Biomedical subjects

Tom Bennett

Publications and source records attributed to Tom Bennett.

10 recordsLinked to original sources

PubMed2006

The Arabidopsis MAX pathway controls shoot branching by regulating auxin transport.

BACKGROUND: Plants achieve remarkable plasticity in shoot system architecture by regulating the activity of secondary shoot meristems, laid down in the axil of each leaf. Axillary meristem activity, and hence shoot branching, is regulated by a network of interacting hormonal signals that move through the plant. Among these, auxin, moving down the plant in the main stem, indirectly inhibits axillary bud outgrowth, and an as yet undefined hormone, the synthesis of which in Arabidopsis requires MAX1, MAX3, and MAX4, moves up the plant and also inhibits shoot branching. Since the axillary buds of max4 mutants are resistant to the inhibitory effects of apically supplied auxin, auxin and the MAX-dependent hormone must interact to inhibit branching. RESULTS: Here we show that the resistance of max mutant buds to apically supplied auxin is largely independent of the known, AXR1-mediated, auxin signal transduction pathway. Instead, it is caused by increased capacity for auxin transport in max primary stems, which show increased expression of PIN auxin efflux facilitators. The max phenotype is dependent on PIN1 activity, but it is independent of flavonoids, which are known regulators of PIN-dependent auxin transport. CONCLUSIONS: The MAX-dependent hormone is a novel regulator of auxin transport. Modulation of auxin transport in the stem is sufficient to regulate bud outgrowth, independent of AXR1-mediated auxin signaling. We therefore propose an additional mechanism for long-range signaling by auxin in which bud growth is regulated by competition between auxin sources for auxin transport capacity in the primary stem.

Arabidopsis↗

PubMed2006

Something on the side: axillary meristems and plant development.

Axillary meristems allow the production of secondary growth axes in the shoot systems of plants. As such they make a large contribution to the plastic developmental potential of plants, allowing them to alter their architecture to suit the prevailing environment conditions. This review focuses on the formation and activity of axillary meristems, across several model species. Current topics and problems in the field are discussed.

Arabidopsis↗

PubMed2006

Grafting.

Grafting provides a simple way to generate chimeric plants with regions of different genotypes, and thus to assess the cell autonomy of gene action. The technique of grafting has been widely used in other species, but in Arabidopsis, its small size makes the process rather more complicated. However, there are now several well-established grafting procedures available, which we described here, and their use has already contributed greatly to understanding of such processes as shoot branching control, flowering, and disease resistance.

Arabidopsis↗

PubMed2005

Implant experience with an implantable hemodynamic monitor for the management of symptomatic heart failure.

INTRODUCTION: Management of congestive heart failure is a serious public health problem. The use of implantable hemodynamic monitors (IHMs) may assist in this management by providing continuous ambulatory filling pressure status for optimal volume management. METHODS AND RESULTS: The Chronicle system includes an implanted monitor, a pressure sensor lead with passive fixation, an external pressure reference (EPR), and data retrieval and viewing components. The tip of the lead is placed near the right ventricular outflow tract to minimize risk of sensor tissue encapsulation. Implant technique and lead placement is similar to that of a permanent pacemaker. After the system had been successfully implanted in 148 patients, the type and frequency of implant-related adverse events were similar to a single-chamber pacemaker implant. R-wave amplitude was 15.2 +/- 6.7 mV and the pressure waveform signal was acceptable in all but two patients in whom presence of artifacts required lead repositioning. Implant procedure time was not influenced by experience, remaining constant throughout the study. CONCLUSION: Based on this evaluation, permanent placement of an IHM in symptomatic heart failure patients is technically feasible. Further investigation is warranted to evaluate the use of the continuous hemodynamic data in management of heart failure patients.

Biosensing Techniques↗

PubMed2005

Development of implantable devices for continuous ambulatory monitoring of central hemodynamic values in heart failure patients.

