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Biomedical subjects

H Baier

Publications and source records attributed to H Baier.

At least 37 records · Page 2Linked to original sources
PubMed1994

Heterogeneous microvascular coronary vasodilation by adenosine and nitroglycerin in dogs.

We investigated the effects of adenosine and nitroglycerin (NTG) on coronary microvessel diameters (intravital fluorescence microscopy) and coronary perfusion (radioactive microspheres). Measurements were performed during baseline conditions (intravenous piritramid) and during controlled hypotension (mean arterial pressure approximately 60 mmHg) induced by halothane, adenosine, and NTG. Coronary vascular resistance (CVR) remained unchanged during halothane (-7%) but decreased during adenosine (-76%) and NTG (-29%). Coronary arteriolar diameters increased during all experimental steps. In the smallest vessels (20-40 microns), diameters increased by 14, 43, and 42% during halothane-, adenosine-, and NTG-induced hypotension, respectively. Diameter increases were less pronounced in larger vessels. The uniform action of adenosine and NTG in 20- to 500-microns arterial vessels is in contrast to the pronounced differences in reduction of CVR. Preferential dilation of arterioles < 20 microns or recruitment of coronary microvessels by adenosine might account for the more pronounced decrease of CVR during adenosine. Intracoronary application of adenosine (0.8 mg.kg-1.h-1) and NTG (1, 5, and 25 micrograms.kg-1.h-1) equally caused near-maximum dilation of coronary arterioles > 100 microns. However, NTG dilation of arterioles < 100 microns was dose dependent and exceeded large-vessel dilation only with the highest concentration of NTG.

Adenosine↗
PubMed1994

Tracheal mucosal edema in hydrostatic pulmonary edema.

Airway edema has been described in heart failure, and, in animal experiments, airway narrowing was observed with elevated left atrial pressure (Pla). On the basis of double-indicator-dilution principles using helium and dimethylether, we were able to measure a water compartment of the tracheal mucosa (VH2O) in dogs. Hypervolemia with an attendant increase in Pla caused by infusion of 2 liters of dextran increased VH2O from 368 +/- 71 (SE) to 794 +/- 177 microliters (P < 0.01). Pulmonary arterial wedge and central venous pressures (Pcv) rose concomitantly. Increases in pulmonary arterial wedge and Pcv by a left atrial balloon catheter produced similar increases in VH2O, whereas increases in Pcv alone by a right atrial balloon did not increase VH2O. Increasing VH2O by dextran infusion was associated with an increase in pulmonary resistance from 1.16 +/- 0.19 to 2.15 +/- 0.24 cmH2O.l-1.s (P < 0.01). These observations show that fluid accumulation in the lung during pulmonary congestion also involves extraparenchymal airways and is related to Pla rather than right atrial pressure. This indicates that sufficient collateral drainage exists during right-sided but not left-sided pressure elevations.

Anesthesia↗
PubMed1994

Olfactory glomeruli in the zebrafish form an invariant pattern and are identifiable across animals.

Glomeruli are anatomical and possibly functional modules in the vertebrate olfactory bulb. We investigated the spatial arrangement of glomeruli in the olfactory bulbs of adult zebrafish (Brachydanio rerio). A solution of the lipophilic tracer Dil was injected into the nasal cavities. Axons of sensory neurons projecting from the olfactory epithelium into the bulb were traced anterogradely, thus labeling the whole population of glomeruli. The glomerular distribution was analyzed in detail by confocal laser-scanning microscopy. We find that a typical olfactory bulb contains a small number of about 80 glomeruli that have a stereotyped configuration in all animals investigated. All glomeruli exhibit bilateral symmetry. Twenty-two single glomeruli could be identified from animal to animal by their characteristic position and morphology. The remaining glomeruli either are embedded in glomerular plexus and therefore cannot be delineated reliably, or belong to a densely clustered subpopulation of on average 49 glomeruli in the dorsal olfactory bulb. No sexually dimorphic glomeruli were identified. To test whether glomerular constancy is specific for the zebrafish, we performed similar tracing experiments in the goldfish and found several indications for a similar invariance of glomeruli in this species. The remarkable stereotypy of this pattern is reminiscent of the insect olfactory system and has been demonstrated here for the first time in a vertebrate. It will now be possible to examine whether these identifiable glomeruli are functionally specialized in terms of odor processing. If so, zebrafish may emerge as a tractable model system for studies on olfactory coding.

