Use Of Pulsatile Flow Research Articles

Renal haemodynamics and oxygenation during and after cardiac surgery and cardiopulmonary bypass.

Acute kidney injury (AKI) is a common complication following cardiac surgery performed on cardiopulmonary bypass (CPB) and has important implications for prognosis. The aetiology of cardiac surgery-associated AKI is complex, but renal hypoxia, particularly in the medulla, is thought to play at least some role. There is strong evidence from studies in experimental animals, clinical observations and computational models that medullary ischaemia and hypoxia occur during CPB. There are no validated methods to monitor or improve renal oxygenation during CPB, and thus possibly decrease the risk of AKI. Attempts to reduce the incidence of AKI by early transfusion to ameliorate intra-operative anaemia, refinement of protocols for cooling and rewarming on bypass, optimization of pump flow and arterial pressure, or the use of pulsatile flow, have not been successful to date. This may in part reflect the complexity of renal oxygenation, which may limit the effectiveness of individual interventions. We propose a multi-disciplinary pathway for translation comprising three components. Firstly, large-animal models of CPB to continuously monitor both whole kidney and regional kidney perfusion and oxygenation. Secondly, computational models to obtain information that can be used to interpret the data and develop rational interventions. Thirdly, clinically feasible non-invasive methods to continuously monitor renal oxygenation in the operating theatre and to identify patients at risk of AKI. In this review, we outline the recent progress on each of these fronts.

Endothelial hyperpermeability after cardiac surgery with cardiopulmonary bypass as assessed using an in vitro bioassay for endothelial barrier function

BackgroundThe mechanisms causing increased endothelial permeability after cardiopulmonary bypass (CPB) have not been elucidated. Using a bioassay for endothelial barrier function, we investigated whether endothelial hyperpermeability is associated with alterations in plasma endothelial activation and adhesion markers and can be attenuated by the use of pulsatile flow during CPB. MethodsPatients undergoing cardiac surgery were randomized to non-pulsatile (n+20) or pulsatile flow CPB (n+20). Plasma samples were obtained before (pre-CPB) and after CPB (post-CPB), and upon intensive care unit (ICU) arrival. Changes in plasma endothelial activation and adhesion markers were determined by enzyme-linked immunosorbent assay. Using electric cell–substrate impedance sensing of human umbilical vein endothelial monolayers, the effects of plasma exposure on endothelial barrier function were assessed and expressed as resistance. ResultsCardiopulmonary bypass was associated with increased P-selectin, vascular cell adhesion molecule-1, and von Willebrand factor plasma concentrations and an increase in the angiopoietin-2 to angiopoietin-1 ratio, irrespective of the flow profile. Plasma samples obtained after CPB induced loss of endothelial resistance of 21 and 23% in non-pulsatile and pulsatile flow groups, respectively. The negative effect on endothelial cell barrier function was still present with exposure to plasma obtained upon ICU admission. The reduction in endothelial resistance after exposure to post-CPB plasma could not be explained by CPB-induced haemodilution. ConclusionThe change in the plasma fingerprint during CPB is associated with impairment of in vitro endothelial barrier function, which occurs irrespective of the application of a protective pulsatile flow profile during CPB. Clinical trial registrationNTR2940.

A Meta-Analysis of Renal Function After Adult Cardiac Surgery With Pulsatile Perfusion.

The aim of this meta-analysis was to determine whether pulsatile perfusion during cardiac surgery has a lesser effect on renal dysfunction than nonpulsatile perfusion after cardiac surgery in randomized controlled trials. MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials were used to identify available articles published before April 25, 2014. Meta-analysis was conducted to determine the effects of pulsatile perfusion on postoperative renal functions, as determined by creatinine clearance (CrCl), serum creatinine (Cr), urinary neutrophil gelatinase-associated lipocalin (NGAL), and the incidences of acute renal insufficiency (ARI) and acute renal failure (ARF). Nine studies involving 674 patients that received pulsatile perfusion and 698 patients that received nonpulsatile perfusion during cardiopulmonary bypass (CPB) were considered in the meta-analysis. Stratified analysis was performed according to effective pulsatility or unclear pulsatility of the pulsatile perfusion method in the presence of heterogeneity. NGAL levels were not significantly different between the pulsatile and nonpulsatile groups. However, patients in the pulsatile group had a significantly higher CrCl and lower Cr levels when the analysis was restricted to studies on effective pulsatile flow (P < 0.00001, respectively). The incidence of ARI was significantly lower in the pulsatile group (P < 0.00001), but incidences of ARF were similar. In conclusion, the meta-analysis suggests that the use of pulsatile flow during CPB results in better postoperative renal function.

