Pulsatile Flow Group Research Articles

Continuous versus Pulsatile Flow in 24-Hour Vascularized Composite Allograft Machine Perfusion in Swine: A Pilot Study

IntroductionMultiple perfusion systems have been investigated on vascularized composite allografts, with various temperatures and different preservation solutions, most using continuous flow (CF). However, physiological flow is pulsatile and provides better outcomes in kidney and lung ex vivo perfusions. The objective of this pilot study is to compare pulsatile flow (PF) with CF in our 24-h subnormothermic machine perfusion protocol for swine hindlimbs. MethodsPartial hindlimbs were harvested from Yorkshire pigs and perfused with a modified Steen solution at 21°C for 24 h either with CF (n = 3) or with pulsatile flow (PF) at 60 beats/min (n = 3). Perfusion parameters, endothelial markers, and muscle biopsies were assessed at different timepoints. ResultsOverall, lactate levels were significantly lower in the PF group (P = 0.001). Glucose uptake and potassium concentration were similar in both groups throughout perfusion. Total nitric oxide levels were significantly higher in the PF group throughout perfusion (P = 0.032). Nitric oxide/endothelin-1 ratio also tends to be higher in the PF group, reflecting a potentially better vasoconductivity with PF, although not reaching statistical significance (P = 0.095). Arterial resistances were higher in the PF group (P < 0.001). Histological assessment did not show significant difference in muscular injury between the two groups. Weight increased quicker in the CF group but reached similar values with the PF after 24 h. ConclusionsThis pilot study suggests that PF may provide superior preservation of vascularized composite allografts when perfused for 24 h at subnormothermic temperatures, with potential improvement in endothelial function and decreased ischemic injury.

Effects of Pulsatile Flow on Phosphorylcholine Coated Oxygenator and Arterial Filter

Objective: We aimed to compare the effects of pulsatile/nonpulsatile flow on phosphorylcholine coated (PC) oxygenator fibers, arterial filters by using scanning electron microscope (SEM). Methods: Eleven patients were randomly divided into two groups, as; nonpulsatile and pulsatile flow groups (NP and P groups) by using PC oxygenators. The oxygenator fiber samples were examined under SEM to compare the thickness of absorbed blood proteins and amount of blood cells on the surface of oxygenators. Arterial filters were also analysed by SEM regarding the captured blood elements or particles. Results: The mean fiber thickness from the axial images were calculated as 46.9 m and 47.6 m at group P and NP respectively which is statistically insignificant. Evaluation of the blood samples that were extracted from the arterial filter bring out higher amount of fibrin network and blood cells on fibers at group NP. Conclusion: We concluded that there is lesser amount of blood components on the fibers of arterial filter at pulsatile flow. Coating of oxygenators is beneficial in case of surface biocompatibility and pulsatile perfusion develops lower amount of blood elements on arterial filter.

Acute Response of Human Aortic Endothelial Cells to Loss of Pulsatility as Seen during Cardiopulmonary Bypass

Cardiopulmonary bypass (CPB) results in short-term (3–5 h) exposure to flow with diminished pulsatility often referred to as “continuous flow”. It is unclear if short-term exposure to continuous flow influences endothelial function, particularly, changes in levels of pro-inflammatory and pro-angiogenic cytokines. In this study, we used the endothelial cell culture model (ECCM) to evaluate if short-term (≤5 h) reduction in pulsatility alters levels of pro-inflammatory/pro-angiogenic cytokine levels. Human aortic endothelial cells (HAECs) cultured within the ECCM provide a simple model to evaluate endothelial cell function in the absence of confounding factors. HAECs were maintained under normal pulsatile flow for 24 h and then subjected to continuous flow (diminished pulsatile pressure and flow) as observed during CPB for 5 h. The ECCM replicated pulsatility and flow morphologies associated with normal hemodynamic status and CPB as seen with clinically used roller pumps. Levels of angiopoietin-2 (ANG-2), vascular endothelial growth factor-A (VEGF-A), and hepatocyte growth factor were lower in the continuous flow group in comparison to the pulsatile flow group whereas the levels of endothelin-1 (ET-1), granulocyte colony stimulating factor, interleukin-8 (IL-8) and placental growth factor were higher in the continuous flow group in comparison to the pulsatile flow group. Immunolabelling of HAECs subjected to continuous flow showed a decrease in expression of ANG-2 and VEGF-A surface receptors, tyrosine protein kinase-2 and Fms-related receptor tyrosine kinase-1, respectively. Given that the 5 h exposure to continuous flow is insufficient for transcriptional regulation, it is likely that pro-inflammatory/pro-angiogenic signaling observed was due to signaling molecules stored in Weible-Palade bodies (ET-1, IL-8, ANG-2) and via HAEC binding/uptake of soluble factors in media. These results suggest that even short-term exposure to continuous flow can potentially activate pro-inflammatory/pro-angiogenic signaling in cultured HAECs and pulsatile flow may be a successful strategy in reducing the undesirable sequalae following continuous flow CPB.

