The numerical analysis of pressure-flow curves in infancy

Lung resistance (RL) and airway resistance (Raw) were measured in 33 healthy and sick infants. Using strict criteria for quality control, calibrated pressure-flow (P-V) curves were produced with the aid of a computer so that resistance could be analyzed at several points over the breathing cycle. In a subgroup of 11 infants from whom simultaneous measurements were obtained, values of RL and Raw were comparable, suggesting that the tissue component may make only a minimal contribution to lung resistance in infants. For both RL and Raw, the P-V relationship remained linear up to 50% maximum inspiratory flow in all infants. At other points of the respiratory cycle, there were marked changes in resistance, values calculated between points of mid-isovolume or peak pressure being significantly higher than those measured over the linear portion of inspiratory flow. While no single value can accurately reflect the changes in respiratory resistance that occur during the breathing cycle, the authors suggest that for purposes of comparison, RL or Raw should be measured as the slope of the inspiratory loop from the origin up to 50% of maximum inspiratory flow. From a calibrated tidal pressure flow curve values of resistance over other portions of the breathing cycle can easily be determined.

Isolation and characterization of glyoxylate dehydrogenase from the fungus Sclerotium rolfsii

Glyoxylate dehydrogenase (glyoxylate:NAD+ oxidoreductase) was purified 600-fold in three steps from crude extracts of the fungus Sclerotium rolfsii (Corticium rolfsii Curzi). Two of the purification steps involved dye-affinity chromatography. The enzyme is a tetramer of Mr 250 000, with identical subunits of Mr 57 000. Inhibition studies suggest that there is one essential thiol group per active site.

Pulmonary compliance in sick low birthweight infants. How reliable is the measurement of oesophageal pressure?

Measurements of dynamic lung compliance (Cdyn) were made on 42 occasions in a group of 15 intubated very low birthweight infants with respiratory distress syndrome, using an oesophageal balloon and pneumotachograph system. Values of Cdyn were compared with those of total respiratory system compliance (Crs) using an occlusion technique. Ten very low birthweight infants with no respiratory disease were similarly studied while breathing through a facemask. The occlusion tests for oesophageal balloon assessment were unsatisfactory in 14 of 15 intubated infants, but in only 3 of the 10 normal infants. Values of Cdyn were poorly reproducible and correlated poorly with Crs. We conclude that in sick intubated preterm infants oesophageal pressure (and hence Cdyn) cannot be reliably measured, but that Crs may be a useful parameter of lung stiffness.

The effect of posture on the sympathoadrenal response to theophylline infusion

We studied the effect of posture on the sympathoadrenal response to intravenous theophylline in six normal subjects. On three separate occasions they received an intravenous infusion of either theophylline (6 mg/kg) while supine, theophylline (6 mg/kg) while standing or saline as placebo while standing. With the subjects standing theophylline caused tremor, a peak heart rate of 99 +/- 6 beats/min, and an elevation of plasma cyclic AMP from 9.3 +/- 0.7 to 15.1 +/- 1.7 nmol/1 (mean +/- s.e. mean). There was a small, but significant, elevation of plasma adrenaline, noradrenaline and glucose. The elevation in plasma catecholamines was insufficient to explain either the sympathomimetic effects of theophylline or the rise in plasma cyclic AMP. Theophylline had little or no effect with the subjects supine. The mean peak theophylline concentration following infusion was significantly higher with the subjects upright than when supine (18.3 c.f. 12.4 mg/l, P less than 0.025). However, adequate plasma levels of theophylline were obtained in all subjects when lying or supine. Analysis of individual data suggests that differences in plasma levels of theophylline are unlikely to account for the increased effects seen on standing. The mechanism of action of theophylline cannot be explained by increased secretion of catecholamines alone. Theophylline appears to amplify the increased sympathetic activity associated with standing and this is probably by phosphodiesterase inhibition.

Clinical range of neonatal rotavirus gastroenteritis

A baby admitted to a special care baby unit with profuse watery diarrhoea was found to have a rotavirus infection. A total of 196 babies were admitted to the unit over the next year. Routine stool samples were taken weekly from all babies and additional samples were taken from all babies who developed clinical signs suggesting sepsis. A total of 76 babies excreted rotavirus; 32 of these developed a diarrhoeal illness, 12 of whom were severely ill with bloody diarrhoea and abdominal distension; and two had perforations. The smaller, sicker babies who stayed in hospital longer were more likely to acquire infection; colostrum did not confer protection against rotavirus or symptomatic infection. The outbreak of rotavirus declined independently of the measures taken to eradicate it. Our findings suggest that neonatal rotavirus infection may occasionally cause severe gastrointestinal problems.

Organization of an information system for food and nutrition programmes in Costa Rica

This paper discusses the information needed for multidisciplinary planning aimed at reducing nutritional deprivation in Costa Rica. In recent years, an approach has been developed for organizing data and information so as to define and described target groups of households. The development of a functional classification, a central activity of the Sistema de Información en Nutrición (SIN), is described and a preliminary description of the population groups affected by malnutrition presented. The major objectives of SIN are outlined and the possibilities of applying the same system to other countries discussed.

The specificity of the S1 and S2 subsites of elastase

Esters of tetrapeptides of the general formula ethoxycarbonyl-prolyl-alanyl-X-Y where either X or Y was an alanine residue were synthesised and their cleavage by elastase studied. It was found that variation of the alcohol moiety between methyl, cyclohexyl and nitrophenyl residues had no effect on the catalytic rate constant for cleavage of ethoxycarbonyl-prolyl-dialanyl-alanine esters demonstrating that acylation is much faster than deacylation for this system and also that non-productive binding is not kinetically significant. The effect of changing the amino acid residue in position X was small compared with that of change in position Y. The presence of valine and serine residues in position Y produced the highest specificity constant but the highest catalytic rate constant was found for a leucine residue in this position. The results are discussed in terms of the binding of the substrate to the enzyme.

The identity of the elastase-associated acidic endopeptidase and chymotrypsin C from porcine pancreas

The preparations of chymotrypsin C (EC 3.4.21.2) and an acidic endopeptidase from porcine pancreas have been repeated using published procedures. The acidic endopeptidase showed lower activity than chymotrypsin C in all comparative experiments, but it was possible to precipitate a fraction from the acidic endopeptidase preparation which contained all the protein and was identical with chymotrypsin C. It is concluded that the acidic endopeptidase is identical with chymotrypsin C but it is contaminated by an inert non-protein material to which it is firmly bound. The formation of a precipitate, at low ionic strength, from mixtures of chymotrypsin C and elastase (EC 3.4.21.11) is independent of the availability of the active site of either enzyme.