, 833 IU/graft). Explantation and histologic evaluation was performed 5 weeks after treatment. Data were evaluated at comparable anatomic locations. These studies demonstrated the development of intimal hyperplasia in both groups with no statistically significant differences in the intimal thickening between the two treatment groups. It is hypothesized that vessel wall damage occurs at the time of thrombosis with the adherence of thrombus to the wall, and that this may be as important in producing intimal hyperplasia as the effects of carefully performed balloon thrombectomy or lytic therapy.

Animals↗
PubMed1997

Effect of pulsatile pressure on the breaking strength and movement of Prolene sutures.

PURPOSE: Most studies of sutures used in vascular surgery have used steadily applied loads. But in vivo, sutures are subject to pulsatile pressures. Pulsatile pressures could weaken sutures, or they could be beneficial by helping to slide the suture, thereby equilibrating the tension between unevenly tightened loops. This study examined the effect of pulsatile pressures on the strength and movement of polypropylene (Prolene) sutures. METHODS: Segments of pig thoracic aorta were cannulated and studied in a tissue bath in vitro at 37 degrees C. A longitudinal arteriotomy was made and then closed with running 6-0 Prolene. Vessels were subjected to (1) no pressure; (2) 100 mm Hg steady pressure; or (3) 112/65 mm Hg pulsatile pressure. After 48 hours the sutures were studied for breaking strength. In a second, separate set of experiments, longitudinal arteriotomies were closed using running suture lines. These were constructed with either several loose loops or several overly tight loops. Fine wires were affixed to the suture loops to permit photographic recording of suture movement. RESULTS: There was no difference in breaking force among 68 sutures that had been subjected to (1) no pressure; (2) 100 mm Hg steady pressure; or (3) 112/65 mm Hg pulsatile pressure. These also were no different than sutures that were not sewn into arteries. These findings indicate that neither steady nor pulsatile pressures weaken Prolene sutures. In the second set of experiments, it was found that pulsatile pressure did cause movement of suture lines where there were loose loops (p < 0.05). However, neither steady nor pulsatile pressures caused movement of loops in suture lines that contained normal and overly tight loops. CONCLUSIONS: Neither steady nor pulsatile physiologic pressures weaken 6-0 Prolene sutures that have been used to close a longitudinal arteriotomy. These pressures can cause movement of loose suture lines, but do not equilibrate the tension between normal and overly tight suture loops. Overly tight loops may place excessive load on a suture line.

Blood Pressure↗
PubMed1997

The effects of different corticosteroids on the healing colon anastomosis and cecum in a rat model.

Corticosteroids are known to adversely affect wound healing in experimental skin models; however, their effect on healing colonic anastomoses is still disputed. Different steroids have not been compared to each other in the same study. We studied the effect of equipotent doses of dexamethasone, hydrocortisone, and methylprednisolone on healing colon anastomoses in a rat model. High-dose steroid therapy was started 2 days prior to the operation and continued until the bursting pressures were measured at 5 and 7 days after the surgery. Anastomotic bursting pressure was not decreased for any of the steroid treatments when compared to the control, but the frequency of anastomotic rupture in the dexamethasone group at day 5 was significantly higher than either of the other steroid groups or the control group (P < 0.01). Bursting pressures of the intact cecum were lower in all the steroid-treated groups compared with the control group. We concluded that dexamethasone slows the rate of wound healing, but short-term high-dose steroid therapy does not decrease the strength of the anastomoses as measured by bursting pressure.

Adrenal Cortex Hormones↗
PubMed1997

Venous flow through coiled and noncoiled umbilical cords. Effects of external compression, twisting and longitudinal stretching.

OBJECTIVE: To examine the association between umbilical cord coiling and perinatal morbidity. STUDY DESIGN: Ten umbilical cord segments, six coiled and four noncoiled, were categorized according to Strong's coiling index and were examined experimentally. The umbilical arteries and vein were perfused, pressurized, placed in a saline bath at 37 degrees C and subjected to compression, twisting and stretching while measuring venous flow. RESULTS: There was no statistically significant difference in umbilical venous flow between coiled and noncoiled cords when external compression, twisting and longitudinal stretching were applied to the cord segments. CONCLUSION: Differences in morbidity associated with umbilical cord coiling should not be attributed simply to mechanical factors, and other mechanisms should be sought.