Pulmonary Atelectrauma. Biophysical Insights into Mechanisms of Damage and Prevention

Mechanical ventilation is inarguably a necessary life-sustaining medical treatment for acute respiratory distress syndrome. However, mechanical stresses and strains exerted on the delicate tissues of the airways and alveoli may result in ventilation-induced lung injury (VILI). This presentation describes the coupling between fluid flows, mechanical stresses, and surfactant biophysical interactions that occurs during the recruitment of obstructed airways and alveoli that can result in atelectrauma. Our investigations couple computational simulation with in vitro experimental investigations. We idealize the system as an airway that is lined with epithelial cells, with reopening occurring through the migration of a finger of air that displaces the obstruction. Mechanical stress fields and surfactant transport processes are assessed by computational fluid dynamic simulation, flow visualization is completed with microparticle image velocimetry, and cell damage is evaluated using biomimetic airway constructs of respiratory bronchioles. These studies demonstrate the strong coupling between interfacial flows and atelectrauma. Finally, we asked whether it is possible to enhance the surface activity of endogenous surfactant, using unsteady flows to reduce atelectrauma. Our investigations demonstrate that the use of pulsatile flow to enhance surfactant function provides an opportunity for “endogenous surfactant delivery” that diminishes epithelial damage and thus may reduce VILI.

A meta-analysis of pulmonary function with pulsatile perfusion in cardiac surgery.

The aim of this study was to determine whether pulsatile or nonpulsatile perfusion had a greater effect on pulmonary dysfunction in randomized controlled trials. MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials were used to identify available articles published before April 13, 2013. A meta-analysis was conducted on the effects of pulsatile perfusion on postoperative pulmonary function, intubation time, and the lengths of intensive care unit (ICU) and hospital stays. Eight studies involving 474 patients who received pulsatile perfusion and 496 patients who received nonpulsatile perfusion during cardiopulmonary bypass (CPB) were considered in the meta-analysis. Patients receiving pulsatile perfusion had a significantly greater PaO2 /FiO2 ratio 24 h and 48 h post-operation (P < 0.00001, both) and significantly lower chest radiograph scores at 24 h and 48 h post-operation (P < 0.00001 and P = 0.001, respectively) compared with patients receiving nonpulsatile perfusion. The incidence of noninvasive ventilation for acute respiratory insufficiency was significantly lower (P < 0.00001), and intubation time and ICU and hospital stays were shorter (P = 0.004, P < 0.00001, and P < 0.00001, respectively) in patients receiving pulsatile perfusion during CPB compared with patients receiving nonpulsatile perfusion. In conclusion, our meta-analysis suggests that the use of pulsatile flow during CPB results in better postoperative pulmonary function and shorter ICU and hospital stays.

Impact of Pulsatile Perfusion on Clinical Outcomes of Neonates and Infants With Complex Pathologies Undergoing Cardiopulmonary Bypass Procedures

The aim of this clinical trial was to evaluate the pulsatile perfusion mode in pediatric patients who had complex cardiac pathologies according to Jenkins stratifications (category 4) undergoing cardiopulmonary bypass procedures (CPB). Patients with transposition of great arteries (TGA) and ventricular septal defect (VSD) were included in this clinical study. Eighty-nine consecutive pediatric patients undergoing open heart surgery for repair of TGA-VSD were prospectively entered into the study and were randomly assigned to either the pulsatile perfusion group (Group P, n = 58) or the nonpulsatile perfusion group (Group NP, n = 31). There were no differences between groups in terms of demographical and intraoperative parameters. The pulsatile group needed significantly less inotropic support (P < 0.05) and had lower lactate levels (P < 0.001), higher urine output (P < 0.01), and higher albumin levels (P < 0.05). In addition, the pulsatile group had less ICU (P < 0.01) and hospital stays (P < 0.001). We conclude that the use of pulsatile flow is a better option and should be considered for repair of the complex congenital heart defects.

