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Biomedical subjects

D J Farrar

Publications and source records attributed to D J Farrar.

At least 19 recordsLinked to original sources
PubMed2001

A new method of monitoring recovery and weaning the Thoratec left ventricular assist device.

BACKGROUND: Recent scientific and clinical data suggest that chronic mechanical ventricular unloading may lead to myocardial recovery. Evaluating and monitoring patients for myocardial recovery and the optimal methods of weaning the left ventricular assist device are not well defined. METHODS: Six patients with advanced heart failure and severe mitral regurgitation have undergone successful bridge to recovery using a Thoratec left ventricular assist device. Data that details their monitoring for myocardial recovery and weaning from the left ventricular assist device were prospectively collected. RESULTS: Clinical data collected during the recovery phase included chest roentgenogram, echocardiography, plasma norepinephrine, tumor necrosis factor-alpha, bioimpedance, and cardiopulmonary exercise testing (peak oxygen consumption). Normalization of these variables with a 10% increase in the peak oxygen consumption was obtained before weaning. The Thoratec device rate and percent systole were manipulated to allow gradual reloading of the ventricle. The weaning process occurred for more than 5 to 10 days to allow time for observation of the ventricle and its response to the increasing workload. CONCLUSIONS: Select patients with advanced congestive heart failure and severe mitral insufficiency can benefit from mechanical device support. We describe our technique of monitoring for myocardial recovery using clinical variables. Our technique of weaning allows for gradual reloading of the ventricle and a longer period of observation before device removal. Additional research is needed to determine which variables will accurately predict long-term myocardial recovery and the optimal weaning method.

Adult↗
PubMed2001

A versatile intracorporeal ventricular assist device based on the thoratec VAD system.

BACKGROUND: As patients are supported for longer durations with paracorporeal Thoratec left ventricular and biventricular assist devices (longest durations: 515 and 457 days, respectively), there is a need for implantable options. METHODS: We are developing a small, simple, and versatile intracorporeal ventricular assist device (IVAD) for left, right, or biventricular support as an alternative to the large, implantable, pulsatile left ventricular assist device (LVAD) systems available today. The new device is based on the Thoratec paracorporeal VAD that has been used in more than 1,400 patients weighing from 17 to 144 kg and for durations exceeding 1 year including patient discharge (using the portable driver). RESULTS: The IVAD has the same blood flow path and Thoralon polyurethane blood pumping sac as the paracorporeal VAD, but the housing is a smooth contoured, polished titanium alloy. The IVAD has a new sensor to detect when the pump is full and empty, and is controlled with the Thoratec TLC-II portable VAD driver, which is a small, briefcase-sized, battery-powered, pneumatic control unit. A small flexible (9 mm OD) percutaneous pneumatic driveline for each VAD is tunneled out of the body from the LVAD or right VAD in a pre- or intraperitoneal position. Small size and simplicity are the major advantages of the new device. The IVAD weight (339 g) and implanted volume (252 mL) are approximately one-half that of the current implantable pulsatile electromechanical LVAD systems. CONCLUSIONS: The small size of the IVAD should not only allow support of a large range of patient sizes and body habitus, but also provide options for implantable left, right, or biventricular support. By implanting only the mechanically simple blood pump, the more complex control unit is external, where it can be serviced and replaced without surgery. The IVAD with the portable driver will be a viable alternative to large implanted electromechanical systems and should address a larger segment of the physically diverse patient population.

Animals↗
PubMed2001

Multicenter experience with the thoratec ventricular assist device in children and adolescents.

BACKGROUND: Patient size is 1 determinant in selecting a mechanical circulatory support device. The current pulsatile ventricular assist devices (VADs) were designed primarily for average-sized adults. The flexibility of the Thoratec VAD, however, has encouraged physicians to use it in a significant number of intermediate-sized older children and adolescents. METHODS: We conducted a retrospective study in 58 children and adolescents <18 years (41 boys, 17 girls) who had been supported with the Thoratec VAD in 27 centers worldwide as of December 1999. Mean patient age was 13.8 years (range, 7 to 17 years), and mean patient weight and body surface area were 51.6 kg (range, 17 to 93 kg) and 1.5 m(2) (range, 0.7 to 2.1 m(2)), respectively. RESULTS: Thirty-five patients (60%) survived to transplantation and 6 (10%) to recovery of the native heart, respectively; 38 were discharged from the hospital (66%). In the transplanted group, post-transplantation survival was 97%. Patient age and size were not associated with significantly increased risk for death or adverse events. Fifteen patients (27%) had 18 neurologic events during support, and 6 of these were fatal. Left atrial cannulation proved a risk factor for neurologic complications. CONCLUSIONS: The Thoratec VAD has successfully been used in a large number of children and adolescents with similar morbidity and mortality results as with adults. The risk of neurologic complications may be increased, particularly in patients cannulated in the left atria.

