Measurement of bronchial blood flow in the sheep by video dilution technique.

Bronchial blood flow was determined in five adult anaesthetised sheep by the video dilution technique. This is a new fluoroscopic technique for measuring blood flow that requires only arterial catheterisation. Catheters were placed into the broncho-oesophageal artery and ascending aorta from the femoral arteries for contrast injections and subsequent videotape recording. The technique yields bronchial blood flow as a percentage of cardiac output. The average bronchial artery blood flow was 0.6% (SD 0.20%) of cardiac output. In one sheep histamine (90 micrograms) injected directly into the bronchial artery increased bronchial blood flow by a factor of 6 and histamine (90 micrograms) plus methacholine (4.5 micrograms) augmented flow by a factor of 7.5 while leaving cardiac output unchanged. This study confirms the high degree of reactivity of the bronchial circulation and demonstrates the feasibility of using the video dilution technique to investigate the determinants of total bronchial artery blood flow in a stable animal model avoiding thoracotomy.     

Effective blood flow and recirculation rates in internal jugular vein twin catheters: measurement by ultrasound velocity dilution

The ultrasound dilution technology (Transonic Systems, Ithaca, NY) is a reliable method to assess blood flow (Qb) and recirculation rates (R) in vascular access during hemodialysis. However, the information available on these parameters for central venous dialysis catheters remains scarce at this point. Real Qb and R were evaluated in 33 well-functioning TwinCath (Medcomp, Harleysville, PA) inserted as mid- or long-term hemodialysis vascular access (mean duration since insertion, 270 +/- 253 days); all were implanted into the right internal jugular vein with their multiperforated distal tips located in the superior vena cava or right atrium. Several types of dialysis machines were used (Monitral and AK100, Hospal-Gambro, Lyon, France; 2008E and 4008E, Fresenius, Bad Homburg, Germany). Real Qb was measured with the ultrasound dilution method and compared with the set Qb (indicated by the dialysis machine); R, also evaluated by ultrasound dilution, was evaluated at various Qb with nonreversed lines; therefore, a total of 121 measures were performed. Arterial and venous pressures (PA and PV) were recorded simultaneously. The 33 measures at a set Qb of 200 mL/min showed a mean effective Qb of 210 +/- 18 mL/min and a mean R of 5.3 +/- 5.3%. At a Qb of 300 mL/min, 33 repeated measures resulted in mean effective Qb of 303 +/- 21 mL/min and R of 8.5 +/- 7.0%; 28 measures performed at a set Qb of 350 mL/min showed that the effective Qb was 336 +/- 24 mL/min and that R was 7.8% +/- 6.7%. Finally, an effective Qb of 372 +/- 26 mL/min and an R of 10.9 +/- 8.6% were found for the 27 measures performed at an indicated Qb of 400 mL/min. The difference between indicated and effective Qb was particularly significant for set Qb equal to or above 350 mL/min (P < 0.001). Variable correlations were observed between obtained parameters: Qb eff and R (r = 0.34), PV and R (r = 0.36), Qb eff and PV (r = 0.78), Qb eff and PA (r = 0.71), and PV and PA (r = 0.53). In conclusion, TwinCath delivers an effective Qb of nearly 375 mL/min when Qb is set at 400 mL/min on most dialysis machines. Mean R in TwinCath varies between 5% and 11% for Qb within the range of 200 to 400 mL/min. In well-functioning TwinCath, the ratio between PV and Qb remains usually below 0.5.     

A prospective study of the determinants of vein graft flow velocity: Implications for graft surveillance

