[An extended evaluation of a neuroleptanesthesia for the guinea pig with analysis of mixed expiratory gases during spontaneous breathing. Effects of fasting on the cardiorespiratory system and metabolism]. / Eine erweiterte Evaluation der Neurolept-Anästhesie für Meerschweinchen mit einer Analyse gemischt-exspiratorischer Gase während Spontanatmung. Wirkung des Fastens auf das kardiorespiratorische System und den Metabolismus.

The artificially ventilated guinea pig was frequently used for neurophysiological and respiratory studies. This species is also preferable for an evaluation of hemoglobin based artificial oxygen carriers, because its oxygen hemoglobin binding is very similar to that of man. But the narcosis of this animal-species is very difficult, because of cardiorespiratory depression induced by conventional procedures. The following intraperitoneal administered neuroleptanesthesia was proved in guinea pigs: 0.2 mg Fentanyl (Janssen/D), 10 mg Droperidol (Janssen/D) and 400 mg Urethan in 10 ml isotonic sodium chloride solution per kg body weight. Our new animal model with a special valve system enables to assess the gas exchange under spontaneous breathing, cardiovascular and the acid-base parameters. The vital parameters of animals were stable over 6 hours and very close to those of awake animals, especially the arterial average blood pressure. For that reason, this established neuroleptanesthesia of guinea pigs is preferable for research purpose. The fasted animals show significantly decreased values of arterial blood pH (7,345 vs. 7401), of heart frequency (244 vs. 277 min(-1)), and of ventilation value (167 vs. 205 ml/min) compared to non-fasted animals.

A model of stepwise isovolaemic blood exchange in anaesthetised, spontaneously breathing rats to evaluate the oxygen transport efficiency of artificial oxygen carriers.

Our research pursues the production of hypo-oncotic artificial oxygen carriers, based on artificial covalently cross-linked hyperpolymeric mammalian haemoglobins. To evaluate their in vivo efficiency in oxygen delivery to the tissue we developed a small animal model of stepwise isovolaemic blood exchange in anaesthetised, spontaneously breathing rats. With the aid of a two-way respiratory micro valve for small animals the overall oxygen uptake by the tissue of the animal can be determined. Measurements of oxygen contents in arterial and mixed venous blood and of some further blood parameters together with known oxygen-binding characteristics of artificial and native oxygen carriers, permits the determination of the way the two oxygen carriers contribute to the overall oxygen uptake. These so-called partial oxygen net to transport rates (i.e. partial oxygen uptakes), related to the corresponding intravascular mass flow of the transporters, are characteristic measures of the efficiency of the oxygen transporter, the so-called oxygen transport quality. Other biological indicators for an adequate oxygen supply are oxygen-dependent changes of ventilation, cardiac output, heart rate, and systemic vascular resistance. The performance of artificial oxygen carriers is elucidated by a comparison with experimental results from the analogous treatment of rats with non oxygen-transporting plasma expanders.

A model for evaluation of artificial oxygen carriers regarding circulation, respiration and metabolism in anesthetized spontaneously breathing guinea pigs.

The evaluation of artificial oxygen carriers requires experiments with suitable animals. Many investigators do this with the classical laboratory animal, the rat, but it has a quite different oxygen pressure of half saturation (p50 = 36 mmHg) from that of humans (26 mmHg). It was demonstrated that induced changes of the p50 value in animals provokes substantial changes in important cardiovascular parameters. Therefore, we decided to develop a guinea pig model for evaluation of artificial oxygen carriers, because it has a p50 of about 24 mmHg that is very similar to that of man. We found an anesthesia combination using fentanyl/droperidol/urethane to be very suitable for the narcosis, because important cardiovascular and respiratory parameters remain normal. Our model allows assessment of arterial pressure, oxygen uptake, carbon dioxide release, cardiac output, total peripheral resistance, shock index, blood lactate level, and, in particular, it allows to differentiate the oxygen transport in blood. We evaluated two hemoglobin-based oxygen carriers: bovine and porcine hemoglobin polymerized with glutaraldehyde in isoncotic solution (n = 3). Control experiments (n = 4) were done with an isotonic albumin solution. The protocol comprised a so-called exchange phase (I) with different degrees of hemodilution and a so-called time phase (II), an observation period with a hematocrit of 10% over about 3 hours. In the control group substantial changes in mean arterial pressure, total peripheral resistance, shock index, oxygen uptake and of blood lactate level were seen. All these effects were prevented by the artificial oxygen carriers tested. The carriers proved to be very effective, as small quantities in blood effectively restored these parameters, presumably via synergetic effects. Moreover, the experiments clearly revealed the limitation of hemodilution, at least in guinea pigs: below a hematocrit of 20% all parameters mentioned above changed significantly. The animal model presented proved to be appropriate for the evaluation of artificial oxygen carriers.

Molar masses and structure in solution of haemoglobin hyperpolymers--a common calibration of size exclusion chromatography of these artificial oxygen carriers.

We are developing artificial oxygen carriers for medical use, based on synthetic polymers--so-called hyperpolymers--obtained by cross-linking mammalian haemoglobins. One requirement with respect to the polymers is that they should not increase the oncotic pressure of blood remarkably--this can be realized by high molecular weights of the polymers with a narrow distribution. They may act as a oxygen transporting blood additive, and--in combination with a plasma expander--as a blood substitute. Another important and desired property of the artificial oxygen carrier is a low viscosity, which--first--is due to a high degree of uniformity of the polymer size (or molar mass) distribution and--second--is influenced by the so-called structure in solution of the haemoglobin hyperpolymers. In this paper former determinations of molar masses--with size exclusion chromatography (SEC)--and of the structure in solution--using viscometric measurements--of hyperpolymers of human haemoglobin, synthetized with glutaraldehyde and with bis(thioisocyanato) benzenesulfonic acid as cross-linkers, were extended to hyperpolymers of bovine and pyridoxylated porcine haemoglobin, cross-linked with glycolaldehyde. These determinations were done by applying a new iterative procedure. Within a range of error all SEC calibration curves found were the same for all hyperpolymers investigated. So-called MARK-HOUWINK or structure in solution diagrams (logarithm of intrinsic viscosity versus logarithm of molar mass) yield equal straight lines for all the haemoglobin polymers. The first derivatives of these lines are the MARK-HOUWINK exponents which has a mean value of 0.38. These results indicate that there exists a common SEC calibration line for all different polymer haemoglobins produced with comparable preparative procedures. This calibration line differ significantly from that of native globular proteins--haemoglobin hyperpolymers are less compact--so a calibration of SEC with globular proteins for the determination of molar masses of haemoglobin polymers is erroneous. Furthermore, the structure in solution of the hyperpolymers is clearly different from that of flexible, randomly coiled, linear artificial polymers: hyperpolymers are more compact. A possible explanation is that the hyperpolymers--according to a great number of functional amino groups of haemoglobin-contain many intra-polymeric cross-links, and thus are at least import branched polymers or even macromolecular networks of the constituting haemoglobin "monomers".