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Biomedical subjects

E A Trowbridge

Publications and source records attributed to E A Trowbridge.

At least 19 recordsLinked to original sources
PubMed1995

The physical demands of riding in National Hunt races.

Heart rate (fc) and post-competition blood lactate concentration ([La+]) were studied in seven male professional National Hunt jockeys over 30 races. The fc response for individual races followed a similar pattern for all subjects. The mean peak fc recorded during competition was 184 beats.min-1 (range 162-198 beats.min-1) with average fc during the races ranging from 136 to 188 beats.min-1. During consecutive races the recovery fc did not return to resting values. The mean [La+] was 7.1 mmol.l-1 (range 3.5-15.0 mmol.l-1). The conclusions of this study suggest that riding in National Hunt races is a physically demanding occupation. The muscular activity in this profession requires a high metabolic drive and produces a significant cardiorespiratory response.

Adult↗
PubMed1992

Isolation of circulating megakaryocytes in man.

Recovery of the small numbers of megakaryocytes (MKs) known to be present in normal blood is difficult because of their low frequency. Isolation of circulating MKs was achieved using a modified filtration system in which untreated blood was passed through 5 microns polycarbonate membranes. MKs were retained while most other blood cells passed through the membranes. Four groups of MKs were identified in May Grünwald-Giemsa stained filters of blood from peripheral, central and umbilical veins and umbilical arteries. Type 1 MKs were nuclei with no visible cytoplasm. Types 2, 3 and 4 were nuclei with increasing amounts of cytoplasm. Type 4 MKs, possessing copious cytoplasm, were rarely isolated from peripheral venous blood but were more regularly encountered in central venous and cord blood. Filtration of whole blood through polycarbonate membranes is a useful technique for the isolation of circulating MKs, which are a normal physiological occurrence. Their presence is consistent with the production of platelets in the placenta during intra-uterine life, and subsequently in the pulmonary circulation.

Hemofiltration↗
PubMed1990

The size and number of bone marrow megakaryocytes in malignant lymphoma and their relationship to abnormalities in platelet count.

Platelet counts were measured routinely in 718 volunteer blood donors and 124 patients with malignant lymphoma. When considered by gender, the mean platelet counts of the patients with malignant lymphoma were significantly increased when compared to controls (P less than 0.01). In addition, 9% of males and 4% of females with lymphoma exhibited a thrombocytosis, in which their platelet counts exceeded the upper limit of the normal platelet count for control subjects (defined as 2 SDs in excess of the mean value). Megakaryocyte whole size, cytoplasmic and nuclear sizes, and megakaryocyte numbers were also quantified in bone marrow obtained from the iliac crest of 5 hematologically normal subjects and 26 patients with malignant lymphoma. Mean megakaryocyte sizes were significantly greater in subjects with lymphoma, when compared to control values (P less than 0.05). No significant differences in megakaryocyte numbers in bone marrow were observed between the two groups. For subjects with malignant lymphoma, platelet count was found to be significantly positively correlated with megakaryocyte size. The results of this study suggest that the elevated platelet count associated with malignant lymphoma is mediated by an increase in the size of the megakaryocytes in the bone marrow.

Adolescent↗
PubMed1990

Electrical impedance assessment of muscle changes following exercise.

Electrical impedance measurements have been assessed as a method of detecting changes in striated muscle following vigorous exercise. Transverse and longitudinal resistivities of the calf and thigh have been measured before and after four subjects ran a half marathon (21 km). No changes were observed in longitudinal resistivity but transverse resistivity rose by an average of 7% following the race. These results are consistent with changes in the muscle fibre membranes or interstitial fluid content.

Adult↗
PubMed1990

Megakaryocyte ploidy in thrombocytosis: improved microdensitometric measurements with a new image analysis system.

Megakaryocyte (MK) nuclear deoxyribonucleic acid (DNA) content was measured on a new image analysis system. Feulgen-stained bone marrow aspirate smears were analysed from 9 patients with thrombocytosis. Average optical density (OD) of stained nuclei was evaluated by pixel discrimination over 128 grey levels. Projected nuclear area was delineated manually. The product of these two parameters gave an index of nuclear DNA content. Neutrophils were used as 2N reference cells. Reproducibility of OD, nuclear area and their product was excellent for individual cells (CV less than 2.0% for MKs, less than 4.0% for neutrophils). The average CV for DNA content of 18 groups of 10 neutrophils was 5.5% (range 3.0-9.7%). A significant linear regression existed between MK nuclear area and DNA content (p much less than 0.001) for 627 MKs in essential thrombocythaemia (ET) and 346 MKs in reactive thrombocytosis (RT). Compared with RT, more 8N and 64N MKs were seen in ET (p less than 0.05). 128N MKs were unique to ET. Image analysis of MK ploidy may assist the clinical discrimination between primary and secondary thrombocytosis.

