Biomedical subjects

M P Lilly

Publications and source records attributed to M P Lilly.

At least 19 recordsLinked to original sources

PubMed2005

Two-dimensional metal-insulator transition as a percolation transition in a high-mobility electron system.

By carefully analyzing the low temperature density dependence of 2D conductivity in undoped high-mobility n-GaAs heterostructures, we conclude that the 2D metal-insulator transition in this 2D electron system is a density inhomogeneity driven percolation transition due to the breakdown of screening in the random charged impurity disorder background. In particular, our measured conductivity exponent of approximately 1.4 approaches the 2D percolation exponent value of 4/3 at low temperatures and our experimental data are inconsistent with there being a zero-temperature quantum critical point in our system.

Journal Article↗

PubMed2003

Resistivity of dilute 2D electrons in an undoped GaAs heterostructure.

We report resistivity measurements from 0.03 to 10 K in a dilute high mobility 2D electron system. Using an undoped GaAs/AlGaAs heterojunction in a gated field-effect transistor geometry, a wide range of densities, 0.16 x 10(10) to 7.5 x 10(10) cm(-2), are explored. For high densities, the results are quantitatively shown to be due to scattering by acoustic phonons and impurities. In an intermediate range of densities, a peak in the resistivity is observed for temperatures below 1 K. This nonmonotonic resistivity can be understood by considering the known scattering mechanisms of phonons, bulk, and interface ionized impurities. Still lower densities appear insulating to the lowest temperature measured.

Journal Article↗

PubMed2001

Tibial bypass using complex autologous conduit: patency and limb salvage.

Over an 8-year period, we performed 93 lower extremity bypasses using complex autologous conduits, which included (1) contralateral greater saphenous vein (GSV), (2) composite GSV, (3) superficial femoral vein, (4) lesser saphenous vein, (5) cephalic or basilic veins, and (6) composite-sequential (PTFE and vein) grafts. These grafts represented 16% of all infrainguinal bypasses during this period, and all grafts were performed to treat limb-threatening ischemia. Survival, patency, and limb salvage were examined by the life-table method. Primary graft patency was 46 and 38% at 3 and 5 years. Assisted-primary patency was 62 and 59%, and secondary graft patency rates were 68 and 64% at 3 and 5 years. Twenty-nine bypasses (31%) required revision to restore or maintain patency. The 3-year limb salvage rate was significantly better when revision was performed for graft stenosis than for graft thrombosis (90% vs. 46%, p < 0.05). Overall limb salvage rate was 73% at 5 years. The mortality rate was 5.4% and the 5-year survival was 51%. Complex autologous tibial bypasses provided acceptable long-term limb salvage in patients with severe ischemia and inadequate ipsilateral GSV. The increased operating time and complexity required did not produce prohibitive operative risks. Postoperative graft surveillance in these complex vein bypasses allowed revision in many cases before graft occlusion occurred and significantly improved long-term limb salvage.

Age Factors↗

PubMed2001

Fenoldopam infusion associated with preserving renal function after aortic cross-clamping for aneurysm repair.

BACKGROUND: Cross-clamping of the descending aorta during operative repairs causes sudden, significant reductions in renal function that may persist well beyond arterial clamp release. Commonly used agents, such as dopamine and mannitol, have not consistently affected renal outcome in these high-risk patients. Fenoldopam mesylate is a novel, highly selective dopamine type-1 agonist that preferentially dilates the renal and splanchnic vasculature, but has not been investigated in patients undergoing prolonged aortic clamping for whom adverse renal outcomes should be more likely. METHODS AND RESULTS: Twenty-two adult patients without significant pre-existing renal dysfunction and presenting for elective repairs of abdominal aortic aneurysms were studied. Fenoldopain mesylate was infused after obtaining baseline values ranging from 0.1 to 1.0 microg/kg/min for the first 24 hours postoperatively to maintain mean arterial pressure +/-25% baseline. Serial renal function indices, including creatinine clearance and electrolyte fractional excretions, were measured at baseline, at aortic clamping and unclamping, and post-clamp release, and were estimated through hospital discharge. Creatinine clearance fell during abdominal exploration and clamping, reaching a nadir with clamp removal. Partial recovery occurred by 2 hours after clamp removal, and returned to baseline values by postoperative day 1 and thereafter. Fractional excretions rose rapidly throughout the operative phase. Total fenoldopam dose was directly related to the baseline creatinine clearance; after clamp removal, creatinine clearance was directly related to the mean arterial pressure at the lowest dose of fenoldopam, and inversely related to the mean arterial pressure at clamp release. CONCLUSIONS: In elderly patients with severe vascular disease undergoing aneurysmal repairs, the use of a fenoldopam infusion in this open-label, uncontrolled trial was associated with a relatively rapid return of renal function to baseline values, despite profound decreases during aortic cross-clamping. Further studies will be necessary to investigate how fenoldopam infusions compare with traditional therapies.

