Quantification of Perfusion Modes in Terms of Surplus Hemodynamic Energy Levels in a Simulated Pediatric CPB Model

Renal and Cerebral Hypoxia and Inflammation During Cardiopulmonary Bypass

Cardiac surgery-associated acute kidney injury and brain injury remain common despite ongoing efforts to improve both the equipment and procedures deployed during cardiopulmonary bypass (CPB). The pathophysiology of injury of the kidney and brain during CPB is not completely understood. Nevertheless, renal (particularly in the medulla) and cerebral hypoxia and inflammation likely play critical roles. Multiple practical factors, including depth and mode of anesthesia, hemodilution, pump flow, and arterial pressure can influence oxygenation of the brain and kidney during CPB. Critically, these factors may have differential effects on these two vital organs. Systemic inflammatory pathways are activated during CPB through activation of the complement system, coagulation pathways, leukocytes, and the release of inflammatory cytokines. Local inflammation in the brain and kidney may be aggravated by ischemia (and thus hypoxia) and reperfusion (and thus oxidative stress) and activation of resident and infiltrating inflammatory cells. Various strategies, including manipulating perfusion conditions and administration of pharmacotherapies, could potentially be deployed to avoid or attenuate hypoxia and inflammation during CPB. Regarding manipulating perfusion conditions, based on experimental and clinical data, increasing standard pump flow and arterial pressure during CPB appears to offer the best hope to avoid hypoxia and injury, at least in the kidney. Pharmacological approaches, including use of anti-inflammatory agents such as dexmedetomidine and erythropoietin, have shown promise in preclinical models but have not been adequately tested in human trials. However, evidence for beneficial effects of corticosteroids on renal and neurological outcomes is lacking. © 2021 American Physiological Society. Compr Physiol 11:1-36, 2021.

The effect of pulsatile versus non-pulsatile flow during cardiopulmonary bypass on cerebral oxygenation: A randomized trial

BACKGROUND

The present study aims to compare regional oxygen supply determined by Near-Infrared Spectroscopy in the course of pulsatile perfusion with non-pulsatile perfusion during cardiopulmonary bypass in patients undergoing valvular heart surgery.

METHODS

In this prospective randomized single-blinded trial, we enrolled adult subjects aged 18-65 years scheduled for elective valvular heart repair/replacement surgery with non-stenotic carotid arteries, employing a consecutive sampling method. Eligible patients were then randomly assigned in a 1:1 ratio to pulsatile or non-pulsatile perfusion during aortic cross-clamp. The primary outcome was regional cerebral oxygenation monitored by Near-Infrared Spectroscopy in each group.

RESULTS

Seventy patients were randomly assigned, and each group comprised 35 patients. Mean age was 46.8 and 46.5 years in pulsatile and non-pulsatile groups, respectively. There were no significant between-group differences in regional cerebral oxygen saturation at different time points of cardiopulmonary bypass (p-value for analysis of variance repeated measures: 0.923 and 0.223 for left and right hemispheres, respectively). Moreover, no significant differences in regional cerebral oxygen saturation levels from baseline between pulsatile and non-pulsatile groups at all desired time points for the left (p = 0.51) and right (p = 0.22) hemispheres of the brain were detected.

CONCLUSION

Pulsatile perfusion during cardiopulmonary bypass does not offer superior regional cerebral oxygenation measured by Near-Infrared Spectroscopy than non-pulsatile perfusion during cardiopulmonary bypass. Nonetheless, the efficacy of pulsatile flow in the subgroup of patients in whom cerebral blood flow is impaired due to carotid artery stenosis needs to be explored and evaluated by this method in future studies.

Transient perioperative inflammation following lung transplantation and major thoracic surgery with elective extracorporeal support: a prospective observational study

Background

The clinical relevance of inflammation induced by elective perioperative extracorporeal membrane oxygenation (ECMO) usage as an integral part of modern lung transplantation (LUTX) remains elusive. The aim of this study was to determine the perioperative cytokine response accompanying major thoracic surgery employing different extracorporeal devices comprising ECMO, cardiopulmonary bypass (CPB), or no extracorporeal circulation in relation to inflammation, clinically tangible as increased sequential organ failure assessment (SOFA) score, called SOFA.

