PubMed Health⌕ Search

Biomedical subjects

T G Lynch

Publications and source records attributed to T G Lynch.

At least 19 recordsLinked to original sources
PubMed1992

Duplex scans before subclavian vein catheterization predict unsuccessful catheter placement.

Subclavian catheterization in patients with cancer is associated with up to a 38% incidence of subclavian vein thrombosis. These thrombi seldom recanalize. The persistent occlusion of the subclavian vein may hinder subsequent catheter placement. To determine the frequency of this occurrence and to determine if preoperative duplex scanning could identify these individuals, we performed preoperative duplex scanning in 22 patients who had previously had an indwelling subclavian catheter for chemotherapy. Subsequent subclavian vein catheterization was attempted without knowledge of the results of the duplex scan. Nineteen scans were normal. Of these, 18 patients underwent successful catheter placement. In one patient, catheterization was unsuccessful and an intraoperative venogram showed a focal obstruction of the proximal portion of the subclavian vein. Three scans showed noncompressibility of the vein, and catheter placement was unsuccessful in these three veins. In patients who have had previous subclavian catheters, persistent obstruction of the vein prevents subsequent catheter placement in 14%. Duplex scanning before subsequent catheter placement generally identifies these individuals.

Bone Marrow Transplantation↗
PubMed1991

Limitations of magnetic resonance imaging and ultrasound-directed (duplex) scanning in the diagnosis of subclavian vein thrombosis.

To investigate the potential role of magnetic resonance imaging and duplex scanning in the diagnosis of catheter-induced subclavian vein thrombosis, we correlated the results of 43 arm phlebograms with duplex scans; 28 of these phlebograms were also correlated with magnetic resonance imaging scans of the thoracic veins. Eighteen of the 43 phlebograms were normal, and all had normal magnetic resonance imaging and duplex studies. Eleven subclavian veins were totally occluded on phlebography; all had duplex scans, and five were also scanned with magnetic resonance imaging. Duplex scans detected 6 of 11 occlusions, whereas magnetic resonance imaging detected 4 of the 5 occlusions scanned. The five occlusions that were not detected by either magnetic resonance imaging or duplex scans were short segmental occlusions of the medial one third of the left subclavian vein. Of 14 nonocclusive thrombi seen on phlebography, duplex scans correctly identified 8. Magnetic resonance imaging was done on eight nonocclusive thrombi but identified only two. All abnormal findings on duplex scanning and magnetic resonance imaging were confirmed by phlebography. Short occlusions of the proximal portion of the left subclavian vein were often undetected by duplex scanning but occasionally seen with magnetic resonance imaging. Neither modality was sensitive to the presence of nonocclusive mural thrombi. Magnetic resonance imaging is highly reliable in ruling out the presence of a thrombotic process in the subclavian vein, but it may on occasion fail to detect the presence of subclavian thrombi. For this reason, in cases with suspected subclavian vein thrombosis magnetic resonance imaging cannot be used as the only diagnostic modality.(ABSTRACT TRUNCATED AT 250 WORDS)

Catheterization, Central Venous↗
PubMed1991

Utility of duplex ultrasound in the diagnosis of asymptomatic catheter-induced subclavian vein thrombosis.

Asymptomatic thrombosis of the subclavian vein is common after placement of indwelling catheters. The sequelae of these thrombi are not known. Investigation is hampered by the requirement for venography for diagnosis; consequently, a noninvasive method of diagnosis would be welcome in this context. We have studied prospectively 32 subclavian catheters to determine the usefulness of duplex ultrasound in diagnosing asymptomatic thrombosis. Sixteen arm venograms were normal and all gave normal duplex scans. No false-positive scans were obtained. Eleven venograms demonstrated nonocclusive mural thrombi. Only three of these were seen with duplex ultrasound. Five totally occlusive thrombi were seen on venography, of which only two were detected with duplex sonography. The three thrombi not found with duplex ultrasound were short proximal venous occlusions. The insensitivity of this technique to asymptomatic subclavian thrombi limits its usefulness as a screening tool.

Blood Flow Velocity↗
PubMed1988

Doppler ultrasound, laser Doppler, and perfusion fluorometry in bowel ischemia.