The Effects of Pulsatile Cardiopulmonary Bypass on Acute Kidney Injury

Protective effect of pulsatile flow cardiopulmonary bypass (CPB) on the occurrence of acute renal injury is still a matter of debate. The objective of this study was to compare the effects of pulsatile and non-pulsatile cardiopulmonary bypass on kidneys using Urinary neutrophil gelatinase-associated lipocalin (NGAL) and interleukin-18 (IL-18) as the markers of renal injury. 85 consecutive patients with normal preoperative renal function were prospectively enrolled in the study. Pulsatile perfusion (Group P) and non-pulsatile perfusion (Group NP) was used in 42 and 43 of the patients, respectively, during aortic cross-clamping period. NGAL and IL-18 were analyzed using ELISA in urine samples obtained preoperatively, and at 2, 12, and 24 h after CPB. There was no significant difference between the groups in terms of perioperative renal function tests. IL-18 levels measured at 12 h after CPB were significantly lower in Group P, compared to Group NP (p<0.05). Urinary NGAL levels measured at 2 and 12 h were higher in Group NP; however, the difference was insignificant. In the subgroup of patients with a cross clamp time ≥45 minutes (pulsatile CPB, group P1, n = 33; non-pulsatile CPB, group NP1, n = 33), IL-18 levels measured at 12 hours after CPB were significantly lower in Group P1. Urinary NGAL concentrations measured at 2 and 12 hours in Group P1 were also significantly lower than that in Group NP1 (p = 0.048 and 0.043, respectively). Low IL-18 and NGAL levels found in the pulsatile perfusion group might suggest the use of pulsatile flow resulted in better kidney protection.

Analysis of pulsatile flow and its role on particle removal from surfaces

The use of pulsatile flow for energy efficient particle removal from surfaces is evaluated through modeling calculations. The governing equation for pulsatile flow in a channel between parallel plates with an oscillatory pressure input is solved and wall shear stress, identified as a measure for particle removal, calculated for fixed power input. It is observed that as the frequency of oscillation is increased the average wall shear stress with an oscillatory pressure input is higher than the corresponding steady state value only above a critical frequency. Similar results are obtained for pulsatile flow in a pipe. Explanation for this observation is presented based on how velocity profile changes as a function of frequency and consequently its effect on wall shear stress versus power dissipated. Based on these observations we propose that there is a critical frequency above which an oscillatory pressure input will be energy efficient for particle removal.

Benefits of Pulsatile Perfusion on Vital Organ Recovery During and After Pediatric Open Heart Surgery

Controversy continues concerning the utilization of pulsatile flow during cardiopulmonary bypass (CPB) procedures with regard to improved patient outcomes. We evaluated 215 consecutive pediatric patients undergoing open heart surgery for repair of congenital heart disease who were prospectively entered into the study and randomly assigned to either the pulsatile perfusion group (group P, n = 151) or the nonpulsatile perfusion group (group NP, n = 64). All patients received identical surgical, perfusional, and postoperative care. Major complications and clinical outcome were documented. There were no statistically significant differences seen in either preoperative or operative parameters between the two groups (age, body surface area, weight, X-clamp and CPB time, base flow, flow rates, and hemofiltration). Group P, compared with group NP, had significantly less inotropic support (number of agents 1.4 +/- 0.07 vs. 2 +/- 0.12, p = 0.0012; dopamine 7.14 +/- 0.28 vs. 9.04 +/- 0.42 microg 32 x kg x min, p = 0.00025; dobutamine 4.12 +/- 0.3 vs. 5.3 +/- 0.6 microg 32 x kg x min, p = 0.036), adrenalin (0.026 +/- 0.005 vs. 0.046 +/- 0.005 microg 32 x kg x min, p = 0.021), shorter intubation period (10.26 +/- 1.04 vs. 18.64 +/- 1.99 hours, p = 0.021), shorter duration of intensive care unit (ICU) (1.53 +/- 0.07 vs. 2.75 +/- 1.19 days, p = 0.012), and hospital stay (6.71 +/- 0.19 vs. 11.16 +/- 0.58 days, p = 0.002). Although there were no significant differences in either creatinine, enzyme levels, and drainage amounts between two groups, lower lactate levels 16.27 +/- 2.02 vs. 24.66 +/- 3.05 mg/dl, p = 0.00034), higher albumine levels (3.15 +/- 0.03 vs. 2.95 +/- 0.06 mg/dl, p = 0.046), and higher urine output (602.82 +/- 21.5 vs. 505.55 +/- 34.2 ml/d, p = 0.016) during ICU period was observed in group P compared with group NP, respectively. We concluded that the use of pulsatile flow resulted in improved patient outcomes in terms of preserving better cardiac, renal, and pulmonary functions in the early post-CPB period.

