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Biomedical subjects

B P Griffith

Publications and source records attributed to B P Griffith.

At least 379 records · Page 21Linked to original sources
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Dynamic biventricular response to alterations in preload in patients undergoing left ventricular device implantation.

Ventricular interdependence is important for the successful use of a left ventricular assist device (LVAD) because the filling of the device depends on right ventricular (RV) function as well as the interactions between the ventricles. The pulmonary arterial (PAP) and systemic arterial (AP) response to inferior vena caval (IVC) occlusion before and after insertion of an LVAD in 15 patients was used to "dissect out" the determinants of these interactions. PAP and AP were recorded during each IVC occlusion and peak systolic values calculated for each beat. Linear regression analysis was used to calculate the slope (k) between peak systolic AP values and peak systolic PAP values. k, a measure of preload responsiveness of the heart, is predominantly linear. k is relatively "flat" in selected LV failure patients pre-LVAD but increases significantly (P < 0.001) after LVAD (0.67 +/- 0.55 vs. 2.71 +/- 1.39). The increase in this parameter after LVAD suggests that the loss of RV-to-LV ventricular interdependence in patients with congestive heart failure appears to recover somewhat once an LVAD is inserted.

Adolescent↗
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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↗
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Protocol for releasing Novacor left ventricular assist system patients out-of-hospital.

Between September 1984 and April 1995, the Novacor left ventricular assist system (LVAS) has provided more than 13,000 days of mechanical circulatory support to cardiac transplant candidates in the United States and Europe. The duration of support of these 312 patients has ranged between 1 and 370 days, with an average support of 40 days, including use of the console based system and the wearable system. Of this group, 21% have been supported for more than 60 days, with an average support of 118 days. We have seen that patients who have been supported for more than 30 days have recovered from the effects of LVAS implant surgery and have shown a potential for rehabilitation from morbid congestive heart failure. Few changes to the pump settings or the medical orders have been needed after the third postoperative week. The reliability of the LVAS and the degree to which patients can be rehabilitated suggest that restricting patients to a hospital environment is unnecessary. In addition, the increasing wait for a donor heart, the quality of life that can be achieved, and the high cost of inpatient care make it desirable to discharge patients from the hospital and allow them to await a donor heart in a more home-like setting.

Ambulatory Care↗
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Estimation of left ventricular function in patients with a left ventricular assist device.

Patients with profound left ventricular (LV) dysfunction supported by a left ventricular assist device (LVAD) may have recovery of LV function, but current methods for assessing this are difficult or not readily available. A new method to estimate LV performance was tested in 6 patients on LVAD (age, 47 +/- 12 years). Simultaneous measures of LV cross-sectional area (substitute for volume) using transesophageal echocardiographic automated border detection and femoral arterial pressure (substitute for LV ejection pressure) were recorded during brief periods on and off LVAD. During the LVAD off period, femoral arterial pressure and LV area signals were combined on-line to generate arterial pressure-LV area loops. The slope of the linear regression line connecting the end systolic points generated during LV filling after LVAD off was used as an estimate of end systolic elastance denoted by Ees. The average Ees was 3.8 +/- 3.1 mmHg/cm2. These values are significantly lower than those of 13 control patients (22.3 +/- 15.4 mmHg/cm2). This method of estimating Ees may be clinically useful in assessing LV recovery in patients on LVAD after extended support.

Adult↗
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A gait-powered autologous battery charging system for artificial organs.

The quality of life of patients relying on electrically powered artificial organs is currently restricted by the limited energy availability provided by portable batteries. As these patients become increasingly ambulatory, and are developing more active lifestyles, this limitation grows more apparent. Coincidentally, these patients may themselves be capable of generating electrical power as a consequence of their physical activity. Extraction of this latent autologous energy could, in turn, be used to augment charging of internal batteries--thus untethering the patient from external power for extended periods of time. In this study, the viability of deriving energy associated with natural human ambulation has been evaluated. The kinematic components of gait were evaluated to identify the largest useful forces and moments that may be harnessed as an energy source, while presenting minimal "perceived" work for the patient. It was found that the ground reaction forces associated with the heel strike and toe-off phases of the gait represent the greatest potential for usable energy. This study uses a piezoelectric array within the midsole of the shoe for the conversion of mechanical to electric energy. This power could then be easily coupled in tandem with existing transcutaneous transformers for augmenting or temporarily replacing external power sources.