Adult↗

PubMed2000

Potentiated response of corticotropin (ACTH) to repeated moderate hemorrhage requires amygdalar neuronal processing.

We examined the role of the amygdala in the potentiation of the corticotropin (ACTH) response to a 10 mg/kg hemorrhage by a 1-hour episode of equivalent hypovolemia done 24 h earlier. Unanesthetized rats were studied on the fourth (D1) and fifth (D2) day after chronic implantation of arterial and venous catheters. Immunocytochemistry for Fos protein indicated that neurons in the central and medial nuclei of the caudal amygdala were activated by hemorrhage. We then tested the effect of excitotoxic destruction of the neurons in these areas by bilateral injections of ibotenic acid 10 days prior to catheter placement. In rats that were hemorrhaged on both D1 and D2, the responses of ACTH and corticosterone increased significantly from the first (H1) to the second hemorrhage (H2) in a control group injected with saline (p < 0.05) and in lesioned groups without bilateral damage of the Fos-responsive areas (p < 0.01). In the group with bilateral damage to these sites, the responses to H1 and H2 did not differ. Additional rats had H1 on D2 to control for the long-term effects of the chronic cannulation. The responses of ACTH to H1 on either D1 or D2 did not differ between the saline-injected controls and any of the lesioned groups. In contrast, the response of ACTH to H2 on D2 in rats with bilateral damage of the caudal amygdala was not significant and was less than the response of ACTH to H2 in both rats with unilateral damage of this area (p < 0.05) and those injected with saline (p < 0.05). We conclude that bilateral neuronal processing within the caudal amygdala is required for the potentiation of the response of ACTH to H2 by H1.

Adrenal Glands↗

PubMed2000

Post-surgical recovery and time-of-day mask potentiated responses of ACTH to repeated moderate hemorrhage in conscious rats.

We determined how changes in the responsiveness of the hypothalamo-pituitary-adrenal (HPA) system that accompany experimentation affect facilitation of HPA responses to hemorrhage. Hemorrhage (10 ml/kg over 3 min) was performed in conscious, chronically prepared rats. Blood was sampled over 1 h followed by reinfusion of shed blood. Hemorrhage was performed either once or twice separated by 24 h in different groups of animals. To test the effect of the circadian variation in responsiveness, rats were hemorrhaged on days 4 and 5 after surgery either in the morning (AM) or in the afternoon (PM). The response of ACTH to hemorrhage on day 4 was greater in the PM than in the AM (P<0.01). The ACTH response to the second hemorrhage on day 5 was greater than that to hemorrhage on day 4 only in the AM group (P<0.01). Thus, facilitation of ACTH responses by prior hemorrhage was evident only in the AM. To determine the effects of surgical recovery, additional experiments were done in the AM either early (days 3 and 4) or later (days 6 and 7) after surgery. In these experiments, hemorrhage was performed in all rats on days 4 and 7 and either hemorrhage or blood sampling alone was performed on day 3 and 6. ACTH did not increase in rats with sampling and no hemorrhage. ACTH increased more after an initial hemorrhage on day 3 than on day 6 (P<0.01). ACTH response to hemorrhage on day 4 was greater when preceded by hemorrhage vs sampling on day 3 (P<0.01). ACTH response to hemorrhage in rats bled twice did not differ on day 3 and day 4. On day 7, the response of ACTH in rats that had hemorrhage on day 6 was greater than both their own response on day 6 and the response of a control group with sampling on day 6 (P<0.01). These results demonstrate potentiation of ACTH responses to hemorrhage by an earlier similar hemorrhage, but clearly indicate that enhanced sensitivity of the HPA to hemorrhage either by circadian factors or by surgery can mask this effect.