Adolescent↗
PubMed2000

The thoratec ventricular assist device: a paracorporeal pump for treating acute and chronic heart failure.

The Thoratec Ventricular Assist Device (VAD) System (Thoratec Laboratories, Pleasanton, CA) is a paracorporeal pump that can provide univentricular or biventricular assistance for patients with heart failure. The system consists of a prosthetic ventricle that has a blood-pumping chamber of Thoralon (Thoratec Laboratories) polyurethane, cannulas for univentricular or biventricular support, and either a hospital-based pneumatic drive console or a portable battery-powered drive unit. For biventricular assistance, 2 pumps are used. The Thoratec voluntary registry indicates that, as of May 2000, this system had been implanted in 1,376 patients, mainly for bridging to transplantation (828 patients) or postcardiotomy support (195 patients); the remaining 353 patients received a hybrid configuration of the device or had incomplete information, so they are not included in this analysis. In the 828 bridge-to-transplant patients, the Thoratec system provided biventricular assistance in 472 cases, left ventricular assistance in 326 cases, and right ventricular assistance in 30 cases for up to 515 days. During the support period, the cardiac index increased significantly from 1.4 +/- 0.8 L/min/m2 to 3.0 +/- 0.5 L/min/m2 (with biventricular assistance and left ventricular cannulation). Sixty percent of the 828 patients underwent transplantation, and the posttransplant survival rate was 86%. In the 195 patients who needed postcardiotomy support, VADs were used for up to 80 days for cardiac recovery. Thirty-eight percent of the patients were weaned from the VAD, and 59% of the weaned group were discharged from the hospital. In addition, 49 postcardiotomy patients were considered for transplantation; of these, 32 received a transplant and 23 were discharged. Patient mobility is being improved by the use of a portable driver. The Thoratec VAD is suitable for a wide range of applications, and efforts are underway to facilitate patient mobility and allow hospital discharge. An intracorporeal version of the VAD, which is currently under development, will help achieve these goals.

Adult↗
PubMed2000

Development of a prosthetic coronary artery bypass graft.

BACKGROUND: The patient population undergoing repeat coronary revascularization is increasing, with estimates of approximately 15% of these patients in need of alternative conduits. Pre-existing conditions may limit the availability of suitable autogenous vessels for complete coronary revascularization. As an alternative, previous investigators have attempted to develop prosthetic conduits for coronary artery bypass grafting (CABG), but as yet without clinical success. To be of clinical benefit, a prosthetic graft would require demonstrated patency at least as good as a marginal quality autogenous vessel used in the same position, without unexpected adverse effects. The use of a prosthetic graft may also reduce surgical complications associated with conduit harvesting and thereby enhance the speed of patient recovery. METHODS: Our group has investigated the potential of a novel synthetic small diameter vascular graft (2.5- to 3.5-mm diameter), as an alternative conduit for CABG. The graft is designed with three distinct layers composed of Thoralon, a proprietary polyetherurethaneurea with a silicone-based surface modifying additive. This biomaterial is the same material successfully used for the thromboresistant blood-contacting surfaces of an FDA approved and clinically successful ventricular assist device. RESULTS: Aria grafts underwent extensive preclinical testing in sheep with results to over one year that demonstrate the graft's biocompatibility, biodurability, and ability to maintain patency in both peripheral access graft and coronary applications. Compassionate use human coronary implants have been performed in 27 patients in the coronary position in Canada and Europe. Although incomplete, the data demonstrate no device related serious injury or and all surviving patients have remained symptom free. CONCLUSIONS: A prosthetic coronary artery bypass graft has been developed and has undergone extensive pre-clinical testing and preliminary clinical use. Based upon the results, a prospective, randomized, controlled clinical study, the AEGIS/Canada (AlternativE Graft Investigational Study) trial using the Aria graft in the coronary position in human patients is underway. Additionally, a pre-IDE submission has been submitted to the FDA to expand the AEGIS clinical trial device to the United States.

