Thomas Schröder

Electrical impedance tomography in monitoring experimental lung injury

ObjectiveTo apply electrical impedance tomography (EIT) and the new evaluation approach (the functional EIT) in monitoring the development of artificial lung injury.DesignAcute experimental trial.SettingOperating room for animal experimental studies at a university hospital.SubjectsFive pigs (41.3 ± 4.1 kg, mean body weight ± SD).InterventionsThe animals were anaesthetised and mechanically ventilated. Sixteen electrodes were attached on the thoracic circumference and used for electrical current injection and surface voltage measurement. Oleic acid was applied sequentially (total dose 0.05 ml/kg body weight) into the left pulmonary artery to produce selective unilateral lung injury.Measurements and resultsThe presence of lung injury was documented by significant changes of PaCO2 (40.1 mmHg vs control 37.1 mmHg), PaO2 (112.3 mmHg vs 187.5 mmHg), pH (7.35 vs 7.42), mean pulmonary arterial pressure (29.2 mmHg vs 20.8 mmHg) and chest radiography. EIT detected 1) a regional decrease in mean impedance variation over the affected left lung (−41.4% vs control) and an increase over the intact right lung (+ 20.4 % vs control) indicating reduced ventilation of the affected, and a compensatory augmented ventilation of the unaffected lung and 2) a pronounced fall in local baseline electrical impedance over the injured lung (−20.6 % vs control) with a moderate fall over the intact lung (−10.0% vs control) indicating the development of lung oedema in the injured lung with a probable atelectasis formation in the contralateral one.ConclusionThe development of the local impairment of pulmonary ventilation and the formation of lung oedema could be followed by EIT in an experimental model of lung injury. This technique may become a useful tool for monitoring local pulmonary ventilation in intensive care patients suffering from pulmonary disorders associated with regionally reduced ventilation, fluid accumulation and/or cell membrane changes.

Need for Active Left-Ventricular Decompression during Percutaneous Cardiopulmonary Support in Cardiac Arrest

During ventricular fibrillation, myocardial hemodynamic and metabolic effects of percutaneous cardiopulmonary support (PCPS) were analyzed in 11 adult sheep (body weight 77-112 kg). During supported fibrillation, an abrupt increase in left-ventricular pressures with alignment to aortic pressures was observed in 2 animals, which was probably due to spontaneous aortic regurgitation, and resulted in deterioration of coronary perfusion. In 9 animals, left-ventricular pressures rose from 22.9 +/- 4.9 to 31.2 +/- 7.9 mm Hg elevating left ventricular wall stress from 16,750 +/- 8,745 to 28,835 +/- 8,892 dyn/cm2 after 10 min of PCPS-supported fibrillation (mean flow rate 4.5 +/- 0.7 liters/min). Simultaneously, myocardial perfusion pressures decreased from an average of 32.4 +/- 11.7 to 22.3 +/- 9.4 mm Hg and myocardial lactate release was observed. Additional transapical LV venting using a 9-Fr catheter led to a decrease in both LV pressure (to 25.7 +/- 5.3 mm Hg) and wall stress (to 20,612 +/- 7,499 dyn/cm2). Left-ventricular decompression decreased myocardial oxygen consumption (from 5.3 +/- 1.4 to 4.8 +/- 0.9 ml/min.100 g), and reduced myocardial lactate release, which indicates myocardial protection. Protective effects were most pronounced using 12-Fr-, and 21-Fr-venting cannulas (with 21 Fr: decrease in myocardial oxygen consumption to 2.7 +/- 0.6 ml/min.100 g, and reversal of myocardial lactate release to lactate uptake during fibrillation). Conclusions. Hemodynamic and metabolic data clearly demonstrate the deleterious effects of PCPS to the unvented left ventricle during cardiac arrest. The results emphasize the need for active left-ventricular decompression during PCPS in ventricular fibrillation.

