PubMed Health⌕ Search

Biomedical subjects

L Hofstra

Publications and source records attributed to L Hofstra.

32 records · Page 2Linked to original sources
PubMed1996

Enhanced cellular proliferation in intact stenotic lesions derived from human arteriovenous fistulas and peripheral bypass grafts. Does it correlate with flow parameters?

BACKGROUND: Vascular interventions are often complicated by the development of intimal thickening, leading to stenosis. Cellular proliferation is a key event in stenosis formation in animals, but the role of cell proliferation in intimal thickening in humans is still unclear. Furthermore, the relation between proliferation in human stenotic lesions and flow parameters has not been established. METHODS AND RESULTS: We studied the proliferation patterns of 35 anatomically intact human stenotic lesions derived from either peripheral bypasses (normal flow) or hemodialysis AV fistulas (high flow) with the use of Ki-67, a cell proliferation marker. Local flow parameters were assessed with ultrasound. Proliferation patterns were similar in AV fistula and bypass stenoses. In the intima, proliferation was highest in the area just below the endothelium (AV fistulas, 3.6%; bypasses, 3.5%; P = NS). In adjacent nonstenotic vessel segments that were used as controls, proliferation rate in the intima was 0.3%. Double-labeling studies revealed that subendothelial-intimal proliferation consisted mainly (90%) of vascular smooth muscle cells, whereas proliferation in the other layers of the vessel wall also consisted of endothelial cells and macrophages. Blood flow velocity was negatively correlated with subendothelial-intimal proliferation (r = -.61, P < .05). The endothelial cell coverage of the lumen was positively correlated with proliferation (r = .85, P < .01). CONCLUSIONS: These data suggest enhanced cellular proliferation in human stenotic tissue derived from AV fistulas and peripheral bypass grafts. Furthermore, high proliferation rates seem to be associated with endothelial cell coverage of the lumen and low local flow velocities.

Adult↗
PubMed1996

Reflex sympathetic dystrophy: does sympathetic dysfunction originate from peripheral neuropathy?

BACKGROUND: Sympathetic dysfunction in reflex sympathetic dystrophy (RSD) has been purported to consist of an afferently-induced increase in efferent sympathetic nerve impulses (somato-sympathetic reflex) and/or denervation-induced supersensitivity to catecholamines. In addition, both the central and peripheral nervous systems have been claimed to be involved. It was the aim of this study to obtain more insights into these underlying mechanisms. METHODS: In the affected extremeties of 42 patients with RSD we investigated as indirect measures of sympathetic (dys)function: (1) skin blood flow and the vasoconstrictive response to dependency of skin microvessels by means of laser Doppler flowmetry (distal to the site of trauma), (2) relative distention of the brachial artery and changes in relative distention consequent to a cold pressor test by means of ultrasonic vessel wall tracking (proximal to the site of trauma), and (3) arterial blood pressures by means of the Finapres technique. Both provocation tests induce a sympathetically mediated response. Patients were divided into three categories according to their perception of skin temperature in their injured limb (stage I, stationary warmth sensation; stage II, intermittent warmth and cold sensation; or stage III, stationary cold sensation). RESULTS: Distal to the site of trauma, when compared with controls, skin blood flow was increased at stage I and decreased at stages II and III, whereas the vasoconstrictive response to dependency was impaired at all three stages. Proximally, when compared with controls, relative distention of the brachial artery and its response to the cold pressor test were decreased at all three stages. No differences were observed in pulse pressure between patient groups and controls. CONCLUSIONS: These results suggest that sympathetic dysfunction in extremities of patients with RSD distal to the site of trauma consists of hypersensitivity to catecholamines at stages II and III as a result of autonomic denervation at stage I, whereas proximal to the site of trauma sympathetic nerve impulses may be increased at all three stages.

Adult↗
PubMed1996

Prosthetic arteriovenous fistulas and venous anastomotic stenosis: influence of a high flow velocity on the development of intimal hyperplasia.

Stenotic intimal thickening at the venous end of prosthetic arteriovenous (AV) fistulas for hemodialysis has been associated with perianastomotic mismatch in elastic properties between prosthesis and vein and high flow velocities. In a prospective study, we investigated the role of flow velocity on the occurrence of intimal hyperplasia in prosthetic AV fistulas in hemodialysis patients. In 24 patients, the flow velocities were assessed in the distal graft and the outflow vein postoperatively, with the use of vessel wall Doppler tracking, a noninvasive ultrasound technique. The initial velocity in the venous anastomoses was correlated with the occurrence of stenoses during follow-up (2 years). The detection of a stenosis was performed with both Duplex ultrasound and angiography. In 4 cases a stenosis developed in the venous anastomosis, in 8 cases in the venous outflow segment, and in 4 cases at both sites. Higher flow velocities around the venous anastomosis was observed in fistulas developing a stenosis at this site as compared with the nonstenotic fistulas (p < 0.05). The occurrence of stenoses in prosthetic AV fistulas in or adjacent to the venous anastomosis is not associated with a mismatch in elastic properties, but with high flow velocity.