Design and characterisation of a wall motion phantom

Arterial wall motion is an essential feature of a healthy cardiovascular system and it is known that wall motion is affected by age and disease. In recent years, methods have been developed for measurement of wall motion with the intention of providing diagnostically useful information. An issue with all of these techniques is the accuracy and variability of both wall motion and derived quantities such as elasticity, which requires the development of suitable test tools. In this paper, a vessel wall phantom is described for use in ultrasound studies of wall motion. The vessel was made from polyvinyl alcohol (PVA) subjected to a freeze-thaw process to form a cryogel (PVA-C). The elastic modulus, acoustic velocity and attenuation coefficient varied from 57 kPa, 1543 m s −1 and 0.18 dB cm −1 MHz −1 for one freeze-thaw cycle to 330 kPa, 1583 m s −1 and 0.42 dB cm −1 MHz −1 for 10 freeze-thaw cycles. Wall motion was effected by the use of pulsatile flow produced from a gear pump. The use of a downstream flow resistor removed gross distortions in the wall motion waveform, possibly by removal of reflected pressure waves. However, a low amplitude 20 Hz oscillation remained, which is unphysiologic and thought to be caused by the vibration of the distended PVA-C vessel. (E-mail: P.Hoskins@ed.ac.uk)

Cardiopulmonary Bypass and Renal Injury

Renal dysfunction following cardiopulmonary bypass (CPB) is well recognized. The extent of perioperative renal impairment ranges from subclinical injury to established renal failure requiring dialysis. Its incidence varies considerably, depending on the definition and criteria used in the different studies. Acute renal failure (ARF) affects 1-5% of patients and remains a major cause of morbidity and mortality. Co-morbidities, including diabetes mellitus, impaired left ventricular function and advanced age, are recognized predisposing factors. The pathophysiology is multifactorial and is thought related to the systemic inflammatory response and renal hypoperfusion secondary to extracorporeal circulation. Non-pulsatile flow during CPB is thought to be an important aetiological factor, resulting in renal vasoconstriction and ischaemic renal injury. A theoretical reduction in the incidence and severity of postoperative renal impairment has been proposed by advocating the use of pulsatile flow during CPB, or eliminating CPB, especially in high-risk patients. The current evidence, however, is conflicting. Several large observational studies, including a large proportion of high-risk patients, have demonstrated a significant reduction in the frequency of renal failure in patients undergoing off-pump surgery. As older, sicker patients increasingly constitute the cardiac surgical population, the incidence of postoperative renal injury is likely to increase. Further studies addressing various renoprotective strategies in higher-risk patients are awaited.

