Vascular delay of the latissimus dorsi provides an early hemodynamic benefit in dynamic cardiomyoplasty.

OBJECTIVES: Dynamic cardiomyoplasty (CMP) as a surgical treatment for chronic heart failure improves functional class status for most patients. However, significant hemodynamic improvement with latissimus dorsi muscle (LDM) stimulation has not been consistent. The current protocols do not allow early LDM stimulation after CMP surgery. We hypothesized that vascular delay of LDM would increase myocardial assistance after CMP and allow early (48-h) LDM stimulation after CMP. METHODS: Mongrel dogs (n = 24) were divided in four groups: 1) controls (n = 6), single-stage CMP; 2) Group ES (n = 6), single-stage CMP with early LDM stimulation beginning 48 h, postoperatively; 3) Group VD (n = 6), vascular delay of the LDM followed by CMP without early LDM stimulation, and 4) Group VDES (n = 6), vascular delay of LDM (14-18 days), followed by CMP with early stimulation (48 h postoperatively). Two weeks after CMP, global cardiac dysfunction was induced by injecting microspheres into the left coronary artery. LDM-assisted (S) beats were compared with nonstimulated beats (NS) by measuring aortic pressure (AoP), LV pressure, aortic flow, and by calculating first derivative of LV contraction (+/-dP/dt), stroke volume (SV), and stroke work (SW). RESULTS: In ES, LDM stimulation had no effect on the hemodynamic parameters. In the other groups, LDM stimulation significantly (p < 0.05) increased AoP, LVP, dP/dt, SV, and SW. However, these increases were much larger in VD and VDES. In VD, LDM stimulation increased peak AoP by 21.5+/-3.8 mm Hg, LVP by 22.1+/-4.1 mm Hg, dP/dt by 512+/-163 mm Hg/sec, SV by 10.4+/-2.3 mL, and SW by 22.1+/-5.4 g/m(-1). Similarly, in VDES, LDM stimulation increased peak AoP by 24.1+/-4.7 mm Hg, LVP by 26.2+/-4.3 mm Hg, dP/dt by 619+/-47 mm Hg/sec, SV by 6.5+/-0.7 mL, and SW by 16.7+/-4.1 g/m(-1). CONCLUSIONS: In dogs with global LV dysfunction, CMP after vascular delay resulted in a significant improvement in hemodynamic function measured 2 weeks after surgery. This improvement was not provided by single-stage CMP with or without early stimulation. Vascular delay of the LDM before surgery may play an important role for early benefit after CMP, shorten the overall muscle training period, as well as increase hemodynamic response to LDM stimulation.     

Electrocardiogram-synchronized rotational speed change mode in rotary pumps could improve pulsatility

Continuous-flow left ventricular assist devices (LVADs) have greatly improved the prognosis of patients with end-stage heart failure, even if continuous flow is different from physiological flow in that it has less pulsatility. A novel pump controller of continuous-flow LVADs has been developed, which can change its rotational speed (RS) in synchronization with the native cardiac cycle, and we speculated that pulsatile mode, which increases RS just in the systolic phase, can create more pulsatility than the current system with constant RS does. The purpose of the present study is to evaluate the effect of this pulsatile mode of continuous-flow LVADs on pulsatility in in vivo settings. Experiments were performed on eight adult goats (61.7 ± 7.5 kg). A centrifugal pump, EVAHEART (Sun Medical Technology Research Corporation, Nagano, Japan), was installed by the apex drainage and the descending aortic perfusion. A pacing lead for the detection of ventricular electrocardiogram was sutured on the anterior wall of the right ventricle. In the present study, we compared pulse pressure or other parameters in the following three conditions, including Circuit-Clamp (i.e., no pump support), Continuous mode (constant RS), and Pulsatile mode (increase RS in systole). Assist rate was calculated by dividing pump flow (PF) by the sum of PF and ascending aortic flow (AoF). In continuous and pulsatile modes, these assist rates were adjusted around 80-90%. The following three parameters were used to evaluate pulsatility, including pulse pressure, dp/dt of aortic pressure (AoP), and energy equivalent pulse pressure (EEP = (∫PF*AoP dt)/(∫PF dt), mm Hg). The percent difference between EEP and mean AoP is used as an indicator of pulsatility, and normally it is around 10% of mean AoP in physiological pulse. Both pulse pressure and mean dp/dt max were decreased in continuous mode compared with clamp condition, while those were regained by pulsatile mode nearly to clamp condition (pulse pressure, clamp/continuous/pulsatile, 25.0 ± 7.6/11.7 ± 6.4/22.6 ± 9.8 mm Hg, mean dp/dt max, 481.9 ± 207.6/75.6 ± 36.2/351.1 ± 137.8 mm Hg/s, respectively). In clamp condition, %EEP was 10% higher than mean AoP (P = 0.0078), while in continuous mode, %EEP was nearly equivalent to mean AoP (N.S.). In pulsatile mode, %EEP was 9% higher than mean AoP (P = 0.038). Our newly developed pulsatile mode of continuous-flow LVADs can produce pulsatility comparable to physiological pulsatile flow. Further investigation on the effect of this novel drive mode on organ perfusion is currently ongoing.     