Anastomosis, Surgical↗
PubMed1995

A noninvasive method to estimate wall shear rate using ultrasound.

Wall shear stress (blood viscosity x wall shear rate), imposed by the flowing blood, and blood pressure are the main mechanical forces acting on a blood vessel wall. Accurate measurement of wall shear stress is important when investigating the development of vascular disease, since both high and low wall shear stresses have been cited as factors leading to vessel wall anomalies. Furthermore, in vitro studies have shown that endothelial cells, which play a key role in the function of the underlying arterial wall, undergo a variety of structural and functional changes in response to imposed shear stress. However, there is practically no knowledge about the influence of wall shear stress on the arterial wall in vivo because of the difficulty in measuring this stress in terms of magnitude and time variation. The method presented in this article to measure the time-dependent wall shear rate in the main arteries is based on the evaluation of velocity profiles determined by means of ultrasound, using off-line signal processing. Pulsed ultrasound is well suited for this application since it is noninvasive. The processing performed in the radio-frequency (RF) domain consists of a mean frequency estimator preceded by an adaptive vessel wall filter. In a pilot study (30 measurements in the carotid artery of five healthy volunteers) we investigated the reproducibility of our method to estimate wall shear rate as compared with the reproducibility of the measurement of blood flow velocity in the middle of the vessel. The coefficient of variation was on the order of 9% for blood flow velocity estimation, and for wall shear rate estimation on the order of 5%.

Adolescent↗
PubMed1995

Early experience with stretch polytetrafluoroethylene grafts for haemodialysis access surgery: results of a prospective randomised study.

OBJECTIVE: The purpose of this study was to evaluate the results and complications of standard ePTFE versus stretch ePTFE AV fistulas. DESIGN: Prospective randomised trial. SETTING: University Hospital. MATERIALS: During a 2-year period 37 patients received 17 stretch and 20 standard ePTFE graft AV fistulas. CHIEF OUTCOME MEASURES: Patients were evaluated for the occurrence of complications and graft patency. Regular Duplex scans were performed to detect stenoses in the fistula circuit. MAIN RESULTS: Thrombotic events occurred in 40% of the standard ePTFE grafts, compared to 12% of the stretch ePTFE prostheses (p < 0.001). The incidence of puncture complications was similar in both groups. The cumulative primary patency rate in the stretch ePTFE group was significantly higher compared to the standard ePTFE group (1-year patency rates of 59% and 29%, respectively; p < 0.01). No differences in the duration of puncture site bleeding were observed. Duplex scanning showed a significantly greater number of stenoses in the standard ePTFE grafts. CONCLUSIONS: The new stretch ePTFE prosthesis has better primary patency rates and less stenoses due to intimal hyperplasia as compared to standard ePTFE grafts.

Arm↗
PubMed1995

Anastomotic intimal hyperplasia in prosthetic arteriovenous fistulas for hemodialysis is associated with initial high flow velocity and not with mismatch in elastic properties.

Stenotic intimal thickening at the venous end of prosthetic arteriovenous (AV) fistulas for hemodialysis has been associated with perianastomotic mismatch in elastic properties, and low shear rates. In a prospective way, the role of these factors on the occurrence of intimal hyperplasia in prosthetic AV fistulas in hemodialysis patients was investigated. In 24 hemodialysis patients, the elastic properties were assessed in the distal graft segment and the outflow vein postoperatively with the use of Vessel Wall Doppler Tracking (VWDT), a noninvasive ultrasound technique. In addition, normalized peak systolic velocity (nPSV) was calculated from diameter (VWDT) and peak systolic velocity. The initial mismatch around the venous anastomoses and local nPSV were correlated with the occurrence of stenoses during follow-up (2 yr). The detection of a stenosis was performed with both Duplex ultrasound and angiography. In four cases, a stenosis developed in the venous anastomosis; in eight cases, a stenosis developed in the venous outflow segment; and in four cases, stenoses developed at both sites. A better initial match in elastic properties around the venous anastomosis was observed in the fistulas developing a stenosis at this site as compared with the nonstenotic fistulas (P < 0.05). The initial local nPSV values at the site of the later stenosis were higher in the fistulas developing a stenosis as compared with the nonstenotic fistulas (P < 0.05). It was concluded that the occurrence of stenoses in prosthetic AV fistulas for hemodialysis in or adjacent to the venous anastomoses is associated with a high initial flow velocity but not with a mismatch in elastic properties.