Animals↗
PubMed1999

Megestrol acetate: promises and pitfalls.

Recent reports suggest that effective antiretroviral therapy, resulting in a plasma HIV load that has been reduced to undetectable levels, may itself prevent HIV- and opportunistic infection-associated weight loss and lead to substantial weight gain. Although these data are encouraging, it is clear that a significant proportion of patients will require, in addition, specific treatment for HIV-associated wasting. Megestrol acetate, in the dosage range of 400 to 800 mg/day, is a useful appetite stimulant for the prevention and treatment of HIV-associated wasting, particularly in women. Patients need to be advised of possible adverse effects and monitored closely. Megestrol acetate stimulates weight gain mostly through an increase in body fat and is therefore most effective in combination with a muscle-building exercise program, where appropriate, and an anabolic agent (steroid or growth hormone) to maintain or increase lean body mass.

Appetite Stimulants↗
PubMed1998

Importance of preoperative liver function as a predictor of survival in patients supported with Thoratec ventricular assist devices as a bridge to transplantation.

UNLABELLED: Patient selection is crucial for the success of ventricular assist devices as a bridge to heart transplantation. PURPOSE: The objective of this study was to identify preoperative markers for survival and end-organ recovery in patients having a ventricular assist device. METHODS: A retrospective study was performed on 32 severely ill patients with end-stage cardiac failure being mechanically bridged to heart transplantation with the Thoratec Ventricular Assist Device System (Thoratec Laboratories Corporation, Pleasanton, Calif) in a single center between 1984 and 1995. The preoperative cardiac index averaged 1.6 L/min per square meter with a pulmonary capillary wedge pressure of 29 mm Hg. Because of a high incidence of hepatic or renal dysfunction, or both (total bilirubin: 3.5 +/- 6.2 mg/dL; creatinine: 2.0 +/- 1.3 mg/dL), biventricular support was used in most patients (28/32). A total of 30 preoperative and 4 perioperative variables were evaluated for their association with survival and liver recovery. RESULTS: Nineteen patients (59.4%) survived to transplantation and 13 died. All 19 patients undergoing transplantation were discharged alive with a 1-year survival of 94.4%. All patients without liver recovery died of multiorgan failure. Direct and indirect bilirubin measurements were the only significant predictors for survival to discharge (P = .036, .045); all other factors failed to show significance. As direct bilirubin levels increased (normal range, 3 times normal, and >3 times normal), patient survival decreased (82 %, 56%, and 33 %, respectively). In addition, bilirubin and liver enzyme levels before insertion of the assist device were significantly associated with liver recovery during support with the device. CONCLUSION: In our patient population with ventricular assist devices, liver function is the most predictive factor of patient survival in bridging to transplantation.

Adult↗
PubMed1997

Preoperative and postoperative comparison of patients with univentricular and biventricular support with the thoratec ventricular assist device as a bridge to cardiac transplantation.

OBJECTIVES: The goal of this study was to determine whether there are differences in populations of patients with heart failure who require univentricular or biventricular circulatory support. METHODS: Two hundred thirteen patients who were in imminent risk of dying before donor heart procurement and who received Thoratec left (LVAD) and right (RVAD) ventricular assist devices at 35 hospitals were divided into three groups: group 1 (n = 74), patients adequately supported with isolated LVADs; group 2 (n = 37), patients initially receiving an LVAD and later requiring an RVAD; and group 3 (n = 102), patients who received biventricular assistance (BiVAD) from the beginning. RESULTS: There were no significant differences in any preoperative factors between the two BiVAD groups. In the combined BiVAD groups, pre-VAD cardiac index (BiVAD, 1.4 +/- 0.6 L/min per square meter, vs LVAD, 1.6 +/- 0.6 L/min per square meter) and pulmonary capillary wedge pressure (BiVAD, 27 +/- 8 mm Hg, vs LVAD, 30 +/- 8 mm Hg) were significantly lower than those in the LVAD group, and pre-VAD creatinine levels were significantly higher (BiVAD, 1.9 +/- 1.1 mg/dl, vs LVAD, 1.4 +/- 0.6 mg/dl). In addition, greater proportions of patients in the BiVAD groups required mechanical ventilation before VAD placement (60% vs 35%) and were implanted under emergency conditions than in the LVAD group (22% vs 9%). The survival of patients through heart transplantation was significantly better in patients who had an LVAD (74%) than in those who had BiVADs (58%). However, there were no significant differences in posttransplantation survival through hospital discharge (LVAD, 89%; BiVAD, 81%). CONCLUSION: Patients who received LVADs were less severely ill before the operation and consequently were more likely to survive after the operation. As the severity of illness increases, patients are more likely to require biventricular support.

