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Biomedical subjects

P Johnson

Publications and source records attributed to P Johnson.

At least 505 records · Page 28Linked to original sources
PubMed1982

Pediatric intensive care: factors that influence outcome.

Four hundred sixty-one consecutive admissions to the Pediatric Intensive Care Unit (PICU) were evaluated using the Therapeutic Intervention Scoring System (TISS). Patients requiring an increased level of care, defined as TISS points greater than or equal to 10, accounted for 75% of patient days in the ICU. Within this group, the primary reason for admission to the ICU was congenital heart disease, trauma, malignancy, respiratory failure, and sepsis. Survival was inversely related to TISS points, through TISS itself could not differentiate between survivors and nonsurvivors. The mortality rates for children who had a congenital malformation, a cardiac arrest before admission, or who developed acute failure secondary to other disease processes were significantly increased. Comparison of critically ill children and adults using TISS showed mortality rates that were similar. Assuming that the cost of intensive care is related to both seriousness of illness (assessed by TISS) and length of hospitalization, in this pediatric population the cost of hospitalization was not disproportionately high for nonsurvivors compared to survivors. Reduction in mortality rates in a PICU population will be dependent on factors largely uncontrollable buy ICU practitioners. This will come about by reduction in the numbers of congenital malformations and the prevention of childhood trauma.

Adolescent↗
PubMed1982

A comparison of episodic heart-rate patterns in the fetus and newborn.

Fourier analysis was applied to episodes of high and low heart-rate variation in the near-term fetus. The spectral densities of the variations in pulse intervals from 1 to 7 cycles/min, were almost identical with those found by De Haan et al. (1977) in the newborn infant during both active and quiet sleep. A computer programme, designed to separate low and high heart-rate variation episodes in the fetus, identified seven of the eight quiet sleep episodes in four infants. None of the other neonatal behavioural states had low heart-rate variation. It was concluded that, with other published data, there is increasing, although indirect, evidence that low heart-rate variation episodes indicate quiet sleep in the human fetus near term.

Electrocardiography↗
PubMed1982

Asynchronous respiratory activity of the diaphragm during spontaneous breathing in the lamb.

1. Direct simultaneous recordings from chronically implanted electrodes in different parts of the diaphragm were made in young lambs in which laryngeal adductor (thyroarytenoideus) and intercostal electromyograms, airflow, tracheal pressure and electrocorticogram and electro-oculograms for behavioural state were also recorded.2. An asynchrony of diaphragmatic contraction occurred which was dependent on sleep state. The vertebral portion showed maximal post-inspiratory activity while the lateral paratendinous portion usually terminated abruptly with end-inspiration, reciprocating closely with the onset of expiratory laryngeal adductor activity during quiet sleep. The contraction of the sternal portion was similar to the vertebral portion. In active (rapid eye movement) sleep there was no expiratory laryngeal constriction and post-inspiratory activity occurred in all portions of the diaphragm. During the characteristic bursts of rapid breathing in active sleep all post-inspiratory activity disappeared and the diaphragm contracted synchronously.3. General anaesthesia (Halothane/N(2)O or Nembutal) abolished expiratory laryngeal adductor activity and the discharge pattern became similar in all parts of the diaphragm.4. Intrathoracic vagotomy of Xylocaine blockade below the recurrent laryngeal nerves abolished post-inspiratory activity in all parts of the diaphragm, in contrast to the effect on expiratory laryngeal adductor activity which increased.5. Sustained ;tonic' electromyographic activity was often recorded from the costal and to a lesser extent the paratendinous portion of the diaphragm. This activity related to adjacent intercostal activity:ipsilateral intercostal blockade with local anaesthetic (Xylocaine 1%) abolished both the intercostal and the ;tonic' activity of the costal margins of the diaphragm. Conversely ipsilateral phrenic nerve blockade abolished all but the ;tonic' activity which related to intercostal activity.6. Interpretation of the respiratory activity of the diaphragm could not be made adequately from conventionally placed electrodes (i.e. costal, sternal slip or surface) during spontaneous breathing in unanaesthetized lambs. Simultaneous recordings showed that while expiratory flow and duration were actively controlled by expiratory laryngeal adductor activity and the diaphragm, the latter performed asynchronously. While both laryngeal and diaphragmatic expiratory functions were substantially under vagal control, the former increased and the latter decreased with reduced vagal input.