Methods

In this prospective, observational pilot study 42 consecutive patients with end-stage pulmonary disease undergoing LUTX; 15 patients with chronic thromboembolic pulmonary hypertension (CTEPH) undergoing pulmonary endarterectomy and 15 patients with lung cancer undergoing major lung resections were analysed. Cytokine serum concentrations and SOFA were determined before, at end of surgery and in the following postoperative days.

Results

LUTX on ECMO and pulmonary endarterectomy (PEA) on CPB triggered an immediate increase in cytokine serum concentrations at end of surgery: IL-6: 66-fold and 71-fold, IL-10: 3-fold and 2.5-fold, ST2/IL-33R: 5-fold and 4-fold and SOFA: 10.5±2.8 and 10.7±1.7, that decreased sharply to baseline levels from postoperative day 1–5. Despite low perioperative mortality (3 patients, 4.1%) extremely high SOFA ≥13 was associated with mortality after LUTX. Delta-SOFA distinguished survivors from non-survivors: −4.5±3.2 vs. −0.3±1.5 (P=0.001). Increased IL-6 serum concentrations were predictive for increased SOFA (sensitivity: 97%, specificity: 80%). Peak cytokine serum concentrations correlated with ECC duration, maximal lactate, transfusion of red-blood-cells, fresh-frozen-plasma, and catecholamine support.

Conclusions

LUTX and PEA on extracorporeal circulation with an excellent outcome triggered an immediate rise and concomitant fall of inflammation as observed in cytokine serum concentrations and SOFA. High absolute SOFA in the presence of an uncomplicated postoperative course may pertain to specific management strategies rather than organ failure.

The design modification of advanced ventricular assist device to enhance pulse augmentation and regurgitant flow shut-off

The new Advanced ventricular assist device (Advanced VAD) has many features such as improving pulsatility and preventing regurgitant flow during pump stoppage. The purpose of this study was to evaluate the effects of design modifications of the Advanced VAD on these features in vitro. Bench testing of four versions of the Advanced VAD was performed on a static or pulsatile mock loop with a pneumatic device. After pump performance was evaluated, each pump was run at 3000 rpm to evaluate pulse augmentation, then was stopped to assess regurgitant flow through the pump. There was no significant difference in pump performance between the pump models. The average pulse pressure in the pulsatile mock loop was 23.0, 34.0, 39.3, 33.8, and 37.3 mm Hg without pump, with AV010, AV020 3S, AV020 6S, and AV020 RC, respectively. The pulse augmentation factor was 48%, 71%, 47%, and 62% with AV010, AV020 3S, AV020 6S, and AV020 RC, respectively. In the pump stop test, regurgitant flow was -0.60 ± 0.70, -0.13 ± 0.57, -0.14 ± 0.09, and -0.18 ± 0.06 L/min in AV010, AV020 3S, AV020 6S, and AV020 RC, respectively. In conclusion, by modifying the design of the Advanced VAD, we successfully showed the improved pulsatility augmentation and regurgitant flow shut-off features.

Body Perfusion during Adult Cardiopulmonary Bypass is Improved by Pulsatile flow with Intra-Aortic Balloon Pump

Purpose

To evaluate if the use of an intra-aortic balloon pump (IABP) during cardioplegic arrest improves body perfusion.

Methods

158 coronary artery bypass graft (CABG) patients were randomized to linear cardiopulmonary bypass (CPB) (n=71, Group A) or automatic 80 bpm intra-aortic ballon pump (IABP) induced pulsatile CPB (n=87, Group B). We evaluated hemodynamic response by Swan-Ganz catheter, inflammation by cytokines, coagulation and fibrinolysis, transaminase, bilirubin, amylase, lactate and renal function (estimated glomerular filtration rate (eGFR), creatinine, and incidence of renal insufficiency and failure).

