1,721,012 research outputs found
Comment on Borges et al. "Regional lung perfusion estimated by electrical impedance tomography in a piglet model of lung collapse"
No full text
Cardiac-related impedance changes obtained by electrical impedance tomography: an acceptable parameter for assessment of pulmonary perfusion?
No full textHow absolute EIT reflects the dependence of unilateral lung aeration on hyper-gravity and weightlessness?
No full textWe studied the influence of three gravity levels (0, 1 and 1.8 g) on unilateral lung aeration in a left lateral position by the application of absolute electrical impedance tomography. The electrical resistivity of the lung tissue was considered to be a meaningful indicator for lung aeration since changes in resistivity have already been validated in other studies to be proportional to changes in lung volume. Twenty-two healthy volunteers were studied during parabolic flights with three phases of different gravity, each lasting similar to 20-22 s. Spontaneous breathing at normal tidal volume V-T and at increased V-T was performed. During transition to hyper-gravity mean expiratory resistivities (+/- SD in Omega m) increased at normal V-T in the upper (right) lung from 7.6 +/- 1.5 to 8.0 +/- 1.7 and decreased from 5.8 +/- 1.2 to 5.7 +/- 1.2 in the lower ( left) lung. Inspiratory resistivity values are 8.3 +/- 1.6 to 8.8 +/- 1.8 (right) and 6.3 +/- 1.3 to 6.0 +/- 1.3 (left). At increased V-T, the changes in resistivities at end-expiration were 7.7 +/- 1.5 to 8.0 +/- 1.7 (right) and 5.8 +/- 1.2 to 5.7 +/- 1.2 (left). Corresponding end-inspiratory values are 9.9 +/- 1.9 to 10.0 +/- 2.0 (right) and 8.6 +/- 2.1 to 7.9 +/- 2.0 (left). During weightlessness, the distortion in the lungs disappeared and both lungs showed a nearly identical aeration, which was between the levels displayed at normal gravity. The small increase in resistivity for the upper lung during transition to hyper-gravity from 1 to 1.8 g at increased V-T suggests that the degressive part of the pressure-volume curve has already been reached at end-inspiration. The results for a left lateral position are in agreement with West's lung model which has been introduced for cranio-caudal gravity dependence in the lungs
Propofol and thiopental attenuate the contractile response to vasoconstrictors in human and porcine coronary artery segments
No full textThe effects of propofol and thiopental on three vasoconstrictors, acetylcholine, histamine, and serotonin were studied in isolated porcine and human coronary artery rings. Propofol and thiopental attenuated the contractile response to all mediators in a dose-dependent manner. This dilating effect was fairly weak using low concentrations (propofol 1 mu g mL(-1) and 10 mu g mL(-1), thiopental 5 mu g mL(-1) and 10 mu g mL(-1)). In the presence of high concentrations (propofol 100 mu g mL(-1), thiopental 50 mu g mL(-1)) marked relaxation was observed (propofol -32% up to -49%, P < 0.05; thiopental -23% up to -67%, P < 0.05). These dilating effects were seen both in intact and denuded rings, the differences were not significant. Human coronary artery segments were relaxed by thiopental (-22% to -76%) and propofol (-11% to -67%) to a similar extent. Our data indicate that propofol and thiopental relax isolated coronary segments in a dose-dependent manner, and that there is no evidence that these effects are dependent of endothelial factors
Ketamine attenuates the contractile response to vasoconstrictors in isolated coronary artery rings
No full textObjective: Ketamine was shown to increase coronary blood flow. It was the aim of this study to answer the question whether ketamine directly dilates coronary arteries. Methods: Using the model of isolated vessel rings we studied the effects of ketamine (2.5, 25, and 250 mug ml(-1)) on the contractile response to three vasoconstrictors, acetylcholine, histamine, and serotonin in porcine coronary artery segments. Other rings were contracted with KCl or PGF(2a) and then treated with ketamine (5 up to 500 mug ml(-1) added cumulatively). Results: Ketamine dose-dependently dilated coronary arteries in concentrations beyond those used in clinical practice. In intact rings ketamine racemate (250 mug ml(-1)) attenuated contractions mediated by acetylcholine by 38.8 +/- 2.8%, histamine by 33.0 +/- 4.4% and serotonin by 42.1 +/- 3.7% (p < 0.05). There were no differences between intact and denuded rings (acetylcholine 38.5 +/- 2.8%, histamine 26.6 +/- 4.7%, serotonin 30.0 +/- 3.2%). With low concentrations of ketamine (2.5 mug ml(-1)) a slight tendency towards a contraction was recorded (n.s.). In rings precontracted with either KCl or PGF(2a) ketamine caused a small enhancement of contraction (KCl: 101.4 +/- 0.4%, PGF(2a): 101.3 +/- 1.4%) when administered in low concentration (5 mug ml(-1)), but almost complete relaxation (KCl: 0.4 +/- 1.3%, PGF(2): 0.0 +/- 5.4%) in high concentration (500 mug ml(-1)). Conclusions: it is concluded that ketamine dose-dependently dilates porcine coronary arteries in concentrations beyond those used in clinical practice and that this effect is independent of endothelial function
Activation of the K+ channel BKCa is involved in the relaxing effect of propofol on coronary arteries
