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Biomedical subjects

K Messmer

Publications and source records attributed to K Messmer.

566 records · Page 32Linked to original sources
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Analysis of laser Doppler flux motion in man: comparison of autoregressive modelling and fast Fourier transformation.

In order to investigate laser Doppler (LD) flux motion in healthy subjects and patients with peripheral arterial occlusive disease (PAOD), spectrum analysis of LD signals is needed. Autoregressive analysis (AR) is presented as an alternative method of power spectrum estimation. This procedure is compared to the commonly used fast Fourier transform algorithm (FFT) by describing the analytical power of both spectra in the analysis of flux motion waves. LD signals were recorded from the forefoot of 8 healthy volunteers and 11 patients with different degrees of PAOD. The flux, concentration of moving blood cells and velocity signal was digitized and stored for off-line analysis. Special software was designed to calculate AR and FFT spectra of the LD signals and to compare the suitability of both methods for the spectral analysis of LD recordings. Additionally, three-dimensional spectrum diagrams were calculated to demonstrate time-dependent flux changes during standardized provocation maneuvers. AR facilitates the determination of frequency and amplitude of flux motion waves as compared to the FFT. Low frequency-large amplitude waves (LF waves) were detected in both groups. High frequency-small amplitude waves (HF waves), which predominantly appear in severe ischemia, were observed in 7 of the 11 patients and in 2 of the 8 controls. The spectra revealed pulsatile waves in all healthy controls, but only in 1 of the 11 patients. AR modelling allows a reliable description of important flux motion components and has considerable advantages in spectral estimation of LD signals as compared to the FFT.

Algorithms↗
PubMedDate not supplied

An improved intravital microscopy system.

The use of intravital microscopy as a tool for studying the microcirculation has increased greatly over the last several decades. Early microscopes provided the first pictures of the microcirculation, but were cumbersome to use and subjected the tissue to a high light intensity, a problem which has recently become the subject of much discussion. The goal of this project was therefore to build a more ergodynamic microscope which minimizes the light exposure to the tissue. The automation of the microscope controls provides a platform on which other options can be built into the microscope, such as an autofocus feature. Furthermore, the use of the Optimas software also opens the possibility for on-line data processing.

Arterioles↗
PubMedDate not supplied

Cardiovascular monitoring of elective aortic aneurysm repair using methods of chaos analysis.

INTRODUCTION: Biological signals like arterial blood pressure (ABP) and electrocardiograms are usually displayed in a linear fashion. The often very complex structure may, however, be better described by phase space plots and time-delayed vectors, enabling an advantageous display of the dynamics contained in the signal. The potentials of such a display were investigated during elective aortic aneurysm repair, where profound haemodynamic changes frequently occur. METHOD: The peripheral volume pulse was recorded at a digit using noninvasive near infrared photoplethysmography (NIRP). All patients (n = 20, mean age 72.8 years) were invasively monitored using arterial and Swan Ganz catheters. The ABP signal was continuously recorded with a computer (sample rate 128 Hz). Two different phase space plots, [x(t), y(t + 8/128 s) and x(t), d(x(t + 8/128 s) - x(t))/dt] were calculated for the NIRP and the ABP signals and continuously displayed. The stability was subjectively assessed and the fractal dimension calculated using the 'Hausdorff dimension'. The correlation between stability, fractal dimension and frequently used parameters of patient monitoring were investigated. RESULTS: All patients included in the study had an uncomplicated operation. Cardiac index (CI) and oxygen delivery (DO2) increased, and systemic vascular resistance (SVR) decreased following declamping of the aorta. The ABP signal was generally more stable. After declamping of the aorta, 14 of 16 NIRP signals became unstable, and 9 of 14 ABP signals destabilised. The time required for stabilisation of the signal varied between the individual patients. Thirty minutes after declamping, 11 of 12 ABP signals were stable, whereas 3 out of 9 NIRP signals still revealed an unstable pattern. A fractal dimension was calculated by box counting, which revealed a linear regression over two orders of magnitude in a log-log plot (Hausdorff dimension between 1.19 and 1.71). The mean fractal dimension for NIRP was significantly higher than that of the ABP signal. On clamping and declamping of the aorta, a trend to a higher fractal dimension (p = 0.08) was observed for both signals analysed. No correlation was observed between the fractal dimension and ABP, SVR index, CI, DO2 index and oxygen consumption. DISCUSSION: The dynamic changes of the signals were emphasised when they were displayed as phase space plots calculated by time-delayed vectors. The time series of the signal revealed a fractal dimension, and the observed increase at the critical time points of the operation, where the need for cardiovascular regulation is most pronounced, support the contention that a physiological system based on non-linear behaviour may enable a rapid response to haemodynamic challenges. An on-line display of phase space plots calculated by time-delayed vectors may in future provide a valuable method of monitoring for high-risk patients.

Aged↗
PubMedDate not supplied

Hypertonic volume therapy: feasibility in the prevention and treatment of multiple organ failure and sepsis.

