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Biomedical subjects

M J O'Brien

Publications and source records attributed to M J O'Brien.

At least 109 records · Page 6Linked to original sources
PubMed1977

Respiratory muscle EMG in newborns: a non-intrusive method.

A non-intrusive method of recording the EMG of respiratory muscles with electronic suppression of the ECG artifact and averaging with a running window was employed in newborn infants at term to study respiratory patterns in different behavioural states. There are clear state-related differences in the diphragmatic and intercostal activity patterns. During most of the time in state 1 (quiet sleep) sustained tonic activity is found in the diaphragm as well as in intercostal muscles, but is virtually absent during state 2 (active sleep). During state 1 intercostal activity slightly precedes diaphragmatic activity whereas in state 2 both muscles contract about synchronously and vary widely in their amplitude. During periodic breathing the inspiratory EMG activity is absent in the pauses, but tonic activity may be present during periodic breathing in state 1. Isolated respiratory pauses with silence in the respiratory muscles occur in state 1 after sighs and starties with deep inspirations. During state 2 many respiratory pauses accompany gross movements and simultaneous laryngeal muscle activity suggests upper airway occlusion. Respiratory pauses without movements cannot be due to general alpha-motoneuron inhibition, because chin muscle activity may be seen at the same time. Gross movements often act as a reset mechanism for increase or decrease in tonic activity and phasic respiratory activity. Some speculations on the neural mechanisms of respiratory control based on the preliminary findings from the EMG recordings are mentioned.

Apnea↗
PubMed1977

Nodular transformation of the liver: report of a case.

Cases of portal hypertension, other than those caused by cirrhosis, are uncommon. We report a rare disorder of the liver parenchyma causing portal hypertension, which can be difficult to diagnosis ante mortem, even with a full liver work-up including biopsy.

Humans↗
PubMed1976

Algal glyceraldehyde-3-phosphate dehydrogenases. Conversion of the NADH-linked enzyme of Scenedesmus obliquus into a form which preferentially uses NADPH as coenzyme.

Scenedesmus obliquus contains two glyceraldehyde-3-phosphate dehydrogenases (EC 1.2.1.-) one of which uses NADH as its preferred coenzyme (D-enzyme) and the other NADPH (T-enzyme). On incubation of the D-enzyme with cysteine and a 1,3-diphosphoglycerate-generating system the specific activity with NADH as coenzyme decreased whilst that with NADPH increased by a factor of 10. The components of the generating system had no effect on the D-enzyme individually and it is concluded that 1,3-diphosphoglycerate was probably responsible for the change in nucleotide specificity. The coenzyme specificity of the T-enzyme was not affected by such treatment. A similar type of activation occurred to a lesser extent on incubation of the D-enzyme with 2,3-diphosphoglycerate. The NADPH-dependent activity of the D-enzyme could also be promoted by incubation with NADPH. However, in this case the activation was less than that seen with either 1,3- or 2,3-diphosphoglycerate. The change in coenzyme specificity of the D-enzyme occurred in parallel with changes in sedimentation behaviour. Initially, a single boundary of S20,w equals 14.5 S was present, but on conversion to NADPH-dependent activity by incubation with the 1,3-diphosphoglycerate-generating system, new boundaries of 7.5 S and 5.5 S appeared. The first of these corresponds in sedimentation coefficient to the native T-enzyme. On removal of 1,3-diphosphoglycerate the 7.5 S boundary disappeared accompanied by an increase in that of 14.5 S, whilst the 5.5 S boundary persisted. These changes are consistent with the reversible conversion of the D-enzyme into a form similar to the native T-enzyme in response to cysteine and 1,3-diphosphoglycerate. These effects may be explained if acylation of the active site of the D-enzyme by 1,3-diphosphoglycerate results in displacement of the bound nucleotide, thus promoting nucleotide exchange. These findings are consistent with the kinetic mechanism established for other glyceraldehyde-3-phosphate dehydrogenases. Similar activation was seen in extracts of other species of the Chlorophyta but not in other photosynthetic organisms. The significance of this type of activation of enzyme activity to the metabolism of these species of algae is discussed.