Adrenocorticotropic Hormone↗

PubMed1999

Duplex ultrasound insertion of inferior vena cava filters in multitrauma patients.

BACKGROUND: Techniques for placement of inferior vena cava (IVC) filters have undergone continued evolution from open surgical exposure of the venous insertion site to percutaneous insertion in most cases today. However, the required transport either to an operating room or interventional suite can be complex and potentially hazardous for the multiply injured trauma patient who may require ventilator support, controlled intravenous infusions, or skeletal immobilization. Increased experience with color-flow duplex scanning for routine IVC imaging and portability of ultrasound equipment have suggested the usefulness of duplex-guided IVC filter insertion (DGFI) in critically ill trauma and intensive care unit (ICU) patients. METHODS: A total of 25 multitrauma/ICU patients were considered for DGIF. Screening color-flow duplex scans were performed on all patients, and obesity or bowel gas prevented ultrasound imaging in 2 cases, leaving 23 patients suitable for DGFI. In each case, the IVC was imaged in the transverse and longitudinal planes. The right renal artery was identified as it passed posterior to the IVC and was used as a landmark of the infrarenal segment of the IVC. All procedures were performed at the bedside in a monitored ICU setting using percutaneous placement of titanium Greenfield filters. Duplex scanning after insertion was used to document proper placement, and circumferential engagement of the filter struts in the IVC wall. An abdominal radiograph was also obtained in each case to confirm proper filter location. Duplex ultrasound imaging was repeated within 1 week of insertion to assess IVC and insertion site patency. RESULTS: DGFI was successful in all cases. The filter was deployed at a suprarenal level in one case, as was recognized at the time of postprocedural scanning. Three patients died as a result of their injuries but there were no pulmonary embolism deaths. Repeat duplex scanning was obtained in 17 patients, and revealed no case of IVC or insertion site thrombosis. CONCLUSIONS: Vena caval interruption can be safely performed under ultrasound guidance in a monitored, ICU environment. In selected multiply injured trauma patients, this will reduce the risk, complexity and cost of transport for these critically ill patients. DGFI also reduces procedural costs compared with an operating room or interventional suite, and eliminates intravenous contrast exposure. Preprocedural scanning is essential to identify patients suitable for DGFI, and careful attention must be paid to the known ultrasonographic anatomical landmarks.

Adult↗

PubMed1999

The prevalence of carotid artery stenosis in patients undergoing aortic reconstruction.

BACKGROUND: Coronary artery disease occurs frequently in patients undergoing aortic reconstruction, and it has been presumed that internal carotid artery occlusive disease is also common. This has led to the practice of screening for and repairing significant carotid lesions in asymptomatic patients prior to aortic reconstruction. The purpose of this study was to determine the true prevalence of internal carotid artery disease in these patients. METHODS: The records of 240 patients who underwent duplex ultrasound screening for carotid artery disease prior to aortic reconstruction were reviewed. Surgery was performed for aortic aneurysm (AA) or aorto-iliac occlusive disease (AO). The prevalence of hyperlipidemia and coronary artery disease was similar between the two groups, but tobacco use, hypertension, and diabetes mellitus differed. RESULTS: Internal carotid artery stenosis > or = 50% occurred in 26.7% of the total group (64 of 240 cases). Stenosis > or = 50% was more common in the AO group (40 of 101 cases, 39.6%) than the AA group (24 of 139 cases, 17.3%, P = 0.0001). Severe disease (70% to 99%) was also more common in the AO group than the AA group (9.9% versus 3.6%, P = 0.0464). CONCLUSION: Internal carotid artery disease occurs commonly in patients undergoing aortic reconstruction, and screening is worthwhile. Significant disease is more common in patients with aorto-iliac occlusive disease than in those with aortic aneurysm, although atherosclerotic risk factors occur with varying frequency in the two groups. These findings suggest that additional factors may contribute to the higher prevalence of internal carotid artery stenosis in aorto-iliac occlusive disease.