In vitro performance of trans-valve left ventricular assist device installed at aortic valve position

In this study, we developed a trans-valve left ventricular assist device (LVAD) that unites a rear-impeller axial-flow blood pump (AFBP) and a polymer membrane valve placed at the aortic valve position. The diameter and length of the rear impeller AFBP was 12 and 63 mm, respectively. The polymer membrane valve was similar to the jelly-fish valve consisting of a valve leaflet made of silicone rubber (thickness 0.5 mm), valve ring (diameter: 25 mm), and valve spokes. The trans-valve LVAD was examined in a mock circulation. An implantable pulsatile flow (PF) VAD was connected to an atrial reservoir to simulate the left ventricle (LV), and the Hall valve was worn in the inflow port, and the trans-valve LVAD was placed in the outflow port as an outflow valve. When the motor rotational speed increased to 26 400 rpm, the mean aortic flow increased from 4.2 to 5.3 L/min, mean aortic pressure increased from 83.4 to 100 mm Hg, and mean motor current of the implantable PF VAD decreased from 1.18 to 0.94 A (unloading effect on LV −21%). The energy equivalent pressure increased from 85.2 to 102 mm Hg, and surplus hemodynamic energy (SHE) decreased by −15.4% from the baseline. In conclusion, the trans-valve LVAD has an advantage of preserving pulsatility without any complicated mechanism and is a novel and promising LV support device.     

Chemoreflexes: an experimental study

HYPOTHESIS: Transmyocardial laser revascularization (TMLR) will not denervate the heart, because it does not destroy all of the afferents. This study was designed to determine if stimulation of cardiac sympathetic and vagal afferents from an area of the left ventricle treated with TMLR could evoke reflex effects, and thus whether TMLR would denervate the heart. METHODS: The effect of TMLR on reflexes evoked by chemically stimulating cardiac afferents was examined in 9 dogs. Bradykinin and capsaicin were applied topically or injected into the left anterior descending coronary artery before and after TMLR and after bilateral vagotomy and sympathectomy. Aortic (AoP) and left ventricular pressures (LVP) and electrocardiography were monitored. The first derivatives of LVP (dP/dt) were calculated. RESULTS: Topical bradykinin elicited variable hemodynamic responses. Topical capsaicin evoked pressor responses, increasing mean (+/- SEM) AoP (105+/-9 to 115+/-9 mm Hg; P<.001) and positive dP/dt (+dP/dt) (1032+/-81 to 1159+/-10 mm Hg/s; P<.01) before TMLR. Intracoronary capsaicin evoked a depressor response before TMLR. Pressor responses remained intact after TMLR with increases in mean AoP and +dP/dt (115+/-6 to 128+/-5 mm Hg and 1039+/-98 to 1136+/-100 mm Hg/s, respectively; P<.01). Depressor responses also remained intact after TMLR (91+/-10 vs 101+/-11 mm Hg [P<.02], and 865+/-104 vs 931+/-104 mm Hg/s [P<.05], respectively). Hemodynamic responses were diminished after bilateral vagotomy and abolished after bilateral sympathectomy. CONCLUSION: Since activation of cardiac afferent nerves and reflex responses remained intact after TMLR, but changed after vagotomy or sympathectomy, TMLR does not denervate the heart sufficiently to be the cause of improved angina after TMLR.     