Purpose: Serial monitoring of vein graft peak systolic flow velocity (PSFV) has been endorsed as a technique for vein graft surveillance with low values (<45 cm/sec) considered a marker for impending graft failure. Optimal application of this method requires an understanding of the factors affecting PSFV in normal grafts. A prospective evaluation of 46 consecutive elective infrainguinal vein grafts (6 popliteal/29 tibial/11 pedal) was undertaken to assess the major determinants of PSFV.Methods: Factors recorded for each patient included vein graft diameter (VGD), measured outflow resistance (MOR), conduit length, outflow level (popliteal/tibial/pedal), inflow level (femoral/popliteal), systolic blood pressure, cardiac ejection fraction, the presence of a patent plantar arch, and Society for Vascular Surgery/International Society for Cardiovascular Surgery resistance scoring. MOR was measured by occluding graft inflow and infusing saline solution through a proximal graft cannula at 60 cc/min while simultaneously recording the pressure at the distal anastomosis via a separate cannula. MOR was calculated by dividing the resultant pressure by the infusion rate. MORs were expressed in resistance units and were measured before and after the infusion of papaverine (MOR_(PAP)). PSFVs and VGDs were measured 4 to 6 cm from the distal anastomosis 3 weeks after surgery with duplex scanning (60 degree angle with midstream sample volume).Results: PSFVs ranged from 22 to 148 cm/sec and averaged 83.4 ± 4.8 cm/sec. Pedal bypass grafts had significantly lower PSFVs (64 ± 10 vs 89.5 ± 5 cm/sec, p = 0.02) and significantly higher MOR_(PAP)s (0.86 ± 0.15 vs 0.51 ± 0.05 resistance units, p = 0.05) than bypasses to the popliteal/tibial level. When subjected to univariate analysis the factors correlating with PSFV were MOR (r = -0.59, p = 0.0001), MOR_(PAP) (r = -0.69, p = 0.0001) VGD (r = -0.31, p = 0.06), the Society for Vascular Surgery/International Society for Cardiovascular Surgery score (r = -0.35, p = 0.04), inflow level (r = -0.47, p = 0.002), and outflow level (r = -0.35, p = 0.03). When subjected to multiple regression analysis, only MOR_(PAP) (r ² = 0.51, p = 0.001) and VGD (r ² = 0.14, p =0.001) contributed significantly to the overall model (r ² = 0.65, p = 0.0001) withMOR_(PAP)) eliminating the effect of the other variables. The multiple regression model predicts PSFV as follows: PSFV = 176 + VGD_(mm)( -11.7) + MOR_(PAP))( -63.4).Conclusions: Clinically successful and hemodynamically normal vein grafts have widely variable, yet predictable flow characteristics that are influenced primarily by outflow resistance and VGD. This wide variability suggests that no single lower threshold value for PSFV is universally applicable in identifying all grafts at risk for failure. Detection of focal areas of flow acceleration within the graft may be more accurate in identifying grafts at risk for failure. (J VASC SURG 1994;19:259-67.)     

Validation of haemodialysis recirculation and access blood flow measured by thermodilution.

BACKGROUND: Recirculation (R) and access blood flow (Qac) measurements are considered useful indicators of adequate delivery of haemodialysis. It was the purpose of this study to compare measurements of R and Qac obtained by two different techniques which are based on the same principle of indicator dilution, but which differ because of the characteristics of the injection and detection of the different indicators used. METHODS: Recirculation measured by a thermal dilution technique using temperature sensors (BTM, Fresenius Medical Care) was compared with recirculation measured by a validated saline dilution technique using ultrasonic transducers placed on arterial and venous segments of the extracorporeal circulation (HDM, Transonic Systems, Inc.). Calculated access flows were compared by Bland Altman analysis. Data are given as mean +/- SD. RESULTS: A total of 104 measurements obtained in 52 treatments (17 patients, 18 accesses) were compared. Recirculation measured with correct placement of blood lines and corrected for the effect of cardiopulmonary recirculation using the 'double recirculation technique' was -0.02 +/- 0.14% by the BTM technique and not different from the 0% measured by the HDM technique. Recirculation measured with reversed placement of blood lines and corrected for the effect of cardiopulmonary recirculation was 19.66 +/- 10.77% measured by the BTM technique compared with 20.87 +/- 11.64% measured by the HDM technique. The difference between techniques was small (-1.21 +/- 2.44%) albeit significant. Access flow calculated from BTM recirculation was 1328 +/- 627 ml/min compared with 1390 +/- 657 ml/min calculated by the HDM technique. There was no bias between techniques. CONCLUSION: BTM thermodilution yields results which are consistent with the HDM ultrasound dilution technique with regard to both recirculation and access flow measurement.     

