K. Meßmer

Technical report—a new chamber technique for microvascular studies in unanesthetized hamsters

SummaryAn experimental model was designed for direct, quantitative studies of hemodynamic and morphologic parameters in the microcirculation. It consists of implanting a modified Algire chamber in the dorsal skin flap of hamsters and the implementation of two permanent catheters in jugular vein and carotid artery. The microcirculation was studied using intravital microscopy and television techniques for in situ measurements of blood cell velocity and vascular diameters.Due to the poor contrast between blood cells, blood capillaries and surrounding s.c. tissue, microvascular beds were visualized using fluorescent microscopy after i.v. injection of 0.2 ml of 5% FITC-Dextran 150. The combination of optical elements and low amounts of FITC-Dextran improved the contrast of the televised image without changing macro- and microhemodynamic parameters, and blood plasma was delineated as bright structure against the substantially darker background of red blood cells and surrounding tissue. This permitted the quantitative study of practically all blood vessels within a given field of s.c. tissue in unanesthetized animals. Blood cell velocity in arterioles was 0.7–1.1 mm/s, 0.2–0.7 mm/s in midcapillaries and reached 0.6 mm/s in collecting venules. Since i.v. injection of drugs and systemic pressure measurements are possible in this model, it provides a unique means for studying the reactivity of the microcirculation over a prolonged period.

Non-invasive temperature mapping using MRI: comparison of two methods based on chemical shift and T1-relaxation

PURPOSE To implement and evaluate the accuracy of non-invasive temperature mapping using MRI methods based on the chemical shift (CS) and T1 relaxation in media of various heterogeneity during focal (laser) and external thermal energy deposition. MATERIALS AND METHODS All measurements were performed on a 1.5 T superconducting clinical scanner using the temperature dependence of the water proton chemical shift and the T1 relaxation time. Homogeneous gel and heterogeneous muscle phantoms were heated focally with a fiberoptic laser probe and externally of varying degree ex vivo by water circulating in a temperature range of 20-50 degrees C. Magnetic resonance imaging data were compared to simultaneously recorded fiberoptic temperature readings. RESULTS Both methods provided accurate results in homogeneous media (turkey) with better accuracy for the chemical shift method (CS:+/-1.5 degrees C, T1:+/-2.0 degrees C). In gel, the accuracy with the CS method was +/-0.6 degrees C. The accuracy decreased in heterogeneous media containing fat (T1:+/-3.5 degrees C, CS: +5 degrees C). In focal heating of turkey muscle, the accuracy was within 1.5 degrees C with the T1 method. CONCLUSION Temperature monitoring with the chemical shift provides better results in homogeneous media containing no fat. In fat tissue, the temperature calculation proved to be difficult.

Neurological impairment in rats after subarachnoid hemorrhage--a comparison of functional tests.

Functional outcome has become a key parameter for the determination of the efficacy of therapeutic interventions. Unfortunately, functional tests are not established for filament perforation induced subarachnoid hemorrhage (SAH). Therefore, we evaluated generally applied functional tasks for their potential to discriminate between various degrees of neuronal damage. Rats were subjected to SAH by an endovascular filament and were randomly assigned to controls treated with 0.9% NaCl, moderately neuroprotective therapy with 7.5% NaCl, and highly effective neuroprotection by 7.5% NaCl+6% dextran 70 (HSD). Functional deficit was quantified daily using beam balance task, prehensile traction task, rotarod, a 6-point motor function score and a general neurological 100-point score. Only the HSD group exhibited significantly more surviving neurons at postoperative day 7. Despite significant variations in histomorphometry, beam balance, prehensile traction and rotarod failed to distinguish between groups. On the other hand, the 100-point neuroscore showed improved neurological recovery on postoperative day 1 for HSD. The 100-point neuroscore failed to discriminate between treatment arms at later time points and therefore seems to reflect predominantly early neurological dysfunction. In conclusion, the results of pure motor tasks after experimental SAH in rats should be carefully interpreted. The integration of a test regimen to examine long term cognitive deficits after rat SAH might be valuable to gain additional information about the functional consequences of morphological damage.