In Vitro Evaluation of a Pulsatile Assist Device for a Centrifugal Pump Using a New Principle

Abstract: To induce a pulsatile flow in a centrifugal pump, we developed a new device (pulsatile assist device for centrifugal pump: PADCP) using a new concept. This device consists of a flexible polyurethane tube with an air chamber which is connected to the arterial side of the centrifugal pump circuit directly. A mock circulation system was used for evaluation of this PADCP. Thirty to 40 mm Hg of pulse pressure was obtained under 3–6 L/min of flow rate. By increasing the driving pressure of the PADCP from 200 to 600 mm Hg in a mock system, 4–48 mm Hg of pulse pressure was gained accompanied by a decrease in pump flow and increased left atrial pressure. The decreased pump flow and increased left atrial pressure were recovered easily by increasing the flow rate of the centrifugal pump. Pressures at the proximal site of the PADCP were less than 500 mm Hg. The PADCP was useful to induce a pulsatile flow in a centrifugal pump.     

Left ventricular pressure and volume unloading during pulsatile versus nonpulsatile left ventricular assist device support

BACKGROUND: Nonpulsatile axial or centrifugal pumps are the latest generation of left ventricular assist devices (LVAD). Whether left ventricular (LV) unloading and outcome in these devices is similar to pulsatile LVADs during long-term support has not been investigated. We compared LV unloading and mortality between different types of LVAD support (pulsatile versus nonpulsatile). METHODS: In 31 patients undergoing long-term LVAD implantation (nonpulsatile = 10, pulsatile = 21) preoperative and postoperative echocardiographic and hemodynamic assessment with right heart catheterization had been obtained. RESULTS: All patients had similar echocardiographic, hemodynamic, and clinical heart failure characteristics at baseline. The degree of LV pressure unloading was the same in both device types, caused by similar reduction of mean pulmonary pressure (18.6 +/- 5.1 versus 18.3 +/- 7.5 mm Hg) and pulmonary capillary wedge pressure (8.9 +/- 4.4 versus 8.0 +/- 7.0 mm Hg). Left ventricular volume unloading was pronounced with a pulsatile device owing to a statistically significant higher pump output (5.1 +/- 1.0 L/min) in comparison with nonpulsatile LVADs (3.6 +/- 0.9 L/min, p < 0.001). Echocardiographic-determined end-systolic indicators confirm this augmentation in pulsatile LVADs. Etiology or the time interval of hemodynamic reassessment had no impact in left ventricular pressure unloading, but LV volume unloading decreased between day 60 and 120 in patients with nonpulsatile LVADs. The preoperative and postoperative transplant mortality was comparable in both groups. CONCLUSIONS: Left ventricular pressure unloading is similar in patients with nonpulsatile as compared with pulsatile implantable long-term assist devices. Left ventricular volume unloading is pronounced in pulsatile LVADs.     

Left stellate ganglion block has only small effects on left ventricular function in awake dogs before and after induction of heart failure

