The performance of thermoelectric (TE) materials has improved tremendously over the past decade. The intrinsic thermal and electrical properties of state-of-the-art TE materials demonstrate that the ...potential for widespread practical TE applications is very large and includes TE generators (TEGs) for automotive waste heat recovery. TE materials for automotive TEG applications must have good intrinsic performance, be thermomechanically compatible, and be chemically stable in the 400 K to 850 K temperature range. Both
n
-type and
p
-type varieties must be available at low cost, easily fabricated, and durable. They must also form robust junctions and develop good interfaces with other materials to permit efficient flows of electrical and thermal energy. Among the TE materials of interest for automotive waste heat recovery systems are the skutterudite compounds, which are the antimony-based transition-metal compounds RTE
4
Sb
12
, where R can be an alkali metal (e.g., Na, K), alkaline earth (e.g., Ba), or rare earth (e.g., La, Ce, Yb), and TE can be a transition metal (e.g., Co, Fe). We synthesized a considerable quantity of
n
-type and
p
-type skutterudites, fabricated TE modules, incorporated these modules into a prototype TEG, and tested the TEG on a production General Motors (GM) vehicle. We discuss our progress on skutterudite TE module fabrication and present module performance data for electrical power output under simulated operating conditions for automotive waste heat recovery systems. We also present preliminary durability results on our skutterudite modules.
Background
Peripartum cardiomyopathy (PPCM) is a rare cause of heart failure (HF), presenting with left ventricular (LV) systolic dysfunction either at the end of pregnancy or in the months following ...delivery. In rare cases, PPCM leads to severe impairment of LV function, refractory cardiogenic shock or advanced HF. LV assist devices (LVAD) have been shown to be a feasible treatment option in advanced HF. However, little is known about long‐term outcomes and prognosis of PPCM patients undergoing LVAD implantation.
Methods
A retrospective analysis of data from PPCM patients undergoing LVAD implantation in two tertiary centers with respect to long‐term outcomes was performed.
Results
Twelve patients of median age 30 (18–39) years were included. Eight patients were experiencing cardiogenic shock (INTERMACS 1) at implantation. Seven patients were implanted within 1 month of their PPCM diagnosis. Median duration of LVAD support was 19 (2–92) months with median follow up of 67 (18–136) months (100% complete). In‐hospital and 1‐year mortality were 0% and 8.3%, respectively. Two patients died on LVAD support, four patients were successfully bridged to transplantation, two patients are still on LVAD, and four were successfully weaned due to sufficient LV recovery (one died after LV function deteriorated again).
Conclusion
LVAD treatment of decompensated end‐stage PPCM is feasible. Early LVAD provision led to hemodynamic stabilization in our cohort and facilitated safe LV recovery in one third of these young female patients.
Peripartum cardiomyopathy (PPCM) is a rare cause of heart failure (HF) appearing towards the end of pregnancy or in the months following delivery and seldom leads to refractory cardiogenic shock or advanced HF. We retrospectively analyzed data on PPCM patients undergoing LV assist devices (LVAD) implantation in two tertiary centers. Implantation of LVAD is feasible in PPCM patients – provision of mechanical support led to stabilization of the cardiac situation and facilitated recovery of LV function in one third of these young female patients.
Introduction:
Acute peripartum cardiomyopathy complicated by cardiogenic shock is a rare but life-threatening disease. A prolactin fragment is considered causal for the pathogenesis of peripartum ...cardiomyopathy. This analysis sought to investigate the role of early percutaneous mechanical circulatory support with micro-axial flow-pumps and/or veno-arterial extracorporeal membrane oxygenation in combination with the prolactin inhibitor bromocriptine in refractory cardiogenic shock complicating peripartum cardiomyopathy.
Methods and results:
In this single-centre analysis, five peripartum cardiomyopathy patients with refractory cardiogenic shock received mechanical circulatory support with either Impella CP microaxial pump only (n=2) or in combination with veno-arterial extracorporeal membrane oxygenation (n=3) in the setting of biventricular failure. All patients were mechanically ventilated. In all cases mechanical circulatory support was combined with bromocriptine therapy and early administration of levosimendan. All patients survived the acute phase of refractory cardiogenic shock. Mechanical circulatory support using a micro-axial pump allowed to significantly reduce catecholamine dosage. Remarkably, early left ventricular support with micro-axial flow-pumps resulted in myocardial recovery whereas delayed Impella (mechanical circulatory support) implantation was associated with poor left ventricular recovery.