Heart Transplantation↗
PubMed1995

Isolated systolic and diastolic ventricular interactions in pacing-induced dilated cardiomyopathy and effects of volume loading and pericardium.

BACKGROUND: Interactions between the closely coupled right and left ventricles are known to play important roles as determinants of ventricular function, and the purpose of this study was to evaluate their effects in a model of heart failure. METHODS AND RESULTS: A dilated cardiomyopathy resulting in congestive heart failure (CHF) was produced in pigs by rapid ventricular pacing at 230 beats per minute for 1 week. Blood was rapidly withdrawn from the left ventricular (LV) apex into a prosthetic ventricle, and the instantaneous effects on the right ventricle were studied during volume loading and before and after pericardiectomy. The systolic interaction gain between the right and left ventricles (Gs) was calculated as the ratio of changes in mean systolic pressure during isolated systolic LV unloading. Diastolic ventricular interaction gain (Gd) was calculated as the ratio of changes in mean diastolic pressures during LV unloading in the last 150 ms of diastole. With the pericardium closed, all interaction gains were significantly increased during volume loading from a right ventricular end-diastolic pressure of 3 to 9 mm Hg: Gs from 0.045 +/- 0.014 to 0.063 +/- 0.020 mm Hg/mm Hg (normal pigs) and from 0.077 +/- 0.040 to 0.103 +/- 0.019 (CHF pigs) and Gs from 0.196 +/- 0.116 to 0.493 +/- 0.117 mm Hg/mm Hg (normal pigs) and from 0.174 +/- 0.101 to 0.341 +/- 0.165 (CHF pigs). When the pericardium was opened, Gd was significantly reduced to 0.145 +/- 0.071 and 0.129 +/- 0.026 mm Hg/mm Hg (normal and CHF pigs, respectively), but Gs showed no significant change (0.067 +/- 0.027 and 0.109 +/- 0.012 mm Hg/mm Hg for normal and CHF pigs, respectively), and both were also significantly increased during volume loading. Gs was significantly greater in CHF versus normal pigs under all conditions, but there were no differences in Gd between CHF and normal pigs. CONCLUSIONS: These results suggest that dilated cardiomyopathy increases systolic but not diastolic interactions, that the pericardium increases diastolic but not systolic ventricular interactions, and that volume loading with and without the pericardium opened increases both systolic and diastolic interactions.

Animals↗
PubMed1995

Chronic fatigue syndrome. 1: Etiology and pathogenesis.

Chronic fatigue syndrome (CFS) is a disorder of unknown etiology characterized by debilitating fatigue and other somatic and neuropsychiatric symptoms. A range of heterogeneous clinical and laboratory findings have been reported in patients with CFS. Various theories have been proposed to explain the underlying pathophysiologic processes but none has been proved. Research findings of immunologic dysfunction and neuroendocrine changes suggest the possible dysregulation of interactions between the nervous system and the immune system. Without a clear understanding of its etiopathogenesis, CFS has no definitive treatment. Management approaches have been necessarily speculative, and they have evolved separately in a number of medical and nonmedical disciplines. The results of several controlled treatment studies have been inconclusive. An accurate case definition identifying homogeneous subtypes of CFS is needed. The integration of medical and psychologic treatment modalities and the use of both biologic and psychologic markers to evaluate treatment response will enhance future treatment strategies.

Antidepressive Agents↗