Left stellate ganglion block (LSGB) results in acute sympathetic denervation of the left ventricular (LV) posterobasal wall. We investigated the effects of LSGB in chronically instrumented awake dogs before and after the induction of pacing-induced congestive heart failure. Twelve dogs were instrumented for measurement of global hemodynamics [LV pressure (LVP)], its first derivative (dP/dt), cardiac output (CO), and regional myocardial function (systolic posterobasal segment length shortening, mean velocity [SLmv]). Before the induction of heart failure (n = 12), LSGB did not affect CO [3.2+/-1.4 (control, mean +/- SD) vs. 3.3+/-1.6 L/min (LSGB, P = 0.45)] and SLmv (11.1+/-4.0 vs. 10.8+/-4.0 mm/s, P = 0.16), but slightly reduced LVP (130+/-12 vs. 125+/-14 mm Hg, P = 0.04), dP/dt(max) (3614+/-755 vs. 3259+/-644 mm Hg/s, P = 0.003) and dP/dt(min) (-3153+/-663 vs. -2970+/-725 mm Hg/s, P = 0.03). During heart failure (n = 8), global hemodynamics [CO (2.8+/-1.2 vs. 2.7+/-1.2 L/min, P = 0.04), LVP (119+/-6 vs. 112+/-9 mm Hg, P = 0.01), dP/dt(max) (1945+/-520 vs. 1824+/-554 mm Hg/s, P = 0.03) and dP/dt(min) (-2402+/-678 vs. -2243+/-683 mm Hg/s, P = 0.04)], as well as regional myocardial function, were significantly different after LSGB [SLmv] (8.0+/-3.8 vs. 6.9+/-3.4 mm/s, P = 0.02)]. In conclusion, even during heart failure, the hemodynamic changes after LSGB are small, confirming its broad margin of safety.     

Estimation of Left Ventricular Recovery Level Based on the Motor Current Waveform Analysis on Circulatory Support with Centrifugal Blood Pump

In a mock circulatory loop simulating the left heart bypass using a centrifugal blood pump, analysis of the motor current waveform of the centrifugal pump was performed to derive a useful parameter to evaluate the status of ventricular function. The relationship between the peak, amplitude, and the peak of the fundamental frequency of the power spectral density of the periodic motor current waveform (MCpsdP) that reflected the pulsatile ventricular pressure, and the peak of the left ventricular pressure (LVP) was examined. Although both peak and amplitude of the motor current waveform showed an excellent correlation with the peak LVP, they failed to predict the opening of the aortic valve. The MCpsdP that corresponds to the frequency of the heart rate showed an excellent correlation with the peak LVP throughout the LVP levels, but the slope between them changed with the opening of the aortic valve. Thus, it is possible to follow the change in the LVP and detect even the opening of the aortic valve, and, hence, the recovery of the left ventricle. However, the slope of the linear regression equation varied, depending on the pump speed. This result implies that the MCpsdP can be possibly used to follow the change of ventricular function during circulatory assistance with a centrifugal blood pump as well as to control the pump speed in response to varying ventricular function.     

Evaluation of left ventricular assist device performance and hydraulic force in a complete mock circulation loop

Centrifugal pump performance characteristics are vital in determining the ability of a prototype left ventricular assist device (LVAD) to meet the physiological circulation requirements of the cardiovascular system. These characteristics influence the static hydraulic forces encountered by the pump impeller, which determine the required load stiffness of suspension type bearings to minimize impeller touchdown. Performance investigations were conducted on an LVAD design while characterizing the impeller static hydraulic forces of various impeller/volute configurations. The pumps were inserted into a complete systemic and pulmonary mock circulation rig configured to provide suitable nonpulsatile or simulated pulsatile left heart failure environments. The single volute and closed shroud impeller configuration exhibited lowest radial (0.01 N) and axial (3 N) force at nonpulsatile design flow conditions, respectively. Normal hemodynamic conditions of 5.1 L/min at 94 mm Hg were re-established upon inserting the device into the left heart failure environment, where the pump operated along the nonpulsatile characteristic curve for 2200 rpm. The operational limits on this curve were dictated by the required pressure differential across the pump during systolic and diastolic periods. The reduction of left atrial pressure (25 to 8 mm Hg) indicated the alleviation of pulmonary congestion. The ability for the LVAD to support circulation in a left heart failure environment was successfully demonstrated in the mock circulation loop. The impeller hydraulic force characteristics attained will aid the bearing designer to select the best volute and impeller configuration to minimize impeller touchdown in magnetic, hydrodynamic or mechanical type bearing applications.     

