The objective of this investigation was to compare pulsatile versus nonpulsatile perfusion modes in terms of surplus hemodynamic energy (SHE) levels during cardiopulmonary bypass (CPB) in a simulated neonatal model. The extracorporeal circuit consisted of a Jostra HL-20 heart-lung machine (for both pulsatile and nonpulsatile modes of perfusion), a Capiox Baby RX hollow-fiber membrane oxygenator, a Capiox pediatric arterial filter, 5 feet of arterial tubing and 6 feet of venous tubing with a quarter-inch diameter. The circuit was primed with a lactated Ringers solution. The systemic resistance of a pseudo-patient (mean weight, 3 kg) was simulated by placing a clamp at the end of the arterial line. The pseudo-patient was subjected to five pump flow rates in the 400 to 800 ml/min range. During pulsatile perfusion, the pump rate was kept constant at 120 bpm. Pressure waveforms were recorded at the preoxygenator, postoxygenator, and preaortic cannula sites. SHE was calculated by use of the following formula {SHE (ergs/cm) = 1,332 [((integral fpdt) / (integral fdt)) - Mean Arterial Pressure]} (f = pump flow and p = pressure). A total of 60 experiments were performed (n = 6 for nonpulsatile and n = 6 for pulsatile) at each of the five flow rates. A linear mixed-effects model, which accounts for the correlation among repeated measurements, was fit to the data to assess differences in SHE between flows, pumps, and sites. The Tukey multiple comparison procedure was used to adjust p values for post hoc pairwise comparisons. With a pump flow rate of 400 ml/min, pulsatile flow generated significantly higher surplus hemodynamic energy levels at the preoxygenator site (23,421 +/- 2,068 ergs/cm vs. 4,154 +/- 331 ergs/cm, p < 0.0001), the postoxygenator site (18,784 +/- 1,557 ergs/cm vs. 3,383 +/- 317 ergs/cm, p < 0.0001), and the precannula site (6,324 +/- 772 ergs/cm vs. 1,320 +/- 91 ergs/cm, p < 0.0001), compared with the nonpulsatile group. Pulsatile flow produced higher SHE levels at all other pump flow rates. The Jostra HL-20 roller pump generated significantly higher SHE levels in the pulsatile mode when compared with the nonpulsatile mode at all five pump flow rates.

Unreliable quantification of flow pulsatility has hampered many efforts to assess the importance of pulsatile perfusion. Generation of pulsatile flow depends upon an energy gradient. It is necessary to quantify pressure flow waveforms in terms of hemodynamic energy levels to make a valid comparison between perfusion modes during chronic support. The objective of this study was to quantify pressure flow waveforms in terms of energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE) levels in an adult mock loop using a pulsatile ventricle assist system (VAD). A 70 cc Pierce-Donachy pneumatic pulsatile VAD was used with a Penn State adult mock loop. The pump flow rate was kept constant at 5 L/min with pump rates of 70 and 80 bpm and mean aortic pressures (MAP) of 80, 90, and 100 mm Hg, respectively. Pump flows were adjusted by varying the systolic pressure, systolic duration, and the diastolic vacuum of the pneumatic drive unit. The aortic pressure was adjusted by varying the systemic resistance of the mock loop EEP (mm Hg) = (integral of fpdf)/(integral of fdt) SHE (ergs/cm3) = 1,332 [((integral of fpdt)/(integral of fdt))--MAP] were calculated at each experimental stage. The difference between the EEP and the MAP is the extra energy generated by this device. This difference is approximately 10% in a normal human heart. The EEP levels were 88.3 +/- 0.9 mm Hg, 98.1 +/- 1.3 mm Hg, and 107.4 +/- 1.0 mm Hg with a pump rate of 70 bpm and an aortic pressure of 80 mm Hg, 90 mm Hg, and 100 mm Hg, respectively. Surplus hemodynamic energy in terms of ergs/cm3 was 11,039 +/- 1,236 ergs/cm3, 10,839 +/- 1,659 ergs/cm3, and 9,857 +/- 1,289 ergs/cm3, respectively. The percentage change from the mean aortic pressure to EEP was 10.4 +/- 1.2%, 9.0 +/- 1.4%, and 7.4 +/- 1.0% at the same experimental stages. Similar results were obtained when the pump rate was changed from 70 bpm to 80 bpm. The EEP and SHE formulas are adequate to quantify different levels of pulsatility for direct and meaningful comparisons. This particular pulsatile VAD system produces near physiologic hemodynamic energy levels at each experimental stage.