Animals↗
PubMed1992

Axon guidance by gradients of a target-derived component.

Spatial gradients of axon guiding molecules have long been suspected to provide positional and directional cues for retinal ganglion cell axons growing within the optic tectum. With the identification of a guiding activity from tectal cell membranes, it has become possible to investigate the potential physiological significance of molecular gradients for retinal growth cone behavior in vitro. A subset of retinal growth cones, those from the temporal half, were highly sensitive to small concentration changes of the guiding component. The degree of response was correlated with the strength of the gradient. These findings demonstrate that the neural growth cone can read gradients of surface-associated information.

Animals↗
PubMed1992

Coronary microcirculation during halothane, enflurane, isoflurane, and adenosine in dogs.

We investigated the effects of clinically administered volatile anesthetics and of adenosine on the microvasculature of the in situ beating canine heart. Thirteen dogs were studied during general anesthesia with an opioid (piritramide), which was infused throughout the experiments. Measurements were obtained in each animal at control (piritramide only) and during hypotension (mean arterial pressure 60 mmHg) induced by halothane, enflurane, isoflurane, and adenosine. Using epiillumination and fluorescence microscopy, 354 arterial microvessels with diameters from 20 to 450 microns were examined through all experimental periods. Hypotension by halothane, enflurane, isoflurane, and adenosine reduced coronary vascular resistance by 13%, 23%, 40%, and 85%, respectively. Coronary venous PO2 was unchanged from control with halothane (+/- 0%) and enflurane (+7%) and significantly increased with isoflurane (+16%) and adenosine (+65%). Left ventricular blood flow decreased significantly during halothane (-35%) and enflurane (-23%); was unchanged from control during isoflurane (-9%); but significantly increased during adenosine (+397%). Coronary arterial and arteriolar diameters increased with all hypotensive agents. Vasodilation was least with halothane, intermediate with enflurane and isoflurane, and most pronounced with adenosine. Diameters increased considerably more in vessels with initial diameters below 100 microns as opposed to larger vessels. Calculation of microvascular segmental resistances revealed that the maximum conductance changes during volatile anesthetics were located in the vessel segments visualized by microscopy, i.e., in vessels larger than 20 microns. However, this was not the case with adenosine. We conclude that volatile anesthetics induce coronary vasodilation by preferentially acting on vessels with diameters from 20 microns to approximately 200 microns, whereas adenosine, in addition, has a pronounced impact on the small precapillary arterioles.

Adenosine↗
PubMed1992

Dilation of coronary microvessels by adenosine induced hypotension in dogs.

An experimental model was established for fluorescence video microscopy of coronary microvessels. Nineteen dogs were anesthetized with a narcotic. Catheters were placed for hemodynamic monitoring and sampling of arterial and coronary venous blood. Myocardial perfusion was measured with radioactive microspheres. Following thoracotomy, movements of the myocardial surface area under investigation were restricted by a specially designed heart holder. Plasma was stained with FITC labelled dextran. Diameters were determined in arteriolar and venular microvessels greater than or equal to 20 microns. Measurements were performed during baseline conditions, i.e. only the basic anesthetic drug was applied, and during coronary vasodilation by continuous infusion of adenosine in a randomized sequence. Mean arterial pressure was reduced from 85 +/- 2 mmHg during baseline to 59 +/- 1 mmHg by infusion of 16.9 +/- 2.2 mg.kg-1.h-1 adenosine. Adenosine increased left ventricular blood flow by 253%, left ventricular oxygen demand remained unchanged. A total of 495 arteriolar and 170 venular diameters were measured during baseline condition and during adenosine infusion. Arteriolar diameters increased in all vessel segments between 20 and 600 microns, however, arterioles below a critical size of 100 microns had a greater dilating capacity than larger arterioles. Maximal decrease of segmental resistance occurred in 20-40 microns arterioles and amounted to 74%, which is less than the 82% decrease of total coronary resistance. Venular diameter changes, too, were more pronounced in smaller vessels.