No full textBackground 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
Improvements in the image quality of ventilatory tomograms by electrical impedance tomography
No full textWe present an improved approach to image ventilation in functional electrical impedance tomography (f-EIT). It combines the advantages of the two established procedures of calculating standard deviation as a functional parameter of ventilation (SD method) and the so-called filling capacity (FC method). The SD method quantifies the local impedance variation over a series of tomograms for each pixel; the FC method is based on the slope of a linear fit of regional versus the global impedance change. Tidal volume V(T) is displayed linearly by the SD method in f-EIT; it is, however, sensitive to noisy data. The FC method is much more robust with respect to noise but does not display the tidal volume VT. We combined the advantages of both techniques in a new VT method which is based on raw data. It saves computing time and is suitable for both f-EIT and absolute EIT (a-EIT). We separated the raw data into two representative sets: end expiratory and end inspiratory. This was accomplished by calculating the global time course of the relative impedance changes from the raw data. In this time course, we determined all frame numbers (indices) of end expiration and end inspiration. These frame numbers were used to calculate one mean expiratory and one mean inspiratory raw data frame. Reconstruction by difference imaging directly reflects the mean tidal volume V(T) during the acquired frame series. The effect of the improvement by the VT method was investigated at different noise levels by adding artificial noise from 0 to 100 mu V(rms) to a real raw dataset. The robustness with regard to noise of the VT method was similar to that of the FC method. The practical value of suppression of non-ventilatory impedance changes, artefacts and noise was tested by studying ten healthy subjects (four females, six males) during normal breathing. We found a highly significant improvement in the image quality (p < 0.001) of ventilation for this group of volunteers
Impedance analyser module for EIT and spectroscopy using undersampling
No full textIn this paper we present the concept, the design and the test procedure for a DSP-based high-precision and high-performance wide-band (up to 10 MHz) bioimpedance analyser module for application in EIT or bioimpedance spectroscopy. The module implements a digital concept with appropriate signal conditioning hardware for voltage and current measurement, early signal digitization and subsequent digital signal processing in order to calculate the components of impedance (or admittance). At low frequencies, the module utilizes the conventional direct conversion method, whereas at high frequencies the undersampling technique is used. The advantages of the described system are the following: (a) the frequency range is extended to higher frequencies, (b) the number of data sampled per time interval is significantly reduced, and (c) the current consumption and the costs of the ADCs can be significantly reduced. The validation procedure is per-formed by comparing the measured and theoretical values of the magnitude and the phase of the impedance for a commonly used tissue model. The module offers an accuracy of better than 0.012% for the magnitude of impedance and better than 0.02 degrees for the phase
Ketamine attenuates the contractile response to vasoconstrictors in isolated coronary artery rings
No full textObjective: Ketamine was shown to increase coronary blood flow. It was the aim of this study to answer the question whether ketamine directly dilates coronary arteries. Methods: Using the model of isolated vessel rings we studied the effects of ketamine (2.5, 25, and 250 mug ml(-1)) on the contractile response to three vasoconstrictors, acetylcholine, histamine, and serotonin in porcine coronary artery segments. Other rings were contracted with KCl or PGF(2a) and then treated with ketamine (5 up to 500 mug ml(-1) added cumulatively). Results: Ketamine dose-dependently dilated coronary arteries in concentrations beyond those used in clinical practice. In intact rings ketamine racemate (250 mug ml(-1)) attenuated contractions mediated by acetylcholine by 38.8 +/- 2.8%, histamine by 33.0 +/- 4.4% and serotonin by 42.1 +/- 3.7% (p < 0.05). There were no differences between intact and denuded rings (acetylcholine 38.5 +/- 2.8%, histamine 26.6 +/- 4.7%, serotonin 30.0 +/- 3.2%). With low concentrations of ketamine (2.5 mug ml(-1)) a slight tendency towards a contraction was recorded (n.s.). In rings precontracted with either KCl or PGF(2a) ketamine caused a small enhancement of contraction (KCl: 101.4 +/- 0.4%, PGF(2a): 101.3 +/- 1.4%) when administered in low concentration (5 mug ml(-1)), but almost complete relaxation (KCl: 0.4 +/- 1.3%, PGF(2): 0.0 +/- 5.4%) in high concentration (500 mug ml(-1)). Conclusions: it is concluded that ketamine dose-dependently dilates porcine coronary arteries in concentrations beyond those used in clinical practice and that this effect is independent of endothelial function
- …