Bedside assessment of cerebral blood flow by double-indicator dilution technique

BACKGROUND: Currently, quantitative measurement of global cerebral blood flow (CBF) at bedside is not widely performed. The aim of the present study was to evaluate a newly developed method for bedside measurement of CBF based on thermodilution in a clinical setting. METHODS: The investigation was performed in 14 anesthetized patients before coronary bypass surgery. CBF was altered by hypocapnia, normocapnia, and hypercapnia. CBF was measured simultaneously by the Kety-Schmidt inert-gas technique with argon and a newly developed transcerebral double-indicator dilution technique (TCID). For TCID, bolus injections of ice-cold indocyanine green were performed via a central venous line, and the resulting thermo-dye dilution curves were recorded simultaneously in the aorta and the jugular bulb using combined fiberoptic thermistor catheters. CBF was calculated from the mean transit times of the indicators through the brain. RESULTS: Both methods of measurement of CBF indicate a decrease during hypocapnia and an increase during hypercapnia, whereas cerebral metabolic rate remained unchanged. Bias between CBF(TCID) and CBFargon was -7.1+/-2.2 (SEM) ml x min(-1) x 100 g(-1); precision (+/- 2 x SD of differences) between methods was 26.6 ml x min(-1) x 100 g(-1). CONCLUSIONS: In the clinical setting, TCID was feasible and less time-consuming than alternative methods. The authors conclude that TCID is an alternative method to measure global CBF at bedside and offers a new opportunity to monitor cerebral perfusion of patients.     

Mechanical agitation and serial dilution: an option for anterior cruciate ligament graft sterilization

Contamination of tissue grafts can occur during anterior cruciate ligament reconstruction, necessitating decontamination. This study examined whether mechanical agitation and serial dilution provides greater bacterial eradication of experimentally contaminated bone-patellar tendon-bone grafts compared with antibiotic soak or pulsatile lavage. Forty bone-patellar tendon-bone grafts were contaminated with a bacterial suspension derived from operating room floor cultures. Four groups of specimens underwent immediate culture (control), antibiotic soak, pulsatile lavage, or mechanical agitation and serial dilution. The number of colony-forming units (CFU) for each group was statistically compared using t and chi-square tests. Each method of decontamination yielded a statistically significant reduction in CFU compared with the control. Analysis of positive versus negative cultures demonstrated a statistically significant difference between mechanical agitation and serial dilution compared with the other 2 methods. Mechanical agitation and serial dilution was the only method with 0 CFU and provided superior and consistent sterilization of experimentally contaminated grafts compared with antibiotic soak and pulsatile lavage.     

Pancreaticoduodenal graft in the rat: an original microsurgical technique

The authors describe an original surgical technique for pancreatic transplantation carried out on an experimental rat model which duplicates as closely as possible the anatomic-functional situation of a pancreatic graft in man (one arterovenous vascular peduncle with one functioning kidney only). The technique entails a microanastomosis between the mesenteric artery and the portal vein of the donor organ with the left renal artery and vein of the recipient. This method appears to be technically encouraging and particularly useful in studying the early phases of ischemic graft injuries, a field in which the authors are particularly interested.     

Reliability of cerebral blood flow measurements by transcerebral double-indicator dilution technique.

BACKGROUND AND OBJECTIVE: The recently developed transcerebral double-indicator dilution technique has proven to be a feasible monitoring alternative to measure global cerebral blood flow at the bedside. However, the short-term repeatability of transcerebral double-indicator dilution measurements has not yet been investigated. The present study was designed to investigate the accuracy in terms of reliability for repeated transcerebral double-indicator dilution measurements to assess global cerebral blood flow during a definite carbon dioxide challenge in a clinical trial. METHODS: The investigation was performed in 10 patients scheduled for elective coronary artery bypass grafting. After induction of anaesthesia, repeated cerebral blood flow measurements using transcerebral double-indicator dilution were performed during target normocapnia, hypocapnia and hypercapnia. For transcerebral double-indicator dilution measurements, a bolus injection of ice-cold indocyanine green was administered into a central vein. The resulting thermal dye dilution curves were recorded simultaneously in the aorta and the jugular bulb using combined fibreoptic thermistor catheters. Cerebral blood flow was calculated from the mean transit times of the indicators through the brain. Additionally, transcranial Doppler sonography was simultaneously performed to measure transient changes in the cerebral blood flow velocity. RESULTS: Transcerebral double-indicator dilution measurements revealed a reasonable coefficient of repeatability with 9.1, 9.7 and 20.2 mL min-1 100 g-1 during normo-, hypo- and hypercapnic conditions, respectively. However, a total of 20% of the administered measurements had to be rejected for methodological reasons. CONCLUSIONS: Repeated measurements with the transcerebral double-indicator dilution method show a reasonable repeatability. With consideration to the limitations of the transcerebral double-indicator dilution technique, this new method proves to be a reliable monitoring tool to measure global cerebral blood flow at the bedside.     

