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Biomedical subjects

J B Towne

Publications and source records attributed to J B Towne.

At least 91 records · Page 5Linked to original sources
PubMed1989

Identification of Staphylococcus epidermidis vascular graft infections: a comparison of culture techniques.

Culture of prosthetic material is routinely used to exclude or implicate infection in the pathogenesis of late-appearing graft complications. In a canine model of aortic graft infection caused by a bacterial biofilm, the influence of culture media (blood agar and tryptic soy broth) and mechanical surface biofilm disruption (tissue grinding and ultrasonic oscillation) on microorganism recovery was determined. Dacron prostheses colonized in vitro with Staphylococcus epidermidis were implanted in the infrarenal aortas of 36 dogs. After 3 weeks an infection with anatomic characteristics of late graft infection in humans was present. Explantation (+/- surface biofilm disruption) of infected grafts showed broth culture was superior (p less than 0.001) to agar media in confirming infection. The recovery rate of S. epidermidis was 30% with agar media, was 72% with broth media alone, and was 83% with broth media plus biofilm disruption. In situ replacement of infected grafts plus parenteral antibiotics resulted in early (1 month) healing of 31 grafts without signs of infection. All replacement grafts were sterile when cultured in broth media alone, but the addition of biofilm disruption isolated the study strain from eight (22%) of 36 grafts (p less than 0.01). Biofilm disruption by tissue grinding or sonication increased bacteria recovery equally. When biofilm bacterial concentration was less than 100 colony-forming units/cm2 of graft, only culture in broth media reliably recovered microorganisms. In the absence of perigraft inflammation, microbiologic recovery techniques that identify bacterial biofilms are necessary to exclude infection in studies concerning the pathogenesis of late graft complications or the treatment of S. epidermidis prosthetic infections.

Animals↗
PubMed1989

Medical students' perceptions of cheating.

In 1985, 683 students at a large private upper-midwestern medical school were surveyed concerning the appropriateness of traditional cheating behaviors and behaviors related to professional misconduct and dishonesty in patient care. They also rated the acceptability of various rationalizations for these behaviors. The students agreed that traditional forms of academic cheating are inappropriate, but they did not agree about the appropriateness of certain behaviors in the areas of patient care and professional misconduct.

Crime↗
PubMed1989

Monitoring functional patency of in situ saphenous vein bypasses: the impact of a surveillance protocol and elective revision.

Implementation of a protocol that monitored in situ saphenous vein bypass hemodynamics for low-flow states provided insight into the pathophysiologic characteristics and time course of graft failure. From 1981 to 1988, 250 in situ bypasses to popliteal (n = 83) or tibial (n = 167) arteries were performed in 231 patients. Indications for operation included critical limb ischemia in 232 cases (93%), popliteal aneurysm in 11 cases (4%), and disabling claudication in seven cases (3%). Arterial pressure measurements, continuous-wave Doppler spectral analysis, and duplex ultrasonography were used to assess patency, detect hemodynamic changes indicative of graft stenosis, and localize anatomic hemodynamic changes indicative of graft stenosis. Seventy grafts with correctable anatomic lesions (retained venous valves, graft stenosis, arteriovenous fistula, native vessel atherosclerosis) that decreased graft blood flow or ankle arterial pressure or both were identified. Correction of vein conduit or anastomotic lesions comprised 73 (77%) of the 95 revisions performed. Vein-patch angioplasty of a stenosis was the most common secondary operation performed. Graft revision was highest in the perioperative period (10% at 30 days), decreased to 7% per 6-month interval until 18 months, and was 3% per year thereafter. The primary patency rate of grafts not identified to have a correctable lesion was 86% at 4 years, a level similar to the secondary patency of 81% for grafts requiring one or multiple revisions. The surveillance protocol identified grafts with correctable lesions before thrombosis thereby permitting elective revision of patent grafts. Hemodynamic studies confirmed that a frequent mechanism of late failure of grafts was the development of a low-flow state produced by lesions not amenable to revision.

Adult↗
PubMed1989

Blunt tibial artery trauma: predicting the irretrievable extremity.