Adenosine↗
PubMed1991

Left ventricular surface tissue oxygen pressures determined by oxygen sensitive multiwire electrodes in pigs.

STUDY OBJECTIVE: Polarographic oxygen sensitive electrodes can be used to measure tissue oxygen pressures on the surface of the beating heart. The purpose of the study was to clarify the significance of these PO2 determinations. DESIGN: Changes in left ventricular surface oxygen pressures, subendocardial or subepicardial wall functions (ultrasonic dimension technique), and blood flow (radioactive microsphere technique) were correlated during different degrees of acute coronary artery stenoses in pigs. EXPERIMENTAL MATERIAL: 19 anaesthetised open chest pigs, 28-40 kg body weight, were studied during different degrees of constriction of the left anterior descending artery which did not influence overall left ventricular function or irreversibly damage the myocardium. MEASUREMENTS AND MAIN RESULTS: Highly significant (p less than 0.001) correlations (each % delta) were obtained for surface tissue oxygen pressures (y) with subepicardial (y = 0.002 e 0.10x; r = 0.89) and subendocardial (y = 1.44 e 0.04x; r = 0.98) blood flow values, as well as with subendocardial function (y = 82.4 + 0.22x; r = 0.89); a significant correlation was also obtained for subendocardial function (y) with subendocardial blood flow (y = 66.0 + 0.28x; r = 0.69). However, no significant correlation was obtained for polarographic tissue PO2 with subepicardial segment function, indicating that regional function was maintained when tissue PO2 recordings were not much above 0 kPa and when blood flow was reduced by 25 to 30%. CONCLUSIONS: Oxygen pressures of the superficial layers of the left ventricle are relatively high at normal values of oxygen consumption but decrease rapidly if blood supply is reduced. Regional wall function is preserved at low oxygen pressures. Polarographic surface PO2 electrodes hence can be used to study influences of experimental interventions on oxygenation of the normally perfused and of the moderately ischaemic myocardium.

Animals↗
PubMed1990

Corticosteroids as adjunctive therapy for severe Pneumocystis carinii pneumonia in the acquired immunodeficiency syndrome. A double-blind, placebo-controlled trial.

BACKGROUND: Preliminary reports suggest that patients with the acquired immunodeficiency syndrome (AIDS) and Pneumocystis carinii pneumonia may benefit from the addition of corticosteroid treatment to antibiotic therapy. METHODS: We conducted a double-blind, placebo-controlled trial to assess the efficacy of adjunctive corticosteroids in patients with AIDS and severe P. carinii pneumonia. Patients with marked abnormalities in gas exchange who had been treated with antibiotics for less than 72 hours were randomly assigned to receive either methylprednisolone (40 mg) or placebo every 6 hours for 7 days, in addition to treatment for 21 days with trimethoprim-sulfamethoxazole. The primary outcome measures were survival until hospital discharge and the development of respiratory failure. RESULTS: Twenty-three patients were enrolled in the study; there were no significant differences in base-line clinical or laboratory measures between the two treatment groups. Of 12 patients treated with corticosteroids, 9 (75 percent) survived until hospital discharge, as compared with only 2 of 11 placebo recipients (18 percent) (P less than 0.008). Respiratory failure developed in nine placebo recipients, as compared with only three patients treated with corticosteroids (P less than 0.008). No patient required the interruption or discontinuation of corticosteroid or antibiotic treatment because of toxicity or a complicating event. Because of the marked difference in survival, it was deemed unethical to continue the trial, and the study was terminated. CONCLUSIONS: Early adjunctive corticosteroid therapy can improve survival and decrease the occurrence of respiratory failure in patients with AIDS and severe P. carinii pneumonia.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Epicardial oxygen tensions during changes in arterial PO2 in pigs.

