Rolf Klemm

Development of an Implantable Pulse Oximeter

A long-term implantable photoplethysmographic sensor system is proposed. The system employs an elastic cuff which is directly wrapped around an arterial blood vessel. The optically transparent cuff is equipped with light emitting diodes and a photo transistor including the technology of pulse oximetry. The sensor will permit real-time, continuous monitoring of important vital parameters such as arterial blood oxygen saturation and pulse rate over a long-term period in vivo. We emphasize on the specific requirements for design and instrumentation of the implantable sensor and discuss first in vitro data acquired with that new photonics-based sensor.

Effect of cannula position in the thoracic aorta with continuous left ventricular support: four-dimensional flow-sensitive magnetic resonance imaging in an in vitro model

OBJECTIVES Left ventricular assist devices (LVADs) have become an important treatment option for heart failure patients. However, altered blood flow patterns are suspected to affect perfusion in the aorta or cause structural changes to the aortic root, leading to regurgitation and valve dysfunction or thrombus formation. The purpose of this study was to evaluate flow patterns in a realistic in vitro model system using four-dimensional flow-sensitive magnetic resonance imaging. METHODS A magnetic resonance compatible model system was developed consisting of an aorta connected to a VAD simulating the pulsatile flow of the native heart. An LVAD was connected to the aorta model via three different cannula positions. Flow patterns in the entire system as well as flow rates in predefined positions for reduced and zero cardiac output were evaluated. RESULTS Cannula position influences flow patterns and flow rates in the entire thoracic aorta. For a residual cardiac output, a larger anastomosis and a decreased flow rate of the LAVD result in a higher flow rate and smaller retrograde flow in the ascending aorta when compared with a smaller anastomosis or a cannula position in the descending aorta. Pronounced flow turbulences in the aorta were observed for the cannula position in the descending aorta. CONCLUSIONS In the setting of reduced cardiac output, as commonly observed in patients on LVAD therapy, a large anastomosis to the ascending aorta for the outflow cannula induces the least-adverse flow patterns in the aortic root. Our approach may aid in a better understanding of LVAD-induced flow-pattern changes. Optimization of the cannula position and anastomosis may help to prevent the progression of aortic valve-regurgitation and thrombus formation.

Neuron-specific enolase correlates to laboratory markers of haemolysis in patients on long-term circulatory support

OBJECTIVES Neuron-specific enolase (NSE) is used as a diagnostic tool in neuropathies, cerebral diseases or traumata and for some tumours. Furthermore, it is also expressed by erythrocytes and platelets and has been linked to haemolysis ex vivo as a laboratory issue. Chronic haemolysis is frequently associated with mechanical circulatory support by ventricular assist device (VAD) or total artificial heart (TAH). Therefore, we compared NSE with indicators of haemolysis in VAD and TAH patients. METHODS We included 599 data sets of 97 patients who underwent VAD or TAH implantation. NSE, haptoglobin (HAPT), haemopexin (HPX), free haemoglobin (frHB), lactate dehydrogenase activity (LDH), platelet counts and total bilirubin (TBIL) in plasma were analysed. Further, all major cerebral events were assessed. RESULTS NSE correlated to frHB (rs = 0.553) and to LDH (rs = 0.695). An inverse correlation was found with HAPT (rs = -0.484) and HPX (rs = -0.398). Thirty-two patients suffered neurological events. Within the time frame of 1 day before to 4 days after a neurological event, correlations of NSE to HAPT (rs = -0.540) and HPX (rs = -0.611) in negative and to frHB (rs = 0.757), LDH (rs = 0.862) and TBIL (rs = 0.549) in positive direction were established (all P < 0.05). Furthermore, haemolysis was graded into three groups for severe, moderate or no or only slight haemolysis. NSE values differed correspondingly between these groups (P < 0.001). CONCLUSION NSE correlates to laboratory parameters indicative of haemolysis in VAD and TAH patients. Our data suggest an influence of intravascular haemolysis on NSE. Therefore, the parameter should be used with caution when it is used to assess cerebral damage.