DNA↗
PubMed1989

Pericardial heterografts: a comparative study of suture pull-out and tissue strength.

The force required to pull sutures out of glutaraldehyde fixed bovine pericardium, for four different suture bites: 0.5 mm, 1 mm, 1.5 mm and 2.0 mm, was compared with the tissue strength. The mean suture pull-out force was significantly lower than the tissue strength for all bites, with a minimum value of 2.86 +/- 1.02 N for the 0.5 mm bite and a maximum value of 6.32 +/- 0.77 N for the 2.0 mm bite. The mean force which produced failure of the chemically modified pericardium was 15.49 +/- 8.48 N. The mean force at pull-out of the sutures lay on a regression line: force at failure = 1.68 + 2.25 x Bite. A video film of the experiments showed that the suture does not cut through the pericardium. It pulls a V-shaped band of collagen fibre bundles through the stationary pericardium. Eventually this band breaks away from the free edge of the tissue specimen. The specimens under uniaxial load failed by laminate debonding of two layers of tissue, rupture of the serosal surface layer followed by shear and fibre slippage. These results indicate that any suture which bears load, during the normal functioning of a heart valve substitute, will be a source of weakness, compared to the overall tissue strength. As a consequence the alignment/holding suture of the Standard Ionescu-Shiley valve and the modified stitch of the low profile valve are likely to be potential sites of fatigue failure.

Biomechanical Phenomena↗
PubMed1989

Local variation in the tearing strength of chemically modified pericardium.

Forty squares of tissue, 40 mm X 40 mm, were harvested from bovine pericardium fixed in glutaraldehyde free of tension. Two parallel dumb-bell specimens were excised from each square. In 20 pairs of adjacent samples, two 1 mm cuts were introduced into one of the samples at the centre of the dumb-bell. The other 20 pairs were used as controls. There was no significant difference in tensile strength of the paired samples tested without cuts, but there was marked variation in the strength of the tissue in different squares. There was a significant positive correlation between the strength of the paired samples. Introduction of artificial tears produced a significant reduction in the strength of the tissue locally. However, a significant positive correlation between the sample with tears and the sample without tears was still maintained. Failure of the tissue under uniaxial load was observed dynamically by using a Panasonic video camera with zoom and magnification facilities illuminated by an oblique low-power light source placed behind the specimen. All samples, with or without tears, failed by rupture of a layer of tissue, laminate debonding and shear, followed by fibre slippage through the viscoelastic embedding matrix.

Animals↗
PubMed1989

The tearing strength of glutaraldehyde fixed bovine pericardium.

Destructive uniaxial load tests were performed on bovine pericardium that had been chemically modified by glutaraldehyde fixation. To investigate the tearing strength of this tissue, an artificial tear, in the form of a 2mm notch, was introduced into the test specimens. Specimens without a notch, harvested from the same sites in the pericardial sac but from different sacs, were used as controls. A video system with zoom and lens magnification facilities combined with low power oblique illumination was used to observe the events leading to tissue failure. Analysis of variance demonstrated that there was no overall significant difference in tensile strength or percentage strain at fracture between the test specimens with a tear and the control specimens without a tear. Rupture of the tissue occurred following laminate debonding by shear and fibre slippage through the viscous ground matrix.

Animals↗
PubMed1989

Automated haematology: construction of univariate reference ranges for blood cell count and size.

The theory of reference ranges advocated by the International Committee for Standardization in Haematology (ICSH) was tested experimentally for an aperture impedance and a flow cytometric system. The reference sample was drawn from volunteer blood donors and the sampling procedure carefully standardised. Subjects were partitioned for gender and smoking habits, and their ages noted. Reference ranges were constructed from Gaussian statistics, after objective evaluation of the data, based on an assumed occurrence of one false positive measurement in every twenty samples. Different reference ranges were obtained on the two different systems for some haematological parameters, and partitioning also produced differences in calculated reference ranges. We conclude that strict adherence to the ICSH recommendations is almost impossible. Nevertheless, it is important that all laboratories should construct their own local reference ranges for their specific analytical systems before cost effective clinical decisions can be made.

