Biomedical subjects

D D Shaw

Publications and source records attributed to D D Shaw.

At least 37 records · Page 2Linked to original sources

PubMed1977

Regional distribution of coronary blood flow during left ventriculography in anesthetized dogs.

Changes in total and regional left coronary blood flow in response to ventriculography were studied using electromagnetic and microsphere techniques. Correlation of coronary flows by these methods showed excellent agreement (r = 0.947). Ventriculography produced a characteristic triphasic response in total flow and in endocardial/epicardial perfusion ratios. Changes in coronary flow can be explained as a result of hypotension and vasodilatation.

Angiocardiography↗

PubMed1977

Accuracy of estimates of contrast media concentration.

An animal model was used to prepare 18 experimental roentgenograms with differing dilutions of Conray 400 in each renal pelvis. Fifty radiologists were asked to estimate the iodine concentrations after they had been shown examples with known iodine concentrations. It was found there was a great deal of variation in the ability of individual subjects to accurately estimate the iodine concentration present. When the urinary iodine was less than 25 mg/ml, contrast estimations became grossly unreliable. At higher concentrations, the average performance of the sixty subjects was fairly clos to observed densotimetric readings. This study demonstrates that the ability to estimate iodine concentration is similar to other perceptive abilities in demonstrating both thereshold sensitivity and a near normal distribution among observes of the ability to judge perceptable differences in contrast media density.

Absorptiometry, Photon↗

PubMed1976

Comparative chiasma analysis using a computerised optical digitiser.

A new computerised technique has been devised for measuring the distribution of chiasmata along diplotene bivalents. The method involves the introduction into the field of view of the microscope, of a fine light spot which can be accurately manipulated along the chromosomes of each bivalent. The data recorded include (a) the positions of the chiasmata along the bivalent in terms of their relative distances from the centromere and (b) the individual bivalent and cellular chiasma frequencies. -- The method has been applied to the analysis of chiasma distribution patterns in the two known species of the genus Caledia, C. species nova 1 and C. captiva and in two chromosomal races of the latter. Statistical tests indicate that within bivalents at least 40% of the comparative distribution patterns of chiasmata between races and species are significantly different. Similar comparisons between populations within races reveal only 18% significant differences. -- The observed distribution patterns of chiasmata in this genus suggest that chiasma formation is sequential from centromere to telomere. -- The variation in the frequency and distribution of chiasmata between races and species suggests that the interference distances between successive chiasmata are, at least partially, independent of chiasma frequency and position. -- The interracial and interspecific differences in chromosome structure are correlated with changes in chiasma pattern.

Analog-Digital Conversion↗

PubMed1976

Population cytogenetics of the genus Caledia (Orthoptera: Acridinae). II. Variation in the pattern of C-banding.

The distribution of constitutive heterochromatin has been investigated in four chromosomal races of the grasshopper Caledia captiva (2n=23 male/24 female) by the C-banding technique. Each of the four races was found to have a distinctive banding pattern which is associated with the inter-racial differences in chromosomal rearrangements. The "Ancestral" race has a telocentric chromosome complements with large procentric C-bands which are structurally double on six pairs of chromosomes. The centromeres are unstained. The "General Purpose" race has a C-banding pattern very similar to that seen in other Acridine grasshoppers with the majority of its chromosomes showing a centromeric localisation of the bands. The two southern races, which show a complex polymorphism for presumed pericentric inversions on all twelve chromosomes, also show an unusually high level of interstitial and terminal C-bands. The different locations and numbers of these bands allow unambiguous identification of all the chromosome pairs within the complement. In two cases, there is good evidence to indicate that a C-band redistribution between acrocentric and metacentric chromosomes has occurred by pericentric inversion. Furthermore, C-band variation on the long arm of the metacentric X-chromosome indicates the presence of a large paracentric inversion. This double inversion system has involved over 95% of the X-chromosome. The interstitial and terminal C-bands probably have not resulted from heterochromatin movement within the complement but, more likely, have arisen by saltatory duplication of pre-existing sequences on the chromosome. A new nomenclature system for banded chromosomes is proposed which allows most kinds of chromosomal restructuring and rearrangement to be adequately enumerated.

Animals↗

PubMed1976

Population cytogenetics of the genus Caledia (Orthoptera: Acridinae). I. Inter- and intraspecific karyotype diversity.

The genus Caledia acontains two species. C. species nova 1 is restricted to the Oriomo Plateau of S. W. Papua and has a complement of twelve telocentric chromosomes. The second species C. captiva has a much wider distribution pattern--from S.W. Papua in the North, down the entire Eastern seaboard of Australia to Southern Victoria. It is also found in the Northern Territory. Although the chromosome number is the same as C. species nova 1, four major and distinct chromosomal races can be distinguished in C. captiva.--The basic "ancestral" race is found in Tropical North Queensland at the base of the Cape York Peninsula. All twelve chromosomes are telocentric and the karyotypic organization is similar to that found in C. species nova 1 and in other Acridines. A second, "general purpose" karyotypic race has a wide distribution between S. W. Papua, Arnhem Land and the East Australian coast as far South as Brisbane. It is considered a derivative form of the "ancestral" type and is fixed for small pericentric inversions on seven pairs of chromosomes. In the South-Eastern Queensland region there exists a further race which carries large pericentric inversions on all the autosomes and the X chromosome. The situation here is confounded since the basic chromosomes can be represented as either acro- or telocentrics. Various levels of polymorphism for the inversions exist between different chromosomes in different populations indicating considerable differentiation within this zone. This race is almost completely surrounded by the "general purpose" karyotype where the races are contiguous in certain parts of the range.--The South-Eastern corner of Australia is characterised by a chromosome race quite different from those found further North. Here a complex pericentric inversion system exists involving a series of seven small inversions and larger inversions on chromosomes 1, 2, 4 and 10. Chromosomes 2 and 4, in particular, are highly polymorphic.--The presence and persistence of these 4 chromosomal races can be accounted for in terms of the known climatic changes which have occured in this region in the recent past.

Adaptation, Biological↗

PubMed1975

The effect of angiotensin-II during ventriculography in dogs with normal coronary arteries.

Left ventriculography was performed with and without angiotensin-II in dogs with normal coronary arteries. Concomitant administration of angiotensin significantly attenuated the myocardial depression associated with ventriculography. The beneficial effect of angiotensin may be due to its ability to maintain aortic diastolic pressure and thus flush the contrast material from the myocardium more rapidly, at least in animals without imposed coronary stenosis.

Angiocardiography↗

PubMed1974