Improved accuracy and objectivity in the evaluation of intestinal viability has been reported by some investigators using Doppler ultrasound, and more recently laser Doppler velocimetry and perfusion fluorometry. To compare the sensitivity and clinical applicability of these techniques, intestinal viability was evaluated by each method in nine 15- to 50-cm loops of small bowel prepared by division of the mesenteric vasculature in five anesthetized dogs. The sensitivity of Doppler ultrasound was 86%, of laser Doppler flow velocity 85%, of laser Doppler index 94%, and of perfusion fluorometry 95%. Though the sensitivity of Doppler ultrasound is significantly less than that of laser Doppler and perfusion fluorometry, this is not unexpected since the latter two techniques are more quantitative than Doppler ultrasound. Clinically, Doppler ultrasound compares favorably with laser Doppler and perfusion fluorometry, and its low cost and simplicity suggest its adjunctive use in the operative setting.

Animals↗
PubMed1987

Poststenotic flow velocity changes as a function of stenosis geometry.

We used an in vitro pulsatile flow model to examine the velocity profile distal to a variable nonaxisymmetric stenosis. Using a continuous-wave Doppler velocimeter, the peak systolic frequency was determined distal to the stenosis and in planes parallel and perpendicular to the long axis of the stenosis. In both planes, an exponential regression best describes the relationship between peak systolic frequency and reduction in cross-sectional area. Regressions at each point of insonation diverged as a direct function of reduction in cross-sectional area and as an indirect function of distance from the stenosis. At each point of insonation, regressions representing the relationship in the mutually perpendicular planes diverged in direct proportion to reduction in cross-sectional area. Slopes were greater in parallel planes of insonation. These data demonstrate that two variables, distance and geometry, may influence the results of spectral analytic studies.

Arterial Occlusive Diseases↗
PubMed1987

Vascular complications related to drug abuse.

Vascular complications resulting from drug abuse constitute a widespread and common clinical problem. A 3-year experience with 32 vascular complications (13 arterial, 19 venous) related to intravenous drug abuse is reported. Fourteen (48%) of the 29 patients in this series presented with septic vascular complications. These infections were a major cause of morbidity and mortality, resulting in two hospital deaths and a disrupted arterial repair. In addition, intra-arterial drug injection caused digital gangrene in two patients. Early recognition, diagnostic arteriography and venography, and planned therapeutic interventions are possible if a high level of suspicion is maintained.

Adult↗
PubMed1986

Microprocessor-controlled pulsatile flow loop for hemodynamic studies.

Validation of spectral analytic techniques in the clinical assessment and quantitation of vascular stenoses has been aided by use of in vitro flow loops. We have used a recently developed microprocessor-controlled pulsatile flow model to examine the influence of varying stenoses on Doppler-shifted peak systolic frequencies. A nonaxisymmetric, vertically oriented stenosis was produced by extrinsic compression of latex rubber tubing 12 mm in diameter, reducing the cross-sectional area (CSA) by 25, 40, 50, 60, 70, 85, and 97%. A rolling diaphragm pump, driven through a slider-crank mechanism by a microprocessor-controlled stepper motor, generated characteristic arterial pulse waves at a rate of 75 cycles per minute. Using an 8 MHz, continuous-wave, directional Doppler velocimeter, the Doppler-shifted frequencies were recorded at the stenosis. Four sets of observations were made at each of the stenoses, and the peak systolic frequency (PSF) was determined using a spectrum analyzer. The PSF in the absence of an obstructing stenosis was 2.56 +/- 0.03 (KHz +/- SEM). This increased significantly (P less than 0.05) to 4.80 +/- 0.09 when the CSA was reduced by 50%, to 5.90 +/- 0.37 when the CSA was reduced by 60% (P less than 0.05), to 8.40 +/- 0.10 when the CSA was reduced by 70% (P less than 0.05), and to 17.84 +/- 0.89 when the CSA was reduced by 85% (P less than 0.05). These data establish the utility of this pulsatile flow model, confirming the direct relationship between the Doppler-shifted PSF and the percentage reduction in CSA.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed1986

Effects of prostacyclin injections and infusions on canine femoral hemodynamics.

The use of prostacyclin (PGI2) infusions has been recommended in the management of patients with severe distal arteriopathy, who are not candidates for conventional bypass procedures. Further clarification regarding the route of administration and the optimal dose of this potent vasodilator, however, is needed before controlled clinical trials are initiated. We measured bilateral femoral arterial blood flow electromagnetically in seven anesthetized adult mongrel dogs. Systemic arterial pressure and cardiac output were also measured. Central venous and femoral arterial injections of PGI2 were administered in five doses ranging from 10(-4) to 10(0) micrograms X kg-1 to study the dose response. PGI2 was also infused intravenously and intra-arterially for 20 minutes at a dose of 10(-1) micrograms X kg-1 X min-1. Femoral arterial injections of PGI2 in doses from 10(-4) through 10(0) micrograms X kg-1 caused significant (p less than 0.05) and dose-dependent increases in ipsilateral femoral arterial blood flow. Intravenous injections of PGI2 caused no significant changes in the dose range from 10(-4) to 10(-2) micrograms X kg-1 but resulted in a significant (p less than 0.05) reduction in femoral arterial flow and systemic arterial pressure at doses of 10(-1) and 10(0) micrograms X kg-1. The femoral arterial infusion of PGI2 produced a significant and sustained increase in femoral arterial flow that was not observed during the intravenous infusion. Arterial pressure was unchanged with intra-arterial PGI2 but was significantly reduced during the intravenous infusion. The beneficial hemodynamic effects of intra-arterial PGI2 suggest that further clinical trials should employ this route of administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