Impeller inner diameter in a miniaturized centrifugal blood pump

To design a miniaturized centrifugal blood pump, the impeller internal diameter (ID), which is a circle diameter on the inner edge of the vane, is considered one of the important aspects. Hydraulic performance, hemolysis, and thrombogenicity were evaluated with different impeller IDs. Two impellers were fabricated with an outer diameter of 35 mm, of which 1 had an 8 mm ID impeller and the other had a 12 mm ID. These impellers were combined with 2 different housings in which the inlet port was eccentrically positioned 3.8 and 4.5 mm offset from the center. The hydraulic performance and hemolysis were evaluated in a mock circuit, and thrombogenicity was evaluated in a 2 day ex vivo study with each impeller housing combination. Both impellers required 3,000 rpm in the 3.8 mm offset inlet to attain 5 L/min against 100 mm Hg (left ventricular assist device condition). The 8 mm ID impeller required 3,200 rpm, and the 12 mm ID impeller required 3,100 rpm in the 4.5 mm offset housing. The normalized index of hemolysis was 0.0080 +/- 0.0048 g/100 L in the 8 mm ID impeller with the 3.8 mm offset and 0.022 +/- 0.018 g/100 L with 4.5 mm offset. The 12 mm ID impeller had 0.068 +/- 0.028 g/100 L with the 3.8 mm offset and 0.010 +/- 0.002 g/100 L with the 4.5 mm offset. After the 2 day ex vivo study, no blood clot was formed around the top bearing in all the pump heads. The 8 mm ID impeller with 3.8 mm offset inlet and the 12 mm ID impeller with the 4.5 mm offset had less hemolysis compared to the other pump heads that were subjected to 14 day ex vivo and 10 day in vivo studies. The 8 mm ID impeller with the 3.8 mm offset inlet had a blood clot around the top bearing after the 14 day ex vivo study. No thrombus was found around the top bearing of the 12 mm ID impeller with the 4.5 mm offset in the 10 day in vivo study. These results suggest that the ID does not greatly change the hydraulic performance of a small centrifugal blood pump. The proper combination of the impeller ID and inlet port offset obtains less hemolysis. The larger impeller ID is considered to have less thrombogenicity around the top bearing.     

The intra-aortic cannula pump: A novel assist device for the acutely failing heart.

OBJECTIVE: The intra-aortic cannula pump is a catheter pump designed to support the acutely failing heart. It expels blood from the left ventricle into the ascending aorta in a pulsatile flow pattern. The aim of the study was to analyze the hemodynamic performance of this new intracardiac support system in acute heart failure. METHODS: A 24F cannula was studied in a series of 16 sheep. Hemodynamic changes were assessed in the nonfailing, the moderately failing, and the severely failing heart. Heart failure was induced by an injection of microspheres into the left anterior descending coronary artery. The cannula was inserted through the aortic arch and introduced through the aortic valve into the left ventricle. RESULTS: Cannula insertion was feasible in all animals. Flow through the intra-aortic cannula flow was increased to a maximum of 3 L/min. No hemodynamic changes were observed in the nonfailing heart. A significant increase in cardiac output was observed in the moderately and severely reduced left ventricle (2.67 +/- 0.7 L to 3.51 +/- 0.83 L; P =.001; and 1.18 +/- 0.77 L to 2.43 +/- 0.44 L; P =.001, respectively). A drop in left atrial pressure was achieved in moderate and severe heart failure (14.1 +/- 5.93 mm Hg to 9.71 +/- 2.63 mm Hg; P =.0001; and 23 +/- 7.16 mm Hg to 11.2 +/- 2.55 mm Hg; P = 0.0001, respectively). Systolic and diastolic systemic blood pressures increased in the severely failing heart (57.3 +/- 12.8 mm Hg to 75.4 +/- 11.2 mm Hg; P =.0001; and 35.6 +/- 8.2 mm Hg to 60 +/- 14.3 mm Hg; P =.0006, respectively). CONCLUSIONS: Hemodynamic data demonstrate the beneficial effects of the intra-aortic cannula pump in moderate and severe heart failure. The intra-aortic cannula pump represents a new modality for the treatment of acute heart failure.     