Biventricular cannulation is superior regarding hemodynamics and organ recovery in patients on biventricular assist device support

BACKGROUND Adequate pump flow is a prerequisite for recovery of end-organ failure and outcome in patients treated with a biventricular assist device (BiVAD). We hypothesized that hemodynamics and organ recovery would improve after biventricular, apical cannulation compared with right atrial cannulation. METHODS Between 2003 and 2009, we treated 31 patients (21 men, 10 women; mean age, of 43 ± 15 years) with a paracorporeal BiVAD (Thoratec BVAD, Pleasanton, CA). In 15 of 31 patients, the inflow cannula of the right VAD (RVAD) was positioned inside the right ventricle (RV) through the RV apex (biapical) instead of the right atrium (conventional). We analyzed pump flow, driving pressure, and vacuum of the Thoratec driving console and recovery of kidney (creatinine, blood urea nitrogen) and liver function (bilirubin). RESULTS Mean duration of BiVAD support was 84 ± 72 days. BiVAD weaning was successful in 4 of 31 patients (13%), 12 underwent cardiac transplantation (39%), and 15 (48%) died. We observed significantly higher pump flow of the LVAD and RVAD in patients after biapical cannulation compared with those with conventional cannulation (LVAD, 5.6 ± 0.4 vs 5.1 ± 0.3 liters/min, p = 0.002; and RVAD: 4.9 ± 0.3 vs 4.2 ± 0.3 liters/min, p < 0.001). This superior circulatory support correlated with faster recovery of kidney function. CONCLUSION Cardiac support with a BiVAD is hemodynamically more effective after biventricular apical cannulation compared with conventional right atrial cannulation. Consequently, higher pump flow results in better end-organ recovery using biapical cannulation.

Short-term heart and lung support: extracorporeal membrane oxygenation and extracorporeal life support

In the last few years, progress in engineering has helped to develop minimized systems for extracorporeal membrane oxygenation and circulatory support. However, despite progress in engineering, the use of these systems still requires a trained team with special skills to be a beneficial and safe tool in the care of critically ill patients. The described indications and proceedings are based on the daily experience of the Freiburg group using these systems both on site in our own hospital and for transport purposes from primary care hospitals into our center of maximum care. The aim of this review is to share our hands-on experience in urgent/emergent implantations and therefore contribute to the knowledge within the growing community of users in this specialized field of extracorporeal support.

Three-dimensional flow characteristics in ventricular assist devices: impact of valve design and operating conditions.

OBJECTIVE The use of paracorporeal ventricular assist devices has become a well-established procedure for patients with cardiogenic shock. However, implantation of ventricular assist devices is often associated with severe complications, such as thrombosis inside the ventricular assist device and subsequent embolic events. It was the purpose of this study to use flow-sensitive 4-dimensional magnetic resonance imaging for a detailed analysis of the 3-dimensional (3D) flow dynamics inside a clinical routine ventricular assist device and to study the effect of different system adjustments and a new valve design on flow patterns. METHODS A routinely used clinical paracorporeal ventricular assist device was integrated into a magnetic resonance-compatible mock loop. Flow-sensitive 3D magnetic resonance imaging was performed to measure time-resolved 3-directional flow velocities (spatial resolution ∼ 1.2 mm, temporal resolution = 42.4 ms) in the entire device under ideal conditions (full fill, full empty, ejection fraction = 88%), insufficient filling (ejection fraction = 81%), and insufficient emptying (ejection fraction = 67%) of the pump chamber. In addition, a new valve design was evaluated. Flexible control and monitoring of pressures at inlet and outlet were used to generate realistic boundary conditions. RESULTS Flow pattern changes for different operating conditions were clearly identified and included reduced velocities during systolic outflow for impaired filling (78% reduction in pump flow compared with optimal operating conditions) and impaired clearing of the pump chamber for insufficient emptying (52% reduction). For all operating conditions, 3D visualization revealed vortex flow inside the ventricular assist device at typical locations of thrombus formation near the valve systems. Most noticeably, the new valve design provided similar global ventricular assist device function (pump flow 3.6 L/min), but vortex formation was eliminated. CONCLUSIONS The results of this study provide insight into the mechanisms underlying possible thrombus formation inside a ventricular assist device and the effect of different system adjustments. The presented methods may permit the optimization of future ventricular assist device systems with respect to optimal flow conditions.

Emergency repair of a broken Jarvik 2000 power connector using a paper-clip.