Chlorella↗
PubMed1976

Algal glyceraldehyde-3-phosphate dehydrogenase. Pyridine-nucleotide requirements of two enzymes purified from Scenedesmus obliquus.

Two enzymes with glyceraldehyde-3-phosphate dehydrogenase activity have been purified from heterotrophically grown Scenedesmus obliquus by ion-exchange chromatography and gel filtration. The D-enzyme has a molecular weight of 550000 and a VNADH: VNADPH ratio of 16 whereas the T-enzyme has a molecular weight of 140000 and a VNADH:VNADPH ratio of 0.15. The two enzymes, however, are very similar with regard to their Michaelis constants for the reduced pyridine nucleotides, pH optimum, subunit size and ultraviolet absorption.

Chlorophyta↗
PubMed1976

Muscle activity and postural behaviour in newborn infants. A polymyographic study.

In a group of 9 healthy newborns, spontaneous activity of different muscles was studied for 6 or 8 hours by means of surface electromyography on the 5th or 6th day of life. According to the local nursing routine the infants were placed in alternating left and right side positions. Averaged EMG activities were analysed with respect to behavioural states and observed postural behaviour. An improved recording technique and the logarithmic presentation of averaged EMG activities allowed the study of characteristics of tonic activity in state 1. The chin muscles showed the most specific EMG pattern in state 1. Chin muscle quiescence was observed during only 15% of that state. Lack of tonic activity was observed more in the beginning than at the end, but never in the middle of state 1. By visual analysis of 41 patterns of averaged EMG activities from the chin muscle it was found that increases of tonic activity only happen stepwise following concomitant phasic activities. Relaxation of tonic activity is either asymptotic or abrupt or by steps. The latter two are especially characteristic for the transition to state 2. Long periods of sustained tonic activity and low motility were characteristic for a long lasting state 1. The interval between the beginning of state 1 and the first increase of tonic activity varied more than the interval between the end of state 1 and the final drop of tonic activity back to the noise level. Other muscles showed less tonic activity in state 1: the neck area (sterncleidomastoid muscle 48% of state 1 time, trapezius m. 32%) was followed by the muscles of the forearm (extensor carpi m. 18%, flexor carpi m. 16%). These muscles also lead the rank order of the modulation of tonic activity. Tonic activity sustained for more than 30 sec. was not observed in state 2, except during transitions. In state 2 as in state 1 the muscles from chin, neck and upper extremities were more active than the muscles from the lower extremities. Durations of activities ranged from 28% (chin) to 13% (ant. tibialis) of state 2 time. No dominance of flexor muscles, which might account for the observed flexed posture, was found. Systematically changed side positions during the recording had no consistent effect on either motility or presence of tonic activity when corresponding muscles from the upper- and the lower-lying body side were compared during state 1. Likewise in state 2 no consistent effect on the total duration of phasic activity was observed. The results are discussed in relation to other known state dependent motor phenomena. It is suggested that sustained tonic activity results from an increased gain of the gamma-loop which may also contribute to the regularity of respiration. Differences between muscles probably reflect maturational and functional differences.

Action Potentials↗
PubMed1973

Transportation of sick neonates, 1972: an unsatisfactory aspect of medical care.

An analysis of personnel and facilities used for transfer of sick newborn infants to the Neonatal Intensive Care Unit of The Hospital for Sick Children, Toronto during the months November 1971 and February to April 1972 showed many deficiencies. In many instances severely ill patients were accompanied by inadequately trained staff, transport incubators were either inadequate to maintain the babies' temperatures or were used inappropriately, resuscitation facilities were not available and oxygen concentrations could neither be measured nor varied as desired.Infants who weighed less than 1500 g. at birth and who died following transfer had significantly lower mean body temperatures on arrival at the referral hospital than those who survived. Mean transport incubator temperatures were too low in all groups of infants but were lower in those who died, although the difference was not statistically significant.

Age Factors↗