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Biomedical subjects

W M Blackshear

Publications and source records attributed to W M Blackshear.

At least 19 recordsLinked to original sources
PubMed1994

Infrainguinal endovascular in situ saphenous vein bypass: ongoing results.

PURPOSE: With 70 cm "cutter" valvulotomes for valvulotomy and an electronically steerable nitinol catheter to occlude venous tributaries with platinum coils, endovascular in situ saphenous vein (EISV) bypass can be safely performed from within the saphenous vein. To determine whether EISV bypass could reduce hospital length of stay (LOS) and perioperative morbidity without compromising patency, another 53 EISV bypasses for limb salvage were performed. METHODS: Tributary occlusion was accomplished with only fluoroscopic surveillance with a new, smaller, and more steerable silicone-tipped nitinol catheter. RESULTS: Two (3.7%) wound complications occurred. The mean hospital LOS after operation was 4.2 days (range 2 to 29 days). All tributaries initially embolized remained occluded, and three "missed" arteriovenous fistulas were identified during follow-up extending to 15 month (mean 8.4 months). Eighty-eight percent (49 of 54) of phase II bypasses remained patent, whereas life-table analysis of all bypasses (phase I and II) was 77% (69/99) at 24 months follow-up (mean 13.6 months). By comparison, 41 infrainguinal saphenous vein in situ bypasses with "classic" open techniques were performed concurrently. The mean postoperative LOS was 11.6 days (range 4 to 42 days), wound complications occurred in 24% (10) of patients, and two "missed" arteriovenous fistulas were identified during follow-up. Eighty-three percent (34 of 41) of bypasses remain patent at 24 months follow-up (mean 16.2 months). CONCLUSIONS: If EISV bypass long-term patency rates remain similar to classic in situ bypass patency results, the additional benefits of decreased hospital LOS, reduced wound-related complications, shortened recuperation, and therefore increased health care savings gives this endovascular technique strong consideration as the possible future operation for infrainguinal saphenous veins in situ bypass.

Aged↗
PubMed1994

The small abdominal aortic aneurysm: the eternal dilemma.

In order to evaluate morbidity and mortality after elective resection of abdominal aortic aneurysms (AAA) as it relates to aneurysm size, a retrospective review of 111 elective aneurysmectomies over a 5 year period was undertaken in a VA population. Thirty seven AAA's measured < 5 cm in diameter and 74 were > or = 5 cm by CT scan. Patients with small AAA (S-AAA) were significantly younger (mean 64 years) than those with large AAA (L-AAA) (mean 69 years) (p < 0.003). Both groups were similar with respect to prevalence of cardiovascular, pulmonary and renal disease. Aortic cross-clamping time was significantly shorter in L-AAA, possibly because those with S-AAA had a higher prevalence of associated occlusive disease requiring more femoral anastomoses (p < 0.04). Postoperatively six patients (8%) had a myocardial infarction (MI) in the L-AAA group and four (5%) of these died. In contrast no patient with S-AAA suffered a postoperative MI. The rates of non-cardiac complications and length of hospital stay were not significantly different between the two groups. However, the patients with L-AAA stayed longer in ICU (p < 0.05) and the overall combined morbidity rate was significantly higher in this group (p < 0.02). Our results suggest that resection of S-AAA upon diagnosis in acceptable risk patients appears to be the safest overall therapeutic plan.

Aged↗
PubMed1991

Myointimal hyperplasia as a result of balloon-catheter thromboembolectomy.

The balloon-tipped embolectomy catheter is widely utilized in the treatment of arterial thromboemboli, significantly improving mortality and limb salvage rates. However, early and late complications related to catheter-tip injury and balloon trauma continue to occur and compromise the results of surgical intervention. Myointimal hyperplasia is an example of an unusual late complication induced by balloon-related arterial wall trauma. Myointimal hyperplasia is a commonly recognized healing response of the arterial wall to endothelial injury but is rarely reported after balloon-catheter thromboembolectomy. The extensive nature of the injury increases the incidence of limb loss. The pathophysiologic nature of this process is reviewed, and pertinent structural details such as intimal thickening and disruption of the internal elastic lamina are presented. The pathogenesis of myointimal hyperplasia suggests guidelines for catheter use during embolectomy that may further reduce the incidence of this unusual complication.

Adult↗
PubMed1988

Bilateral upper extremity ischemia after administration of dihydroergotamine-heparin for prophylaxis of deep venous thrombosis.

Prolonged arterial spasm as a complication of ergot-containing medications has been reported since antiquity. This article describes our experience with a patient who had severe bilateral arterial spasm in the upper extremities 6 days after the initiation of a regimen of dihydroergotamine and heparin for prophylaxis against deep venous thrombosis. The spasm was refractory to oral calcium channel blocking agents and direct intraarterial infusion of tolazoline (Priscoline). However, intraarterial nitroglycerin produced a prompt and dramatic improvement in symptoms and in physical and arteriographic findings. This experience suggests that intraarterial nitroglycerin may be an appropriate first choice for ergot-induced arterial spasm.