Aged↗

PubMed1999

Arterial reconstruction with deep leg veins for the treatment of mycotic aneurysms.

PURPOSE: Mycotic pseudoaneurysms (MPA) remain challenging clinical problems. Primary surgical management includes control of hemorrhage and debridement of the infected arterial wall. Because critical ischemia may develop after arterial resection, revascularization has been a secondary goal of treatment. Standard anatomic graft placement or prosthetic bypass grafting has been compromised by a high rate of recurrent infection. Extra-anatomic reconstruction is preferred, with the basic goals being threefold: (1) the use of autogenous graft material to reduce the risk of reinfection; (2) the avoidance of significant size mismatches; and (3) graft placement that is anatomically inaccessible, because drug abuse causes many of these lesions. This study reviews a recent series of MPAs applying these treatment goals. METHODS: In a 2-year period, the superficial femoral and proximal popliteal veins were used in the repair of eight MPAs of the common femoral (5), common iliac (1), and brachial (1) arteries, and the infrarenal aorta (1). Most patients (5 of 7) were known intravenous drug users, who had a painful pulsatile mass in an injection area. Two patients had systemic sepsis, one patient with an infected common iliac pseudoaneurysm and one patient with an MPA of the infrarenal aorta. The diagnosis of MPA was made by means of duplex/computed tomography scanning and confirmed by means of arteriography in all cases. RESULTS: Obturator bypass grafting was performed by using a reversed deep leg vein in the five femoral MPAs. An ilioiliac, cross-pelvic bypass grafting procedure with a deep vein was used to repair an MPA of the common iliac artery. A deep vein was also used as a "pantaloon" aortobiiliac graft and for a brachial artery repair. Staphylococcus aureus was revealed by means of cultures in nearly all cases. Distal arterial perfusion was normal after reconstruction. Patients had no significant postoperative leg swelling. No new venous thrombosis below the level of deep vein harvest was revealed by means of duplex scanning. There were no septic complications. CONCLUSION: The superficial femoral/popliteal veins may be particularly useful for limb revascularization in patients with MPAs. This autogenous conduit provides an excellent size-match and a suitable length for reconstruction, because peripheral, axial arteries are generally affected. No clinically significant limb morbidity was related to deep vein removal. Late follow-up is challenging in such cases, but will be required to accurately determine the durability of this strategy.

Adult↗

PubMed1999

Assessment of ocular perfusion after carotid endarterectomy with color-flow duplex scanning.

PURPOSE: The purpose of this study was to assess the effect of carotid endarterectomy (CEA) on ocular perfusion with the measurement of the ophthalmic artery (OA) and the central retinal artery (CRA) flow velocities with color-flow ocular duplex scanning (ODS). Ocular hemodynamics also were examined in a subset of patients with visual symptoms in an attempt to characterize the origin of the ocular symptoms and their response to surgery. METHODS: Twenty-five patients with internal carotid artery stenoses (>/=70%) underwent 29 CEAs. All the patients underwent ODS for the measurement of the peak systolic velocity (PSV) in the OA and the CRA of the ipsilateral eye before and after CEA. The preoperative and postoperative flow velocities were compared in all the patients and in the patients with and without visual symptoms. RESULTS: The preoperative PSV in the OA was 21.6 +/- 2.2 cm/s and in the CRA was 7.7 +/- 0.7 cm/s. These values were reduced as compared with normative values (OA, 37.8 cm/s; CRA, 10.7 cm/s). After CEA, the PSV increased significantly in both vessels (postoperative OA, 38.6 +/- 2.5 cm/s, P <.0001; postoperative CRA, 12.1 +/- 0.9 cm/s, P =.0008). Fifteen of the 29 CEAs were performed for visual symptoms. The patients with ocular symptoms had significantly lower preoperative PSVs in the CRA as compared with those patients without visual symptoms (CRA with ocular symptoms, 6.5 +/- 0.8 cm/s; CRA with no ocular symptoms, 9.4 +/- 0.9 cm/s; P =.02). The PSV in the OA was not significantly lower in the patients with ocular symptoms. Eight patients (28%) were found to have reversed OA flow before surgery, but only three patients had ocular symptoms. All eight patients had normal antegrade flow in the OA after surgery. CONCLUSION: Severe carotid stenosis may be associated with reduced ocular perfusion, which can be quantitatively evaluated with ODS. Reduced OA and CRA flow velocities are corrected with successful CEA. The patients with ocular symptoms were observed to have significant reductions in CRA flow velocities. Reversed flow in the OA was not a marker for ocular symptoms in this study. ODS can identify global ocular ischemia and may be helpful in the evaluation of patients with atypical visual symptoms or with amaurosis fugax and no evidence of retinal emboli.