Better preservation of endothelial function and decreased activation of the fetal renin-angiotensin pathway with the use of pulsatile flow during experimental fetal bypass

Objective: Pulsatile flow was shown to overcome the progressive rise in peripheral and placental vascular resistances observed during steady-flow bypass, this rise being counteracted by inhibition of nitric oxide synthase. This study quantifies the release of endothelial vasoactive substances during a 60-minute in utero model of fetal bypass. Methods: Fetuses were randomly allocated into 1 of 2 groups (steady flow, n = 8, or pulsatile flow, n = 13) and subjected to bypass through central cannulation and perfusion with either a centrifugal or pulsatile (125 beats · min–1) blood pump. Results: Lactate concentration was high, starting at fetal exteriorization and increasing during fetal preparation in the 2 groups. Once bypass was established, the rise was significant only in the steady-flow group. Plasma nitric oxide metabolites, similar before bypass, reached higher levels during pulsatile flow at the end of bypass (99 ± 9 vs 82 ± 23 μmol · L–1; P = .037). Levels of urinary nitric oxide metabolites were significantly higher in the pulsatile-flow than in the steady-flow group (764 ± 143 vs 508 ± 240 μmol · L–1; P = .005). Plasma cyclic guanosine monophosphate levels increased after 30 minutes of bypass in the pulsatile-flow group (25 ± 18 vs 12 ± 8 pmol · mL–1; P = .004), and urinary cyclic guanosine monophosphate excretion was higher in the pulsatile-flow group (517 ± 450 vs 118 ± 78 pmol · mL–1; P = .024). Plasma endothelin-1 levels increased in the 2 groups and were higher in the steady-flow group at 30 minutes (27 ± 5 vs 23 ± 2 pg · mL–1; P = .04) and 60 minutes of bypass (39 ± 7 vs 32 ± 6 pg · mL–1; P = .04). Plasma renin concentration increased significantly during bypass only in the steady-flow group (26 ± 10 vs 57 ± 42 in ng A1 · mL–1 · h–1; P = .04). Conclusions: Improved placental and peripheral perfusion during fetal pulsatile-flow bypass may be mediated by preservation of fetal/maternal endothelial nitric oxide biosynthetic mechanisms and/or decreased activation of the fetal renin-angiotensin pathway. (J Thorac Cardiovasc Surg 2000;120:770-7)

Contrast-Enhanced color doppler US in malignant portal vein thrombosis

To assess the role of contrast-enhanced color Doppler US in the differential diagnosis of benign and malignant portal vein thrombosis. Fifty-six patients with portal vein thrombosis underwent color and power Doppler US examination before and after i.v. injection of galactose-palmitic acid suspension. The criterion for diagnosing the presence and extension of thrombosis was the lack of visualization of portal vein flow in a segment of the portal vein. The criterion for diagnosing malignant portal vein thrombosis was the detection of pulsatile arterial flow, either hepatopetal or hepatofugal, in the thrombus. The US data were correlated with the types of portal vein thrombosis. Among the 56 patients, there were 40 benign and 16 malignant portal thromboses. Unenhanced Doppler US detected continuous blood flow in 24 benign thromboses and pulsatile in 3 malignant thromboses. No flow, either continuous or pulsatile, was detected in 16 cases with benign thrombosis and in 13 cases with malignant thrombosis. Contrast-enhanced Doppler US allowed to assess pulsatile flow in 15 cases with malignant thrombosis (94%). The use of pulsatile flow as diagnostic criterion of malignant thrombosis yielded a sensitivity of 57% and a specificity of 95% with conventional Doppler US, whereas contrast-enhanced US achieved a sensitivity of 94% and a specificity of 100%. Contrast-enhanced Doppler US is a reliable diagnostic tool for assessing malignant portal vein thrombosis.

Mass transfer efficiency of a commercial hollow fibre oxygenator during six-hour in vitro perfusion with steady and with pulsatile blood flow

Detailed data about the behaviour of commercial membrane oxygenators with pulsatile blood flow are rarely available. This work deals with an experimental evaluation of the effects induced on gas transfer efficiency by pulsatile perfusion of a hollow fibre oxygenator (Monolyth Sorin Biomedica). The oxygenator was subjected to two in vitro trials both carried out with identical experimental protocols except for the flow type, steady and pulsatile. A roller pump with pulsatile module (Stockert Instrument) was used to generate both flow types. Three different mean blood flow rates (3.2, 4.0 and 4.8 Umin) were tested. The experiments lasting six hours were carried out using bovine blood with inlet conditions according to AAMI standard requirements. Blood samples were withdrawn every hour and the calculated gas transfer obtained in the two sessions were compared. The device proved to be well-designed for steady flow and to be liable to similar gas transfer performance when used in pulsatile conditions. Furthermore, the use of pulsatile flow rather than steady flow provided more consistent conditions and resulted in a higher eventual oxygen transfer efficiency (final mean difference = 6.2%, p &lt; 0.05), proving to be able to avoid any performance decays. (Int J Artif Organs 1998; 21:97–106)