Patients suffering blunt leg trauma resulting in below-knee fracture, tibial artery injury, and soft-tissue damage are at major risk for amputation. In an attempt to identify the factors which may forecast limb loss despite vascular surgical repair, all patients with tibial fractures admitted between 1980-1988 were reviewed. Forty-four of 366 (12%) patients presented with clinical evidence of tibial artery injury. Twenty-seven of these 44 patients had angiographic evidence of at least one patent tibial vessel providing adequate distal flow. The remaining 17 patients required operative repair of injured tibial arteries because of persistent distal ischemia. The amputation rate was 35% (6/17--4 BKA, 2 AKA), three of these having patent vascular repairs at the time of the amputation. Operative indications for amputation were ischemic nonviable muscle in three patients, and severe soft-tissue wound infection in three. Patients who required amputation had a significantly greater incidence (Fisher's exact test) of three or more fascial compartments involved in muscular injury (p = 0.005), two or more injured tibial vessels (p = 0.01), failed vascular reconstruction (p = 0.03), a cadaveric foot at initial exam (p = 0.03), and severe muscle crush injury or muscle tissue loss (p = 0.03). No extremity was salvaged when more than two of these factors was present, and a failed vascular reconstruction led to limb amputation in all cases. These factors will predict an irretrievable extremity following blunt tibial artery trauma, allowing amputation before life-threatening wound sepsis develops.

Adolescent↗
PubMed1989

Use of the internal jugular vein for carotid patch angioplasty.

The internal jugular vein is an excellent source of autogenous tissue for carotid artery reconstruction because of its availability in the operative incision, adequate size, and ability to be harvested without morbidity. For 153 of 453 consecutive carotid reconstructions, the durability of the internal jugular vein (n = 76) and the greater saphenous vein (n = 77) as a patch angioplasty was compared. Mean postoperative follow-up was 17 months (1 to 52 months). The vein-patched carotid-bifurcation was studied by means of duplex ultrasonography to assess patency, detect restenosis, and measure cross-sectional diameter during systole. No carotid bifurcation occluded after operation. No ruptures or aneurysmal dilatations of the vein patches were observed. The maximum diameter (mean +/- SD) of the carotid patch angioplasties constructed with internal jugular vein (9.4 +/- 1.9 mm) was similar to patches made with greater saphenous vein (9.6 +/- 1.7 mm). In 95 patients serial duplex examinations demonstrated maximum diameter changes of the vein-patched internal carotid artery ranging from an increase of 3.5 mm to a decrease of 3.0 mm. Asymptomatic restenosis (greater than 50% diameter reduction) was detected in 2/95 (2.1%) patients. Because of the premium placed on the saphenous vein for peripheral arterial reconstruction and coronary artery bypass grafting, the ipsilateral internal jugular vein should be used more frequently for carotid patch angioplasty.

Adult↗
PubMed1988

Hemodynamics of in situ saphenous vein arterial bypass.

Doppler-derived blood flow velocity and limb blood pressure measurements were used to characterize the hemodynamics of 128 in situ saphenous vein arterial bypasses. The magnitude and configuration of the graft velocity waveform was the best predictor of clinical outcome. Successful bypasses had antegrade flow throughout the pulse cycle and a blood flow velocity above 40 cm/s. A low graft blood flow velocity (less than 40 cm/s) was associated with technical error or early graft failure due to poor runoff. The return of normal limb blood pressure correlated with a technically satisfactory bypass but was measured in only 50% of limbs on the first day after surgery. In 28 bypasses with high blood flow velocity (mean +/- SD) in systole (102 +/- 20 cm/s) and diastole (35 +/- 11 cm/s), postoperative limb blood pressure was initially low (mean ankle-brachial pressure index = 0.68) due to restriction of blood flow through small-diameter (less than 4-mm) venous conduits. As revascularization hyperemia abated, diastolic blood flow velocity decreased and limb blood pressure normalized. Despite the high blood flow velocity and pressure gradient associated with flow-restrictive venous conduits, limb ischemic symptoms resolved, and graft patency was not decreased. An understanding of graft and limb hemodynamics after in situ bypass grafting is critical when noninvasive diagnostic techniques are used to document technical adequacy and for postoperative surveillance.

Adult↗
PubMed1988

Protein C deficiency. A cause of unusual or unexplained thrombosis.