Results

IABP induced Surplus Hemodynamic Energy was 15.8±4.9 mmHg, with higher mean arterial pressure during cross-clamping (p=0.001), and lower indexed systemic vascular resistances during cross-clamping (p=0.001) and CPB discontinuation (p=0.034). IL-2 and IL-6 were lower, while IL-10 proved higher in Group B (p<0.05). Group B showed lower chest drainage (p<0.05), transfusions (p<0.05), INR (p<0.05), and AT-III (p=0.001), together with higher platelets, aPTT (p<0.05), fibrinogen (p<0.05) and D-dimer (p<0.05). Transaminases, bilirubin, amylase, lactate were lower in Group B (p<0.05); eGFR was better in Group B from ITU-arrival to 48 hours, both in preoperative kidney disease Stages 1–2 (p<0.03) and Stage 3 (p<0.05), resulting in lower creatinine from ITU-arrival to 48 hours (p<0.03). Incidence of renal insufficiency (p=0.004) and need for renal replacement therapy (p=0.044) was lower in Group B Stage 3. Group B PaO2/FiO2 and lung compliance improved from aortic declamping to the first day (p<0.003) with shorter intubation time (p=0.01).

Conclusion

Pulsatile flow by IABP improves whole-body perfusion during CPB.

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.

Intraaortic counterpulsation during cardiopulmonary bypass impairs distal organ perfusion

BACKGROUND

Recent studies have focused on the use of fixed-rate intraaortic balloon pumping (IABP) during cardiopulmonary bypass (CPB) to achieve pulsatile flow. Because application of an IABP catheter may represent a functional obstruction within the descending aorta, we explored the effect of IABP-pulsed CPB-perfusion with special attention to perfusion above and below the IABP balloon.

METHODS

Sixteen animals received an IABP catheter that remained turned off position (NP group, n = 8) or was switched to an automatic mode of 80 beats/min during CPB (PP group, n = 8). Flow-data and pressure-data were obtained above and below the IABP balloon. Tissue perfusion was evaluated by microspheres.

RESULTS

IABP-pulsed CPB-perfusion, as assessed at 30 minutes on CPB, increased proximal mean aortic pressure (p < 0.05) and carotid artery blood flow (p < 0.001), but decreased distal mean aortic pressure (p < 0.001). The decrease of distal mean aortic pressure in the PP group was associated with a 75 % decrease (p < 0.001) of renal tissue perfusion. During nonpulsed perfusion the respective variables remained essentially unchanged compared with pre-CPB levels.

CONCLUSIONS

Using IABP as a surrogate to achieve pulsatile perfusion during CPB contributes significantly to lowered aortic pressure in the distal portion of aorta and impaired tissue perfusion of the kidneys. The results are focusing on effects that may contribute to organ dysfunction and acute kidney injury. Consequently, assessment of perfusion pressure distal to the balloon should be addressed whenever IABP is used during CPB.

Shear stress, energy losses, and costs: a resolved dilemma of pulsatile cardiac assist devices

Cardiac assist devices (CAD) cause endothelial dysfunction with considerable morbidity. Employment of pulsatile CAD remains controversial due to inadequate perfusion curves and costs. Alternatively, we are proposing a new concept of pulsatile CAD based on a fundamental revision of the entire circulatory system in correspondence with the physiopathology and law of physics. It concerns a double lumen disposable tube device that could be adapted to conventional cardiopulmonary bypass (CPB) and/or CAD, for inducing a homogenous, downstream pulsatile perfusion mode with lower energy losses. In this study, the device's prototypes were tested in a simulated conventional pediatric CPB circuit for energy losses and as a left ventricular assist device (LVAD) in ischemic piglets model for endothelial shear stress (ESS) evaluations. In conclusion and according to the study results the pulsatile tube was successfully capable of transforming a conventional CPB and/or CAD steady flow into a pulsatile perfusion mode, with nearly physiologic pulse pressure and lower energy losses. This represents a cost-effective promising method with low mortality and morbidity, especially in fragile cardiac patients.