Artificial Organs↗
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A design improvement strategy for axial blood pumps using computational fluid dynamics.

During the initial stages of concept development of non traditional axial flow pumps, numeric simulation offers an attractive advantage. Computational fluid dynamics (CFD) provides the rationale to evolve the design numerically such that undesirable flow features may be significantly mitigated before a physical prototype is fabricated. The initial design of a novel axial flow blood pump is shown through CFD analysis to exhibit large regions of reverse flow. Such fluid dynamic behavior not only decreases the pump's hydrodynamic efficiency, but, more significantly, increases its overall potential for blood trauma and thrombogenesis. The design improvement strategy consists of creating a geometric model of the blood wetted surfaces and changing the associated geometric parameters such that more desirable fluid dynamic behavior is systematically attained with each incremental modification. The fluid flow through each new pump design is analyzed by numerically solving the incompressible Navier-Stokes equations in rotating coordinates. Marked improvements in the major fluid dynamic aspects of the axial flow pump were observed over an evolutionary sequence of four generations of pump design.

Biomechanical Phenomena↗
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The vasoregulatory role of endothelium derived nitric oxide during pulsatile cardiopulmonary bypass.

The role of pulsatile flow as a physiologic stimulus for endothelium mediated vasoregulation is poorly understood. Furthermore, non pulsatile flow, which is associated with increased vascular resistance and end-organ failure, has been demonstrated to lead to a decrease in nitric oxide (NO) production in vitro. Anesthetized pigs (23.4 +/- 0.3 kg) were placed on cardiopulmonary bypass using either non pulsatile or pulsatile perfusion for 60 min. In both groups, animals were maintained with a constant mean aortic flow (1.0-1.3 L/min). Serum samples obtained during bypass were assayed for the stable end-products of NO (nitrate [NO3-] and nitrite [NO2-]) by a method based on the Greiss reaction. Systemic vascular resistance was higher after 60 min in the non pulsatile (3712.5 +/- 481.2 dyne sec cm(-5)) vs the pulsatile group (2672.6 +/- 427.0 dyne sec cm(-5)), but not statistically significant (p > .05). However, NO production was decreased in the non pulsatile flow group (27 +/- 6%) vs the pulsatile flow group (14 +/- 5%) at a statistically significant level (p < .005). The results suggest that non pulsatile flow is associated with diminished endothelial shear stress and a reduction in endothelial nitric oxide production. This may contribute to the detrimental physiologic effects observed in prolonged non pulsatile flow states.

Animals↗
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ECMO support for adult patients with acute respiratory failure.

The authors analyzed factors that may influence the outcome of adult patients with respiratory failure who were treated with ECMO. Between December 1990 and July 1995, the authors used ECMO to support 33 patients (age range, 17-56 years) with respiratory failure from adult respiratory distress syndrome (ARDS; n = 9), primary graft failure after lung transplantation (n = 16), late graft failure after lung transplantation (n = 5), and miscellaneous reasons (n = 3). Twenty (61%) patients were successfully weaned from ECMO, and 13 (39%) survived to hospital discharge. Venoarterial ECMO was used in 46% of survivors, compared with 60% of nonsurvivors (p = 0.43). The time on mechanical support before ECMO and the duration on ECMO for survivors and nonsurvivors was 2.9 +/- 1.8 days vs 5.0 +/- 1.3 days (p = 0.35), and 6.5 +/- 1.8 days vs 5.7 +/- 1.1 days (p = 0.68), respectively. Compared with the nonsurvivors, survivors had higher PF ratios (PaO2/FIO2; 104 +/- 33 vs 81 +/- 8, p = 0.43) before ECMO was initiated, although the differences were not significant. Among the patients who received ECMO for primary graft failure, 75% were weaned from ECMO, and 56% survived to discharge. ECMO is beneficial for adult patients with respiratory failure, especially those with primary graft failure after lung transplantation.

Acute Disease↗
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Progress on development of the Nimbus-University of Pittsburgh axial flow left ventricular assist system.