Evaluation of hemolysis in the VentrAssist implantable rotary blood pump

The VentrAssist implantable rotary blood pump (IRBP) is an implantable centrifugal blood pump with a hydrodynamically suspended impeller; optimal efficiency requires small running clearances (70-300 microm). The effect of running clearance and polish on hemolysis was evaluated in vitro. Three different human blood suspensions were compared: phosphate buffered saline (PBS), plasma volume expander (Hemaccel), and whole blood. The test conditions were: blood hematocrit 30%, flow rate 5 L/min, pressure across pump 100 mm Hg, 6 h flow period, and 37 degrees C. Normalized Index of Hemolysis (NIH) for the Biomedicus BP-80, used as a control, was: 0.0040 +/- 0.0023 (n = 9; x +/- SD) and 0.00014 +/- 0.00009 (n = 5) for pooled blood suspensions in PBS and Hemaccel respectively, and 0.00053 +/- 0.0002 (n = 3) in whole blood. Hemolysis was reduced by improved surface finish and unaffected by running clearance. NIH for the VentrAssist IRBP with 0.2 microm Ra surface finish was 0.000167 +/- 0.00007 (n = 4) g/100 L in whole human blood, demonstrating minimal hemolysis.     

Pulsatile Total Artificial Heart Using a Reversible Rotary Pump

Abstract: A pump circuit was assembled and examined for use as an implantable artificial heart. The circuit consisted of a gear pump and 4 artificial heart valves. Mitral and pulmonary arterial valves were placed at the inflow port of the pump, and aortic and tricuspid valves were placed at the outflow port. The mitral and the tricuspid valves were connected to each reservoir at 10 mm Hg, and the aortic and the pulmonary arterial valves were connected to the head tanks at 80 and 20 mm Hg, respectively. The pump discharged pulsatile flows into both systemic and pulmonary arteries alternately by switching the direction of rotation periodically. Because the rated discharge was 1.7 L/min for the gear pump used, the measured flow rate was 0.8-0.75 L/min at a heart rate of 60–110 bpm.     

Dynamic characteristics of a magnetically levitated impeller in a centrifugal blood pump

Centrifugal blood pumps that employ hybrid active/passive magnetic bearings to support noncontact impellers have been developed in order to reduce bearing wear, pump size, the power consumption of the active magnetic bearing, and blood trauma. However, estimates made at the design stage of the vibration of the impeller in the direction of passive suspension during pump operation were inaccurate, because the influence of both the pumping fluid and the rotation of the impeller on the dynamic characteristics was not fully recognized. The purpose of this study is to investigate the dynamic characteristics in a fluid of a magnetically levitated rotating impeller by measuring both the frequency response to sinusoidal excitation of the housing over a wide frequency range and the displacement due to input of a pulsatile flow during left ventricular (LV) assist. The excitation tests were conducted under conditions in which the impeller was levitated in either air or water, and with or without rotation. The experimental and analytical results indicate that vibration of the impeller due to the external force in water was decreased, compared with that in air due to the hydraulic force of water. The axial resonant frequency rose quadratically with rotational speed, and the tilt mode had two resonant frequencies while rotating due to the gyroscopic effect. With the pump inserted into a mock systemic circulatory loop, the dynamic stability of the impeller when pulsatile pressure was applied during LV assist was verified experimentally. The amplitudes of vibration in response to the pulsatile flow in the passively constrained directions were considerably smaller in size than the dimensions of initial gaps between the impeller and the pump housing.     

Preliminary in vivo study of an intra-aortic impeller pump driven by an extracorporeal whirling magnet