Conclusion:
Mechanical circulatory support in patients with refractory cardiogenic shock complicating peripartum cardiomyopathy was associated with a 30-day survival of 100% and a favourable outcome. Notably, early left ventricular unloading combined with bromocriptine therapy was associated with left ventricular recovery. Therefore, an immediate transfer to a tertiary hospital experienced in mechanical circulatory support in combination with bromocriptine treatment seems indispensable for successful treatment of peripartum cardiomyopathy complicated by cardiogenic shock.
Left ventricular assist devices (LVAD) are increasingly used in patients with end stage heart failure. The HeartAssist 5 and aVAD LVADs offer telemetric monitoring capabilities. Here we report our ...initial single centre experience with the largest telemonitoring cohort of LVAD patients.
Eleven patients (9 males) received a telemonitoring-capable LVAD and were included in our telemonitoring cohort. Waveforms and alarm data were obtained from the telemonitoring system and hospital records were reviewed for clinical data.
Mean age at LVAD implantation was 59±5.1 years (mean ± standard deviation). Seven patients had non-ischemic cardiomyopathy and 4 patients had ischemic cardiomyopathy. Median LVEF at implant was 16% (IQR, 15-20%). The total follow-up time was 2,438 patient-days. A total of 6,216 alarm messages were generated in 11 patients. Most common were low flow alarms due to hypovolemia, followed by low flow alarms because of suspected pump thrombosis. One patient died during follow-up, one received a cardiac transplant and one had the LVAD explanted because of pump thrombosis. Pump thrombosis was suspected in 5 patients with 8 episodes of sudden flow decreases and laboratory signs of haemolysis.
Real-time telemonitoring of LVAD pump flow, motor speed and power consumption is a promising tool in the follow-up of LVAD recipients. Trending pump flow over hours or days can assist in the early detection of complications, especially flow reductions due to hypovolemia and LVAD thrombosis. Further studies are warranted to delineate the impact of remote monitoring on patients' prognosis.
Left ventricular assist devices (LVAD) are increasingly used in patients with advanced heart failure, and available devices and surgical techniques have strongly evolved over time. Adequate ...recompensation of patients before surgery is important for optimal surgical outcomes. However, patients with terminal heart failure frequently suffer from cardiorenal syndrome, which complicates recompensation by medical means. Here, we report on the use of an Impella 5.5 microaxial pump for supporting a patient with severely decompensated heart failure before LVAD implantation, which resulted in hemodynamic stabilization and effective recompensation prior to surgery.
•Temporary MCS with microaxial pumps unloads heart, lungs and end organs in advanced heart failure and shock.•Temporary MCS helps recompensating patients before LVAD surgery.•The Impella 5.5 offers more than 5 L/min blood flow and thereby serves as a true temporary VAD.•Temporary MCS should be considered early, if recompensation by medical means proves ineffective.
Bi2Te3-Sb2Te3 Superlattices Grown by Nanoalloying König, Jan D.; Winkler, M.; Buller, S. ...
Journal of electronic materials,
05/2011, Letnik:
40, Številka:
5
Journal Article, Conference Proceeding
Recenzirano
In this work, Bi
2
Te
3
-Sb
2
Te
3
superlattices were prepared by the nanoalloying approach. Very thin layers of Bi, Sb, and Te were deposited on cold substrates, rebuilding the crystal structure of ...V
2
VI
3
compounds. Nanoalloyed super- lattices consisting of alternating Bi
2
Te
3
and Sb
2
Te
3
layers were grown with a thickness of 9 nm for the individual layers. The as-grown layers were annealed under different conditions to optimize the thermoelectric parameters. The obtained layers were investigated in their as-grown and annealed states using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive x-ray (EDX) spectroscopy, transmission electron microscopy (TEM), and electrical measurements. A lower limit of the elemental layer thickness was found to have
c
-orientation. Pure nanoalloyed Sb
2
Te
3
layers were
p
-type as expected; however, it was impossible to synthesize
p
-type Bi
2
Te
3
layers. Hence the Bi
2
Te
3
-Sb
2
Te
3
superlattices consisting of alternating
n
- and
p
-type layers showed poor thermoelectric properties.