Effect of suture technique on blood velocity waveforms in the microvascular anastomosis of autogenous vein graft

In using autogenous vein grafts in microvascular surgery, maintenance of compliance at the site of anastomosis is of importance in achieving patency. Using high-frequency, 20 MHz, pulsed Doppler ultrasonography to monitor blood flow velocity through the vein graft, we have evaluated the effects of continuous and interrupted suture technique on anastomotic compliance in vessels less than 1.5 mm in diameter. In 15 dogs, 15 procedures of each technique, using the continuous technique in one limb and the interrupted technique on the contralateral limb, patency rates for both techniques, documented by arteriography, are 100% at a mean follow-up of 11 weeks. There were no significant differences in the blood velocity profile and pulsatility proximally, distally, and at the graft site between continuous and interrupted technique. This study confirms the suggestion that autogenous vein graft has sufficient elasticity to maintain normal arterial blood velocity waveforms.     

Cortical ultrasound velocity as an indicator of bone status

Normative population data are reported here for velocity of ultrasound in tibial cortical bone in a population-based sample of both men and women (n=371). The cortical measurement is highly precise with reproducibility of the order of 0.5%. As with heel and patellar trabecular velocity, tibial cortical velocity declines with age from the fourth through the ninth decades. The rate is 1.7 m/s per year in men and 4.1 m/s per year in women. Tibial cortical velocity values correlate with patellar velocity and with forearm mineral, with correlation coefficients ranging from + 0.46 to +0.54 in women and +0.27 to +0.43 in men (P<0.002 for all). Tibial velocity averaged 77–104 m/s lower (2–3%: equal to about 1 SD of the young adult normal distribution) in individuals with a history of low-energy appendicular fractures (P<0.05), and the difference remained significant after adjusting for age. However, there were no perceptible differences in tibial velocity for those with and without vertebral fractures. Odds ratios derived from logistic regression showed an approximate twofold increase in likelihood of low-energy appendicular fracture for every standard deviation decrement in velocity. Comparison of tibial velocity with patellar velocity and forearm density in the same individuals revealed tibial velocity to be more strongly associated with appendicular fractures than patellar velocity for women and about the same for men, and less strongly associated than patellar velocity for vertebral fractures. We conclude that tibial cortical velocity provides useful information about bone status in populations at risk for osteoporosis, and seems particularly well suited for assessing appendicular fracture risk.     

Characterizing flow distributions in AV fistulae for haemodialysis access

Background. The arteriovenous fistula is the most widely used means of enabling vascular access for chronic haemodialysis. When interest in vascular access was at its height, in the 1970s, a substantial amount of work was carried out on the physiology of arteriovenous fistulae and on the relationship between fistula flow and patency. One omission in the catalogue of studies was research into the distribution of flow in the fistula and the effects on surgical outcome. Method. To address this issue, 30 patients with end-to-side radiocephalic fistulae were studied. Flow measurements were made intraoperatively, and at various intervals postoperatively using colour-flow ultrasonography. Results. In 22 cases, the development of the fistula was monitored at regular intervals for periods of up to 27 months. In seven of the 30 fistulae, flow in the distal artery was antegrade, while in the remaining 23, distal artery flow was retrograde. The proportion of fistula flow supplied by the proximal and distal arteries varied considerably. Conclusion. Despite the wide range of flow distributions in the fistulae studied, flow distribution did not appear to affect fistula maturation or long-term function.     

Blood flow in renal carcinomas evaluated by a dye dilution technique and angiography.

In 31 patients with renal carcinoma referred for angiography, rapid sequence angiography was performed in 25. In 18 of the patients determination of renal blood flow and related parameters was made in conjunction with the angiography. Carcinomas with high and medium-high differentiation comprised Group I, while those with medium and poor differentiation constituted Group II. In both groups a positive correlation was demonstrated between the renal blood flow and the tumour area. In group I, positive correlation (t greater than 2) was demonstrated between the vascular volume and the tumour area, between the vascular resistance and the emptying time of the tumour arteries and the normal renal arteries. There was some degree of shunting of blood in all tumours. Comparison of the arterial emptying time of the tumour arteries with the parenchymal arteries does not allow of staging of renal carcinomas. The degree of shunting may be an indication of the degree of malignancy and poor differentiation.     

