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Biomedical subjects

P F Lawrence

Publications and source records attributed to P F Lawrence.

At least 37 records · Page 2Linked to original sources
PubMed1991

A comparison of absorbable suture and argon laser welding for lateral repair of arteries.

Conventional vascular anastomoses between autogenous vessels are performed with nonabsorbable sutures. Recently, use of absorbable sutures and laser-assisted vascular anastomoses has been advocated because of their improved healing characteristics. This study compared arterial repairs with the argon laser, absorbable suture, and nonabsorbable suture for technical characteristics including additional suture and overall success rates, burst strength, and cost. Absorbable and nonabsorbable suture closures were comparable with respect to technique, but laser-assisted vascular anastomosis was technically more demanding and required almost twice as much time for completion. The argon laser successfully closed only 58.6% of the arteriotomies, and 90% of the closures required additional sutures for complete hemostasis. All sutured arteriotomies were successfully completed by use of either absorbable or nonabsorbable suture. Burst strength was similar for all groups, but was uniformly greater than 300 mm Hg for sutured repairs, whereas two of five laser-assisted closures burst below 300 mm Hg. Finally, costs for purchasing ($35,000) and operating ($300/hr.) an argon laser make laser-assisted vascular anastomosis much more expensive than sutured repair. These data suggest argon laser-assisted vascular anastomoses are more technically demanding, less successful, and more expensive than conventional sutured anastomoses when evaluated in large caliber arteries in a canine model. Absorbable suture, however, is comparable to conventional nonabsorbable sutured arterial repairs in expense, handling characteristics, and success rates with the added advantage of eliminating permanent foreign body in the arterial wall when it is absorbed.

Absorption↗
PubMed1991

Initial evaluation of absorbable polydioxanone suture for peripheral vascular surgery.

The long-term integrity of an autogenous vascular anastomosis is primarily dependent on the strength of tissue healing; therefore permanent mechanical support of an autogenous anastomosis with sutures is unnecessary. In this study we evaluated monofilament absorbable polydioxanone as an alternative to polypropylene for suturing autogenous vascular tissue during adult peripheral vascular operations. We used polydioxanone suture for 21 vascular procedures in 20 patients. We evaluated suture handling characteristics during operation and then followed patients with clinical assessments and serial duplex scans to monitor for pseudoaneurysms, anastomotic narrowing, and vessel patency. Indications for surgery included limb salvage (67%), dialysis access (23%), traumatic arteriovenous fistula and claudication (5% each). The operative procedures included infrainguinal bypass (57%), arteriovenous fistula formation (24%), thromboembolectomy (14%), and arteriovenous fistula repair (5%). Polydioxanone sutures were placed in 39 separate test sites (35 arterial, 4 venous). No deaths occurred during operation. Polydioxanone suture was found to have handling characteristics similar to polypropylene. During mean patient follow-up of 7.2 +/- 0.6 months, we found no cases of anastomotic narrowing or pseudoaneurysms. Actuarial test site patency at 1, 3, and 6 months was 97%, 97%, and 86%, respectively. Polydioxanone suture has handling properties that are acceptable for use in vascular applications, and it provides adequate mechanical support for sutured vessels to heal. A randomized trial comparing polydioxanone with polypropylene suture will be necessary to determine whether the lack of permanent foreign material in vascular anastomoses can improve long-term patency.

Anastomosis, Surgical↗
PubMed1990

The effects of laser energy on the arterial wall.

Laser energy has been proposed as a method of resecting atherosclerotic plaque since the mid 1960s. However, only over the past several years have we come to understand some of the unique interactions of the laser with cardiovascular tissue. In laser angioplasty a major challenge has been choosing the optimal laser and duration of laser exposure to achieve adequate resection of plaque, while minimizing such complications as thrombosis, perforation, embolization, aneurysm formation, and accelerated atherosclerosis. Ultimately we must develop a more selective laser that resects plaque while leaving adjacent arterial wall uninjured. This review describes the physics of laser energy, the different lasers available for use in the cardiovascular system, laser-arterial wall interactions, and some of the limitations of laser angioplasty.

Arteriosclerosis↗
PubMed1990

Techniques for color flow sonography of the lower extremity.

Color flow sonography permits noninvasive examination of the deep venous system in the lower extremity. In many patients, the modality is sufficiently accurate to serve as the sole diagnostic procedure for suspected deep venous thrombosis. Over 1,500 color flow sonographic examinations of the lower extremity have been performed at our institutions with various scanning techniques. For the inexperienced sonographer, we describe our current technique, which is easy, quick, accurate, and well tolerated by patients.

Color↗
PubMed1990

Symptomatic lower extremity deep venous thrombosis: accuracy, limitations, and role of color duplex flow imaging in diagnosis.