Indicator loss during injection in the thermodilution system

SummaryThe exact determination of cardiac output in man is still a most difficult task in clinical medicine. Good results have been reported recently using the thermodilution method. Here cold saline is used as indicator. The existence of a high temperature gradient towards blood results in an instantaneous temperature exchange. In model and dog experiments it was demonstrated, that heat exchange starts already during the application of the indicator. Although indicator loss in the syringe is negligible, the indicator is warmed up already during its passage through the injection catheter. This was demonstrated by a mapping of the temperature variations around a catheter “in vivo” and by simulated injections in dogs. Using a thermistor with high frequency response a temperature rise of 8°C has been recorded. The application of a calculated correction factor should help to increase the accuracy of such a dilution system.ZusammenfassungDie exakte quantitative Bestimmung des Herzzeitvolumens bei Patienten in der Intensivpflege ist immer noch mit Problemen behaftet. Neuerdings wurde über gute Erfahrungen mit der Kälteverdünnungsmethode berichtet. Dabei verwendet man eisgekühlte Kochsalzlösung als Indicator. Das Bestehen eines hohen Temperaturgradienten gegenüber Blut und Gewebe hat einen sofortigen Temperaturaustausch zur Folge. In Modell- und Tierexperimenten konnte gezeigt werden, daß der Wärmeaustausch bereits bei der Injektion beginnt. Unbedeutend ist die Aufwärmung in der Injektionsspritze, wesentlich jedoch im Injektionskatheter. Intravasale Messungen am Katheter und Registrierungen bei simulierten Injektionen am Tier demonstrierten eine signifikante Erwärmung des Injektates. Mit Hilfe eines Thermofühlers von hohem Frequenzgang konnte ein Temperaturanstieg um 8°C gemessen werden. Bei der Anwendung von kaltem Indicator sollte der hier errechnete Korrekturfaktor verwendet werden, was die Genauigkeit der Kälteverdünnungsmethode entscheidend beeinflussen könnte.

Ischemia at 4°C: a novel mouse model to investigate the effect of hypothermia on postischemic hepatic microcirculatory injury

Hypothermia of the ischemic organ at 4°C protects hepatic microcirculation from ischemia-reperfusion (IR) injury. The effect of hypothermia during ischemia was investigated in animal models using liver transplantation and storage of the harvested organ in cold preservation solutions. No investigation of the isolated influence of hypothermia at 4°C of the ischemic organ on hepatic IR injury exists, due to the lack of an appropriate animal model. Therefore, the aim of our present study was to develop such a model using intravital video fluorescence microscopy (IVM). In C57BL/6 mice, a reversible isolated ischemia of the left liver lobe was induced for 90 min, followed by 240 min of reperfusion. The temperature of the ischemic organ was adjusted to either 4°C or 37°C by superfusion with 0.9% NaCl. Sham-operated animals without IR served as controls. The hepatic microcirculation was analyzed using IVM at 30 min and 240 min after reperfusion by quantifying sinusoidal perfusion and leukocyte-endothelial cell interaction in postsinusoidal venules. At the end of the experiment, blood and tissue samples were taken for measurement of liver enzyme activities and light and electron microscopy. Mean arterial pressure and body temperature were kept constant throughout the experiment, while the temperature of the ischemic liver lobe was adjusted to predefined levels. After normothermic ischemia, hepatic microvascular perfusion was significantly impaired compared with sham-operated animals. Perfusion failure was significantly reduced in hypothermic livers and did not differ from livers of the sham-group. Liver enzyme activities in the normothermic group were significantly higher than in the sham and hypothermic groups. Light and electron microscopy revealed severe histological alterations at 37°C ischemia, whereas at 4°C ischemia only minimal lesions were encountered. Our novel model allows for isolated adjustment of ischemic liver lobe temperature without changing body temperature and systemic macrohemodynamic parameters. Hypothermia at 4°C largely attenuates postischemic microvascular perfusion injury of the liver.

Limited hemodilution in hemorrhagic shock in dogs: Effects on central hemodynamics and the microcirculation in skeletal muscle

SummaryThe keyproblem of hemorrhagic shock consists in decreased tissue nutrition and tissue drainage from metabolites with subsequent hypoxic cellular damage. In two groups of 50 dogs the effect of whole blood (n = 30) versus hemodilution with dextran-60 (n = 20) was evaluated from central hemodynamics, capillary blood flow and transcapillary exchange from tissue to blood in skeletal muscle by use of a double isotope technique. Following a period of hemorrhagic hypotension either all the shed blood or dextran-60 were infused. Hemodilution with dextran produced a decrease in hematocrit to 20%, lowered effeciently blood viscosity and TPR and increased cardiac output to 160% of control. Capillary blood flow and exchange were nearly doubled as compared to the control level. Retransfusion of blood caused only transient normalization with rapid deterioration in central and peripheral hemodynamics, together with an increase in blood viscosity. The viscosity depressant effect of hemodilution is discussed as key factor causing the better immediate response to dextran infusion in hemorrhagic shock.

Validierung des „OPS imaging“ Verfahrens an der Rattenleber

Hintergrund: Storungen der hepatischen Mikrozirkulation sind wesentlich an der Pathophysiologie der postischamischen Organdysfunktion nach Leberchirurgie sowie Trans-plantation beteiligt. Die quantitative Analyse der Mikrozirkulation war bisher jedoch nuram Tiermodell moglich.