Pulsatile Versus Nonpulsatile Flow During Cardiopulmonary Bypass: Extent of Hemolysis and Clinical Significance.

Pulsatile flow has been used during cardiopulmonary bypass (CPB) for decades and its use is increasing with advancing extracorporeal technology. Pulsatile flow generates higher circuit pressures and shear forces than nonpulsatile flow at comparable pump flow and patient mean arterial pressure. Very little is known about the effect this has on erythrocytes. We included 62 adult patients (32 in the pulsatile group and 30 in the nonpulsatile group) undergoing elective coronary artery bypass grafting in this prospective observational study. Blood samples were collected at routine sampling times throughout surgery and were analyzed for the presence of free heme and globin using mass spectroscopy. Patient characteristics, CPB, and aortic cross-clamp times, pump flow as well as patient mean arterial pressure were similar in both groups. Maximum circuit pressure in the pulsatile flow group was statistically significantly higher than that in the nonpulsatile flow group (257.12 vs. 190.64 mmHg, p < 0.0001). Both heme and globin levels were higher in the pulsatile flow group. This reached statistical significance with globin at 30 minutes of CPB and with heme after aortic unclamping. We conclude that pulsatile CPB using roller pumps results in a greater extent of hemolysis. The clinical significance, however, is not yet known.

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.

Feasibility Study of Pulsatile Left Ventricular Assist Device for Prolonged Ex Vivo Lung Perfusion

Exvivo lung perfusion (EVLP) has the potential to increase the donor pool for lung transplantation by facilitating resuscitation and extended evaluation of marginal organs. Current EVLP methodology employs continuous flow (CF) pumps that produce non-pulsatile EVLP hemodynamics. In this feasibility study, we tested the hypothesis that a pulsatile flow (PF) pump will provide better EVLP support than a CF pump through delivery of physiologic hemodynamics. Porcine lungs were supported in an EVLP model by centrifugal CF (n= 3) or PF (n= 4) left ventricular assist devices. Lungs were ventilated at 4 to 5 mL/kg, 0.21 fraction of inspired oxygen (FiO2), and perfused with an acellular, albumin-based solution corrected for osmolarity, acid-base balance, and carbon dioxide pressure (≤20 hours at 30°C) for a minimum of 12 hours support. Prostaglandin E1 and 30% albumin were infused continuously. Hemodynamic, respiratory, and blood gas parameters were continuously monitored and digitally recorded hourly. Parenchymal biopsies were used for quantification of wet to dry weight ratio. All lungs maintained function in the EVLP circuit for a minimum of 12 hours (mean 14.7 ± 1 hours) and demonstrated minimal edema formation. The PF EVLP produced higher pulsatility as demonstrated by greater energy equivalent pressure and surplus hemodynamic energy compared with CF EVLP (p < 0.05). There were no statistically significant differences in pulmonary impedance, arterial partial pressure of oxygen/fraction of inspired oxygen, wet to dry weight ratio, and peak airway pressure between CF and PF EVLP. The CF and PF EVLP systems successfully maintained lungs 12+ hours using a modified Steenperfusate (XVIVO Perfusion, Inc, Goteborg, Sweden); however, there were no statistically significantdifferences between CF and PF groups despite higher pulsatility, suggesting that PF may not offer immediate benefits over CF for prolonged exvivo lung preservation.

