Biomedical subjects

J P Kerrigan

Publications and source records attributed to J P Kerrigan.

11 recordsLinked to original sources

PubMed1996

Long-term animal survival with an implantable axial flow pump as a left ventricular assist device.

We are developing an axial flow blood pump with Nimbus Inc. (AxiPump). For in vivo evaluation the AxiPump has been used as a left ventricular assist device with a left ventricular and descending aorta cannulation and implantation in a small pocket on the left lateral abdominal wall just posterior to the costal margin. Electrical and flow probe leads exit the body transcutaneously. A purge line that delivers the purge fluid for lubrication of the seal between the rotor and stator bodies in the purge fluid bearing system is tunneled with the other leads. Following acute animal studies, 3 animals have been supported for over 1 month with this AxiPump system. All laboratory results were within normal limits except during a recovery period from surgical damage. Hemolysis was not a serious problem. In the first case, the purge system failed at 28 days, and in the second and third cases, the nonpurge bearing system worked well for 57 and 52 days, respectively. Bearings are still under development in this kind of pump. However, this success encourages us to improve the AxiPump as a long-term assist device.

Animals↗

PubMed1996

High-resolution fluorescent particle-tracking flow visualization within an intraventricular axial flow left ventricular assist device.

Flow visualization is typically applied in blood pump development to both confirm the design expectations and identify regions that may be predisposed to blood element deposition and trauma. Rotary pumps, in particular, place high demands on the technique chosen to visualize the flow given the limited visual accessibility of the flow path and the high impeller speeds. Fluorescent image-tracking velocimetry currently is used at the University of Pittsburgh Medical Center to visualize flow accurately inside of these pumps both qualitatively and quantitatively. Flow patterns under steady conditions within an intraventricular axial flow, left ventricular assist pump (prototype No. 7, SUN Medical Technology Research Corporation, Nagano, Japan) were investigated using this technique. The flow fields at the impeller-stator interface and at the pump outlet were given specific attention. This allowed the assessment of the fluid dynamics throughout the hydrodynamic design limits of the pump.

Biomechanical Phenomena↗

PubMed1996

Controller for an axial flow blood pump.

A rotary blood pump inherently provides only one noninvasive "observable" parameter (motor current) and allows for only one "controllable" parameter (pump speed.) To maintain the systemic circulation properly, the pump seed must be controlled to sustain appropriate outlet flows and perfusion pressure while preventing pulmonary damage caused by extremes in preload. Steady-state data were collected at repeated intervals during chronic trials of the Nimbus AxiPump (Nimbus, Inc., Rancho Cordova, California, U.S.A.) in sheep (n = 7) and calves (n = 12). For each data set, the pump speed was increased at increments of 500 rpm until left ventricular and left atrial emptying was observed by left atrial pressure diminishing to zero. The effect of decreasing preload was evaluated perioperatively by inferior vena cava occlusion at a constant pump speed. Fourier analysis established a relationship between changes in the pump preload and the power spectra of the pump current waveform. Based on these results, a control method was devised to avoid ventricular collapse and maintain the preload within a physiologic range. The objective of this controller is the minimization of the second and third harmonic of the periodic current waveform. This method is intended to provide a noninvasive regulation of the pump by eliminating the need for extraneous transducers.

Animals↗

PubMed1995

An improved left ventricular cannula for chronic dynamic blood pump support.

Ventricular unloading with dynamic blood pumps can be markedly affected by the geometry of the cannula tip within the ventricular chamber. Due to the ability of these pumps to develop significant negative inflow pressure, existing cannula tips designed for passively filling blood pumps can be predisposed to inflow occlusion by intraventricular anatomic structures. A novel "trumpet" mouth cannula was constructed to overcome this limiting problem. This design was based on two criteria: to provide additional stenting to the ventricular apex, and to assure placement of the tip opening relative to the endocardial surface. This prototype cannula was evaluated in vivo against conventional caged, blunt, and tapered designs to assess anatomic and hemodynamic interaction within the ventricular apex. Post mortem examination revealed the inflow tract to be devoid of myocardial obstruction in all cases. These initial studies indicate that a trumpet mouth cannula can provide satisfactory hemodynamic performance required by dynamic blood pumps.

Animals↗

PubMed1986

Pediatric nasal resistance and lower anterior vertical face height.