To achieve the aim of long-term heart-assist with a simple implantable device, we have been trying to develop a minimal intra-aortic impeller blood pump driven by an extracorporeal magnetic device. The purpose of the current study was to evaluate its feasibility by acute in vivo animal tests. The minimal intra-aortic pump was a cage-supported rotor-impeller, 17 mm in diameter with a total length of 30 mm. The driving magnet, mounted extracorporeally, was 55 mm in diameter and 50 mm in length. Seventeen dogs weighing from 28-34 kg were used in the study. After thoracic incision, heparin (50 U/kg) was infused. The impeller pump was inserted into the aortic chamber via a prosthetic vessel and fastened. Thin tubes were inserted into the left ventricular apex and the femoral artery to monitor the left ventricular (LV) and the aortic pressure. After closing the thoracic cavity, the extracorporeal whirling magnet, turned by an electric motor, was placed tightly against the thoracic wall parallel to the intra-aortic pump. The experiments, each lasting for about 40 min, were successful in 7 animals; the other 10 animals died of bleeding during pump implantation and were excluded from the experiment. The peak systolic pressure of the left ventricle could be considerably decreased by the pump and was reduced to as low as 28 mm Hg at a rotational speed of 9,000 rpm, showing that the simple intra-aortic impeller was effective in unloading the natural heart. The novel left ventricular assist device (LVAD) concept of an intra-aortic impeller pump, driven by an extracorporeal magnetic device, is feasible.     

Motor Current Waveforms as an Index for Evaluation of Native Cardiac Function During Left Ventricular Support with a Centrifugal Blood Pump

Control of ventricular assist devices (VADs) for native heart preservation should be attempted, and it could be one strategy for dealing with the shortage of donors in the future. In the application of a nonpulsatile blood pump for ventricular assistance from its apex to the aorta, the bypass flow and hence motor current of the pumps change in response to the ventricular pressure change. Utilizing these intrinsic characteristics of the continuous flow pumps, this study investigated whether or not motor current could be used as an index for continuous monitoring of native cardiac function. In Study 1, a centrifugal blood pump (CFP) VAD was installed between the apex and descending aorta of a mock circulatory loop. In this model, a baseline with a preload of 10 mm Hg, afterload of 40 mm Hg, and left ventricular (LV) systolic pressure of 40 mm Hg was used. The pump rpm were fixed at 1,300, 1,500, and 1,700, and LV systolic pressure was increased up to 140 mm Hg by a step of 20 mm Hg while observing the changes in LV pressure, motor current, pump flow, and aortic pressure. In Study 2, in vivo experiments were performed using 5 sheep. A left heart bypass model was created using a centrifugal pump from the ventricular apex to the descending aorta. The LV pressure was varied through administration of dopamine while observing the changes in LV pressure, pump flow, motor current, and aortic pressure at 1,500 and 1,700 rpm. An excellent correlation was observed both in vitro and in vivo studies in the relationship between motor current and LV pressure. In Study 1, the correlation coefficients were 0.77, 0.92, and 0.99 for 1,300, 1,500, and 1,700 rpm, respectively. In Study 2, they were 0.90 (Animal 1), 0.82 (Animal 2), 0.89 (Animal 3), 0.93 (Animal 4), and 0.70 (Animal 5) respectively for 1,500 rpm, and 0.94 (Animal 2), 0.85 (Animal 3), 0.94 (Animal 4), and 0.89 (Animal 5) respectively, for 1,700 rpm. The relationship between motor current and pump flow and LV pressure showed an unstable correlation in an in vivo study. These results suggest that motor current amplitude monitoring could be useful as an index for the control of VADs for native heart preservation.     

Centrifugal blood pump with a hydraulically-levitated impeller for a permanently implantable biventricular assist device

A permanently implantable biventricular assist device (BVAD) system has been developed with a centrifugal pump which is activated by a hydraulically-levitated impeller. The pump impeller floats hydraulically into the top contact position; this position prevents thrombus formation by creating a washout effect at the bottom bearing area, a common stagnant region. The pump was subjected to in vitro studies using a pulsatile mock circulation loop to confirm the impeller's top contact position and the swinging motion produced by the pulsation. Eleven in vivo BVAD studies confirmed that this swinging motion eliminated blood clot formation. Twenty-one pumps im-planted for up to three months did not reveal any thrombosis in the pumps or downstream organs. One exception was a right pump which was exposed to severe low flow due to the kinking of the outflow graft by the accidental pulling of the flow meter cable. Three ninety-day BVAD studies were achieved without thrombus formation.     