BACKGROUND: Care and management of patients with congestive heart failure (CHF) is a major health-care challenge. The value of acute hemodynamic data in assessing heart failure has been questioned in some studies, while more intensive hemodynamic monitoring has been reported to improve patient care in others. A series of patient studies are reported here that were conducted to identify device requirements and verify the feasibility of continuous hemodynamic monitoring in CHF patients and devices for remote transfer and use of these data. METHODS AND RESULTS: The results of four separate studies in 68 CHF patients who received systems for chronic hemodynamic monitoring between 1992 and the present are reviewed. One early study was with five patients followed for 7-16 months and another study was with nine patients followed for 4-22 months. A third study included 21 patients followed up to 39 months, and the fourth study included 32 patients implanted in 1998-99 with many of them still in follow-up. These studies support the technical feasibility of implanted devices and the external instrumentation required to transfer and manage the collected data. They also support the long-term stability and accuracy of these systems. Three additional acute studies conducted with 30 patients and chronic data from 53 of the 68 patients with the implanted systems are presented that support the feature included in the newer monitors--the ability to reliably estimate pulmonary artery diastolic pressures from the right ventricular pressure signal. CONCLUSIONS: Development of implantable technology to measure several hemodynamic variables in ambulatory CHF patients is feasible. External instrumentation needed to remotely acquire data from the implanted devices has been verified. The potential to eliminate the uncertainties associated with the use of acute, invasive hemodynamics and the ability to evaluate long-term ambulatory hemodynamic patterns is provided. These findings set the stage for determining the potential clinical value of these systems in impacting the care of chronic CHF patients.

Electrocardiography, Ambulatory↗

PubMed2005

Trans-telephonic monitoring of continuous haemodynamic measurements in heart failure patients.

The development of an implantable haemodynamic monitor (IHM) has made possible the home monitoring of a patient's central haemodynamic trends during daily living. We have evaluated the usability and transmission success of such a system over a 3.2-year period. Patients with an IHM were able to transmit the stored data every week to a Web server, where trend plots and tables of haemodynamic variables could be viewed by the health-care staff concerned. Data transfer was examined from August 2000 to November 2003. During this period, 148 patients had an IHM implanted. Over the study period, 7791 data transmissions were performed and an average of 286 downloads per month were sent to the Web server. In all, 86% of data transmissions were successful, although 10% required more than one attempt. The study demonstrated that telemonitoring of haemodynamic data from an IHM was feasible. A patient survey showed that the technology was user-friendly and that the training material provided sufficient information for patients and their families to install and use the transmission equipment at home. It also suggested that transmission success was independent of patient age or gender.

Adult↗

PubMed2004

Six years follow-up of an implanted SvO(2) sensor in the right ventricle.

INTRODUCTION: Mixed venous oxygen saturation (SvO(2)) is a standard invasive measure used in the management of congestive heart failure patients. The reliability of a long-term SvO(2) sensor remains unproven. METHODS: Nine patients (NYHA Class I/II, n=2/7) were implanted with a dual chamber pacemaker modified to utilize a right ventricular SvO(2) lead (Medtronic Inc., Models 8007/4327A IPG/Lead). Invasive studies compared sensor SvO(2) to reference (Optical Swan-Ganz catheter) at 0, 3 and 9 months. Symptom limited tests (Bike(max)) with metabolic assessment and arterial oxygen saturation measurements performed 1-7 days, 3.5 and 9.5 months post-implant allowed for cardiac output calculations. Long-term sensor performance was confirmed by submaximal tests, Bike(subm) in years 1-3, and Walk(in-place) every 6 months for the duration of follow-up. RESULTS: Sensor SvO(2) readings were stable over time when compared to the Swan-Ganz Catheter. Non-invasive CO measured during Bike(max) was in normal ranges for this patient population, 3.7+/-0.9 l/min at rest and 8.4+/-2.2 l/min at peak-exercise. Resting SvO(2) values from Bike(subm) and Walk(in-place) did not change significantly over time (P>0.1 vs. 1 year) and neither did the change from rest to peak exercise during Bike(subm) (P>0.05 vs. 1 year) or Walk(in-place) (P>0.05 vs. 4 year). CONCLUSION: While limited in size, this small pilot study suggests that long-term monitoring of SvO(2) by implanted devices may be feasible. The clinical value remains to be proven in future studies.

Aged↗

PubMed2003

Ongoing right ventricular hemodynamics in heart failure: clinical value of measurements derived from an implantable monitoring system.