Ultrasound-guided cannulation versus the landmark-guided technique for acute haemodialysis access

Background. The correct placement of large-bore venous catheters plays an important role in the management of haemodialysis patients. Whilst the procedure for landmark-based placement of these catheters is well known, the technique is not without significant morbidity and mortality. Complications include arterial puncture, haematoma, and pneumothorax. The procedure may be further complicated in these patients by venous thrombosis and abnormal vein position from multiple previous attempts at venous access. Methods. Data on the use of ultrasound guidance versus anatomical landmarks for the placement of internal jugular vein (n=69) and femoral vein (n=30) dialysis access was retrospectively analysed over a 13-month period. Data collected included age, sex, duration on dialysis, number of vein cannulation sets required, number of attempts for successful cannulation, salvage of failed cannulation using landmark-based technique by ultrasound guidance, and the complication rate. Results. Internal jugular vein cannulation using ultrasound was ultimately successful in 96.67% compared to 82% in the landmark group. The vein was entered on the first attempt in 83.3% of patients with ultrasound compared to 35.9% of the landmark group (P<0.0001). Seven patients in whom the landmark technique was unsuccessful had access placed under ultrasound guidance. There were fewer carotid artery punctures in the ultrasound group (7.7 versus 0%, P=n.s.). In the femoral vein group, the vein was entered on the first attempt in 85.7% of patients with ultrasound compared to 56.25% of the landmark group. (P=n.s.). Conclusions. The use of ultrasound guidance is associated with fewer complications and is more likely to lead to cannulation of the vein at the first attempt in haemodialysis patients.     

The variation in vein graft flow velocity with luminal diameter and outflow level.

Duplex scanning has recently been used to monitor the patency of infrainguinal vein grafts. Empirically derived criteria that have been used for identifying the failing graft have never accounted for the effect of vein graft diameter or varying outflow resistance, despite the fact that they are major determinants of flow. We prospectively examined the variation in graft peak systolic flow velocity with graft diameter and outflow level in a consecutive series of 68 patients with 72 normally functioning vein grafts returning for routine follow-up. Images were obtained of vein grafts with a duplex scanner throughout their lengths, and the distal peak systolic flow velocity and intraluminal diameters were recorded. There were 15 popliteal, 26 tibial, and 21 inframalleolar grafts. The mean ankle-brachial index of inframalleolar grafts was 1.01 +/- 0.04 and did not differ significantly from tibial (0.96 +/- 0.03) or popliteal (0.93 +/- 0.06) grafts (p = 0.32). Grafts to the three outflow levels differed significantly in diameter, with inframalleolar grafts measuring 3.95 +/- 0.17 mm, tibial grafts 4.78 +/- 0.21 mm, and popliteal grafts 5.65 +/- 0.38 mm (p = 0.0001). In a similar manner inframalleolar grafts had significantly lower peak systolic flow velocities (59.1 +/- 3.4 cm/sec) than tibial (77.2 +/- 5.6 cm/sec) or popliteal (71.0 +/- 7.6 cm/sec) grafts (p = 0.04). Inframalleolar grafts did not demonstrate a significant correlation (r = -0.21, p = 0.29) between peak systolic flow velocity and graft diameter. Conversely, both tibial (r = -0.49, p = 0.005) and popliteal (r = -0.73, p = 0.002) grafts demonstrated significant inverse correlations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical validation of glucose pump test (GPT) compared with ultrasound dilution technology in arteriovenous graft surveillance.

BACKGROUND: Blood flow (Qa) measurements are an important step in the surveillance protocol of haemodialysis vascular access (VA). The glucose pump test (GPT) is a new test for Qa measurement based on the dilution of a constant glucose infusion. The aim of this study is to verify the clinical accuracy of GPT in a graft surveillance protocol with sequential Qa measurements. METHODS: In 30 chronic haemodialysis patients with graft, we compared monthly sequential Qa measurements performed with GPT in pre-dialysis and the ultrasound dilution technique (HD01 device Transonic Systems Inc., USA) during dialysis. The colour Doppler ultrasonography study (CDU) was our reference standard for the diagnosis of stenosis. The endpoints were the graft thrombosis or PTA treatment. RESULTS: According to the K/DOQI guidelines we could identify the thrombosis high-risk grafts when Qa was <600 ml/min or <1000 ml/min with a decrease >25% in serial Qa measurements. HD01 yielded 27 of 112 high-risk Qa measurements (21 Qa <600 ml/min; mean 406+/-145 ml/min; 6 deltaQa >25%; mean 43+/-7%). In 12 of 27 cases the CDU control did not show haemodynamically significant stenoses (false positive); 15 of 27 cases were confirmed high-risk accesses by CDU and did PTAs (HD01 specificity 86%). GPT yielded 14 of 112 high-risk Qa measurements (8 Qa <600 ml/min; mean 404+/-135 ml/min; 6 deltaQa >25%; mean 38+/-8%) and all had severe stenoses and underwent PTA treatments showing a GPT specificity of 100%. The CDU study allowed us to correctly assess the Qa negative cases. HD01 method had 10 false negative cases (treated or clotted grafts with a Qa >600 ml/min and deltaQa <25%) with a sensitivity of 60%, while GPT had 11 false negative cases with a sensitivity of 56%. The diagnostic accuracy tested with the ROC curves was similar with both tests (area under the curve was 0.762 and 0.752 with GPT and ultrasound dilution, respectively; P = 0.985). The diagnostic efficiency (percentage of grafts with agreement between test result and factual situation) was 90 and 80% (P = 0.056) for GPT and HD01, respectively. CONCLUSION: Compared with HD01, the GPT had a lower false positive rate and similar diagnostic accuracy and efficiency. The clinical implication is a smaller number of unnecessary, invasive procedures (angiographies or PTAs), without increasing the thrombosis risk. This study has shown that GPT is an accurate, quick and economic test for Qa monitoring.     

