Deep inspiration leads to sympathetically mediated vasoconstriction at the fingertip. This so-called inspiratory gasp
response (IGR) is usually assessed by laser Doppler fluxmetry (LDF) and provides interesting information on the activity
of the sympathetic nervous system. In this study we investigated if simple maneuvers which affect microcirculation have
an effect on the IGR. For this we detected IGR with LDF in rest, after elevation of the arm to lower capillary filling, after
venous congestion to increase capillary filling, and after heating up in warm water to induce vasodilation. Capillary
filling was monitored with the Erlangen Microlightguide Spectrophotometer (EMPHO) by determination of the relative
hemoglobin concentration. We found that IGR was not affected by microcirculatory starting conditions. Therefore, we
conclude that diagnostic results of the IGR are not influenced by different capillary filling levels.
This study compares ear photoplethysmography (PPG) and electrocardiogram (ECG) in providing accurate heart beat intervals for use in calculations of heart rate variability (HRV, from ECG) or of pulse rate variability (PRV, from PPG) respectively. Simultaneous measurements were taken from 44 healthy subjects at rest during spontaneous breathing and during forced metronomic breathing (6/min). Under both conditions, highly significant (p > 0.001) correlations (1.0 > r > 0.97) were found between all evaluated common HRV and PRV parameters. However, under both conditions the PRV parameters were higher than HRV. In addition, we calculated the limits of agreement according to Bland and Altman between both techniques and found good agreement (< 10% difference) for heart rate and standard deviation of normal-to-normal intervals (SDNN), but only moderate (10-20%) or even insufficient (> 20%) agreement for other standard HRV and PRV parameters. Thus, PRV data seem to be acceptable for screening purposes but, at least at this state of knowledge, not for medical decision making. However, further studies are needed before more certain determination can be made.
Laser Doppler fluxmetry (LDF) or photopletysmography (PPG) are frequently used as non-invasive tools for the detection of the so-called “inspiratory gasp response” (IGR), a vasoconstrictive episode provoked by a voluntary deep inspiration. According to our knowledge, a rigorous comparison of both methods has not been reported in the literature. Therefore, the aim of the study was to compare the detection of IGR with LDF and PPG. We investigated 14 young and healthy volunteers. A PPG and a LDF probe were applied to adjacent fingertips of the dominant hand (thumb/index finger). After baseline measurements the subjects were asked to perform a deep inspiration with time intervals of 90 sec., 60 sec., 30 sec., and 15 sec. We found that both methods are useful to detect individual IGR. However, overall correlation of IGR amplitude detected with LDF and PPG was poor (r=0.433). Surprisingly, there was a continuous increase of the correlation coefficient from the first (r=0.105) or second (r=0.184) IGR to the fifth (r=0.727) IGR. These results imply that experimental data obtained with PPG and LDF are not equivalent and therefore one has to be cautious regarding the comparison and interpretation of results obtained with these two different methods.
Until today monitoring of immediate drug tissue interaction in living organs is an unsolved problem. However, for the development of new drugs and the improvement of medical therapy outcome it would be helpful to get new tools to visualize drug effects on tissue directly. With the EMPHO II SSK and a 3D-scanning device we detected changes of functional structures in an isolated perfused pig heart model after adding commonly used drugs like verapamil, nitroglycerin and salviae miltiorrhizae (Chinese herbal drug). In the paper the results are presented.
Light scattering in living heart tissue is mainly caused by mitochondria, but also by actin and myosin filaments, glycogen particles and others. In living tissue these subcellular structures are not stable but rather in a permanent change. Thus, one should be able to perceive the status of scattering structures by measurement of backscattered light in microvolumes. Our recent efforts aimed at detecting these structures by use of micro lightguides and scanning tissue spectroscopy technique (EMPHO II SSK) at isolated perfused pig hearts. The paper describes the technical principles of the scanning technique and gives an overview of our latest results.
It is attractive to perform a kind of comparative physiology between two completely different organs. The heart is an organ able to suck blood from vena cava into atria and pump the blood from ventricles through aorta into periphery while liver is a kind of biochemical factory. Sizeable morphological differences exist between the two organs. However, many similarities are found by optical sensors on the level of regulation such as distribution of blood flow in supply units, decrease of oxygen uptake under conditions of activity or rest. The shape of histograms of HbO2 is almost equal in all organs, while the mean values of intracapillary HbO2 reveal differences thus shifting the histogram more or less. For human life the diffusive masstransfer between capillaries and cells is of extraordinary importance. The multicomponent system of this microcosm is not really known. However, for the opening of this unknown world of endothelial cells of capillaries and cells of organs optical sensor systems are now available for investigations of a very great number of diseases.
