Browsing by Author "Hellige, Gerhard"

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 marched 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.

Background and aim of the study: The study aim was to investigate whether: (i) by detection of changing acoustic sound phenomena, minimal changes in prosthetic valve function may be detected earlier than with echocardiography, invasive diagnosis or clinically; (ii) patients can record and pass on signals with a high level of reproducibility from any location via the Internet; and (iii) clinical data evaluation permits conclusions to be drawn on changes in the functional state of a prosthetic replacement valve. Methods: Simulation studies were carried out using a mock circulation device. Aortic valve replacement (AVR) using extracorporeal circulation was performed in pigs, valve function was artificially disturbed, and valve sounds were recorded. Patients were equipped with briefcase-like devices to record their valve sounds after AVR and to transfer them via the Internet. Results: Simulation studies produced a typical sound spectrum for each tested valve that remained constant under variable conditions. Experiments in animals proved that minimal changes in prosthetic valve function led to a significant change in the sound phenomena. The degree of sensitivity was significantly greater than that in echocardiographic control experiments. All patients in the clinical study regularly recorded and passed on their signals. Surveys revealed high acceptance and easy handling of the compiled devices. Valve dysfunctions were not detected. Conclusion: On-line registration of acoustic sound phenomena and ECG seems suited to detect minimal changes in prosthetic function. In particular, the registration of flow, acoustics and ECG envisaged at the next level opens up diverse potential applications for Internet-based, remote monitoring of patients following cardiac surgery or cardiologic treatment.

Background and objective: Propofol may cause undesirable hypotension due to vasodilation. The underlying mechanisms are not completely understood. We investigated the mechanisms by which propofol relaxes vascular segments. Methods: We studied the effect of propofol on isolated porcine coronary artery rings precontracted with potassium chloride or prostaglandin F-2alpha. Results: Propofol, in a concentration-dependent manner, relaxed all segments at concentrations of 5 mug mL(-1) and above. This relaxation was unaltered in the presence of N-omega-nitro-L-arginine, indomethacin, diltiazem and glibenclamide. Tetraethylammonium chloride, an inhibitor of the BKCa K+ channel (a high conductance Ca2+-sensitive K+ channel), dose-dependently attenuated the vasodilating effect of propofol (P<0.001). Conclusions: Our results suggests that the activation of the BKCa channel may contribute to the vasodilating effect of propofol, hereby causing hyperpolarization of the smooth muscle membrane and reduction of smooth muscle tone.

Myoglobin is known to become nephrotoxic when released in greater amounts from skeletal muscle into the general circulation during shock. The present study deals with the question as to whether a myoglobin-induced increase in vascular tone additionally contributes to the detrimental role of this protein in hypovolemic shock. Anesthetized rats were subjected to 250 mg(.)kg(-1.)h(-1) myoglobin infused i.v.. during hemorrhagic hypotension of 50 mmHg. Shock survival time was measured, as were blood flow and vascular resistance in kidney, intestine, brain, and heart, using the microsphere method. Rats subjected to only myoglobin or hemorrhage survived a period of >120 min; in contrast, rats, exposed to both myoglobin and hemorrhage died at 68 9 min. When the animals subjected to only hemorrhage and to myoglobin/hemorrhage were compared, significantly lower values were found in the latter group with respect to blood flow in the kidney (1.7 +/- 0.1 vs. 0.2 +/- 0.05 ml(.)min(-1.)g(-1)), small intestine (1.0 +/- 0.1 vs. 0.5 +/- 0.1 ml(.)min(-1.)g(-1)), cardiac output (112 +/- 5 vs. 62 +/- 10 ml(-1.)min(-1.)kg(-1)), and significantly higher values of total peripheral vascular resistance (0.45 +/- 0.02 vs. 0.81 +/- 0.12 mmHg(.)min(.)ml(-1.)kg) at 50 min of hypotension. It is assumed that these effects of myoglobin are induced by its ability to scavenge endogenous nitric oxide, because a modified, non-nitrosylable myoglobin was unable to induce such effects. The results support the view that a pathological release of myoglobin into the general circulation causes increases in vascular resistance of vital organs that may contribute to decompensation of tissue supply when occurring in hypovolemic shock.