Assessing Endothelial Responsiveness After Cardiopulmonary Bypass: Insights on Different Perfusion Modalities

Cardiopulmonary bypass (CPB) exerts several deleterious effects on inflammatory pathways. Most of these can be related to an endothelial insult leading to endothelial dysfunction. To date, the degree of endothelial damage only has been evaluated on a cellular and molecular level, but no studies exist looking at the functional effects of CPB on the endothelium. Previous studies hypothesized a negative effect of continuous flow as opposed to the physiologic pulsatile flow. The aim of the present retrospective study was to investigate how different perfusion modalities during CPB (ie, continuous v pulsatile flow) or its avoidance differently impact endothelial function. Cardiovascular operating room and intensive care unit of a large tertiary University Hospital in Monza, Italy. Flow-mediated dilatation (FMD) of the brachial artery was assessed in 29 patients undergoing elective myocardial revascularization. Ten patients receiving continuous-flow CPB, 10 receiving pulsatile-flow CPB, and 9 scheduled for beating-heart revascularization were studied. Patients were studied at baseline (after induction of general anesthesia), after CPB upon intensive care unit (ICU) admission after surgery, and on the first postoperative day before discharge from the ICU (on average, 24 hours after CPB discontinuation). The continuous-flow CPB group demonstrated a significant reduction in FMD after CPB, (12.8% ± 9.7% v 1.6% ± 1.5%, p<0.01), which lasted up to the first postoperative day (5.9% ± 4.1%). On the other hand, FMD did not change in the pulsatile-flow group (12.5% ± 10.5%, 11.0% ± 7.2%, and 16.6% ± 11.7%, respectively). FMD also was unaffected in the beating-heart group, thus suggesting a direct effect of CPB itself on endothelial function. In conclusion, in this study population of adult patients undergoing elective coronary revascularization, continuous-flow CPB markedly impaired endothelial function, although this was not the case with pulsatile-flow CPB. This study posed the rationale for further investigations on the potential value of FMD to predict cardiovascular events in these patients.

Pulsatile versus non-pulsatile flow to reduce cognitive decline after coronary artery bypass surgery: A randomized prospective clinical trial

BackgroundIn this prospective study, we aimed to compare the effect of pulsatile and non-pulsatile flow on the cognitive functions in patients undergoing coronary artery bypass surgery. MethodsPatients scheduled for their first coronary artery bypass surgery (n = 148) were randomly assigned to the pulsatile flow group (Group A, n = 75) or non-pulsatil group (Group B, n = 73). Cognitive performance was assessed with (MoCA) montreal cognitive assessment test performed by psychologists before coronary artery bypass surgery and 1 month after the operation. ResultsMild cognitive impairment was seen in 12 (16%) patients and serious cognitive impairment was seen in 1 (1.33%) patient in the pulsatile flow group. In the other group, mild cognitive impairment was detected in 23 (31.50%) patients and serious cognitive decline was found in 3 (4.10%) patients. Mean MoCA scores were 25.86 ± 2.62 in group A and 22.12 ± 2.20 in group B. The difference between two groups was statistically significant (P = 0.041). ConclusionsWe suggest that pulsatile flow has beneficial effects to decrease cognitive dysfunction in patients undergoing on-pump coronary artery bypass surgery.

Arterial wall histology in chronic pulsatile-flow and continuous-flow device circulatory support

Continuous-flow (CF) ventricular assist devices (VAD) are an established option for treatment of end-stage heart failure. However, the effect of long-term CF with lack of peripheral arterial wall motions on blood pressure regulation and end-organ arterial wall sclerosis, especially in the case of long-term support (> 3 years), remains unclear. Tissue samples obtained at autopsy from liver, kidney, coronary arteries, and brain from 27 VAD recipients supported for > 180 days between 2000 and 2010 were histologically examined to assess vascular alterations, including perivascular infiltrate, intravascular infiltrate, wall thickness, thrombosis, endothelial cell swelling, vessel wall necrosis, and peri-vascular fibrosis. Pulsatile-flow (PF) devices had been inserted in 9 patients and CF devices had been inserted in 16. The pathologist was blinded to the group distribution. Demographic, pharmacologic, and clinical data were retrospectively analyzed before surgery and during the follow-up period of up to 24 months. Median duration of support was 467 days (range, 235-1,588 days) in the PF group and 263 days (range, 182-942 days) in the CF group. Demographic and clinical data before and after surgery were similar. Amiodarone was more often used during follow-up in CF group than in the PF group (61% vs 10%, p = 0.009). Throughout the follow-up period, mean arterial pressure did not differ between recipients of the 2 pump types, nor did systolic and diastolic pressure, except at 2 weeks after VAD implantation, when systolic blood pressure was higher (p = 0.05) and diastolic lower (p = 0.03) in the PF group. Histologic studies did not identify any relevant differences in arterial wall characteristics between the 2 groups. Long-term mechanical circulatory support with CF devices does not adversely influence arterial wall properties of the end-organ vasculature.

