Alan R. Rider

Physiologic Benefits of Pulsatile Perfusion During Mechanical Circulatory Support for the Treatment of Acute and Chronic Heart Failure in Adults

A growing population experiencing heart failure (100,000 patients/year), combined with a shortage of donor organs (less than 2200 hearts/year), has led to increased and expanded use of mechanical circulatory support (MCS) devices. MCS devices have successfully improved clinical outcomes, which are comparable with heart transplantation and result in better 1-year survival than optimal medical management therapies. The quality of perfusion provided during MCS therapy may play an important role in patient outcomes. Despite demonstrated physiologic benefits of pulsatile perfusion, continued use or development of pulsatile MCS devices has been widely abandoned in favor of continuous flow pumps owing to the large size and adverse risks events in the former class, which pose issues of thrombogenic surfaces, percutaneous lead infection, and durability. Next-generation MCS device development should ideally implement designs that offer the benefits of rotary pump technology while providing the physiologic benefits of pulsatile end-organ perfusion.

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.

Microemboli detection and classification by innovative ultrasound technology during simulated neonatal cardiopulmonary bypass at different flow rates, perfusion modes, and perfusate temperatures.

The objective of this study was to detect and classify the number and size of gaseous microemboli in a simulated pediatric model of cardiopulmonary bypass. Tests were conducted at five different flow rates (400–1,200 ml/min in 200 ml/min increments), pulsatile versus nonpulsatile perfusion modes, and under normothermic, hypothermic, and deep hypothermic (35°C, 25°C, and 15°C) conditions, yielding 180 total experiments. The circuit was primed with lactated Ringer’s solution and filled with heparinized bovine blood. At the beginning of each experiment, 5 ml of air were injected into the venous line via the luer port of the oxygenator. Microemboli were quantified and classified by size for 5 minute segments at three transducer sites: postpump, postoxygenator, and postarterial filter. The purge line of the arterial filter was closed during all experiments. In all but one experiment, 90% of emboli at the postpump site were found to be smaller than 40 &mgr;m. At the postarterial filter site, nearly 99% of the emboli were smaller than 40 &mgr;m. Additionally, increasing microemboli counts were observed when the flow rate was increased and when the temperature was decreased. Lower temperatures, higher flow rates, and pulsatile perfusion were all associated with higher emboli counts. The majority of gaseous microemboli found in the simulated circuit was significantly below 40 &mgr;m; the smallest level detectable by traditional Doppler devices.

Pulsatile perfusion during cardiopulmonary bypass procedures in neonates, infants, and small children.

Multiple factors influence the outcome of cardiopulmonary bypass (CPB) procedures in pediatric patients with congenital heart defects. The benefit of pulsatile over nonpulsatile perfusion is one such factor that continues to be widely debated among researchers, perfusionists, and surgeons. However, by accurately measuring pulsatile flow in terms of energy equivalent pressure and surplus hemodynamic energy, pulsatile perfusion is clearly seen to replicate the physiologic heart in a manner unparalleled by nonpulsatile perfusion. Studied benefits of pulsatile perfusion in pediatric patients include increased vital organ blood flow and improvement in postoperative recovery. Also, the components of the extracorporeal circuit used in CPB are directly related to pulsatility and have a profound effect on hemodynamics in the circuit and the patient. Therefore, pulsatility and surplus hemodynamic energy delivery to the patient can be maximized by choosing the best performing heart-pumps, oxygenators, arterial filters, and cannulae. Furthermore, in using the most optimal circuit components available, the CPB procedure under pulsatile perfusion can proceed efficiently. Currently, the outcomes resulting from pulsatile perfusion in pediatric and adult patients, as well as animal models, are well documented. However, more multilaboratory efforts are necessary to understand and further validate the benefits of pulsatile perfusion in pediatric patients.

Effects of the pulsatile flow settings on pulsatile waveforms and hemodynamic energy in a PediVAS centrifugal pump.