The aim of the study was to validate the ability of electrical impedance tomography (EIT) to detect local changes in air content, resulting from modified ventilator settings, by comparing EIT findings with electron beam computed tomography (EBCT) scans obtained under identical steady-state conditions. The experiments were carried out on six anesthetized supine pigs ventilated with five tidal volumes (VT) at three positive end-expiratory pressure (PEEP) levels. The lung air content changes were determined both by EIT (Goe-MF1 system) and EBCT (Imatron C-150XP scanner) in six regions of interest, located in the ventral, middle, and dorsal areas of each lung, with respect to the reference air content at the lowest VT and PEEP, as a change in either local electrical impedance or lung tissue density. An increase in local air content with VT and PEEP was identified by both methods at all regions studied. A good correlation between the changes in lung air content determined by EIT and EBCT was revealed. Mean correlation coefficients in the ventral, middle, and dorsal regions were 0.81, 0.87, and 0.93, respectively. The study confirms that EIT is a suitable, noninvasive method for detecting regional changes in air content and monitoring local effects of artificial ventilation.

We investigated five different methods which can be applied to quantitatively construct functional tomograms of the lungs. The focus was on the sensitivity of functional tomograms to errors in acquired data. To quantify this sensitivity, theoretical, error-free data sets of well-known properties were artificially generated based on a 'living thorax model'. Physiological time courses and a typical distribution of errors caused by a typical Goe-MF II EIT system were used for the calculations which encompassed a range up to 50 times greater than the initial error level (4 mu V(rms max)-400 mu V(rms max)). Additionally, low-pass filtering and principal component analysis (PCA) were used to quantify the effect of preprocessing the raw data. The results demonstrate that all methods based on fitting the local to the global time course were superior to the common functional tomograms utilizing standard deviation or maximum and minimum detection. Ventilation distribution was best quantified by the so-called VT methods. Filling capacity-a lung tissue property-was least dependent on increasing error levels. The errors introduced by filtering are significant with respect to a quantitative analysis of ventilation distribution. A preprocessing of raw data by applying a PCA performed well on the data sets which had been constructed but were, nonetheless, realistic. This approach appears to be highly promising for application on real data which is known to be erroneous.

Objective: The aim of our study was to determine the effect of the irregular spontaneous breathing pattern and posture on the spatial distribution of ventilation in neonates free from respiratory disease by the non-invasive imaging method of electrical impedance tomography (EIT). Scanning of spontaneously breathing neonates is the prerequisite for later routine application of EIT in babies with lung pathology undergoing ventilator therapy. Design: Prospective study. Setting: Neonatal intensive care unit at a university hospital. Patients: Twelve pre-term and term neonates (mean age: 23 days; mean body weight: 2,465 g; mean gestational age: 34 weeks; mean birth weight: 2,040 g). Interventions: Change in body position in the sequence: supine, right lateral, prone, supine. Measurements and results: EIT measurements were performed using the Gottingen GoeMF I system. EIT scans of regional lung ventilation showing the distribution of respired air in the chest cross-section were generated during phases of rapid tidal breathing and deep breaths. During tidal breathing, 54.5+/-8.3%, 55.2+/-10.5%, 59.9+/-8.4% and 54.2+/-8.5% of inspired air (mean values +/- SD) were directed into the right lung in the supine, right lateral, prone and repeated supine postures respectively. During deep inspirations, the right lung ventilation accounted for 52.6+/-7.9%, 68.5+/-8.5%, 55.4+/-8.2% and 50.5+/-6.6% of total ventilation respectively. Conclusion: The study identified the significant effect of breathing pattern and posture on the spatial distribution of lung ventilation in spontaneously breathing neonates. The results demonstrate that changes in regional ventilation can easily be determined by EIT and bode well for the future use of this method in paediatric intensive care.

To determine the effect of age and posture on regional lung ventilation, eight young (26 +/- 1 years, mean +/- S.D.) and eight old (73 +/- 5 years) healthy men were studied by electrical impedance tomography in four body positions (sitting, supine, right and left lateral). The distribution of gas into the right and left lung regions was determined in the chest cross-section during tidal breathing at the resting lung volume, near residual volume and total lung capacity, as well as forced and slow vital capacity maneuvers. In the young, significant posture-dependent changes in gas distribution occurred during resting tidal breathing whereas they were absent in the elderly. In the older subjects, the contribution of the right lung to global ventilation fell with the transition from sitting to supine posture during both full expiration maneuvers. During forced vital capacity, the high flow rate and early airway closure in the dependent lung, occurring at higher volumes in the elderly, minimized the posture-dependency in gas distribution which was present during the slow maneuver. Our study revealed the significant effect of age on posture-dependent changes in ventilation distribution. (C) 2004 Elsevier B.V. All rights reserved.