The value of laser Doppler velocimetry and transcutaneous oxygen tension determination in predicting healing of ischemic forefoot ulcerations and amputations in diabetic and nondiabetic patients.

The ability to predict successful healing of ulcerations and amputations of the ischemic forefoot continues to be a major clinical challenge, particularly in diabetic patients whose systolic Doppler ankle pressures are often artifactually elevated. We have used the techniques of laser Doppler velocimetry (LD) and transcutaneous oxygen tension monitoring (tcPO2) to quantitatively measure skin blood flow in the distal foot. Fifty-nine limbs were studied (48 patients), of which 37 (63%) were in diabetic and 22 (37%) in nondiabetic patients. All patients were admitted with ischemic ulcerations or gangrenous changes of the forefoot or digit. Twenty transmetatarsal or digital amputations were performed; the remainder of the lesions were débrided and allowed to heal by secondary intention or were covered by a skin graft. Before operation, the systolic pressure (expressed in millimeters of mercury, mean +/- SEM) was measured by Doppler technique at the ankle, and the ankle/arm index calculated (n = 59 limbs). The tcPO2 (also expressed in millimeters of mercury, mean +/- SEM) was measured from the dorsal foot (n = 56). The baseline skin blood flow velocity (SBFV) and pulse wave amplitude (PWA) were measured with the LD (expressed in millivolts, mean +/- SEM) on the plantar aspect of the foot (n = 53 limbs). Criteria for successful healing included a tcPO2 of more than 10 mm Hg, the combination of an LD-SBFV of more than 40 mV and an LD-PWA of more than 4 mV, and an ankle systolic pressure of more than 30 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Amputation Stumps↗
PubMed1986

Doppler-derived percentage systolic window and the quantitation of arterial stenosis.

Peak systolic frequency (PSF) and percentage systolic window (%SW) are spectral parameters used to characterize poststenotic flow velocity patterns. The PSF, obtained using a continuous-wave (CW) Doppler velocimeter, has been used more frequently, however, in the quantitation of carotid occlusive disease. The authors have employed a microprocessor-driven pulsatile flow model to evaluate more completely the relationship between stenosis and the %SW. Using an 8 MHz CW Doppler probe, the Doppler-shifted frequencies were recorded at 1, 2, 3, 4, and 5 diameters distal to a variable, nonaxisymmetric stenosis, which reduced the cross-sectional area (CSA) 25, 40, 50, 60, 70, 85, and 97 per cent. Four sets of observations were made and the %SW derived using a spectrum analyzer. At one diameter from the stenosis, the relationship between the %SW (Y) and the reduction in CSA (X) is best described by two first-order regressions (Y = MX + B). The slope of the relationship from 0 to 60 per cent reduction in CSA is nearly flat, -0.052, while there is a significant (P less than 0.05) decrease in the slope, -1.538, when the CSA is further reduced from 60 to 97 per cent. Beyond 1 diameter, the relationship is best described by a single linear regression, the gradual slope of which does not permit clinically useful comparisons. These data explain the lack of strong correlation between CSA and %SW when the data are evaluated over the entire range of stenoses. However, they do indicate that the %SW may be a useful correlate if it is obtained within one diameter of the stenosis.

Arterial Occlusive Diseases↗
PubMed1985

Results of revascularization and amputation in severe lower extremity ischemia: a five-year clinical experience.