Hypothermer Kreislaufstillstand nach totalem Blutaustausch beim Hund

SummaryTotal body washout (hct < 1%) in hypothermia was performed in 31 dogs using either a crystalloidal or a colloidal perfusate. Blood exchange and cooling was achieved by means of partial bypass and heat exchanger. Short lasting blood exchange for crystalloids without cardiac arrest resulted in 66% survival of the animals. When in addition circulatory arrest was established for 30 min at 14°C oesophageal temperature blood exchange for crystalloids was not tolerated. All four animals of this group died within 19 hours presenting massive interstitial edema. Replacement of the crystalloidal perfusate by a colloidal solution (2.5g% Dextran 60 in Ringers Lactate) and establishing circulatory for 30 or 60 min resulted in survival rates of 71% and 50% respectively. The use of the colloidal perfusate effectively prevented edema formation. Death could not be correlated with the parameters controlled.ZusammenfassungBei 31 Hunden wurde in Hypothermie ein totaler Blutaustausch (HKT < 1%) mit kristalloidem oder kolloidhaltigem Perfusat durchgeführt. Austausch und Kühlung erfolgten mittels partieller, extracorporaler Zirkulation und Wäremeaustauscher. Die Überlebensrate der Tiere betrug nach Blutaustausch mit kristalloidem Perfusat ohne Kreislaufstillstand 66%. Wurde zusätzlich ein Kreislaufstillstand von 30 min bei 14°C induziert, verstarben alle vier Tiere bei generalisiertem interstitiellen Ödem; die mittlere Überlebenszeit betrug 19 Stunden. Bei Blutaustausch gegen kolloidhaltiges Perfusat (2,5% Dextran 60) betrug die Überlebensrate nach Kreislaufstillstand von 30 bzw. 60 min 71 bzw. 50%. Durch die Anwendung des kolloidhaltigen Perfusates konnte die Ödementwicklung weitgehend verhindert werden. Der Tod der Tiere konnte durch die gemessenen Parameter nicht erklärt werden.Total body washout (hct less than 1%) in hypothermia was performed in 31 dogs using either a crystalloidal or a colloidal perfusate. Blood exchange and cooling was achieved by means of partial bypass and heat exchanger. Short lasting blood exchange for crystalloids without cardiac arrest resulted in 66% survival of the animals. When in addition circulatory arrest was established for 30 min at 14 degrees C oesophageal temperature blood exchange for crystalloids was not tolerated. All four animals of this group died within 19 hours presenting massive interstitial edema. Replacement of the crystalloidal perfusate by a colloidal solution (2.5 g% Dextran 60 at Ringers Lactate) and establishing circulatory for 30 or 60 min resulted in survival rates of 71% and 50% respectively. The use of the colloidal perfusate effectively prevented edema formation. Death could not be correlated with the parameters controlled.

Einfluß der Thrombozyten-Endothelzell-Interaktion auf den hepatischen Ischämie-Reperfusionsschaden

Background: In the recent literature, a potential role for platelets in the development of hepatic ischemia-reperfusion (I/R) injury has been discussed. The aim of this study was to investigate the impact of platelets on microvascular hepatic I/R injury using intravital microscopy. Methods: In C57BL/6 mice, an in situ ischemia of the left liver lobe was induced for 90 min. Platelets were separated from a syngeneic donor, labeled ex vivo using rhodamine 6G, and infused i.v. after 20 min of reperfusion. Leukocytes were stained by i.v. injection of rhodamine 6G. Platelet- and leukocyte-endothelial cell interactions were analyzed using intravital microscopy within identical postsinusoidal venules in a sham group, an I/R group, and an I/R group after i.v. administration of an anti-fibrinogen antibody (n = 7 each). For the determination of hepatocellular damage, the activities of AST and ALT were measured at the end of the experiment. Results: After 90 min of normothermic ischemia, numbers of permanently adherent platelets and leukocytes as well as liver enzyme activities were markedly increased. Administration of anti-fibrinogen antibody resulted in an attenuation of platelet adhesion, whereas the interaction of leukocytes with the postischemic endothelium was not affected. The activities of ALT and AST were significantly reduced compared to the non-treated group. Conclusion: Our data demonstrate that hepatic I/R induces platelet-endothelial cell interaction in postsinusoidal venules. The selective blockade of platelet adhesion preserved the cellular integrity of the liver. In conclusion, our results suggest that platelets play a critical role in hepatic I/R injury.

Systematische Analyse der Temperaturabhängigkeit des mikrovaskulären Ischämie-Reperfusionsschadens der Leber

Eine systematische Analyse der Temperaturabhangigkeit des mikrovaskularen Ischamie-Reperfusionsschadens der Leber liegt bislang nicht vor, daher ist die optimale Temperatur fur die Leberprotektion nicht bekannt.