The aim of this study was to elucidate the influence of four neuromuscular blocking substances on coronary vascular tone using the model of isolated porcine coronary artery segments. We studied the effects of four muscle relaxants, atracurium, pancuronium, rocuronium, and vecuronium (0.1, 1, and 10 mu g mL(-1) each), on the contractile response to three vasoconstrictors: acetylcholine, histamine, and serotonin. None of the neuromuscular blocking agents under investigation exerted a significant influence on the vasoconstricting effects of these mediators except for pancuronium, which dose-dependently attenuated acetylcholine-mediated contractions (-10.8% attenuation far 10 mu g mL(-1) pancuronium, P < 0.05). There was no difference between vessels with intact endothelium and denuded preparations. It is concluded that high-dose pancuronium exerts an antimuscarinic effect in vascular smooth muscle. The other neuromuscular agents studied do not alter vascular reactivity of isolated porcine coronary arteries.

The aim of our study was to check the effect of varying blood volume in the chest and gravity on the distribution of ventilation and aeration in the lungs. The change in intrathoracic blood volume was elicited by application of lower body negative pressure (LBNP) of -50 cmH(2)O. The variation of gravity in terms of hypogravity (similar to 0g) and hypergravity (similar to 2g) was induced by changes in vertical acceleration achieved during parabolic flights. Local ventilation magnitude and end-expiratory lung volume were determined in eight human subjects in the ventral and dorsal lung regions within a transverse cross-section of the lower chest by electrical impedance tomography. The subjects were studied in a 20 degrees head-down tilted supine body position during tidal breathing and full forced expirations. During tidal breathing, a significant effect of gravity on local magnitude of ventilation and end-expiratory lung volume was detected in the dorsal lung regions both with and without LBNP. In the ventral regions, this gravity dependency was only observed during LBNP. During forced expiration, LBNP had almost no effect on local ventilation and end-expiratory lung volume in either lung region. Gravity significantly influenced the end-expiratory lung volumes in dorsal lung regions. The results indicate that exposure to LBNP exerts a less appreciable effect on regional lung ventilation than the acute changes in gravity.

The development of the mammalian heart is characterized by substantial changes in myocardial performance. We studied the ontogeny of myocardial function with and without various inotropic interventions in the developing isolated, antegrade-perfused rabbit heart (2d, 8d, 14d, 28d, n = 96). Myocardial function was related to the protein expression of the sarcolemmal Na+-Ca2+ exchanger and to the sarcoplasmic Ca2+-ATPase. In neonatal hearts an age-dependent increase in maximal developed pressure velocity (dP/dt(max)) by 45% and peak negative pressure velocity (dP/ dt(min)) by 75 % within days 2 to 8 were observed. In response to inotropic intervention with isoproterenol, ouabain, calcium and the Na+-channel modulator BDF 9148, dP/dt(max) and dP/dt(min) increased in a concentration dependent manner. Significant differences between neonatal, juvenile and adult hearts could be demonstrated in a repeated measurement ANOVA model on the concentration-response curves for BDF 9148 (dP/dt(max) and dP/dt(min)), ouabain (dP/dt(min)) and calcium (dP/dt(min)), but not for isoproterenol. At the maximum isoproterenol concentration of 1 mumol/l, the increase in dP/dt(max) and dP/dt(min) was significantly higher in adult compared to neonatal hearts (t-test, p < 0.01). The significant decline of the Na+-Ca2+ exchanger protein expression from neonatal (1822 +/- 171) to adult hearts (411 +/- 96 S.E.M. [units per 20 mug protein], p < 0.01) was related to an increase in myocardial function (dP/dt(max) r = 0.63, p < 0.01, dP/dt(min) r = 0.62, p < 0.01). Contractility, relaxation and the observed positive inotropic effects were in general significantly lower in neonatal compared to adult hearts. In the individual heart an increase in contractility and relaxation was related to a decrease in Na+-Ca2+ exchanger expression.

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 degreesC) and normothermia (37 degreesC) 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 degreesC compared with 28 degreesC, and was increased by the addition of calcium in nor-mothermia: 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. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.