Arm↗
PubMed1987

Pulsed Doppler frequency and carotid stenosis.

Two hundred and forty-two internal carotid arteries (ICA) were evaluated by independently interpreted arteriography and pulsed Doppler spectrum analysis using ultrasonic arteriography to evaluate the ability of peak systolic frequency (PSF) to predict the degree of internal carotid stenosis. Mean PSF in the 129 (53.3%) high grade ICA stenoses of greater than 50% diameter reduction was 6.55 +/- 0.14 (SEM) khz, while mean PSF in the 113 (46.7%) low grade (less than 50% diameter reduction) stenoses was 3.38 +/- 0.12 (SEM) kHz (P less than 0.0001). Receiver-operator characteristic (ROC) analysis revealed that PSFs of 4.5 kHz (sensitivity 87%, specificity 88%) and 5.0 kHz (sensitivity 83%, specificity 93%) were best for identifying a 50% diameter stenosis. Positive predictive value of 5.0 kHz was 93% (107/115) and negative predictive value was 82.7% (105/127). Linear regression analysis of PSF in kHz versus percentage diameter reduction yielded the equation: % stenosis = 10.7 (PSF) - 4.1 (r = 0.76). A nonlinear equation was also derived: % stenosis = 61.9 - 33.5 (PSF) + 8.7 (PSF)2 - 0.5 (PSF)3 (r = 0.77). Based on this analysis peak systolic frequency criteria measured by pulsed Doppler spectrum analysis appear to be useful for distinguishing high grade from low grade stenoses. Both the linear and nonlinear equations further suggest that PSF can more precisely quantitate the degree of ICA luminal narrowing.

Carotid Artery Diseases↗
PubMed1987

Influence of sequential pneumatic compression on postoperative venous function.

Sequential external pneumatic compression (SEPC) has been reported to decrease the incidence of acute deep venous thrombosis in postoperative patients by a direct mechanical action on the lower extremity veins and/or by inducing alterations in systemic fibrinolysis. To evaluate the effect of SEPC on venous function in the postoperative patient, pre- and postoperative venous capacitance (VC) and outflow (VO) were measured in a series of general surgical patients. In phase I, 17 limbs were evaluated in patients who had been fully ambulatory preoperatively and at complete bed rest postoperatively. VC decreased from 3.19 +/- 0.43 cc/100 cc of tissue (mean +/- standard error of the mean) preoperatively to 2.08 +/- 0.34 cc/100 cc of tissue postoperatively (p less than 0.05) and VO decreased from 87.2 +/- 10.6 cc/100 cc of tissue/min preoperatively to 58.1 +/- 8.7 cc/100 cc of tissue/min postoperatively (p less than 0.025). In phase II SEPC was begun preoperatively and continued for 24 hours postoperatively on one limb of 20 patients. SEPC prevented the decrease in VC and VO both in the pumped leg (VC-2.65 +/- 0.26 cc/100 cc of tissue preop, 2.40 +/- 0.18 cc/100 cc of tissue postop, p greater than 0.2; VO-72.3 +/- 5.9 cc/100 cc of tissue/min preop, 66.2 +/- 5.3 cc/100 cc of tissue/min postop, p greater than 0.2) and in the unpumped limb (VC-2.85 +/- 0.18 cc/100 cc of tissue preop, 2.41 +/- 0.24 cc/100 cc of tissue postop, p greater than 0.05; VO-66.1 +/- 5.2 cc/100 cc of tissue/min preop, 66.7 +/- 6.7 cc/100 cc of tissue/min postop, p greater than 0.5).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Continuous-wave Doppler in the intraoperative assessment of carotid endarterectomy.

A sterile 8.5 MHz continuous-wave Doppler probe was used intraoperatively to evaluate the technical result of 229 consecutive carotid endarterectomies. Primary areas of evaluation included the proximal point of plaque transection and the internal and external carotid arteries at and distal to the termination of the endarterectomy. Subjective interpretation was made of the Doppler audio signal. Signs associated with inadequate technical results were a high-frequency signal indicative of luminal narrowing with a reduction in frequency distal to the area of stenosis, absence of a Doppler signal indicating occlusion, and a weak monophasic flow signal indicating poor distal perfusion. Abnormal signals were identified in 10 internal carotid arteries (4.3%) which prompted intraoperative angiography in eight and immediate reopening of the artery in an additional two. Significant lesions were identified in seven arteries (70%). Twenty external carotid lesions (8.7%) were detected by Doppler and in 19 cases (95%) a significant stenosis or obstruction was found when the vessel was reopened. Auscultation of a continuous-wave Doppler signal with a sterile probe at operation appears to have a high positive predictive value in the identification of both internal and external carotid stenoses. It is rapid, safe, relatively inexpensive, and avoids the problems associated with routine intraoperative angiography.

Auscultation↗
PubMed1984

Correlation of hemodynamically significant internal carotid stenosis with pulsed Doppler frequency analysis.