Familial hypercoagulable states are a collection of syndromes characterized by an inherited deficiency of various proteins involved in the control of coagulation and include antithrombin III, plasminogen, protein C, and protein S. Affected patients usually develop venous thrombosis as adults. During a 15-month interval, we identified five patients with venous thrombosis accompanied by protein C deficiency. Four patients presented with deep venous thrombosis, which was recurrent in two, and one patient developed mesenteric venous thrombosis. The kindred of this last patient suggested an autosomal dominant genetic transmission of protein C deficiency. Patients' ages at the time of diagnosis of disease ranged from 28 to 41 years. All patients had low levels of protein C (range, 34 to 67 U/dL; normal, 70 to 130 U/dL). All patients were treated with heparin sodium immediately and then given long-term oral anticoagulation therapy with warfarin sodium. Protein C deficiency is a predisposing factor to the development of venous thrombosis that has only recently been recognized. Treatment of symptomatic protein C deficiency requires short-term heparin therapy followed by long-term oral anticoagulation therapy with warfarin. Oral anticoagulation treatment must be initiated slowly with no loading dose to avoid warfarin-associated skin necrosis. Patients with unexplained or unusual thrombosis, especially if it occurs at an early age, and patients with recurrent episodes of lower limb venous thrombosis should have their protein C levels measured. If a deficiency is documented, long-term warfarin anticoagulation therapy is recommended.

Adult↗
PubMed1988

Turbulence occurring after carotid bifurcation endarterectomy: a harbinger of residual and recurrent carotid stenosis.

The goal of carotid endarterectomy is to remove an obstructing or embologenic lesion and reconstruct a durable arterial segment free of flow abnormality. The technical adequacy of 250 endarterectomy sites in 235 patients was assessed at operation by pulsed Doppler spectral analysis and arteriography and was correlated with postoperative patency, the incidence of residual and recurrent stenosis, and clinical outcome. Duplex scanning was used after operation to categorize disease severity. At operation, 10 patients (4%) had angiographic and Doppler flow abnormalities identified in the internal carotid artery. Vessel exploration identified intimal flaps, platelet aggregation, or stricture. Residual flow disturbances at the endarterectomy site correlated with perioperative thrombosis and stroke, angiographic abnormalities, primary closure of the arteriotomy, and a postoperative duplex scan consistent with stenosis. In 175 patients (182 sites) with normal arterial flow after carotid bifurcation endarterectomy, no thrombotic events occurred and the incidence of recurrent stenosis (life-table analysis) was zero at 3 months, 5% at 1 year, and 9% at 2 years. The incidence of occlusion and recurrent stenosis was increased (8% at 3 months, 18% at 1 year, and 21% at 2 years) in 68 arteries with residual flow disturbance identified at operation. Assessment of endarterectomy sites for turbulence identifies anatomic lesions that threaten patency and increase the incidence of residual and recurrent stenosis.

Aged↗
PubMed1988

Abnormalities of the fibrinolytic system as a cause of upper extremity ischemia: a preliminary report.

Abnormalities of the fibrinolytic system can result in unusual or unexplained clotting that occurs spontaneously or after minor trauma. We identified five patients with limb-threatening arterial thrombosis of the upper extremity associated with either a low level of plasminogen or an abnormal immunoreactive plasminogen. All patients had extensive thrombosis of the brachial, radial, and ulnar arteries. Two patients had concomitant thrombus of the subclavian artery, which in one patient was associated with distal embolization to the hand. There was no evidence of atherosclerosis in any patient. Detection of an abnormal plasminogen level was done by immunoelectrophoresis of the patient's serum with antiplasminogen sera. In these patients a separate immunoreactive band located near the anode and distinct from the normal single plasminogen band was detected. Because of extensive thrombosis of the arterial system, exploration of the brachial artery, as well as the origin of all the forearm vessels, was necessary for complete balloon catheter thrombectomy. Prompt diagnosis and treatment are necessary to prevent the catastrophic complication of arm or hand amputation. Patients with an abnormal plasminogen level should receive perioperative heparin therapy and long-term warfarin to prevent recurrent thrombotic episodes.

Adult↗
PubMed1988

Infection of vascular prostheses caused by bacterial biofilms.

A canine model was developed to study the efficacy of graft replacement as treatment for vascular prosthesis infections from Staphylococcus epidermidis. Infrarenal aortic graft infections were established in 18 dogs by implantation of Dacron prostheses colonized in vitro with a slime-producing strain of S. epidermidis to form an adherent bacteria-laden biofilm (5 X 10(6) colony-forming units/cm2 graft). Study animals developed a graft infection with anatomic and microbiologic characteristics typical of late prosthetic graft infections in humans (sterile perigraft exudate, absent graft incorporation, and normal serum leukocyte count and sedimentation rate). The S. epidermidis study strain was isolated from 14 of 18 explanted grafts (78%) by mechanical disruption of the graft surface biofilm and culture in broth media. Four dogs with sterile graft cultures had histologic evidence of bacterial infection. The established prosthetic surface biofilm infection was treated by graft excision, parenteral cefazolin, and graft replacement with a Dacron or polytetrafluoroethylene (PTFE) vascular prosthesis. One month after graft replacement, no PTFE graft had signs of infection, but perigraft exudate and inflammation involved three of nine Dacron grafts (33%). The study strain was recovered from four of nine PTFE grafts (44%) and two of nine Dacron (22%) replacement grafts (p greater than 0.05). Prosthetic replacement of Dacron prostheses infected by S. epidermidis as a bacteria-laden surface biofilm can result in early graft healing, but persistent colonization of one third of replacement grafts signify that recurrent clinical infection remains a risk.