Objective: The aim of the study was to investigate the effect of lung volume changes on end-expiratory lung impedance change (ELIC) in mechanically ventilated patients, since we hypothesized that ELIC may be a suitable parameter to monitor lung volume change at the bedside. Design: Clinical trial on patients requiring mechanical ventilation. Settings: Intensive care units of a university hospital. Patients: Ten mechanically ventilated patients were included in the study. Intervention Patients were ventilated in volume-controlled mode with constant flow and respiratory rate. In order to induce changes in the end-expiratory lung volume (EELV), PEEP levels were increased from 0 mbar to 5 mbar, 10 mbar, and 15 mbar. At each PEEP level EELV was measured by an open-circuit nitrogen washout manoeuvre and ELIC was measured simultaneously using Electrical Impedance Tomography (EIT) with sixteen electrodes placed on the circumference of the thorax and connected with an EIT device. Cross-sectional electro-tomographic measurements of the thorax were performed at each PEEP level, and a modified Sheffield back-projection was used to reconstruct images of the lung impedance. ELIC was calculated as the average of the end-expiratory lung impedance change. Results: Increasing PEEP stepwise from 0 mbar to 15 mbar resulted in an linear increase of EELV and ELIC according to the equation: y =0.98 x -0.68, r(2) =0.95. Conclusion: EIT is a simple bedside technique which enables monitor lung volume changes during ventilatory manoeuvres such as PEEP changes.

To investigate the localization of the earliest damage in ischemic and ischemic-reperfused myocardium, anesthetized rats were subjected to coronary occlusion for 15, 30, 45, or 90 min. One-half of the animals in each group had no reperfusion, whereas the other half was reperfused for 14 min. With the use of histological methods, preferentially in the periphery of the area at risk, localized zones were detected that lacked the hypoxia-specific increase in NADH fluorescence. The extent of these areas displaying injured tissue was found to be significantly smaller in the ischemic-nonreperfused hearts than in the ischemic-reperfused organs (15-min ischemia: 0.22 +/- 0.12% vs. 43.0 +/- 5.0%; 30-min ischemia: 5.7 +/- 2.7% vs. 64.6 +/- 2.9%; 45- min ischemia: 5.6 +/- 1.2% vs. 66.0 +/- 7.5%; 90-min ischemia: 39.3 +/- 5.5% vs. 86.7 +/- 1.8% of the area at risk). The results point to a localized initiation of the damage close to the surrounding oxygen-supplied tissue during ischemia and an expansion of this injury by intercellular actions into yet-intact areas upon reperfusion.

Background: Neonatal hearts are less susceptible to developing myocardial dysfunction after hypoxia and/or ischemia than adult hearts. Differences in intracellular calcium homeostasis may be responsible for reduced calcium overload of the immature myocardium leading to the observed protection against ischemia. Objective: To assess differences in baseline and post-ischemic gene expression of calcium handling proteins after ischemia in neonatal and adult rabbit hearts. Methods: We used isolated antegrade perfused rabbit hearts (age 2 days, 28 days, n = 32), which were exposed to ischemia and hypothermia simulating myocardial stunning comparable to neonatal asphyxia. Gene and protein expression of the sodium-calcium exchanger (NCX), the sarco-endoplasmatic reticulum Ca(2+)-ATPase 2a (SERCA) and calsequestrin (CSQ) were measured using quantitative real-time PCR and Western blotting. Results: After ischemia and reperfusion in neonatal and adult hearts, a significant decrease in myocardial performance was re-corded. At the mRNA level, significant differences in the baseline expression of NCX, SERCA and CSQ between neonatal and adult hearts were observed. In neonatal post-ischemic hearts, NCX and CSQ expression were significantly higher at the mRNA level than in controls. In contrast, SERCA expression remained unchanged in neonatal hearts and decreased in adult hearts compared to the non-ischemic controls. Conclusion: These findings suggest that changes in gene expression of calcium handling proteins may be involved in the different susceptibility of neonatal compared to adult hearts to developing myocardial dysfunction after ischemia. Copyright (c) 2006 S. Karger AG, Basel.

Gravity-dependent changes of regional lung function were studied during normogravity, hypergravity, and microgravity induced by parabolic flights. Seven healthy subjects were followed in the right lateral and supine postures during tidal breathing, forced vital capacity, and slow expiratory vital capacity maneuvers. Regional 1) lung ventilation, 2) lung volumes, and 3) lung emptying behavior were studied in a transverse thoracic plane by functional electrical impedance tomography (EIT). The results showed gravity-dependent changes of regional lung ventilation parameters. A significant effect of gravity on regional functional residual capacity with a rapid lung volume redistribution during the gravity transition phases was established. The most homogeneous functional residual capacity distribution was found at microgravity. During vital capacity and forced vital capacity in the right lateral posture, the decrease in lung volume on expiration was larger in the right lung region at all gravity phases. During tidal breathing, the differences in ventilation magnitudes between the right and left lung regions were not significant in either posture or gravity phase. A significant nonlinearity of lung emptying was determined at normogravity and hypergravity. The pattern of lung emptying was homogeneous during microgravity.