Small-volume resuscitation by means of bolus infusion of hypertonic saline solutions was first applied for the primary treatment of severe hemorrhagic and traumatic shock and promptly restored central hemodynamics and regional organ blood flow. Mechanisms of action are diverse--i. maintenance of high cardiac output (direct myocardial stimulation; increase in intravascular volume); ii. maintenance of peripheral arterial vasodilation (effect of hyperosmolality; plasma volume effect) and iii. reduction of tissue edema (shifting of tissue water along the osmotic gradient). These mechanisms promote the restoration of the severely impaired microcirculation frequently seen also in sepsis. Hypertonic volume therapy has been the object of several experimental studies of acute hyperdynamic endotoxemia, however, a greater number of clinical studies have to be developed for the better understanding of the positive, and perhaps hazardous, effects of small-volume resuscitation in sepsis and multiple organ failure. The aim of this paper is to review the concepts involving such solutions, and their potential use in treatment of profound hypovolemia and microcirculatory deterioration associated with sepsis and endotoxic shock.

Blood Circulation↗
PubMedDate not supplied

A porcine model of hyperdynamic endotoxemia: pattern of respiratory, macrocirculatory, and regional blood flow changes.

Systemic sepsis and multiple organ failure are frequent and often fatal complications after major surgery and trauma. In contrast to the biphasic hemodynamic pattern characteristically seen in patients, most experimental animal models have failed to reproduce the early, hyperdynamic phase of sepsis and endotoxemia. We have designed a standardized model of endotoxemia, which is elicited by continuous IV infusion of Salmonella abortus equi endotoxin in anesthetized juvenile pigs (age 8-12 weeks). The plasma concentration of endotoxin--as evaluated by the LAL test--is significantly elevated within less than half an hour following the start of endotoxin administration and is accompanied by a rapid fall of the leukocyte count in peripheral blood. High cardiac output and low systemic vascular resistance reflect a hypercirculatory state, during which left ventricular filling pressure is maintained by carefully monitored volume substitution (6% dextran 60). In the present investigation, different doses of endotoxin (3.8 and 11.4 micrograms/kg, respectively) were infused intravenously and investigated for their effect on respiratory, macrocirculatory, and regional blood flow alterations. The development of respiratory deterioration depended on the duration of endotoxin administration and on the height of endotoxin plasma levels. In all animals, a high cardiac output was maintained throughout 3.5 hr of endotoxemia. Regional blood flow to the myocardium and liver increased, whereas blood flow to the gastrointestinal tract and the spleen was compromised without difference between both groups. It is concluded that this porcine model should provide the potential for further insight into the early pathophysiological mechanisms involved in the development of multiple organ failure in patients with sepsis and endotoxemia.

Animals↗
PubMedDate not supplied

The effects of Celecoxib on inflammation and synovial microcirculation in murine antigen-induced arthritis.

OBJECTIVE: There is controversy about the effects of cyclooxygenase-2 (COX-2) on adhesion molecules and the microvasculature in inflamed tissue. Thus, the aim of this study was to assess COX-2-expression in Antigen-induced Arthritis (AiA) and to investigate the effects of selective COX-2 inhibition by Celecoxib (4-[5-(4-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl] benzenesulfonamide) (CXB), on synovial microcirculation and adhesion molecule expression in arthritic as well as healthy mice. METHODS: Balb/c mice were allocated to 4 groups; 2 control groups with saline or CXB and 2 groups with AiA which also received saline or CXB (30 mg/kg BW in 0.3 ml solution). The severity of arthritis was assessed by changes in the transverse joint diameter On day 14 after AiA-induction, the patella tendon of the left knee joint was microsurgically resected and intravital fluorescence microscopy on synovial tissue was performed. Finally, the knee joint was removed for histology and immunohistochmistry. RESULTS: COX-2-expression in the inflamed synovium was demonstrated by immunohistochemistry. Application of Celecoxib resulted in a significant reduction in the rolling leukocyte fraction as well as in the number of leukocytes adherent to the endothelium (0.25 +/- 0. 1 and 96 +/- 34 cells/mm2 respectively) in comparison to the untreated animals with AiA (0.44 +/- 0.03 and 206 +/- 22 cells/mm2 respectively). Additionally, CXB-treated arthritic animals showed significantly less knee joint swelling and reduced adhesion molecule expression. CONCLUSION: In the present study, COX-2 expression in the synovial tissue of mice with AiA could be demonstrated. Selective COX-2 inhibition with CXB resulted in reduced leucocyte-endothelial cell interactions and decreased adhesion molecule expression. Evidence for a protective role of COX-2 in mouse AiA was not found.

Animals↗
PubMedDate not supplied

Tissue protection by anti-ischemic drugs.

Ischemia followed by reperfusion is associated with typical microvascular disturbances characterized by capillary perfusion break-down (no-reflow), accumulation and adhesion of leukocytes to the microvascular endothelium (reflow-paradox) and impairment of endothelial barrier function, indicating the onset of cellular and/or organ dysfunction. Therapeutic approaches aiming at the prevention of microvascular failure elicited by ischemia/reperfusion, have to be devided into measures interfering with 1) the insult induced during the ischemic period and its consequences from cellular energy depletion and 2) the microvascular disturbances induced during the reperfusion/reoxygenation period. Using various microcirculation models in hamster and/or mouse allowing for chronic visualization of the microcirculation in striated muscle and skin, different therapeutic strategies have been investigated in our laboratory to protect the tissue from the manifestation of postischemic microvascular disturbances. The results are discussed with respect to the potential mode of action of the various therapeutic strategies performed.

Animals↗