Systolic and mean pressure gradients across internal carotid stenoses were measured at the time of carotid endarterectomy in the arteries of 90 patients, all of whom underwent angiography. Eighty-two of these patients also had pulsed Doppler ultrasonic arteriography with real-time spectrum analysis. There were 71 (79%) high grade stenoses of greater than 50% diameter reduction by angiography. Significant systolic pressure gradients (greater than or equal to 10 mmHg) were identified in 41 patients (46%), 38 (46%) of whom underwent ultrasonic evaluation. A pulsed Doppler frequency measured within the stenosis equal to or greater than 6.5 kiloHertz had a sensitivity of 94.7% (36/38) in identifying pressure reducing lesions with a specificity of 47.7% (21/44). Positive predictive value was 61% (36/59). Angiographic criteria (50% diameter reduction) exhibited a sensitivity of 97.6% (40/41), a specificity of 36.7% (18/49) and a positive predictive value of 56.3% (40/71). Negative predictive value was 94.7% for angiography and 91.3% for ultrasonic arteriography. A pulsed Doppler frequency equal to or greater than 6.5 kiloHertz appears to accurately identify lesions that are at risk to reduce distal internal carotid pressure under operative conditions with a sensitivity similar to angiography. This criterion has a positive predictive value and specificity that is slightly superior to angiography and a high negative predictive value. Pulsed Doppler spectrum analysis provides physiologic information relative to blood flow velocity that is complimentary to the anatomic data provided by angiography for assessing the potential for hemodynamic significance of internal carotid stenoses.

Blood Pressure↗
PubMed1984

Exercise testing in lower-extremity arterial occlusive disease.

Exercise tolerance testing has wide application in the detection and quantitation of lower-extremity claudication. Serial follow-up after operative or nonoperative therapy permits an accurate, objective assessment of the course of the disease in each limb. Unmasking of occult aortoiliac disease, identification of pseudoclaudication, and assessment of the relative contribution of other systemic disorders in exercise limitation are further advantages of this technique. Routine exercise tolerance testing has merit for the initial and subsequent evaluations when symptoms of leg pain are produced solely by exercise.

Arteriosclerosis Obliterans↗
PubMed1982

Noninvasive carotid evaluation using pulsed Doppler imaging for patients with ophthalmic disorders.

Pulsed Doppler imaging provides an accurate, noninvasive technique for evaluation of the carotid bifurcation. We have found it useful in evaluating patients with amaurosis fugax and ocular emboli. It can also be used to evaluate blood flow within ocular and orbital tumors. The continuous wave Doppler is useful for detection of abnormal orbital blood flow in patients with dural-cavernous fistulae.

Adolescent↗
PubMed1982

Doppler sonography in the diagnosis of dural carotidcavernous fistula.

Intracranial dural fistulas in the region of the cavernous sinus usually occur in middle-aged or elderly women in whom physical findings of ocular pulsation, orbital bruit, and ocular injection are subtle or absent. We examined a 19-year-old man with hemophilia who had a red, mildly proptosed left eye. Typical features of a carotidcavernous sinus fistula were absent except for the presence of dilated, tortuous episcleral vessels. Directional Doppler ultrasound evaluation detected retrograde blood flow in the left frontal vein and thus confirmed the presence of an arteriovenous shunt. After a selective internal carotid angiogram demonstrated a shunt from a dural branch of the internal carotid artery, the patient's symptoms remitted spontaneously. Directional Doppler ultrasonography is a noninvasive test that can detect the presence of a low flow, retrobulbar arteriovenous shunt in the region of the cavernous sinus.

Adult↗
PubMed1981

Spectral analysis of Doppler velocity patterns in normals and patients with carotid artery stenosis.

A computerized pattern recognition program was utilized to assess the predictive ability of various parameters obtained from the spectra of ultrasonic pulsed Doppler signals from the carotid arteries. The most accurate features selected by linear regression analysis were the natural log (ln) of the ratio of the mean velocity in the internal carotid artery compared to that in the common carotid artery, and the ln of the maximum velocity, the ln of the maximum frequency, and the square of the fractional broadening term, all of which were measured at peak systole in the internal carotid artery. Using the combination of the velocity ratio and the fractional broadening term, the average difference in the estimated percentage stenosis, as compared to that obtained by arteriography, was 12.8%.

Arteriosclerosis↗
PubMed1980

Natural history of above- and below-knee femoropopliteal grafts.

Postoperative physiologic data were reviewed in 74 patients with 85 femoropopliteal bypass grafts. Documented progression of atherosclerosis occurred in the aortoiliac segment in 18 limbs and in the popliteal and tibioperoneal vessels in 14 limbs, although aortoiliac disease was more often responsible for graft failure. Grafts with good postoperative runoff as determined by hemodynamic measurements had a statistically significant higher patency rate than those with poor runoff. Nearly half of the limbs with a progressive postoperative decline in the ankle-arm index ultimately had graft occlusion. Rapid progression of popliteal artery atherosclerosis distal to an above-knee graft was not a significant problem.

Aneurysm↗