A simple method to check the dynamic performance of electrical impedance tomography systems

The test concept as well as the design of a simple resistor phantom suitable for the evaluation of the properties of electrical impedance tomographic (EIT) systems is presented. Input and transfer impedance of the phantom are matched with those of the human thorax. Amplitude of the local impedance variations similar to in vivo conditions (ventilation) can be intentionally set to perform measurements on different states. The theoretical potential differences between the electrodes are calculated. The evaluation procedure is performed in terms of the local amplitude of the relative impedance change as well as the local distribution of noise. The whole procedure can be applied either to compare quantitatively the performance of different EIT data acquisition systems or to determine the amount of measurement disturbance caused by the external electrical environment in clinical settings.

Effects of epinephrine on the myocardial performance and haemodynamics of the isolated rat heart during moderate hypothermia — importance of calcium homeostasis

Controversies exist concerning myocardial performance in hypothermia. We have studied the effects of epinephrine on myocardial function at various calcium concentrations in moderate hypothermia (28 degrees C) and normothermia (37 degrees C) using an isolated antegrade perfused rat heart. The maximum pressure velocity (dP/dt(max)) developed was significantly higher in normothermia compared with hypothermia and was improved by the addition of calcium in both circumstances. Peak negative pressure velocity (dP/dt(min)) was significantly higher at 37 degrees C compared with 28 degrees C, and was increased by the addition of calcium in normothermia; in contrast to hypothermia, in which no change of dP/dt(min) was observed. A reduction in cardiac output and stroke volume by hypercalcaemia was observed in hypothermia. The addition of epinephrine improved dP/dt(max) and dP/dt(min), but had a depressive effect on stroke volume and cardiac output at normal and elevated calcium concentrations. Myocardial efficiency was significantly higher during hypothermia compared with normothermia, but was impaired by epinephrine during hypothermia. The variable or even paradoxical effects of epinephrine suggest the need for careful haemodynamic monitoring and determination of calcium levels in hypothermia. The impairment of myocardial performance may be explained by impaired diastolic relaxation and calcium overload.

Left-Ventricular Unloading by Transvalvular Axial Flow Pumping in Experimental Cardiogenic Shock and during Regional Myocardial Ischemia

The efficacy of the transfemoral left-ventricular assist device Hemopump (HP; 21 Fr outer diameter) was examined in experiments with adult sheep in two different models of cardiogenic shock (tachycardia shock; ischemia shock), and during ventricular fibrillation. During tachycardia (high frequency pacing-induced; n = 14), HP assist led to a significant increase in cardiac output (from 2.2 to 2.8 liters/min), mean aortic pressure (from 47.6 to 65.6 mmHg), and myocardial perfusion pressure (from 25.5 to 59.0 mmHg). Simultaneously, a normalization of body oxygen-uptake (from 1.4 to 2.5 ml/min.kg), a decrease in myocardial oxygen consumption (from 6.1 to 4.8 ml/min.100 g), and a normalization of myocardial lactate metabolism were observed during HP assist. During regional myocardial ischemia (PTCA balloon occlusion of the proximal LAD (3.5 min; n = 12), HP assist led to significant decrease in LV end-diastolic pressure (from 21.1 to 12.1 mmHg), and increase in diastolic aortic pressure (from 58 to 67 mmHg) resulting in significant increase in coronary perfusion pressure. In the early reperfusion period, myocardial release of both lactate and potassium was significantly lowered with HP assist. During ventricular fibrillation (induced by electrical stimulation; n = 9), HP flow rates decreased from 2.5 (after 10 min) to 2.1 liters/min (after 30 min). Mean aortic pressures simultaneously decreased from 64.0 to 54.6 mmHg. Perfusion conditions were sufficient for maintenance of aerobic myocardial metabolism, but were borderline for peripheral circulation. Our hemodynamic and metabolic data demonstrate beneficial effects of cardiac assist with the Hemopump 21 Fr in both tachycardia-induced severe cardiogenic shock and during acute regional myocardial ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Risk of left ventricular loading during percutaneous cardiopulmonary support in cardiac arrest