Animals↗
PubMed1988

Hemodynamics of vein graft stenosis.

The hemodynamics of 56 femorodistal saphenous vein bypasses (in situ [n = 53] or reversed [n = 3]) identified to have residual or recurrent graft stenoses were characterized with Doppler-derived blood flow velocity and resting limb systolic pressure measurements. The magnitude and configuration of the graft blood flow velocity waveform were the best predictors of graft stenosis. Transformation of the graft blood flow velocity waveform from a triphasic to a monophasic or biphasic configuration coupled with a low (less than 45 cm/sec) or decrease (greater than 30 cm/sec) in peak systolic blood flow velocity relative to initial postoperative levels reliably predicted the presence of a remote occlusive lesion. In 20 (36%) of the 56 limbs, the ankle-brachial systolic pressure index (ABI) did not identify graft stenosis. The low sensitivity of ABI in the identification of graft stenosis was due to insignificant decrease (less than 0.15) of ABI (n = 11), incompressibility of the tibial arteries (n = 6), or residual occlusive lesions after surgery (n = 3). Duplex scanning of grafts with low blood flow velocity localized the site of stenosis in 31 (86%) of 36 patients examined. Graft revision increased systolic blood flow velocity from 33 +/- 9 to 77 +/- 18 cm/sec (mean +/- one standard deviation) a velocity similar to immediate postoperative levels (74 +/- 17 cm/sec). Resting ABI increased from 0.61 +/- 0.2 to 0.92 +/- 0.1 after graft revision. Four grafts with low systolic blood flow velocity (range 18 to 40 cm/sec) not revised occluded 5 to 45 days later.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1988

Accuracy of duplex scanning in the detection of stenosis after carotid endarterectomy.

The results of duplex ultrasonography in grading stenosis after carotid endarterectomy (78 sites) were compared with those of contrast angiography in 71 patients studied for recurrent or contralateral occlusive disease of the carotid bifurcation. Duplex and angiographic studies were performed within one month of each other at a mean postoperative interval of 44 months (range 3 to 122 months). Stenosis of the common carotid (CCA) and internal carotid artery (ICA) was classified into five disease categories (normal or less than 15% diameter reduction [DR], 16% to 49% DR, 50% to 75% DR, greater than 75% DR, and occlusion). The overall accuracy of duplex scanning compared with angiography in predicting recurrent carotid bifurcation disease was 83%, a level of agreement similar to classification of disease involving the nonoperated, contralateral bifurcation (overall accuracy 87%). Recurrent stenosis (greater than 50% DR) or occlusion of the CCA or ICA after endarterectomy was identified with an accuracy of 97%. Overestimation of severity of recurrent stenosis accounted for 11 of 13 duplex classification errors (85%). Presence of moderate (30% to 50% DR) recurrent stenosis of the CCA, tortuosity of the ICA, and severe contralateral carotid bifurcation disease were associated with velocity spectra that predicted a more severe recurrent stenosis at the endarterectomy site compared with angiographic grading. The level of agreement between duplex scanning and angiography was comparable to the interobserver variability in angiographic interpretation. The accuracy reported justifies the use of duplex scanning to grade the severity of carotid bifurcation recurrent stenosis and to follow these lesions for disease progression.

Carotid Artery Diseases↗
PubMed1988

Monocular ischemia--the influence of carotid atherosclerosis versus primary ocular disease on prognosis.

The etiology of monocular ischemia influences the clinical manifestation and long-term neurologic and visual prognosis. During a 10-year period, 140 patients with monocular visual symptoms were evaluated and assigned to a carotid bifurcation occlusive disease group (group I) or a primary ocular disease group (group II) on the basis of angiographic findings and ophthalmologic evaluation. Patients with symptoms secondary to emboli from the carotid bifurcation tended to have a shorter duration of blindness and a lower incidence of permanent blindness initially and during follow-up. The presence of Hollenhorst plaques or retinal artery occlusion did not have any discriminatory diagnostic value since the incidence was similar in both patient groups. Since both primary eye disease and carotid bifurcation occlusive disease can be initially seen as monocular ischemia, carotid angiography and ophthalmologic consultation are necessary to select those patients who will benefit from carotid endarterectomy.