Nimbus Inc. (Rancho Cordova, CA) and the University of Pittsburgh have completed the second year of development of a totally implanted axial flow blood pump under the National Institutes of Health Innovative Ventricular Assist System Program. The focus this year has been on completing pump hydraulic development and addressing the development of the other key system components. Having demonstrated satisfactory pump hydraulic and biocompatibility performance, pump development has focused on design features that improve pump manufacturability. A controller featuring full redundancy has been designed and is in the breadboard test phase. Initial printed circuit layout of this circuit has shown it to be appropriately sized at 5 x 6 cm to be compatible with implantation. A completely implantable system requires the use of a transcutaneous energy transformer system (TETS) and a diagnostic telemetry system. The TETS power circuitry has been redesigned incorporating an improved, more reliable operating topography. A telemetry circuit is undergoing characterization testing. Closed loop speed control algorithms are being tested in vitro and in vivo with good success. Eleven in vivo tests were conducted with durations from 1 to 195 days. Endurance pumps have passed the 6 month interval with minimal bearing wear. All aspects of the program continue to function under formal quality assurance.

Heart-Assist Devices↗
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Novel ventricular apical cannula: in vitro evaluation using transparent, compliant ventricular casts.

The geometric configuration of the cannula connection to the left ventricular (LV) apex was studied with respect to several characteristics defining functionality and compatibility. The authors had previously determined, through in vivo studies in sheep, that the design of the cannula used with a dynamic blood pump for LV circulatory support can significantly affect the hemodynamics by improving both the bypass flow rate and the fluid dynamics within the ventricle. The tip of the cannula can aid in preventing wall to wall ventricular collapse, as well as septal shift, due to reduced LV pressure. Proper surgical placement of the cannula with respect to the endocardial surface of the LV can also be simplified by the tip geometry. To investigate the anatomic interaction and fluid dynamics of apical cannulation, transparent compliant casts of bovine LVs were fabricated for in vitro flow visualization. Two different heart geometries were cast, end systolic and end diastolic. The latter was fitted with a pericardial mitral valve and pressurized in a pulsatile fashion to simulate the wall movement of a beating heart. The internal flow and anatomy were visualized with fluorescent particle tracking velocimetry. These studies were performed with conventional cannula tips, as well as a novel, trumpet mouth cannula. The visualization clearly shows the dramatic differences in flow between the geometries tested, and strongly advocates a trumpet mouth design. This novel tip demonstrated excellent placement, beneficial stenting, and improved blood flow by reducing apical stasis and recirculation. Ongoing evaluation of these and future geometries include the application of in vitro endoscopy, quantitative velocimetry, and extension to dilated human ventricles.

Cardiac Catheterization↗
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Chronic animal health assessment during axial ventricular assistance: importance of hemorheologic parameters.

Chronic testing of the Nimbus/UOP Axial Flow Pump was performed on 22 calves for periods of implantation ranging from 27 to 226 days (average, 74 days). The following parameters were measured: plasma free hemoglobin, blood and plasma viscosity, erythrocyte deformability and mechanical fragility, oxygen delivery index (ODI), blood cell counts, hematocrit, hemoglobin, blood urea nitrogen, creatinine, bilirubin, total protein, fibrinogen, and plasma osmolality. Most of the above parameters were stable during the full course of support. Compared with baseline, statistically significant differences during the entire period of implantation were only found in: hematocrit (p<0.001), hemoglobin (p<0.005), red blood cell (RBC) count (p<0.001), and whole blood viscosity (p<0.01). Plasma viscosity and ODI were mostly stable during the period of implantation. In some animals, an acute increase in fibrinogen concentration, plasma and blood viscosity, and a decrease in ODI were found to be early signs of the onset of infection. A small (10%) decrease in deformability of RBCs was found during the first 2 weeks after implantation. This alteration in RBC deformability was highly correlated (r = 0.793) with changes in total plasma protein concentration that fell more than 15% (p<0.001) during the same period. Mechanical fragility of RBCs was found to be slightly increased after implantation. Plasma free hemoglobin remained close to baseline level (p>0.2). After the first 2 weeks of the postoperative period, pump performing parameters for all animals were consistent and stable. In general, the Nimbus/UOP Axial Flow Pump demonstrated basic reliability and biocompatibility and did not produce significant alterations in the mechanical properties of blood or animal health status. The pump provided adequate hemodynamics and was well tolerated by the experimental animal for periods as long as 7.5 months. Monitoring rheologic parameters of blood is very helpful for evaluation of health during heart-assist device application.

Animals↗
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Quality of life outcomes in left ventricular assist system inpatients and outpatients.