Thromboembolic events (TE) associated with circulatory support devices are a major source of mortality and morbidity. Clinically, the lowest TE rates are claimed with devices that incorporate textured blood-contacting materials. The textured materials currently used in circulatory assist devices are composed of small, attached fibers that form the boundaries of connected cavities. These cavities entrap blood components to form a "neointimal" layer, which is believed to minimize thromboembolic events. We believe that the three-dimensional surface topography of blood-contacting materials is a major controlling factor in the formation of a stable neointimal layer upon the material. Particle-cast cavities were used to form geometric features in segmented polyurethane. This microtextured material was incorporated as part of a flexible blood-contacting surface in a blood pump that was implanted as a left ventricular assist device in calves. The structure, thickness, stability, and development of the neointimal layer were then evaluated. These preliminary studies have shown that a stable neointimal layer can be formed upon the particle-cast surfaces. The results also indicate that the cavity size on the particle-cast surfaces has a significant effect on neointimal adhesion. The methods employed can be used in the design of future circulatory support devices.

No abstract

Thrombosis limits the success of ventricular assist devices as the demand for alternatives to heart transplants is increasing. This study mapped the occurrence of thrombosis in a left ventricular assist system (LVAS) to better understand the biologic response to these devices. Nine calves divided into two groups were implanted with LVAS for 28 to 30 days. One group was anticoagulated, whereas the second group received no long-term anticoagulation. The blood-contacting poly(urethane urea) surfaces of blood sacs in the LVAS were examined for macroscopic thrombi upon retrieval. The sac was partitioned into eight sections and imaged for thrombi by scanning electron microscopy. No difference in thrombosis was observed macroscopically between the groups. Anticoagulation appeared to result in reduction of platelet-like structures, but the presence of fibrin-like structures remained similar between groups. Regional differences correlating with high and low shear stress regions were observed. At the macroscale, fewer thrombi were recorded in the high shear stress ports. At the microscale, features resembling fibrin were observed primarily in the ports and platelet-like features were common in lower shear stress regions. These variations in thrombosis with anticoagulation and location are likely due to varied fluid dynamics within the LVAS blood sac.

In vitro durability testing was conducted on the Penn State/3M electric total artificial heart (ETAH) to determine device durability and to evaluate device failures. A specialized mock circulatory loop was developed for this testing. Customized software continuously acquired data during the test period, and failures were analyzed using FMEA (failure modes and effects analysis) and FMECA (failure modes, effects, and criticality analysis) principles. Redesigns were implemented when appropriate. Reliability growth principles were then applied to calculate the 1 and 2 year reliability. The 1 and 2 year reliability of the Penn State/3M ETAH was shown to be 96.1% and 59.9%, respectively, at 80% confidence.

The Capiox oxygenator had a significantly lower pressure drop in both pulsatile and non-pulsatile perfusion modes. For each oxygenator, the SHE levels were significantly higher in the pulsatile mode.

A method for real-time in vitro observation of cavitation on a prosthetic heart valve has been developed. Cavitation of four blood analog fluids (distilled water, aqueous glycerin, aqueous polyacrylamide, and aqueous xanthan gum) has been documented for a Medtronic/Hall prosthetic heart valve. This method employed a Penn State Electrical Ventricular Assist Device in a mock circulatory loop that was operated in a partial filling mode associated with reduced atrial filling pressure. The observations were made on a valve that was located in the mitral position, with the cavitation occurring on the inlet side after valve closure on every cycle. Stroboscopic videography was used to document the cavity life cycle. Bubble cavitation was observed on the valve occluder face. Vortex cavitation was observed at two locations in the vicinity of the valve occluder and housing. For each fluid, cavity growth and collapse occurred in less than one millisecond, which provides strong evidence that the cavitation is vaporous rather than gaseous. The cavity duration time was found to decrease with increasing atrial pressure at constant aortic pressure and beat rate. The area of cavitation was found to decrease with increasing delay time at a constant aortic pressure, atrial pressure, and beat rate. Cavitation was found to occur in each of the fluids, with the most cavitation seen in the Newtonian fluids (distilled water and aqueous glycerin).