The Realization of a Pulsatile Implantable Impeller Pump with Low Hemolysis

A pulsatile implantable impeller pump with low hemolysis was developed without markedly increasing the complexity of the system compared with the nonpulsatile pump. The key to the question is to design a three-dimensional impeller with twisted vanes, compacted by an axial helical spiral and a radial logarithmic spiral so as to reduce the turbulent shear in the pump as the impeller changes its rotations per minute periodically to generate a physiologic pulsatile flow. Both mathematic computation of velocity distribution in the impeller and geometric illustration of the velocity triangle at the top of the vane have demonstrated that the peripheral velocity variation of blood cells in a twisted impeller will be less than that in an untwisted impeller. Thus, the main mechanical factor of hemolysis in the impeller pump, namely, the turbulent shear, should be reduced because it is proportional to the product of velocity variations measured in two perpendicular directions. In the in vitro experiments, the pump delivered 4 L/min mean flow at 100 mm Hg mean pressure (pulsed between 80-120 mm Hg) for more than 3 h in a circulatory model containing 700 ml of fresh citrated porcine blood. Every half hour, the free hemoglobin level in the plasma was tested, and the resulting index of hemolysis was about 0.020, slightly more than that of a nonpulsatile impeller pump developed in Shanghai. To compare hemolysis, the index of hemolysis of this pump is about 1/6 of that of the self-made diaphragm pump and 1/13 of that of the Polystan Pulsatile Pump.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of cardiac function during left ventricular assist by a centrifugal blood pump

In this study, the effects on varying cardiac function during a left ventricular (LV) bypass from the apex to the descending aorta using a centrifugal blood pump were evaluated by analyzing the left ventricular pressure and the motor current of the centrifugal pump in a mock circulatory loop. Failing heart models (preload 15 mm Hg, afterload 40 mm Hg) and normal heart models (preload 5 mm Hg, afterload 100 mm Hg) were simulated by adjusting the contractility of the latex rubber left ventricle. In Study 1, the bypass flow rate, left ventricular pressure, aortic pressure, and motor current levels were measured in each model as the centrifugal pump rpm were increased from 1,000 to 1,500 to 2,000. In Study 2, the pump rpm were fixed at 1,300, 1,500, and 1,700, and at each rpm, the left ventricular peak pressure was increased from 40 to 140 mm Hg by steps of 20 mm Hg. The same measurements as in Study 1 were performed. In Study 1, the bypass flow rate and mean aortic pressure both increased with the increase in pump rpm while the mean left ventricular pressure decreased. In Study 2, a fairly good correlation between the left ventricular pressure and the motor current of the centrifugal pump was obtained. These results suggest that cardiac function as indicated by left ventricular pressure may be estimated from a motor current analysis of the centrifugal blood pump during left heart bypass.     

Myocardial metabolism during fixed-rate pulsatile left ventricular bypass

Fixed-rate pulsatile cardiopulmonary bypass may improve subendocardial perfusion during ventricular fibrillation and has been employed during intermittent aortic cross-clamping. Variable-rate pulsatile left heart bypass that is governed by venous inflow and is asynchronous to the electrical activity of the heart is currently used in clinical practice. To study the effect of fixed-rate pulsation on myocardial metabolism during left heart bypass, six adult pigs underwent alternating periods of pulsatile (PLS) and nonpulsatile (NPLS) centrifugal pump left atrial-to-aortic bypass in randomized block design. Coronary sinus, aortic, and bypass circuit flows were recorded. Oxygen content and lactate concentration of coronary sinus and aortic blood were measured. Pulsatility index and pulse power index during pulsatile bypass were 4.4 and 4.7 (cycles/s)2, respectively. Percent bypass was maximal at a mean pulsation rate of 41.3 and averaged 92.2 and 91.3 for PLS and NPLS, respectively. Myocardial oxygen consumption per minute was reduced 14.3% during NPLS but was unchanged during PLS compared to control (CTRL). Percent lactate extraction was significantly lower than CTRL during NPLS only. Competition for inflow with the ejecting heart appeared to limit circuit pulsation rate and pulse power index. Fixed-rate pulsation is ineffective in reducing myocardial metabolism and should be avoided in left heart bypass.