Continuous-flow pump model study: the effect on pump performance of pump characteristics and cardiovascular conditions

This model study evaluates the effect of pump characteristics and cardiovascular data on hemodynamics in atrio-aortic VAD assistance. The model includes a computational circulatory sub-model and an electrical sub-model representing two rotary blood pumps through their pressure-flow characteristics. The first is close to a pressure generator-PG (average flow sensitivity to pressure variations, -0.047 l mmHg(-1)); the second is closer to a flow generator-FG (average flow sensitivity to pressure variations, -0.0097 l mmHg(-1)). Interaction with VAD was achieved by means of two interfaces, behaving as impedance transformers. The model was verified by use of literature data and VAD onset conditions were used as a control for the experiments. Tests compared the two pumps, at constant pump speed, in different ventricular and circulatory conditions: maximum ventricular elastance (0.44-0.9 mmHg cm(-3)), systemic peripheral resistance (781-1200 g cm(-4) s(-1)), ventricular diastolic compliance C p (5-10-50 cm(3) mmHg(-1)), systemic arterial compliance (0.9-1.8 cm(3) mmHg(-1)). Analyzed variables were: arterial and venous pressures, flows, ventricular volume, external work, and surplus hemodynamic energy (SHE). The PG pump generated the highest SHE under almost all conditions, in particular for higher C p (+50 %). PG pump flow is also the most sensitive to E max and C p changes (-26 and -33 %, respectively). The FG pump generally guarantees higher external work reduction (54 %) and flow less dependent on circulatory and ventricular conditions. The results are evidence of the importance of pump speed regulation with changing ventricular conditions. The computational sub-model will be part of a hydro-numerical model, including autonomic controls, designed to test different VADs.

Pulsatile versus nonpulsatile flow during cardiopulmonary bypass: microcirculatory and systemic effects

BACKGROUND

Controversy exists regarding the optimal perfusion modality during cardiopulmonary bypass (CPB). Here we compare the effects of pulsatile versus nonpulsatile perfusion on microvascular blood flow during and after CPB.

METHODS

High-risk cardiac surgical patients were randomly assigned to have pulsatile (n=10) or nonpulsatile (n=10) flow during CPB. The sublingual microcirculation was assessed using orthogonal polarization spectral imaging. Hemodynamic and microvascular variables were obtained after anesthesia (baseline), during CPB, and post-CPB.

RESULTS

Compared with baseline, a normal microcirculatory blood flow pattern was accomplished at all time points under pulsatile flow conditions. Peaking 24 hours postoperatively, a higher proportion of normally perfused microvessels occurred under pulsatile versus nonpulsatile flow (56.0%±3.9% vs 33.3%±4.1%; p<0.05). Concurrently, pulsatility resulted in a reduction in the prevalence of pathologic hyper-dynamically perfused vessels (6.0%±3.4% vs 19.6%±8.8%; p<0.05). Leukocyte adherence decreased relative to the nonpulsatile group both during and after CPB. Furthermore, peak lactate levels were reduced under pulsatile flow conditions postoperatively.

CONCLUSIONS

Pulsatile perfusion is superior to nonpulsatile perfusion at preserving the microcirculation, which may reflect attenuation of the systemic inflammatory response during CPB. We suggest the implementation of pulsatile flow can better optimize microvascular perfusion, and may lead to improved patient outcomes in high-risk cardiac surgical procedures requiring prolonged CPB time.

Analysis of pulsatile and nonpulsatile blood flow effects in different degrees of stenotic vasculature

Vessel lumens that have been chronically narrowed by atherosclerosis should be increased in flow velocity and intrastenotic area pressure to maintain an equal flow. This might be followed by a decrease in hemodynamic energy, leading to a reduction of tissue perfusion. In this study, we compared hemodynamic energies according to degrees of stenotic vasculature between pulsatile flow and nonpulsatile flow. Cannuale with 25, 50, and 75% diameter stenosis (DS) were located at the outlet cannula. Using the Korea Hybrid ventricular assist device (KH-VAD) (pulsatile pump: group A) and Biopump (nonpulsatile pump: group B), constant flow of 2 L/min was maintained then real-time flow and velocity in the proximal and distal part of the stenotic cannula were measured. The hemodynamic energies of two groups were compared. At 75% DS, proximal energy equivalent pressure (EEP) delivered to the distal end was only 41.9% (group A) and 42.5% (group B). As the percent EEP fell below 10%, pulsatility disappeared from the 50% stenosis in group A. The surplus hemodynamic energy (SHE) of group B at all degrees of stenosis must have been 0, which was also the case of group A at 75% stenosis. This research evaluated the hemodynamic energy on various degrees of DS in both pulsatile and nonpulsatile flow with mock system. Using a pulsatile pump, pulsatility disappeared above 50% DS while hemodynamic energy was maintained. Therefore, our results suggest that pulsatile flow has a better effect than nonpulsatile flow in reserving hemodynamic energy after stenotic lesion.