Clinical Comparison of Pulsatile and Nonpulsatile Perfusion During Cardiopulmonary Bypass

Controversy exists concerning the utilization of pulsatile flow during cardiopulmonary bypass (CPB) with regard to improved patient outcomes. The purpose of the present study was to evaluate pulsatile perfusion in patients undergoing CPB in a clinical setting. Seventy patients undergoing open heart surgery for repair of valvular or congenital heart disease were prospectively entered into the study and were randomly assigned to either pulsatile perfusion (PP, n=35) or nonpulsatile perfusion (NP, n=35) groups. All patients received identical surgical, perfusion, and postoperative care. Study parameters included: rate of spontaneous cardiac conversion, inotropic drug use, urine output, skin temperature, platelet count, fibrinogen concentration, and plasma free hemoglobin level. There were no statistically significant differences seen in either preoperative or operative parameters between groups. The PP group had a significantly higher rate of spontaneous cardiac conversion, less inotropic drug use, earlier recovery of skin temperature, and higher urine output during CPB (908.8 ± 87.2 ml/hr vs. 606.1 ± 57.5 ml/hr, p &lt; .01). There were no significant differences in either platelet count or fibrinogen concentration between groups. There was a steady increase in plasma free hemoglobin during PP, which was not seen in the NP group (p &lt; .01). We conclude that the use of pulsatile flow resulted in improved patient outcomes in maintaining better renal function and preserving cardiac function in the early post-bypass period.

Influence of Membrane Oxygenators on the Pulsatile flow in Extracorporeal Circuits: An Experimental Analysis

An experimental analysis was carried out to evaluate the effects induced by two typical extracorporeal circuits on the pressure and flow generated by a roller pump with a pulsatile module. The hydraulic behaviour of the patient was simulated by means of a mechanical mock-up system consisting of a few lumped parameters reproducing the physiologic vascular impedance. Pressure and flow tracings were acquired at different locations along the circuit using an automatic data acquisition system. Nine lest conditions with different pulse frequency and systolic time values were examined using a mean volumetric flow rate of approximately 4 l/min. A complete analysis of the results obtained in terms of pressure drops and inflow-outflow differences across the components of the arterial line, as well as the calculation of the hydraulic pulsatile power along the circuit, allowed us to assess the influence of the various components upon the pulsatility. The results indicated that the membrane oxygenators tested slightly affect the pulsatility of the flow and the pressure; on the contrary the arterial pipe line is responsible for large damping and head losses. To optimize the use of pulsatile flow for cardiopulmonary bypass it is necessary to reduce the length of the arterial pipe lines thus integrating the circuit as much as possible.

Pulsatile Flow and Simple Flow Control Method During Weaning Period in Centrifugal Pump: Toward More Expanded Usage in Open Heart Surgery

To expand the usage of the centrifugal pump (CP) in open heart surgery, we performed two studies. In the first, we evaluated pulsatile flow in the CP. In vitro pump performance of the Terumo Capiox pump (TCP) and the Sarns Delphin pump (SDP) and increase of free hemoglobin (mg/dl) after driving 6 h were investigated using bovine blood. A roller pump (RP) was used as a comparison. Equally effective pulsatile flow was obtained in both CPs. Hemolysis was less severe in TCP (120 mg/dl) than SDP (210 mg/dl) and RP (320 mg/dl). In the second study, we evaluated a simple flow control method. Flow rate was easily controlled with step-wise clamping of 3-pronged tubing (Triple-flow) without changing rotational speed, regardless of afterload. Fluctuation of flow was much less with this method than with the rotational speed change method. The use of pulsatile flow of TCP, with its minimum increase of hemolysis and the easier flow control method during the weaning process, may expand the usage of CP in open heart surgery.