Arterial hypoxemia decreased epicardial tissue PO2, measured by means of a multiwire surface electrode, as well as coronary venous PO2 and myocardial lactate extraction. Left ventricular blood flow increased, O2 delivery, O2 demand and O2 consumption of the left ventricle remained unchanged. Thus, epicardial and coronary venous PO2 indicated decreased capillary and interstitial PO2 rather than cellular hypoxia. A linear relation between mean epicardial PO2 and coronary venous PO2 proves both parameters equally effective in reflecting changes in myocardial tissue oxygenation. However, PO2 distribution curves provide additional information and epicardial PO2 is superior in models with regional changes of myocardial oxygenation.

Animals↗
PubMed1989

Respiratory mechanics of the loggerhead sea turtle, Caretta caretta.

Respiratory mechanics were evaluated in excised lungs and in spontaneously breathing loggerhead sea turtles (Caretta caretta). Respiratory compliance curves reflect the pressure volume characteristics of the body wall. Compliance values are comparable to those of reptiles having simpler lung structure. Maximum flow rates in excised lungs (18-25 ml.sec-1.kg-1) were only slightly below the range reported for marine mammals. During spontaneous tidal breathing expiratory flow rates (11.8 ml.sec-1.kg-1) were lower than maximum values. In the sea turtle, respiratory adaptations including reduced airway resistance and muscular contribution to breathing are similar to marine mammals. These mechanical specializations shorten breathing time, which contributes to diving performance.

Animals↗
PubMed1988

Tracheal narrowing during histamine-induced bronchoconstriction.

To determine whether tracheal narrowing accompanies histamine-induced bronchoconstriction and whether a cholinergic reflex is involved in the tracheal and bronchial responses, we determined specific pulmonary resistance between the carina and the pleura (sRL) and tracheal volume (Vtr) with an indicator-dilution technique in conscious sheep. Immediately postdelivery of histamine aerosol (7.5 mg histamine base) mean sRL increased by 223% (P less than 0.05), and mean Vtr decreased by 25% (P less than 0.05). The duration of the changes was similar, with a return to base-line values within 60 min. With increasing doses of histamine up to 30 mg, there was a corresponding increase in mean sRL, whereas the maximum effect on Vtr was already reached after 7.5 mg of histamine. Atropine (0.2 mg/kg iv) increased mean Vtr by 77% (P less than 0.05) and blunted the histamine effects on sRL, whereas the histamine effects on Vtr were abolished. Intravenous histamine or carbachol aerosol had similar effects on sRL and Vtr. We conclude that in conscious sheep 1) histamine produces both tracheal and bronchial constriction with a similar time course, 2) there is a base-line vagal tone in the trachea and not the bronchi, 3) the cholinergic reflex component of histamine-induced constriction is greater in the trachea than the bronchi, and 4) this difference between the trachea and bronchi is not due to differential aerosol deposition or cholinergic responsiveness.

Aerosols↗
PubMed1987

Lung mechanical properties in the West Indian Manatee (Trichechus manatus).

Airway dimensions, extent of cartilage reinforcements and lung mechanical properties were examined in excised lungs of the West Indian Manatee (Trichechus manatus). All airways with a mean inside diameter of more than 0.6 mm had complete cartilaginous rings in their walls, and cartilage reinforcement extended into the respiratory bronchi. Expiratory flow rates over the vital capacity range were higher than those encountered in humans varying between 20 and 50% of peak flow at 25% of vital capacity. They were, however, lower than in other marine mammals. The ratio of lung compliance to lung weight was found to be 0.67 ml/(g X cm H2O) compared to 0.18 ml/(g X cm H2O) in terrestrial mammals. This together with a high gas-tissue ratio of 11 mg/g for the inflated manatee lung indicates that strong airway reinforcements are necessary to prevent airway collapse during exhalation.

Animals↗