Effects of pulsatile and nonpulsatile perfusion on cerebral regional oxygen saturation and endothelin-1 in tetralogy of fallot infants

Although benefits of pulsatile flow during cardiopulmonary bypass (CPB) in pediatric heart surgery remain controversial and nonpulsatile CPB is still widely used in clinical cardiac surgery, pulsatile CPB must be reconsidered due to its physiologic features. In this study, we aimed to evaluate the effects of pulsatile perfusion (PP) and nonpulsatile perfusion (NP) on cerebral regional oxygen saturation (rSO₂) and endothelin-1 (ET-1) in pediatric tetralogy of Fallot (TOF) patients undergoing open heart surgery with CPB. Forty pediatric patients were randomly divided into the PP group (n = 20) and the NP group (n = 20). Pulsatile patients used a modified roller pump during the cross-clamp period in CPB, while NP patients used a roller pump with continuous flat flow perfusion. The subjects were monitored for rSO₂ from the beginning of the operation until 6 h after returning to the intensive care unit (ICU). We also monitored the hemodynamic status and ET-1 concentration and plasma free hemoglobin (PFH) in blood samples of all patients over time. Effective PP was monitored in PP patients, and pulse pressure was significantly higher in the PP group than in the NP group (P < 0.01). rSO₂ of the PP group was higher than that of the NP group (P < 0.01) during the cross-clamp period, and this advantage of PP would be maintained until 2 h after patients returned to the ICU (P < 0.05). ET-1 level in blood samples was lower at clamping off and CPB weaning and early ICU period in the PP group than in the NP group (P < 0.01), and ET-1 concentration remained at a normal level after patients were transferred to the ICU 24 h in all patients. PFH levels in the PP group at pre-clamp off and CPB weaned off were higher than those of the NP group (P < 0.05) in these cyanotic patients. PP can increase rSO₂ and improve microcirculation during cross-clamping period in TOF pediatric patients, while PP resulted in more severe hemolysis in these cyanotic patients than NP.

Clinical effectiveness of centrifugal pump to produce pulsatile flow during cardiopulmonary bypass in patients undergoing cardiac surgery

Although the centrifugal pump has been widely used as a nonpulsatile pump for cardiopulmonary bypass (CPB), little is known about its performance as a pulsatile pump for CPB, especially on its efficacy in producing hemodynamic energy and its clinical effectiveness. We performed a study to evaluate whether the Rotaflow centrifugal pump produces effective pulsatile flow during CPB and whether the pulsatile flow in this setting is clinically effective in adult patients undergoing cardiac surgery. Thirty-two patients undergoing CPB for elective coronary artery bypass grafting were randomly allocated to a pulsatile perfusion group (n = 16) or a nonpulsatile perfusion group (n = 16). All patients were perfused with the Rotaflow centrifugal pump. In the pulsatile group, the centrifugal pump was adjusted to the pulsatile mode (60 cycles/min) during aortic cross-clamping, whereas in the nonpulsatile group, the pump was kept in its nonpulsatile mode during the same period of time. Compared with the nonpulsatile group, the pulsatile group had a higher pulse pressure (P < 0.01) and a fraction higher energy equivalent pressure (EEP, P = 0.058). The net gain of pulsatile flow, represented by the surplus hemodynamic energy (SHE), was found much higher in the CPB circuit than in patients (P < 0.01). Clinically, there was no difference between the pulsatile and nonpulsatile groups with regard to postoperative acute kidney injury, endothelial activation, or inflammatory response. Postoperative organ function and the duration of hospital stay were similar in the two patient groups. In conclusion, pulsatile CPB with the Rotaflow centrifugal pump is associated with a small gain of EEP and SHE, which does not seem to be clinically effective in adult cardiac surgical patients.