BackgroundRecently, circulatory assistance with the Hemopump (Johnson and Johnson Interventional Systems, Warren, NJ) and percutaneous cardiopulmonary support (pCPS) devices has been applied in the clinical setting. Because both of these systems work independently of mechanical and electrical heart function, the spectrum of their clinical application could be broader than that of intra-aortic balloon pulsation. MethodsIn a study of 10 sheep with a mean body weight of 97 kg, the effect of pCPS on the coronary circulation was quantified during cardiac arrest and after ventricular fibrillation was induced. ResultsPercutaneous cardiopulmonary support stabilized the hemodynamics adequately (pump rate of about 4.5 L/min; aortic pressure of about 50 mm Hg) and provided sufficient coronary circulation (arteriocoronary-venous difference in lactate [acvdiactate] in the range of +0.1 mmol/L when the left ventricular pressure was low, as during cardiac arrest. However, in sheep in ventricular fibrillation we found spontaneous increases in left ventricular pressure that occurred sometimes slowly (n=7; mean left ventricular pressure 36 ± 1.1 mm Hg), sometimes rapidly (n=2), and led to an alignment of left ventricular and aortic pressure. During left ventricular loading the coronary circulation deteriorated and myocardial metabolism switched to anaerobic pathways (acvdlactale in the range of −0.5 mmol/L). Moreover, in some cases (n=4) a parallel rise in pulmonary pressure (in the range of 34 to 46 mm Hg) occurred that resulted in serious damage to the lung. ConclusionsIn summary, left ventricular function should be carefully monitored during pCPS in cardiac arrest. The monitoring of pulmonary capillary wedge pressure is of limited value for estimating the left ventricular pressure load: in most of the animals in this study there was no parallel increase in pulmonary pressure. We conclude that catheter techniques for support of the left ventricular or pulmonary circulation could be considered a valid treatment alternative.

Effect of the Hemopump in cardiogenic shock and in the early stage of regional myocardial ischemia

Currently available left-heart bypass systems are exceedingly elaborate with regard to both implantation and handling (17). Thus, in patients with cardiogenic shock, these systems are not routinely used, with the exception of occasional postcardiotomy and bridging to transplant-applications (6). Up to now, only intraaortic balloon counter-pulsation (IABP) has gained major clinical relevance in treatment of patients with cardiogenic shock (6,12). Counterpulsation leads to an improvement of cardiac energy balance, reducing left-ventricular (LV) pressure load and increasing coronary perfusion pressure. However, with this technique clinical improvement depends on residual left-ventricular function, and many patients who have ventricular failure refractory to IABP require a more complete form of mechanical support.

Left-ventricular unloading by transvalvular axial flow pumping in experimental cardiogenic shock and during regional myocardial ischemia

The efficacy of the transfemoral left-ventricular assist device Hemopump (HP; 21 Fr outer diameter) was examined in experiments with adult sheep in two different models of cardiogenic shock (tachycardia shock; ischemia shock), and during ventricular fibrillation. During tachycardia (high frequency pacing-induced; n = 14), HP assist led to a significant increase in cardiac output (from 2.2 to 2.8 liters/min), mean aortic pressure (from 47.6 to 65.6 mmHg), and myocardial perfusion pressure (from 25.5 to 59.0 mmHg). Simultaneously, a normalization of body oxygen-uptake (from 1.4 to 2.5 ml/min.kg), a decrease in myocardial oxygen consumption (from 6.1 to 4.8 ml/min.100 g), and a normalization of myocardial lactate metabolism were observed during HP assist. During regional myocardial ischemia (PTCA balloon occlusion of the proximal LAD (3.5 min; n = 12), HP assist led to significant decrease in LV end-diastolic pressure (from 21.1 to 12.1 mmHg), and increase in diastolic aortic pressure (from 58 to 67 mmHg) resulting in significant increase in coronary perfusion pressure. In the early reperfusion period, myocardial release of both lactate and potassium was significantly lowered with HP assist. During ventricular fibrillation (induced by electrical stimulation; n = 9), HP flow rates decreased from 2.5 (after 10 min) to 2.1 liters/min (after 30 min). Mean aortic pressures simultaneously decreased from 64.0 to 54.6 mmHg. Perfusion conditions were sufficient for maintenance of aerobic myocardial metabolism, but were borderline for peripheral circulation. Our hemodynamic and metabolic data demonstrate beneficial effects of cardiac assist with the Hemopump 21 Fr in both tachycardia-induced severe cardiogenic shock and during acute regional myocardial ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)