Showing papers by "Jan H.M. Tordoir published in 2002"

The effect of chronic flow changes on brachial artery diameter and shear stress in arteriovenous fistulas for hemodialysis.

Abstract: Background: Vessel wall adaptation to acute or chronic flow changes is regulated by shear stress (SS) at the endothelium. This hypothesis was tested in the brachial artery (BA) of patients receiving an arteriovenous fistula (AVF) for hemodialysis vascular access. Methods: The acute and sustained effects were evaluated in 13 patients. Pre-operatively and postoperatively on predetermined time-points BA diameter and shear rate (SR) were measured. SS was calculated from whole blood viscosity and SR. Analysis was performed with Wilcoxon's test and ANCOVA multivariate analysis. Results: Acutely, mean SS increased (475%, p<0.05), peak-to-peak SS decreased (37%, p<0.05) and peak SS remained constant. BA diameter increased (15%, p<0.05). After one year a further increase was observed (r=0.59, p<0.001), plus an increase in mean SS (r=0.78, p<0.001). Peak-to-peak SS remained constant. Conclusion: Our results indicate that after AVF placement an acute increase in SS results in an acute increase of vessel diameter. However, one year of sustained high blood flow does not result in restoration of mean SS.

Renovascular disease in patients with hypertension: detection with duplex ultrasound.

Abstract: The aim of this study was to evaluate the accuracy of duplex ultrasound for the diagnosis of renovascular disease in a cohort of hypertensive patients. In 78 patients suspected of renovascular hypertension on clinical grounds duplex ultrasound examination of the renal arteries was performed. Renal angiography was used as the standard of reference. Duplex ultrasound was inconclusive in 11 kidneys (7%). None of the supernumerary renal arteries was detected with duplex ultrasound. The overall prevalence of significant renovascular disease (> or =50% stenosis) was 20%. Based on the combination of parameters at thresholds commonly applied in current literature: ie PSV(max) >180 cm/sec and RAR >3.5 the overall sensitivity of duplex ultrasound for detection of haemodynamically significant renovascular disease was 50.0% with a specificity of 91.3% (PPV: 87.9%; NPV: 59.1). Lowering the thresholds for both parameters improved the test results at the cost of a significant increase of false positive examinations. In a population of hypertensive patients clinically suspected of renovascular hypertension, only limited results for duplex ultrasound could be acquired in the detection of renovascular disease. This result, in combination with the wide range of sensitivities and specificities published in international literature and the relatively large number of incomplete examinations does not support the general application of duplex ultrasound as a screening procedure for detection and assessment of renovascular disease.

Brachial artery shear stress is independent of gender or age and does not modify vessel wall mechanical properties.

Abstract: The objective of the present study was to obtain brachial artery (BA) baseline shear stress (SS) values in healthy volunteers and to relate this to gender and age. Peak and mean wall shear rate (SR) were noninvasively measured in 30 healthy subjects using an SR estimation system. Arterial diameter and wall characteristics were obtained with a wall tracking system. SS was estimated from SR and calculated whole blood viscosity. Intrasubject variability and the effects of age and gender were assessed. Intrasubject variability of BA peak and mean SR were 16.2% and 28.6%. Baseline peak (≈ 3.0 ± 0.7 Pa) and mean SS (≈ 0.5 ± 0.2 Pa) were not gender-dependent, nor were they influenced by age. No vessel wall parameter related to BA SS. No differences in BA SS were observed between the genders and no influence of age was apparent. Our results indicate that the BA adequately responds to chronic changes in blood flow. (E-mail:r.dammers@bf.unimaas.nl)

Chlamydia pneumoniae Serology Is Associated With Thrombosis-Related but Not With Plaque-Related Microembolization During Carotid Endarterectomy

Abstract: Background and Purpose — Chlamydia pneumoniae has repeatedly been associated with atherosclerotic disease. Our study was designed to clarify whether this association is based on C pneumoniae -induced transformation of a stable into an unstable atherosclerotic plaque or on stimulation of hypercoagulability leading to increased thrombotic arterial occlusions by C pneumoniae infection. Transcranial Doppler ultrasonographic monitoring of the middle cerebral artery during carotid endarterectomy offers the opportunity to study, before removal of the plaque, atherothrombotic emboli dislodging from an unstable carotid plaque (plaque-related emboli) and emboli related to (excessive) thrombus formation at the endarterectomy site after removal of the plaque and restoration of flow (thrombosis-related emboli). Methods — C pneumoniae IgA (≥1/16) and IgG (≥1/64) seropositivity was assessed in 53 patients with symptomatic carotid artery disease undergoing carotid endarterectomy. The removed carotid plaques were studied histologically to assess plaque instability. Results — Plaque- and thrombosis-related emboli were registered in 43 patients with an adequate transtemporal window. IgA seropositivity (58%) was associated significantly with thrombosis-related embolization ( P =0.030) but not with plaque-related embolization or with histological plaque instability. Conclusions — C pneumoniae serology is associated with microembolization after endarterectomy and restoration of flow. Since these microemboli represent platelet aggregations and are related to cerebrovascular complications, our data suggest that C pneumoniae infection contributes to cerebrovascular events in patients with carotid artery disease through stimulation of thrombosis.

Hemodynamics of venous cuff interposition in prosthetic arteriovenous fistulas for hemodialysis.

Abstract: Purpose: The durability of prosthetic arteriovenous fistulas (AVF) for hemodialysis is jeopardized by thrombotic occlusions due to intimal hyperplastic stenoses. In arterial reconst