Pulsatile flow during cardiopulmonary bypass preserves postoperative microcirculatory perfusion irrespective of systemic hemodynamics

The onset of nonpulsatile cardiopulmonary bypass is known to deteriorate microcirculatory perfusion, but it has never been investigated whether this may be prevented by restoration of pulsatility during extracorporeal circulation. We therefore investigated the distinct effects of nonpulsatile and pulsatile flow on microcirculatory perfusion during on-pump cardiac surgery. Patients undergoing coronary artery bypass graft surgery were randomized into a nonpulsatile (n = 17) or pulsatile (n = 16) cardiopulmonary bypass group. Sublingual mucosal microvascular perfusion was measured at distinct perioperative time intervals using sidestream dark field imaging, and quantified as the level of perfused small vessel density and microvascular flow index (vessel diameter < 20 μm). Microcirculation measurements were paralleled by hemodynamic and free hemoglobin analyses. The pulse wave during pulsatile bypass estimated 58 ± 17% of the baseline blood pressure waveform. The observed reduction in perfused vessel density during aorta cross-clamping was only restored in the pulsatile flow group and increased from 15.5 ± 2.4 to 20.3 ± 3.7 mm/mm(2) upon intensive care admission (P < 0.01). The median postoperative microvascular flow index was higher in the pulsatile group [2.6 (2.5-2.9)] than in the nonpulsatile group [2.1 (1.7-2.5); P = 0.001]. Pulsatile flow was not associated with augmentation of free hemoglobin production and was paralleled by improved oxygen consumption from 70 ± 14 to 82 ± 16 ml·min(-1)·m(-2) (P = 0.01) at the end of aortic cross-clamping. In conclusion, pulsatile cardiopulmonary bypass preserves microcirculatory perfusion throughout the early postoperative period, irrespective of systemic hemodynamics. This observation is paralleled by an increase in oxygen consumption during pulsatile flow, which may hint toward decreased microcirculatory heterogeneity during extracorporeal circulation and preservation of microcirculatory perfusion throughout the perioperative period.

Neurocognitive function in destination therapy patients receiving continuous-flow vs pulsatile-flow left ventricular assist device support

The HeartMate II (Thoratec Corp, Pleasanton, CA) continuous-flow left ventricular assist device (LVAD) improved survival in destination therapy (DT) patients during a randomized trial compared with pulsatile-flow LVADs. This study documented changes in cognitive performance in DT patients from that trial to determine if there were differences between continuous-flow and pulsatile-flow support. Data were collected in a sub-study from 96 HeartMate II continuous-flow and 30 HeartMate XVE pulsatile-flow LVAD patients from 12 of the 35 trial sites that followed the same serial neurocognitive (NC) testing protocol at 1, 3, 6, 12, and 24 months after LVAD implantation. Spatial perception, memory, language, executive functions, and processing speed were the domains assessed with 10 standard cognitive measures. Differences over time and between LVAD type were evaluated with linear mixed-effects modeling. From 1 to 24 months after LVAD implantation, changes in NC functions were stable or showed improvement in all domains, and there were no differences between the continuous-flow and pulsatile-flow groups. Data at 24 months were only available from patients with the continuous-flow LVAD due to the limited durability of the HeartMate XVE device. There was no decline in any NC domain over the time of LVAD support. Missing data not collected from patients who died could have resulted in a bias toward inflated study results. The NC performance of advanced heart failure patients supported with continuous-flow and pulsatile-flow LVADs shows stabilization or improvement during support for up to 24 months.