Aged↗

PubMed1999

Surgically confirmed incorporation of a chronically retained neurointerventional microcatheter in the carotid artery.

A woman reported painful thrombosis of the superficial femoral artery 16 months after a transfemoral microcatheter was glued into a cerebral arteriovenous malformation and transected at the groin. When the catheter was removed, a portion was found to be incorporated into the wall of the carotid artery. This case demonstrates that portions of a retained microcatheter may be incorporated into the arterial wall while other portions may remain mobile and cause late peripheral arterial symptoms.

Adult↗

PubMed1998

Can intrarenal duplex waveform analysis predict successful renal artery revascularization?

PURPOSE: No currently available noninvasive test can preoperatively predict a successful outcome to renal revascularization. Resistance measurements from the renal parenchyma obtained with duplex sonography reflect the magnitude of intraparenchymal disease, and patients with extensive intrarenal disease may respond less favorably to revascularization. To address this question, we reviewed our (primarily) operative experience in patients undergoing renal artery revascularization, and compared the blood pressure (BP) and renal function response with resistance measurements obtained from the kidney both before and after revascularization. METHODS: During a 56-month period, 31 consecutive renal artery revascularizations (25 surgical and 6 percutaneous angioplasties) were performed in 23 patients (21 atherosclerotic, 2 fibromuscular dysplasia). Duplex sonography was performed in each patient before and after revascularization, and parenchymal diastolic/systolic (d/s) ratios were calculated. BP and renal function response to intervention were compared with measurements of intrarenal flow patterns before and after revascularization. RESULTS: Mean parenchymal peak systolic velocity was significantly higher after repair in all patients (pre-repair: 19.5 +/- 1.3, postrepair: 27.2 +/- 1.7; P < .0001). Despite this, there were no statistical differences between preoperative and postoperative parenchymal d/s ratios. A favorable (cured or improved) BP response was seen in 81% (17 of 21) of revascularizations performed for hypertension. Among these successes, parenchymal d/s ratios were in the normal range (ie, > or = 0.30) both before and after repair (mean prerepair: 0.34 +/- 0.03, mean postrepair: 0.31 +/- 0.03; not significant). In 4 patients in which BP failed to improve after intervention, the d/s ratio was abnormal before surgery (< 0.3), and remained so after revascularization (mean preoperative d/s ratio: 0.18 +/- 0.04, mean postoperative d/s ratio: 0.11 +/- 0.04; P = .003). Mean preoperative parenchymal d/s ratios were significantly higher in all patients with a successful BP response when compared with failures (P = .048). Similarly, among patients with single artery repairs, mean preoperative d/s ratios approached significance in successes vs. failures (success: 0.40 +/- 0.03, failure: 0.21 +/- 0.03; P = .054). A decrease in serum creatinine greater than or equal to 20% was seen in 8 of 18 patients (44%) with ischemic nephropathy. These patients also had normal d/s ratios preoperatively (mean 0.39 +/- 0.04), whereas the 10 patients who failed to improve had significantly lower ratios (mean 0.24 +/- 0.03; P = .041). Kidney length did not correlate with d/s ratio. CONCLUSION: Although we do not believe that duplex sonographic measurement of intrarenal flow patterns alone is an accurate means of assessing main renal artery occlusive disease, the resistive indices seem to reflect the magnitude of intraparenchymal disease, and thus may provide important prognostic information for patients undergoing surgical revascularization. Our data suggest that a preoperative d/s ratio below 0.3 correlates with clinical failure relative to BP and renal function responses.