Anesthesia, General↗
PubMed1982

Differential induction of sister chromatid exchange by chemical carcinogens in lymphocytes cultured from patients with solid tumors.

Three carcinogens with different requirements for activation were used to generate sister chromatid exchange (SCE) in cultured lymphocytes from 22 untreated patients with solid tumors. These data were compared to SCEs produced by incubating lymphocytes, from 44 normal persons, with the same carcinogens. In vitro treatments with butadiene epoxide (0.125 micrograms/ml) show no significant differences in the SCEs generated. However, in vitro treatment with mitomycin-C (0.04 micrograms/ml) did induce significant differences (p less than 0.05) in the distribution of the SCE scores. Treatment of the cultured cells with benzo(a)pyrene (10 micrograms/ml), a carcinogen requiring extensive metabolic activation, significantly (p less than 0.001) altered the distribution of the SCEs generated in vitro. The SCE data suggest that metabolic activities play an important role in the processing of carcinogens in solid tumor patients.

Adolescent↗
PubMed1982

Relative fatty acid composition of serum lecithin in the second half of the normal pregnancy.

Fasting vein blood samples from 21 apparently normal pregnant women were collected in 4-week intervals from the 24th week of gestation until delivery. The relative fatty acid composition of serum lecithin was analyzed by gas-liquid chromatography. Palmitic acid increased successively concomitant with a decrease in stearic acid which indicates that serum lecithin is predominantly synthesized along pathway I. Linoleic acid decreased successively parallel to an increased incorporation of longer polyunsaturated fatty acids and non-essential monoenoic (palmitoleic and oleic) acids. The increased incorporation of longer polyunsaturated fatty acids is suggested to be associated with the increased activity of the deacylation-reacylation cycle. The increase of nonessential monoenoic fatty acids is suggested to be associated with a reduced de novo incorporation of linoleic acid.

Adult↗
PubMed1982

Diastereomeric fortimicin 1,2-epoxides. The preparation of the 1-deamino-2-deoxyfortimicins A and B and the 1,2-di-epi-fortimicins A and B.

The preparation of 1,2-anhydro-2',6'-di-N-benzyloxycarbonyl-1-deaminofortimicin B-4,5-carbamate (4) and its conversion to the two diastereomeric 2',6'-di-N-benzyloxycarbonyl-1-deamino-2-deoxy-1,2-epoxyfortimicin B-4,5-carbamates 7 and 13 are described. The olefin 4 was used for preparation of 1-deamino-2-deoxyfortimicin A (6d) while the beta-epoxide 13 was used for the preparation of 1,2-di-epi-fortimicin A (17b) and 2-amino-1-deamino-2-deoxy-1-hydroxyfortimicin A (19c). The in vitro antibacterial activities of 6d, 17b and 19c are reported.

Aminoglycosides↗
PubMed1982

The relative fatty acid composition of serum lecithin in one woman with essential hypertension superimposed by severe preeclampsia.

A hospitalized woman with essential hypertension complicated by severe preeclampsia was serially studied in the end of her pregnancy and in the puerperal period. The relative composition of serum lecithin fatty acids was analyzed by gas-liquid chromatography. In the present case, the main finding during pregnancy was a dramatic decrease of the linoleic acid parallel to a vast increase of nonessential fatty acids. Of these fatty acids, 20:3 of the oleic acid series was found in an extremely high quantity which may suggest a compensatory mechanism to reduced levels of essential polyenoic fatty acids. It was suggested that the linoleic acid decrement was mainly associated with the disease. These changes were found to be enhancements of differences earlier found between preeclamptic and normal pregnant women.

Fatty Acids↗
PubMed1981

Purification of carnosine synthetase from avian muscle by affinity chromatography and determination of its subunit structure.