Aggressive revascularization of the ischemic lower extremity in atherosclerotic occlusive disease by femoropopliteal (FP) and femorotibial (FT) bypass or profundaplasty (P), as indicated, has been advocated by some authors for all patients. Others have recommended primary amputation, particularly for tibial occlusive disease. To clarify this clinical dilemma, we reviewed the results of 547 procedures performed during the last 5 years: revascularization in 375 (69%) instances and below-knee amputation (BKA) in 172 (31%) cases. Bypass procedures were used in 246 cases: FP in 155 (64%) and FT in 91 (37%). Reversed autogenous saphenous vein (ASV) was used preferentially in 125 (51%) cases, whereas polytetrafluoroethylene (PTFE) was used in 121 (49%) cases. P was performed in 129 instances accompanied by inflow procedures in 92 (71%) of these cases. Cumulative limb salvage (LS) exceeded bypass patency in all categories and resulted in 2- and 5-year LS rates of 83% and 81% for FP with the use of ASV and 52% and 35% for PTFE. The LS rate for FT was 53% and 47%, respectively, for ASV and 20% and 15% for PTFE. Rest pain was successfully relieved by P in 99 cases (77%), whereas healing occurred in only 51% of cases with tissue loss. The perioperative mortality rate for revascularization was 3%; 42% of the group died during follow-up, death usually resulting from complications of atherosclerosis. Of the 172 BKAs, primary healing occurred in 80%, but the perioperative mortality rate was 13%. FP and FT bypasses are preferred procedures if ASV is available, whereas use of PTFE should be limited to FP bypasses only. Rest pain is relieved by P but tissue loss should prompt consideration for bypass. BKA should be considered in cases of severe tibial disease only in the absence of a suitable ASV, as the perioperative mortality rate is high and ultimate rehabilitation (64%) is limited.

Amputation, Surgical↗
PubMed1985

Asymptomatic carotid disease.

The advent of noninvasive screening tests has allowed the identification of an increasing number of patients with asymptomatic carotid stenoses. The management of these patients must be individualized, as the preferred method of therapy has not been established. Such a solution ultimately requires a prospective randomized trial to define the natural history of these lesions and to clearly establish if surgical therapy has a role. Currently, there is a Veterans Administration Cooperative Study underway which will attempt to fill the existing information gap. Specifically being examined is the relationship between subsequent cerebrovascular symptoms and the degree of stenosis, progression of stenosis, contralateral disease and non-carotid operation. This study will not be completed for five years, so that other, current guidelines must be sought. It is essential that any surgeon considering prophylactic carotid endarterectomy demonstrate combined morbidity and mortality figures of less than 3 per cent. The patients being considered must also be an acceptable cardiac risk, as myocardial infarction represents the most common postoperative complication. Until prospective data is available, with a detailed analysis of the degree of stenosis, presence of ulceration and ultimate clinical course, the surgeon undertaking prophylactic endarterectomy must carefully screen his patients and concentrate on groups at high risk. This is especially important as more data on the significant incidence (10 to 15 per cent) of carotid restenosis becomes available. The results of three studies (34, 36, 69) suggest that those patients with hemodynamically significant stenoses, identified noninvasively by OPG techniques, are at a greater risk for cerebral ischemic events than those patients without significant stenoses. In addition, an observed incidence of stroke of 17.5 per cent and an indicence of TIAs of 33 per cent in patients with disease progression demonstrated by OPG-K/CPA. The work of another researcher (71) suggests that patients with carotid stenoses can be observed until symptoms develop or until the stenosis progresses to greater than 80 per cent.(ABSTRACT TRUNCATED AT 400 WORDS)

Arterial Occlusive Diseases↗
PubMed1985

The role of contrast arteriography in suspected arterial injuries of the extremities.

The records of 215 patients presenting with 218 penetrating or blunt injuries to the extremities from 1977 through 1983 have been reviewed. All patients presenting with pulsatile hemorrhage, expanding hematoma, or absent distal pulses were explored immediately. Patients with injuries in close proximity to a major artery but without classical signs of arterial injury were explored routinely from 1977 through 1980. Thereafter, similar patients were evaluated initially with contrast arteriography and explored only if arteriographic abnormalities suggested arterial injury. Routine exploration of proximity injuries has been compared with selective exploration based on contrast arteriography. Sixty-one patients (group 1) underwent routine exploration for proximity injuries. Vascular injuries were detected in ten (16%) patients, while 51 (84%) of the explorations were negative. Eighty-four patients (group 2) with proximity injuries were studied arteriographically. Ten patients (11.9%) were explored on the basis of abnormal arteriograms, and eight arterial injuries were confirmed. Two (2.4%) of the 84 patients in this group had negative explorations. The use of contrast arteriography enabled the authors to reduce their negative exploration rate from 84 to 2.4 per cent in the management of proximity injuries.

Adolescent↗
PubMed1985

Simultaneous determination of brachial and femoral arterial pressures during reactive hyperemia and papaverine vasodilation.