The objective of this study was to test different pulsatile flow settings of the PediVAS centrifugal pump to seek an optimum setting for pulsatile flow to achieve better pulsatile energy and minimal backflow. The PediVAS centrifugal pump and the conventional pediatric clinical circuit, including a pediatric membrane oxygenator, arterial filter, arterial cannula, and ¼ in circuit tubing were used. The circuit was primed with 40% glycerin water mixture. Postcannula pressure was maintained at 40 mm Hg by a Hoffman clamp. The experiment was conducted at 800 ml/min of pump flow with a modified pulsatile flow setting at room temperature. Pump flow and pressure readings at preoxygenator and precannula sites were simultaneously recorded by a data acquisition system. The results showed that backflows appeared at flow rates of 200–800 ml/min (200 ml/min increments) with the default pulsatile flow setting and only at 200 ml/min with the modified pulsatile flow setting. With an increased rotational speed difference ratio and a decreased pulsatile width, the pulsatility increased in terms of surplus hemodynamic energy and total hemodynamic energy at preoxygenator and precannula sites. Backflows seemed at preoxygenator and precannula sites at a 70% of rotational speed difference ratio. The modified pulsatile flow setting was better than the default pulsatile flow setting in respect to pulsatile energy and backflow. The pulsatile width and the rotational speed difference ratio significantly affected pulsatility. The parameter of the rotational speed difference ratio can automatically increase pulsatility with increased rotational speeds. Further studies will be conducted to optimize the pulsatile flow setting of the centrifugal pump.

Evaluation of HL-20 roller pump and Rotaflow centrifugal pump on perfusion quality and gaseous microemboli delivery.

The purpose of this study was to compare the HL-20 roller pump (Jostra USA, Austin, TX, USA) and Rotaflow centrifugal pump (Jostra USA) on hemodynamic energy production and gaseous microemboli (GME) delivery in a simulated neonatal cardiopulmonary bypass (CPB) circuit under nonpulsatile perfusion. This study employed a simulated model of the pediatric CPB including a Jostra HL-20 heart-lung machine (or a Rotaflow centrifugal pump), a Capiox BabyRX05 oxygenator (Terumo Corporation, Tokyo, Japan), a Capiox pediatric arterial filter (Terumo Corporation), and ¼-inch tubing. The total volume of the experimental system was 700mL (500mL for the circuit and 200mL for the pseudo neonatal patient). The hematocrit was maintained at 30% using human blood. At the beginning of each trial, a 5mL bolus of air was injected into the venous line. Both GME data and pressure values were recorded at postpump and postoxygenator sites. All the experiments were conducted under nonpulsatile perfusion at three flow rates (500, 750, and 1000mL/min) and three blood temperatures (35, 30, and 25°C). As n=6 for each setup, a total of 108 trials were done. The total number of GME increased as temperature decreased from 35°C to 25°C in the trials using the HL-20 roller pump while the opposite effect occurred when using the Rotaflow centrifugal pump. At a given temperature, total GME counts increased with increasing flow rates for both pumps. Results indicated the Rotaflow centrifugal pump delivered significantly fewer microemboli compared to the HL-20 roller pump, especially under high flow rates. Less than 10% of total microemboli were larger than 40µm in size and the majority of GME were in the 0-20µm class in all trials. Postpump total hemodynamic energy (THE) increased with increasing flow rates and decreasing temperatures in both circuits using these two pumps. The HL-20 roller pump delivered more THE than the Rotaflow centrifugal pump at all tested flow rates and temperature conditions. Results suggest the HL-20 roller pump delivers more GME than the Rotaflow centrifugal pump but produces more hemodynamic energy under nonpulsatile perfusion mode.

The impact of pump settings on the quality of pulsatility.

The study objective was to evaluate the Jostra HL-20 roller pump under different baseflow and pump head settings with quantified energy values from pressure and flow waveforms, in a simulated pediatric bypass circuit. Pump flow rate was set at 800 mL/min for both pulsatile and nonpulsatile perfusion modes and the mean arterial pressure (MAP) of the pseudopatient was maintained at 40 mm Hg for each experiment. Pulsatile baseflow settings and pump head start points varied with each experiment. Pressure and flow waveforms were recorded at preoxygenator, precannula, and postcannula sites under each pump setting. A total of 91 experiments were performed (n = 7, nonpulsatile; n = 84, pulsatile). Increasing baseflow caused decreases in the mean circuit pressure and surplus hemodynamic energy (SHE) levels for all pump head start times. When increasing pump head start time within each baseflow, values for MAP and SHE increased significantly. Regardless of baseflow or pump head start time, values for mean circuit pressure and SHE were lower for nonpulsatile flow than for pulsatile flow. Total hemodynamic energy values were also significantly higher under pulsatile perfusion and increased pump start times while decreasing with increased baseflows in the circuit. This study concludes that decreased baseflows with increased pump head settings on the Jostra HL-20 roller pump could significantly increase quality of generated pulsatile energy. Further research is necessary to evaluate these various pump settings under microembolic loads and with different circuit components.

A hemodynamic evaluation of the Levitronix Pedivas centrifugal pump and Jostra Hl-20 roller pump under pulsatile and nonpulsatile perfusion in an infant CPB model.