The power connectors of assist devices that link the controller to the driveline are exposed to extreme mechanical stress, especially if they are implanted for permanent use. We report the case of a successful emergency repair of a power connector of a Jarvik 2000 left ventricular assist device by using a paper-clip in a patient who was supported with the device for >7 years at our institution.

Was der Herzchirurg schon immer über die Herz-Lungen-Maschine wissen wollte

ZusammenfassungDie Herz-Lungen-Maschine (HLM) wurde seit ihrer Einführung stetig weiterentwickelt und modifiziert. Trotz aller technischen Neuerungen und Sicherungseinrichtungen an einer modernen HLM treten während der Perfusion Probleme auf, die ein sofortiges und kompetentes Handeln des Kardiotechnikers und des Chirurgen erfordern. Kontinuierliche Kommunikation sowie gegenseitiges Verständnis zwischen Chirurg und Kardiotechniker sind essenziell und deshalb Voraussetzung für den reibungslosen Ablauf von extrakorporaler Zirkulation (EKZ) und auch Operation. Funktionsprinzip, technische Entwicklungen sowie Probleme von HLM und EKZ werden grundlegend dargestellt und näher betrachtet.AbstractThe extracorporeal circulation (cardiopulmonary bypass, CPB) was first introduced for clinical use in 1953. Since then, CPB has improved significantly in all aspects (including reliability, safety, durability, etc.) due to technical innovations and application of research results into clinical practice. Despite the very high standard of the technical equipment and the safety monitoring devices, perfusion problems still occur and require fast and well-trained actions from both the perfusionist and the surgeon. Communication throughout the procedure, as well as mutual understanding of the needs of perfusionists and surgeons are prerequisites for every cardiac surgery procedure with CPB and are of utmost importance if sudden problems with extracorporeal circulation should come up. This review covers all aspects of CPB, knowledge which should be part of the training program of every cardiac surgeon.

Miniaturized pulse oximeter sensor for continuous vital parameter monitoring

A miniaturized photoplethysmographic sensor system which utilizes the principle of pulse oximetry is presented. The sensor is designed to be implantable and will permit continuous monitoring of important human vital parameters such as arterial blood oxygen saturation as well as pulse rate and shape over a long-term period in vivo. The system employs light emitting diodes and a photo transistor embedded in a transparent elastic cu. which is directly wrapped around an arterial vessel. This paper highlights the specific challenges in design, instrumentation, and electronics associated with that sensor location. In vitro measurements were performed using an artificial circulation system which allows for regulation of the oxygen saturation and pulsatile pumping of whole blood through a section of a domestic pigs arterial vessel. We discuss our experimental results compared to reference CO-oximeter measurements and determine the empirical calibration curve. These results demonstrate the capabilities of the pulse oximeter implant for measurement of a wide range of oxygen saturation levels and pave the way for a continuous and mobile monitoring of high-risk cardiovascular patients.

Implementing and Assessing a Standardized Protocol for Weaning Children Successfully From Extracorporeal Life Support: STANDARDIZED WEANING CHILDREN FROM ECLS

Extracorporeal life support (ECLS) weaning is a complex interdisciplinary process with no clear guidelines. To assess ventricular and pulmonary function as well as hemodynamics including end-organ recovery during ECLS weaning, we developed a standardized weaning protocol. We reviewed our experience 2 years later to assess its feasibility and efficacy. In 2015 we established an inter-professional, standardized, stepwise protocol for weaning from ECLS. If the patient did not require further surgery, weaning was conducted bedside in the intensive care unit (ICU). Most of the weaning procedures are guided via echocardiography. Data acquisition began at baseline level, followed by four-step course (each step lasting 10 min), entailing flow-reduction and ending 30 min after decannulation. Moreover, data from the preprotocol era are presented. Between May 2015 and 2017, 26 consecutive patients (18 male), median age 177 days (2 days-20 years) required ECLS with median support of 4 (2-11) days. Excluding eight not weanable patients, 21 standardized weaning procedures were protocolled in the remaining 18 children. Our generally successful protocol-guided weaning rate (with at least 24-h survival) was 89%, with a discharge home rate of 58%. Practical application of the novel standard protocol seems to facilitate ECLS weaning and to improve its success rate. The protocol can be administered as part of standard bedside ICU assessment.