Adult↗
PubMed1994

Assessment of inhomogeneities in elastic properties of in situ and reversed saphenous vein grafts in humans.

The elastic properties of newly implanted in situ (IS, n = 11) and reversed (RV, n = 21) saphenous grafts were studied with the use of Vessel Wall Doppler Tracking. From diameter, diameter change and simultaneously recorded pulse pressure, distensibility coefficient (DC) representing the intrinsic elastic properties and compliance coefficient (CC), a parameter of haemodynamic capacity, were calculated. In order to obtain a mechanical profile, the parameters were assessed at defined sites down the graft and native arterial system. In the RV group the reversal of the grafts resulted in a difference in diameter around the proximal anastomoses (7.4 vs. 4.3 mm, p < 0.01) and from proximal to distal (4.3 vs. 5.9 mm, p < 0.01) in the grafts; around the distal anastomoses no differences in diameter were observed. Due to the natural taper of the in situ grafts, diameter decreased from proximal to distal in the grafts (4.5 vs. 3.2 mm, p < 0.05) and no size differences were found around the anastomoses. In the RV group a decrease in DC was observed from proximal to distal in the grafts; whereas in the IS group no change in DC was found from proximal to distal in the grafts but a decrease in DC was observed around the distal anastomoses. In the RV group, a decrease in CC at the proximal anastomoses was observed (0.25 vs. 0.09 mm2/kPa, p < 0.01). In the IS group no change in CC was observed around the proximal anastomoses and distal anastomoses.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

Short-term variation in the elastic properties of a muscular artery in humans.

1. Information on the interaction between mechanical strain and the elastic properties of large arteries could give insight to the origin of haemodynamic vascular injury, possibly resulting in formation of atherosclerotic plaques. Intra-individual variation in the elastic properties of muscular arteries measured using non-invasive techniques has been observed. This variation could be due to changes in blood pressure, since the elastic properties of muscular arteries are strongly non-linear. 2. The objective of the present study was to evaluate variability in the elastic properties of a muscular artery over a time period of up to 1 h. Furthermore, the relation between changes in elastic properties and alterations in blood pressure was studied. With a non-invasive high-resolution ultrasound technique, the diameter and distension of the femoral artery were assessed by repeated measurements in 10 healthy subjects (mean age 27 +/- 2.9 years) under resting conditions over 40-60 min. Intra-arterial blood pressure of the contralateral common femoral artery and heart rate were recorded simultaneously. From the distension and pulse pressure, the distension/pressure ratio was calculated, a measure of the compliance. For each parameter the variation coefficient was computed. 3. In all subjects a considerable variation was found in distension (mean variation coefficient 14.8%) but not in pulse pressure (mean variation coefficient 3.7%). The expected positive correlation between pulse pressure and distension was absent in eight subjects. As a consequence, large intra-individual variation was found in the distension/pressure ratio (mean variation coefficient 15.3%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Mismatch in elastic properties around anastomoses of interposition grafts for hemodialysis access.

Arteriovenous (AV) fistulas for hemodialysis access, constructed with the use of interposition grafts, are often complicated by intimal hyperplastic stenosis, mainly occurring at the venous anastomosis. In this study, mismatch in elastic properties around the arterial and venous anastomoses of graft AV fistulas in humans was quantified in order to find clues for the predisposition of intimal hyperplasia to develop at the venous anastomosis. The elastic properties of graft AV fistulas in 31 hemodialysis patients were investigated by the use of vessel wall Doppler tracking, 2 wk after construction. Nine saphenous vein grafts, 8 expanded polytetrafluoroethylene (ePTFE) grafts, and 14 stretch-PTFE (sPTFE) grafts were measured at the arterial inflow segment, the proximal graft segment, the distal graft segment, and the venous outflow segment. Area increase (AI), representing the capacity of the vessel wall to store blood volume, and relative distension, representing the intrinsic elastic properties, were calculated from diameter and distension. A decrease in AI was observed in the arterial anastomoses of all graft types. An increase in AI was found in the venous anastomosis of ePTFE and sPTFE grafts. Higher values for AI and relative distension were found at the proximal and distal graft segments of the saphenous vein grafts when compared with the prosthetic grafts. In the sPTFE grafts, the level of AI was maintained along the graft, whereas in the ePTFE grafts, a decrease in AI was found. In the arterial anastomoses of AV fistulas, a decline in the capacity to store blood volume was observed. By contrast, an increase in the capacity to store blood volume was found in the venous anastomoses.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

A new hemostatic puncture closure device for the immediate sealing of arterial puncture sites.