Arteriosclerosis↗
PubMed1987

Surface biofilm disruption. Enhanced recovery of microorganisms from vascular prostheses.

Ultrasonic oscillation (sonication) of explanted vascular prosthetic graft material can disrupt surface biofilms and increase the recovery of adherent microorganisms. Recovery of microorganisms from vascular grafts was studied in a canine model of Staphylococcus epidermidis graft contamination (N = 26) and on graft material excised from patients undergoing femoral anastomotic pseudoaneurysm repair (N = 7). Surface biofilm disruption by sonication significantly increased the incidence of positive cultures of excised graft material compared with broth (P less than .010) and blood agar plate (P less than .005) culture techniques. The S epidermidis was recovered from 31% of the canine vascular grafts and 100% of the clinical specimens. The in vitro production of a glycocalyx "slime" was demonstrated in 73% of the recovered staphylococcal strains. The formation of an adherent bacteria biofilm on implanted vascular prostheses is not an uncommon occurrence and is an important factor in the pathogenesis of anastomotic pseudoaneurysm formation and late graft infection.

Animals↗
PubMed1987

Influence of vein-patch angioplasty on carotid endarterectomy healing.

We studied the influence of venous patching on the patency, endothelial regeneration, and wall healing of endarterectomized carotid arteries in a canine model. Thirteen dogs underwent bilateral common carotid endarterectomies (intimectomy and partial media excision). In each dog, one artery was closed by continuous suture and the contralateral artery was closed by external jugular vein-patch angioplasty; arteries were excised at two postoperative intervals (two to three and four to five weeks) for light, scanning, and transmission electron microscopy. The patency of arteries closed primarily (9/13 [69%]) was not significantly different compared with arteries closed with venous patches (12/13 [92%]). By scanning electron microscopy, regeneration of the endothelial monolayer occurred by migration from the endarterectomy end points and suture lines. Despite survival of the vein-patch endothelium, the rate and pattern of reendothelialization was not altered by venous patching. In both patched and unpatched vessels, endothelial regeneration was incomplete at two to three weeks and completed by four to five weeks. The histologic characteristics of the endarterectomized arterial wall after operation were also not influenced by the closure technique. In contrast with the healing artery wall, vein-patch walls did not develop a thickened intima. Although venous patching does not influence early patency, endothelial regeneration, or wall healing after endarterectomy, vein-patch angioplasty does increase vessel diameter and prevents the development of circumferential intimal thickening, attributes that are beneficial in minimizing restenosis.

Animals↗
PubMed1987

The role of arteriography in acute penetrating trauma to the extremities.

The role of arteriography was studied in a series of 98 patients presenting with acute penetrating trauma to their extremities. We concluded: (1) Following "proximity only" injury, arteriography is indicated since vessel damage may occur despite a lack of either signs or symptoms; proximity only injuries, however, do not require emergency angiography. (2) Negative arteriography is reliable in excluding arterial injury, and (3) not all angiographic abnormalities require surgery.

Adolescent↗
PubMed1987

Application of thrombolytic therapy in vascular occlusive disease. A surgical view.

The use of fibrinolytic agents to control the fibrinolytic enzyme system and lyse pathologic fibrin deposits or thrombus has now assumed a position with anticoagulants and vascular surgery in the physician's therapeutic armamentarium. The principal exogenous activators that are used clinically are streptokinase, urokinase, and tissue plasminogen activator. Acute arterial occlusions are more likely than chronic occlusions to respond to thrombolytic therapy, especially if treatment is instituted within a few hours of onset of symptoms and if the disease is due to embolic material rather than in situ thrombosis. Since the duration of drug infusion necessary to lyse arterial thrombus cannot be predicted, patients in whom tissue viability cannot be determined or in whom ischemia cannot be tolerated during the drug infusion interval are not candidates for intraarterial fibrinolytic drug infusion. In treating patients with venous occlusion, thrombolytic therapy is more effective against proximal clots than in calf thrombosis. No protective effect from pulmonary embolism has been noted in trials comparing heparin with streptokinase. Fifty percent of patients with an initial episode of deep venous thrombosis treated within 72 hours of onset will have complete resolution of thrombus with preservation of valve function.

Arterial Occlusive Diseases↗