In an effort to determine whether nasal obstruction in the pediatric population influences craniofacial and orthodontic development, nasal resistance data were collected from 211 consecutive orthodontic patients by means of active anterior rhinometry. Age-specific nasal resistance standards had been previously accumulated from an unselected representative sample of 498 youngsters, drawn from socioeconomic and demographic backgrounds similar to those of the orthodontic group. Resistance data collected from 211 orthodontic patients were found to fall in an almost linear arrangement, varying inversely with age. Age-specific nasal resistance mean data were found to be consistently higher than comparable age-specific mean data of the unselected comparative sample. When orthodontic nasal resistance data were compared with cephalometric measurements of anterior lower vertical face height in 60 patients, there was a definitive correlation between elevation in nasal resistance and increased lower vertical face-height measurements.

Adolescent↗

PubMedDate not supplied

Dynamic systemic vascular resistance in a sheep supported with a Nimbus AxiPump.

Changes in systemic vascular resistance (SVR) in response to diminished pulse perfusion were analyzed over a dynamic range of flow conditions. An axial flow LVAD (Nimbus AxiPump, Rancho Cordova, CA) was implanted in a sheep for 28 days, during which time SVR was determined over several conditions of posture and excitability. Total arterial resistance (TR) was calculated dynamically as an index of SVR by analysis of pump flow in diastole, and systemic pressure estimated from the characteristic pressure-flow-speed relation of the AxiPump. TR was evaluated over a range of flow rates, including maximum flow--for which the pressures and flows were essentially nonpulsatile. Throughout the course of support, and independent of pulsatility, TR dropped when the sheep stood and was significantly lower than that in the sitting position (P < 0.01). Response to excitement followed the same trend: TR was significantly higher during agitation than during normal temper (P < 0.01). In spite of changes in pulse pressure and flow rate, SVR changes occurred according to expected physiologic responses for pulsatile perfusion. Because pump flow and pressure are sensitive to afterload, the results of these studies suggest that pump speed control must compensate for changes in SVR to maintain acceptable perfusion.

Animals↗

PubMedDate not supplied

Effect of perfluorochemical emulsion on blood trauma and hemorheology.

One of the major problems of development and improvement of heart assist devices is the reduction of blood cell damage. The extremely high levels of shear stress, turbulence, prolonged contact between blood and foreign surfaces, and other abnormal hydrodynamic circumstances have been shown to cause hemolysis, activation of platelets, and changes in mechanical properties of red blood cells. Hemolysis, in turn, can drastically increase red blood cell aggregation at low shear conditions. A new pharmacologic approach to reduce blood trauma and improve rheologic properties of blood subjected to mechanical stress was investigated. These experiments showed that the replacement of 20% of the plasma volume with Fluosol (Alpha Therapeutic Corp., Los Angeles, CA), a perfluorochemical that transports oxygen, reduced mechanical fragility of human (P < 0.01) and ovine (P = 0.054) red blood cells by approximately 30%. The same replacement of plasma with Fluosol reduced hemolysis (plasma free Hb) by approximately 40% compared to control (P < 0.05) during in vitro pumping of blood with a centrifugal pump. A 20% replacement of plasma volume with Fluosol remarkably reduced low shear blood viscosity (from 31.9 +/- 6.1 to 18.2 +/- 4.8 cP, for shear rate gamma = 0.277 sec-1) and erythrocyte sedimentation rate (from 16.7 +/- 9.2 to 3.1 +/- 3.1) mm/hr) in human blood. Decrease of these parameters indicates the reduction of red blood cell aggregation. Results of this study demonstrate the potential feasibility of Fluosol to improve mechanical properties of blood in patients with heart assist devices.

Animals↗

PubMedDate not supplied

Effect of pulsatility and hemodynamic power on recovery of renal function.

Circulatory assist devices are used to treat patients awaiting cardiac transplantation to preserve life as well as to permit recovery of end-organ function. The efficacy of pulseless perfusion versus pulsatile perfusion in the recovery of end-organ function has not been fully determined. In this study, the efficacy of pulseless perfusion compared to pulsatile perfusion on the recovery of renal function after a 30 min period of normothermic ischemia was examined. Pigs were randomly assigned to four groups. In all groups, acute renal ischemia was induced by clamping both renal arteries for 30 min. Reperfusion for 120 min was performed using either pulsatile perfusion or pulseless perfusion at 65 +/- 1.6 mm Hg (Groups I [pulsatile] and II [pulseless]) and at 40 +/- 1.1 mm Hg (Groups III [pulsatile] and IV [pulseless]). After reperfusion, renal blood flow, hemodynamic power (pressure * flow: hemodynamic power), oxygen consumption (VO2), tissue ATP, and urine output (UO) in Groups I, II, and III were significantly higher than in Group IV (p < .01 by ANOVA). Histopathologic examinations were not significantly different between groups. Under hypotensive conditions, pulsatile perfusion improves hemodynamic power delivery to the organ compared to pulseless perfusion. These results suggest that a pulseless pump is acceptable as an assist device when normal flow or perfusion pressure is maintained.