The hemodynamic comparison of the Jostra HL-20 and the Levitronix PediVAS blood pumps is the focus this study, where pressure-flow waveforms and hemodynamic energy values are analyzed in the confines of a pediatric cardiopulmonary bypass circuit. The pseudo pediatric patient was perfused with flow rates between 500 and 900 ml/min (100 ml/min increments) under pulsatile and nonpulsatile mode. The Levitronix continuous flow pump utilized a customized controller to engage in pulsatile perfusion with equivalent pulse settings to the Jostra HL-20 roller pump. Hemodynamic measurements and waveforms were recorded at the precannula location, while the mean arterial pressure was maintained at 40 mm Hg for each test. Glycerin water was used as the blood analog circuit perfusate. At each flow rate 24 trials were conducted yielding a total of 120 experiments (n = 60 pulsatile and n = 60 nonpulsatile). Under nonpulsatile perfusion the Jostra roller pump produced small values for surplus hemodynamic energy (SHE) due to its inherent pulsatility, while the Levitronix produced values of essentially zero for SHE. When switching to pulsatile perfusion, the SHE levels for both the Jostra and Levitronix pump made considerable increases. In comparing the two pumps under pulsatile perfusion, the Levitronix PediVAS produced significantly more surplus and total hemodynamic energy than did the Jostra roller pump each pump flow rate. The study suggests that the Levitronix PediVAS centrifugal pump has the capability of achieving quality pulsatile waveforms and delivering more SHE to the pseudo patient than the Jostra HL-20 roller pump. Further studies are warranted to investigate the Levitronix under bovine blood studies and with various pulsatile settings.

Comparison of four different pediatric 10F aortic cannulae during pulsatile versus nonpulsatile perfusion in a simulated neonatal model of cardiopulmonary bypass.

We compared four commercially available 10F pediatric aortic cannulae with different geometric designs (DLP—Long tip, DLP—Short tip, RMI—Long tip, and Surgimedics—Short tip) during pulsatile versus nonpulsatile perfusion in terms of pressure drops and surplus hemodynamic energy (SHE) levels in an in vitro neonatal model of cardiopulmonary bypass. The pseudo patient was subjected to seven pump flow rates at 100 ml/min increments in the 400–1,000 ml/min range. A total of 44 experiments (n = 22, nonpulsatile; n = 22, pulsatile) were performed at each of the seven flow rates. Surgimedics had significantly higher pressure drops than the other three cannulae at various flow rates during nonpulsatile and pulsatile perfusion, respectively. When the perfusion mode was changed from nonpulsatile to pulsatile flow, SHE levels at both precannula and postcannula sites increased seven to nine times at all flow rates in all four cannulae. Surgimedics generated a significant lower SHE level when compared with the other three cannulae at all flow rates at both precannula and postcannula sites. The results suggest that different geometries of aortic cannulae have a significant impact on pressure drops of the cannulae as well as hemodynamic energy generation and delivery. Pulsatile perfusion generates more “extra” hemodynamic energy when compared with the nonpulsatile perfusion mode with all four cannulae used in this study.

A hemodynamic evaluation of the Medos Deltastream DP1 rotary pump and Jostra HL-20 roller pump under pulsatile and nonpulsatile perfusion in an infant cardiopulmonary bypass model--a pilot study.

This study aims to compare the Jostra HL-20 roller pump to the Medos DeltaStream DP1 rotary pump in terms of pressure and flow waveforms, as well as calculated energies based on pressure/flow relationships, in a simulated pediatric cardiopulmonary perfusion system. The flow rate was set at 1,000 ml/min for each pump, under both pulsatile and nonpulsatile perfusion modes. Mean arterial pressure (MAP) was maintained at 40 mm Hg. Pressure and flow measurements and waveforms were recorded at precannula site in the bypass circuit. Blood analog test fluid was used to simulate blood properties. A total of 24 experiments were performed (n = 12 nonpulsatile and n = 12 pulsatile). A significant increase in surplus hemodynamic energy (SHE) was observed in both pumps under pulsatile perfusion. In contrast, nonpulsatile perfusion generated very little SHE in the Jostra roller pump, whereas no SHE was generated in the Medos rotary pump. However, under pulsatile perfusion, the Medos rotary pump generated more than twice the amount of SHE or “extra” energy than the Jostra roller pump. The total hemodynamic energy was also significantly higher in the Medos rotary pump than the Jostra roller pump, under pulsatile perfusion. This pilot study suggests that the Medos DeltaStream DP1 rotary pump may produce greater hemodynamic energy levels and higher quality physiologic pressure/flow waveforms than the Jostra roller pump. Further investigation of the Medos DeltaStream DP1 rotary pump is necessary to evaluate hemodynamic energy generation under various pump settings, in contrast to different flow rates.