Adult↗
PubMed1988

The tensile strength of natural and chemically modified bovine pericardium.

Nondestructive and destructive uniaxial load tests were performed on natural and chemically modified bovine pericardium. Five specimens were selected from the same sites in different pericardial sacs by using a template. The mean maximum extension of one particular site in both the natural and chemically modified material was significantly greater than that of the other positions at a stress level of 0.6 Nmm.-2 The maximum extensibility of the fixed tissue was significantly greater (p less than 0.01) than that of the natural tissue. There was also an anatomical variation in tensile strength of the natural material which was retained after chemical modification. However, the overall tensile strength of the pericardium was not increased by this procedure. In contrast, glutaraldehyde fixation did increase the percentage strain at which fracture of this biomaterial occurred.

Aldehydes↗
PubMed1988

The mechanics of the anal sphincter complex.

The anal sphincter complex consists of circumferentially arranged muscle fibres, which surround a relatively thick anal lining. This apparatus was modelled mechanistically as two concentric homogeneous isotropic linear elastic cylinders. The inner cylinder (anal lining) was considered to be thick walled, while the outer (the circular muscle) was assumed to be thin walled. The model predicts that the anal sphincter tension varies linearly with luminal diameter. This prediction was confirmed experimentally under normal conditions as well as during external sphincter contraction and internal sphincter relaxation. Under conditions of negligible hoop stress in the anal lining the model also predicts that the intra-luminal pressure falls to zero before the luminal diameter reaches zero. Hence, an autoregulatory mechanism of anal cushion thickening, as the luminal pressure falls to zero, to produce anal closure was proposed. Deficiencies in this autoregulation mechanism may explain anal incontinence and the obstructed defaecation often found in subjects with haemorrhoids.

Adult↗
PubMed1988

A stochastic model of pulmonary platelet production.

Normally, cells reproduce by mitosis. In mammals, a system has evolved that is unique to cell biology. The circulating blood cells called platelets are produced from parent cells called megakaryocytes, but the mechanism of platelet production is not mitosis. At present, both the site and mechanism of production are still debated. This article describes a production mechanism based on a sequence of random binary divisions of the megakaryocyte cytoplasm as it traverses the pulmonary microcirculation. Using the measured megakaryocyte cytoplasmic volumes circulating in the blood of three different mammals, rat, rabbit, and man, a computer simulation of this process is developed. The simulation depends on two separate stochastic processes. The first involves the probability that a division of a cytoplasmic particle of a specified size will occur. The second relates to the relative sizes of the two particles produced by the binary division. These two processes are controlled by three parameters only: a lower threshold L on the platelet volume, below which the probability of a binary division is zero; a parameter lambda which defines the probability of division for volumes larger than this lower threshold; and the standard deviation S of the Gaussian distribution of possible volumes created by the binary division. A minimization scheme is used to establish those values of L, lambda, and S which provide the best fit to the experimental data obtained from the different mammals.

Animals↗
PubMed1988

Human megakaryocyte size varies with anatomical site.

Whole megakaryocyte, megakaryocyte cytoplasmic and nuclear size were evaluated in human bone marrow obtained from posterior iliac crest and rib of subjects undergoing thoracotomy for repair of hiatal hernia. In addition the nuclear DNA content (ploidy) of the cells from each site was measured. Significantly larger mean megakaryocyte (P less than 0.002), and megakaryocyte cytoplasmic volumes (P less than 0.002), and different volume distributions were observed in costal marrow compared to the iliac crest. No change in mean nuclear volume was found. This was paralleled by no significant difference in mean ploidy. This suggests that the variation in megakaryocyte size with anatomical site is determined by the concomitant volume of cell cytoplasm, but not the nuclear volume.

Adult↗
PubMed1988

The mechanism of clavicular fracture. A clinical and biomechanical analysis.

A consecutive series of 150 patients with clavicular fractures is presented. In 81% detailed information regarding the mechanism of the injury was available and, of these, 94% had fractured their clavicle from a direct blow on the shoulder; only 6% had fallen on the outstretched hand. This finding, at variance with commonly held views regarding the mechanism of this injury, was further investigated by biomechanical analysis of the forces involved in clavicular fractures. The biomechanical model supported the clinical findings.

Biomechanical Phenomena↗