Presently, the only commercially available power generating thermoelectric (TE) modules are based on bismuth telluride (Bi
2
Te
3
) alloys and are limited to a hot side temperature of 250 °C due to ...the melting point of the solder interconnects and/or generally poor power generation performance above this point. For the purposes of demonstrating a TE generator or TEG with higher temperature capability, we selected skutterudite based materials to carry forward with module fabrication because these materials have adequate TE performance and are mechanically robust. We have previously reported the electrical power output for a 32 couple skutterudite TE module, a module that is type identical to ones used in a high temperature capable TEG prototype. The purpose of this previous work was to establish the expected power output of the modules as a function of varying hot and cold side temperatures. Recent upgrades to the TE module measurement system built at the Fraunhofer Institute for Physical Measurement Techniques allow for the assessment of not only the power output, as previously described, but also the thermal to electrical energy conversion efficiency. Here we report the power output and conversion efficiency of a 32 couple, high temperature skutterudite module at varying applied loading pressures and with different interface materials between the module and the heat source and sink of the test system. We demonstrate a 7% conversion efficiency at the module level when a temperature difference of 460 °C is established. Extrapolated values indicate that 7.5% is achievable when proper thermal interfaces and loading pressures are used.
We describe materials and device preparation of high temperature capable skutterudite based thermoelectric modules and present their conversion efficiency.
Phase relations in Cr
3
S
4
and the substituted system Cr
3
S
4–
x
Se
x
are studied to determine the influence of chemical substitutions on the thermoelectric properties. In addition to the expected ...equilibrium phase crystallizing in the monoclinic space group
I
2/
m
, some samples exhibit a defect phase with Cr
2
S
3
‐like structure. The defect phase can be observed in a few samples prior to sintering, with the majority being phase‐pure Cr
3
S
4
. The defect phase can, however, be introduced in phase‐pure samples through in situ heating. It can be proven that the defect phase has an influence on the thermoelectric properties, by lowering the electrical and thermal conductivity, while increasing the Seebeck coefficient. Substitution in the anion lattice of Cr
3
S
4
with Se lowers the thermal conductivity. The improvement is mainly achieved through a reduction of the electronic contribution to the thermal conductivity, leading to total values as low as 1.6 Wm
−1
K
−1
for the substituted system in comparison to the pristine material 2.3 Wm
−1
K
−1
.
Phase relations in Cr3S4 and the substituted system Cr3S4–x
Se
x
are studied to determine the influence of chemical substitutions on the thermoelectric properties. In addition to the expected ...equilibrium phase crystallizing in the monoclinic space group I2/m, some samples exhibit a defect phase with Cr2S3‐like structure. The defect phase can be observed in a few samples prior to sintering, with the majority being phase‐pure Cr3S4. The defect phase can, however, be introduced in phase‐pure samples through in situ heating. It can be proven that the defect phase has an influence on the thermoelectric properties, by lowering the electrical and thermal conductivity, while increasing the Seebeck coefficient. Substitution in the anion lattice of Cr3S4 with Se lowers the thermal conductivity. The improvement is mainly achieved through a reduction of the electronic contribution to the thermal conductivity, leading to total values as low as 1.6 Wm−1 K−1 for the substituted system in comparison to the pristine material 2.3 Wm−1 K−1.
Herein, phase relations in Cr3S4 and the substituted system Cr3S4–x
Se
x
are studied. A defect phase occurs that exhibits a Cr2S3‐like crystal structure but retains the stoichiometry of Cr3S4. Electrical and thermal conductivities are affected and both are lowered by the inclusion of the defect phase. Anion substitution with Se suppresses the defect phase and lowers the thermal conductivity.
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