Animals↗

PubMedDate not supplied

In vivo evaluation of the Nimbus axial flow ventricular assist system. Criteria and methods.

Continuing in vivo trials are being conducted at the University of Pittsburgh using the Nimbus axial flow blood pump (AxiPump). To date, 14 sheep experiments have been performed to address several issues related to short-term support. Six acute experiments (< 6 hr) have been performed to assess hemodynamics related to speed regulation and to determine anatomic placement of the pump and cannulae. Eight short-term survival studies lasting up to 6 days have been performed to evaluate biocompatibility and system reliability, and to establish clinical management protocols. The AxiPump has been used as a left ventricular assist device (LVAD), right ventricular assist device (RVAD), and biventricular assist device (BiVAD) with left ventricular and right atrial cannulation. The AxiPump has demonstrated the ability to assume complete support of either the pulmonary or systemic circulation, or both. We have determined that sufficient surgical access may be obtained through left lateral thoracotomy for both LVAD and RVAD insertion. In the absence of post operative anticoagulation therapy, we have detected subclinical renal cortical infarctions in 6 of 8 short-term animals. Thrombus deposition has been observed at the ventricular cannula tip in 4 of 8 cases--necessitating design changes. Two short-term experiments have been terminated because of bleeding--one due to inflow cannula obstruction and one due to cannula failure. Plasma free hemoglobin levels were all below 15 mg/dl, except for one case complicated by inflow obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Fluorescent image tracking velocimetry of the Nimbus AxiPump.

High shear rates and extended residence times causing hemolysis and platelet activation can develop in an assist pump or cannula when inferior flow conditions exist. The high volume output of a miniature axial flow pump presents challenges in avoiding these adverse conditions. To assess the hemodynamics within the continuous flow Nimbus Axi-Pump, vector flow fields inside a translucent inflow cannula and a modified 12 mm AxiPump were mapped. Fluorescent image tracking velocimetry was used to track the motion of neutrally buoyant fluorescent particles (30 microns) using pulsed laser light, high resolution video cameras, and computer image analysis. An acrylic pump housing and cannula were integrated into a mock circulatory loop filled with a Newtonian, optically clear blood analog fluid. The flow parameters were controlled to yield known, physiologic loading conditions, including varying degrees of pulsatility. Cannula flow visualization results exhibited critical recirculation patterns at the bend. These results will be used to further optimize the design of the inflow. Particle impact was seen at the pump inlet in the inducer region of the rotor. Very good attachment of flow from the rotor to stator was observed when the pump operated at normal operating speeds. Intermittent regurgitant flow fields were evident in the presence of increased pulsatility and low pump speed. These results have lead to improvements in impeller design and speed control criteria to avoid potential deleterious flows.

Blood Flow Velocity↗

PubMedDate not supplied

Survival for up to six months in calves supported with an implantable axial flow ventricular assist device.

This paper summarizes the authors' in vivo experience to date with an implantable axial flow blood pump designed for long-term ventricular support. This small, valveless pump with blood-lubricated bearings has been implanted in six calves (83 +/- 6 kg) as a left ventricular assist device (LVAS). The left ventricle and descending thoracic aorta were cannulated by left thoracotomy, and the pump was placed in a subcutaneous pocket below the costal margin. Animals remained hemodynamically stable throughout the course of support during partial left ventricular bypass. Five animals were killed after 15, 27, 52, 57, and 181 days. The longest survivor (181 days) demonstrated normal pump function at the time death. Pump speed was maintained at 10,100 +/- 100 rpm, with an average pump flow rate of 4.9 +/- 0.5 L/min under resting physiologic conditions. Average plasma free hemoglobin was 17.4 +/- 7.5 mg/dl. Renal, hepatic, and hematologic indices remained within physiologic range in all of these animals, except during the immediate postoperative period. Histopathologic analyses of major organs after death revealed small renal cortical infarcts in five of six animals; the remaining organs were normal. These animal studies support the feasibility of this small implanted axial flow pump for long-term ventricular assistance.

Animals↗