Aged↗

PubMed1997

A randomized, prospective trial of deep venous thrombosis prophylaxis in aortic surgery.

OBJECTIVES: To study the incidence of postoperative deep venous thrombosis (DVT) in patients undergoing elective aortic reconstruction and to determine if aggressive DVT prophylaxis would reduce the incidence of DVT in these patients. DESIGN: Randomized, prospective trial. SETTING: University hospital and Veterans Affairs hospital. PATIENTS: One hundred patients undergoing aortic reconstruction for aneurysmal or occlusive disease randomized to receive DVT prophylaxis (treatment group) or no prophylaxis (control group). Exclusion criteria included a history of DVT, long-term anticoagulant use, or a malignant neoplasm. During the study period, 12 patients were ineligible for follow-up. Ninety-eight patients completed the trial, including 50 patients in the treatment group and 48 patients in the control group. Two patients in the control group died postoperatively of unrelated causes. INTERVENTION: Patients in the treatment group received DVT prophylaxis using a combination of low-dose heparin sodium therapy (5000 U every 12 hours) and calf-length intermittent mechanical compression devices. Control patients received no DVT prophylaxis. MAIN OUTCOME MEASURES: The occurrence of acute lower extremity DVT diagnosed by interval venous duplex ultrasound scan surveillance performed on postoperative days 1, 3, and 7. RESULTS: The overall incidence of proximal DVT in this study was 2%. One case of DVT occurred in the treatment group, and the other one occurred in the control group. There was no statistically significant difference (P = .99) in the incidence of DVT between the 2 groups. One patients in the control group had a nonfatal pulmonary embolus (1% of the patients overall). CONCLUSIONS: The incidence of proximal DVT in patients undergoing elective aortic reconstruction is low compared with patients undergoing other major intraabdominal general surgical procedures. The use of aggressive DVT prophylaxis did not reduce the risk of postoperative proximal DVT in this study. The selective use of DVT prophylaxis in patients undergoing elective aortic surgery should be based on associated concomitant or evolving risk factors.

Adult↗

PubMed1997

Regression of proximal deep venous thrombosis is associated with fibrinolytic enhancement.

PURPOSE: Recanalization after acute lower limb deep venous thrombosis (DVT) is well documented, but the precise mechanism and timing of these events has not been well characterized. Regression of DVT has been presumed to result from activation of the endogenous fibrinolytic system. This study was performed to compare measurements of the enzymatic components of the intrinsic fibrinolytic system (tissue plasminogen activator [tPA], plasminogen activator inhibitor [PAI-1]) with the observed morphologic changes in thrombosed venous segments using venous duplex ultrasound scanning (VDUS) at intervals after diagnosis of acute DVT. METHODS: Nineteen patients with acute DVT underwent serial VDUS to assess regression of thrombus at intervals of 1 to 2 weeks, 3 to 6 weeks, 8 to 12 weeks, and 24 to 36 weeks. The extent of thrombus in each limb was quantitated at each interval by VDUS of the residual thrombus present in each of five major axial venous segments: the common femoral, superficial femoral, profunda femoris, popliteal, and tibial veins. Thrombus scores for the group at each interval were compared with baseline scores at diagnosis to calculate the percent residual thrombus. Endogenous fibrinolytic activity was determined at the same intervals by serologic assay of the biologic activities of tPA and its inhibitor PAI-1. RESULTS: Thrombus regression was evident by VDUS at 1 to 2 weeks and progressed such that only 26% of residual thrombus remained at 24 to 36 weeks. Complete resolution of thrombus occurred in 10 of 18 patients (56%) who completed the 9-month study. Baseline mean tPA activity was 0.60 +/- 0.07 IU/ml and increased to 1.31 +/- 0.26 IU/ml at 1 to 2 weeks (p = 0.014). tPA activity remained significantly elevated through the 8 to 12 week interval and returned to baseline at 24 to 36 weeks. PAI-1 activity was elevated relative to an age-matched population at baseline (23.1 +/- 1.8 AU/ml) but remained unchanged throughout the study period. Progression of thrombus was observed in three patients (15.8%). Patients who experienced propagation of thrombus did not have the increased tPA activity that appeared to mark activation of intrinsic fibrinolysis. CONCLUSIONS: Regression of acute DVT begins early and continues for at least 9 months. It is accompanied by significant enhancement of the endogenous fibrinolysis, which appears to be primarily mediated by increased tPA activity. Patients who have thrombus propagation in spite of standard antithrombotic therapy may have failure of activation of endogenous fibrinolysis.