Biomechanical Phenomena↗
PubMed1996

Chronic loading of polypropylene sutures: implications for breakage after carotid endarterectomy.

This study compared the breaking force of acutely and chronically loaded 6-O and 5-O polypropylene sutures. It also examined the effect of graded injuries on those sutures. Studies were performed on 134 6-O and 5-O polypropylene sutures subjected to acute loads, 312 6-O and 5-O sutures subjected to chronic loads, and 377 6-O sutures subjected to quantitative "pinches" with DeBakey forceps to produce graded injuries before chronic loading. The lowest acute breaking force for 6-O polypropylene was 192 g. This occurred in 1.3% of acutely loaded sutures. The single lowest chronic breaking force for 6-O sutures was between 150 and 175 g, occurring in 5% of chronically loaded sutures. Thus, chronically loaded sutures are more likely to break than are acutely loaded ones. All of the chronically loaded sutures broke within the first 48 hr of loading, resembling the time of breakage in patients. The lowest chronic breaking force for 5-O sutures was 300 g, 71% greater than the 175 g for 6-O sutures. Graded pinches of 6-O sutures with DeBakey forceps increased the risk of breakage with chronic loads even more. All of the above data were related to the forces imposed upon a suture when it is used to close a carotid arteriotomy. Safety ratios were lower for chronically loaded 6-O sutures than for acutely loaded 6-O sutures or for chronically loaded 5-O sutures. When used to close a carotid arteriotomy, 6-O polypropylene has an acceptable safety ratio with respect to acute loads, but this is markedly reduced with chronic loading, producing a small but finite risk of breakage. The safety ratio may be reduced to dangerously low levels if the suture is handled improperly. Use of 5-O sutures would greatly increase the safety ratio of the suture line, both acutely and chronically, when polypropylene is used to close a carotid arteriotomy.

Carotid Arteries↗
PubMed1996

Effect of histologic preparation on the cross-sectional area of arterial rings.

Histometric studies are useful for correlating mechanical properties of tissues with morphological characteristics. However, fixation and embedding can cause volume changes and may cause tissue distortion. This study examined 24 rings of unpressurized arteries fixed with formalin, glutaraldehyde, or McDowell's solution and then embedded in paraffin or glycol methacrylate. A ring of each artery was also studied in the fresh state. The tissues were projected at 22X magnification and cross-sectional areas were measured. The dimensions of the fixed rings were compared with that of the fresh tissue. Results showed that embedding with paraffin produced 19-25% shrinkage with all three fixatives, whereas embedding with glycol methacrylate produced 4 to 13% volume expansion with the three fixatives. The least volume expansion occurred with McDowell's solution fixation (4%) and glutaraldehyde fixation (8%). These findings suggest that, when performing histometric studies, one should consider using glycol methacrylate for embedding in order to cause the least volume change.

Animals↗
PubMed1996

Do topical antibiotics provide improved prophylaxis against bacterial growth in the presence of polypropylene mesh?

BACKGROUND: Herniorrhaphies using a foreign body such as mesh can become infected. An experiment was performed in rabbits to compare three methods of antibiotic treatment to prevent the growth of bacteria in mesh-containing wounds. METHODS: This experiment compared preoperative intravenous antibiotics (cefazolin), topical antibiotics applied intraoperatively (bacitracin), and their combination in preventing the quantitative growth of bacteria in a subcutaneous wound containing a polypropylene mesh inoculated with Staphylococcus aureus. The bacteria were inoculated in doses sufficient to deliberately cause the growth of 130.0 +/- 56.4 x 10(4) bacteria per gram of tissue in saline-treated control animals. Quantitative cultures of the mesh and surrounding tissues were obtained 5 days after insertion of the mesh and inoculation of the wound. RESULTS: Experimental data showed that treatment with systemic intravenous antibiotics, topical powdered antibiotics, or their combination all statistically significantly decreased the quantitative cultures grown from the inoculated tissues as compared with saline-treated controls (P<0.05). However, there were no statistically significant differences in quantitative growth among the three methods of antibiotic treatment. CONCLUSIONS: Antibiotics reduced the quantitative growth of bacteria in tissues excised from wounds inoculated with bacteria. However, preoperative intravenous antibiotics, topical powdered antibiotics, and their combination all were equally effective.

Animals↗