Binding capability of microbubbles targeted to VCAM-1 under pulsatile high-shear flow conditions

Objective To assess the binding capability of microbubbles targeted to VCAM-1 using the parallel plate flow chamber mimic the pulsatile high-shear flow conditions of artery. Methods Targeted microbubbles were designed by conjugating monoclonal antibodies against mouse VCAM-1 to the lipid shell of the microbubbles via an avidin-biotin bridge. The binding and retention of targeted microbubbles to VCAM-1 (MBv) immobilized on a culture dish were assessed in a flow chamber at variable shear stress (0.5～ 16.0 dynes/cm2 ). The pulsatile flow conditions were generated and compared to the continuous flow conditions. The retentive ability of MBv was evaluated by the detachment test. Results The marked binding of MBv were seen in pulsatile and continuous flow conditions at low-shear flow conditions of 0.5 ～ 2dyn/cm2 ,but the binding rate in the pulsatile flow group was higher ( P ＜0. 05) than that in the continuous flow conditions. Furthermore,the marked binding of MBv was still noted at the highest shear rates (4～8dyn/cm2) under pulsatile flow conditions, while it was not observed under continuous flow conditions. The half detachment rate of MBv was high up to (20.7 ± 3. 1)dyn/cm2. Conclusions The targeted microbubbles binding to VCAM-1 specific and effective at high-shear stress under pulsatile flow conditions. The molecular ultrasound imaging can be potentially used in the high-shear conditions artery system. Key words: Ultrasonography; Microbubbles; Vascular cell adhesion molecule-1; Shear stress

Neonatal cavopulmonary assist: Benefit of pulsatile pulmonary perfusion

Abstract Introduction: A systemic venous source of pulmonary blood flow reduces the instability associated with Stage I Norwood physiology. We have previously demonstrated neonatal cavopulmonary assist under steady flow conditions. We hypothesized that pulsatile pulmonary perfusion would improve pulmonary hemodynamics. Methods: Lambs (7.2 +/− 1.1 SD kg, age 7.9 +/− 1.5 days) underwent cavopulmonary diversion using bicaval venous-to-main pulmonary artery cannulation. The proximal main pulmonary artery was clamped and the right ventricle vented for egress of coronary venous blood. A miniature centrifugal pump was used to assist cavopulmonary blood flow. Control animals (n = 4) underwent sham surgery. 13 animals received steady flow pulmonary perfusion, and six animals received pulsatile pulmonary perfusion. Hemodynamic and gas exchange data were measured for eight hours. Groups were compared using ANOVA. Results: All animals remained physiologically stable. Cardiac index, systemic arterial pressure, mean pulmonary arterial pressure, vena caval pressure, mean circulatory filling pressure, pO2, and pCO2 were not statistically different between the steady flow and pulsatile flow groups after 8 hours of cavopulmonary assist (P Conclusions: Pulsatile pulmonary perfusion yields a pulmonary vascular resistance comparable to control and lower than steady flow perfusion in a neonatal animal model of univentricular Fontan circulation.

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)

Flow-induced release of endothelium-derived relaxing factor during pulsatile bypass: Experimental study in the fetal lamb

Objective: This study was initiated to test the hypothesis that fetal hemodynamic changes observed under pulsatile flow bypass might be related to the release of endothelium-derived relaxing factor through oscillating shear stress. Methods: Normothermic bypass was instituted in utero in 21 preterm fetal lambs for a 1-hour period through the right atrium and main pulmonary artery. Ultrasonic flowmeters were positioned around the descending aorta and the umbilical artery. The circuit consisted of an oxygenator and a pump set to either continuous flow ( n = 7) or pulsatile flow ( n = 7) and adjusted to maintain a fetal main arterial pressure of 50 mm Hg. In seven other animals, endothelium-derived relaxing factor was blocked by a continuous infusion of N ω-nitro- l-arginine after 30 minutes of pulsatile flow. Results: During the first 30 minutes of bypass, pump flows were significantly lower in the continuous-flow group than in the pulsatile-flow or blocked-flow groups (respectively, 612 ± 144, 907 ± 153 and 987 ± 228 ml/min), with similar changes in aortic and umbilical flows. Systemic vascular resistances were significantly lower in the pulsatile-flow and blocked-flow groups than in the continuous-flow group (550 ± 106 vs 821 ± 212 dynes/sec/cm −5). However, after blockade of endothelium-derived relaxing factor, resistances increased gradually in the blocked-flow group to reach the level of that of the continuous-flow group at the end of bypass (943 ± 77 vs 556 ± 143 dynes/sec/cm −5 in the pulsatile-flow group). Conclusions: Blockade of endothelium-derived relaxing factor after 30 minutes of pulsatile flow returns fetal hemodynamics to continuous flow conditions. The specific inhibitor of endothelium-derived relaxing factor used in this experiment suggests that nitric oxide may be released by fetal endothelium during pulsatile bypass.(J Thorac Cardiovasc Surg 1997;114:738-45)