A simplified scleral graft technique for covering an exposed orbital implant

A simplified method of covering an exposed orbital implant is presented. Donor sclera is placed between Tenon's capsule and the spherical implant without dissecting any tissue planes between the conjunctiva and Tenon's capsule. Technical manipulations and bleeding are thereby minimized. Preplaced absorbable sutures in the periphery of the graft are externalized and tied to the anterior surface of the conjunctiva.     

Duplex ultrasound velocity criteria for the stented carotid artery

OBJECTIVES: Ultrasound velocity criteria for the diagnosis of in-stent restenosis in patients undergoing carotid artery stenting (CAS) are not well established. In the present study, we test whether ultrasound velocity measurements correlate with increasing degrees of in-stent restenosis in patients undergoing CAS and develop customized velocity criteria to identify residual stenosis > or =20%, in-stent restenosis > or =50%, and high-grade in-stent restenosis > or =80%. METHODS: Carotid angiograms performed at the completion of CAS were compared with duplex ultrasound (DUS) imaging performed immediately after the procedure. Patients were followed up with annual DUS imaging and underwent both ultrasound scans and computed tomography angiography (CTA) at their most recent follow-up visit. Patients with suspected high-grade in-stent restenosis on DUS imaging underwent diagnostic carotid angiograms. DUS findings were therefore available for comparison with luminal stenosis measured by carotid angiograms or CTA in all these patients. The DUS protocol included peak-systolic (PSV) and end-diastolic velocity (EDV) measurements in the native common carotid artery (CCA), proximal stent, mid stent, distal stent, and distal internal carotid artery (ICA). RESULTS: Of 255 CAS procedures that were reviewed, 39 had contralateral ICA stenosis and were excluded from the study. During a mean follow-up of 4.6 years (range, 1 to 10 years), 23 patients died and 64 were lost. Available for analysis were 189 pairs of ultrasound and procedural carotid angiogram measurements; 99 pairs of ultrasound and CTA measurements during routine follow-up; and 29 pairs of ultrasound and carotid angiograms measurements during follow-up for suspected high-grade in-stent restenosis > or =80% (n = 310 pairs of observations, ultrasound vs carotid angiograms/CTA). The accuracy of CTA vs carotid angiograms was confirmed (r(2) = 0.88) in a subset of 19 patients. Post-CAS PSV (r(2) = .85) and ICA/CCA ratios (r(2) = 0.76) correlated most with the degree of stenosis. Receiver operating characteristic analysis demonstrated the following optimal threshold criteria: residual stenosis > or =20% (PSV >or =150 cm/s and ICA/CCA ratio > or =2.15), in-stent restenosis > or =50% (PSV > or =220 cm/s and ICA/CCA ratio > or =2.7), and in-stent restenosis > or =80% (PSV 340 cm/s and ICA/CCA ratio > or =4.15). CONCLUSIONS: Progressively increasing PSV and ICA/CCA ratios correlate with evolving restenosis within the stented carotid artery. Ultrasound velocity criteria developed for native arteries overestimate the degree of in-stent restenosis encountered. These changes persist during long-term follow-up and across all grades of in-stent restenosis after CAS. The proposed new velocity criteria accurately define residual stenosis >or =20%, in-stent restenosis >or =50%, and high-grade in-stent restenosis > or =80% in the stented carotid artery.