Acute Disease↗

PubMed1997

Defective fibrinolysis occurs after infrainguinal reconstruction.

PURPOSE: Early thrombosis of infrainguinal bypass grafts may occur as a result of hypercoagulable states. Major surgical procedures are known to induce a procoagulant state that is manifested in part by reduced endogenous fibrinolytic activity or fibrinolytic shutdown. This study was performed to assess the timing and biologic mechanism of fibrinolytic shutdown after infrainguinal bypass procedures by direct assay of the serologic markers of in vivo fibrinolytic activity. METHODS: Twenty patients underwent infrainguinal bypass procedures under epidural anesthesia. Endogenous fibrinolytic activity was assessed by measurement of tissue plasminogen activator (tPA) and its naturally occurring inhibitor, plasminogen activator inhibitor (PAI-1). The tPA and PAI-1 antigen (total protein) levels were determined using enzyme-linked immunosorbent assays, and measurements of in vivo biologic activity were performed using an amidolytic method. Measurements of tPA and PAI-1 were made before surgery, after surgery, and on postoperative days 1, 2, 7, and 30. RESULTS: The mean preoperative PAI-1 activity was 20.6 +/- 1.4 arbitrary units (AU)/ml, which was higher than that of an age-matched population without severe atherosclerosis. PAI-1 activity rose significantly after surgery (29.6 +/- 2.2 AU/ml; p = 0.002) and remained elevated through the second day after surgery. Preoperative tPA activity level was 2.04 +/- 0.59 IU/ml and fell to 0.79 +/- 0.23 IU/ml (p = 0.046) immediately after the bypass procedure. All serologic indicators of fibrinolytic shutdown returned to baseline levels by 72 hours after surgery. No early graft thrombosis or other atherothrombotic complications occurred in these study patients. CONCLUSIONS: Defective endogenous fibrinolytic activity occurs in the early postoperative period after infrainguinal bypass grafting procedures. Diminished endogenous fibrinolytic activity in these patients appears to be mediated by a combination of reduced tPA activity and significantly increased PAI-1 activity. No practical method is available to directly treat postoperative fibrinolytic shutdown, but postoperative antithrombotic therapy may be useful during this period to prevent early graft occlusion related to a relative hypercoagulable state.

Aged↗

PubMed1996

Early duplex scan evaluation of four vena caval interruption devices.

PURPOSE: Transvenous inferior vena cava (IVC) filters are used successfully for prevention of pulmonary embolism (PE), but early thrombotic complications such as insertion site thrombosis (IST) and inferior vena cava thrombosis (IVCT) may occur after placement. The frequency of these complications has been uncertain particularly for the wide variety of newer devices. This study was performed to prospectively evaluate IST and IVCT with color-flow venous duplex ultrasound scanning after four IVC filters were placed: the birds' nest filter, the titanium Greenfield filter, the stainless steel Greenfield filter, and the Simon nitinol filter. METHODS: Percutaneous IVC filters were placed in 174 patients over a 21-month period. A birds' nest filter was used in 39 (22%) cases, a titanium Greenfield filter in 67 (39%) cases, a stainless steel Greenfield filter (25%) in 43 patients, and a Simon nitinol filter in 25 (14%) cases. Filters were placed for major deep venous thrombosis in 113 (63%) patients, after PE in 26 (15%) patients, and with prophylaxis in 35 (20%) patients. All patients had color-flow venous duplex ultrasound scanning of the insertion site and the inferior vena cava 7 to 10 days after placement or before discharge to document IST or VCT. RESULTS: Early IST occurred in 43 (24.7%) cases, and early IVCT was observed in 20 (12%) cases in this series. No significant difference was found in the incidence of IST or IVCT among the four filter types used. The incidence of IVCT was significantly higher in patients having filters placed for PE. Men were more likely to receive a prophylactic filter than women in this study, but thrombotic complications were not related to patient sex. Thrombosis was seen with equal frequency at all insertion sites used. No patient died of PE after filter placement during the study period. CONCLUSIONS: The incidence of thrombotic complications for all devices was higher than has generally been reported. No IVC filter used in this study demonstrated superior performance with regard to these thrombotic complications. As vena cava interruption devices are developed or significantly modified, prospective objective analysis of associated thrombotic complications will allow logical selection for clinical use.

