Modeling the internal dynamics of energy and mass transfer in an imperfectly mixed ventilated airspace.

UNLABELLED: The present paper outlines a modeling approach, which has been developed to model the internal dynamics of heat and moisture transfer in an imperfectly mixed ventilated airspace. The modeling approach, which combines the classical heat and moisture balance differential equations with the use of experimental time-series data, provides a physically meaningful description of the process and is very useful for model-based control purposes. The paper illustrates how the modeling approach has been applied to a ventilated laboratory test room with internal heat and moisture production. The results are evaluated and some valuable suggestions for future research are forwarded. PRACTICAL IMPLICATIONS: The modeling approach outlined in this study provides an ideal form for advanced model-based control system design. The relatively low number of parameters makes it well suited for model-based control purposes, as a limited number of identification experiments is sufficient to determine these parameters. The model concept provides information about the air quality and airflow pattern in an arbitrary building. By using this model as a simulation tool, the indoor air quality and airflow pattern can be optimized.

Evaluation of carbon-11-labelled phenoxy bridged fatty acids for studying myocardial fatty acid metabolism with PET.

A phenylene moiety in the chain of fatty acids was expected to impair metabolic degradation. Three phenoxy-containing [11C]carboxyl-labelled fatty acids were synthesized and evaluated in mice and an in vivo tissue distribution study. Of these three, 1[11C]-3-(p-dodecyloxyphenyl)propionic acid (C12C3) showed the most favourable uptake in the myocardium: 1.2% of the injected dose at 30 min p.i., vs. 0.6% for [11C]palmitate. The metabolic stability of C12C3 and [11C]palmitate was assessed by determining the amount of exhaled [11C]CO2 during a 30-min interval after injection. It was found that the phenoxy moiety in the gamma-position did not prevent the metabolic degradation of C12C3: After 30 min 20.7% of the injected dose was exhaled as [11C]CO2 vs. 12.7% for [11C]palmitate.

Usefulness of residual fractions of L,L-ethylcysteinate dimer (Neurolite) for the preparation of 99Tc(m)-L,L-ethylcysteinate dimer.

According to the reconstitution instructions for the Neurolite labelling kit, the contents of vial A (containing the ligand) is dissolved in 3 ml of saline and 1 ml of the solution is added to vial B (containing 1 ml of phosphate buffer) to which 2 ml of 99Tc(m) generator eluate had previously been added. This implies that 2 out of 3 ml of the ligand solution is not used. We have investigated the radiochemical purity of 99Tc(m)-ECD reconstituted from fractions of the residual solution after storage in a freezer. Fractions of 0.25 ml or 0.5 ml were reconstituted with 1.11 GBq or 3.7 GBq 99Tc(m)-pertechnetate, respectively, after storage at -20 degrees C for periods ranging from 1 day to 4 weeks. In each test situation, except when 0.25 ml fractions were labelled with 3.7 GBq 99Tc(m), 99Tc(m)-ECD was obtained with a radiochemical purity > 95% up to 6 h after reconstitution, as determined using two-strip TLC and reverse-phase HPLC. The results demonstrate that residual portions of Neurolite kits can be efficiently labelled after fractionation and storage in a freezer.

Synthesis and biological evaluation of the four isomers of 99mTc-cysteinyltriglycine, an amino substituted derivative of 99mTc-MAG3.

Cysteinyltriglycine (CYSG3) is a derivative of MAG3 in which the mercaptoacetyl group is replaced by a cysteinyl moiety. This implies the presence of a primary amino group on the ligand, as in case of p-amino-hippuric acid, the compound with the highest renal tubular secretion known. The present study was undertaken to investigate the influence of this amino group on the biological behaviour of complexes of 99mTc with MAG3-like molecules. The L- and D-isomers of cysteinyltriglycine were synthesized as S-benzyl N1-CBO protected precursors. After removal of the protective groups with Na/NH3, the isomers were labelled with 99mTc. This resulted in the formation of two diastereomeric complexes (A and B in the order of HPLC-elution) for each of them. The biodistribution of the four HPLC-purified isomers was tested in mice. Isomers DA and LB showed slightly superior or similar renal excretion characteristics compared to 99mTc-MAG3, whereas the two other isomers were cleared at a lower rate by the kidneys and more through the liver and the intestines. The results indicate that substitution of 99mTc-MAG3 with an amino function may somewhat improve the rate of renal excretion, but the configuration of the 99mTc-labelled complexes appears to be more important to its biological behaviour.