Accurate assessment of aortoiliac occlusive disease often requires direct intraarterial pressure determination. Since these measurements may alter systemic pressure, brachial arterial pressure (BAP) and femoral arterial pressure (FAP) were obtained simultaneously to quantitate these changes. BAP and FAP were measured at rest, and then during vasodilation produced by postischemic reactive hyperemia and intra-arterial injection of papaverine. The gradient between FAP and BAP was used to assess the significance of an aortoiliac stenosis. Sixty-eight observations were performed in 19 limbs. During reactive hyperemia (n = 28), BAP was 142 +/- 7 mm Hg, which was not significantly different from the baseline BAP of 142 +/- 5 mm Hg. However, during thigh tourniquet inflation, BAP increased significantly to 158 +/- 7 mm Hg. Following papaverine injection (N = 21) BAP was 144 +/- 8 mm Hg, which was significantly different from both the baseline BAP (150 +/- 6 mm Hg) and the preinjection BAP (156 +/- 6 mm Hg). Postischemic reactive hyperemia and papaverine vasodilation produced comparable brachial to femoral pressure gradients. Use of baseline BAP is recommended for calculating gradients during reactive hyperemia, since the BAP is significantly elevated during tourniquet occlusion. Simultaneous recording of brachial and femoral pressures is recommended with intra-arterial papaverine injections, since the BAP varies significantly throughout the examination.

Aortic Diseases↗
PubMed1984

Influence of prostacyclin on distribution of canine femoral blood flow.

Prostacyclin (PGI2) has been used clinically in the treatment of ischemic peripheral vascular disease. While intravenous infusions have been reported to be beneficial, the preferred route of administration (intravenous or intraarterial) and the influence of PGI2 on distribution of femoral blood flow have yet to be established. Bilateral femoral arterial blood flow was measured electromagnetically in 10 anesthetized adult mongrel dogs. The distribution of femoral arterial blood flow (FAQ) to skin, muscle, bone, and arteriovenous anastomoses (AVA) was determined by using femoral intraarterial injections of radioactively labeled microspheres before, during, and 30 min after 20-min intravenous (n = 5) and intraarterial (n = 5) infusions of PGI2 at 0.1 microgram kg-1 min-1. Control FAQ was 76 +/- 15 (mean +/- SEM) ml/min and its distribution to skin, muscle, bone, and AVA was 13 +/- 3%, 43 +/- 8%, 17 +/- 4%, and 26 +/- 7%, respectively. Arterial pressure was 127 +/- 7 mm Hg. Intraarterial infusions of PGI2 significantly (P less than 0.05) increased FAQ to 240 +/- 43 ml/min which was sustained throughout the infusion. Distribution of FAQ to skin increased significantly (P less than 0.05) to 47 +/- 8%, while that to the muscle of the thigh decreased to 17 +/- 4% (P less than 0.05). During intravenous infusion of PGI2 at the same concentration, FAQ did not change significantly and its distribution remained unchanged; however, there was a significant (P less than 0.05) reduction in arterial pressure to 78 +/- 6 mm Hg. No significant changes occurred in cardiac output, pulmonary arterial pressure, arterial blood gases, paw or core body temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

The assessment of skin blood flow in peripheral vascular disease by laser Doppler velocimetry.

The helium-neon laser Doppler (LD) is designed to measure skin blood flow velocity (SBFV). Flow velocity and pulse wave amplitude are expressed in millivolts (mv) relative to a zero-flow reference. The authors have reviewed their initial experience in ten persons (20 limbs) without peripheral vascular disease (PVD, group I) and nine patients (12 limbs) with severe PVD (group II). The finger, palm, great toe, and forehead had a significantly (P less than 0.05) greater flow velocity than the plantar and dorsal foot, distal and proximal leg, thigh, chest, arm, and forearm. Baseline and hyperemic SBFV, measured at the great toe, were compared in groups I and II. In group I, the baseline SBFV (mv, mean +/- standard error of the mean (SEM] in the great toe was 197 +/- 38 compared with 67 +/- 12 in group-II patients (P less than 0.05). The pulse wave amplitude (mv, mean +/- SEM) was 77 +/- 14 in group I and 5.4 +/- 1.1 in group II (P less than 0.05). The time to maximal hyperemic response (seconds, mean +/- SEM) in group I was 18 +/- 1.5 compared with 150 +/- 14 in group II (P less than 0.05). LD is a sensitive indicator of changes in SBFV, allowing differentiation between normal persons and patients with PVD. The LD tracing in patients with PVD is characterized by a baseline SBFV that is significantly less than normal and also by the attenuation or absence of pulse waves. The diagnostic accuracy is enhanced by the use of reactive hyperemia.

Adult↗