OBJECTIVES: This study examined the characteristics of continuously measured right ventricular (RV) hemodynamic information derived from an implantable hemodynamic monitor (IHM) in heart failure patients. BACKGROUND: Hemodynamic monitoring might improve the day-to-day management of patients with chronic heart failure (CHF). Little is known about the characteristics of long-term hemodynamic information in patients with CHF or how such information relates to meaningful clinical events. METHODS: Thirty-two patients with CHF received a permanent RV IHM system similar to a single-lead pacemaker. Right ventricular systolic and diastolic pressures, heart rate, and pressure derivatives were continuously measured for nine months without using the data for clinical decision-making or management of patients. Data were then made available to clinical providers, and the patients were followed up for 17 months. Pressure characteristics during optimal volume, clinically determined volume-overload exacerbations, and volume depletion events were examined. The effect of IHM on hospitalizations was examined using the patients' historical controls. RESULTS: Long-term RV pressure measurements had either marked variability or minimal time-related changes. During 36 volume-overload events, RV systolic pressures increased by 25 +/- 4% (p < 0.05) and heart rate increased by 11 +/- 2% (p < 0.05). Pressure increases occurred in 9 of 12 events 4 +/- 2 days before the exacerbations requiring hospitalization. Hospitalizations before using IHM data for clinical management averaged 1.08 per patient year and decreased to 0.47 per patient-year (57% reduction, p < 0.01) after hemodynamic data were used. CONCLUSIONS: Long-term ambulatory pressure measurements from an IHM may be helpful in guiding day-to-day clinical management, with a potentially favorable impact on CHF hospitalizations.

Adult↗

PubMed2002

Continuous ambulatory right heart pressure measurements with an implantable hemodynamic monitor: a multicenter, 12-month follow-up study of patients with chronic heart failure.

BACKGROUND: We describe the performance of an implantable hemodynamic monitor (IHM) that allows continuous recording of heart rate, patient activity levels, and right ventricular systolic, right ventricular diastolic, and estimated pulmonary artery diastolic pressures. Pressure parameters derived from the implantable monitor were correlated to measurements made with a balloon-tipped catheter to establish accuracy and reproducibility over time in patients with chronic heart failure (CHF). METHODS AND RESULTS: IHM devices were implanted in 32 patients with CHF (left ventricular ejection fraction, 29% +/- 11%; range, 14%-62%) and were tested with right heart catheterization at implantation and 3, 6, and 12 months later. Hemodynamic variables were digitally recorded simultaneously from the IHM and catheter. Values were recorded during supine rest, peak response of Valsalva maneuver, sitting, peak of a 2-stage (25-50 W) bicycle exercise test, and final rest period. The median of 21 paired beat-to-beat cardiac cycles was analyzed for each intervention. A total of 217 paired data values from all maneuvers were analyzed for 32 patients at implantation and 129 paired data values for 20 patients at 1 year. The IHM and catheter values were not different at baseline or at 1 year (P >.05). Combining all interventions, correlation coefficients were 0.96 and 0.94 for right ventricular systolic pressure, 0.96 and 0.83 for right ventricular diastolic pressure, and 0.87 and 0.87 for estimated pulmonary artery diastolic pressure at implantation and 1 year, respectively. CONCLUSIONS: The IHM and a standard reference pressure system recorded comparable right heart pressure values in patients with CHF. This implantable pressure transducer is accurate over time and provides a means to precisely monitor the hemodynamic condition of patients with CHF in a continuous fashion.

Adult↗

PubMedDate not supplied

Ambulatory hemodynamic monitoring from an implanted device: components of continuous 24-hour pressures that correlate to supine resting conditions and acute right heart catheterization.

Information from an implantable hemodynamic monitoring system (IHM) aids in management of patients with heart failure. This study identified which components of 24-hour IHM data best estimate resting conditions. Thirty-two patients with heart failure received an IHM in the right ventricular (RV) outflow tract. RV hemodynamics were divided into seven components of a 24-hour recording and were compared with resting supine values. Ambulatory pressures approximating rest were then compared with acute invasive catheterization values. Resting RV pressures from the IHM averaged 41+/-16/10+/-6 mm Hg and estimated pulmonary artery diastolic pressure was 21+/-8 mm Hg. Nighttime (midnight to 4 a.m.) minimum pressures from the IHM best approximated supine resting conditions. RV and pulmonary artery pressures during catheterization were higher than the nighttime minimum, although RV diastolic pressure was not statistically different. Minimum RV and pulmonary artery pressures during nighttime approximate observed resting conditions; invasive catheterization pressures are higher than IHM resting values.

Adult↗