This study empirically evaluates the quality of life (QOL) effects associated with hospital discharge among heart transplant candidates whose lives are maintained by left ventricular support systems (LVAS). Thirty-five LVAS inpatients (18 Novacor, 17 Thoratec) received structured QOL assessments approximately 1 month after device implant. Ten of the patients (8 Novacor, 2 Thoratec) were subsequently discharged to either home or a home-like outpatient facility where their QOL was reassessed. The QOL of LVAS patients, before and after discharge, was compared with that of demographically similar nonhospitalized heart transplant candidates (n = 55) and recipients (n = 97). Their caregivers' QOL was also assessed. The QOL of LVAS outpatients showed statistically significant (p<0.05) advantages over remaining LVAS inpatients and nonhospitalized heart candidates. Advantages appeared in physical, emotional, and social functioning domains. The QOL of LVAS outpatients also improved (p<0.05) over their own QOL before discharge, with the greatest change in physical functional and emotional status. The QOL of LVAS outpatients most closely resembled QOL in the transplant recipients. Family caregivers to LVAS outpatients reported some increases in caregiving burden after patient discharge, but their overall well being was not adversely affected. These data provide an empiric basis for the provision of outpatient programs as appropriate care for eligible LVAS patients.

Activities of Daily Living↗
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Fluid dynamic characterization of operating conditions for continuous flow blood pumps.

As continuous flow pumps become more prominent as long-term ventricular assist devices, the wide range of conditions under which they must be operated has become evident. Designed to operate at a single, best-efficiency, operating point, continuous flow pumps are required to perform at off-design conditions quite frequently. The present study investigated the internal fluid dynamics within two representative rotary fluid pumps to characterize the quality of the flow field over a full range of operating conditions. A Nimbus/UoP axial flow blood pump and a small centrifugal pump were used as the study models. Full field visualization of flow features in the two pumps was conducted using a laser based fluorescent particle imaging technique. Experiments were performed under steady flow conditions. Flow patterns at inlet and outlet sections were visualized over a series of operating points. Flow features specific to each pump design were observed to exist under all operating conditions. At off-design conditions, an annular region of reverse flow was commonly observed within the inlet of the axial pump, while a small annulus of backflow in the inlet duct and a strong disturbed flow at the outlet tongue were observed for the centrifugal pump. These observations were correlated to a critical nondimensional flow coefficient. The creation of a "map" of flow behavior provides an additional, important criterion for determining favorable operating speed for rotary blood pumps. Many unfavorable flow features may be avoided by maintaining the flow coefficient above a characteristic critical coefficient for a particular pump, whereas the intrinsic deleterious flow features can only be minimized by design improvement. Broadening the operating range by raising the band between the critical flow coefficient and the designed flow coefficient, is also a worthy goal for design improvement.

Centrifugation↗
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Human factors issues in ventricular assist device recipients and their family caregivers.

Ultimately, for ventricular assist devices (VADs) to be acceptable as permanent alternatives to heart transplantation, patients' and their families' satisfaction with specific features and risks of VADs must be addressed. Of 42 eligible patients who received VADs between February of 1996 and December of 1998, we interviewed 37 patients (17 Novacor, 18 Thoratec, 2 with both devices) and 20 of their primary family caregivers about device related concerns and reactions. Demographic and health related correlates of respondents' concerns were examined. Eleven patients discharged from the hospital with the VAD in place were then reinterviewed 1 month after discharge. At baseline, patients' general perceptions of the VAD were positive, although 22-52% reported specific concerns, including most often worry about infection (52%), difficulty sleeping due to the position of the driveline (52%), pain at the driveline exit site (46%), worry about device malfunction (40%), and being bothered during the day by device noise (32%). The prevalence of most concerns rose with duration of VAD support. Caregivers' perceptions did not differ significantly from patients' perceptions. Outpatients were somewhat more concerned than inpatients about device noise and risk of stroke, but were markedly less concerned about infection. Across all patients, higher levels of device related concerns were correlated with more physical functional limitations and more psychological distress, and reduced quality of life. Demographic characteristics and device type were not uniformly related to device concerns.

Activities of Daily Living↗
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Relationship of blood pressure and pump flow in an implantable centrifugal blood pump during hypertension.