An extract of chick pectoral muscle was prepared in which the level of carnosine synthetase (L-histidine; beta-alanine ligase (AMP-forming), EC 6.3.2.11) activity was approx. 10-times that of previous preparations. In affinity chromatography studies, this material was applied to a Cibracon blue-agarose column, and elution of carnosine synthetase by carnosine was attempted. Results indicated that the elution was not specific as the eluate contained large amounts of myosin. An (NH4)2SO4 fraction (21--30% satn.) of the crude extract was prepared which, in comparison to the crude extract, had a higher specific activity, was more stable on storage at 4 degrees C and had much lower myosin content. On affinity chromatography of this fraction, apparently homogeneous carnosine synthetase was eluted with carnosine, and the specific activity of the preparation was 1700-times that of the fresh crude extract. Amino acid analysis of the preparation indicated that it had a very high histidine content (141 per 1000 residues). On analysis of the preparation by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS), a polypeptide of Mr 119 000 was observed, whereas gel permeation chromatography of the native enzyme indicated an Mr of 250 000, suggesting that the native enzyme is a dimer.

Amino Acids↗
PubMed1981

Sedimentation properties of native and proteolysed preparations of ox glutamate dehydrogenase.

The concentration-dependent aggregation behaviour of purified ox liver and brain glutamate dehydrogenase preparations was compared with that of commercially-obtained preparations of the liver enzyme, which have recently been shown to have suffered proteolytic cleavage. Although there were no significant differences in these effects, the presence of 3 mM-GTP and 3 mM-NADH had markedly different effects on the two types of preparation. In this situation, at higher protein concentrations the commercially obtained preparations existed in a higher degree of aggregation than those which had not suffered proteolysis. Studies of the effects of GTP and NADH concentrations on the sedimentation coefficients at a fixed enzyme concentration suggested these effects to be largely due to differences in the affinities of the two preparations for nucleotides.

Animals↗
PubMed1981

The effects of surface and macromolecular interactions on the kinetics of inactivation of trypsin and alpha-chymotrypsin.

The autolysis of trypsin and alpha-chymotrypsin is accelerated in the presence of colloidal silica and glass surfaces. It is proposed that adsorption of the enzymes (favoured by electrostatic factors) results in a conformational change that renders the adsorbed enzyme more susceptible to proteolytic attack. Although the adsorbed enzymes are more susceptible to proteolysis, their activity towards low-molecular-weight substrates is not affected, indicating a relatively minor conformational change on adsorption. The rates of autolysis in solution (i.e. in ;inert' vessels) are second-order for both trypsin and alpha -chymotrypsin, with rate constants of 13.0mol(-1).dm(3).s(-1) for trypsin (in 50mm-NaCl at pH8.0 at 25 degrees C) and 10.2mol(-1).dm(3).s(-1) for alpha-chymotrypsin (in 0.1m-glycine at pH9.2 at 30 degrees C). In glass vessels or in the presence of small areas of silica surface (as colloidal silica particles), the autolysis of both trypsin and alpha-chymotrypsin can show first-order kinetics. Under these conditions, saturation of the surface occurs and the fast surface proteolytic reaction controls the overall kinetic order. However, when greater areas of silica surface are present, saturation of the surface does not occur, and, since for a considerable portion of the adsorption isotherm the amount adsorbed is approximately proportional to the concentration in solution, second-order kinetics are again observed. A number of negatively charged macromolecules have been shown similarly to increase the rate of autolysis of trypsin: thus this effect, observed initially with glass and silica surfaces, is of more general occurrence when these enzymes adsorb on or interact with negatively charged surfaces and macromolecules. These observations explain the confusion in the literature with regard to the kinetics of autolysis of alpha-chymotrypsin, where first-order, second-order and intermediate kinetics have been reported. A further effect of glass surfaces and negatively charged macromolecules is to shift the pH-activity curve of trypsin to higher pH values, as a consequence of the effective decrease in pH in the ;microenvironment' of the enzyme associated with the negatively charged surface or macromolecule.

Adsorption↗