Pulsatile perfusion versus conventional high-flow nonpulsatile perfusion for rapid core cooling and rewarming of infants for circulatory arrest in cardiac operation

Thirty consecutive infants undergoing hypothermia and circulatory arrest for repair of ventricular septal defect, transposition of the great vessels, or atrioventricular canal defects were alternately selected for conventional high flow nonpulsatile perfusion or pulsatile perfusion during core cooling and rewarming. All received morphine anesthesia, 30 mg/kg of Solu-Medrol, and 10 to 15 mcg/kg of phentolamine. Those receiving nonpulsatile flow were perfused at a rate of 160 to 180 cc/kg/min with a roller pump and oxygenator with arterial pressure of 50 to 55 mm Hg. In the pulsatile flow group, a roller pump and oxygenator were used, and an especially constructed Datascope PAD (pulsatile assist device) was interposed in the arterial line to provide pulsatile perfusion with 75/40 mm Hg pressure at slightly reduced flow (150 cc/kg/min). The average rectal, esophageal, and tympanic membrane temperatures were reduced to approximately 16 degrees C prior to circulatory arrest. Following repair, perfusion was resumed until these temperatures returned to 37 degrees C. Cooling and rewarming were enhanced by pulsatile perfusion, with over 30% reduction in total pump time. Additionally, the larger patients in the pulsatile group cooled almost as rapidly as the smaller. The rates of decline and subsequent rise of rectal, esophageal, and tympanic membrane temperatures were equal in the pulsatile group, but the rectal temperature lagged far behind in the nonpulsatile group. Urine production during bypass was 100% greater in the pulsatile group. The plasma free hemoglobin was similar in both groups. The average postrewarming pH was 7.31 in the nonpulsatile group and 7.42 in the pulsatile group. Infants receiving pulsatile flow awakened more quickly, were more alert, and required less postoperative mechanical ventilation. We suggest that pulsatile perfusion for core cooling and rewarming of infants is safe and is more rapid and physiological than conventional high-flow nonpulsatile perfusion.

Plasma vasopressin levels and urinary flow during cardiopulmonary bypass in patients with valvular heart disease: Effect of pulsatile flow

The effect of pulsatile flow on plasma vasopressin levels during cardiopulmonary bypass (CPB) was studied in 20 patients undergoing open valve replacement. Routine bypass was used in 10 patients and the AVCO pulsatile bypass pump was utilized in the other 10. In Group I (nonpulsatile) during CPB, the vasopressin level was markedly elevated (3.1 +/- 2 to 80 +/- 22 pg/ml) as was urine flow (0.6 +/- 0.2 to 5.9 +/- 2 ml/min) and urine Na+ concentration (69 +/- 19 to 116 +/- 7 mEq/L). In Group II (pulsatile) during CPB, the vasopressin level (3.8 +/- 3 to 54 +/- 14 pg/ml), urine flow (0.6 +/- 0.1 to 16.2 +/- 4.8 ml/min), and urine Na+ concentrations (61 +/- 13 to 97 +/- 10 mEq/L) were also elevated. The rise in vasopressin and urine Na+ was less in the pulsatile group (p less than 0.05) whereas the urine flow was higher (p less than 0.05). To maintain comparable blood pressure, the pulsatile flow group required significantly higher flows (4.5 +/- 0.2 compared to 3.8 +/- 0.2; p less than 0.05). These data suggest that CPB produces a marked vasopressin stress response which is beyond the physiological range for an antidiuretic effect on the kidney. At these levels vasopressin can exert a vasopressor effect to maintain resistance and affect renal blood flow, as well as producing an Na+ diuresis. The addition of pulsatile flow creates a more physiological situation attenuating the vasopressin response and producing a decrease in systemic resistance and a less pronounced Na+ diuresis.