The purpose of this study was to evaluate the real time relationship between pump flow and pump differential pressure (D-P) during experimentally induced hypertension (HT). Two calves (80 and 68 kg) were implanted with the EVA-HEART centrifugal blood pump (SunMedical Technology Research Corp., Nagano, Japan) under general anesthesia. Blood pressure (BP) in diastole was increased to 100 mm Hg by norepinephrine to simulate HT. Pump flow, D-P, ECG, and BP were measured at pump speeds of 1,800, 2,100, and 2,300 rpm. All data were separated into systole and diastole, and pump flow during HT was compared with normotensive (NT) conditions at respective pump speeds. Diastolic BP was increased to 99.3+/-4.1 mm Hg from 66.5+/-4.4 mm Hg (p<0.01). D-P in systole was under 40 mm Hg (range of change was 10 to 40 mm Hg) even during HT. During NT, the average systolic pump flow volume was 60% of the total pump flow. However, during HT, the average systolic pump flow was 100% of total pump flow volume, although the pump flow volume in systole during HT decreased (33.1+/-5.7 vs. 25.9+/-4.0 ml/systole, p<0.01). In diastole, the average flow volume through the pump was 19.6+/-6.9 ml/diastole during NT and -2.2+/-11.1 ml/diastole during HT (p<0.01). The change in pump flow volume due to HT, in diastole, was greater than the change in pump flow in systole at each pump speed (p<0.001). This study suggests that the decrease of mean pump flow during HT is mainly due to the decrease of the diastolic pump flow and, to a much lesser degree, systolic pump flow.

Animals↗
PubMedDate not supplied

Prevalence and risk of depression and anxiety-related disorders during the first three years after heart transplantation.

Although poor psychological adjustment to organ transplantation appears to be a major contributor to reduced quality of life and increased physical morbidity, the prevalence and risk factors for psychiatric disorder have not been considered beyond the first 12-18 months after transplantation. The authors enrolled a representative sample of 191 heart transplant recipients in a prospective examination of the prevalence, clinical characteristics, and risk factors for DSM-III-R major depressive disorder (MDD), generalized anxiety disorder (GAD), associated adjustment disorders, and posttraumatic stress disorder related to transplant (PTSD-T) during the 3 years postsurgery. Survival analysis indicates that cumulative risks for disorder onset were MDD, 25.5%; adjustment disorders, 20.8% (17.7% with anxious mood); PTSD-T, 17.0%; and any assessed disorder, 38.3%. There was only one case of GAD. PTSD-T onset was limited almost exclusively to the first year posttransplant. Episodes of MDD (but not anxiety disorders) that occurred later posttransplant (8 to 36 months postsurgery) were more likely than early posttransplant episodes to be treated with psychotropic medications. For both MDD and anxiety disorders, later episodes were less likely to be precipitated by transplant-related stressors than other life stressors. Factors increasing cumulative risk for psychiatric disorder posttransplant included pretransplant psychiatric history, female gender, longer hospitalization, more impaired physical functional status, and lower social supports from caregiver and family in the perioperative period. Risk factors' effects were additive; the presence of an increasing number of risk factors bore a dose-response relationship to cumulative risk of disorder.

Adolescent↗
PubMedDate not supplied

The pigtail catheter for pleural drainage: a less invasive alternative to tube thoracostomy.

BACKGROUND: Tube thoracostomy remains the standard of care for the treatment of pneumothoraces and simple effusions. This report describes a favorable experience with the 8.3 French pigtail catheter as a less invasive alternative to traditional chest tube insertion. METHODS: We retrospectively reviewed 109 consecutive pigtail catheter placements. Catheters were inserted under local anesthesia at the bedside without radiographic guidance. Pre- and post-insertion chest radiographs were reviewed to determine efficacy of drainage. RESULTS: Fifty-one of 109 patients (47%) were mechanically ventilated and 26 patients (24%) had a coagulopathy. There were no complications related to pigtail catheter insertion. Seventy-seven pigtail catheters were placed for pleural effusion and 32 for pneumothorax. Mean effusion volume decreased from 43 to 9 percent, and drainage averaged 2899 ml over 97 hours. Mean pneumothorax size diminished from 38 to 1 percent during an average 71-hour placement. Clinical success rates in the effusion and pneumothorax groups were 86 and 81 percent, respectively. CONCLUSION: The pigtail catheter offers reliable treatment of pneumothoraces and simple effusions and is a safe and less invasive alternative to tube thoracostomy.

Adolescent↗