Effect of pulsatile flow during cardiopulmonary bypass on thyroid hormone metabolism

Changes in thyroid hormone levels during and after cardiopulmonary bypass (CPB) are well documented. However, little is known about the effects of pulsatile flow during CPB on thyroid hormone metabolism. To examine the effect of flow pattern, a prospective study was carried out using 30 patients undergoing coronary artery bypass grafting. Fifteen patients had pulsatile flow during CPB and 15, nonpulsatile flow. Serum samples were obtained preoperatively, during bypass, and at 2 and 24 hours postoperatively. Thyroid-stimulating hormone, thyroxine (T 4), triiodothyronine (T 3), free T 4, and free T 3 levels were measured by radioimmunoassay. All measured hormone levels except free T 4 and thyroid-stimulating hormone decreased after the initiation of CPB. There were no differences in preoperative values between the two groups. However, levels of T 3 and free T 3 during and after CPB showed a significant difference between the two groups, with a smaller decrease in patients in whom pulsatile flow was used during bypass ( p < 0.05). Thyroxine, and thyroid-stimulating hormone free T 4 values showed no difference between the two groups at any sampling time. These data provide support for the use of pulsatile flow during CPB to establish a more physiologic state and maintain better thyroid hormone metabolism.

Quantification of vascular stenosis with color Doppler flow imaging: in vitro investigations.

The accuracy of quantifying the degree of vascular stenosis with color Doppler flow imaging (7.5-MHz, linear array system) was determined in an experimental study carried out on six concentric and five eccentric model stenoses (cross-sectional area reduction, 13.4%-93.8%). The measurements were made with use of pulsatile flow at four different flow rates (70.8-339.0 mL/min). The degree of stenosis was calculated from the ratio of prestenotic to intrastenotic flow velocity. The most exact measurement of the degree of stenosis could be achieved with Doppler spectral analysis by determining the maximum peak systolic velocity (r = .994, y = 0.98x - 3.2). With the velocity values derived only from the color-coded image, it was also possible to find the most exact degree of stenosis (r = .995, y = 0.99x - 2.9). For quantification of stenosis, pre- and intrastenotic Doppler spectral analysis is no longer necessary if the stenosis can be imaged sufficiently with color Doppler.

Retracted: Does the technique of cardiopulmonary bypass affect lung water content?

Several efforts have been made to improve the technique of cardiopulmonary bypass (CPB), including the use of pulsatile flow and the modification of cannulation technique. The present study focused upon extravascular lung water (EVLW) in 60 aortocoronary bypass patients subjected to four different perfusion techniques during CPB: group 1 (n = 15): non-pulsatile flow and standard cannulation; group 2 (n = 15); pulsatile flow and standard cannulation; group 3 (n = 15): nonpulsatile flow and monoatrial cannulation (i.e., always "partial" bypass during CPB); group 4 (n = 15): pulsatile flow and monoatrial cannulation. EVLW content was measured using the double-indicator dilution technique with indocyanine green; in addition, various hemodynamic and laboratory variables were measured. Lung water content rose above normal values (mean: 5.79 +/- 0.33 ml/kg) only in the groups submitted to the standard cannulation technique, irrespective of whether the perfusion flow was pulsatile or not (group 1: + 27.4%; group 2: + 25.5%). Pulmonary gas exchange, too, was compromised only in these patients (PaO2 in group 1 -19% and in group 2 -17%; Qs/Qt in group 1 + 36 rel. % and in group 2 + 29 rel. %), whereas all patients with monoatrial cannulation and partial bypass throughout the CPB period showed no rise in EVLW content or Qs/Qt and no drop in PaO2. From the results of this study we conclude that pulsatile perfusion during open heart surgical procedure has no advantages in regard to lung water content. Monoatrial cannulation with partial bypass at all times during CPB, however, seems to be beneficial, probably owing to the maintenance of pulmonary circulation during the bypass period.