Color duplex flow imaging (CDFI) permits pain- and risk-free direct imaging of the deep venous system of the lower extremities. To prospectively ascertain the accuracy and limitations of this technique, CDFI was performed in 75 lower limbs of 69 consecutive patients referred for venographic evaluation of clinically suspected lower extremity deep venous thrombosis (DVT). The CDFI study was obtained within 24 hours of the contrast venogram. Both studies were interpreted without knowledge of the patient's clinical findings or the results of the other test. Contrast venography was regarded as the standard for diagnosis of DVT. Accuracy was 99% for detection of DVT above the knee and 81% below the knee. Sonographic evaluation of the calf veins was technically adequate in 60% of limbs; accuracy was 98% in this group. In the 40% of limbs with technically limited CDFI studies of the calf, accuracy decreased to 57%. Although small nonocclusive thrombi occurred infrequently in this series of symptomatic patients, CDFI missed three of four such thrombi. It is concluded that CDFI, when not technically compromised, is sufficiently accurate to definitively diagnose symptomatic lower extremity DVT.

Adult↗
PubMed1987

The influence of aorta-aneurysm geometry upon stress in the aneurysm wall.

Finite element analysis (FEA), a computer-based method for solving complex structural problems, was used to determine the wall stress distribution in three cases of model infrarenal abdominal aortic aneurysms representing common problems in determining risk of aneurysm rupture. The point of maximum circumferential wall stress in a spherical model aneurysm was located near the junction of the aneurysm and the nondilated aorta, while maximum longitudinal wall stress was located at the point of maximum diameter of the aneurysm. FEA showed that cylindrically shaped constant thickness model aneurysms had a higher maximum circumferential stress (sigma c = 11.9 X 10(5) dyn/cm2) and a comparable maximum longitudinal wall stress (sigma L = 6.6 X 10(5) dyn/cm2) when compared with spherical model aneurysms of the same diameter (sigma c = 8.1 X 10(5) dyn/cm2 and sigma L = 6.2 X 10(5) dyn/cm2). Analysis of the aorta to aneurysm diameter ratio (A:a gradient) indicated that aortic size is important in determining aneurysm wall stress and that the relationship between aortic size and wall stress is dependent upon aneurysm wall thickness. We conclude that the ability of the aneurysm wall to withstand stress in the longitudinal as well as the circumferential direction is an important factor determining aneurysm rupture. Finally, this investigation showed that FEA is a versatile tool for use in studying the mechanics of vascular structures, making it potentially more useful than size alone in estimating the clinical significance of abdominal aortic aneurysms.

Aorta, Abdominal↗
PubMed1987

Endoscopic laser resection of atherosclerotic plaque in a live animal model. A preliminary report on some technical difficulties.

This study was designed to determine whether laser energy could be used effectively to resect atherosclerotic plaque through an endoscope in a live animal model. Twelve adult Yorkshire swine with infrarenal aortic atherosclerosis had a 2.5 mm and/or 3.2 mm diameter fiberscope passed into the aorta from the femoral artery after proximal aortic balloon occlusion. Endoscopic argon laser resection of the atherosclerotic plaque was then attempted in eight pigs with an argon laser fiber (60 to 400 microns). We were able to visualize the raised atherosclerotic plaque in all 12 pigs with the larger 3.2 mm diameter fiberscope, which was easily passed into the aortoiliac system from the 4 mm diameter femoral vessel. The articulating end feature enhanced maneuverability within the lumen and allowed laser fiber direction. The 2.5 mm endoscope did not allow adequate visualization in any pig since the vessel could not be cleared of blood. The 2.5 mm endoscope was also passed from the femoral artery distally into the hind limb and still did not allow adequate visualization of the vessel wall because of persistent luminal blood. The 3.2 mm endoscope enabled vessel wall visualization distal to the femoral artery when the proximal artery was occluded. No aortas were grossly perforated by the laser energy. In all pigs undergoing endoscopic laser resection, raised plaques were removed both grossly and histologically, although the plaque edges were carbonized and frayed as well as vaporized. With the small spot size of the argon fiber, channels were drilled through plaque, frequently with incomplete recanalization of the lumen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Diabetic ulcers: the effect of thermal biofeedback-mediated relaxation training on healing.

The present study was a preliminary investigation into the effect of thermal biofeedback-mediated relaxation training on healing of diabetic ulcers. Subjects were three males who had nonhealing diabetic ulcers of the toe, ankle, and leg, respectively. Treatment consisted of thermal biofeedback training at the ulcer site, handwarming training (in two of the three subjects), and home relaxation practice. Two subjects showed significant healing. Thermal biofeedback-mediated relaxation training may be a useful adjunct to traditional treatments for diabetic foot ulcers.

Biofeedback, Psychology↗
PubMed1986

Radiographic and clinical findings in unusual abdominal aortic aneurysms.

Atherosclerotic abdominal aortic aneurysms typically present either asymptomatically or with abdominal or back pain. Inflammatory, mycotic, and traumatic aortic aneurysms and aneurysms complicated by venous fistula are less common. The different clinical presentations of these latter aneurysms should raise a suspicion to their diagnosis and appropriate preoperative evaluation. The radiographic and clinical features of inflammatory, mycotic, traumatic, and complicated atherosclerotic aneurysms are presented and discussed.

Adult↗
PubMed1985

Responses of atherosclerotic aorta to argon laser.