Long-term conservation of organs by use of hemoglobin-free perfusion of tissue can be applied during heart surgery as well as transplantation of kidney, liver and pancreas. Furthermore, a conservation of organs during times of 24 hours can be very useful for transport of organs in order to prevent reperfusion injury. Decisive prerequisites for the application of such new tools is the applicability of modern optical tissue sensors for precise monitoring of local tissue function.
Subcellular structures play a decisive role in light scattering properties of tissue. Our recent efforts aimed at monitoring these structures by use of micro lightguides and scanning tissue spectroscopy technique (EMPHO II SSK) at isolated perfused organs. With application of 70micrometers lightguides at an isolated perfused pig heart model we were able to improve the resolution to a step size of 20micrometers .
For the quantitative determination of hemoglobin concentration in heart muscle it is important to distinguish between myoglobin and hemoglobin, two dyes with very similar optical absorption properties. With an isolated perfused pig heart model and EMPHO II SSK we measured tissue spectra in the visible range before and after adding erythrocytes to the perfusate. By calculating light intensity differences we were able to show spatial hemoglobin distribution in heart muscle.
Imaging in the microcosm of capillaries and cells in intact tissues opened new fields for research and patient monitoring. The experimental separation of scattering ((mu) s) and absorption ((mu) a) in organs can be improved drastically by visualization of subcellular structures. Improved evaluation techniques which apply matrices for storage of determined optical signals are very favorable.
In organs we can find signal changes between vascular and parenchymal cells. We started to combine spectral measurements by the use of merocyanine in isolated perfused rat liver to analyze the alterations of dc-potentials. There have been first experiments with Merocyanine (M-540) in the seventies with stained axons and hearts to measure optical action potentials (Morad, Salama, et al, 1978). It is reported that the increase of fluorescence response is connected to a depolarization and its decrease to a repolarization. Tissue imaging after staining with this dye should be ideal for a long term interpretation of dc-potential alterations as an analysis of the electrical coupling in different cell types under various experimental conditions like anoxia or temperature changes.
Light scattering in living tissues is mainly caused by subcellular particles like mitochondria. The size of mitochondria changes according to differences in the functional status. Therefore light scattering should be a useful technique for monitoring the functional state in tissues. We investigated functional parameters in our model of the isolated perfused rat liver. For the measurements of light scattering we used the EMPHO SSK Oxyscan. Backscattered light from tissue is shown in 3D images. We found an interesting relation between structures of the liver and the patterns of the relating 3D images. In addition, our underlying spectra show the redox state of cytochromes. This new method of tissue imaging should give the opportunity of new insights into liver function.
Subcellular structures are mainly responsible for light scattering in tissue. Since these structures change their outer shape during hypoxia, backscattered light intensity should be useful in monitoring of tissue in hypoxic or ischemic situations. In a new model of isolated perfused pig heart we investigated the relation between three-dimensional functional structures caused by tissue light scattering and the perfusion pressure during reoxygenation after hypoxia. By use of EMPHO-Oxyscan we could see that there is a clear relation between the perfusion pressure and the level of 3D structures. At very low perfusion pressures there is a delay in recovery of myocardium. Increase in perfusion pressure accelerates the recovery. With functional 3D images created by use of EMPHO-Oxyscan, we now have an instrument for depicting these processes. This technique will be useful in clinical monitoring in cardiac surgery, intraoperative as well as postoperative.
Living tissue of mammals contains a large amount of subcellular particles like mitochondria that are involved in light scattering. Since these particles correlate in a certain way with the functional status of cells, light scattering may be useful for monitoring of functional tissue state. With EMPHO SSK Oxyscan we investigated functional parameters in a new kind of isolated perfused pig heart model. In this perfusion model we use organs obtained from the abattoir that are reperfused by use of a heart-lung machine. By creating 3D images of tissue light scattering we found an interesting relation between morphological structures of myocardium and the patterns of the 3D images. Additionally, we created 3D images of myoglobin oxygenation. Furthermore, we got spectra showing the redox state of cytochromes. We believe that this new kind of tissue imaging method will give us the opportunity to get new insights into myocardial function.
Light scattering in tissue of mammals and humans is affected by subcellular structures. Since these structures correlate well with the status of cells and tissue, light scattering seems to be ideal for monitoring of functional tissue state. By use of EMPHO SSK Oxyscan we investigated functional parameters in a novel kind of isolated perfused pig heart model. In this perfusion model we use organs obtained by the local slaughterhouse that are reanimated at our institute by application of a heart-lung machine. By creating 3D-images of tissue scattering we found an interesting relation between anatomical structures of myocardium and the 3D-images. Additionally, we detected coherence between backscattered light intensity and functional tissue status. Furthermore, we got a sight into the redox state of cytochrome aa3, b and c by creating difference spectra. We believe that this new kind of tissue imaging method will give us the opportunity to get new insights into myocardial function.
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