Adolescent↗

PubMed1995

Venous hemodynamics during impulse foot pumping.

PURPOSE: This study was designed to measure the effect of intermittent pneumatic compression of the plantar venous plexus on popliteal vein (PV) and common femoral vein (CFV) velocities measured by duplex ultrasound scanning. METHODS: Thirty lower limbs in 15 healthy volunteers had venous duplex scanning measurement of PV and CFV velocities before and during foot pumping with an arteriovenous impulse foot pump system. Venous velocities were measured at two pump pressure settings (100 mm Hg, 200 mm Hg) and during two pump impulse durations (short = 1 second, normal = 3 seconds). All limbs were examined with the subjects in the supine position, and then measurements were repeated with subjects in the 15-degree reverse Trendelenburg position. The mean maximum venous velocity (MVV) produced by foot pumping was compared with resting venous velocity at each anatomic location and for each technologic variable. RESULTS: Impulse foot pumping produced a statistically significant increase in MVV in both the PV and the CFV compared with resting velocities. This significant increase was observed for both pressure settings and both impulse durations, and no differences produced by these two individual variables could be detected. The increase in MVV produced by foot pumping was similar for limbs in the supine position and those examined in the reverse Trendelenburg position. The percentage increase in MVV produced by foot pumping was significantly higher in the PV than in the CFV. CONCLUSIONS: Intermittent pneumatic compression of the plantar venous plexus produces measurable increases in venous outflow from the lower limbs of normal subjects. This study seems to justify further evaluation of the effectiveness of this technique for mechanical deep venous thrombosis prophylaxis in selected high-risk patient groups.

Adult↗

PubMed1995

Responses of immunoreactive ACTH and bioactive ACTH to large hemorrhage and resuscitation in conscious dogs.

We studied the effect of fluid resuscitation on immunoreactive adrenocorticotropic hormone (irACTH) and bioactive ACTH (bioACTH) after hemorrhage in conscious dogs. Animals (n = 7) were bled 30% (approximately 25 ml/kg) over 3 min and 30 min later were either resuscitated [43.3 ml/kg 0.9% NaCl (1.8 times hemorrhage volume) over 10 min] or not. Blood was reinfused after 210 min. Animals had both treatments (> 4 days apart). irACTH, bioACTH, cortisol, angiotensin II, and aldosterone increased rapidly after hemorrhage. Resuscitation increased blood volume and cardiac output to resting values, but arterial hypotension persisted. bioACTH and irACTH decreased 40-90 min after hemorrhage in both groups, but each decreased more rapidly after resuscitation. The elimination half-life of bioACTH was shorter than that of irACTH, but neither was affected by resuscitation. The ratio of bioACTH to irACTH followed the same pattern with or without resuscitation. Angiotensin II and aldosterone remained increased without resuscitation but decreased promptly after resuscitation. In conclusion, 1) saline infusion at 1.8 x hemorrhage volume provides effective cardiovascular resuscitation, with resolution of hormonal responses to hemorrhage; 2) although ACTH responses resolved with or without resuscitation, resuscitation produced more rapid resolution without changing the parameters of ACTH elimination; 3) the dynamics of the resolution of the ACTH response to hemorrhage are similar whether induced by stimulus removal or feedback inhibition.

Adrenocorticotropic Hormone↗