Lasers have been advocated to resect atherosclerotic plaques in the cardiovascular system, yet little information is available regarding the effects of laser on the range of occlusive lesions seen in the peripheral arterial tree. This study was conducted to assess the risk of perforation in human cadaveric aorta involved with variable degrees of atherosclerosis. Ten fresh segments of atherosclerotic human aorta were graded for extent of atherosclerosis, then subjected to argon laser energy within 48 hours. Using air as the conduction medium and with the fiber tip 2 or 5 mm from the vessel wall, the argon laser was applied to matched calcified and non-calcified arteries at 3.0-7.0 W and 10.0-13.5 W with energy density identical for matched pairs. Results were compared among segments which were normal in appearance or had only fatty streaks grossly with those with gross regional wall calcification. The mean penetration time (T) for calcified and non-calcified lesions at low and high power outputs was compared. (table; see text) Mean time to perforation and range of time necessary to produce perforation were greater in calcified than non-calcified segments at all power levels employed. These data suggest that atherosclerotic lesions vary in their response to argon laser. The presence of calcium may preclude resection of some plaques and protect against wall perforation.

Aortic Diseases↗
PubMed1985

Femorofemoral bypass with an infrascrotal perineal approach for the patient with an infected groin wound.

A technique is presented for revascularization of patients having a groin wound infection, which minimizes the risk of recurrent graft infection. A femorofemoral bypass with a subcutaneous perineal tunnel is constructed farther from the infected groin wound than the standard subcutaneous suprapubic tunnel. The route of the graft appears to result in neither excessive tension on the graft when the leg is abducted nor kinking of the graft when the leg is adducted. Long-term follow-up will be needed to compare the patency of this route with the standard suprapubic tunnel in patients with an infected groin wound who require a femorofemoral bypass graft.

Arterial Occlusive Diseases↗
PubMed1985

Detection of acute synthetic vascular graft infection with 111In-labeled leukocyte scanning: an animal study.

Synthetic vascular graft infection is characterized by late diagnosis due to indolent and nonspecific symptoms. Indium-111-labeled leukocyte imaging holds promise as a diagnostic tool to identify vascular graft infection, but reported data on its accuracy are somewhat sparse and conflicting. In this study, 13 mongrel dogs received Dacron aortic interposition grafts. Seven grafts were contaminated at the time of surgery by topical ATCC Staphylococcus aureus concentrated at 10(8) organisms/ml. Six control animals received no graft contamination. All infected animals were sacrificed on the second postoperative day after 111In leukocyte scanning. The results showed a sensitivity of 71%, specificity of 100%, and accuracy of 85% for the 111In leukocyte study in detecting early graft infections; false-positive leukocyte scans in the early postoperative period were not a problem as has been reported by others. These data indicate that leukocyte scanning for graft infection detection is likely to be clinically valuable.

Animals↗
PubMed1985

Indium 111-labeled leukocyte scanning for detection of prosthetic vascular graft infection.

Recent animal and human studies have suggested that positive indium 111-labeled leukocyte scans may help establish the diagnosis of vascular graft infection; however, there is little information available about the predictive value of both positive and negative leukocyte scans in larger groups of patients. In this study 31 indium 111 leukocyte scans were performed prior to definitive treatment in 21 patients with suspected vascular graft infections. Patients with more than one leukocyte scan performed had either anatomically distinct sites of infection or rescanning of a potentially infected site after definitive treatment. Scans were performed according to the method of Baker et al., attaching 500 muCi of indium 111 to leukocytes with imaging 24 hours later. All patients with positive scans underwent surgical exploration of the area of leukocyte accumulation, with documentation of purulence and culture of the graft. Patients with negative scans were treated as if scan results were indeterminate and underwent surgical exploration for usual clinical indications; if no exploration was performed, the patient was followed up closely for at least 1 year. Twelve of 12 positive scans showed purulence or culture evidence of infection with three different organisms; in 15 instances of negative scans, two operations were performed with one infection noted, whereas no patient without surgery has had a graft infection at 10 months follow-up. In addition to localizing graft infections, two scans demonstrated a nonvascular site of infection. Positive scans also helped determine the extent of infection along the graft, allowing better planning of the surgical procedure. These results indicate that indium 111-labeled leukocyte scans help document and localize prosthetic vascular graft infections.

Aged↗
PubMed1985

Iliac endarterectomy with crossover ileofemoral bypass grafting for bilateral iliac artery stenosis.

The high-risk patient with claudication or impending limb loss secondary to iliac artery occlusive disease presents a difficult management problem. The morbidity and operative mortality rates of an aortoiliac or aortofemoral bypass procedure can be significant in the elderly or high-risk patient with multiple medical problems. An alternative to the axillofemoral bypass graft and other procedures that have been used in this clinical setting is presented. The combination of endarterectomy of the donor iliac vessel and retrorectus crossover bypass graft has been used in five patients, with good results at 6-month to 2-year follow-up. There have been no operative deaths and a retroperitoneal hematoma has been the only complication. One patient required balloon catheter dilatation of a stenotic vessel distal to the bypass graft for relief of recurrent claudication symptoms. This procedure appears to be a safe and effective therapeutic option in the patient considered an unsuitable candidate for aortofemoral bypass grafting because of advanced age or associated medical problems.

Aged↗