Comparison of perfusion quality in hollow-fiber membrane oxygenators for neonatal extracorporeal life support

Perfusion quality is an important issue in extracorporeal life support (ECLS); without adequate perfusion of the brain and other vital organs, multiorgan dysfunction and other deficits can result. The authors tested three different pediatric oxygenators (Medos Hilite 800 LT, Medtronic Minimax Plus, and Capiox Baby RX) to determine which gives the highest quality of perfusion at flow rates of 400, 600, and 800 mL/min using human blood (36 degrees C, 40% hematocrit) under both nonpulsatile and pulsatile flow conditions. Clinically identical equipment and a pseudo-patient were used to mimic operating conditions during neonatal ECLS. Traditionally, the postoxygenator surplus hemodynamic energy value (SHE(post), extra energy obtained through pulsatile flow) is the one relied upon to give a qualitative determination of the amount of perfusion in the patient; the authors also examined SHE retention through the membrane, as well as the contribution of SHE(post) to the postoxygenator total hemodynamic energy (THE(post)). At each experimental condition, pulsatile flow outperformed nonpulsatile flow for all factors contributing to perfusion quality: the SHE(post) values for pulsatile flow were 4.6-7.6 times greater than for nonpulsatile flow, while the THE(post) remained nearly constant for pulsatile versus nonpulsatile flow. For both pulsatile and nonpulsatile flow, the Capiox Baby RX oxygenator was found to deliver the highest quality of perfusion, while the Minimax Plus oxygenator delivered the least perfusion. It is the authors' recommendation that the Baby RX oxygenator running under pulsatile flow conditions be used for pediatric ECLS, but further studies need to be done in order to establish its effectiveness beyond the FDA-approved time span.

A novel, low cost, disposable, pediatric pulsatile rotary ventricular pump for cardiac surgery that provides a physiological flow pattern

Research is underway to develop a novel, low cost, disposable pediatric pulsatile rotary ventricular pump (PRVP) for cardiac surgery that provides a physiological flow pattern. This is believed to offer reduced morbidity and risk exposure within this population. The PRVP will have a durable design suitable for use in short- to mid-length prolonged support after surgery without changing pumps. The design is based on proprietary MC3 technology which provides variable pumping volume per stroke, thereby allowing the pump to respond to hemodynamic status changes of the patient. The novel pump design also possesses safety advantages that prevent retrograde flow, and maintain safe circuit pressures upon occlusion of the inlet and outlet tubing. The design is ideal for simple, safe and natural flow support. Computational methods have been developed that predict output for pump chambers of varying geometry. A scaled chamber and pump head (diameter = 4 in) were prototyped to demonstrate target performance for pediatrics (2 L/min at 100 rpm). A novel means of creating a pulsatile flow and pressure output at constant RPM was developed and demonstrated to create significant surplus hydraulic energy (>10%) in a simplified mock patient circuit.

A performance evaluation of eight geometrically different 10 Fr pediatric arterial cannulae under pulsatile and nonpulsatile perfusion conditions in an infant cardiopulmonary bypass model

This investigation compared pressure drops and surplus hemodynamic energy (SHE) levels in eight commercially available pediatric aortic cannulae (10 Fr) with different geometries during pulsatile and nonpulsatile perfusion conditions in an in vitro infant model of cardiopulmonary bypass. For each trial, the cannula was placed at the distal end of the arterial line, and the insertion tip was fixed to the inlet of the simulated patient. The pseudo patient was subjected to seven pump flow rates ranging from 400 to 1000 ml/min (at 100 ml/min increments), and the mean arterial pressure was set at a constant 40 mm Hg via Hoffman clamp. Of the eight cannulae, the Surgimedics and THI models had significantly larger pressure drops (48.8 +/- 0.3 mm Hg and 48.3 +/- 1.4 mm Hg, respectively; 600 ml/min pulsatile) compared with the RMI cannula (27.6 +/- 1.2 mm Hg; 600 ml/min pulsatile), which created, on average, half of the pressure drop seen in the poorest performing cannulae. When perfusion mode was switched from nonpulsatile to pulsatile, there was a 7-9 fold increase in delivery of SHE recorded at both the pre- and postcannulae sites, regardless of which cannula was being tested. Despite being classified under the same size (10 Fr), these eight cannulae were found to vary considerably in length, inner diameter, and geometrical design. The results suggest that these differences can have a significant impact on pressure drops, as well as generation and delivery of SHE. Furthermore, it was found that pulsatile perfusion produced more "extra" hemodynamic energy when compared with nonpulsatile perfusion, regardless of cannula model.