After angiography, 6 to 24 hours of bedrest is indicated to assure that adequate hemostasis of the femoral artery has been achieved. Recently, a new hemostatic puncture closure device (HPCD) has been developed, which consists of a resorbable polymer anchor, a resorbable suture, a small collagen plug and an 8Fr delivery device. The device is delivered into the femoral artery through the introducer sheath, the anchor is secured against the intraluminal artery wall, and the collagen plug is deployed on the arterial wall. The prototype of the HPCD was used in 20 patients administered heparin. After insertion of the HPCD, hemostasis was achieved in 1.2 +/- 2.1 minutes; in 2 patients a light pressure dressing was applied for 4 hours to stop oozing. No late bleeding occurred. In 1 patient the positioning suture broke, requiring the application of a pressure bandage. Patients were uneventfully mobilized after 6.7 +/- 3.5 hours. In all patients serial duplex scanning of the femoral artery was performed before and after 1, 7, 30 and 90 days after HPCD placement. In 5 patients a small subcutaneous hematoma close to the site of introduction could be detected by ultrasound 1 day after catheterization. All but 1 patient had normalization of the flow patterns in the femoral artery. It is concluded that: (1) the HPCD is an effective device to achieve immediate hemostasis after arterial catheterization despite antithrombotic therapy, (2) early mobilization was uneventful, (3) duplex ultrasound studies demonstrated only transient changes in the punctured femoral artery, and (4) further investigations are needed to establish the efficacy and safety of the device.

Equipment Design↗
PubMed1993

The role of the spleen in pancreas transplantation.

Early graft thrombosis and rejection of the graft are the two major causes of graft failure in pancreas transplantation. Inclusion of the spleen in the pancreatic graft has been purported as a possible solution to both complications, but severe graft-versus-host disease led to abolishment of this procedure. By irradiating the donor spleen ex vivo during cold storage, we successfully prevented graft-versus-host disease, allowing us to evaluate the advantages of clinical pancreaticosplenic transplantation. This study reports our experience with 12 pancreaticosplenic transplantations. Using Doppler flow measurements, we have been able to examine the hemodynamic advantages. Our results confirm the purported benefit. Vascular resistance indices in the pancreatic graft are significantly lower when the donor spleen is included. This, however, did not lower the incidence of thrombosis (2 out of 12 cases) in our study. Serial radionuclide studies with 99mTc-hexamethyl propylene amine oxime were performed for further evaluation of graft perfusion. With time the spleen uptake diminishes, compatible with atrophy of the organ. This was confirmed histologically. No indication of an immunologic advantage of transplanting the pancreas together with the spleen was found. All patients went through severe rejection crises. A transient reduction in platelet count (55-88%, mean 71%) of preoperative values was observed. This platelet drop is not seen in patients with a pancreas without spleen transplantation. We conclude that in pancreas transplantation, inclusion of the irradiated spleen has no obvious advantages for early graft thrombosis and rejection of the graft.

Adult↗
PubMed1991

Chemonucleolysis in the herniated L3-L4 disk.

In a continuous series of 770 patients with a herniated disk treated by chemonucleolysis, 16 patients had herniation of the L3-L4 disk (2.1%). There were no complications, and none of these 16 patients had open surgery after the initial treatment. A follow-up study was performed after 39 months (range, six to 80 months) in 15 patients. Three patients were for the most part satisfied and 12 patients were fully satisfied with the result of treatment. Residual pain was minor in most patients. Roentgenographic signs of increased disk degeneration were seen in six patients, and reexpansion of the disk to some degree was noted in four patients. Chemonucleolysis is effective for treatment of the herniated L3-L4 disk.

Adult↗
PubMed1990

[Penetrating injuries of the abdomen on the island Curaçao].

A retrospective study was conducted in 60 patients with stab or gunshot wounds to assess whether selective management is also justified if personnel involved has not had a great deal of experience. With selective management the results of the physical examination determine whether a laparotomy will or will not be performed.

Abdominal Injuries↗